The newborn pig is currently the most used species in animal neonatal research. Valid non-invasive monitoring is important in particular for long-term survival of unsedated animals. In the unsedated newborn pig (n = 35, median age 24 h, range 7-48 h) we standardized two-dimensional Doppler echocardiography and determined the normal ranges for cardiac function. Probe positioning had to be adjusted to the V-shaped thorax and the mid-line position of the heart. Six out of the sixteen animals < 20 h had a patent ductus arteriosus compared with one of the twenty animals > 20 h old. One atrial septal defect (5 mm) and one small ventricular septal defect were diagnosed. The average heart size was 0Σ7-0Σ9 % of body weight which is similar to human infants of the same size. The mean aortic diameter was 6Σ0 ± 0Σ5 mm (mean ± S.D.) and cardiac output was 0Σ38 ± 0Σ08 l min-1; both correlate with body weight (r = 0Σ80 and 0Σ73, respectively). Tricuspid regurgitation velocity was 3Σ0 ± 0Σ4 m s-1 (mean ± S.D.), giving an estimated pressure gradient across the tricuspid valve of 37 ± 9Σ7 mmHg. The aortic diameter and the heart weight per kg body weight are comparable to those reported for preterm neonates. The cardiac output and velocities across the four valves are more comparable with term neonates.

Dilator products of nitric oxide synthase (NOS) and cyclooxygenase (COX) may contribute to the low normal pulmonary artery pressure (Ppa). In isolated perfused lungs of ferrets, rabbits and rats we investigated this hypothesis by blockade of NOS with L-NAME (L-nitro-arginine methyl ester) and COX with meclofenamate. There were species differences. Inhibition of either enzyme caused little rise in Ppa in ferrets and rats but inhibition of both enzymes caused huge increases in Ppa. We suggest this might be due to intracellular connections between the excitatory pathways for NOS and COX dilators, such that inhibition of one enzyme leads to activation of the other. Impairment of these endothelial-based enzymes in pulmonary vascular disease might lead to severe pulmonary hypertension. By contrast, in rabbits, comparable doses of L-NAME lead to large rises in Ppa which were reversed rather than amplified by COX blockade. NO seems to protect against some pressor/oedema forming product of COX in this species.

Acetate deriving from microbial fermentation may occur at considerable concentrations in the distal small intestine, where it appears to be absorbed by two different mechanisms: acetate-HCO3- exchange and non-ionic diffusion. Whether acetate affects absorption of other nutrients at this intestinal site is not known. Therefore the influence of acetate (30 mmol l-1) on oligopeptide absorption was studied using an in vitro mucosal uptake technique allowing measurement of substrate uptake across the brush border membrane (BBM). Acetate significantly inhibited mucosal uptake of 14C-labelled glycylsarcosine (Gly-Sar) at pH 6 and pH 7 in the presence of sodium. No inhibition occurred in the absence of sodium. Both acetate and the absence of sodium decreased Vmax of mucosal Gly-Sar uptake without substantially affecting the apparent Km value. Since it is well established that Vmax of peptide transport across the intestinal BBM depends on the size of the transmembrane H+ gradient as a driving force the present findings are in accordance with the assumption that acetate inhibits peptide absorption by attenuating the H+ gradient across the BBM, which depends on the presence of sodium.

The effects of longitudinal stretch on vasoreactivity were assessed in isolated, pressurised arteries from the rat mesentery, rat mid-cerebral and human subcutaneous vascular beds. A stretch-dependent increase in reactivity was observed only in rat third order mesenteric arteries. Longitudinal stretch >> 20 % (force equal to 0·23 ± 0·04 mN) optimises vasoconstrictor responses to noradrenaline and phenylephrine in rat third order mesenteric arteries. Stretch did not affect the vasoconstriction response to depolarisation by 30 mM K+ PSS in any of the arteries studied. Similarly, stretch had no affect on pressure-dependent myogenic responses in rat mid-cerebral arteries. Endothelium-independent and endothelium-dependent mechanisms of vasorelaxation were unaffected by stretch in rat third order mesenteric arteries. Likewise, stretch did not affect vasoreactivity in rat mid-cerebral and human subcutaneous resistance arteries. Our results show that longitudinal stretch in isobaric-mounted rat third order mesenteric arteries is an important methodological consideration. Considering our results, we recommend that isobaric-mounted rat third order mesenteric arteries are stretched >> 20 % to provide optimal experimental conditions for pharmacological studies.

This study examined the effect of the phenylalkylamine calcium channel blocker verapamil, on resting left ventricular (LV) function and O2 uptake rate (VO2) during exercise at maximal and submaximal work rates. Nine older hypertensive (71 years; OH), 10 older sedentary normotensive (69 years; OS), 10 older active (71 years; OA) and 10 young (24 years; Y) individuals volunteered. Studies were completed in the control condition and 4-6 h following 240 mg verapamil SR per os. Resting LV systolic (fractional shortening; FS) and diastolic (early : late (E/A) flow velocity ratio and isovolumic relaxation time (IVRT)) were measured by Doppler echocardiography. Maximal oxygen uptake (VO2,max) and, on subsequent test days, four transitions to and from a 6 min square wave exercise perturbation at a sub-anaerobic threshold intensity of 40 W (OH, OS, OA) or 100 W (Y) for determination of VO2 kinetics were performed on a cycle ergometer. Breath-by-breath VO2 transients were fitted with a monoexponential equation, starting at phase 2 of the response, while heart rate (HR) was fitted from phase 1, for the determination of the time constant of VO2 ([tau]VO2) and HR ([tau]HR). Baseline left ventricular FS was significantly greater in the OS (32 %), OA (34 %) and Y (34 %) than in the OH (23 %) groups, while E/A was significantly greater in the OA (1Σ16) and Y (2Σ34) than in the OH (0Σ9) and OS (0Σ82) groups (P < 0Σ05). Baseline VO2,max was higher and [tau]VO2 faster in the young (41Σ4 ml kg-1 min-1; 25Σ2 s) than in the older groups and in the OA (28Σ8 ml kg-1 min-1; 44Σ3 s) than in both OH (20Σ8 ml kg-1 min-1; 71Σ3 s) and OS (22Σ0 ml kg-1 min-1; 59Σ5 s) groups (P < 0Σ05). Heart rate kinetics showed similar differences to VO2 kinetics among the groups. After verapamil, no significant changes in FS, E/A or IVRT were observed in the OA and Y groups. In the OH group, FS (32 %) and E/A (1Σ15) increased while IVRT decreased significantly (from 0Σ103 to 0Σ07; P < 0Σ05). In the OS group, only E/A increased significantly (0Σ82 to 1Σ0; P < 0Σ05). None of the exercise variables (VO2,max, [tau]VO2 or [tau]HR) were altered for the OA or Y groups. VO2,max increased (from 20Σ8 to 22Σ8 ml kg-1 min-1) in the OH and (from 22Σ0 to 24Σ1 ml kg-1 min-1) in the OS (P < 0Σ05). [tau]VO2 was accelerated from 71Σ3 to 49Σ2 s in the OH group and from 59Σ5 to 48Σ2 s in the OS group (P < 0Σ05). These results suggest that VO2 responses at maximal and submaximal work rates may be dependent upon the initial cardiac pump function of the study population.

This study examined the effect of erythropoietin (EPO) on resting tension and on the responses of rat mesenteric and renal arcuate arteries in vitro to a number of agonists as a possible cause of its blood pressure elevating properties when used therapeutically. Noradrenaline and potassium chloride induced concentration-dependent vasoconstrictions in both vessel types but the basal tension, maximum tension, and the -log concentration producing half-maximal response (pEC50) were altered in the presence of 0·1 or 20 U ml-1 EPO. The thromboxane A2 receptor agonist U46619 induced a constriction of the renal arcuate arteries which was enhanced by EPO at 20 U ml-1, from 1·68 ± 0·34 to 2·64 ± 0·39 mN mm-1 (P < 0·01), but which was unchanged by NG-nitro-L-arginine methyl ester (10-4 m). Serotonin (10-9-10-5 M) caused a concentration-related vasoconstriction in renal arcuate arteries which was shifted to the right in the time control study (P < 0·001) but this was abolished by both 0·1 and 20 U ml-1 of EPO. Acetylcholine induced a relaxation of precontracted mesenteric arteries, by 95·4 ± 1·64 % with an EC50 of 7·08 ± 0·08 M which was reduced (P < 0·001) by 20 U ml-1 EPO to 81·7 ± 3·56 % and 6·10 ± 0·11 M, respectively. The sodium nitroprusside-induced relaxations were unaffected by EPO. The acetylcholine-mediated relaxations in renal arcuate arteries were unchanged by EPO. Bradykinin-induced relaxations in mesenteric and renal arcuate arteries were unaffected by both EPO concentrations. Together these data showed that EPO over a large concentration range had only minor effects on basal tension and the vascular responsiveness of both mesenteric and renal arcuate arteries. The mechanism whereby EPO causes a chronic elevation in blood pressure is unlikely to be due to acute interactions with agonist-mediated responses.

It has been shown that cardiac fibroblasts of the human heart are electrically non-excitable and mechanosensitive. The resting membrane potential of these cells is -15.9 ± 2.1 mV and the membrane resistance is 4.1 ± 0.1 GΩ. Rhythmic contractions of the myocardium associated with stretch of the surrounding tissue produce reversible changes in the membrane potential of cardiac fibroblasts. These mechanically induced potentials (MIPs) follow the rhythm of myocardial contractions. Simultaneous recording of the action potential of cardiomyocytes and MIPs of cardiac fibroblasts demonstrates a delay of 40.0 ± 0.4 ms after the action potential before the appearance of the MIP. Contraction produces a MIP which is more positive or more negative than the reversal potential - the membrane potential due to current injection at which the MIP reverses its direction. Regardless of the initial orientation of the MIP, intracellular polarization increases the amplitude towards the reversal potential if the background MIP had depolarized the membrane or away from the reversal potential if the initial background MIP had hyperpolarized the membrane. Artificial intracellular polarization changed the amplitude but not the frequency of the MIP. The pool of electrically non-excitable mechanosensitive cells, which change their electrical activity during contraction and relaxation of the heart, may play a role in the mechano-electrical feedback mechanism which has to be taken into account in the normal function of the heart as well as in pathological processes.

This study was undertaken to improve the measurement of glomerular filtration rate (GFR) during the acute diuretic phase induced by atrial natriuretic peptide (ANP), which may indeed alter the renal clearance of inulin (GFRCL) due to dead space error. A technique to measure GFR without urine collections was therefore developed in anaesthetized rats prepared as for micropuncture. To do so, arterial blood was periodically collected and renal venous blood was withdrawn simultaneously from a catheter inserted into the left suprarenal vein to determine the renal extraction coefficient of inulin (CEIN). In addition, renal blood flow (RBF) was continuously measured with an electromagnetic flow transducer fitted around the left renal artery to estimate renal plasma flow (RPF). GFR (GFRCE) was then calculated as the product of RPF and CEIN. To study the effects of ANP on GFR, rats were injected I.V. with 10 µl of saline without (n = 6; vehicle) or with 1 µg ANP (n = 6; ANP) and GFRCE and GFRCL were compared before and after each treatment. They did not differ significantly during baseline measurements in each experimental group and were not modified after vehicle. Similarly, RBF remained constant. In contrast, RBF and GFRCE increased rapidly and simultaneously 90 s after ANP, from 9á07 ± 0á25 to 10á07 ± 0á35 (12 %) and from 1á209 ± 0á188 to 1á715 ± 0á190 ml min-1 (42 %), respectively (P < 0á05). GFRCL increased to an even greater extent (88 %). Moreover, the peak enhancement of GFRCL was delayed and occurred 180 s after ANP. The renal clearance of inulin was thus unduly elevated due to sudden changes in the dead space induced by the diuretic effect of ANP. In conclusion, determination of glomerular filtration rate by the method of renal extraction of inulin provided more reliable results than those achieved using the classical method of renal clearance of inulin. Moreover, it was sufficiently sensitive to detect small and transient changes in GFR induced by the injection of 1 µg ANP.

Plasma glucagon concentrations were measured in chronically catheterized fetal ponies and their mothers between 260 days of gestation and term (~ 335 days). Fetal [alpha] cell responses to arginine and variations in fetal glycaemia were also examined during late gestation. Immunoreactive glucagon was present in fetal plasma at 260 days of gestation and its concentration in utero increased after 320 days and then again at birth. Maternal plasma glucagon concentrations were higher after 300 days than earlier in gestation but were lower than the corresponding fetal value throughout the period of gestation studied. Fetal [alpha] cells responded rapidly to intravenous arginine infusion but not to changes in the fetal glucose level induced by maternal fasting for 36 h or by intrafetal infusion of glucose. The maximal increment in fetal plasma glucagon in response to arginine occurred at the end of the 5 min infusion and was positively correlated to the basal pre-infusion plasma glucagon concentrations. Fetal plasma glucagon concentrations were unaffected by either hyper- or hypoglycaemia. In contrast, maternal plasma glucagon levels were significantly increased by fasting. These observations indicate that equine pancreatic [alpha] cells are functional in utero but that they are unresponsive to variations in glycaemia until after birth.

When faced with stress, an organism calls upon several mechanisms to maintain biological homeostasis. The cardiovascular system is the first to respond usually with an increase in arterial pressure and tachycardia. Therefore we investigated the central and peripheral sympathetic responses to acute and chronic starvation in Wistar rats. The noradrenaline (NA) turnover rate was determined in different catecholaminergic nuclei (A1, A2, A5, A6) as well as the arterial blood pressure and heart rate modifications. During acute starvation (3 days of starvation), the NA turnover was increased in the A1 and rostral A2 nuclei as well as in ventricles and kidneys and decreased in the A6 nucleus. During chronic starvation (4 consecutive cycles of 3 days of starvation plus 1 day of feeding), the NA turnover was increased in the A5 and caudal A2 nuclei as well as in ventricles and atria and decreased in the A1 nucleus and kidneys. The arterial blood pressure revealed a gradual decrease during the first 3 days of fasting but the heart rate was not modified. We conclude that starvation should be considered as an unusual state of stress because of the absence of locus coeruleus response (A6 nucleus) despite its well-defined role in stress reactions. One of the manifestations of these central and peripheral noradrenergic changes is the change in blood pressure during the starvation-feeding cycles.

Mechanical properties of the vascular smooth muscle from normal and dystrophin-deficient (mdx) mice were examined. Changes in resting and developed tensions in response to stretch were recorded in isolated portal vein. The vascular segments were elongated in 5 % increments of the 'in situ' length (Lr) up to 1á30Lr. The resting length-tension curves in male mdxmice were similar to normal mice, while a marked decrease in the slope of the curve was noted in female mdx mice. These findings were not affected by atropine, phentolamine, tetrodotoxin or [Ca2+] in the surrounding media. At Lr, the tension of isolated portal vein was characterized by spontaneous synchronized uniform force waves in normal mouse. In contrast, in mdxmouse portal veins an irregular motor pattern characterized by desynchronized force waves with a decrease of amplitude and an increase in frequency was recorded. Extension of the length of the portal vein segment did not increase the spontaneous phasic activity developed in female mdx mice although this was noted with male mdx mice and normal mice. Experiments with chemical depolarizing agents indicated that spontaneous myogenic excitation activated the great majority of vascular smooth muscle cells in normal mouse portal vein, whereas in mdx mice only a reduced number of these cells were excited suggesting that in the mdx mouse the intercellular electronic coupling is altered. In conclusion this study provides the first description of the mechanical activities of portal vein longitudinal muscle and shows that in mdx mice the motor activity is severely disrupted.

Insulin sensitivity of kininogen-deficient rats was compared with that of normal rats using euglycaemic hyperinsulinaemic glucose clamping. Anaesthetized animals were infused with 2-50 mU kg-1 min-1 of insulin and the glucose infusion rates needed to maintain euglycaemia were determined. Maximum glucose uptake, insulin sensitivity index and insulin clearance were reduced in kininogen-deficient rats. Captopril increased the amount of glucose needed to maintain euglycaemia during infusion of 2 and 10 mU kg-1 min-1 of insulin in normal rats, but had no effect in kininogen-deficient rats. Anaesthetized rats of both strains were given an intraperitoneal injection of glucose and the evolution of blood glucose was followed for 120 min. The peak increase was higher in kininogen-deficient rats. Similar larger increases in blood glucose were observed after glucose injection in normal rats previously treated with HOE 140, a bradykinin B2 receptor antagonist. After glucose injection, plasma insulin increased in both groups of rats but reached lower levels in kininogen-deficient animals. These results suggest that bradykinin is involved not only in the clearance of glucose and insulin by the tissues during insulin infusion but also that bradykinin can affect the release of insulin after a glucose load.

Long-term administration of NG-nitro-L-arginine methyl ester (L-NAME) induces development of hypertension and hypertrophy of the left ventricle in rats. The aim of the present study was to demonstrate the effect of chronic L-NAME treatment on DNA and RNA concentration, and protein synthesis in the rat heart, aorta, brain and kidney and to determine the effect of angiotensin converting enzyme (ACE) inhibitor captopril on these potential alterations. Four groups of rats were investigated: control, L-NAME (40 mg kg-1 day-1), captopril (100 mg kg-1 day-1), and L-NAME (40 mg kg-1 day-1) + captopril (100 mg kg-1 day-1). NO synthase activity in the heart, aorta, brain and kidney was found to be decreased in the L-NAME group. In the group of rats treated with L-NAME + captopril, captopril did not affect NO synthase inhibition. Captopril, however, completely prevented development of hypertension and left ventricular hypertrophy in this group. In the L-NAME group, DNA and RNA concentrations, as well as [14C]leucine incorporation, were significantly increased in all the tissues investigated. In the L-NAME + captopril group, captopril completely prevented the enhancement of DNA and RNA concentrations and [14C]leucine incorporation in all tissues compared to the L-NAME group. Moreover, a significant decrease in RNA concentration and [14C]leucine incorporation below control values was found in the captopril group as well as the L-NAME + captopril group in all the tissues investigated. We conclude that captopril prevented the development of hypertension and increase in nucleic acid concentration and protein synthesis in the heart, aorta, brain and kidney in rats treated with L-NAME + captopril. However, this protective effect of captopril was not associated with increased NO synthase activity in this model of hypertension.

Rats were submitted to 14 days of hindlimb suspension in order to examine the contractile and elastic properties of the soleus muscles under disuse conditions. The calcium/strontium activation properties, the maximal shortening velocity (V0), as well as the time behaviour of force transients following quick releases and the T1 curves characterizing the active part of the series elastic elements, were determined on single chemically skinned fibres. After the functional measurements, the fibres were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis in order to analyse both the myosin heavy (MHC) and light (MLC) chain isoforms. According to the MHC and MLC composition, two groups of fibres were defined after hindlimb suspension: a group of slow fibres expressing the slow set of both MHC and MLC isoforms, and a group of fast fibres co-expressing the slow and fast MHC and MLC isoforms with a predominant expression of the fast ones. For the first group, the contractile as well as the elastic properties were found to be close to those of control slow soleus fibres. For the second group, both contractile and elastic properties were modified insofar as they became close to those found in a fast muscle such as the extensor digitorum longus. We suggested that between the two populations found in the soleus muscle after hindlimb suspension the modifications in the contractile properties, as well as the alterations in the elastic characteristics, were concomitant to the changes in both MHC and MLC compositions.

Breathing frequency (fb), tidal volume (VT), and respiratory timing during slow (SR, 8 W min-1) and fast (FR, 65 W min-1) ramp exercise to exhaustion on a cycle ergometer was examined in seven healthy male subjects. Expiratory ventilation (VE), pulmonary gas exchange (VO2 and VCO2) and end-tidal gas tensions (PET,O2 and PET,CO2) were determined using breath-by-breath techniques. Arterialized venous blood was sampled from a dorsal hand vein at 2 min intervals during SR and 30 s intervals during FR and analysed for arterial plasma PCO2 (Pa,CO2). PET,CO2 increased with increasing work rates (WRs) below the ventilatory threshold (VT); at WRs >= 90 % VO2,max, PET,CO2 was reduced (P < 0Σ05) below 0 W values in SR but not in FR. fb and VT were similar for SR and FR at all submaximal WRs, resulting in a similar VE. At exhaustion VE was similar but fb was higher (P < 0Σ05) and VT was lower (P < 0Σ05) in SR ( fb, 51 ± 10 breaths min-1; VT, 2590 ± 590 ml) than in FR ( fb, 42 ± 8 breaths min-1; VT, 3050 ± 470 ml). The time of expiration (TE) decreased with increasing WR, but there was no difference between SR and FR. The time of inspiration (TI) decreased at exercise intensities >= VT; at exhaustion, TI was shorter (P < 0Σ05) during SR (0Σ512 ± 0Σ097 s) than during FR (0Σ753 ± 0Σ100 s). The TI to total breath duration (TI/TTot) and the inspiratory flow (VT/TI) were similar during SR and FR at all submaximal exercise intensities; at VO2,max, TI/TTot was lower (P < 0Σ05) and VT/TI was higher (P < 0Σ05) during SR (TI/TTot, 0Σ473 ± 0Σ030; VT/TI, 5Σ092 ± 0Σ377 l s-1) than during FR (TI/TTot, 0Σ567 ± 0Σ050; VT/TI, 4Σ117 ± 0Σ635 l s-1). These results suggest that during progressive exercise, breathing pattern and respiratory timing may be determined, at least at submaximal work rates, independently of alveolar and arterial PCO2.

In nine 2- to 3-month-old hyperketonaemic piglets the kinetics of glucose and D-[beta]-hydroxybutyrate (D-BHB) metabolism were studied during hypo- and normocalcaemia in paired experiments. Hyperketonaemia (1á3 and 2á5 mmol D-BHB (l plasma)-1) was generated by a stepwise increase of DL-BHB infusion. Hypocalcaemia spontaneously developed in five piglets due to an inherited calcitriol deficiency and was induced in four control piglets by a continuous infusion of Na2-EDTA. The method of single isotopic marker injections of glucose and D-BHB was used to calculate replacement rates, rate constants and half-lives of glucose and D-BHB in plasma. When DL-BHB was infused at the same rate into normo- and hypocalcaemic piglets, hypocalcaemia reduced the rate constant of glucose by 20-30 % and the replacement rate of glucose by 34 %. In the presence of hyperketonaemia, hypocalcaemia increased the rate of replacement of D-BHB by 6-40 %. The replacement rate represents the sum of endogenous production and the rate of DL-BHB infusion. This observation shows that the endogenous production of D-BHB was higher during hypocalcaemia than during normocalcaemia.

The effect of stimulation frequency on intact muscle blood flow was measured by radiolabelled microsphere entrapment. Maximum flow occurred at 4 Hz in both extensor digitorum longus and tibialis anterior (156 ± 13 and 205 ± 24 ml min-1 (100 g)-1, respectively). Regional differences in fibre composition were reflected in the relative flow rates, with functional hyperaemia in the oxidative tibialis anterior core being twice that of the glycolytic cortex at 10 Hz. A consistent difference in flow between legs was noted that may originate from an unequal division of the common iliac artery in rats.

The influence of skin surface cooling and heating on heart rate variability (HRV), blood pressure variability (BPV), and baroreflex sensitivity (BRS) were studied in 11 healthy supine volunteers in air temperatures of 18°C (cool), 24°C (mild), 48°C (warm), and 60°C (hot) in a styrene foam chamber. The high-frequency component of HRV (HFRR) decreased and the ratio of low- to high-frequency components, LFRR/HFRR, increased with skin surface heating. Therefore, a suppression of cardiac vagal nervous activity and an enhancement of cardiac sympathetic nervous activity can be caused by skin surface heating. The low-frequency component of BPV (LFSBP), i.e. the fluctuations of the Mayer waves, increased with skin surface heating. The responses between the very low-frequency components of HRV (VLFRR) and systolic BPV (VLFSBP) to thermal skin stimulation were different, although these variables both were considered to be indicators of the thermoregulatory vasomotor control or renin-angiotensin system. Baroreflex sensitivity (BRS) did not increase with skin surface heating, at least in humans.

The effect of selective vagotomy of the abomasum, pylorus, duodenum and liver on insulin release during the cephalic phase of digestion was investigated in wethers and lactating ewes. Electrical stimulation of the cervical vagus nerves was carried out to test the completeness of the vagotomies performed. In experiment 1, using wethers, the abomasal, pyloric and duodenal branches (ADV; n = 7) or the hepatic, abomasal, pyloric and duodenal branches (HADV; n = 10) of the ventral and/or dorsal vagus nerves were cut; a third group of wethers underwent sham-operation (SO; n = 8). In experiment 2, vagotomy (ADV; n = 5) or sham-operations (SO; n = 5) were carried out in lactating ewes. Jugular blood was drawn before and after presentation of food for glucose and insulin determination (experiments 1 and 2) or before, during and after the electrical stimulation of the peripheral ends of the cut cervical vagus nerves in randomly selected lactating ewes (experiment 3: ADV = 3, SO = 3) and wethers (experiment 4: ADV = 4, HADV = 4, SO = 4), for determination of insulin only. Presentation of food caused an immediate and significant (P < 0.05) rise in plasma insulin levels in SO animals compared with ADV or HADV wethers (experiment 1) or ADV ewes (experiment 2) without any significant change in blood glucose concentrations. In comparison with the SO group the baseline-corrected areas under the insulin response curve were significantly (P < 0.05) smaller for the respective vagotomized groups for periods 1-2, 2-4 and 4-6 min (experiment 1) and 1-2 and 2-4 min (experiment 2) after presentation of food. Total area under the response curve for 10 min was significantly (P < 0.05) lower (experiment 1) and tended (P < 0.10) to be lower (experiment 2) for the vagotomized groups compared with that of the control groups. Direct electrical stimulation of the cervical vagus nerves raised plasma insulin concentrations to significantly (P < 0.05) higher levels in the SO ewes but not in the ADV ewes (experiment 3). It was also evident that in experiment 1, HADV did not have any additive effect over that achieved by ADV alone. These results indicate that the vagal innervation of the gut mediates insulin release during the cephalic phase of feeding in sheep. It is concluded that insulin secretion from the pancreatic β-cells in response to either food-related reflex activation of the vagal nuclei in the hypothalamus or direct cervical vagus nerve stimulation is mediated through the vagal efferent fibres carried in the abomasal, pyloric and duodenal branches of the vagus nerves in sheep.

The role of nitric oxide (NO) in mediating pancreatic endocrine responses to moderate hypoglycaemia has been investigated in conscious unrestrained calves. The synthesis of endogenous NO was inhibited by the administration of N-nitro-L-arginine methyl ester (L-NAME; 100 mg kg-1 I.A.), while sodium nitroprusside was infused continuously (2-4 μg min-1 kg-1 I.V.) to mimic the tonic production of NO. This effectively abolished the rise in plasma pancreatic polypeptide (PP) concentration during moderate hypoglycaemia (0·7 nmol kg-1 insulin I.V.) and significantly reduced the response to more intense hypoglycaemia (2·0 nmol kg-1 insulin I.V.). In contrast, the glucagon response was not significantly affected in either group, although consistently higher plasma glucagon values were obtained in response to the higher dose of insulin following the administration of L-NAME. It is concluded that, in the absence of L-NAME, production of NO contributes to the PP response, but not the glucagon response to hypoglycaemia in this species under physiological conditions.