We examined the cardiovascular and ventrolateral medullary neuronal responses to muscle contraction in the spontaneously hypertensive rat (SHR) and normotensive Wistar-Kyoto rat (WKY) control. Cardiovascular, respiratory and ventrolateral medullary neuronal responses to muscle contraction evoked by tibial nerve stimulation were recorded. SHRs exhibited significantly larger drops in arterial pressure compared to WKYs in response to muscle contraction (P < 0.05). Basal ventrolateral medulla neuronal discharge rates were similar between the SHR and the WKY groups. A majority of neurons recorded responded to muscle contraction in both the WKY (77 %; n = 53) and the SHR groups (68 %; n = 62). There was no difference in the percentage of neurons that responded with an increase (~60 %) or decrease (~40 %) in firing rate between hypertensive and normotensive rats. Pulse wave-triggered averaging techniques showed that most neurons that responded to muscle contraction also possessed a basal firing rhythm temporally related to the cardiac cycle (85 % in WKYs, 83 % in SHRs). However, decreases in neuronal firing rates in response to muscle contraction were significantly greater in SHRs than WKYs. Therefore, we conclude that muscle contraction unmasks a hyperexcitability of neurons in the ventrolateral medulla of SHRs that parallels the heightened blood pressure responses. Experimental Physiology (2001) 86.6, 717-724.

The nature of the immune response following ocular immunization with a protein and a polysaccharide and the effects such immunization have on the activities of cholinergic enzymes in the lacrimal glands of BALB/c mice were examined. Lacrimal glands are highly innervated by sympathetic and parasympathetic nerve fibres and are involved in mucosal immunity and therefore are excellent sites to study neuro-immune interactions. In this report, a T-lymphocyte-dependent protein antigen, keyhole limpet haemocyanin (KLH) and a T-lymphocyte-independent polysaccharide antigen, dextran (DEX) were administered topically to the eyes or intraperitoneally injected. Both routes of immunization produced a strong serum antibody response when KLH was the antigen. DEX, however, evoked a serum antibody response only after intraperitoneal administration. Eosin-haematoxylin staining indicated no histological abnormality or inflammatory changes in any immunized lacrimal glands, but immuno-staining revealed that only in the KLH-treated tissues were IgG-producing plasma cells discernible. Furthermore, KLH-specific antibody was also detectable using an immuno-blot assay in lacrimal glands. Polymerase chain reaction analysis with cytokine-specific primers revealed induction of interleukin-4 (lL-4) in KLH-treated lacrimal glands, but not in DEX or unimmunized tissues. Thus, the nature of the antigen seems important in the induction of the immune response in lacrimal glands. To delineate the effects that immunogenic differences might have on the activities of the cholinergic enzymes, choline acetyl-transferase (ChAT) and acetylcholinesterase (AChE) were assayed using radiolabelled substrates and measuring labelled products. Both ChAT and AChE activities were influenced following KLH immunization, while DEX had only transient effects on ChAT. This is possibly due to the fact that KLH, a protein antigen, is the effective inducer of the specific immune response in the lacrimal gland, while DEX is not. Experimental Physiology (2001) 86.2, 169-176.

Dependent upon the relative speed of pulmonary oxygen consumption (V˙O2) and blood flow (Q˙) kinetics, the exercise off-transient may represent a condition of sub- or supra-optimal perfusion. To date, there are no direct measurements of the dynamics of the V˙O2/Q˙ relationship within the muscle at the onset of the work/recovery transition. To address this issue, microvascular PO2 (PO2,m) dynamics were studied in the spinotrapezius muscles of 11 female Sprague-Dawley rats (weight ~220 g) during and following electrical stimulation (1 Hz) to assess the adequacy of Q˙ relative to V˙O2 post exercise. The exercise blood flow response (radioactive microspheres: muscle Q˙ increased ~240 %), and post-exercise arterial blood pH (7.40 ± 0.02) and blood lactate (1.3 ± 0.4 mM l-1) values were consistent with moderate-intensity exercise. Recovery PO2,m (i.e. off-transient) rose progressively until baseline values were achieved (Δend-recovery exercise PO2,m, 14.0 ± 1.9 Torr) and at no time fell below exercising PO2,m. The off-transient PO2,m was well fitted by a dual exponential model with both fast (τ = 25.4 ± 5.1 s) and slow (τ = 71.2 ± 34.2 s) components. Furthermore, there was a pronounced delay (54.9 ± 10.7 s) before the onset of the slow component. These data, obtained at the muscle microvascular level, support the notion that muscle V˙O2 falls with faster kinetics than muscle Q˙ during the off-transient, such that PO2,m increases systematically, though biphasically, during recovery. Experimental Physiology (2001) 86.3, 349-356.

We have investigated the effect of acidosis on the ECG in isolated rat heart to determine whether acidosis has marked effects on the ECG, and have used pharmacological agents to investigate possible mechanisms whereby acidosis alters the ECG. Acidosis produced a marked decrease in heart rate and an increase in P-R interval with little apparent effect on the duration of the QRS complex. The effects of acidosis did not appear to be due to acidosis-induced changes in transmitter release from severed autonomic nerve terminals within the heart. Experimental Physiology (2001) 86.1, 27-31.

The mechanisms controlling the coronary vascular responses of vessels perfusing the left ventricular (LV) myocardium that is hypertrophied from chronic volume overload are unclear. We hypothesised that endothelial function is compromised, and receptor-mediated contraction is exacerbated, in coronary resistance vessels from rabbits with LV hypertrophy compared to controls. The mitral valve of 10 rabbits was damaged surgically to cause mitral regurgitation and chronic volume overload, resulting in LV hypertrophy (LV hypertrophy rabbits). Echocardiographic assessment at 12 weeks verified that mitral regurgitation was present in LV hypertrophy but not sham-operated, weight- and age-matched animals (control rabbits; n = 17). Percentage increases from weeks 0 to 12 in LV cross-sectional area (47 ± 7 % vs. 2 ± 8 %), LV volume (47 ± 14 % vs. 7 ± 10 %) and LV mass (27 ± 4 % vs. 3 ± 6 %), were greater (all P < 0.05) in LV hypertrophy vs. control rabbits, respectively. At 12 weeks, coronary resistance vessel (~ 130 µm, internal diameter) reactivity was evaluated using wire myography. Endothelium-dependent (i.e. acetylcholine, 10-8-10-5 M) and -independent (i.e. sodium nitroprusside, 10-9-10-4 M) relaxation, and receptor-mediated vasocontraction (i.e. endothelin-1, 10-11-10-7 M) were similar between groups. However, tension development in response to nitric oxide synthase inhibition (10-6 M N G-monomethyl-L-arginine) was greater (P < 0.05) in LV hypertrophy compared to control rabbits. These results indicate that while coronary resistance vessel function is similar between groups, our estimate of basal nitric oxide production is greater in vessels from LV hypertrzophy than control rabbits. Experimental Physiology (2001) 86.6, 725-732.

Effects of brief postganglionic vagal nerve stimulation on the activation sequence of the rabbit sinoatrial (SA) node were investigated. Activation sequences in a small area (7 mm × 7 mm) on the epicardial surface were measured in a beat-to-beat manner using an extracellular potential mapping system composed of 64 modified bipolar electrodes with high-gain and low-frequency band-pass filtering. The leading pacemaker site was recognised clearly from both the activation sequence and the characteristic morphology of the potentials. Vagal stimulation resulted in a short-lasting initial slowing of spontaneous rate followed by a long-lasting secondary slowing; a brief period of relative or absolute acceleration was interposed between the two slowing phases. During these changes of spontaneous rate, the leading pacemaker site shifted in a complex beat-to-beat manner by 1-6 mm alongside the crista terminalis in the superior or inferior direction. For the first spontaneous excitation following stimulation, the greater the slowing, the larger the distance of the pacemaker shift. There was no such linear relationship between the extent of slowing and the distance of pacemaker shift for the subsequent beats. These changes in the leading pacemaker site in response to vagal stimulation may be the result of the functional and morphological heterogeneity of the mammalian SA node in terms of innervation, receptor distribution and ion channel densities. Experimental Physiology (2001) 86.2, 177-184.

The mechanisms which underlie the inotropic actions of phorbol dibutyrate (PDBu), a synthetic compound which can directly activate protein kinase C (PKC), were investigated in guinea-pig isolated ventricular myocytes. Exposure of cells to PDBu (10-7 M) reduced myocyte contraction amplitude to 46 ± 3 % of control (n = 8; P < 0.05) with an associated shortening in action potential duration (action potential duration at 90 % repolarisation (APD90) was reduced to 83 ± 1 % of control; P < 0.05). The negative inotropic actions of PDBu and the shortening in action potential duration were abolished in the presence of a selective PKC inhibitor, Ro31-8220. Calcium transients (constructed from calcium-activated tail currents following interruption of action potentials by voltage clamp to -70 mV) were reduced following exposure to 10-7 M PDBu by 38 ± 2 % (n = 9, P < 0.05). L-type calcium currents were not significantly altered following exposure to 10-7 M PDBu (98 ± 2 % of control; P > 0.05). In contrast, delayed rectifier potassium currents (IK) were enhanced to 154 ± 8 % of control (n = 7; P < 0.05) by 10-7 M PDBu. This enhancement of IK may contribute to the observed shortening in action potential duration observed following exposure to PDBu under the conditions of our experiments. When the action potential configuration was maintained throughout the experiment by applying a voltage-clamp waveform, 10-7 M PDBu still reduced contraction amplitude to 57 ± 3 % of control (P < 0.05). Exposure to 10-7 M PDBu also suppressed spontaneous activity (both spontaneous potential fluctuations induced by the β-adrenergic agonist isoprenaline (40 nM), and transient inward currents induced by the cardiac glycoside ouabain (1 µM) under voltage clamp). It therefore appears that the reduction in myocyte contraction amplitude induced by exposure to PDBu may result in part through mechanisms independent of action potential shortening, which may include direct actions of protein kinase C on the function of the sarcoplasmic reticulum (SR) calcium store and/or on contractile proteins (though action potential shortening would be expected to cause a further decrease as a consequence of reduced calcium loading of the SR). The reduction of spontaneous activity caused by PDBu may also result from changes in the function of the SR store mediated by protein kinase C. Experimental Physiology (2001) 86.5, 561-570.

Blast injuries represent a problem for civilian and military populations. Primary thoracic blast injury causes a triad of bradycardia, hypotension and apnoea. The objective of this study was to investigate the reflex nature of this response and its modulation by vagotomy or administration of atropine. The study was conducted on terminally anaesthetised (alphadolone/alphaxalone, 18-24 mg kg h-1, I.V.) male Wistar rats randomly allocated to the groups indicated below. Blast injuries were produced with compressed air while sham blast involved the sound of a blast only. Primary blast injury to the thorax resulted in a bradycardia (measured as an increase in the interval between beats, or heart period (HP) to 489 ± 37 ms from 133 ± 3 ms with a latency of onset of 4.3 ± 0.3 s, mean ± S.E.M.), hypotension (fall in mean arterial blood pressure (MBP) from 128.1 ± 3.7 mmHg to 34.8 ± 4.1 mmHg, latency of onset 2.0 ± 0.1 s) and apnoea lasting 28.3 ± 2.3 s. Sham blast had no effect. The bradycardia and apnoea following thoracic blast were abolished by cervical vagotomy while the hypotension was attenuated. Atropine (0.3 mg kg-1, I.V.) caused a significant reduction in the bradycardia (HP increasing from 124 ± 3 ms to 142 ± 4 ms) but did not modulate either the hypotension or apnoea. It is concluded that a reflex involving the vagus nerve mediates the bradycardia, apnoea and a component of the hypotension associated with thoracic blast. The pattern of this response is similar to effects that follow stimulation of the pulmonary afferent C-fibres. Experimental Physiology (2001) 86.3, 357-364.

The interstitial fluid pressure (Pisf) has been measured in the exposed superfused mesenteries of anaesthetised rats using the micropipette servo-null technique. When mesenteries were superfused with Ringer-Locke solutions, Pisf was close to atmospheric pressure with mean ± S.E.M. values of -0.46 ± 0.14 cmH2O (n = 22). Superfusing with paraffin oil did not alter Pisf significantly, but Pisf could be lowered considerably by removing fluid from the upper surface of the mesentery. Measurements of Pisf were also made in the tissues immediately outside mesenteric venules as the pressure inside these vessels and the filtration of fluid through their walls was varied. No significant changes in perivascular Pisf could be detected even though the intravascular pressure varied from 20 to 70 cmH2O. Addition of histamine or the mast cell degranulating agent compound 48/80 to the superfusate had no significant effect on Pisf. The findings are relevant to experiments on the permeability of single perfused mesenteric microvessels. They strengthen the assumption, which is made in these studies, that Pisf is close to atmospheric pressure and does not change significantly with changes in the filtration and reabsorption of fluid through the vessel walls. Experimental Physiology (2001) 86.1, 33-38.

In the presence of the muscarinic blocker atropine, the α-adrenoceptor blocker phentolamine and the β-adrenoceptor blocker propranolol (2 mg kg-1 of each, I.P.), the numerical density of parotid acinar secretory granules was reduced by 32 % in response to ascorbic acid (0.5 M) applied on the tongue every 30 s over 30 min in awake rats. This non-adrenergic, non-cholinergic (NANC) response was entirely dependent on an intact auriculo-temporal nerve supply. The NANC mechanisms were found to be potentially responsible for almost all of the exocytotic response that occurs in the absence of the three autonomic receptor blockers. No sympathetic contribution to the exocytotic response was found and furthermore, studies in parasympathetically denervated glands showed that the sympathetic contribution to the salivary flow was small. Experimental Physiology (2001) 86.4, 475-480.

Daily creatine supplements (0.258 g kg-1 ) were administered to adult male Wistar rats (n = 7) in the drinking water. Age matched rats (n = 6) acted as controls. After 5-6 days, contractile properties were examined in soleus and extensor digitorum longus (EDL) muscle strips in vitro at 30 °C. In soleus muscles, creatine supplements decreased the half-relaxation time of the isometric twitch from 53.6 ± 4.3 ms in control muscles to 48.4 ± 5.5 ms but had no effect on twitch or tetanic tension or on twitch contraction time. In EDL muscles twitch tension, tetanic tension, twitch contraction and half-relaxation times were all unaffected by creatine supplements. Creatine supplements increased the fatigue resistance of the soleus muscles but had no effect on that of the EDL muscles. After a 5 min low-frequency fatigue test, tension (expressed as a percentage of initial tension) was 56 ± 3 % in control soleus muscles, whereas that in the creatine-supplemented muscles was 78 ± 6 % (P < 0.01). In the EDL muscles, the corresponding values were 40 ± 2 % and 41 ± 9 %, respectively. The force potentiation which occurred in the EDL muscles during the initial 20-30 s of the fatigue test was 170 ± 10 % of initial tension in the control muscles 24 s after the initial stimulus train but was reduced (P < 0.01) to 130 ± 20 % in the creatine-supplemented muscles. In conclusion, soleus muscle endurance was increased by creatine supplements. EDL endurance was unaffected but force potentiation during repetitive stimulation was decreased. Experimental Physiology (2001) 86.2, 185-190.

We investigated the transport systems that can sustain Na+ and Cl- movements across bovine gall bladder epithelium, focusing on the Na+-H+ exchanger (NHE) family and chloride conductive pathways. Experiments conducted using the fluorescent probe acridine orange (AO) with brush-border membrane vesicles (BBMV) or vesicles obtained from the total epithelium (EMV) demonstrated the presence of a Na+-H+ exchange in both preparations. The use of specific inhibitors indicated the presence of an apical NHE3 exchanger and a NHE1 isoform which should reside in the basolateral membrane. Using reverse transcriptase (RT) PCR, we identified cDNA fragments corresponding to the NHE1, NHE3, Cl--HCO3- (AE2a) transporters and to the CFTR channel. Using the patch-clamp technique, we investigated Cl- conductances on cultured epithelial cells. We found a 5 pS Cl- channel with a voltage-independent open probability, insensitive to stilbenes (SITS), Zn2+ and cAMP. The results suggest that absorption and secretion coexist in calf gall bladder epithelium. A Na+-H+-Cl--HCO3- double exchange may, at least partially, sustain the absorptive function, and a Cl- apical conductive pathway may be involved in secretion. The conductance we observed does not seem to be cAMP-regulated, unlike other mammalian gall bladders. Experimental Physiology (2001) 86.5, 571-583.

Vasoactive intestinal peptide (VIP, 4 µg kg-1 min-1), substance P (3 µg kg-1 min-1) and neurokinin A (2.5 µg kg-1 min-1) were infused intravenously for 30 min in anaesthetized rats and the effects of these peptides on the parotid gland were examined. VIP reduced the numerical density of parotid acinar secretory granules, storing proteins, by 29 % and the glandular amylase activity by 33 %. Substance P reduced the number of secretory granules by 18 % but the amylase activity was unchanged. These results make VIP and substance P likely contributors to the parasympathetic non-adrenergic, non-cholinergic (NANC)-evoked parotid acinar degranulation. Neurokinin A, on the other hand, caused no reduction in granular number but reduced the glandular amylase activity by 19 %, indicating vesicular protein secretion. Experimental Physiology (2001) 86.6, 733-738.

The role of endothelins in the renal damage associated with ischaemic-reperfusion (I-R) injury during organ transplantation was determined by selective blockade of the ETA receptors with the receptor antagonist ABT-627. The integrity of kidney function was determined 2 and 8 weeks after transplantation by investigation of the renal response to angiotensin II. Under pentobarbitone anaesthesia (70 mg kg-1, I.P.), rats underwent a right nephrectomy. Transplantation of the left kidney was performed after 2 h cold ischaemia without or with ABT-627 treatment. Control animals underwent left renal denervation. The renal response to angiotensin II was measured 2 weeks later following blockade of endogenous production of angiotensin II with captopril. A further transplant group was allowed to recover for 8 weeks before the terminal study. In the control group, angiotensin II reduced renal blood flow (RBF), glomerular filtration rate (GFR), urine flow rate (UV), and fractional sodium excretion (FENa) by 29 ± 5 %, 19 ± 4 %, 25 ± 4 % and 32 ± 7 %, respectively. Conversely, in the transplant group, angiotensin II left RBF unchanged and increased GFR (59 ± 12 %) and UV (93 ± 8 %). FENa decreased by 24 ± 9 %. In both the transplant group treated with ABT-627 and the long-term recovery group, the renal response to angiotensin II was normalised. In conclusion, renal transplantation following 2 h cold I-R injury resulted in a temporary abnormal renal response to angiotensin II, which was reversed by ETA receptor antagonism at the time of transplantation. Experimental Physiology (2001) 86.3, 365-372.

The renal excretory responses to volume expansion (VE), by 10 % body wt, were determined in groups of anaesthetised streptozotocin-induced diabetic rats with one denervated and one innervated kidney in the presence and absence of nitric oxide synthase (NOS) inhibitors. VE in diabetic rats increased (P < 0.001) cumulative urine sodium excretion (CuUNaV) to 104 ± 9 and 69 ± 6 µmol min-1 (g kidney wt)-1 in the denervated and in the innervated kidneys, respectively, which were both less (P < 0.001) than in the non-diabetic rats, at 225 ± 14 and 148 ± 14 µmol min-1 (g kidney wt)-1, respectively, in the denervated and the innervated kidney. The non-selective NOS inhibitor, NG-nitro-L-arginine-methyl-ester (L-NAME) given to the diabetic rats with intact renal innervation enhanced CuUNaV after VE by 43 % (P < 0.001), while the combination of L-NAME and renal denervation restored CuUNaV to a value comparable to that of non-diabetic rats. In diabetic rats treated with either a relatively selective inhibitor for the neuronal isoform of NOS, 7-nitroindazole, or a relatively selective inhibitor for the inducible isoform of NOS, aminoguanidine, CuUNaV after VE was similar to the untreated diabetic rats irrespective of whether or not the renal nerves were present. This investigation demonstrated that NO production contributed, at least partly, to the depressed ability to excrete a saline load in diabetes mellitus. The endothelial isoform of NOS was most probably responsible for generating NO which caused the blunted excretory responses. The ability of NO to attenuate the excretory responses to volume expansion was an action independent of the renal innervation status. Experimental Physiology (2001) 86.4, 481-488.

The intracellular concentration of cholesterol is regulated by the balance between endogenous synthesis and exogenous uptake. Oestrogens have been reported to be involved in the physiological regulation of cellular cholesterol content. Relevant reports have focused on long-term responses and there is a lack of information about the relationship between the timing of the oestrogen effect and the regulation of cholesterol homeostasis. The aim of this work has been to set up a systematic picture of the short-term effects induced by oestrogen on hepatic lipid metabolism in vivo and the involvement of some relevant signal transduction pathways. At intervals after oestrogen administration (30 min to 6 h), oestrogen receptor expression and changes in liver cAMP, IP3 and protein kinase C-α (PKC-α) were followed. Changes in the expression of the low density lipoprotein receptor at mRNA and protein levels, and of hydroxy-methyl-glutaryl-CoA reductase activity have been verified. At the same time, the content of hepatic cholesterol, ubiquinone and dolichol and of plasma cholesterol have been determined. Changes of rab 5 and rab 8, small GTP-binding prenylated proteins involved in the transfer of neosynthesised proteins through the cell, have been also checked. In vivo treatment with oestradiol produced no change in cyclic AMP but a rapid increase in IP3, increased PKC-α localisation on the membranes and enhanced expression of the low density lipoprotein receptor in the liver occurred. PKC inhibition completely prevented any increase in low density lipoprotein receptor mRNA in isolated and perfused rat liver. Early changes of ubiquinone and dolichol content and a later reduction in hepatic hydroxy-methyl-glutaryl-CoA reductase activity and plasma cholesterol content were also detectable. A functional role of the IP3 -protein kinase C-α pathway in the induction of the low density lipoprotein receptor is suggested. Experimental Physiology (2001) 86.1, 39-45.

In a previous report, it has been shown that water deprivation significantly affects the two-bottle taste preferences and one-bottle taste acceptance in rats when no food was available during tests. Since no food was available, the course of drinking was never interrupted by eating. Theoretically, if a rat faces a simultaneous choice between food and fluid, and if the course of drinking is interrupted by eating, these conditions might interfere with taste preferences, total fluid intake and eating in thirsty rats. The aims of the present experiments were: to ascertain whether food intake during both two-bottle preference and one-bottle acceptance tests in thirsty rats might be influenced by the palatability of the solutions; to verify whether the availability of food during tests influences taste preference and acceptance, and total fluid intake; to detect variations induced by dehydration on body weight and some plasma and urinary parameters that might interfere with food and fluid intake, taste preference and acceptance. Using naive rats, five groups of rats showing the same taste preferences for one of four prototypical tastes and water were selected. Then, both two-bottle preference (Expt 1) and one-bottle acceptance tests (Expt 2) were performed in rats deprived of water for either 12, 24, 36 or 48 h. The results showed that in both Expt 1 and Expt 2, inhibition of feeding and decrease of body weight during dehydration was very similar in all rats. The presence of food during the tests did not affect taste preference and acceptance. During Expt 1, after severe water deprivation (36 and 48 h), food intake was related to the palatability of the solution paired with water. When rats drank either NaCl or sucrose, they ate less food than rats drinking HCl, quinine, or water. In Expt 2, rats drinking NaCl solution as the only source of fluid ate significantly less food than all other groups. The intake of sucrose and/or NaCl solutions be may explained by two different post-ingestion effects (energetic and osmotic). Since rats drinking either sucrose or NaCl ate less food but drank more fluid, they had a significantly higher fluid/food intake ratio than that of rats who drank water, quinine, or HCl, who ate more food but drank less fluid. The increase of the fluid/food intake ratio in rats drinking sucrose or NaCl was directly correlated with the length of dehydration. Self-denial of food during dehydration may be responsible for overeating and overdrinking during the recovery period after tests. After dehydration lasting for 24 and 48 h, plasma [Na+], [protein], osmolality and haematocrit values increased but [K+] decreased. Urinary volume decreased but urinary [Na+] increased. These results are related to food and fluid intake, taste preference and acceptance after dehydration periods. Experimental Physiology (2001) 86.4, 489-498.

Experiments were performed in the normal rat knee joint to investigate the role of different isoforms of cyclooxygenase (COX) in the regulation of basal joint blood flow. Laser Doppler imaging (LDI) was used to measure articular perfusion, and reverse transcriptase polymerase chain reaction (RT-PCR) for the detection of COX-1 and COX-2 mRNA in joint tissue. Intravenous infusion of indomethacin (a non-selective inhibitor of COX; 0.34 nmol min-1) over 40 min produced a time dependent increase in articular vascular resistance (maximum 22.5 % at 40 min; P < 0.0001, one-way ANOVA) whereas vehicle over a similar time period had no effect in a control group. An equimolar concentration of a highly selective inhibitor for COX-2, SC-236, was administered in a further group of rats but this did not increase articular vascular resistance. While there was no significant difference between the response to vehicle and SC-236 (two-way ANOVA; P = 0.686, n = 6) the response to indomethacin was significantly greater than vehicle or SC-236 (two-way Anova; P < 0.0001, n = 6). COX-1, but not COX-2, was detectable by RT-PCR in all joint tissue samples examined (n = 4). The results of this study indicate that prostaglandins (PGs) play an important role in the maintenance of basal perfusion in the rat knee joint, with COX-1 being the physiologically relevant isoform. Experimental Physiology (2001) 86.2, 191-197.

An investigation was undertaken into the potential role of nitric oxide (NO) and its interaction with renal sympathetic nerves in mediating renal responses to acute saline volume expansion (VE). Groups of anaesthetized Wistar rats with innervated and denervated kidneys were subjected to VE, 0·25 % body wt min-1 for 40 min, in the presence and absence of nitric oxide synthase (NOS) inhibitors, NG-nitro-{fontsize L-arginine-methyl-ester ({fontsize L-NAME, non-selective), aminoguanidine (AG, relatively selective for inducible NOS (iNOS)), and 7-nitroindazole (7-NI, relatively selective for neuronal NOS (nNOS)). Pretreatment with {fontsize L-NAME or AG enhanced the cumulative sodium excretion (CuUNaV) after 40 min VE in the innervated kidneys by 27 and 23 % (both P < 0·001), respectively, compared to the untreated control group, whereas they were without effect in the denervated kidneys. Cumulative urine flow (CuUV) after VE in {fontsize L-NAME- and AG-treated groups was enhanced in both kidneys, by some 17-21 % in the denervated (P < 0·01) and 37-39 % in the innervated kidneys (P < 0·001) by comparison with the corresponding untreated controls. 7-NI had no effect on CuUV, but reduced CuUNaV in the denervated kidneys by 25 % (P < 0·01) when compared to the control group. The results suggested that NO, possibly generated by endothelial NOS (eNOS) and iNOS, was a contributory factor in mediating the renal response to VE. There appeared to be a tonic inhibitory action of NO on water excretion which was renal nerve independent, whereas its impact on sodium handling appeared to be dependent upon a background level of renal nerve activity. Experimental Physiology (2001) 86.1, 47-54.

The hypothesis has been advanced that synovium offers the main resistance to fluid escape from joints, even though it is under 20 µm thick. To test this, fluid was infused into the knee joint cavity of anaesthetised rabbits to set up a pressure gradient, then the profile of periarticular interstitial fluid pressure (Pif) was measured by advancing a micropipette, connected to a servo-null pressure recorder, in steps through a periarticular tissue 'window' until the joint cavity was entered. With intra-articular pressure (Pj) raised to 15 cmH2O (the pressure of an acute joint effusion) the pressure gradient dPif /dx (where x is distance) across the synovial lining was 0.47 ± 0.04 cmH2O µm-1 (n = 10 joints). This was 23.5-fold greater than the gradient in the subsynovium (0.02 ± 0.01 cmH2O µm-1; P < 0.0001, Student's t test), indicating that the hydraulic resistivity of the subsynovium is <=<>4 % of that of the synovium. The pressure profile was not altered by circulatory arrest. To test the hypothesis further, the effect of a stab perforation of the synovial lining on fluid drainage rate ((·Qs) was studied. Perforation raised both ·Qs and the conductance term d ·Qs/dPj more than 10-fold (n = 6 joints; P < 0.0001, ANOVA). The results thus support the view that, despite its thinness, the synovial lining offers the main hydraulic resistance to fluid drainage from a synovial joint. Experimental Physiology (2001) 86.6, 739-747.