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Atherosclerosis is the leading cause of mortality in the developed world. In the United States alone there are approximately 700 000 deaths per year attributable to coronary artery disease, stroke and peripheral vascular diseases (National Center for Health Statistics, 1994). Although national data demonstrate an increase in coronary artery disease prevalence since 1970 (Morano, 1996), there has been a significant decline in mortality from atherosclerosis over the past three decades. Much of this decline may be attributable to risk factor modification. Intriguingly, many of the risk factors for atherosclerosis (hypercholesterolaemia, hypertension, homocysteinaemia, diabetes mellitus and exposure to tobacco) are associated with a reduced elaboration of nitric oxide by the endothelium (endothelium-derived nitric oxide (EDNO)) (Lüscher, Raij & Vanhoutte, 1987; Celermajer et al. 1993; Wu & Meininger, 1995). The result is a perturbation in the normal functions of the endothelium to maintain appropriate vessel calibre and resist the development of atherosclerosis. This endothelial impairment occurs well before any structural changes of atherogenesis are detected. Indeed when otherwise normal vessels are exposed in vitro to oxidized lipoproteins, an impairment in EDNO-dependent vasodilatation can be detected within minutes.It is well documented that risk factor modification has reduced the incidence of morbidity and mortality due to cardiovascular disease (Pasternak, Grundy, Levy & Thompson, 1996). More recently, modification of risk factors has also been shown to restore endothelial function and it may be by this mechanism that morbidity and mortality are curtailed. For example, cigarette smoking, which has been significantly linked to the occurrence of coronary artery disease, is associated with endothelial vasodilator dysfunction (Celermajer et al. 1993). Cessation of smoking appears to improve endothelial vasodilator dysfunction and reverses this increased risk within a few years (Rosenberg, Kaufman, Helmrich & Shapiro, 1985; Ockene, Kuller, Svendsen & Meilahn, 1990). Likewise, lowering cholesterol has been shown to improve endothelial function (Stroes, Koomans, de Bruin & Rabelink, 1995; Treasure et al. 1995) and reduce the incidence of initial and recurrent coronary artery disease events (Sacks et al. 1996). The effect of these therapies on endothelial function may explain their beneficial impact upon clinical events. Indeed, the effect of lipid-lowering therapy on mortality greatly exceeds the rather modest effect upon angiographic measures of lesion progression (Fuster, Gotto, Libby, Loscalzo & McGill, 1996). The success of risk factor modification in reversing endothelial dysfunction and clinical events serves to illustrate the importance of restoring endothelial function by other means. A greater understanding of the involvement of the nitric oxide system in the pathophysiology of vascular disease may provide the basis for new therapeutic strategies.
Basic fibroblast growth factor (bFGF) is a potent mitogen which induces growth of collateral vessels in ischaemic and infarcted myocardium. The effect of systemically administered bFGF on left ventricular (LV) function, myocardial hypertrophy and LV remodelling following acute myocardial infarction (MI) have not yet been fully investigated. Thirty Sprague-Dawley male rats were randomized to receive bFGF (0·5 mg) or rat albumin intraperitoneally for 1 week, beginning immediately after the induction of MI. Five animals served as controls and did not undergo any operation. Animals were killed 6 weeks after surgery and the hearts were perfused and fixed at physiological pressure. Transverse cross-sections from infarcted areas were stained with antibodies against proliferating cell nuclear antigen (PCNA) and Masson-trichrome and analysed with a coloured-image analyser for LV area (mm2), LV cavity diameter (mm), infarcted area (%), and wall thickness (mm) in infarcted and non-infarcted regions. LV area was similar in MI rats and in controls (41·7 ± 6·9 and 43·0 ± 1·5 mm2, respectively) and was significantly larger in MI bFGF-treated (MI/bFGF) animals (47·6 ± 7·1 mm2) (P = 0·023). LV cavity diameter was significantly larger in the MI group than in MI/bFGF and control animals (6·0 ± 0·8, 4·9 ± 1·4, and 4·4 ± 0·8 mm, respectively, P = 0·018). Wall thickness in the non-infarcted region was significantly smaller in MI animals (1·4 ± 0·3 mm) than in MI/bFGF animals (1·6 ± 0·4 mm) and the control group (1·6 ± 0·1 mm) (P = 0·015). The ratio between LV cavity diameter/non-MI wall thickness was higher in MI than in control and MI/bFGF groups (4·8 ± 1·6, 2·7 ± 0·6 and 3·3 ± 1·8, respectively, P = 0·03). Proliferating endothelial cells were significantly more abundant in infarcted than in normal areas in both MI and MI/bFGF groups, but with no significant differences between the groups. Intraperitoneal administration of bFGF did not cause any untoward extracardiac effects. Thus, systemic bFGF administration following acute MI in rats prevents dilatation of the LV, induces hypertrophy of the non-infarcted myocardium and exerts no untoward effects on extracardiac organs.
The aim of this study was to evaluate whether long-term administration of L-arginine, a physiological substrate for the production of nitric oxide, improved blood pressure, heart rate, cardiac hypertrophy and particularly structural changes in the coronary and carotid artery of spontaneously hypertensive rats (SHR). The experiments started with three groups of 10-week-old animals: control Wistar rats, untreated SHR and SHR treated with L-arginine (SHR + L-arginine). L-Arginine was administered to SHR in a daily dose of 300 mg kg-1 intraperitoneally for 6 weeks. Blood pressure and heart rate were recorded each week. At the end of the experiment in one-half of each group heart weight and body weight were determined and the heart weight/body weight index was calculated. In the other animals, the cardiovascular system was perfused via the left ventricle with a glutaraldehyde fixative at 120 mmHg and the coronary and carotid arteries were processed for transmission electron microscopy. The inner diameter and wall thickness (tunica intima and tunica media) were measured on semithin sections. The reliability of the genetic feature in the SHR group was proved by the increased heart weight, heart weight/body weight index, wall thickness and wall thickness/inner diameter ratio of coronary and carotid arteries in comparison to the group of control Wistar rats. Long-term administration of L-arginine did not significantly influence blood pressure and heart rate in comparison with untreated SHR. Neither were any differences found in cardiac hypertrophy or the geometry of the coronary and carotid arteries (thickness of arterial wall, inner diameter, wall/diameter ratio). In conclusion, the changes in the cardiovascular system in SHR were not reversed, or even alleviated, by chronic treatment with L-arginine.
Phloridzin-insensitive D-glucose uptake into enterocytes isolated sequentially from along the crypt-villus axis showed the majority of transport activity to reside in cells from the upper third of the villus. In contrast, total postnuclear glucose transporter 2 (GLUT2) protein content of the cells was high even close to the crypt and was almost constant for the upper 80 % of the villi. A 4 h lumenal perfusion in vivo with 100 mM D-glucose prior to harvesting the enterocytes produced a 2- to 3-fold increase in phloridzin-insensitive D-glucose uptake which extended down 70 % of the villus. Vascular infusion in vivo with either 800 pM gastric inhibitory polypeptide (GIP) or glucagon-like peptide-2 (GLP-2) prior to harvesting enterocytes produced the same response as lumenal glucose, while glucagon like peptide-1 (GLP-1) had no effect. Inclusion of 30 µM brefeldin A (BFA), an inhibitor of protein trafficking, in the lumenal perfusate produced a small, but not significant, increase in the control uptake profile along the villus in isolated enterocytes. However, BFA significantly reduced the upregulation induced by lumenal glucose and vascular GIP and blocked the stimulation produced by vascular GLP-2. Biotinylation of surface proteins and isolation with protein A indicated that there was no change in the membrane abundance of GLUT2 after GLP-2 treatment. These results are discussed in relation to the role of gastrointestinal peptide hormones in controlling intestinal hexose transport and the possibility of protein trafficking being involved in mediating the upregulation of GLUT2 activity in the enterocyte basolateral membrane.
Gut endocrine cells possess the capacity to take up and decarboxylate biogenic amine precursors. Decarboxylation is mediated by aromatic L-amino acid decarboxylase (AADC) which is encoded by mRNAs differing in their 5' untranslated regions (UTR) depending on the usage of alternative first exons, 1a and 1b, each with its own acceptor site (-13 and -8 bases relative to the translation start site, respectively). We describe here a novel splice variant of exon 1a-AADC mRNA in rat antral mucosa. Both exon 1a and 1b mRNAs were expressed in rat antral mucosa, but the 1a form was spliced into the acceptor site usually associated with exon 1b (-8). An enteroendocrine cell line (STC-1) expressed exon 1a or exon 1b mRNAs spliced into the -8 acceptor site of exon 2. Transient transfection of a range of cell lines with reporter constructs revealed that all three 5' UTRs efficiently supported expression of the Luciferase reporter. There is therefore a novel, functional 5' UTR of AADC mRNA in rat antral mucosa; alternative AADC splice variants could provide the capacity for control at the level of mRNA translation.
Potassium transport was measured in isolated chicken colonocytes using 85Rb+ as a tracer for K+. Rb+ was determined by atomic absorption spectrometry. The results revealed that net K+ uptake occurred via at least four mechanisms: (i) Na+,K+-ATPase, (ii) K+-ATPase, (iii) Na+-K+-2Cl- cotransport system and (iv) a mechanism(s) which is resistant to both ouabain and bumetanide. The rate of K+(Rb+) efflux is stimulated by the calcium ionophore A23187, inhibited by either quinine, verapamil or Ba2+, and unaffected by either apamin, 3,4-diaminopyridine (3,4-DAP), H2-DIDS or bumetanide. The A23187-induced increase in K+(Rb+) efflux was abolished by apamin. These findings suggest that K+(Rb+) efflux from chicken colonocytes occurs at least in part through Ca2+-activated K+ channels. The present results also show that all these K+ transport systems are involved in cell volume regulation. Thus, external hyposmolarity decreased net K+(Rb+) uptake mediated by Na+,K+-ATPase, K+-ATPase and the Na+-K+-2Cl- cotransporter and increased K+(Rb+) efflux rate. The opposite was observed under hyperosmotic conditions.
To elucidate the role of corticotrophin-releasing factor (CRF) in the spontaneous rhythmic contractions of pregnant myometrium, isometric contractions of longitudinal myometrial preparations taken from Sprague-Dawley rats (18-21 days gestation) were measured. CRF (0·03-30 nM) significantly increased the amplitude (117 ± 4 % of control at 30 nM, mean ± S.E.M.) and significantly decreased the frequency (74 ± 5 %) in a concentration-dependent manner. The area under the tension curve did not increase (89 ± 8 %). Such effects of CRF were not observed in preparations pretreated with the RP diastereomer of adenosine cyclic 3',5'-phosphorothioate (Rp-cAMPS, 10 µM), an inhibitor of protein kinase A. In preparations pretreated with indomethacin (1 µM), CRF caused little change in the amplitude but significantly decreased the frequency of the contractions. Intracellular cAMP levels in the preparations, measured by enzyme immunoassay, rose when CRF was applied at 30 nM. These results suggest that the slight positive inotropic action of CRF is due to activation of both cAMP and prostaglandin pathways, whereas the negative chronotropic action is due solely to the cAMP signalling pathway.
We have previously shown that feeding 50 ml of colostrum can increase the thermogenic activity of brown adipose tissue (BAT) in newborn lambs maintained at a warm (30¡C) ambient temperature. This study further examines the effect of ambient temperature on BAT and thermoregulation by investigating the response to feeding 50 ml of water. Immediately after vaginal birth, lambs were placed in either a warm (30¡C) or cool (15¡C) environment at ambient temperature and measurements of colonic temperature and heat production were recorded for 6 h. Lambs were fed 50 ml of water when 5 h old. The level of guanosine 5'-diphosphate (GDP) binding was higher, but adrenaline content lower in BAT sampled from lambs maintained at 15¡C compared with those at 30¡C. Feeding was associated with an increase in colonic temperature and plasma concentrations of glucose and non-esterified fatty acids in lambs maintained at 15¡C only. In this group plasma concentrations of adrenaline and dopamine declined after feeding, but noradrenaline concentrations were not influenced by feeding in either group of lambs. O2 consumption and CO2 production were higher in lambs maintained at 15¡C but were not influenced by ambient temperature or feeding. It is concluded that feeding a small volume of water can influence thermoregulation by a mechanism that is dependent on the ambient temperature at which the lamb is maintained.
Growing pigs were fed diets supplying 45 % (low), 70 % (intermediate) and 100 % (high) recommended dietary allowances of calcium (the Ca:P ratio was kept constant), but otherwise adequate in nutrients. The effects of varying calcium and phosphorus intakes on bone and plasma osteocalcin were monitored. Mineral content of the diet did not affect feed conversion and live weight gain. Plasma phosphorus concentrations decreased significantly in pigs fed a low mineral diet compared with those fed the high mineral diet, but there were no changes in plasma calcium and osteocalcin concentrations. Bones from the low mineral group had marked reductions in dry matter, calcium and phosphorus contents, as well as increased collagen, pyridinoline and deoxypyridinoline concentrations: osteocalcin concentrations in bone were unaffected by treatment. The results showed no direct link between osteocalcin and the degree of bone mineralization.
Exposure to a temperature of 14¡C was used to induce a progressive hypothermia in fourteen conscious newborn piglets. Heat production, body (rectal) and skin (between the shoulders) temperatures and shivering intensity assessed as the electromyographic activity (EMG) of longissimus thoracis muscle were measured until body temperature reached 30¡C and during a recovery period of 2 h at an ambient temperature of 24¡C (n = 7) or 34¡C (n = 7). During body cooling, heat production increased up to 9·67 ± 1·28 W (kg BW)-1, but started to decrease below a body temperature threshold of 34·4 ± 0·7¡C. EMG activity increased (P < 0·023) curvilinearly during body cooling; the main increase occurred between body temperatures of 38 and 33¡C (+142 %, P < 0·001), and changes in EMG activity between 33 and 30¡C were not significant (+18 %, P > 0·1). A marked increase in circulating levels of glucose (+312 %, P < 0·001), glucagon (+76 %, P < 0·05), adrenaline (+172 %, P < 0·05) and noradrenaline (+113 %, P < 0·05) occurred during body cooling. Insulin levels were not detectable at 2 h of life and increased during body cooling. During 2 h of rewarming at 24¡C, heat production and EMG activity remained elevated, changes in carbohydrate metabolism were not completely reversed and the final body temperature was only 35·6 ± 0·9¡C. Rewarming of the piglets was faster at 34¡C. There was a net influx of heat into the animals and heat production and shivering activity decreased when body temperature reached 33·9 ± 0·5¡C; the final body temperature was 37·5 ± 0·2¡C. Circulating levels of lactate, glucagon and catecholamines returned to control levels. These results show that in conscious piglets exposed to a constant cold temperature there is an inverse relationship between EMG activity and body temperature during moderate hypothermia and that the thermoregulatory response and carbohydrate metabolism of the piglet are seriously impaired below a body temperature of 34¡C.
A study was undertaken in man to investigate whether during moderate cold stress, the proportion of carbohydrate (CHO) oxidized is increased, and whether prior prolonged exhaustive exercise compromises thermoregulation. Eight euglycaemic men were cooled by a liquid-conditioned suit (1) after an overnight fast (Con) and (2) [similar]2 h after an exercise protocol in which CHO availability was substantially lowered (Post-Ex). The cooling stimulus lasted 90 min (Cooling) and was preceded by a 30 min thermo-neutral baseline phase (Base). In Con, aural temperature (Taural) and the rate of CHO oxidized (CHOox) were not altered from the values at Base during Cooling, whereas the following were increased: the rate of heat production (Hprod, [similar]1·9-fold), thigh electromyographical activity (EMG, [similar]2·5-fold), and the rate of fat oxidized (FATox, [similar]1·7-fold). In Post-Ex, Taural did not decrease from the value at Base during Cooling, and compared with Con, EMG, CHOox and the rate of heat loss were not different, whereas Hprod (P [less than or equal to] 0·01), FATox (P [less than or equal to] 0·01) and mean skin temperature (P [less than or equal to] 0·01) were higher, and Taural was lower (P [less than or equal to] 0·05). It is concluded that during moderate cold stress, shivering thermogenesis is supported by an increase in the oxidation of fat, and despite an alteration in the initial thermoregulatory responses to Cooling [similar]2 h after exhaustive exercise, thermoregulation was not impaired.
Chewing and acid on the tongue evoked a flow of saliva from the duct-cannulated parotid gland of the conscious rat despite pretreatment with atropine and adrenoceptor antagonists. This non-adrenergic, non-cholinergic (NANC) response depended on an intact parasympathetic innervation and was abolished by a tachykinin antagonist. The present findings are consistent with a physiological role for the secretory NANC mechanisms of the salivary glands.
A stress protocol - 6 h of daily immobilization - was applied throughout male rat sexual development. Immobilization caused a small reduction in food intake and body weight gain whereas pair-fed animals had a marginal decrease only in body weight gain. Stress, confirmed by increased plasma adrenocorticotrophic hormone (ACTH) and corticosterone, caused a decrease in plasma luteinizing hormone (LH) after 15 and 60 days of immobilization and in plasma testosterone after 60 days, but produced an opposite androgenic response in pubertal animals (15 days of immobilization). A presumed sympathetic over-stimulation is suggested to account for increased testosterone levels in pubertal stressed rats.
This is the fourth in a series of texts on fetal physiology and the changes occurring during the transitional period from intra- to extra-uterine life, a most critical and dangerous period in human life. The volumes in the series are each devoted to a particular system, the previous three volumes being devoted to the crucial areas of circulation, respiration and growth. The fourth volume follows the established format, considering first fetal development and perinatal changes, then pathophysiology and finally applying the information to clinical conditions. There is emphasis on the importance of basic research and animal models to clinical practice. The text therefore will appeal to a wide audience from undergraduate students of the basic sciences to clinicians working in the field of neonatal medicine. It is well presented and, in general, well illustrated.There are major differences in fluid balance between the fetus and adult. Apart from the fact that the fetus develops in a fluid environment, the tissues have a higher water content and overall the fluid shifts are greater. The text opens with a summary of the developmental stages of the kidney and the development of functional characteristics, in particular the endocrine function of the kidney and renally active hormones. Areas of current interest are highlighted including the ontogeny and regulation of water channels. Dynamics of fluid balance and the importance of the lymphatic system, fetal swallowing and exchange with amniotic fluid are considered in the next three chapters. More might have been said of transplacental flow and the altered fluid status of the mother. The section on basic physiology closes with a useful review of the changes in renal function observed at birth.The next section, that on pathophysiology, considers abnormalities in renal development whether as a result of congenital abnormalities, renal agenesis and obstructive uropathies or as a result of fetal growth retardation. The final chapter of this section is devoted to hydrops fetalis, a pathological increase of interstitial and total fetal body water. The many possible causes are reviewed.The final, clinical section centres on a detailed consideration of the management and correction of obstructive uropathies, fetal oedema, oligohydramnios and polyhydramnios. The relative advantages and disadvantages of available diagnostic and therapeutic interventions are comprehensively covered. The final chapter on management of postnatal disorders brings together many of the themes developed in earlier sections.This multiauthored book employs a wide range of expertise and presents critical consideration not found in standard texts. This fact, together with the focus on both basic science and practical aspects of fetal and neonatal medicine, makes the text a valuable source of reference. The production of a series of separate volumes rather than a single comprehensive text has resulted in relatively rapid publication with references up to 1996 being cited.