Immediate hemodynamic effects of a dopamine-receptor agonist (fenoldopam) in patients with essential hypertension

Systemic, splanchnic, and renal hemodynamics, intravascular volume, and reflexive and endocrine changes were measured before and after a single dose of fenoldopam, a novel antihypertensive agent that acts through stimulation of specific dopamine receptors. A 13% reduction in mean arterial pressure was mediated by a fall in total peripheral resistance association with an increase in cardiac index, heart rate, stroke volume, left ventricular ejection rate, and circumferential fiber shortening. Renal blood flow increased, thereby reducing the renal vascular resistance by more than 40%. In contrast, splanchnic hemodynamics failed to change. Likewise, there were no changes in intravascular volume, plasma renin activity, or norepinephrine, serum aldosterone, or prolactin levels.

Angiotensin II mediates increased small intestinal fluid absorption with extracellular volume depletion in the rat

The purpose of this study was to determine if the increase in small intestinal fluid absorption observed after extracellular fluid (ECF) reduction is mediated by angiotensin II (AII). Infusion of AII at doses that increase plasma levels of the hormone within the physiological range stimulates jejunal fluid absorption. In contrast, at pharmacological doses that result in plasma AII levels unlikely to be encountered normally, the hormone inhibits absorption and/or stimulates jejunal secretion. The AII stimulation of jejunal fluid absorption is potentiated by nephrectomy, suggesting that the endogenous levels of AII are related to and have an important role in regulation of the cellular level of its own receptors. Extracellular volume reduction as a result of sodium depletion, nonhypotensive hemorrhage, or water deprivation increases jejunal fluid absorption 30-40% above control values. This increase in jejunal absorption after ECF reduction is not affected by adrenalectomy, but is abolished by nephrectomy, either alone or in combination with adrenalectomy. Captopril, prazosin, and peripheral sympathectomy also abolish the increase in jejunal absorption following ECF depletion. It is suggested that AII is generated after ECF reduction and increases jejunal fluid absorption by facilitating the release of norepinephrine from enteric sympathetic nerves. Thus, AII is a physiologically important mediator of jejunal fluid absorption.

Dopamine modulates sodium-dependent aldosterone responses to angiotensin II in humans

Studies have shown that dopamine inhibits angiotensin II (AII)-induced aldosterone secretion in bovine adrenal cells in vitro, but does not alter aldosterone responses to AII in sodium-replete normal humans. We investigated six normal men with plasma cortisol concentrations less than 2 micrograms/dl during oral administration of dexamethasone 0.5 mg every 6 hours for 2 days and in balance at 10 mEq sodium/day intake (UNa V 22 +/- 5 mEq/24 hr). The subjects received either dopamine 4 micrograms/kg/min or vehicle intravenously (i.v.) for 270 minutes on 2 consecutive days. After 120 minutes of dopamine infusion, AII was given in cumulative doses of 0.5, 1, 2, 4, and 6 pmol/kg/min i.v., each dose for 30 minutes. Control plasma aldosterone concentrations before vehicle or dopamine were 12 +/- 2 (mean +/- 1 SE) and 15 +/- 3 ng/dl, respectively. Aldosterone responses to AII were greater with vehicle than dopamine at AII doses of 4 and 6 pmol/kg/min (p less than 0.02). The slope of the AII-aldosterone dose-response curve was steeper with vehicle (0.36) than with dopamine (0.13), p less than 0.0001. Plasma renin activity and serum potassium concentrations were similar with vehicle and dopamine. Dopamine inhibits AII-induced aldosterone secretion during sodium deficiency in humans.

Acute hypoxemia and hypercapnia: increase in plasma catecholamines in conscious dogs

To systemically evaluate the effects of acute hypoxemia and hypercapnic acidosis on the sympathetic nervous system, five unanesthetized mongrel dogs were studied during acute hypoxemia [arterial O2 tension (PaO2) 33 +/- 2 Torr], acute hypercapnic acidosis [arterial CO2 tension (PaCO2) 53 +/- 1 Torr; pH, 7.19 +/- 0.02], and combined acute hypoxemia and hypercapnic acidosis (PaO2, 36 +/- 1 Torr; PaCO2, 52 +/- 1 Torr; pH, 7.18 +/- 0.02). Combined acute hypoxemia and hypercapnic acidosis resulted in increased mean arterial pressure, cardiac output, and heart rate. Moreover, combining acute hypoxemia and hypercapnic acidosis acted synergistically to increase circulating norepinephrine and epinephrine. Acute hypoxemia alone and acute hypercapnic acidosis alone resulted in reversible increases in mean arterial pressure, cardiac output, heart rate, and circulating norepinephrine. Although plasma epinephrine concentrations increased during acute hypoxemia, circulating epinephrine was unchanged during acute hypercapnic acidosis. These data indicate that acute hypoxemia and hypercapnic acidosis result in synergistic increase in circulating catecholamines.

Possible mechanism of action of metoclopramide-induced aldosterone secretion: in vivo and in vitro studies in the sheep

To define further the mechanism by which metoclopramide, a dopamine antagonist, stimulates aldosterone secretion, seven lambs were injected iv with metoclopramide during a constant infusion of 5% dextrose in water and again during a constant infusion of trimethapan, a ganglionic blocker. In addition, suspensions of adrenal zona glomerulosa cells from the lambs were incubated in vitro in the presence of various concentrations of metoclopramide and known secretagogues. Plasma aldosterone concentrations increased in response to both metoclopramide and trimethaphan. However, during the trimethaphan infusion, no further increase in plasma aldosterone concentrations occurred after metaclopramide injection. In vitro, aldosterone concentrations in the zona glomerulosa cell suspensions increased in the presence of ACTH, potassium, and angiotensin II, but no increase in aldosterone concentration occurred in the presence of metoclopramide. These results suggest that in the sheep, metoclopramide stimulates aldosterone secretion by an indirect mechanism. This mechanism may involve the autonomic nervous system, since ganglionic blockade appeared to abolish the aldosterone response to metoclopramide.

Synergistic effects of acute hypoxemia and hypercapnic acidosis in conscious dogs. Renal dysfunction and activation of the renin-angiotensin system

The effects of acute hypoxemia and hypercapnic acidosis were examined in five unanesthetized dogs in which sodium intake was controlled at 80 mEq/24 hours for 4 days prior to study. Each animal was studied during combined acute hypoxemia and hypercapnic acidosis (Pao2 = 36 +/- 1 mm Hg, Paco2 = 52 +/- 1 mm Hg, pH = 7.18 +/- 0.02), acute hypoxemia alone (Pao2 = 32 +/- 1 mm Hg, Paco2 = 32 +/- 1mm Hg, pH = 7.34 +/- 0.01), and acute hypercapnic acidosis alone (Pao2 = 82 +/- 2 mm Hg, Paco2 = 51 +/- 1 mm Hg, pH = 7.18 +/- 0.02). Although mean arterial pressure, cardiac output, and heart rate increased during combined hypoxemia and hypercapnic acidosis, effective renal plasma flow and glomerular filtration rate decreased. In addition, filtered sodium load and urinary sodium excretion decreased during combined hypoxemia and hypercapnic acidosis. Either acute hypoxemia or hypercapnic acidosis alone resulted in increased mean arterial pressure, cardiac output, and heart rate. However, in contrast to their combined effects, renal hemodynamic function was unchanged and natriuresis was observed. Measurement of plasma renin activity and angiotensin II concentrations indicated that hypoxemia or hypercapnic acidosis alone resulted in moderate activation of the renin-angiotensin system. Moreover, combined hypoxemia and hypercapnic acidosis acted synergistically resulting in major renin-angiotensin activation. Systemic angiotensin II blockade using 1-sarcosine, 8-alanine, angiotensin II (2 micrograms/kg per min) during combined acute hypoxemia and hypercapnic acidosis resulted in decreased renal hemodynamic function. We conclude that acute hypoxemia and hypercapnic acidosis act synergistically to increase mean arterial pressure, diminish renal hemodynamic function and activate the renin-angiotensin system. Systemic angiotensin inhibition studies suggest activation of the renin-angiotensin system maintains renal hemodynamic function during combined hypoxemia and hypercapnic acidosis, instead of mediating the renal vasoconstriction.

Dopaminergic inhibition of aldosterone secretion in man is independent of the autonomic nervous system

To determine whether the plasma aldosterone response to metoclopramide, a dopamine antagonist, is mediated by the autonomic nervous system in man, five healthy male volunteers were injected with metoclopramide during an infusion of either 5% dextrose in water or trimethaphan, a ganglionic blocker. Despite evidence of ganglionic blockade during the trimethaphan infusion, the aldosterone response to metoclopramide remained intact. This suggests that the aldosterone response to metoclopramide is not mediated by the autonomic nervous system in man as it appears to be in the sheep, and suggests species variation in the mechanism of this this mineralocorticoid response.

Suppression of basal and stimulated noradrenergic activities by the dopamine agonist bromocriptine in man

This study was designed to determine the effects of dopaminergic receptor stimulation on basal and stimulated catecholamine release in man. Five normal white male volunteer subjects were studied in metabolic balance at constant 150-meq sodium, 60-meq potassium intake and then daily for 8 days on an isocaloric constant diet of 10 meq sodium and 60 meq potassium/day in each of two separate protocols. In one protocol, the subjects received the dopamine agonist bromocriptine for 14 days before and during the study; in the other protocol, placebo was substituted for bromocriptine. During normal sodium intake, bromocriptine suppressed supine plasma norepinephrine concentrations from 193 +/- 10 to 159 +/- 9 pg/ml (P = 0.01). Dietary sodium depletion increased supine plasma norepinephrine concentrations in subjects taking placebo from 193 +/- 10 to 229 +/- 10 pg/ml (P less than 0.001). Bromocriptine prevented the supine plasma norepinephrine response to sodium depletion. After discontinuation of bromocriptine treatment, supine plasma norepinephrine concentrations returned to placebo control values. Upright posture stimulated an increase in plasma norepinephrine concentrations from 193 +/- 10 to 419 +/- 30 pg/ml (P = 0.0001) during normal sodium intake, and bromocriptine suppressed this response from 419 +/- 30 to 286 +/- 29 pg/ml (P = 0.004). Dietary sodium depletion enhanced the plasma norepinephrine response to upright posture, and bromocriptine markedly suppressed this enhancement. After discontinuation of bromocriptine treatment, supine and upright plasma norepinephrine concentrations returned to placebo control values. Bromocriptine induced a parallel downward shift in the inverse hyperbolic relationship between the plasma norepinephrine concentration and urinary sodium excretion in erect subjects, and decreased overnight urinary norepinephrine excretion in supine subjects from 1.1 +/- 0.1 to 0.6 +/- 0.1 ng/h (P = 0.0002). No consistent effects of bromocriptine on plasma epinephrine or dopamine concentrations were observed. The results of this study strongly suggest an inhibitory action of dopamine receptor stimulation by bromocriptine on basal and stimulated norepinephrine output at noradrenergic nerve terminals in the central nervous system and/or the periphery.

Metabolic and blood pressure responses to hydrocortisone in the syndrome of apparent mineralocorticoid excess

A syndrome of low renin hypertension in childhood with apparent mineralocorticoid excess associated with a defect in the peripheral metabolism of cortisol has been described previously in 2 patients. In these patients, decreased secretion rates of glucocorticoids, mineralocorticoids, and sex steroids have been demonstrated. In a 10(10/12)-yr-old girl with this disorder, continuous iv administration of hydrocortisone in doses of 5, 10, 15, and 20 mg/day resulted in an increase in blood pressure and a decrease in serum potassium concentration. The addition of spironolactone during the continued administration of 20 mg/day hydrocortisone did not result in a decrease in blood pressure. Withdrawal of hydrocortisone and continued administration of spironolactone alone resulted in a decrease in blood pressure, a rise in serum potassium concentration, and a fall in serum sodium concentrations. These studies suggest that an abnormality in cortisol action or metabolism causing cortisol to behave as a potent mineralocorticoid may account for this syndrome of apparent mineralocorticoid excess.

Control of renal function by intrarenal angiotensin II

The purpose of this study was to determine if endogenous angiotensin II affects renal function in conscious dogs after sodium restriction. Intrarenal infusion of the angiotensin receptor antagonist saralasin at doses between 0.13 and 2.5 micrograms/kg X min rapidly attenuated pressor responses produced by systemic injections of angiotensin I over a 90-min period. In contrast, intrarenal infusion of the peptide antagonist at 0.07 microgram/ kg X min did not alter the pressor response to injected angiotensin I. Infusion of angiotensin II into the kidney at 0.1 microgram/min reduced urine output by 50% and was totally inhibited by simultaneous infusion of 0.07 micrograms/kg X min saralasin. Intrarenal infusion of saralasin at 0.07 micrograms/kg X min into sodium-restricted conscious dogs increased effective renal plasma flow, glomerular filtration rate, and sodium, potassium and water excretion, whereas urine osmolarity and free water formation were unchanged. These data demonstrate that saralasin can be effectively confined to the renal mass after intrarenal infusion at a dose capable of inhibiting angiotensin action and that endogenous angiotensin plays an important role in maintaining renal function after sodium restriction.

Bromocriptine does not inhibit the aldosterone response to sodium depletion

This study was designed to investigate the influence of the dopamine agonist, bromocriptine, on the renin-angiotensin-aldosterone system during dietary sodium restriction. Five normal white male volunteer subjects were studied in metabolic balance at constant 150 meq sodium, 60 meq potassium intake, and then daily for 7 days on an isocaloric constant diet of 10 meq sodium and 60 meq potassium/day. The subjects were studied once during administration of bromocriptine and again in the presence of bromocriptine placebo. After a stepwise daily decrease in urinary sodium excretion, sodium balance was achieved on the sixth day of low sodium intake. Renal sodium conservation in response to dietary sodium restriction was associated with parallel increases in PRA, plasma aldosterone concentration, and urinary aldosterone excretion. These changes were not significantly different during placebo and bromocriptine administration. Bromocriptine was active at the pituitary dopamine receptor, as serum PRL concentrations were suppressed to undetectable levels. The results indicate that bromocriptine does not alter the response of the renin-angiotensin-aldosterone system to sodium restriction.

Renal and cardiovascular responses to acute hypercapnic acidosis in conscious dogs: role of renin--angiotensin

Patients with pulmonary dysfunction and CO2 retention have renal hemodynamic abnormalities accompanied by increased plasma renin activity. To determine if hypercapnia impairs renal function, particularly through the renin-angiotensin system, the effects of acute hypercapnic acidosis (HC), using 8.5% CO2, were measured in five unanesthetized dogs during (a) the intact state; (b) renin-angiotensin antagonism using either 1-sarcosine, 8-glycine angiotensin II ( [Sar1, Gly8] AII) or SQ 14,225; and (c) exogenous angiotensin II infusion. As partial arterial carbon dioxide pressure (PaCO2) increased (p less than 0.05) from control (C) of 35 +/- 1 (SEM) to 48 +/- 1 mm Hg during HC, arterial pH fell (p less than 0.05) from 7.36 +/- 0.01 to 7.24 +/- 0.005. Renal function was uncompromised with HC, and glomerular filtration rate (GFR) and urinary sodium excretion increased (p less than 0.05) despite a fourfold rise in plasma renin activity from C of 0.6 +/- 0.3 to 2.2 +/- 0.8 ng AI ml-1 h-1 during HC. Administration of [Sar1, Gly8] AII during HC did not consistently alter systemic or renal hemodynamic responses, and effects of SQ 14,225 during HC were also observed during normocapnia. Although systemic vascular responses to exogenous AII infusion were similar, the renal vasoconstrictor response was antagonized during HC with unchanged GFR and renal blood flow. These findings indicate that despite activation of the renin-angiotensin system, acute hypercapnic acidosis is unassociated with impairment of renal function in unanesthetized dogs. This may be related to diminished renal vascular AII responsiveness during hypercapnia.

Acute dopaminergic inhibition of aldosterone secretion is independent of angiotensin II and adrenocorticotropin

To clarify whether dopaminergic inhibition of aldosterone secretion is physiologically dependent on stimuli from tropic hormones, we attempted to block angiotensin II (AII)- and ACTH-mediated increases in the plasma aldosterone concentration (PAC) with dopamine in normal human subjects. The effect of dopamine on metoclopramide-induced aldosterone secretion also was studied. Six normal male subjects in metabolic balance on a 150 meq/day sodium and 60 meq/day potassium intake received AII infusion at 2, 4, and 6 pmol/kg . min, each dose for 30 min, on each of 2 consecutive days. On the first day, the subjects received a vehicle infusion from 60 min before to the end of the AII infusion; on the second day, dopamine (4 micrograms/kg . min) was substituted for vehicle. AII in the presence of vehicle increased PAC from 5.4 +/- 1.3 to 19.9 +/- 2.9 ng/100 ml; AII in the presence of dopamine increased PAC from 4.8 +/- 0.5 to 19.5 +/- 1.8 ng/100 ml (P = NS). After an interval of 3 weeks on an ad libitum diet, the same protocol was repeated except that ACTH (5, 10, and 20 U/h) was substituted for AII. ACTH in the presence of vehicle increased PAC from 8.1 +/- 2.7 to 27.3 +/- 3.1 ng/100 ml; in the presence of dopamine, ACTH increased PAC from 4.7 +/- 0.5 to 34.9 +/- 6.1 ng/100 ml (P = NS). Metoclopramide increased PAC from 4.5 +/- 0.6 to 17.8 +/- 2.3 ng/100 ml in the presence of vehicle and from 4.4 +/- 0.5 to 7.2 +/- 0.7 ng/100 ml in the presence of dopamine (P less than 0.01). Dopamine did not decrease basal PAC. Dopamine inhibits increases in aldosterone secretion induced by dopamine antagonist but does not alter AII- or ACTH-induced steroid secretion. Acutely, dopaminergic inhibition of aldosterone secretion is independent of AII and ACTH.

Importance of plasma angiotensin concentrations in a comparative study of responses to angiotensin in the maturing newborn lamb

Plasma angiotensin concentrations were measured in a longitudinal study of the vascular, renal, and adrenal responses to infusions of angiotensin II (AII) in the maturing newborn lamb. Basal plasma concentrations of angiotensin increased with age and correlated with the rising arterial pressure that occurred with maturation. However, age was a stronger determinant of arterial pressure than was plasma angiotensin concentration. For any given dose of AII per kilogram of body weight, the actual plasma angiotensin concentration achieved increased as the lambs matured and gained weight. Therefore, a comparative study of biologic responses to AII in maturing animals must be based on actual plasma angiotensin concentrations achieved rather than on dose of AII infused per kilogram of body weight. When analyzed on the basis of actual plasma angiotensin concentration, the increase in arterial pressure and the suppression of plasma renin activity in response to increasing plasma angiotensin concentrations did not differ significantly as the lambs matured. However, the increment in plasma aldosterone concentrations in response to increasing plasma angiotensin concentrations was diminished in immature lambs (less than 18 days) when compared to the aldosterone responses in the same lambs at older ages.

Importance of plasma angiotensin concentrations in a comparative study of responses to angiotensin in the maturing newborn lamb

Plasma angiotensin concentrations were measured in a longitudinal study of the vascular, renal, and adrenal responses to infusions of angiotensin II (AII) in the maturing newborn lamb. Basal plasma concentrations of angiotensin increased with age and correlated with the rising arterial pressure that occurred with maturation. However, age was a stronger determinant of arterial pressure than was plasma angiotensin concentration. For any given dose of AII per kilogram of body weight, the actual plasma angiotensin concentration achieved increased as the lambs matured and gained weight. Therefore, a comparative study of biologic responses to AII in maturing animals must be based on actual plasma angiotensin concentrations achieved rather than on dose of AII infused per kilogram of body weight. When analyzed on the basis of actual plasma angiotensin concentration, the increase in arterial pressure and the suppression of plasma renin activity in response to increasing plasma angiotensin concentrations did not differ significantly as the lambs matured. However, the increment in plasma aldosterone concentrations in response to increasing plasma angiotensin concentrations was diminished in immature lambs (less than 18 days) when compared to the aldosterone responses in the same lambs at older ages.

Acute and chronic intrarenal alpha- and beta- adrenergic receptor stimulation of renin release in the conscious dog

The effect of continuous intrarenal infusion of norepinephrine, isoproterenol, and methoxamine on renin release was studied in the uninephrectomized conscious dog. Chronic intrarenal infusion of norepinephrine produced a biphasic curve of plasma renin activity (PRA) and a sustained 25 mm Hg increase in mean arterial pressure (MAP). The initial increase in PRA peaked at 3 hours, after which PRA returned to control levels. Alpha- or beta-adrenergic antagonists did not attenuate the initial rise in PRA. The PRA increased again after 48 hours of chronic intrarenal norepinephrine infusion and remained elevated thereafter. The second rise in PRA was increased by 30% with alpha-adrenergic blockade. Chronic intrarenal isoproterenol administration produced a similar increase in PRA, which peaked at 3-5 hours and then returned to control levels. In contrast to norepinephrine, chronic isoproterenol administration did not result in a second increase in PRA. At the end of the chronic isoproterenol infusion period, beta-adrenergic receptor refractoriness was demonstrated, as PRA did not increase significantly in response to a fourfold increase in the dose of isoproterenol. An increase in PRA was produced by acute intrarenal infusion of methoxamine. This increase in PRA was blocked by phentolamine, suggesting a vascular alpha-adrenergic receptor-mediated release of renin.

Ontogeny of blood pressure and the renin-angiotensin-aldosterone system. Sequential studies in the newborn lamb

To test the hypothesis that the rise in arterial pressure occurring with maturation is due to an increase in the vascular responsiveness to angiotensin II, sequential cumulative doses of angiotensin II were infused intravenously into chronically catheterized newborn lambs maintained on a constant, weight-adjusted sodium intake from birth to 8 weeks of age. Basal mean arterial pressure correlated with both age and weight, but age was a stronger determinant of mean arterial pressure than was weight. No change in the mean arterial pressure response to angiotensin II occurred with maturation. Basal plasma renin activity and plasma aldosterone concentrations were low and did not change significantly with age. Therefore, in the newborn lamb in the sodium replete state, age is a better determinant of arterial pressure than is weight. However, an age-related change in vasoconstrictor responsiveness to angiotensin II does not occur and, therefore, cannot account for the rise in arterial pressure that is observed with maturation.

Decreased plasma and urinary dopamine during dietary sodium depletion in man

This study was designed to investigate the influence of dietary sodium restriction on plasma and urine dopamine levels. Five normal white male volunteer subjects wee studied in metabolic balance at constant 150 meq sodium, 60 meq potassium intake and then daily for 7 days on an isocaloric constant diet of 10 meq sodium and 60 meq potassium/day. With dietary sodium restriction, urinary sodium excretion decreased from 152 +/- 13 meq/day in stepwise fashion to 7 +/- 1 meq/day (P less than 0.001) on day 7. On the first day of dietary sodium restriction, a sodium deficit of 122 meq was associated with a decrease in supine plasma dopamine concentration from 58 +/- 10 to 45 +/- 7 pg/ml (P less than values for 2 days but decreased again to 43 +/- 12 pg/ml (P less than 0.05) on day 4 of sodium restriction and remained significantly lower than control on days 5-7 of sodium restriction (P less than 0.01). Supine plasma norepinephrine concentration increased from 193 +/- 34 to 232 +/- 29 pg/ml (P less than 0.05) on day 1 of sodium restriction and remained elevated during each subsequent day of low sodium intake (P less than 0.001). Supine plasma epinephrine concentration was unchanged by sodium restriction. Urinary dopamine excretion decreased from 12 +/- 2 to 8 +/- 1 microgram/h (P less than 0.05) on day 2 of sodium restriction and remained significantly low during each subsequent day of low sodium intake. Urinary norepinephrine was unchanged by sodium restriction. The data indicate a variable decrease in plasma dopamine concentration and a constant decrease in urinary dopamine excretion during the course of dietary sodium restriction in man.

Interactions between angiotensin peptides and the sympathetic nervous system mediating intestinal sodium and water absorption in the rat

The purpose of this study was to determine the locus of interaction of angiotensin peptides with the sympathetic nervous system leading to alterations in jejunal sodium and water transport. At low physiological doses, angiotensin II (AII) stimulates jejunal sodium and water absorption, while at high doses peptide inhibits absorption and/or stimulates secretion. Both the stimulation of jejunal transport and the inhibition of absorption were expressed in adrenalectomized rats. However, the stimulation of jejunal water absorption was abolished and a potentiated inhibition of transport was expressed in peripherally sympathectomized rats (intact adrenal medulla) and in normal rats after administration of guanethadine, phentolamine, and prazosin. The angiotensin analog (Sar1 Leu8)-AII has low efficacy and is a potent competitive antagonist of the parent peptide in pressor and myotropic systems, but is a full agonist with even greater potency than AII in stimulating jejunal transport. The increased water transport in response to (Sar1 Leu8)-AII is not secondary to enhanced renal renin release, as the analog also stimulated jejunal transport in the presence of captopril and after bilateral nephrectomy. The stimulation of absorption in response to (Sar1 Leu8)-AII alone or together with AII was abolished by phentolamine. These data demonstrate that AII-increased intestinal absorption is secondary to the release of norepinephrine from nerve endings in the jejunum and that AII inhibition of absorption is not mediated by the sympathetic nervous system. The analog (Sar1 Leu8)-AII is a full agonist in the stimulation of jejunal transport (increased norepinephrine release), but antagonizes the inhibitory response to high doses of AII. Angiotensin peptides are potent modulators of intestinal sodium and water absorption.

Changes in an electroneutral transport process mediated by angiotensin II in the rat distal colon in vivo

The purpose of these experiments was to determine if angiotensin II mediates the stimulation of water transport in the rat distal colon via an electroneutral mechanism. Amphotericin B (36 micrograms/ml) added to the mucosal surface of the colon significantly increased potential difference (pd) and short circuit current (scc) and significantly decreased resistance. Replacement of the luminal contents of the colon with 150 mM choline chloride decreased pd and scc while resistance remained unchanged. Increased colon resistance occurred on cooling the animals. Thus both increased and decreased pd, scc, and resistance could be measured with the preparation used in this study. The distal colon in vivo is sensitive to angiotensin II since low infusions (7 pmol/kg . min) stimulate water transfer 180% above controls. Transmural pd, resistance, and scc were measured in the distal colon, while the response to the hormone was monitored by measurement of jejunal water transport in the same animals, Intravenous infusion of angiotensin II at a subpressor dose (7 pmol/kg . min) significantly stimulated jejunal water absorption in the absence of any change in transmural pd, resistance, or scc measured in the distal colon. However, infusion of a pressor dose of angiotensin II (700 pmol/kg . min) significantly inhibited jejunal water absorption but again did not alter the electrical properties of the distal colon. These data suggest that angiotensin II can stimulate and inhibit intestinal water transport via electroneutral mechanisms. Thus, the actions of this hormone contrast with that of aldosterone, which stimulates intestinal sodium and water transport by electrogenic mechanisms.

Responses of blood pressure and angiotensin-converting enzyme activity to acute captopril administration in normotensive and hypertensive rats

The purpose of these experiments ws to determine the dose of captopril which resulted in essentially complete blockade of tissue and plasma converting enzyme activity (CEA) and to correlate the effect of this dose of inhibitor on blood pressure and CEA in a number of normotensive and hypertensive rat models. Oral administration of captopril (0.3-10 mg/kg) induced a dose-related attenuation of CEA in plasma freshly drawn from normotensive conscious rats. After storage at -20 or 4 C before assay, both captopril-treated and untreated plasmas displayed markedly greater CEA. The converting enzyme inhibitor induced a parallel shift to the right of angiotensin I-induced blood pressure responses, reaching a 100-fold displacement of dose-dependent responses in the presence of 10 mg/kg captopril. Sixty minutes after oral administration of 10 mg/kg captopril, plasma CEA was blocked completely in all normo- and hypertensive models studied. This dose of the inhibitor reduced blood pressure in the sodium-deplete normotensive rat, the spontaneously hypertensive rat, and the initial phase two-kidney, one-clip Goldblatt rat but not in the sodium-replete normotensive rat, the spontaneously hypertensive rat, the mineralocorticoid hypertensive rat, or the chronic phase of two-kidney, one-clip Goldblatt rat. It is concluded that acute administration of captopril at a dose which results in complete blockade of plasma converting enzyme and severe attenuation of tissue converting enzyme reduces blood pressure in animals with high PRA but not in animals in which the PRA is low. (Endocrinology 108: 536, 1981)

Response of rat jejunum to angiotensin II: role of norepinephrine and prostaglandins

At low doses, angiotensin II (AII) stimulates jejunal sodium and water absorption in the pentobarbital sodium-anesthetized rat. This response to the hormone can be blocked by cycloheximide and has a rapid onset and decay, indicating that any protein involved must have a short half-life and/or fast turnover. At high doses, AII inhibits jejunal absorption by a process that does not involve protein synthesis and has a rapid onset but slow decay. The AII-induced inhibition of water absorption can be abolished, and a net stimulation ensues after pretreatment of the animals with meclofenamate or indomethacin, suggesting that at high doses AII stimulates intestinal prostaglandin biosynthesis. The AII analogue, [Sar1,Leu8]AII, significantly stimulated jejunal water absorption and was devoid of any inhibitory response at any dose administered. Simultaneous infusion of low doses of [Sar1,Leu8]AII and AII resulted in a stimulation of water transport, while simultaneous infusion of high dose [Sar1,Leu8]AII and AII also stimulated water absorption. It is suggested that the AII analogue is a full agonist with regard to stimulation of jejunal transfer but antagonizes the inhibitory response to high doses of AII. A model consistent with these data is discussed.

Demonstration of a primary antidiuretic action of angiotensin II: effects of intrarenal converting enzyme inhibition in the conscious dog

This study was designed to determine whether angiotensin II of renal origin physiologically mediates free water production by the kidney. The effect of renal arterial infusion of the angiotensin-converting enzyme inhibitor, teprotide, on renal function was studied under conditions of hydropenia and hydration in uninephrectomized conscious dogs after 5 days of equilibration on a normal or low sodium diet. In low sodium animals, intrarenal infusion of teprotide (0.25 microgram/kg.min) after 12 h of water restriction elicited marked increases in the glomerular filtration rate (GFR) and free water formation. After 24 h of water restriction, vasopressin (10 microU/min) was infused iv to achieve an effective maximal urine concentration. Under these conditions, the inhibitor again increased the GFR and free water formation. After the production of a state of stable hydration, intrarenal infusion of teprotide also increased the GFR and free water formation. In the normal sodium animals, intrarenal infusion of the converting enzyme inhibitor (2.5 microgram/kg.min) in 12-h hydropenic dogs failed to change the GFR but increased free water formation, while the inhibitor decreased effective renal plasma flow and free water formation in normal sodium, hydrated animals. These data suggest that angiotensin II of renal origin plays an important role in the control of free water production by the kidney.

Dopaminergic inhibition of metoclopramide-induced aldosterone secretion in man. Dissociation of responses to dopamine and bromocriptine

This study was designed to investigate the role of dopaminergic mechanisms in the control of aldosterone secretion in man. Five normal male subjects in metabolic balance at 150 meq sodium/d and 60 meq potassium/d constant intake received the specific dopamine antagonist, metoclopramide, 10 mg i.v. on 2 consecutive d. On the 1st d, the subjects received an infusion of 5% glucose solution (vehicle) from 60 min before to 60 min after metoclopramide administration; on the 2nd d, an infusion of dopamine 4 mug/kg per min was substituted for vehicle. Metoclopramide in the presence of vehicle increased plasma aldosterone concentrations from 2.4+/-1.1 to a maximum of 17.2+/-2.8 ng/100 ml (P < 0.01) and serum prolactin concentrations from 7.5+/-5.0 to a maximum of 82.2+/-8.7 ng/ml (P < 0.01). Dopamine 4 mug/kg per min did not alter basal plasma aldosterone concentrations, but blunted the aldosterone responses to metoclopramide significantly; in the presence of dopamine, plasma aldosterone concentrations increased from 3.1+/-0.5 to 6.2+/-1.4 ng/100 ml (P < 0.05) in response to metoclopramide. The incremental aldosterone responses to metoclopramide were significantly lower in the presence of dopamine than with vehicle. Dopamine 4 mug/kg per min suppressed basal prolactin to <3 ng/ml and inhibited the prolactin responses to metoclopramide; serum prolactin concentrations increased to a maximum of 8.5+/-2.3 ng/ml with metoclopramide in the presence of dopamine. The subjects were studied in the same manner except that dopamine 2 mug/kg per min was administered instead of the 4-mug/kg per min dose. Dopamine 2 mug/kg per min attenuated the aldosterone and prolactin responses to metoclopramide, but was less effective than the 4-mug/kg per min dose of dopamine. Metoclopramide 10 mg i.v. was administered to five additional subjects after pretreatment with the dopamine agonist, bromocriptine, 2.5 mg or placebo at 6 p.m., midnight, and 6 a.m. before study. Bromocriptine suppressed basal serum prolactin levels and completely inhibited the prolactin responses to metoclopramide. In contrast, bromocriptine did not alter basal plasma aldosterone concentrations or the aldosterone responses to metoclopramide. Plasma renin activity, plasma cortisol, and serum potassium concentrations were unchanged by metoclopramide, dopamine, or bromocriptine. The results of this study suggest that the aldosterone response to metoclopramide is mediated by metoclopramide's antagonist activity at the dopamine receptor level. The results further suggest dissociation of the responses to the dopamine agonists, dopamine and bromocriptine, and indicate that a new type of dopamine receptor may inhibit aldosterone secretion.

Percutaneous transluminal dilatation of the renal arteries: techniques and results

The techniques and results of percutaneous transluminal angioplasty (TPA) of the renal arteries were evaluated in 20 hypertensive patients with 25 renal artery stenoses. Follow-up angiograms have been obtained in nine patients. Many patients had evidence of both essential and angiotensinogenic hypertension. Eleven patients had evidence of severe diffuse atherosclerotic disease, and nine patients had evidence of renal insufficiency. The mean systolic pressures before and after PTA were 203.80 and 150.30, respectively. The mean diastolic pressures before and after PTA were 117.45 and 85.95, respectively. Ten patients were cured. Six patients with long histories of hypertension and a recent increase in blood pressure were classified as having blood pressure easier to control with antihypertensive medication following PTA. Three patients failed to respond to PTA, and one patient was a technical failure. The advantages of this technique include avoidance of general anesthesia and a major surgical procedure, decreased cost, and a shortened hospital stay. The technique can be easily repeated if necessary, and future surgical intervention is not precluded if the method is unsuccessful.

Effects of rat adrenal homogenate on induction of atherosclerosis in cholesterol-fed rabbits

Virgin male Sprague-Dawley rats are resistant to atheroma formation. An adrenal homogenate from such rats delayed the increase in serum cholesterol concentrations in cholesterol-fed New Zealand white rabbits. More importantly, aortic atherosclerosis was markedly reduced when compared to a similar population fed cholesterol without adrenal homogenate for 14 weeks. The nature of the active constituent in this homogenate and its mode of action are unknown.

Ischemic cardiovascular complications concurrent with administration of captopril. A clinical note

Administration of potent vasodepressor agents such as the angiotensin converting enzyme inhibitor, captopril, may precipitate myocardial ischemic events in patients with coronary artery disease, particularly if this treatment is preceded by a discontinuation of beta-blocking drugs such as propranolol. In one case studied, a patient experienced three episodes of angina pectoris under these conditions; in another, acute anterior myocardial infarction was suspect.

Hypercalcemia associated with chronic lymphocytic leukemia

A patient with chronic lymphocytic leukemia (CLL) is described in whom hypercalcemia occurred in association with elevation of the peripheral lymphocyte count and expansion of total tumor mass. Hypercalcemia was ameliorated with the institution of chemotherapy for the leukemic process and subsequent fall in WBC count and decrease in total tumor burden; hypercalcemia recurred with relapse of the leukemic process. The serum immunoreactive parathyroid hormone (iPTH) concentration, when measured, was inappropriately elevated for the degree of hypercalcemia. The hypercalcemia would appear to be a direct consequence of the leukemia, and possibly involved secretion of a parathyroid hormone-like polypeptide by the CLL cells. Although a possible role for either an osteoclast-activating substance or prostaglandins was not excluded, they would not account for the elevated serum iPTH levels observed.

Identification and differentiation of surgically correctable hypertension due to primary aldosteronism

During a protocol study for the evaluation of patients with primary aldosteronism, a variety of diagnostic studies were employed in an attempt to identify patients with primary aldosteronism and to differentiate patients with adrenal adenoma from patients with idiopathic adrenal hyperplasia. In this study, we are able to demonstrate the utility of (1) absent postural increase in plasma aldosterone concentration, (2) adrenal scanning and (3) normalization of blood pressure with spironolactone therapy in identifying patients with primary aldosterone excess who have an adrenal adenoma, surgical removal of which results in eliminating their hypertension.

Estimating compliance with diuretic therapy: urinary hydrochlorothiazide-creatinine ratios in normal subjects

We gave 21 healthy young men 100 mg of hydrochlorothiazide daily to determine whether or not urinary detection of the drug was feasible as a measure of compliance on a standard antihypertensive regimen. All subjects took the drug daily for 6 days, after which they were divided into four groups with differing patterns of medication administration. Urine hydrochlorothiazide and creatinine measurements were obtained to validate the urinary hydrochlorothiazide-creatinine ratio (UHCR) as an accurate quantitative index of compliance. The subjects achieved a constant level of UHCR of 13 +/- 3.0 within 48 hours of hydrochlorothiazide administration. The UHCR levels decreased to 5.0 +/- 0.8 48 hours after discontinuation of the drug (p less than 0.001). UHCR values in the range of 13 +/- 6 indicate that the subject has ingested hydrochlorothiazide 24 hours previously. The UHCR is a potentially useful means of assessing compliance in hypertensive patients taking hydrochlorothiazide.

Hemodialysis-resistant hypertension: control with an orally active inhibitor of angiotensin-converting enzyme

In two patients with end stage renal disease and dialysis-resistant hypertension, the orally active inhibitor of angiotensin-converting enzyme, captopril (SQ14,225; 2-D-methyl-3-mercaptopropranoyl-L-proline, dramatically lowered blood pressure both before and during dialysis. This agent holds promise as an alternate to bilateral nephrectomy in such patients.

Effects of metoclopramide and bromocriptine on the renin-angiotensin-aldosterone system in man. Dopaminergic control of aldosterone

This study was designed to investigate the possible role of dopaminergic mechanisms in the control of the renin-angiotensin-aldosterone system in normal man. Six normal male subjects in metabolic balance at 150 meq sodium, 60 meq potassium constant intake received the specific dopamine antagonist, metoclopramide, 10 mg i.v. or placebo followed by angiotensin II infusion 1 h later on 2 consecutive days. Metoclopramide increased plasma aldosterone concentration from 8.2+/-2.2 to 21.0+/-3.3 ng/100 ml (P < 0.005) and plasma prolactin concentration from 18.0+/-4.0 to 91.7+/-4.0 ng/ml (P < 0.001) within 15 min of its administration. At 1 h, plasma aldosterone and prolactin concentrations remained elevated at 16.8+/-2.1 ng/100 ml (P < 0.01) and 86.8+/-15.9 ng/ml (P < 0.005), respectively. Angiotensin II at 2, 4, and 6 pmol/kg per min further increased plasma aldosterone concentration to 27.2+/-3.4, 31.9+/-5.7, and 36.0+/-6.7 ng/100 ml (P < 0.02), respectively. Placebo did not alter plasma aldosterone or prolactin concentrations, but angiotensin II increased plasma aldosterone concentration to 13.7+/-2.4, 19.0+/-1.9, and 23.3+/-3.2 ng/100 ml (P < 0.005). The increment of plasma aldosterone concentration in response to angiotensin II was similar after metoclopramide or placebo. The six subjects also received the dopamine agonist, bromocriptine, 2.5 mg or placebo at 6 p.m., midnight, and 6 a.m. followed by angiotensin II infusion on 2 consecutive d. Bromocriptine suppressed prolactin to <3 ng/ml. After placebo, plasma aldosterone concentration increased from 5.2+/-1.4 to 12.3+/-1.7, 17.2+/-2.2, and 21.8+/-3.5 ng/100 ml (P < 0.01) and after bromocriptine from 7.2+/-1.0 to 14.7+/-3.0, 19.8+/-3.2, and 23.4+/-1.6 ng/100 ml (P < 0.001) with each respective angiotensin II dose. No difference in the response to angiotensin II after bromocriptine or placebo was observed. Plasma renin activity, free 11-hydroxycorticoid concentration, and serum potassium concentration were unchanged by metoclopramide or bromocriptine. The results suggest that aldosterone production is under maximum tonic dopaminergic inhibition which can be overridden with stimulation by angiotensin II in normal man.

Activity of [des-aspartyl1]-angiotensin II in primary aldosteronism

This study describes the effects of [des-Aspartyl(1)]-angiotensin II ([des-Asp]-AII) on blood pressure and aldosterone production in patients with primary aldosteronism due to aldosterone-producing adrenal adenoma (APA) and idiopathic adrenal hyperplasia (IHA), and in normotensive control subjects. 10 patients with primary aldosteronism, 7 with APA and 3 with IHA, and 6 normotensive control subjects were placed on a constant 150-meq sodium diet for 4 days. [des-Asp]-AII was infused for 30 min at 6, 12, and 18 pmol/kg per min. Three groups of patients were identified on the basis of aldosterone response to [des-Asp]-AII. Group I, composed of normotensive control subjects, showed incremental increases in plasma aldosterone concentration from 6+/-1 to 14+/-3 ng/100 ml (P < 0.01) with [des-Asp]-AII infusion. Group II, composed of patients with primary aldosteronism, showed incremental increases in plasma aldosterone concentration from 33+/-8 to 65+/-13 ng/100 ml (P < 0.05) with 12 pmol/kg per min of [des-Asp]-AII. Group III, also composed of patients with primary aldosteronism, showed no increase of plasma aldosterone concentration with [des-Asp]-AII. Groups I and II showed similar percentage increases in plasma aldosterone concentration (P = NS). Group III showed significantly lower aldosterone responses than group I (P < 0.01). Group II included all patients with IHA and two patients with APA. Group III included only patients with APA. The blood pressure responses to [des-Asp]-AII of subjects in group I did not differ significantly from those of groups II or III.Thus, patients with IHA and a subgroup of patients with APA showed responsiveness to [des-Asp]-AII which was limited to adrenal cortical stimulation of aldosterone biosynthesis. This suggests that adrenal responsiveness to angiotensin is a major control mechanism in some forms of primary aldosteronism. The differential adrenal responsiveness to [des-Asp]-AII in patients with APA indicates either that there are two distinct subpopulations of APA, or that alteration in tumor response to angiotensin occurs during the natural progression of the disease history.

Pseudohypoaldosteronism: multiple target organ unresponsiveness to mineralocorticoid hormones

The first report of a 7-month-old male with pseudohypoaldosteronism in which unresponsiveness to mineralocorticoids has been demonstrated in the kidney, colon, and sweat and salivary glands is presented here. This is documented by urinary, salivary, and sweat sodium wasting in the presence of elevated urinary aldosterone excretion, plasma aldosterone concentration, and PRA. There was no mineralocorticoid response in the kidney or salivary or sweat glands to the administration of high doses of 9 alpha-flurocortisol. Furthermore, in this patient, the colonic mucosal cells failed to respond to exogenous aldosterone administration. Repeat evaluation at 25 months of age showed persistence of the sodium wasting and multiple target organ insensitivity to administered mineralocorticoid. Since this patient has defective mineralocorticoid response in the major sodium-conserving organs, the only therapy possible was administration of sodium to compensate for total sodium loss.

Poorly differentiated lymphocytic lymphoma with ectopic parathormone production: visulization of metastatic calcification by bone scan

Metastatic soft tissue calcification is known to occur in hypercalcemia and is usually present in the kidneys, stomach and lungs. 1--3 This case presents two unusual features: 1) ectopic parathormone production in association with poorly differentiated lymphocytic lymphoma; and and 2) uptake of 99mTc-pyrophosphate in the liver in the absence of demonstrable abnormality at autopsy. The more usual sites of metastatic calcification also showed uptake of the radionuclide. We will discuss metastatic soft tissue calcification, ectopic parathyroid hormone production, hypercalcemia in malignancy and bone scan agent localization in soft tissues.

Evidence for a splanchnic sodium input monitor regulating renal sodium excretion in man. Lack of dependence upon aldosterone

Eight normal male subjects were placed on a constant 10 mEq sodium, 60 mEq potassium diet for 5 days. At 8:00 a.m. on the 5th day, the subjects were given a standard dose of 100 mEq of sodium orally or intravenously. Subjects receiving oral sodium also received 200ml of 5% dextrose in water intravenously, and those receiving intravenous sodium also received placebo capsules orally. Water intake and posture were controlled. The subjects then returned to a free diet for 1 month and subsequently were restudied by using the opposite route of sodium administration. The subjects given the oral sodium load excreted greater quantities of sodium in their urine than those repleted intravenously. The differential natriuresis was significant as early as 2 hours after sodium loading. Plasma aldosterone concentration was similar irrespective of the route of sodium administration. Six patients with primary adrenocortical insufficiency and documented hypoaldosteronism were studied with the same protocol after 5 days of 50 mEq sodium, 60 mEq potassium intake. They also had significantly greater natriuresis after oral than intravenous sodium administration. The data suggest the presence of a splanchnic input monitor for sodium which partially regulates renal sodium excretion and is not dependent upon a turn-off mechanism for aldosterone secretion.

The immediate pressor effect of saralasin in man

An immediate pressor response to [Sar1-Ala8]-angiotensin II (saralasin) is described in all of 16 hypertensive subjects. Blood pressure rose within 1-3 min, peaked at 4-6 min, then returned toward baseline. Plasma norepinephrine and dopamine beta-hydroxylase activity were unchanged by saralasin, indicating that the pressor response is not mediated by saralasin-induced catecholamine release. Ten normal renin hypertensives had diastolic pressor responses of 19.4 +/- 3.3 mm Hg. After 5 weeks of diuretic therapy, the diastolic pressor responses to saralasin were decreased to 4.9 +/- 2.4 mm Hg. Six low renin hypertensives had diastolic pressor responses of 26.2 +/- 6.2 mm Hg, but 5 weeks of diuretic therapy did not decrease these pressor responses significantly. In two normal and two low renin hypertensives, the diastolic blood pressure rose to levels greater than 150 mm Hg. The amplitudes of the immediate pressor responses were inversely correlated with the base-line plasma renin activities, r = -0.46. The data support the concept that the agonist activity of saralasin occurs at the angiotensin II vascular receptor level with clinical expression mediated by sodium and/or volume changes.