摘要:

The mechanisms whereby atrial natriuretic factor (ANF) induces natriuresis are not clarified. Here, the effects of ANF and the cGMP analogue, 8‐bromo‐cGMP, on Na+, K+‐ATPase activity in microdissected segments from rat medullary thick ascending limb of Henle (TAL) were evaluated. ANF‐induced cGMP accumulation and the cellular handling of intracellularly produced cGMP were also investigated, by measuring the accumulation of extracellular cGMP in suspensions of tubules from outer medulla, enriched in TAL, and of isolated glomeruli.ANF dose‐dependently inhibited Na+, K+‐ATPase activity in isolated TAL in a parallel fashion with increasing cGMP accumulation in OM tubules. For both parameters, pharmacological concentrations (≥ 10−6 m) of ANF were needed to induce a significant effect. 8‐Bromo‐cGMP mimicked the inhibitory effect of ANF. The increase in the intracellular cGMP level in response to ANF was dose‐dependently reflected in the extracellular level. This finding contrasted with that in the glomerular preparation, where cGMP in response to ANF accumulated entirely intracellularly. Also in glomeruli, high (≥ 10−6 m) concentrations of ANF were needed to induce a significant effect on cGMP accumulation.In conclusion, ANF inhibited Na+, K+‐ATPase activity in TAL and the effect was mimicked by 8‐bromo‐cGMP. cGMP, produced in response to ANF, was extruded from the tubular e

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00099.x

出版商:Blackwell Science Ltd.    

年代:1997

数据来源: WILEY

摘要:

Milk secretion represents a major route for electrolyte and water excretion in the dairy goat. The aims of this study were to investigate whether the mammary gland is a target site for atrial natriuretic peptide (ANP) in the goat and whether ANP affects mammary sodium and water secretion. Receptor autoradiography using125I‐ANP as radioligand revealed specific binding sites in the secretory tissue of the mammary gland. The radioligand was totally displaced by unlabelled ANP, but not by brain natriuretic peptide or the ANP fragment c‐ANP4–23, indicative of ANP‐A receptor preference. To elucidate the role of ANP in milk secretion, ANP (30 ng kg−1min−1; 120 min) or 0.15 mNaCl (control) were administeredin vivo. The ANP infusions caused haemoconcentration, but did not change milk flow or the concentrations of sodium, potassium, lactose, fat and protein in the milk. The results show that the mammary gland of the goat expresses ANP‐specific binding sites, however, a physiological role of ANP in goat mammary gland function remai

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00124.x

出版商:Blackwell Science Ltd.    

年代:1997

数据来源: WILEY

摘要:

Pituitary adenylate cyclase activating peptide (PACAP)‐38. injected Lv. to the anaesthetized rat. evoked secretion of saliva from the three major salivary glands. the submandibular glands responding with the greatest and the sublingual glands with the smallest volumes. The parotid saliva was rich in amylase and protein. In vitro. pieces of parotid and submandibular gland tissues released K+and protein in response to PACAP‐38. with atropine and adrenoceptor antagonists present. The blood flow in the submandibular gland increased in response to PACAP‐38. despite a marked fall in mean aortic blood pressure. PACAP is a vasoactive intestinal peptide (VIP)‐like neuropeptide. A comparison between the two peptides showed PACAP‐38 to be more effective than VIP with respect to vascular responses and less or equi‐effective with VIP with respect to the secretory responses. thus suggesting the involvement of PACAP type I and type II receptors. respectively PACAP‐38 and ‐27 were present in the parotid gland as judged by radioimmunoassay. the concentration of the former being about twice that of the latter. Parasympathetic denervation. by cutting the auricula‐temporal nerve. reduced the total parotid gland contents of PACAP‐38 and ‐27 by 23 and 44%. respectively (compared with a previously demonstrated 95% reduction of VIP). Sympathetic de nervation. section of the facial nerve or treatment with the sensory neurotoxin capsaicin did not affect the content of PACAP. The difference in efficacy between PACAP and VIP in the vascular and secretory responses as well as the difference in localization suggest that the two peptides play different physiological roles i

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00010.x

出版商:Blackwell Science Ltd.    

年代:1997

数据来源: WILEY

摘要:

Neural control of the circulation was evaluated during static exercise in 19 subjects by the determination of heart rate (HR), mean arterial pressure (MAP), cardiac output (CO) and plasma catecholamines. Influence from central command was evaluated during contractions with weakened muscles following partial curarization and reflex influence from metaboreceptors was assessed by post‐exercise muscle ischaemia. Static handgrip increased HR and more so MAP and CO and MAP remained elevated during post‐exercise muscle ischaemia. With partial curarization plasma catecholamines were also increased (P<0.05). Two‐leg extension increased all variables and during post‐exercise muscle ischaemia elevations of HR, MAP and CO were maintained (P<0.05). With partial curarization HR, MAP and plasma noradrenaline were even greater during the contraction. With the involvement of both legs during static exercise, reflex influence from the muscles elevated blood pressure by way of HR and CO and the importance of central command was detectable for HR and MAP as plasma catecholamines became elevated. However, the results indicate a separation between a central command influence on HR and CO related to an increase in plasma catecholamines during a handgrip, while the reflex influence on blood pressure was directed towards total peripheral res

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00115.x

出版商:Blackwell Science Ltd.    

年代:1997

数据来源: WILEY

摘要:

The effects of exercise detraining on resting finger arterial blood pressure (BP), the carotid‐cardiac vagal baroreflex, and BP and heart rate (HR) responses to mental arithmetic and forehead cold exposure were studied in young (19 ± 1.1 years) normotensive women with parental history of hypertension. Following 8 weeks of aerobic exercise for 25 min, 3 days week−1at an intensity of 60% V˙O2 peak, subjects ceased training for 6–8 weeks. After detraining, V˙O2 peak(mL kg−1min−1) was reduced by 11.5% (41.1 ± 6.9 to 36.4 ± 4.8) coincident with an ≈ 10 %increase in submaximal exercise heart rate. Responses to the laboratory tasks were then compared. Detraining was accompanied by increases (P<0.05) in resting systolic (SBP) (113.6 ± 8.9 to 121.2 ± 9.0), diastolic (DBP) (63.0 ± 8.4 to 68.3 ± 6.8), and mean arterial (MAP) (78.7 ±8.4 to 84.2 ± 7.3) BP (mmHg). None of the above changes occurred in sedentary matched‐control subjects. Systolic blood pressure was elevated during forehead cold exposure and MAP was elevated during mental arithmetic after detraining, but the rates of response and recovery for SBP, DBP and MAP were not altered by detraining. Despite higher submaximal exercise HR after detraining, HR responses to autonomic challenges, including the carotid‐cardiac vagal baroreflex, were unchanged between training and detraining. Our results indicate that exercise detraining increases resting finger arterial BP in young normotensive women at risk for hypertension with no effects on the rate of response or recovery of heart rate and BP during autonomic tasks known to elicit sympathetic and carotid‐cardiac vagal activities in this population. The use of auscultatory brachial artery pressures in a similar study of women diagnosed with hypertension will clarify the cl

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00116.x

出版商:Blackwell Science Ltd.    

年代:1997

数据来源: WILEY

摘要:

During exercise the transcranial Doppler determined mean blood velocity (Vmean) increases in the middle cerebral artery (MCA) and reflects cerebral blood flow when the diameter at the site of investigation remains constant. Sympathetic activation could induce MCA vasoconstriction and in turn elevate Vmeanat an unchanged cerebral blood flow. In 12 volunteers we evaluated whether Vmeanrelates to muscle sympathetic nerve activity (MSNA) in the peroneal nerve during rhythmic handgrip and post‐exercise muscle ischaemia (PEMI). The luminal diameter of the dorsalis pedis artery (AD) was taken to reflect the MSNA influence on a peripheral artery. Rhythmic handgrip increased heart rate (HR) from 74 ± 20 to 92 ± 21 beats min−1and mean arterial pressure (MAP) from 87 ± 7 to 105 ± 9 mmHg (mean ± SD;P < 0.05). During PEMI, HR returned to pre‐exercise levels while MAP remained elevated (101 ± 9 mmHg). During handgrip contralateral MCA Vmeanincreased from 65 ± 10 to 75 ± 13 cm s−1and this was more than on the ipsilateral side (from 63 ± 10 to 68 ± 10 cm s−1;P < 0.05). On both sides of the brain Vmeanreturned to baseline during PEMI. MSNA did not increase significantly during handgrip (from 56 ± 24 to 116 ± 39 units) but the elevation became statistically significant during PEMI (135 ± 86 units,P < 0.05), while AD did not change. Taken together, during exercise and PEMI, Vmeanchanged independent of an elevation of MSNA by more than 140% and the dorsalis pedis artery diameter was stable. The results provide no evidence for a vasoconstrictive influence of sympathetic nerve activity on medium size

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00126.x

出版商:Blackwell Science Ltd.    

年代:1997

数据来源: WILEY

摘要:

A previous study showed that adult female dancers have a high percentage of type I fibres in vastus lateralis. similar to that of endurance‐trained female runners ar female cross‐country skiers. It is not known if dancers already at an early age are characterized by a high percentage of type I fibres or develop a high percentage of type I fibres as a consequence of dance training. Furthermore. the muscle fibre composition of male dancers has not previously been studied. Therefore the aim of the study was to analyse skeletal muscle fibre characteristics in 10‐year‐old and 20‐year‐old dancers of both sexes. Age‐matched boys and girls whose physical activity was average for their age groups served as controls. Muscle biopsies for histochemical analysis were obtained from vastus lateralis using the percutaneous needle technique. The major finding of the present study was that the vastus lateralis of young dancers of both sexes had a higher percentage of type I fibres than that of controls. Moreover. the higher type I percentage was seen not only in 20 year aids. but also in 10 year aids. who had begun their dance training at a professional level only a few weeks earlier. No significant difference in this respect was found between female and male dancers. In conclusion. the muscle fibre type composition in young dancers of both sexes differs from that of the average individual of the same age and is characterized by a high percentage of

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00012.x

出版商:Blackwell Science Ltd.    

年代:1997

数据来源: WILEY

摘要:

Our previous studies have indicated that endogenous nitric oxide serves as a physiologically important inhibitor of vascular tone during acute haemorrhage. This vasodilator action attenuates the concomitant reflex adrenergic constriction and thereby prevents critical reduction of tissue blood flow. The present study aimed to evaluate the overall importance of this nitric oxide regulation for survival after acute haemorrhage. This was done by comparative observations of survival time and circulatory. metabolic and histopathological changes after an acute standardized lethal blood loss (45%) in cats exposed to nitric oxide synthase (NOS) inhibition and in matched control animals with intact nitric oxide regulation. NOS inhibition was instituted by intravenously administered N‐nitro‐L‐arginine methyl ester. The survival time averaged 2 h 49 min in the NOS‐blocked animals and 10 h 14 min in the control animals (P  0.001). NOS inhibition thus reduced the posthaemorrhagic survival time to  30% of that in the control cats. Haemorrhage in the NOS‐blocked animals led to rapidly developing arterial hypotension. increased anaerobic metabolism. metabolic lactacidosis. hyperkalaemia. and morphological tissue damage especially in heart and liver. in spite of maintained arterial normoxia, which signifies tissue hypoxia caused by seriously impaired nutritional blood supply. At the time of death of the NOS‐blocked cats. the control animals still exhibited a virtually normal circulatory/metabolic state. A much later. and more slowly developing circulatory/metabolic deterioration was observed in the control animals. These differences between the two groups of animals indicate that nitric oxide release. by its vasodilator action. to a significant extent helps to maintain an adequate nutritional blood supply to the tissues in ac

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00117.x

出版商:Blackwell Science Ltd.    

年代:1997

数据来源: WILEY

摘要:

The cardiac capillarity in adult rats reared at 5°C for 68 generations was studied with a double staining method for alkaline phosphatase and dipeptidylpeptidase IV. Capillary density. proportions of arteriolar. intermediate and venular capillary portions and capillary domain area were measured in the left ventricular wall. Compared with the control rats which had been brought back from the low temperature at the 12th generation and reared at 25°C since then. the heart and the cardiac cells were hypertrophied. total capillary density increased and the capillary domain areas were reduced along the capillary path from the arteriolar to venular capillary portions. The number of the venular capillary portions showed no significant change but the arteriolar and intermediate capillary portions significantly increased. All these changes suggest that the cardiac capillary network was better developed in the cold‐reared rats than in control rats. In the cold‐adapted rats the hypertrophic changes in cardiac cells are thus accompanied by improvements in the oxygen delivery capacity. This adaptation provides a basis for the maintenance of increased thermogenesis in many organs. The changes cannot be established by several weeks exposure to low temperature. but only after rats have been bred in a cold room for generations. Keywords capillarity. cap

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00100.x

出版商:Blackwell Science Ltd.    

年代:1997

数据来源: WILEY

摘要:

In the pig eye. oxygen and glucose consumption in the outer retina are reduced in light compared to the consumption in the dark and most of the glucose consumed is metabolized to lactate both in light and in the dark. In the present study. in order to characterize the metabolism of glucose in the inner retina. blood was collected from an artery and from a plexus on the optic nerve draining blood from the retina. Arteriovenous concentration differences for glucose. lactate and oxygen were determined. Observations were made in dark‐adapted eyes and then after light adaptation. The consumption of oxygen and glucose and the lactate formation in the inner retina were calculated on the basis of these observations and recent data for retinal blood flow. In dark‐adapted eyes. approx. 69% of the glucose was oxidized and approx. 20% was used in lactate formation. After 5‐10 min of exposure to constant light. the levels of oxygen consumption and lactate formation were no different from those in darkness. The results indicate that lactate formation is a normal property of the pig inner retina. but that it is much less pronounced than in the outer part. The metabolism of the inner retina in constant light is similar to that in darkness. A comparison with data for the outer retina indicates that oxygen consumption in the inner retina in constant light is approx. 47% of that in the whole retina. while for glucose consumption and lactate production. the corresponding figures are approx. 12 and 8%. respect

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00030.x

出版商:Blackwell Science Ltd.    

年代:1997

数据来源: WILEY