摘要:

The characteristics of brachiocephalic and carotid sinus baroreceptors with non‐medullated afferents have been studied in rabbits. The conduction velocities of 18 non‐medullated fibers arising from the brachiocephalic baroreceptors were 0.4–0.8 m/s (0.59±0.03 m/s, mean ± SE) and their thresholds were 74–104 mmHg (84±2 mmHg). 29 non‐medullated carotid sinus baroreceptor afferents had thresholds ranging from 60 to 125 mmHg (92±3 mmHg). Their conduction velocities were 0.5–1.1 m/s (0.65±0.05 m/s). Blood pressure‐baroreceptor response curves of both the brachiocephalic and the carotid sinus baroreceptors were constructed. As the aortic arch non‐medullated baroreceptor afferents, the brachiocephalic and the carotid sinus baroreceptors with non‐medullated afferents exhibited thresholds about 30 mmHg higher than the medullated ones, considerably lower firing rates, comparatively rapid adaptation and remarkable irregular discharge pattern. It is suggested that the non‐medullated baroreceptor afferents are of little importance for the cardiovascular regulation under normal conditions but are likely to play an important role during a sudden r

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1983.tb07172.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

The sympathetic control of the carotid sinus baroreceptor activity was studied in rabbits. Stimulation of the cervical sympathetic trunk (10 Hz, 1 ms, 4–12 V) elicited an increase in discharge frequency of the non‐medullated baroreceptor afferents but not of the medullated fibers. An isolated carotid sinus area preparation was used to examine the influence of noradrenaline perfusion on baroreceptor activity. Non‐medullated baroreceptor afferents, but not the medullated afferents, responded to noradrenaline perfusion (10‐6g/ml) with a significant increase in firing rate. Short‐term resetting of the baroreceptors was also studied with the same preparation. After perfusing the sinus at a hypertensive level for 30 min the pressure‐response curves of both the non‐medullated and the medullated baroreceptor afferents shifted to the right with increased thresholds and decreased maximal discharge frequencies. The extent of the short‐term resetting was greater in non‐medullated afferents than in medullated ones. It is concluded that the carotid sinus baroreceptors with non‐medullated afferents are under the sympathetic control. The physiological significance o

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1983.tb07173.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

8 subjects were exposed to the Stroop mental performance test in a design with alternating hourly periods of rest and stress. During each period one urine sample and several venous plasma samples were obtained. Heart rate responded rapidly to initiation and termination of the stress exposure with increases and decreases respectively. Both urinary and plasma adrenaline increased significantly during stress. The plasma response was immediate and sustained. Neither urinary, nor plasma noradrenaline were significantly increased by the test. Plasma noradrenaline, however, increased significantly on termination of the exposure to stress. It was suggested that the latter effect may be due to muscle sympathetic nerve activity decreasing during stress and increasing following stress. The sample‐to‐sample variation was more than 20% of the mean for both catecholamines, indicating the need for frequent sampling to reliably reflect plasma levels. The mean intraindividual plasma/urine correlation was r̄=0.70 (p<0.001) for adrenaline and r̄=0.40 (p<0.05) for noradrenaline. When only resting periods were considered, no significant correlations remained, apparently due to a reduced range of variation and accompanying reduced signal‐to‐noise ratio. It is concluded that both urinary and plasma adrenaline may be useful in the evaluation of changes in sympatho‐adrenal activity du

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1983.tb07174.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Immunoreactive plasma glucagon and secretin in the rat was elevated 48 hours after nephrectomy and ureteral ligation. Since kidneys obstructed by ureteral ligation were unable to remove glucagon and secretin from the blood, renal handling of glucagon and secretin must include glomerular filtration. Insulin and somatostatin levels were significantly elevated 48 hours after nephrectomy, but not after ureteral ligation, indicating partial uptake from peritubular capillaries.

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1983.tb07175.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

The effects of central cooling and exterior heating on serum concentrations of thyrotropin (TSH), growth hormone (GH), and norepinephrine were studied in 10 normal males under resting conditions. Cooling was induced by ingestion of ice while the subjects were immersed in water of a temperature prone to elicit only minor cutaneous thermal reflexes. TSH and thyroid hormones changed neither during cooling nor during heating. Cooling induced a virtually complete suppression of GH‐secretion whereas heating had the opposite effect: pronounced increase, also without previous cooling. Plasma norepinephrine rose by a factor of 2.5 and 1.7 during cooling and heating, respectively. It is concluded that the pituitary‐thyroid system does not take part in short‐term thermoregulation in man–as opposed to the situation in some smaller mammals. The mechanisms and the physiological role of the GH‐responses to cooling and heating are as yet unknown, but the latter stimulus is an advantageous tool in clinical and pathophysiological studies of pituitary function as it is both safe and c

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1983.tb07176.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

In conscious rats prostaglandin E2‐ and F2aexcretion rates increased from about 20 to more than 100 pg/min/g kidney weight as urine flow decreased from about 10 to below 1 μ/min/g kidney weight following 24 h of water deprivation confirming previous data from surgically prepared rats (Leyssac&Christensen 1981b). There was no difference in this response between rats on a normal sodium diet and severely sodium depleted rats. Additional supply of polyunsaturated fatty acids in the food did not influence the results. Elevated levels of prostaglandin excretion did not correlate with urine osmolality. The reliability of the radioimmunoassays used was documented by comparison with measurements by gas chromatography‐mass spectrometry. The analysis showed that these two methods provide almost identical estimates of urinary PGE2and PGF2acontent. It is concluded that renal prostaglandin production is activated by a negative feedback mechanism as tubular and/or urine flow rate decreases towards subnormal va

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1983.tb07177.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

A sensitive device for recording of mechanical activity in isolated small blood vessels with calibres down to 100 μm is described. This equipment was used to examine the mechanical properties of rat cerebral arteries. The ultrastructure of the preparations was investigated by light‐, transmission, and scanning electron‐microscopy. In general the walls of the middle cerebral and basilar arteries consisted of 3 layers of smooth muscle cells, which occupied approximately 80% of the total wall thickness. The present technique preserved the integrity of the vessel wall and caused no observable damage to the smooth muscle or endothelial cells. Neither the basilar nor the middle crebral arteries developed spontaneous phasic contractions under standard conditions. Potassium excess (124 mM) induced a biphasic contractile response characterized by a fast and partly transient increase in tension (phase A), followed by a slowly developing sustained contraction (phase B). The responses to K+were strong, highly reproducible and not influenced by pH changes in the range 6.9‐7.8, making K+‐stimulation suitable for testing of vascular contractility. Length‐tension measurements were performed on relaxed and K+‐activated basilar arteries. The mechanical behaviour of the vessels conformed to a sliding‐filament model of muscular contraction. Using the “Maxwell model” of a muscle, the length at which the contractile element produced maximum active tension was established. The passive wall tension at this length (˜ 1 mN/mm) averaged only about 20% of the total wall tension the arteries were capable of producing when activated by K+. Under isometric conditions the K+‐contracted basilar artery developed a maximum active wall stress of approximately 240 mN/mm2. In the light of the mechanical data obtained from the length‐tension measurements, the optimum resting wall tension for registration of vascular responses is discussed. It appears that the present in vitro system can be of great value in investigations of the smooth muscle function

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1983.tb07178.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

The vascular α‐adrenoceptors in isolated feline cerebral, lingual and mesenteric arteries were characterized and compared. In the middle cerebral artery the relative order of potency for agonists was: clonidine>oxymetazoline>noradrenaline>phenylephrine which indicates that the postjunctional α‐receptor in this vessel is of α2‐type. This view is further supported by the finding that yohimbine, but not prazosin, had a potent, mainly competitive blocking action. In peripheral arteries, clonidine was without effect. In these vessels, the potency difference between phenylephrine and oxymetazoline was more than 40 times less than in cerebral vessels. The pA2‐values for prazosin correlated well with pA2‐values found for the interaction of this drug with α1‐receptors in a variety of other tissues, thus suggesting the occurrence of an α1‐receptor in these arteries. However, the pA2‐values for yohimbine and rauwolscine correlated well with an α2‐receptor, suggesting also the presence of α2‐receptors. Schild plots for prazosin and rauwolscine in lingual arteries displayed slopes significantly lower than unity, which also supports the view of a mixture of α1‐and α2‐receptors in these vessels. However, the Schild plots for the antagonists in mesenteric arteries did not differ significantly from unity, a finding possibly indicating the presence of an α‐receptor unable to differentiate between substances that in other tissues act pr

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1983.tb07179.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

The pressures in the renal interstitial space seem to have important influence on the setting of the sensitivity of the tubuloglomerular feedback that controls the glomerular filtration rate (GFR), and on the rate of proximal tubular fluid reabsorption. Measurements were made of interstitial pressure conditions, GFR, renal plasma flow (RPF), urinary excretion of sodium and potassium, and plasma renin activities in dehydrated animals and normopenic controls, before and after saline volume expansion (5% of body weight and hour). Colloid osmotic pressure, estimated from the protein concentration in renal hilar lymph, was 7.5 mmHg in the dehydrated animals (controls 2.8 mmHg) and decreased to 3.1 (controls 1.7 mmHg) after volume expansion. The lymph flow rate was increased in both groups of animals after volume expansion. Interstitial hydrostatic pressure, measured in the subcapsular space, was 2–3 mmHg in dehydrated and control animals and increased to 3–4 mmHg after volume expansion. In dehydrated rats GFR and RPF was reduced to 60% of the control values, but after volume expansion they regained control values. After volume expansion, urinary excretion of fluid and electrolytes increased more in controls than in dehydrated rats. Plasma renin activity was dereased in both groups of rats after volume expansion. Thus, in dehydrated animals there was a high colloid osmotic pressure and a low hydrostatic pressure in the renal interstitium, while after volume expansion the oncotic pressure fell and the hydrostatic pressure rose. The effect of volume expansion was found to be dependent on the preceding volume balance situation in the ani

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1983.tb07180.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

To study the influence of the tubuloglomerular feedback control (TGF) on the regulation of glomerular filtration rate (GFR) during dehydration, micropuncture experiments were performed on surface nephrons of dehydrated rats. Dehydration was achieved by withdrawal of food and water for 24 h. The urine flow rate decreased to 1.5 μl/min (controls 2.9 μl/min) and GFR decreased in these rats to 0.80 ml/min (controls 1.22). TGF was studied by two different micropuncture procedures. With the first technique the changes in proximal stop‐flow pressure in response to changes of the late proximal microperfusion rate were measured. With this technique the perfusion rate necessary to induce a half maximal stop‐flow pressure response, the turning point, was also determined. An increased TGF sensitivity was found in dehydrated rats, as indicated by increased stop‐flow pressure responses (35 versus 26%) and decreased turning points (16 versus 21 nl/min). With the second micropuncture technique the single nephron GFR (SNGFR) was measured at distal and proximal tubular sites, in the same nephron. Distal SNGFR was decreased during dehydration to 32.2 nl/min, versus 42.7 nl/min in controls. A significant difference between paired SNGFR measurements in the same nephron was observed during dehydration, the proximal value being 5.3 nl/min higher than the distal, whereas this difference was not seen in control rats. This finding indicates that activation of the feedback mechanism takes place to reduce SNGFR. It is concluded that the decrease in whole kidney GFR is partly caused by the observed increase in feedback activity. The present results are also in agreement with our earlier hypothesis that the hydrostatic and oncotic pressure conditions within the interstitial space surrounding the macula densa cells modulate the sensitivity of the tubuloglomerular feedback me

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1983.tb07181.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY