[Renin and hypertension, physiological or pathological agents?]

Development of concepts on sodium regulation in XX century

The 20th century is the time of the birth of many scientific areas, including the physiology of the kidneys and water-salt metabolism. This article is devoted to the history of the development of one of its directions - the issue of regulation of sodium homeostasis in the body. This article is the first attempt in the Russianspeaking space to summarize the achievements in the study of sodium regulation. For many decades, scientists from different countries have studied the influence of various factors on sodium excretion: blood pressure, atrial peptides, hormones of the neurohypophysis and adrenal glands, renal nerves, infusion of various substances, etc. It was found that sodium excretion does not directly depend on changes in blood pressure and glomerular filtration rate. Atrial peptides causing natriuresis were discovered, their structure and mechanism of action were described in detail. The role of the hormones of the neurohypophysis - vasopressin and oxytocin - in the excretion of sodium, as well as the role of aldosterone and angiotensin II in the reabsorption of this cation was shown. It has been shown that the administration of hypertonic solutions of sodium chloride causes a greater natriuretic response than the administration of other substances (sodium sulfate and acetate, glucose, mannitol, etc.), and the idea of the existence of sodium-s ensitive receptors has also been put forward.

Functional Zonation of the Adult Mammalian Adrenal Cortex

The standard model of adrenocortical zonation holds that the three main zones, glomerulosa, fasciculata, and reticularis each have a distinct function, producing mineralocorticoids (in fact just aldosterone), glucocorticoids, and androgens respectively. Moreover, each zone has its specific mechanism of regulation, though ACTH has actions throughout. Finally, the cells of the cortex originate from a stem cell population in the outer cortex or capsule, and migrate centripetally, changing their phenotype as they progress through the zones. Recent progress in understanding the development of the gland and the distribution of steroidogenic enzymes, trophic hormone receptors, and other factors suggests that this model needs refinement. Firstly, proliferation can take place throughout the gland, and although the stem cells are certainly located in the periphery, zonal replenishment can take place within zones. Perhaps more importantly, neither the distribution of enzymes nor receptors suggest that the individual zones are necessarily autonomous in their production of steroid. This is particularly true of the glomerulosa, which does not seem to have the full suite of enzymes required for aldosterone biosynthesis. Nor, in the rat anyway, does it express MC2R to account for the response of aldosterone to ACTH. It is known that in development, recruitment of stem cells is stimulated by signals from within the glomerulosa. Furthermore, throughout the cortex local regulatory factors, including cytokines, catecholamines and the tissue renin-angiotensin system, modify and refine the effects of the systemic trophic factors. In these and other ways it more and more appears that the functions of the gland should be viewed as an integrated whole, greater than the sum of its component parts.

Drug discovery in renin-angiotensin system intervention: past and future

The renin-angiotensin system (RAS) plays a central role in the control of blood pressure in the body and the way this interacts with other systems is widely recognized. This has not always been the case and this review summarizes how our knowledge has evolved from the initial discovery of renin by Tigerstedt and Berman in 1898. This includes the identification of angiotensin in the 1950s to the proposed relationship between this system, hypertension and ultimately cardiovascular disease. While the RAS is far more complex than originally thought, much is now known about this system and the wide ranging effects of angiotensin in the body. This has enabled the development of therapies that target the various proteins in this pathway and hence are implicated in disease. The first of these treatments was the angiotensin converting enzyme inhibitors (ACE-Is), followed by the angiotensin receptor blockers (ARBs), and more recently the direct renin inhibitors (DRIs). Clinical outcome trials have shown these drugs to be effective, but as they act at contrasting points in the RAS, there are differences in their efficacy and safety profiles. RAS blockade is the foundation of modern combination therapy with a calcium channel blocker and/or a diuretic given to reduce blood pressure and limit the impact of RAS activation. Other options that complement these treatments may be available in the future and will offer more choice to clinicians.

Renin-angiotensin-aldosterone system blockade for cardiovascular diseases: current status

Activation of the renin-angiotensin-aldosterone system (RAAS) results in vasoconstriction, muscular (vascular and cardiac) hypertrophy and fibrosis. Established arterial stiffness and cardiac dysfunction are key factors contributing to subsequent cardiovascular and renal complications. Blockade of RAAS has been shown to be beneficial in patients with hypertension, acute myocardial infarction, chronic systolic heart failure, stroke and diabetic renal disease. An aggressive approach for more extensive RAAS blockade with combination of two commonly used RAAS blockers [ACE inhibitors (ACEIs) and angiotensin receptor blockers (ARBs)] yielded conflicting results in different patient populations. Combination therapy is also associated with more side effects, in particular hypotension, hyperkalaemia and renal impairment. Recently published ONTARGET study showed ACEI/ARB combination therapy was associated with more adverse effects without any increase in benefit. The Canadian Hypertension Education Program responded with a new warning: 'Do not use ACEI and ARB in combination'. However, the European Society of Cardiology in their updated heart failure treatment guidelines still recommended ACEI/ARB combo as a viable option. This apparent inconsistency among guidelines generates debate as to which approach of RAAS inhibition is the best. The current paper reviews the latest evidence of isolated ACEI or ARB use and their combination in cardiovascular diseases, and makes recommendations for their prescriptions in specific patient populations.

Control of aldosterone secretion: a model for convergence in cellular signaling pathways

Aldosterone secretion by glomerulosa cells is stimulated by angiotensin II (ANG II), extracellular K(+), corticotrophin, and several paracrine factors. Electrophysiological, fluorimetric, and molecular biological techniques have significantly clarified the molecular action of these stimuli. The steroidogenic effect of corticotrophin is mediated by adenylyl cyclase, whereas potassium activates voltage-operated Ca(2+) channels. ANG II, bound to AT(1) receptors, acts through the inositol 1,4,5-trisphosphate (IP(3))-Ca(2+)/calmodulin system. All three types of IP(3) receptors are coexpressed, rendering a complex control of Ca(2+) release possible. Ca(2+) release is followed by both capacitative and voltage-activated Ca(2+) influx. ANG II inhibits the background K(+) channel TASK and Na(+)-K(+)-ATPase, and the ensuing depolarization activates T-type (Ca(v)3.2) Ca(2+) channels. Activation of protein kinase C by diacylglycerol (DAG) inhibits aldosterone production, whereas the arachidonate released from DAG in ANG II-stimulated cells is converted by lipoxygenase to 12-hydroxyeicosatetraenoic acid, which may also induce Ca(2+) signaling. Feedback effects and cross-talk of signal-transducing pathways sensitize glomerulosa cells to low-intensity stimuli, such as physiological elevations of [K(+)] (< or =1 mM), ANG II, and ACTH. Ca(2+) signaling is also modified by cell swelling, as well as receptor desensitization, resensitization, and downregulation. Long-term regulation of glomerulosa cells involves cell growth and proliferation and induction of steroidogenic enzymes. Ca(2+), receptor, and nonreceptor tyrosine kinases and mitogen-activated kinases participate in these processes. Ca(2+)- and cAMP-dependent phosphorylation induce the transfer of the steroid precursor cholesterol from the cytoplasm to the inner mitochondrial membrane. Ca(2+) signaling, transferred into the mitochondria, stimulates the reduction of pyridine nucleotides.

Pseudohyperaldosteronism: pathogenetic mechanisms

Pseudohyperaldosteronism is characterized by a clinical picture of hyperaldosteronism with suppression of plasma renin activity and aldosterone. Pseudohyperaldosteronism can be due to a direct mineralocorticoid effect, as with desoxycorticosterone, fluorohydrocortisone, fluoroprednisolone, estrogens, and the ingestion of high amounts of glycyrrhetinic acid. A block of 11-hydroxysteroid-dehydrogenase type 2 (11HSD2), the enzyme that converts cortisol into cortisone, at the level of epithelial target tissues of aldosterone, is involved in other cases. This mechanism is related either to a mutation of the gene, which encodes 11HSD2 (apparent mineralocorticoid excess syndrome and some cases of low renin hypertension) or to an acquired reduction of the activity of the enzyme due to glycyrrhetinic acid, carbenoxolone, and grapefruit juice. In other cases saturation of 11HSD2 may be involved as in severe Cushing's syndrome and chronic therapy with some corticosteroids. Recently, an activating mutation of the mineralocorticoid receptor gene has been described. Another genetic cause of pseudohyperaldosteronism is the syndrome of Liddle, which is due to a mutation of the gene encoding for beta and gamma subunits of the sodium channels.

Angiotensin II and aldosterone regulation

The circulating renin-angiotensin system is a major regulator of the secretion of the adrenocortical hormone, aldosterone. This renin-angiotensin aldosterone system is important in the control of salt and water balance and blood pressure. This review describes the historical background leading to the discovery of aldosterone in the 1950s and the recognition in the 1960s that angiotensin II was involved in its control. Although angiotensin II is important in the regulation of aldosterone secretion, its action is influenced by multiple other factors, especially potassium and atrial natriuretic peptide. In addition to the circulating renin-angiotensin system, a local renin-angiotensin system is present in the zona glomerulosa cell. This local system also appears to be involved in the regulation of aldosterone production. The mechanism by which angiotensin II stimulates the adrenal zona glomerulosa cell is described in some detail. Angiotensin II interacts with the angiotensin receptor (AT1) membrane receptor that is coupled to cellular second messengers. Specific AT1 receptor antagonists are now clinically used to block angiotensin II's action on various target organs, including the adrenal gland.

Interrelationships between angiotensin, norepinephrine, epinephrine, aldosterone secretion, and electrolyte metabolism in man

Oversecretion of aldosterone is a consistent finding in the syndrome of malignant hypertension. Infusion of angiotensin has been consistently shown to induce an increased secretion of aldosterone by the adrenal cortex in normal human subjects. Because renal damage is so prominent in malignant hypertension, it seems possible that renin release and then aldosterone oversecretion by the adrenal cortex are involved in the pathogenesis of this disorder.

These findings support the possibility that there is a renal-adrenal system which operates for the normal regulation of electrolyte balance. This system might function to maintain and protect renal perfusion by promoting sodium retention via stimulation of the adrenal cortex.

Our recent work has been predicated on the possibility that aldosterone secretion is chiefly regulated by 1 specific trophic hormone (possibly angiotensin), oversecretion of which accounts for the increased secretion of aldosterone observed in various other conditions.

Preliminary studies designed to investigate the possible role of angiotensin in the marked oversecretion of aldosterone found in cirrhosis have been reported. It has been observed that patients with cirrhosis and ascites may be less sensitive to both angiotensin and norepinephrine so that more drug is required to produce a given pressor response. Further-more, aldosterone secretion could not be augmented by administering angiotensin in these patients. While several interpretations are possible, these findings are consistent with the view that the adrenal cortex is already maximally stimulated by circulating endogenous angiotensin.

Because of reduced pressor responsiveness, increased amounts of angiotensin could circulate without causing hypertension. This hypothesis awaits actual demonstration of increased amounts of circulating renin or angiotensin in this condition (and others) associated with aldosteronism.

Proper study of the interrelationships between pressor substances, aldosterone secretion, and sodium balance requires that effects of the different types of pressor agents be compared under similar circumstances. Thus, both norepinephrine and angiotensin affect the renal excretion of electrolytes. Both can cause a natriuresis in normal or hypertensive subjects. In normal subjects, the natriuresis occurs inconsistently but seems more readily induced after sodium depletion.

Angiotensin has been found to produce a marked increase in sodium excretion in patients with cirrhosis and ascites who have increased aldosterone secretion. In equipressor doses, the natriuresis of angiotensin is of strikingly greater magnitude than that of norepinephrine, possibly indicating that the peptide affects tubular transport of sodium. The natriuresis effected by these pressor agents seems independent of their effect on aldosterone secretion because medullary hormones often suppress aldosterone output, whereas angiotensin increases it.

Further study is necessary to define more specifically the conditions which determine these responses and interrelationships. The results to date support the view that an aldosterone-regulating hormone (possibly angiotensin) could be elaborated as a result of a critical change in intrarenal pressure.

EFFECT OF PROLONGED HYPOXIA UPON GRANULARITY OF RENAL JUXTAGLOMERULAR CELLS

The various experimental models used in previous studies of the juxtaglomerular apparatus do not permit the effect of changes in oxygen tension of the renal parenchyma to be separated from that of changes in distension of the renal arterial bed. To study the isolated effect of prolonged hypoxia, three groups of rats, matched for weight, were kept in low oxygen, room air, and high oxygen environment for two weeks. The animals were pair-fed with the hypoxic rats serving as the determinant group. Supplemental injections of sodium chloride were given daily to avoid the effect of sodium deprivation on the juxtaglomerular cells. It was found that the hematocrits and also the granularity of the juxtaglomerular cells were significantly increased in the hypoxic rats as compared to the other two groups. Blood pressures, serum sodium levels, and urinary excretion of sodium were comparable among the three groups. These findings demonstrate that increased granularity of the renal juxtaglomerular cells can be induced by prolonged hypoxia.

RENAL EFFECTS OF ANGIOTENSIN II INFUSIONS IN NORMOTENSIVE PREGNANT AND NONPREGNANT WOMEN

Normotensive pregnant women are relatively resistant to angiotensin II in that they give smaller pressor responses and show smaller reductions in urine flow and sodium and chloride excretions than do normotensive nonpregnant women.

Women early in the third trimester of pregnancy are more resistant to angiotensin II than are women at term, with respect to the effect upon sodium and chloride excretions.

The less pronounced renal effects of angiotensin II in pregnant women cannot be attributed merely to error caused by increase in the dead space of the urinary tract.

A specific template-assembled peptidic agonist for the angiotensin II receptor subtype 2 (AT2) and its effect on inferior olivary neurones

We synthesized a molecule composed of two angiotensin II 4-8 pentapeptide fragments attached to a carrier molecule (TA), according to the template-assembled synthetic proteins concept. This molecule was investigated for receptor binding on angiotensin type-1 and type-2 receptors (AT1 and AT2) and its biological activity was determined by iontophoretic experiments on neurones of the inferior olive (ION) that express only AT2 receptors. TA binds exclusively to the AT2 receptor and mediates an agonistic angiotensin-II effect on the ION. TA is the first agonist available to study the direct stimulation of AT2 receptors.

Angiotensin and the brain

A brief account for the renal renin-angiotensin system (RAS), its inhibitors and receptors, as for the presence of an intrinsic cerebral RAS is initially provided. The review is then focused upon the circumventricular organs as cerebral targets for blood-borne angiotensin II (Ang II) and on centrally mediated Ang II effects. These concern influences upon the cardiovascular system, water balance, sodium balance, and ACTH-cortisol secretion.

The renin system for long-term control over vasoconstriction and sodium-volume homeostasis in the spectrum of hypertension: three new frontiers in research

This morning I have presented something old and something new and I have tried to point out what I think are some promising areas of current research. In the past two decades we have made great strides in our understanding of hypertensive mechanisms. We now know that essential hypertension can no longer be viewed an a single entity. Its heterogeneity in renin patterns is matched by heterogeneity in response or lack of response of individual patients to different types of drugs, and by heterogeneity in risk and prognosis. Analysis of renin system patterns has proven to be very productive for enabling us to understand the participation of the vasoconstriction or volume factors that inevitability work to maintain all hypertensive states. This bipolar analysis of hypertensive phenomena in turn has led to better diagnosis and to more specific treatment of individual patients. In our present state of knowledge, we still need to understand why the renin system so often inappropriately participates in maintenance or causation of the hypertensive state and why it fails to turn itself off in medium or high renin patients. In the low renin patients we do not understand why renal sodium retention occurs nor how it produces sustained increases in peripheral resistance. Three of many potentially exciting areas for expanding our knowledge are the prorenin problem, the natriuretic hormone problem, and the recently discovered relationships between the divalent cations, calcium and magnesium, and the concurrent renin system patterns in the renin subgroups of essential hypertension. Perhaps one of these areas will serve as an appetizer for the participants here today, and in particular for the man we honor, Franz Gross.

Renin, renin inhibition and antihypertensive therapy

Research over the last 25 years established the renin-angiotensin-aldosterone system's important role in electrolyte and blood pressure homeostasis as well as in the pathophysiology of hypertension for which renin suppressive drugs, angiotensin antagonists and converting enzyme inhibitors provided selective pharmacological tools. Pharmacological interference with the renin-angiotensin axis in addition to reducing angiotensin-mediated vasoconstriction reduces angiotensin's effect on aldosterone, alpha-adrenoceptor mediated vasoconstriction and central activation of sympathetic nerve activity. Renin measurements serve as an endocrine marker for the activity and reactivity of the sympathetic nervous system reflecting a beta-adrenoceptor mediated response which tends to decrease with older age. Therefore, as younger the patient and as higher pretreatment renin as better the antihypertensive response to converting enzyme inhibitors and betablockers is. As lower renin and as older the age diuretic agents and calcium antagonists are more effective, the hyporesponsive renin being a co-determinant of pressure response in these patients.

Markedly elevated specific renin levels in the adrenal in genetically hypertensive rats

The specific renin (EC 3.4.99.19) activity in the adrenal of spontaneously hypertensive rats was determined by a method that is capable of distinguishing renin from nonspecific renin-like activity of proteases by using specific antibody to renin. The renin level in the adrenals of adult spontaneously hypertensive rats with established hypertension was found to be 6-8 times as high as that of the normotensive control Wistar-Kyoto strain. The large difference in the adrenal renin level was observed even in 3-wk-old rats in which hypertension has not yet developed. The adrenal renin level was increased by bilateral nephrectomy in both the hypertensive and normotensive strains. A larger quantity of renin was found in the adrenal cortex than in the medulla, and the difference between the hypertensive strain and the normotensive strain was more prominent in the cortex than in the medulla. These results suggest possible involvement of adrenal renin in the development and in the early maintenance phase of hypertension in this animal mode of human essential hypertension by affecting the adrenocortical or adrenomedullary activity, or both.

Historical perspectives on the renin-angiotensin-aldosterone system and angiotensin blockade

Advances leading to recognition of the relation of the renin-angiotensin system to aldosterone include: (1) development of analytic techniques for measuring aldosterone, (2) discovery of an aldosterone-stimulating factor in circulating plasma, (3) the finding that a potent aldosterone-stimulating factor is secreted by the kidney, (4) evidence that synthetic angiotensin II increases aldosterone secretion, (5) fractionation of crude kidney extracts and the finding that aldosterone-stimulating factor is renin, (6) the observation that high plasma renin activity occurs in secondary aldosteronism, and (7) recognition that the renin-angiotensin-aldosterone system occurs in congestive heart failure and in renovascular and malignant hypertension. The early use of blocking agents for the renin-angiotensin system is described along with the landmarks of progress. These include the observations that: (1) arterial pressure decreases in experimental renovascular hypertension in response to angiotensin blockade, (2) angiotensin provides important support for arterial pressure in low cardiac output states including congestive heart failure, (3) the kidney participates in this important compensatory mechanism, and (4) cellular receptors for angiotensin are present in the two inner zones of the adrenal cortex.

Is the renin system necessary?

Numerous studies have been carried out to assess the role of the renin system in sustaining abnormally high blood pressure and in contributing to various other cardiovascular disorders such as congestive heart failure, ascites, and shock. The clinical use of potent and specific inhibitors of the renin-angiotensin system has produced important application in the treatment of high blood pressure, severe congestive cardiac failure and experimental hemorrhagic shock. Only in the state of considerable sodium depletion does blockade of the renin system produce any untoward effect, i.e. hypotension. These results are very similar to those obtained previously in patients with bilateral nephrectomy. They raise the question whether under conditions of our present salt-eating habits the renin system is really necessary.

Angiotensin II and renal hypertension in dog, rat and man: effect of converting enzyme inhibition

The role of the renin-angiotensin system in the pathogenesis of one-clip, two-kidney hypertension has been studied in man, dog and rat. Particular attention has been paid to peripheral plasma concentrations of angiotensin II in different circumstances; angiotensin II infusion has been combined with radioimmunoassay to construct angiotensin II/blood pressure dose-response curves. The effect of converting enzyme inhibitors has been studied, precautions being taken to avoid obtaining falsely high values for plasma angiotensin II because of cross-reaction with angiotensin I in these circumstances. The initial phase of one-clip, two-kidney hypertension is attributable to the direct pressor effect of the immediate rise in plasma angiotensin II. Subsequently, plasma angiotensin II is relatively lower, although blood pressure remains high. This upward resetting of the plasma angiotensin II/blood pressure relationship can be mimicked by infusing angiotensin II chronically at low dose. After reconstruction of a stenosed renal artery, or excision of a post-stenotic kidney, the angiotensin II/blood pressure relationship returns slowly to normal. In this second phase of one-clip, two-kidney hypertension, the long-term administration of saralasin, or of converting enzyme inhibitor, can also return arterial pressure to normal; brief administration of these drugs is less effective or ineffective. The results are compatible with, although they do not conclusively establish, an important slow pressor action of the renin-angiotensin system in the second phase of one-clip, two-kidney hypertension. This provides a rational basis for the use of captopril clinically in this condition.

Regulation of renin release and intrarenal formation of angiotensin. Studies in the isolated perfused rat kidney

1. Isolated rat kidneys were perfused at a constant pressure of 90 mmHg in a single-pass system with either a cell-free medium or a suspension of washed bovine red blood cells, free of the components of the renin-angiotensin system. In red blood cell perfused kidneys renal haemodynamics and sodium reabsorption corresponded closer to values observed in the intact rat than in cell-free perfused kidneys. 2. In red blood cell-perfused kidneys in the absence of plasma renin substrate autoregulation of renal blood flow was almost complete at pressures above 90 mmHg, provided that perfusion pressure was changed rapidly. 3. Renin release varied inversely with perfusion pressure within a pressure range from 50 to 150 mmHg; the greatest changes of renin release occurred, when perfusion pressure was reduced from 90 to 70 mmHg; maximal stimulation of renin release was observed at 50 mmHg. After reduction of perfusion pressure, renin release immediately started to rise and reached a new level within 5 min. Local reduction of perfusion pressure in small arteries and arterioles by the injection of microspheres induced a short-lasting decrease in renal plasma flow and a transient stimulation of renin release. 4. High concentrations of furosemide stimulated renin release by a direct intrarenal mechanism. 5. Isoproterenol stimulated renin release in low concentrations without a concomitant vasodilation, whereas high concentrations induced an increase in both renal plasma flow and renin release. The effects of isoproterenol were completely blocked by propranolol. 6. Sodium nitroprusside induced similar increases in renal plasma flow, as did high concentrations of isoproterenol, but only a small and slow increase in renin release was observed. 7. Angiotensin II (AII) suppressed renin release in concentrations corresponding to plasma levels measured in the intact rat independently of its vasoconstrictor effects, whereas vasopressin in antidiuretic concentrations did not affect renin release. 8. AII, AI, synthetic tetradecapeptide renin substrate (TDP), crude and purified rat plasma renin substrate induced a dose-dependent reduction in renal plasma flow. SQ 20 881, a competitive inhibitor of converting enzyme, and low doses of 1-Sar-8-Ala-AII (saralasin), a competitive antagonist of AII, did not change renal plasma flow, whereas high concentrations of saralasin had a vasoconstrictor effect on their own. 9. Saralasin inhibited the vasoconstrictor effects of AII and TDP to a similar degree. SQ 20 881 inhibited the vasoconstrictor effects of AI and purified renin substrate, but did not influence the actions of TDP and the crude renin substrate preparation. 10. From these data it is concluded, that AI is converted into AII within the kidney at a rate of 1-2%. The vasoconstriction induced by the crude renin substrate probably does not involve the AII receptors. TDP may act by itself on the AII receptors or via the direct intrarenal formation of AII...

Impaired potency for feedback regulation of glomerular filtration rate in DOCA escaped rats

The present experiments were performed to study the effect of chronic extracellular volume expansion on the magnitude of tubulo-glomerular feedback responses in the rat kidney. Extracellular volume expansion was achieved by giving isotonic saline as drinking water and by injecting DOCA in a dose of 2.5 mg/kg - day. When Ringer perfusion rate through the loop of Henle was elevated in control rats (receiving only saline as drinking water) stop flow pressure (SFP) fell by an average of 0.47 +/- 0.81 mm Hg (mean +/- S.D.) and 7.93 +/- 2.85 mm Hg at the flow rate steps of 0--15 nl/min and 15--40 nl/min respectively. SN-GFR was reduced by a mean of 1.3 +/- 0.97 nl/min (0--15 nl/min) and 10.3 +/- 2.45 nl/min (15--40 nl/min). In DOCA treated rats the mean reductions of SFP were 0.98 +/- 0.9 mmHg and 2.1 +/- 1.4 mmHg and of SN-GFR 0.06 +/- 1.8 nl/min and 1.94 +/- 2.3 nl/min. Thus, significantly smaller changes of both SFP and SN-GFR were found in DOCA treated animals when flow rate was elevated from 15--40 nl/min. Net loop NaCl absorption rates did not significantly differ between control and DOCA rats. Renin activity of 5 pooled microdissected glomeruli was 15.6 +/- 17.1 ng/hr-0.1 ml in control and 2.94 +/- 2.6 ng/hr-0.1 ml in DOCA treated rats (P less than 0.01). It is possible therefore that the reduced feedback reactivity in DOCA treated rats is related to the diminished juxtaglomerular renin activity.

Sensitization of the Adrenal Cortex to Angiotensin II in Sodium-Deplete Man

The effect of sodium depletion on the dose-response relationships of angiotensin II to aldosterone and blood pressure was studied. Arterial plasma angiotensin II and aldosterone and arterial blood pressure were measured before and during the incremental infusion of angiotensin II into sodium-replete and sodium-deplete subjects. Sodium depletion caused a distinct steepening of the angiotensin Il-aldosterone dose-response curves in four of five subjects and a concurrent diminution in the pressor effect of angiotensin II. Administration of angiotensin II did not demonstrably alter the half-life of aldosterone. Sodium depletion did not change the plasma concentrations of sodium or potassium, but it was accompanied by a significant increase in plasma levels of 11-hydroxycorticosteroids and magnesium. The contrasting effects of sodium depletion on the aldosterone and the pressor dose-response curves favored sodium retention. These results are consistent with an important role for the renin-angiotensin system in the control of aldosterone secretion in man.

Genetic influence on the renin-angiotensin system: low renin activities in hypertension-prone rats

Two strains of rats with opposite, genetically determined predispositions to hypertension were compared. Rats from the hypertension-prone strain had significantly lower plasma and kidney renin activities than did rats from the hypertension-resistant strain. Although renin activities were modified by NaCl intake and blood pressure, significant differences between the two strains were present with all four experimental regimens used: low-NaCl diet, high-NaCl diet, unilateral renal artery constriction, and unilateral renal artery constriction plus contralateral nephrectomy. Therefore, we concluded that renin activities along with blood pressure were modified by genetic influences in these two strains of rats.