VERAPAMIL-INDUCED SECRETION OF ACTIVE AND INACTIVE RENIN IN CONSCIOUS SHEEP

1. Regulation of plasma active and inactive renin was investigated using conscious sheep with indwelling artery, vein and bladder catheters. Control and experimental studies were carried out in the same animals on different days. 2. The calcium antagonist drug verapamil was given as an initial bolus injection (0.5 mg/kg) followed by a continuous infusion (0.1 mg/kg per h) over a 2.5 h period. 3. Plasma active and inactive renin changed in parallel. Both were significantly increased within 15 min of the initial drug dose and both attained a peak increase after 45 min. Thereafter, the two forms of renin returned to basal levels despite continued infusion of the drug. 4. Effective renal plasma flow (C_PAH) was also transiently increased by verapamil and followed a similar time course to changes in plasma active and inactive renin concentration. Arterial blood pressure, however, remained suppressed by verapamil for the duration of the study. 5. Verapamil did not alter urine flow or sodium and potassium excretion rates. 6. These results are discussed in relation to the possible link between intrarenal haemodynamics and renin secretion in conscious and in anaesthetized animals and also in relation to the concept that variation in the relative amounts of active and inactive renin secreted in differing physiological situations represents a mechanism for regulating the renin-angiotensin system.     

HAEMORRHAGE-INDUCED SECRETION OF ACTIVE AND INACTIVE RENIN IN CONSCIOUS AND PENTOBARBITONE-ANAESTHETIZED SHEEP

The response of plasma levels of active and inactive renin to haemorrhage was investigated in sheep with indwelling artery and vein catheters. In conscious animals, loss of 10% of estimated blood volume over a 5 min period increased plasma active renin by a mean of 59%, a surprisingly small change. Plasma inactive renin also increased, but only by 86%. Maximum increases in both forms of renin occurred within 1 h of the haemorrhage. The effects of an equivalent blood loss were investigated in pentobarbitone-anaesthetized sheep maintained in an upright posture using padded slings. Anaesthesia per se had no effect on plasma active or inactive renin. In anaesthetized sheep, 3 h after haemorrhage, plasma active renin had increased by 403% and inactive renin by 299% above control values, but a plateau (maximum) response was not reached during this time. In both conscious and anaesthetized animals the haemorrhage-induced increases in active and inactive renin occurred in parallel. It appears that haemorrhage of this intensity is a comparatively mild stimulus to increase plasma renin concentration in conscious sheep but is much more effective in anaesthetized animals. This may be linked to anaesthetic-induced increases in prostaglandin synthesis within the kidney.     

SERUM ANGIOTENSIN CONVERTING ENZYME ACTIVITY AND PLASMA RENIN ACTIVITY IN EXPERIMENTAL MODELS OF RATS

1. Serum angiotensin converting enzyme activity (ACEA) and plasma renin activity (PRA) were determined in rats under different experimental conditions such as: nephrotic syndrome (NS), bilateral nephrectomy (BN), renovascular hypertension (RH), dehydration (DEH), anaesthesia (AN), low sodium diet (LSD) and high sodium diet (HSD), and injection with propranolol (PRO) and isoprenaline (ISO). 2. PRA increased in LSD, AN, NS, RH, DEH and IPT groups, and decreased in HSD, BN, and PRO groups. Serum ACEA did not change in RH, HSD, IPT, DEH, AN, and PRO groups, increased in NS group, and decreased in LSD and BN groups. 3. Serum ACEA changed in the opposite direction to PRA only in the LSD group. This finding suggests that ACE may limit the full expression of the renin-angiotensin system in the LSD group, but not in the other groups.     

EFFECT OF SODIUM INTAKE AND SODIUM DELIVERY TO THE MACULA DENSA ON RENAL RENIN CONTENT AND JUXTAGLOMERULAR APPARATUS MORPHOLOGY

Active and inactive renin were measured in individual juxtaglomerular apparatus (JGA) and in whole kidney homogenates. The morphology of the JGA was examined in microbiopsy glomerular specimens and in kidneys fixed by arterial perfusion. In rats on high and normal salt intake the total renin content of a single JGA was 14 (s.e.m. = 3) and 29 (s.e.m. = 4) ng AI/h, respectively. The amount of cystoplasm occupied by renin granules was 20% and 27%. Crystalline cores were seen in 1.5% and 7% of the granules, respectively. Increased delivery of NaCl to the macula densa did not alter total renin, but decreased inactive renin from 30% to 0, crystalline core-containing cells from 33% to 14% and decreased the percentage of granules with crystalline cores from 12% to 2.2%. Increased sodium in the diet and increased delivery of NaCl to the macula densa decreased the proportion of renin present in the inactive form and decreased the proportion of crystalline cores. These coincidental alterations suggest that crystalline cores contain inactive renin and suggest that the delivery of sodium to the macula densa activates renin.     

THE EFFECT OF PHENTOLAMINE ON ACTIVE AND INACTIVE RENIN RELEASE IN HUMAN RENOVASCULAR HYPERTENSION

1. Phentolamine was infused at low increasing doses (0.2, 0.3, 0.4 and 0.5 mg/min) in five patients with unilateral renal artery stenosis measuring active and inactive (cryoactivable) renin in the renal veins from the stenosed and nonstenosed kidney and in a peripheral vein. 2. PRA values from the stenosed kidney (11.59, s.e.m. = 5.79 pmol ang I/ml per h) were higher than those in the peripheral vein (5.19, s.e.m. =2.64) while these latter were similar to those from the contralateral kidney (5.09, s.e.m. =2.93). Phentolamine significantly increased PRA from the stenosed kidney and in the peripheral vein in a dose-related manner. PRA changes were unrelated both to blood pressure decrements and to heart rate increments induced by the drug. 3. Before phentolamine, inactive renin from the stenosed kidney (5.19, s.e.m. = 2.84 pmol ang I/ml per h) did not differ significantly from that on the contralateral side (3.15, s.e.m. = 1.96) and in the peripheral vein (4.40, s.e.m. = 1.96). Phentolamine induced significant (P < 0.005) increments of inactive renin only from the stenosed kidney at the doses of 0.3, 0.4 and 0.5 mg/min. Inactive renin from the contralateral kidney was unchanged and it tended to increase, but not to a significant extent, in the peripheral vein. A highly significant relationship was found between active and inactive renin from the stenosed kidney (r = 0.79, P < 0.001, n= 25) and in peripheral blood (r = 0.71, P < 0.001, n= 25) but not from the stenosed kidney (r = 0.29, n= 25). 4. These results suggest that phentolamine, infused at low increasing doses causes an increase of PRA only in the stenosed kidney, an action which does not seem to be wholly explained by either sympathetic nervous system activation or decrease of renal perfusion pressure, and which suggests an action on intrarenal a-adrenoreceptors. Furthermore, phentolamine stimulated inactive renin release only from the stenosed kidney without evidence of intrarenal conversion of the inactive into the active form.     

DYNAMIC CHANGES IN PLASMA INACTIVE RENIN LEVELS IN BARTTER''S SYNDROME AFTER ADMINISTRATION OF CAPTOPRIL AND ANGIOTENSIN II

Changes in plasma active and inactive renin concentration (ARC and IRC) after captopril administration and angiotensin II (AII) infusion were studied in six patients with Bartter's syndrome. A single oral dose of captopril (8-25 mg) lowered the blood pressure and increased both ARC and IRC. AII infusion elevated blood pressure, suppressed ARC and increased IRC. In this syndrome of high renin levels, infused AII appeared to increase inactive renin secretion by reducing its conversion to active renin. On the other hand, an acute fall in AII levels and/or renal perfusion pressure by captopril increased both active and inactive renin. This indicates that the increase in the secretion of inactive renin, stimulated by captopril, might exceed any increase in its conversion to active renin in patients with Bartter's syndrome, in whom the production of renin is accelerated, and conversion of inactive renin to active renin probably already operates near its maximum.     

EFFECT OF MINERALOCORTICOIDS AND SALT LOADING ON RENIN RELEASE, RENAL RENIN CONTENT AND RENAL RENIN mRNA IN MICE

1. DOCA and 9 alpha-fludrocortisone were given to mice on a high-sodium diet for periods of up to 20 weeks, resulting in decreases in plasma renin concentration, renal renin concentration and renal renin mRNA with both treatments. 2. Plasma renin concentration was suppressed prior to suppression of renin mRNA and renal renin levels, indicating that suppression of synthesis and secretion of renin occur separately. 3. The decrease in renal renin concentration that occurred with DOCA was greater and more rapid than the decrease that occurred with 9 alpha-fludrocortisone, suggesting that DOCA caused intra-renal breakdown of renin. 4. When DOCA was given to mice on a low-sodium diet, plasma renin concentration and renal renin concentration increased, indicating that the effects of DOCA on renin levels were dependent on dietary sodium. 5. Renin secretion and synthesis appeared to be controlled by different mechanisms and sodium balance has an important effect on both processes.     

THE ROLE OF THE MACULA DENSA IN RENIN SYNTHESIS

1. The role of the macula densa in renin synthesis was studied using mice with one hydronephrotic kidney. 2. Renin synthesis was assessed by measurement of renal renin, renal mRNA for renin and plasma renin. 3. Sodium depletion stimulated mRNA and renal renin to a similar extent in the hydronephrotic and contralateral kidney. 4. Enalapril stimulated mRNA concentration in both kidneys but renal renin did not rise in the hydronephrotic kidney. 5. Propranolol did not alter the response to sodium depletion in either kidney. 6. The macula densa is not crucial for the stimulation of renin synthesis following sodium depletion. However, it may regulate renin production after mRNA synthesis, possibly by controlling the conversion of prorenin to renin.     

EFFECT OF GONADOTROPINS AND PREGNANCY ON PRORENIN AND RENIN IN THE RAT

1. Stimulation of adult female rats with pregnant mare serum gonadotropin (PMSG) and human chorion gonadotropin (hCG) increased active plasma renin about two-fold, but caused only a slight increase of plasma prorenin. The concentrations of active renin and prorenin in the ovaries, and active renin in the uterus all increased about two-fold 2 days after stimulation with PMSG. The prorenin in the uterus was below detection in unstimulated rats and did not change consistently after PMSG. 2. Active renin and prorenin in plasma were unchanged in relation to pregnancy, except for a slight decrease of prorenin in the third trimester. In the first and third trimester the concentration in the ovaries of active renin and prorenin was decreased to about one-third of that in normal female rats. In contrast active renin in the uterus was increased about two-fold in the first trimester, whereas prorenin did not change consistently. 3. Our results confirm that gonadotropins and pregnancy affect the renin-angiotensin system in rats. However, the changes in the plasma seem to be much smaller than those previously reported in humans. Accordingly, our results do not support a systemic role of prorenin for reproduction in the rat.     

THE ROLE OF THE RENAL NERVES IN RENIN SYNTHESIS

1. Renin synthesis and secretion were studied in Balb/c mice with a denervated left kidney. 2. Denervation inhibited renin secretion. 3. Denervation reduced the renal renin content. 4. Denervation reduced renal renin mRNA. 5. Renal denervation inhibits renin secretion by blocking the synthetic system prior to mRNA formation.     

STRUCTURE OF HUMAN RENIN AND EXPRESSION OF THE RENIN GENE

The amino acid sequence of human renin was identified for the first time. This was determined from the nucleotide sequence of exons in the human renin gene identified in a genomic library by recombinant DNA techniques. Examination of amino acid residues involved in the enzymatic hydrolysis by human renin of the unique Leu10-Val11 bond of human angiotensinogen revealed features peculiar to this highly specialized aspartyl protease. The expression of the renin gene was examined with a hybridization probe for renin mRNA in sections and extracts of tissues. In the submandibular gland of mice renin mRNA, like renin, increased during development and in response to testosterone in females; sodium depletion increased renin mRNA in kidney.     

AUTORADIOGRAPHIC LOCALIZATION OF ACTIVE RENIN IN THE JUXTAGLOMERULAR APPARATUS OF THE DOG KIDNEY: EFFECTS OF SODIUM INTAKE

1. The effects of dietary sodium intake on active renin binding in the juxtaglomerular apparatus (JGA) of superficial and juxtamedullary cortex of the dog kidney were examined by quantitative in vitro autoradiography using a radiolabelled renin inhibitor [¹²⁵I]-H77, which has high affinity for dog renin. 2. Changes in sodium intake resulted in marked alterations of active renin binding in the radiolabelled JGA. In comparison with the control kidney (190.8 ± 7.7 Bq/mm³), a higher density of binding occurred in the labelled JGA of sodiumdepleted kidney (277.7 ± 6.2 Bq/mm³), while a lower density of binding was found in the labelled JGA of sodium-loaded kidney (99.3 ± 7.4 Bq/mm³). 3. Active renin binding in the labelled JGA was significantly higher in superficial JGA than in their juxtamedullary counterparts, irrespective of sodium intake. 4. Pre-incubation with trypsin (0.5mg/mL), a procedure known to activate prorenin, markedly increased active renin binding in the labelled JGA of control (+～ 35%; P < 0.01), and sodium-loaded kidneys (+～ 75%; P < 0.01), but had little effect on binding in the labelled JGA of the sodium-depleted kidney (± 5–10%; NS). The proportions of active renin as a percentage of total renin were 60, 75 and 95% in the labelled JGA of sodium-loaded, control, and sodium-depleted kidneys, respectively. 5. Emulsion microscopic autoradiography revealed that the binding was exclusively localized in the JGA, including the afferent and efferent arterioles, macula densa and extraglomerular mesangium. Labelling extended to the interlobular arteries in sodium depleted kidney. 6. These results indicate that autoradiography combined with the in vitro binding of radiolabelled renin inhibitors may provide a useful tool to measure active and prorenin renin and thereby study the physiological regulation of renin in the kidney.     

CIRCULATING LEVELS OF ACTIVE, TOTAL AND INACTIVE RENIN (PRORENIN), ANGIOTENSIN I AND ANGIOTENSINOGEN IN CARBON TETRACHLORIDE-TREATED RATS

1. Plasma renin activity (PRA), plasma angiotensin I concentration (ANG I), plasma angiotensinogen concentration (PAC) and the plasma levels of active, total and inactive renin (prorenin) were measured in rats with carbon tetrachloride (CCl₄)-induced acute renal failure. Rats were treated with a single oral dose of CCl₄ (2.5 mL/kg) and killed 1, 2, 3 and 7 days later. 2. On days 1–3 PRA, ANG I and PAC decreased and increased on day 7. Active renin fell on days 2 and 3, total renin (trypsin treatment) augmented on day 1 and diminished on day 3, prorenin and per cent prorenin increased on days 1 and 2. Angiotensin I concentration paralleled PRA and PAC. The CCl₄-induced decrease in PRA was secondary to the fall in active renin and in PAC. Total renin augmented as a consequence of the elevation of prorenin. Renal function, evaluated by serum urea, serum creatinine and creatinine clearance, decreased on days 1 and 2 when PRA was low and plasma prorenin was high. 3. These data do not support the involvement of the circulating active renin-angiotensin system (RAS) in the pathophysiology of acute renal failure induced by CCl₄, however, increased prorenin levels were associated with the decrease in renal function.     

IN VIVO AND IN VITRO EFFECTS OF ATRIAL NATRIURETIC PEPTIDE ON RENIN RELEASE

1. This study investigated the effect of atrial natriuretic peptide on renin release from the kidney. The in vitro direct effect was examined in the animal experiment using renal cortical slices of rat, and the in vivo effect was observed in the human infusion study. 2. In the in vitro experiments, alpha-human atrial natriuretic peptide (alpha-hANP) ranging 10(-9) to 10(-6) mol/L did not change the basal renin release rate from the renal cortical slices (-9% at 10(-6) mol/L, NS). Isoproterenol (10(-6) mol/L) increased renin release by 40% (P < 0.001), whereas angiotensin II (10(-6) mol/L) suppressed it by 48% (P < 0.001). However, alpha-hANP did not affect the stimulative effect of isoproterenol or the inhibitory effect of angiotensin II. 3. Also in the human study, infusion of 25 ng/kg per min alpha-hANP failed to change the plasma renin activity in normotensive subjects (-4%) or patients with essential hypertension (+5%), or even in patients with raised renin levels such as renovascular hypertension (+10%) or congestive heart failure (-13%). 4. These results put forth negative views on the direct involvement of atrial natriuretic peptide in renin release from the juxtaglomerular apparatus.     

CHANGES IN RENAL RENIN GENE EXPRESSION IN FETAL SHEEP†

1. Renin gene expression was investigated in kidneys from 13 foetal and four adult sheep. 2. The levels of renal renin and mRNA in foetuses were greater than those in adult sheep (P < 0.001). 3. There was no significant difference in renin mRNA levels between foetuses aged 91 and 134 days (term 150 days). 4. The levels of renin gene expression were higher (178±5 units; P < 0.001) in foetuses at 142 days than levels in 91 (144±4 units) and 134 days old foetuses (146±6 units). 5. It is concluded that the high level of renin gene expression in the foetal kidney in responsible for the high levels of renin in the foetal circulation.     

EFFECTS OF ENALAPRIL AND DUP753 ON RENIN SYNTHESIS IN MICE WITH ONE HYDRONEPHROTIC KIDNEY

1. Renin synthesis and secretion were investigated in mice with one hydronephrotic kidney. 2. Enalapril and Dup753 stimulated renin synthesis to a similar extent in the hydronephrotic and normal kidney. 3. Hydronephrosis did not prevent an increase in renin mRNA caused by enalapril and Dup753. 4. The results therefore indicate that the macula densa does not appear to be crucial for renin synthesis in the kidney under the inhibition of angiotensin II. 5. Thus angiotensin II plays an important role controlling renin gene expression in both the normal and hydronephrotic kidneys.     

THE EFFECT OF DOCA AND 9α-FLUDROCORTISONE ON RENAL RENIN CONTENT AND PRODUCTION

1. DOCA and 9 alpha-fludrocortisone were given to rats. 2. Plasma renin fell rapidly with both treatments. 3. Renal renin fell slowly to a low level. 4. Renal renin fell to a lower level with DOCA than with 9 alpha-fludrocortisone. 5. When DOCA and 9 alpha-fludrocortisone were stopped plasma renin levels rose rapidly and the renal renin levels increased. 6. The data suggest that synthesis is altered rapidly but it takes a prolonged time for the kidney to become depleted of renin due to the high tissue stores and the associated inhibition of release.     

ACTIVE AND INACTIVE RENIN IN CRITICALLY ILL PATIENTS

The relationship between active (A) and inactive (I) plasma renin concentrations (PRC) was examined in critically ill patients to test for intravascular renin activation in states of shock and tissue damage. Critically ill patients had significantly elevated APRC and lowered IPRC:APRC ratio compared with age and sex matched healthy subjects. IPRC in the critically ill was similar to the control group. During blood donation normal volunteers showed a twofold increase in APRC. The rise in APRC was proportionately greater than for IPRC, with a subsequent fall in IPRC:APRC ratio. In both critically ill patients and blood donors elevated APRC was associated with decreased IPRC:APRC ratio, consistent with either consumption of the inactive renin zymogen or preferential secretion of the active form. Individual critically ill patients displayed markedly depressed ratios but with only moderately elevated APRC, a pattern suggestive of intravascular renin activation. Consistent evidence for intravascular or extravascular activation of renin was not apparent.     

ANGIOTENSINS II AND III PREVENT CAPTOPRIL-INDUCED RENIN RELEASE IN THE RAT

1. The effects of exogenous angiotensins II and III (50 pmol/min i.v.) on plasma renin release following captopril injection (5 mg/kg, i.v.) were studied in anaesthetized Sprague-Dawley rats, to determine whether angiotensin II blockade is the major mechanism by which captopril induces renin release. 2. Captopril produced a 12-fold increase in plasma renin concentration compared with saline-injected controls. This was completely reversed by pre-infusion of angiotensin II or III. 3. The fall in blood pressure following captopril treatment was also abolished by angiotensins II and III pre-infusion. Noradrenaline pre-infusion (200-800 ng/min, i.v.) also prevented the captopril-induced hypotension but did not alter the rise in plasma renin. 4. Ureteric ligation did not significantly reduce captopril-induced renin release suggesting that acute changes in sodium excretion or delivery of electrolyte to the macula densa were not involved in renin release. 5. These findings suggest that captopril induces renin release by inhibiting angiotensin II feedback control of renin secretion and that angiotensin III may also modulate renin release.