Role of angiotensin in normal blood pressure regulation

Summary Antiangiotensin II plasma induced transitory hypotension in rats when 0.2 ml was injected intravenously in normal males (either awake or anaesthetized), into binephrectomized females or into some males which had been nephrectomized 18–22 or 42–53 hours previously. Antiangiotensin II did not affect the blood pressure of male rats when given between 24 and 26 hours after nephrectomy. Antiangiotensin resulted in a 10–200 fold increase in the dose of angiotensin required to produce a measurable change in blood pressure, and also significantly reduced reactivity to l-noradrenaline.A remaining plasma renin activity was constantly found in binephrectomized females and in most of binephrectomized males. Plasma renin activity was significantly higher in the former than in the latter. It is concluded that angiotensin plays a role in the maintanance of blood pressure, in normal rats, in binephrectomized females and in some binephrectomized males.This work was supported by Grant 67-00-517 from D.G.R.S.T. (Délégation Générale à la Recherche Scientifique et Technique).This study was presented in part at the third Annual Meeting of the European Society for clinical Investigation, Scheveningen, Holland, April 26th 1969, and at the National Meeting of the American Federation for clinical Research, Atlantic City, N.J., U.S.A., May 4th 1969.     

Blood pressure maintenance in awake dehydrated rats: renin, vasopressin, and sympathetic activity

The role of vasopressin, the renin system, and sympathetic activity in sustaining blood pressure in the dehydrated state was investigated in normotensive nonanesthetized male Wistar rats. After 48-h dehydration, plasma arginine vasopressin was 14.0 +/- 1.7 pg/ml and plasma norepinephrine 0.46 +/- 0.05 ng/ml. In another group of rats in which the angiotensin converting enzyme inhibitor (MK 421, 5 mg po twice daily) was administered throughout the dehydration period, blood pressure was reduced by more than 20% (P less than 0.001), and both plasma arginine vasopressin and norepinephrine were higher at 23.4 +/- 3.9 pg/ml (P less than 0.01) and 0.83 +/- 0.07 ng/ml (P less than 0.01), respectively. Taken together, in rats with or without converting enzyme blockade, there was an inverse correlation between mean blood pressure and plasma arginine vasopressin (r = 0.67, P less than 0.01) as well as plasma norepinephrine (r = 0.82, P less than 0.01) levels. The acute administration of a specific vasopressin pressor inhibitor (dPVDAVP) reduced mean blood pressure in the rats with a blocked renin system by 16.9 mmHg (P less than 0.001). In rats without converting enzyme inhibition, the induced fall was only 6.4 mmHg. These results indicate that following 48-h dehydration the renin angiotensin system interacts with the vasopressin secretory mechanism to sustain blood pressure, with renin playing a predominant role. They further suggest that, following blockade of the renin system, activation of the sympathetic nervous system probably also contributes to blood pressure maintenance.     

The effect of isoprenaline infusion on renal renin and angiotensinogen gene expression in the anaesthetised rat

In this study, we investigated the ability of acute infusions of isoprenaline to alter renin and angiotensinogen gene expression in the kidney of rats anaesthetised with chloralose-urethane. Groups of rats received I.V. infusions of either saline or the beta-adrenoceptor agonist isoprenaline at 400 ng x kg(-1) x min(-1) for 4 h. The isoprenaline infusion caused a sustained decrease in mean blood pressure of approximately 20 mmHg (P < 0.01), an increase in heart rate of 50 beats x min(-1) (P < 0.01) and reductions in urine flow and sodium excretion of 80-90 % (both P < 0.01). Renal blood flow and glomerular filtration rate were transiently reduced by 21 % (P < 0.01) and 61 % (P < 0.001), respectively, in the first hour, recovering to baseline levels after 4 h of infusion. At the end of the study, plasma renin activity was raised approximately 6-fold (P < 0.01) while renal renin and angiotensinogen mRNA levels were 1.8- and 1.5-fold higher (both P < 0.05) compared to the control group (saline infusion). The isoprenaline-induced renin secretion could have been mediated via the activation of beta-adrenoceptors resulting in the exocytosis of renin-containing granules, with a smaller contribution being due to reduced renal haemodynamics. The increase in renal renin gene expression in response to isoprenaline was probably due primarily to the intracellular signalling processes acting directly on nuclear mechanisms. Similarly, the increased renal angiotensinogen gene expression most probably reflected a direct action of the isoprenaline. These findings provide evidence that catecholamines are involved in mechanisms that rapidly alter the expression of the genes of the renin-angiotensin system within the kidney.     

Étude chez le rat des variations du débit individuel de filtration glomérulaire des néphrons superficiels et profonds en fonction de l'apport sodé

Résumé La distribution intrarénale des débits de filtration glomérulaire par néphron (fg) est étudiée en fonction de l'apport sodé chez trois groupes de rats: normaux, carencés en sodium et surchargés en sodium. Les fg ont été déterminées soit indirectement par la méthode de Hanssen soit grâce à une modification de cette méthode qui procure directement les valeurs absolues [23].Chez les rats normaux, la fg est égale à 27,9 nl/min pour les néphrons superficiels et à 38,5 nl/min pour les néphrons juxtamédullaires. Il n'existe pas de différence décelable entre les fg de nos rats sans sel et celles de nos rats normaux. Chez les rats surchargés en sel, les fg des néphrons superficiels et juxtamédullaires passent respectivement à 52,4 nl/min et à 52,7 nl/min.Au cours de nos surcharges sodées l'augmentation de filtration glomérulaire du rein résulte donc d'une augmentation de la fg de tous les néphrons. Celle-ci est cependant nettement plus marquée pour les néphrons superficiels et le rapport fg néphrons superficiels/fg néphrons juxtamédullaires qui est de 0,7 environ chez les rats normaux et sans sel, atteint 1,0 au cours de nos surcharges sodées. Ainsi dans cette dernière condition physiologique l'hétérogénéité fonctionnelle des néphrons disparaît. La variation des fg est discutée en fonction de ce que l'on sait de la variation de la distribution intrarénale de la rénine sous l'influence de l'apport sodé.

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Variations in glomerular filtration rate of single superficial and deep nephrons under various conditions of sodium intake in the rat

Summary The intrarenal distribution of single glomerular filtration rates (SGFR) was studied in rats previously fed a normal or a low sodium diet during antidiuresis, or in rats previously fed a high sodium diet during hypertonic saline diuresis. SGFR were determined either indirectly by Hanssen's technique, or directly by means of a modification of this technique which gives absolute values [23].In the normal rats, the mean value of SGFR of superficial and juxtamedullary nephrons was equal to 27.9 nl/min and 38.5 nl/min, respectively. There was no appreciable difference between SGFR in our normal and salt-deprived rats. In the salt-loaded rats, the mean value of SGFR of superficial and juxtamedullary nephrons reached 52.4 nl/min and 52.7 nl/min, respectively.Therefore, the increase of the GFR of the whole kidney during salt loading was due to an increase of SGFR of all the nephrons. However, the increase of SGFR was more important for the superficial ones and the ratio SGFR superficial nephrons/SGFR juxtamedullary nephrons which was 0.7 in the normal rats reached 1.0 in the salt-loaded rats, indicating that there was no more functional heterogeneity of nephrons during our salt loadings. The variation of SGFR is discussed in relation to the sodium dependent variation of the intrarenal distribution of renin observed by many authors.

Ce travail a été, en partie, présenté au 4ème Congrès International de Néphrologie, Stockholm 1969.     

Effects of long-term inhibition of neuronal nitric oxide synthase on blood pressure and renin release

Nitric oxide (NO) produced by neuronal NO-synthase (nNOS) in macula densa cells may be involved in the control of renin release. 7-Nitro indazole (7-NI) inhibits nNOS, and we investigated the effect of short- (4 days) and long-term (4 weeks) 7-NI treatment on blood pressure (BP), plasma renin concentration (PRC) and glomerular filtration rate (GFR) in rats on different salt diets. Rats were divided into three groups and given low-salt (LS), normal (C) and high-salt (HS) diets. Each diet group was subdivided into two groups treated either with 7-NI or vehicle. Long-term 7-NI-treated rats (LS and C) showed increased BP compared with controls (LS: 149 +/- 4 vs. 133 +/- 3; C: 146 +/- 4 vs. 127 +/- 4 mmHg). Blood pressure in HS rats did not differ from that in controls. Plasma renin concentration was stimulated in LS-rats (251 +/- 64 mGU mL(-1)) compared with C and HS rats (42 +/- 8 and 39 +/- 5 mGU mL(-1), respectively) but was not significantly affected by chronic 7-NI treatment (350 +/- 103, 49 +/- 10 and 50 +/- 15 mGU mL(-1) in LS, C and HS, respectively). In rats treated with 7-NI for 4 days, no effect on BP was seen, but PRC was increased in 7-NI treated LS rats compared with vehicle treated LS rats (107 +/- 15 vs. 56 +/- 1 mGU mL(-1)). Stimulation of PRC in LS rats was further enhanced by 7-NI after 4 days of treatment, but not affected in rats treated for 4 weeks. This suggests that inhibition of nNOS stimulates renin release but that this stimulatory effect in the long run might be depressed by the increase in blood pressure.     

Renin System of the Kidney in ISIAH Rats with Inherited Stress-Induced Arterial Hypertension

The renal renin system was studied in ISIAH rats with inherited stress-induced arterial hypertension. The expression of genes for renin (Ren1) and cyclooxygenase (Cox-2) was evaluated in renal tissue of ISIAH and WAG rats (normotensive control). Basal gene expression for Ren1 and Cox-2 in ISIAH rats was much lower than in WAG rats. Water deprivation for 11 h was followed by a 4-fold increase in Cox-2 gene expression in ISIAH rats. The increase in gene expression was insignificant in WAG rats (by 30%). Renin gene expression in renal tissue of ISIAH and WAG rats remained practically unchanged after water deprivation. We conclude that a change in Cox-2 gene expression after short-term water deprivation serves as a reliable criterion for functional strain of the renal renin system in hypertensive ISIAH rats. Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 147, No. 2, pp. 134–138, February, 2009     

Tubuloglomerular feedback in rat kidneys of different renin contents

Variations in flow rate through the loop of Henle in the range of 0--50 nl/min were induced using pressure controlled microperfusion. Simultaneously, with the aid of a second pressure-microperfusionsystem, the glomerular function of the same nephron was studied by continuous measurement of two parameters, early proximal flow rate (EPFR) and/or stop flow pressure (SFP). Elevation of loop perfusion above physiological values (40 nl/min) resulted in a drop of EPFR and SFP, whereas lowering perfusion rates had no effect. This feedback behaviour was studied in kidneys with different renin contents to test the role of the renin-angiotensin system in the mediation of the macula densa signal to the adjacent glomerular vessels. Renal renin content, measured after micropuncture experiments by incubation with substrate followed by radioimmunoassay of angiotensin I, was unaltered in control (Ia) and heminephrectomized rats (Ib), lowered in contralateral kidneys of 2 kidneys Goldblatt hypertensive rats (IIa), in DOCA- and salt-loaded rats (IIb), and in DOCA-, salt-loaded and heminephrectomized rats (IIc), and it was evaluated in clipped kidneys of Goldblatt hypertension rats (IIIa). Micropuncture evaluation of the tubuloglomerular feedback behaviour in these experimental groups revealed the following results: 1. a feedback response under all conditions independent of the widely varying renin contents (1000-fold), 2. an asymmetrical behaviour of the feedback response in all kidneys as demonstrated by suppression of EPFR and SFP at elevated loop flow rates, but no change of these parameters when loop flow was interrupted. 3. compared to controls the decrease of each GFR parameter between 0 and 40 nl/min loop perfusion was lower in DOCA- and salt-loaded rats (IIb, IIc). Additional heminephrectomy (IIc) had no further influence on the reduced feedback response in DOCA- and salt-loaded rats, whereas this maneuver reduced the renal renin content drastically. A somewhat higher response than in controls was found in heminephrectomized rats (IIb) and in clipped kidneys of Goldblatt hypertensive rats (IIIa). These different magnitudes of feedback responses do not correlate with the renal renin content. It has been concluded, therefore, that renal renin activity is not the sole determinant of the effectiveness of the tubuloglomerular feedback response.     

Effects of placental insufficiency on the ovine fetal renin-angiotensin system

We postulated that chronic placental insufficiency would be associated with reduced expression of renal renin and angiotensinogen genes in the fetal sheep. Placental development was restricted in ewes by removing the majority of caruncles prior to mating (placentally restricted (PR) group). The weights of PR fetuses were significantly reduced (P < 0.05, 2.98 +/- 0.33 kg) compared to control fetuses (4.20 +/- 0.30 kg). Kidney weights were also significantly reduced in the PR fetuses (P < 0.05, 8.4 +/- 0.9 g) compared with control fetuses (12.2 +/- 1.3 g). The ratios of renal renin/-actin mRNA levels were significantly reduced in PR fetuses (P < 0.001, 0.35 +/- 0.02) when compared to control animals (0.98 +/- 0.13). The renal angiotensinogen mRNA/18S rRNA ratio was significantly lower (P < 0.05, 0.28 +/- 0.13) in PR fetuses compared with control fetuses (0.72 +/- 0.10), while hepatic angiotensinogen was unaffected. There was a positive correlation between renal renin mRNA and renal angiotensinogen mRNA levels (r = 0.65, P < 0.05, n = 12). It is unlikely that these changes in renal angiotensinogen and renin mRNA were due to the small increment in plasma cortisol levels (< 5 nmol l-1). There was, however, a positive correlation between arterial PO2 and renal renin mRNA (r2 = 0.77, P < 0.01). Plasma renin levels were not different between the two groups. Thus, restriction of nutrient and oxygen supply throughout fetal life was associated with suppression of renal renin and renal angiotensinogen gene expression, with no effect on hepatic angiotensinogen mRNA levels. This specific suppression of fetal renal renin and angiotensinogen expression could alter the activity of the intrarenal RAS and so affect growth and development of the kidney.     

Renin release by renin-depleted rats following hypotensive haemorrhage and anesthetics

1. Renin-depletion, described as a decrease in renal cortex and plasma renin levels, was produced by clipping one renal artery of a rat and leaving the contralateral kidney in place (two kidney one clip hypertension). One month later the clipped kidney was removed and after 24 h recovery such rats were found to be renin depleted: renal cortex and plasma renin levels were 8 and 63% of normal respectively.
2. Such renin depleted rats were incapable of releasing renin (as judged by increase in plasma renin level) in response to severly hypotensive haemorrhage and had very blunted renin release responses to pentobarbital and urethane anesthesia (59 and 17% of normal respectively).
3. Our results confirm the hypothesis that a low renal renin status is associated with low basal and stimulated renin release. We suggest that the renin depleted rat may be a useful model for the study of the role of the renin angiotensin system in phenomena such as blood pressure compensation following hypotensive haemorrhage and drinking induced by beta-adrenoreceptor agonists.

     

The role of a renal thirst factor in drinking induced by extracellular stimuli

1. Rats in normal fluid balance drank water 1-2 hr after complete ligation of the inferior vena cava either above or below the renal veins. At the same time there was a fall in urine flow and excretion of electrolyte, especially after caval ligation above the renal veins, so that the animals ended the initial 6 hr period in positive fluid balance.2. Caval ligation was relatively ineffective as a stimulus to drinking after bilateral nephrectomy, but was effective in rats made anuric by ureteric ligation.3. Rats subjected to caval ligation and offered a choice between water and 1.8% saline (w/v) drank water, despite the increasing hypotonicity of the body fluids thereby resulting.4. During the secondary polydipsia, which generally occurred on about the third day after caval ligation as renal function was recovering, there was an increased preference for 1.8% saline.5. Constriction of the aorta above the renal arteries, or constriction of both renal arteries, also caused drinking, oliguria and the development of positive fluid balance.6. Constriction of the aorta below the renal arteries, or after nephrectomy, was ineffective as a stimulus to drinking.7. Saline extracts of renal cortex caused rats in normal water balance to drink. Activity was destroyed by boiling the extract for 10 min. Renal medullary and hepatic extracts were without effect on drinking.8. It proved impossible to separate dipsogenic and pressor activities of renal extracts during the different stages of fractionation which lead to the production of renin; disappearance of one activity was invariably accompanied by disappearance of the other.9. Dipsogenic and pressor actions were greater in nephrectomized rats than in normal rats.10. Both extractable dipsogenic factor and extractable pressor activity were reduced by treating the rat with DOCA and saline for several weeks beforehand.11. The renal dipsogen therefore has similar properties to renin. It may prove to be identical with renin, particularly in view of the fact that angiotensin also stimulates drinking.12. Adrenalectomy did not affect drinking induced by renin or by caval ligation.13. It is concluded that the renin angiotensin system may play a role in the genesis of the thirst which follows certain extracellular stimuli.     

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.     

The renin-angiotensin system in rats with hereditary hydronephrosis

The renin-angotensin system was studied in rats suffering from hereditary hydronephrosis in which normal blood pressure, hyperkalemia, and damage to the renal medulla and distal tubules were found. An increased serum creatinine level, decreased creatinine clearance and increased 24 hrs urine volume were observed in rats with bilateral hydronephrosis. When compared to rats with normal kidneys, bilaterally hydronephrotic animals exhibited elevated plasma renin activity (9.9 +/- 1.3/S.E./ng AI/ml/hr vs. 2.4 +/- 0.4 in rats with normal kidneys), and decreased renal renin concentration (78 +/- 4 mug AII/g vs. 132 +/- 5). No correlation between the extent of kidney damage and renal renic concentration was found. After the hyperkalemia of the hydronephrotic rats was corrected, there were significant increases in both plasma renin activity and renal renin concentration, but the renal renin concentration remained significantly lower than that observed in animals with normal kidneys. The results suggest that renin production and/or storage capacity are diminished in hydronephrotic kidneys.     

Vasopressin and renin response to dehydration in aged rats

Abnormalities in neurohypophyseal function have been postulated to contribute to the alterations in fluid and electrolyte balance observed during aging. In this study, parameters of fluid and electrolyte balance were evaluated during chronic water deprivation in old (30 months) and young (3 months) Fischer 344 rats. The increases in serum vasopressin (VP) and renin concentrations observed in the 3 month animals following chronic water deprivation were absent in the aged rats (p<0.05 and p<0.02, respectively). This occurred in spite of apparently comparable alterations in fluid volume and osmolality (assessed by changes in body weight, hematocrit and plasma osmolality). Relative to body weight, VP content of the neural lobe was significantly reduced and was more severely depleted by dehydration in aged rats than in young rats. Thus, inadequate neurohypophyseal hormone stores may contribute to the inability of the aged animals to attain elevated serum VP concentrations during chronic stimulation. Several parameters of renal function were examined in the aged rats. Although none of the old rats were in renal failure, they all showed some indication of reduced renal function. In spite of renal abnormalities including reduced concentrating capabilities, the old rats did demonstrate a significant antidiuretic response to dehydration. However, with prolonged fluid deprivation, they were unable to attain serum VP or renin concentrations comparable to that achieved by the young rats.     

Effect on renin release of inhibiting renal nitric oxide synthesis in anaesthetized dogs

Nitric oxide plays an important role in the regulation of basal renal blood flow. This study was performed to examine whether selective inhibiti± of renal nitric oxide synthesis affects renin release in vivo. Accordingly, in six barbiturate-anaesthetized dogs renin release was examined before and after intrarenal infusion of the selective inhibitor of nitric oxide synthesis, N^G-nitro-l -arginine (NOARG). NOARG was infused into the renal artery to yield a renal arterial blood concentration of 0.4 μmol ml^-1. NOARG did not change systemic arterial blood pressure and glomerular filtration rate, but reduced basal renal blood flow by 26 ± 2%. Urine flow, sodium and potassium excretion were reduced after inhibition of renal nitric oxide synthesis. Basal renin release (3 ± 2 μg AI min^-1) was not altered by NOARG infusion (1 ± 1 μg AI min^-1). To stimulate renin release the renal artery was constricted to a renal perfusion pressure of 50 mmHg. At this perfusion pressure infusion of NOARG reduced renin release significantly from 48 ± 11 μg AI min^-1to 14 ± 4 μg AI min^-1. In conclusion, inhibition of renal nitric oxide synthesis reduces basal renal blood flow and reduces renin release stimulated by renal arterial constriction. These findings indicate that renal nitric oxide modulates both renal blood flow and renin release in vivo.     

Nitric oxide and the role of blood pressure variability to the kidney.

Blood pressure variability is buffered by at least two mechanisms: the arterial baroreceptor reflex and nitric oxide (NO). Only recently is the importance of blood pressure variations on cardiovascular control being investigated. Here we report of a study performed in conscious dogs, in which renovascular hypertension was induced. Reduction of renal arterial pressure (RAP) to 85 mmHg for 24 h elicited profound hypertension by 60 mmHg (vs. control: 110 +/- 3 mmHg; P < 0.01). This was accompanied by reduced volume and sodium excretion (-48% of control, P < 0.01 and -80% of control, P < 0.01, respectively) and augmented renin release by more than two-fold (P < 0.01). This intervention was compared with a protocol in which RAP was reduced to the same mean value, however, RAP oscillated by +/-10 mmHg at 0.1 Hz. This manoeuvre led to a transient increase in NO3 excretion in urine (P < 0.01), blunted antidiuresis (-14% of control) as well as antinatriuresis (-40% of control) and attenuated the increased renin release by 30% (P < 0.05). In consequence, the magnitude of blood pressure increase was only half as high as that observed during static reduction of RAP (P < 0.01). It is concluded that blood pressure oscillations to the kidney have a profound influence on water and electrolyte balance and on renin release, which alleviates the onset of Goldblatt hypertension.     

Inhibitory effect of endothelin on renin release in dog kidneys

To investigate the effect of endothelin on renin release, experiments were performed in barbiturate-anaesthetized dogs with denervated kidneys. Intrarenal infusion of endothelin (1 ng min^-1kg^-1body wt) reduced renal blood flow (RBF) from 145 ± 10 ml min^-1to 98 ± 9 ml min^-1without altering renin release (1 ± 1 μg angiotensin I (AI) min^-1). Renin release was then increased either by renal arterial constriction or ureteral occlusion. When renal arterial pressure was reduced to 50 mmHg, renin release averaged 79 ± 20 μg AI min^-1in six dogs and fell significantly to 24 ± 6 μg AI min^-1during endothelin infusion. During ureteral occlusion the inhibitory effect of endothelin on renin release either during inhibition of β-adrenergic activity with propranolol or after inhibiting prostaglandin synthesis by indomethacin during intrarenal infusion of isoproterenol was examined. After propranolol administration ureteral occlusion increased renin release from 5 ± 2 μg AI min^-1to 38 ± 12 μg AI min^-1in six dogs. Subsequent intrarenal endothelin infusion (1 ng min^-1kg^-1body wt) during maintained ureteral occlusion reduced renin release to 10 ± 3 μg AI min^-1. In six other dogs prostaglandin synthesis was inhibited by indomethacin. Subsequent infusion of isoproterenol (0.2 μg min^-1kg^-1body wt) to stimulate β-adrenoceptor activity increased renin release from 13 ± 4 μg AI min^-1to 68 ± 8 μg AI min^-1during ureteral occlusion. Intrarenal endothelin infusion (1 ng min^-1kg^-1body wt) reduced renin release to 22 ± 3 μg AI min^-1during continuous isoproterenol infusion and ureteral occlusion. Hence endothelin inhibits renin release induced by renal arterial constriction or ureteral occlusion. Similar inhibitory effects whether renin release was raised by increasing prostaglandin synthesis or by stimulating β-adrenergic activity suggest a direct effect of endothelin on the juxtaglomerular cells.     

Vasopressin and renin response to dehydration in aged rats

Abnormalities in neurohypophyseal function have been postulated to contribute to the alterations in fluid and electrolyte balance observed during aging. In this study, parameters of fluid and electrolyte balance were evaluated during chronic water deprivation in old (30 months) and young (3 months) Fischer 344 rats. The increases in serum vasopressin (VP) and renin concentrations observed in the 3 month animals following chronic water deprivation were absent in the aged rats (p<0.05 and p<0.02, respectively). This occurred in spite of apparently comparable alterations in fluid volume and osmolality (assessed by changes in body weight, hematocrit and plasma osmolality). Relative to body weight, VP content of the neural lobe was significantly reduced and was more severely depleted by dehydration in aged rats than in young rats. Thus, inadequate neurohypophyseal hormone stores may contribute to the inability of the aged animals to attain elevated serum VP concentrations during chronic stimulation. Several parameters of renal function were examined in the aged rats. Although none of the old rats were in renal failure, they all showed some indication of reduced renal function. In spite of renal abnormalities including reduced concentrating capabilities, the old rats did demonstrate a significant antidiuretic response to dehydration. However, with prolonged fluid deprivation, they were unable to attain serum VP or renin concentrations comparable to that achieved by the young rats.     

A sensitive method for determination of renin activity in the single juxtaglomerular apparatus of the rat kidney

Summary We have established a method for the determination of renin activity in minute amounts of tissue. This method was used for single juxtaglomerular apparatuses (JGA's) of rats. Enzyme kinetic studies were performed to establish the optimal conditions for microdissected JGA's, using purified rat renin and its substrate.Maximal formation of angiotensin occurs at pH 6.5. The effect of incubation and homogenization time, temperature, substrate and renin concentration on the angiotensin formation rate was studied.For the studies reported here purified rat renin substrate was used. The purification methods revealed a substrate content of appr. 1000 ng/mg protein. This highly purified rat renin substrate improved the sensitivity of renin determination in micro amounts of tissue. Hence renin activity of single microdissected JGA's could be quantitatively determined within 1 hour of incubation in a volume of 0.1 ml. Mean renin activity in 18 JGA's from rats kept on standard Altromin diet was 15.2±S.D. 7.0 ng/0.1 ml·hour.Supported by the Deutsche Forschungsgemeinschaft.     

The influence of nephrectomy,ureteral ligation,and of estradiol on plasma renin substrate in unilaterally nephrectomized rats

Summary The effects of three experimental conditions on the concentration of plasma renin substrate were studied with special reference to plasma renin concentration in unilaterally nephrectomized rats.After simultaneous bilateral nephrectomy the maximum increase in plasma renin substrate was 17 times higher than normal within 24 h, while in rats which were unilaterally nephrectomized 10 days previously, followed by the removal of the remaining kidney (two-step bilateral nephrectomy), the maximum increase in plasma renin substrate was markedly suppressed (6-fold of normal). The maximum increases in plasma renin substrate by estradiol treatment in normal and unilaterally nephrectomized rats were about the same, associated with similarly decreased plasma renin concentrations. The similar increase in plasma renin substrate was found after ureteral ligation in unilaterally nephrectomized rats and bilateral ligation of the ureters in normal rats. This was the case where the plasma renin concentrations changed differently after ureteral ligation. After two-step bilateral nephrectomy plus estradiol treatment the maximum increase in plasma renin substrate was found to be higher than that found after two-step bilateral nephrectomy, but was lower than that after simultaneous bilateral nephrectomy.It is suggested that under the pathological conditions that stimulate renin substrate production, the plasma rein substrate concentration is less affected by circulating renin.This work was supported in part by a grant No. 048212 from the Japanese Ministry of Education