Psychosocial stimuli and human plasma renin activity

The effects of several types of acute psychosocial stimuli on plasma renin activity (PRA) were studied in normotensive healthy subjects. Puzzle-solving produced an increase in blood pressure but no significant change in PRA, although two of seven subjects did respond with large increases in PRA. Watching a disturbing movie also raised blood pressure, but did not alter PRA. In contrast, a combination of novelty, fear, and/or anticipation did constitute a significant stimulus for renin secretion; this was evidenced by the fact that naive subjects (who were not told in advance what to expect) had significantly higher PRAs on the first day of the 2-day puzzle-solving study. PRA on this day correlated strongly with anxiety proneness, as did the decrease from day 1 to day 2. We conclude that meaningful psychosocial stimuli can enhance renin secretion in susceptible individuals.     

Effects of unilateral nephrectomy on plasma renin substrate and renin concentration in rats

Effects of unilateral nephrectomy on plasma renin concentration and renin substrate (angiotensinogen) concentration were studied over an experimental period of 10 days in rats. The maximum increase in plasma renin substrate concentration after bilateral nephrectomy was 9 times higher than the preoperative level. Very low but measureable plasma renin concentrations were found in rats nephrectomized bilaterally 24 hrs previously. In unilateral nephrectomized rats the concentration of renin substrate in plasma increased maximumly 3.5-fold within 24 hrs after the operation and on the third day it was decreased to half of the maximum level. Even 10 days after uninephrectomy the concentration of plasma renin substrate was significantly higher than that of normal rats. Twenty four hours after unilateral nephrectomy plasma renin concentration decreased to similar low levels as those found in bilateral nephrectomized rats. The decreased concentration of plasma renin, however, returned to normal 3 days after uninephrectomy. The inverse relationship was seen between the concentrations of plasma renin and plasma renin substrate. However, substrate concentration in plasma rised faster and longer than plasma renin decreased.     

Effects of exogenous renin and sodium load on renin activity in unilaterally nephrectomized rats

Summary Effects of injection of homologous renin and sodium load given through 1.5% saline as drinking water on plasma renin activity and renin content of the kidneys were studied in rats with intact kidneys (group A) and in unilaterally nephrectomized rats (group B). During an experimental period of 10 days, blood pressure was measured four times. At the end of the experiment, the plasma renin activity and the renal content of renin were determined.Renin injection did not cause a rise in blood pressure in both groups. In unilaterally nephrectomized rats, renin content of the remaining kidney increased significantly. This increase was suppressed either by the renin injection or the salt load, whereas neither the renin injection not the salt load affected renal content of renin in group A. In unilaterally nephrectomized rats, the renin injection or the sodium load induced a significant decrease in plasma renin activity when compared to rats in group A.     

Effects of behavioral stimuli on plasma interleukin-1 activity in humans at rest

Interleukin-1 (IL-1) bioassays were done on 208 serum samples drawn from 7 volunteers, over several hours at 5-minute intervals, before, during, and after a relaxation-related behavioral stimulus. Individuals showed up to a 267% increase (t[29] = 7.750, p = 1 × 10⁻⁷.) in IL-1, and for the group, a mean 48.1% elevation (t[5] = 4.128, p =.003) occurred, during the stimulus interval relative to baseline. When baselines were repeated, IL-1 activity rapidly returned toward baseline values. Suggestions to picture one's immune cells fighting illness appeared to have no uniform effect for all subjects. Such rapid changes in plasma IL-1, concomitant with stimuli, indicate a new way to alter immune function and further understand disease susceptibility.     

Effects of caffeine on plasma renin activity, catecholamines and blood pressure.

Using a double-blind, randomized, cross-over protocol, we studied the effect of a single dose of oral caffeine on plasma renin activity, catecholamines and cardiovascular control in nine healthy, young, non-coffee drinkers maintained in sodium balance throughout the study period. Caffeine (250 mg) or placebo was administered in a methylxanthine-free beverage to overnight-fasted supine subjects who had had no coffee, tea or cola in the previous three weeks. Caffeine increased plasma renin activity by 57 per cent, plasma norepinephrine by 75 per cent and plasma epinephrine by 207 per cent. Urinary normetanephrine and metanephrine were increased 52 per cent and 100 per cent respectively. Mean blood pressure rose 14/10 mm Hg one hour after caffeine ingestion. There was a slight fall and then a rise in heart rate. Plasma caffeine levels were usually maximal one hour after ingestion but there was considerable individual variation. A 20 per cent increase in respiratory rate correlated well with plasma caffeine levels. Under the conditions of study caffeine was a potent stimulator of plasma renin activity and adrenomedullary secretion. Whether habitual ingestion has similar effects remains to be determined.     

Effect of tolbutamide on plasma renin activity.

The effect of tolbutamide on renin secretion in rats was studied in vivo, and in vitro. Administration of tolbutamide in doses of 12.5 and 25 mg/kg body wt ip to two groups of rats produced no significant change in plasma renin activity compared to the control group. In the in vitro experiments renal cortical slices were incubated with increasing concentrations of tolbutamide (0--4 mg/ml). No significant increase in the net renin production was observed, whereas the concentration of cyclic AMP increased significantly in the incubation medium. These findings suggest that in the intact rats tolbutamide does not increase plasma renin activity. In the renal cortical experiments although tolbutamide increased cyclic AMP production, the increase may not have been sufficient to stimulate the net renin production. These results are of biological significance because of the possible effects of tolbutamide and increased plasma renin activity on the cardiovascular system.     

Effects of acute exercise and prolonged exercise training on blood pressure,vasopressin and plasma renin activity in spontaneously hypertensive rats

Summary The purpose of this study was to investigate the effect of swimming training on systolic blood pressure (BP_s), plasma and brain vasopressin (AVP), and plasma renin activity (PRA) in spontaneously hypertensive rats (SHR) during rest and after exercise. Resting and postexercise heart rate, as well as blood parameters such as packed cell volume (PCV), haemoglobin concentration (Hb), plasma sodium and potassium concentrations ([Na⁺], [K⁺]) osmolality and proteins were also studied. Hypophyseal AVP had reduced significantly after exercise in the SHR, whereas PRA had increased significantly in the Wistar-Kyoto (WKY) strain used as normotensive controls. Plasma AVP concentration increased in both strains. By the end of the experiment, training had reduced body mass and BP_s by only 10% and 6%, respectively. Maximal oxygen uptake was increased 10% and plasma osmolality 2% by training. The postexercise elevation of heart rate was not significantly attenuated by training. A statistically significant reduction in postexercise plasma osmolality (10%) and [Na⁺] (4%) was observed. These results suggested that swimming training reduced BPS. Plasma and brain AVP played a small role in the hypertensive process of SHR in basal conditions because changes in AVP contents did not correlate with those of BP_s. Moreover, there were no differences between SHR and WKY in plasma, hypophyseal and hypothalamic AVP content in these basal conditions. Finally, during moderate exercise a haemodilution probably occurred with an increase of plasma protein content. This was confirmed by the exercise-induced increase of plasma AVP and the reduction of hypophyseal AVP content, suggesting a release of this hormone, which probably contributed to the water retention and haemodilution. This investigation showed that swimming training produced an attenuation of the raised resting blood pressure in this strain and that plasma and brain AVP played a negligible role in the maintenance of hypertension in basal conditions. However, during training, this hormone may have played a role, training having induced simultaneously a decrease in BP_s and plasma AVP.     

Plasma renin activity in renal hypertensive rats

Summary Plasma renin activity was estimated in normal and in renal hypertensive rats, in the unanesthetized state, in ether or in urethane anesthesia. Renal hypertension was induced by partially constricting one renal artery without touching the opposite kidney. In the unanesthetized state plasma renin activity in renal hypertensive rats was slightly, though very variably, increased (45 percent). Ether anesthesia had no influence on plasma renin activity in either normotensive or hypertensive rats. Urethane anesthesia lowered blood pressure in normotensive controls by 20 mm Hg, and caused a more than threefold increase in plasma renin activity. In renal hypertensive rats urethane depressed blood pressure by 40 mm Hg and induced a more than sixfold increase of plasma renin activity.The results suggest that the plasma renin activity in rats with renal hypertension induced by partially constricting one renal artery and leaving the contralateral kidney untouched is not necessarily augmented. This conclusion is compatible with observations in hypertensive humans with unilateral renal artery stenosis. The previous finding of a large increase of plasma renin activity in this type of experimental hypertension is an artefact due to urethane anesthesia.U. Helmchen und U. Kneissler supported by Deutsche Forschungsgemeinschaft.P. Churchill supported by National Science Foundation, Post-Doctoral Grant Number 49072, U.S.A.L. Peters-Haefeli, G. Peters and G. Schaechtelin supported by Fonds National Suisse de la Recherche Scientifique, Grant No. 53153.     

Effect of sodium restriction on plasma renin activity and renin granules in rat kidney.

The present study was carried out to procure detailed information on the relationship between chronic sodium restriction and renin content of kidneys at a subcellular level in the rat. Renin granules (RG) were separated by a discontinuous sucrose-density gradient (from 1.2 to 1.7 M) centrifugation. In control rats, RG were mainly recovered in the fractions corresponding to 1.5 M sucrose, whereas most of the mitochondria, lysosomes, and microsomes equilibrated in upper fractions. The RG fraction contained approximately 60% of total granular renin activity. Low sodium intake for 4 wk resulted in a 12.4-fold increase in plasma renin activity and led to a 2.6-fold increase in renin activity of the RG fraction. But in sodium-restricted rats there was no alteration in the distribution pattern of renin activity on sucrose-density gradients, indicating that there was no change in the density of RG. These results provide evidence for increased renin activity in storage granules following chronic sodium restriction.     

Effects of AVP and DDAVP on plasma renin activity and electrolyte excretion in conscious dogs.

Uninephrectomized adult female dogs with chronic indwelling catheters were maintained on a low sodium diet and studied without anesthesia. Following hydration with 3% dextrose, an intravenous infusion of either arginine vasopressin (AVP) or of 1-desamino-8-D-arginine vasopressin (DDAVP) was begun. The dose was calculated to achieve a near maximal physiological plasma concentration of AVP, or an equimolar concentration of DDAVP. Both AVP and DDAVP increased urinary osmolality from less than 60 to over 800 mosmol/kg H2O within 1 h. AVP infusion increased mean arterial pressure and renal electrolyte excretion and decreased heart rate and plasma renin activity (PRA), while DDAVP was without effect on these parameters. AVP infused into the renal artery at doses which did not alter systemic pressure and heart rate caused kaliuresis and reduced PRA. We conclude that the AVP-induced inhibition of renin secretion and increase in renal electrolyte excretion are not secondary to increased tubular permeability to water, but must represent a more specific action of AVP which is not shared by DDAVP.