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.     

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.     

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.     

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.     

EFFECT OF LONG-TERM TREATMENT WITH AN ANGIOTENSIN-CONVERTING ENZYME INHIBITOR ON THE RENIN-ANGIOTENSIN SYSTEM IN SPONTANEOUSLY HYPERTENSIVE RATS

1. To obtain information on regulation of the brain renin-angiotensin system, the effect of long-term administration of angiotensin-converting enzyme (ACE) inhibitor on brain renin and angiotensinogen mRNA was studied. 2. Spirapril (3 mg/kg) was orally administered daily for 8 weeks to spontaneously hypertensive rats (SHR) from 12 weeks after birth. Renin and angiotensinogen mRNA in the brain and kidney were then quantitated by Northern blot analyses with [32P]-labelled rat renin and angiotensinogen cDNA as hybridization probes. Plasma renin activity (PRA), angiotensin II (AII) concentration, plasma ACE activity and brain tissue ACE activity were also measured. 3. Compared with the control group, the Spirapril-treated group had significantly lower blood pressure (P less than 0.01), significantly higher PRA (P less than 0.01), a not significantly different plasma AII concentration, and lower plasma and brain ACE activities (P less than 0.01). Interestingly, the brain renin and angiotensinogen mRNA levels of the two groups were similar, but the renal renin mRNA level was significantly higher in the Spirapril-treated group (P less than 0.01). 4. These results indicate that the mRNA levels of brain renin and angiotensinogen were not affected by chronic ACE inhibition in the circulation and suggest that AII in the brain might not be affected by systemic ACE inhibition.     

INCREASE IN SERUM TOTAL ANGIOTENSIN-CONVERTING ENZYME ACTIVITY WITH ENALAPRIL THERAPY IN HUMANS: A CONTROLLED TRIAL

1. In a controlled, randomized double-blind trial, 15 patients with essential hypertension were treated with enalapril 5-20 mg/day, or doxazosin 1-8 mg/day, during a 7 week dose titration phase. This was followed by 7 weeks of combined treatment with doxazosin and enalapril. 2. Blood was taken after a 2 week placebo run-in phase, and at 3 and 7 weeks in the single-agent and combined treatment phases, for measurement of plasma renin activity (PRA), plasma angiotensin II (AII), plasma aldosterone and serum free and total angiotensin-converting enzyme (ACE) activities. 3. Doxazosin had no effect on serum free or total ACE activities. 4. Enalapril reduced serum free ACE activity and increased serum total ACE activity, which at 7 weeks was significantly greater than in patients receiving doxazosin. 5. In those patients who received enalapril, 10 mg/day for 3 weeks and then 20 mg/day for 4 weeks (n = 12), with or without doxazosin, mean serum total ACE activity increased by 51%. PRA was also increased in this group, but there were no changes in plasma AII or aldosterone concentrations.     

RENIN AND ANGIOTENSIN-CONVERTING ENZYME GENOTYPES IN PATIENTS WITH ESSENTIAL HYPERTENSION AND LEFT VENTRICULAR HYPERTROPHY

1. The associations between left ventricular hypertrophy (LVH) and specific alleles of the renin and angiotensin-converting enzyme (ACE) genes were studied in patients with essential hypertension and normal blood pressure. 2. LVH was present in 42% of those with essential hypertension (n= 72) and 17% of those with normal blood pressure (n= 44). 3. The frequency of each renin allele was the same in hypertensive and in normotensive patients. Renin allele frequencies were also the same for those with LVH and those with normal cardiac mass. When only hypertensives were considered, renin alleles were in the same proportion for the groups with and without LVH. Similarly, ACE alleles were not associated with essential hypertension nor with elevated cardiac mass. 4. We conclude that, in this population, variations in the renin or ACE genes do not contribute significantly to the development of LVH or to essential hypertension.     

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.     

PRORENIN AND ACTIVE RENIN CONCENTRATIONS IN OVARIAN FOLLICULAR FLUID INCREASE AFTER THE LH PEAK IN SUPEROVULATED HEIFERS

1. The aim was to analyse the in vivo variations with time of prorenin and active renin and their relationship to steroid hormones in ovarian follicular fluid during follicular growth in heifers. 2. Thirty one beef heifers were assigned to two groups after oestrous synchronization: an unstimulated and a follicle-stimulating hormone (FSH)-treated (superovulated) group. Within each group, animals were slaughtered at different times of the follicular phase of the oestrous cycle. Ovarian follicular fluids were aspirated and analysed for the concentrations of active renin, prorenin, oestradiol-17β (E₂) and progesterone (P₄). 3. Prorenin and active renin concentrations in follicular fluid remained constant until the luteinizing hormone (LH) peak, after which time they increased four- and two-fold, respectively, in superovulated heifers. 4. In follicular fluid, prorenin and active renin correlated negatively with oestradiol and E₂/P₄ ratio but positively with progesterone during follicular growth in superovulated heifers. Prorenin also correlated negatively with oestradiol and E₂/P₄ ratio in unstimulated heifers. 5. The increase of renin concentrations in ovarian follicles after the LH peak and the correlations to steroid hormones suggest an important role of the ovarian renin-angiotensin system in bovine follicular growth and maturation.     

ACCURATE DETERMINATION OF THE SIZE OF THE FIRST INTRON DELETION IN THE RENIN GENE OF SHR FROM AN AUSTRALIAN COLONY

1. It has been reported that the first intron of the renin gene of the spontaneously hypertensive rat (SHR) is shorter than that of the Wistar-Kyoto (WKY) rat, suggesting a role for this difference in the development of hypertension. 2. The genealogy of some Australian SHR colonies has raised doubts about its similarity to the Japanese, American and European colonies. 3. The polymerase chain reaction (PCR) technique has been used with primers identical to the flanking region of the first intron of the renin gene to determine its length in SHR, WKY and Sprague-Dawley (SD) from an Australian colony. 4. The size of the first intron of the renin gene in SHR, WKY and SD was found to be approximately 3870, 4550 and 5000 base pairs, respectively, results which agree with those previously published. 5. It was concluded that the first intron deletion, and its size, has been conserved in an Australian SHR colony.     

COMPARISON OF NEURITE OUTGROWTH WITH NEUROFILAMENT PROTEIN SUBUNIT LEVELS IN NEUROBLASTOMA CELLS FOLLOWING MERCURIC OXIDE EXPOSURE

1. The objectives of the study were to establish that inhibition of neuronal differentiation in culture (assessed by neurite outgrowth) can be used as a broad spectrum in vitro measure of neurotoxicity. 2. To establish whether a rapid measure of neurite outgrowth could be used. Thus the study examined the relationship between the degree of neurite outgrowth assessed directly by image analysis and neurofilament protein subunit levels measured by an ELISA. 3. SKNSH neuroblastoma cells, exposed for up to 6 days to mercuric chloride during initiation and continuation of differentiation, had lower levels of neurofilament proteins than unexposed cells. 4. Preliminary data from parallel examinations of neurite outgrowth assessed by image analysis and neurofilament protein subunit levels assessed by ELISA support a correlation when neurofilament protein levels are decreased by sub-cytotoxic doses of mercuric chloride in SKNSH cells.     

IS ALDOSTERONE/RENIN RATIO USEFUL TO SCREEN A HYPERTENSIVE POPULATION FOR PRIMARY ALDOSTERONISM?

The ratio of aldosterone to renin in plasma was measured in samples collected from 79 hypertensive patients. Eighteen patients with primary aldosteronism had ratios ranging from 25 to 677 (mean 183) when measured on 34 occasions, while 16 normal subjects had ratios of 3.3-21 (mean 11.3). Of the remaining 61 patients with ratios ranging from 1.8 to 184, 15 patients have ratios greater than 25 and are under investigation for primary aldosteronism, which appears highly likely in five and has been excluded in two. The aldosterone/renin ratio appears promising as a screening test for primary aldosteronism. Consistency and the effects of sodium and potassium balance and of antihypertensive medications require further study.     

EFFECT OF ETHAMSYLATE ON CARRAGEENAN-INDUCED RAT PAW OEDEMA: A COMPARISON WITH INDOMETHACIN

1. Ethamsylate (diethylammonium 2,5-dihydroxybenzene sulfonate, Dicynene), a systemic haemostatic agent with an unknown mechanism of action, was tested for anti-inflammatory activity using the carrageenan-induced rat paw oedema test. 2. Ethamsylate was shown to be an effective anti-inflammatory agent with a time course and amplitude of effect similar to that of indomethacin, although the potency was only about 4% of that for indomethacin. 3. When ethamsylate and indomethacin were co-administered they did not show additive effects, suggesting that they do not share a common mode of action. It is proposed that ethamsylate, like indomethacin, may inhibit prostaglandin synthesis. Ulceration produced by indomethacin, it is suggested that it may prove to be a useful addition to, or replacement for, indomethacin in the treatment of inflammatory disorders.     

EQUINE ANGIOTENSIN CONVERTING ENZYME: A ZINC METALLOENZYME

1. Angiotensin I converting enzyme from horse plasma has been extensively purified and shown to be homogeneous by disc-gel electrophoresis. 2. The metal ion involved in the catalytic reaction of the enzyme has been identified for the first time as zinc by atomic absorption spectrometry. 3. A number of other physicochemical properties of the enzyme are described and compared with results obtained by other investigators. The molecular weight was determined by gel filtration to be 113 000 daltons. The pH maximum was found to be 7.4. The chloride activation of the enzyme appears to act by facilitation of substrate binding to the enzyme. 4. By use of enzyme inhibitors, tyrosine has been implicated as a functional residue at the active site of the enzyme. 5. The enzyme shows a fairly high degree of specificity towards its substrates.     

A COMPARISON OF THE HAEMODYNAMIC EFFECTS OF DIETARY SODIUM RESTRICTION AND ACUTE SODIUM DEPLETION IN THE CONSCIOUS SHEEP

The use of a low Na, low K sorghum grain diet supplemented with intraruminal electrolyte infusions has enabled dietary manipulation of sodium status to be studied in the sheep. Dietary sodium restriction reduced urinary sodium excretion within 24 h with maximal retention after 3 days. There were no other substantial metabolic or haemodynamic changes. A more severe form of sodium deficiency produced by parotid salivary drainage resulted after only 2 days in a sodium deficit 3-4 times that seen with 14 days of sodium restriction. Extracellular fluid volume and cardiac output decreased. Blood pressure was unchanged but there was an increase in peripheral resistance and plasma renin concentration.     

VASODILATORY EFFECTS OF MILRINONE ON PULMONARY VASCULATURE IN DOGS WITH PULMONARY HYPERTENSION DUE TO PULMONARY EMBOLISM: A COMPARISON WITH THOSE OF DOPAMINE AND DOBUTAMINE

1. The limited therapeutic role of pulmonary vasodilation reflects lack of their selectivity for the pulmonary vasculature, and many drugs have been evaluated for effectiveness; however, none has gained widespread clinical use. 2. Milrinone (MIL) is a newly synthetized phosphodiesterase inhibitor, which has potent positive inotropic and vasodilatory effects. 3. The present study shows the effects of MIL on the pulmonary circulation in dogs with pulmonary hypertension due to autologous muscle-induced pulmonary embolism, and also demonstrates a comparison with those of dopamine and dobutamine. 4. As MIL showed potent vasodilatory effects on the pulmonary vasculature, it had a potential clinical role in the treatment of pulmonary hypertension.     

THE SYNDROME OF HYPERTENSION AND HYPERKALAEMIA WITH NORMAL GFR. A UNIQUE PATHOPHYSIOLOGICAL MECHANISM FOR HYPERTENSION?

Based on 28 reported patients, constant features of the syndrome of hypertension and hyperkalaemia are hyperkalaemia, hyperchloraemia, normal renal glomerular function and, in all adult patients, hypertension. Inconstant features include short stature, intellectual impairment and muscle weakness. Levels of renin and aldosterone are low, but respond to dietary salt restriction and diuretic therapy, both of which reverse the hypertension and hyperkalaemia. The basic abnormality is excessive renal sodium retention, leading to chronic suppression of renin and aldosterone; the latter is then hyporesponsive to the hyperkalaemic stimulus. Dietary salt loading or impaired production of any natriuretic or chloriuretic factor (for example atrial natriuretic peptide or renal natriuretic prostaglandins) would predispose to development of the syndrome. With normal GFR, this appears to be a unique mechanism for hypertension and hyperkalaemia.     

CHARACTERIZATION OF SUBSTANCE P-INDUCED BRONCHOCONSTRICTION IN THE GUINEA-PIG: A COMPARISON WITH ACETYLCHOLINE

Substance P (0.5-8.0 micrograms/kg, i.v.) induced bronchoconstriction in anaesthetized, mechanically-ventilated guinea-pigs, comprising increases in airways resistance and decreases in dynamic compliance. These bronchoconstrictor responses were unaffected by bilateral vagotomy, pretreatment with pheniramine (2 mg/kg, i.v.) or by pretreatment with atropine (100 micrograms/kg, i.v.). Acetylcholine-induced (4-32 micrograms/kg, i.v.) bronchoconstriction was prevented by atropine pretreatment, whereas bilateral vagotomy inhibited responses to acetylcholine. Ganglionic blockade using hexamethonium (20 mg/kg, i.v.) potentiated both substance P and acetylcholine on airways resistance and dynamic compliance. Indomethacin (1 or 5 mg/kg, i.v.) did not affect substance P-induced bronchoconstriction, whereas the higher dose enhanced acetylcholine-induced increases in airways resistance. In addition, aspirin pretreatment (20 mg/kg, i.v.) did not alter the bronchoconstrictor potency for either substance P or acetylcholine. On the other hand, the combined cyclo-oxygenase/lipoxygenase inhibitors eicosatetraynoic acid (ETYA, 20 mg/kg, i.v.) and BW755C (20 mg/kg, i.v.) potentiated both acetylcholine and substance P on airways resistance and dynamic compliance. The results suggest that substance P-induced bronchoconstriction may be modulated by the sympathetic nervous system and does not appear to be influenced by vagal or histaminergic mechanisms. The failure of indomethacin or aspirin to affect substance P-induced bronchoconstriction, together with the enhancing effects of ETYA and BW755C pretreatments, provide evidence consistent with the existence of a bronchodilator mechanism which may be inhibited by compounds inhibiting lipoxygenase enzymes.