Fatty acids enhance vascular alpha-adrenergic sensitivity

Hypertensive patients are heavier and have a more centralized body fat distribution, which is associated with risk factor clustering and resistance to insulin's actions, including suppression of plasma nonesterified fatty acids. We postulated that abnormalities of nonesterified fatty acids contribute to the increased vascular alpha-adrenergic reactivity and tone observed in our previous studies of obese hypertensive subjects. To test this hypothesis, in two separate protocols 10% Intralipid was infused into a dorsal hand vein with heparin to activate lipoprotein lipase and raise fatty acid levels locally. In protocol 1, the effects of Intralipid/heparin compared with those of 5% dextrose/heparin on dorsal hand vein sensitivity to phenylephrine were assessed by use of the linear variable differential transformer technique in 8 normotensive subjects. In protocol 2, the effects of Intralipid/heparin were compared with those of saline/heparin on hand vein responses to both phenylephrine and angiotensin II in 11 normotensive African American women. Intralipid/heparin reduced the dose of phenylephrine required to produce 50% of the maximal venoconstrictor response from 582 to 137 ng/min (compared with dextrose/heparin, P < .01) in protocol 1 and from 293 to 137 ng/min (compared with saline/heparin, P < .01) in protocol 2. Intralipid/heparin did not significantly alter hand vein responses to angiotensin compared with saline/heparin. These data suggest that abnormalities of nonesterified fatty acids in obese hypertensive patients with risk factor clustering may contribute to their increased neurovascular tone.

Lead increases aldosterone production by rat adrenal cells

Exposure to lead has been postulated to contribute to elevated blood pressure in humans and has been shown to raise blood pressure in animals. The mechanism of action of lead on blood pressure is unknown. We fed lead to rats in their drinking water and then examined the production of aldosterone by their adrenal cells in vitro. We also measured excretion of aldosterone and corticosterone by intact rats stimulated with corticotropin, with and without lead treatment. At a dose (273 ppm) that raised blood levels to 30 to 40 micrograms/dL, comparable to blood levels in exposed humans, lead induced increased aldosterone secretion in vitro and in vivo. The effect of lead was most evident when cells or animals were stimulated with aldosterone secretagogues. Experiments in vitro indicate that exposure to lead in vivo increases activity of one or more steps in the late pathway of aldosterone biosynthesis. The results suggest that the hypertensive effect of lead involves relative hyperaldosteronism and may be most evident when secretion of this hormone is stimulated.

Specificity and mechanism of fatty acid inhibition of aldosterone secretion

We have shown that unesterified, unsaturated long-chain fatty acids inhibit angiotensin II (AII) binding to receptors in adrenal glomerulosa cells. In this report, we show that oleic and arachidonic acids are specific inhibitors of the AT1 subtype of angiotensin receptor, and exert no effect on receptors of the AT2 subtype. By contrast, decanoic acid is a weak inhibitor of the AT2 subtype only. Our previous work on a post-receptor locus of inhibition by fatty acids of aldosterone biosynthesis showed that the 18-oxidase step is uniquely sensitive. In brief, the first and last steps involved in angiotensin-stimulated aldosterone secretion are particularly sensitive to inhibition by fatty acids. These results suggest a specific role for unesterified fatty acids in regulation of salt and water metabolism.

Relationships among plasma aldosterone, high-density lipoprotein cholesterol, and insulin in humans

To investigate the pathogenesis of hypertension in patients with obesity and insulin resistance and to explore the role of plasma lipids, we studied 30 subjects at the end of 7 days of low (20 mEq/d) then high (200 mEq/d) sodium diets. Glucose and insulin tolerance tests were performed at the end of each week and blood and urine collected for measurements of plasma aldosterone, renin activity, electrolytes, insulin, and lipoproteins. There was a strong negative correlation between plasma aldosterone and high-density lipoprotein cholesterol during both diets. There were weaker positive correlations between plasma aldosterone and insulin or triglycerides. When the aldosterone-renin ratio was the dependent variable and the correlation controlled for serum potassium, the inverse relationship with high-density lipoprotein cholesterol and the positive correlation with insulin remained, but only during the high salt diet. Subjects were divided into three groups based on high-density lipoprotein cholesterol. Subjects with the lowest high-density lipoprotein cholesterol levels showed the highest aldosterone, plasma triglycerides, body mass index, and waist-to-hip ratio. Those subjects also demonstrated the greatest resistance to insulin action on glucose and plasma unesterified fatty acids. There was a weak direct correlation between plasma aldosterone and systolic blood pressure during the high salt diet. These data suggest that high aldosterone levels may be a link between dyslipidemia, insulin resistance, and hypertension, a relationship made more evident by high salt intake.

Renin and aldosterone are higher and the hyperinsulinemic effect of salt restriction greater in subjects with risk factors clustering

Separate lines of evidence suggest that abdominal obesity, insulin, and renin are independent risk factors for coronary heart disease. Since insulin levels are higher in abdominally obese subjects and may enhance renin and aldosterone production, these risk factors may not be entirely independent. Moreover, the renin-angiotensin system may contribute to insulin resistance. These observations suggest that some inconsistencies in the literature regarding the effects of salt restriction on insulin may be explained by baseline anthropometric and metabolic differences in the subjects studied. To examine these issues, 29 volunteers with a range of risk factors were studied after 1 week each on isocaloric 20 and 200 mmol/day NaCl diets. Measurements included ambulatory blood pressures, plasma renin and aldosterone, and responses to oral glucose and intravenous insulin. Subjects were divided into three groups based on a composite score reflecting the risk factor cluster associated with abdominal obesity and hyperinsulinemia. The nine subjects with the highest scores had significantly greater values for renin and aldosterone on both the high and low salt diets than the nine subjects with the lowest scores. Fasting insulin and triglycerides, the insulin response to oral glucose, and plasma aldosterone all rose significantly more with salt restriction in the high than in the low risk subjects. Plasma renin activity also tended to increase more on the low salt diet in the high risk group. Ambulatory blood pressures were greater on the low than the high salt diet only in the high risk group.(ABSTRACT TRUNCATED AT 250 WORDS)

Lateral diffusion and fatty acid composition in vascular smooth muscle membrane from stroke-prone spontaneously hypertensive rats

We measured membrane fluidity and fatty acid composition in cultured vascular smooth muscle cells from stroke-prone spontaneously hypertensive and Wistar-Kyoto normotensive rats. Membrane fluidity was measured as a lateral diffusion of 5 N (octadecanoyl) aminofluorescein using fluorescence microscopy and fluorescence recovery after photobleaching. Fatty acid composition of membrane fractions was measured using high performance liquid chromatography. Lateral diffusion was significantly lower (the membrane had lower fluidity) in vascular smooth muscle cells from stroke-prone spontaneously hypertensive rats as compared to those cells isolated from Wistar-Kyoto reference strain. The ratio of arachidonic acid to total fatty acids was 0.058 +/- 0.007 in the plasma membrane from stroke-prone spontaneously hypertensive rats and 0.036 +/- 0.005 in that from Wistar-Kyoto rats, P = .005. Similarly, the ratios of arachidonic to oleic acid and arachidonic to palmitic acid were significantly greater in cells from stroke-prone spontaneously hypertensive rats (P = .002 for difference in each ratio). These results show decreased lateral diffusion (decreased membrane fluidity) in vascular smooth muscle cells from stroke-prone spontaneously hypertensive rats. This is associated with increased content of arachidonic acid, the major precursor of prostaglandins and other eicosanoids. We postulate that local changes in the unsaturated fatty acid composition related to arachidonic acid storage and release contribute to reduced membrane fluidity in stroke-prone spontaneously hypertensive rats.

Assessment of blood pressure during treatment with naproxen or ibuprofen in hypertensive patients treated with hydrochlorothiazide

This study determined the effect of nonsteroidal anti-inflammatory drug (NSAID) administration on blood pressure in hypertensive patients taking hydrochlorothiazide (HCTZ). Ninety-seven patients with mild essential hypertension and a musculoskeletal indication for NSAID use were studied in a three-phase, multi-center, double-blind, randomized, parallel study based in 15 academic and community clinics. Patients served as their own controls. Patients with stable hypertension, not taking antihypertensive or NSAID medications, were treated with HCTZ 50 mg/day. After 4 to 5 weeks of treatment and documented stable blood pressure, naproxen 375 mg twice a day or ibuprofen 800 mg three times a day was added. Blood pressure was measured at 2 and 4 weeks of NSAID therapy. The average diastolic blood pressure was 97.5 +/- 2.4 mm Hg and the average of the mean arterial pressure (MAP) was 116.8 +/- 6.04 before treatment with HCTZ. Hydrochlorothiazide treatment decreased diastolic blood pressure to 83.1 +/- 5.6 mm Hg, and MAP to 101.1 +/- 6.5 mm Hg. With naproxen or ibuprofen treatments, mean diastolic blood pressure increased less than 3 mm Hg. At 2 weeks, ibuprofen increased diastolic blood pressure by 2.6 mm Hg (P = .004) and naproxen increased diastolic blood pressure 0.7 mm Hg (P = .40). Both ibuprofen and naproxen significantly increased diastolic pressure at 4 weeks (2.1 mm Hg, P = .042; and 1.8 mm Hg, P = .043, respectively). There was no correlation between the pre-NSAID blood pressure and the magnitude of change after 2 or 4 weeks of treatment. Changes in MAP reflected a pattern similar to diastolic pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Bovine adrenal glomerulosa and fasciculata cells exhibit 28.5-kilodalton proteins sensitive to angiotensin, other agonists, and atrial natriuretic peptide

Protein synthesis by bovine adrenal glomerulosa and fasciculata cells in response to various modulators of steroid synthesis was examined using [35S]methionine labeling and two-dimensional gel electrophoresis. Both cell types responded to steroidogenic stimuli with rapid changes in a family of 28- to 30-kilodalton (kDa) proteins similar to those described in rat fasciculata by Epstein and Orme-Johnson. In glomerulosa, angiotensin-II (AII), potassium, and (Bu)2cAMP stimulated the appearance of two 28.5-kDa proteins (no. 3 and 4) with pI values of 6.44 and 6.33 and decreased labeling of two other 28.5-kDa proteins (no. 1 and 2) with pI values of 6.9 and 6.59. The rank order of potency on aldosterone synthesis and that on proteins 1-4 were the same: (Bu)2cAMP > AII > potassium. Atrial natriuretic peptide blocked the effects of AII on all four proteins and on aldosterone synthesis. Adrenal secretagogues also affected labeling of four slightly larger (30 kDa) proteins (no. 5-8). Corresponding proteins in each quartet are separated by the same difference in isoelectric points. These eight proteins may represent a core protein systematically modified in a number of ways. Aldosterone synthesis in glomerulosa, like glucocorticoid synthesis in fasciculata, requires ongoing protein synthesis. The 28- to 30-kDa proteins increased by steroidogenic stimuli in both cells and decreased by atrial natriuretic peptide in glomerulosa may be the proteins whose synthesis is crucial to acute control of steroidogenesis. Our results indicate that these proteins are made in response to calcium- or calcium/phosphoinositide-dependent mechanisms as well as by cAMP.

Mechanism of fatty acid inhibition of aldosterone synthesis by bovine adrenal glomerulosa cells

Previous work from this laboratory has suggested that the adrenal glomerulosa is under tonic inhibition by fatty acids. The purpose of the present work was to define the mechanism by which fatty acids inhibit aldosterone synthesis. Experiments with isolated bovine adrenocortical cells showed the following. 1) Fatty acids inhibited angiotensin-II-stimulated and (Bu)2cAMP-stimulated aldosterone synthesis with similar potencies. 2) Inhibition of aldosterone synthesis was highly dependent on fatty acid chain length and degree of unsaturation as well as on configuration of double bonds. Oleic acid was the most potent inhibitor among fatty acids prominent in plasma. 3) Cortisol synthesis was less sensitive to oleic acid inhibition than was aldosterone synthesis. 4) Pregnenolone synthesis by angiotensin-II-stimulated adrenal glomerulosa cells was relatively insensitive to oleic acid. 5) For both glomerulosa and fasciculata cells, cortisol synthesis from 21-deoxycortisol, which requires the participation of P450(21), was relatively insensitive to fatty acids. Cortisol synthesis from corticosterone by fasciculata cells, which requires the participation of P450(17) alpha, was also insensitive to oleic acid. These are microsomal enzymes. 6) In glomerulosa cells, aldosterone synthesis from added corticosterone, which requires the 18-oxidase function of P450(11) beta, a mitochondrial enzyme, was potently inhibited by fatty acids; cortisol synthesis from 11-deoxycortisol by glomerulosa cells, which requires P450(11) beta, was less sensitive to inhibition, and cortisol synthesis from 11-deoxycortisol by fasciculata cells was even less sensitive. 7) Aldosterone synthesis from exogenous 18-hydroxycorticosterone was potently inhibited by oleic acid. Thus, fatty acids are potent inhibitors of the 18-oxidase function of the mitochondrial enzyme P450(11) beta, whereas nonmitochondrial steroidogenic enzymes and the 11-hydroxylase function of P450(11) beta are relatively insensitive to fatty acids. The special sensitivity of aldosterone synthesis to fatty acid inhibition appears to result from the unusual susceptibility of the 18-oxidase function of the mitochondrial steroidogenic enzyme P450(11) beta. This mechanism would allow differential regulation of aldosterone vs. cortisol production by unesterified fatty acids.

Fatty acids may regulate aldosterone secretion and mediate some of insulin's effects on blood pressure

Experiments in vitro and observation made in humans suggest that some unesterified fatty acids (FA) participate, as inhibitors, in the regulation of aldosterone secretion. Removal of FA from adrenal glomerulosa cells with albumin increases the responses to angiotensin II (AII) and dibutyryl cyclic AMP. Micromolar concentrations of some FA including arachidonic, oleic, linoleic, eicosapentaenoic, and docosahexaenoic inhibit aldosterone secretion by adrenal glomerulosa cells. Inhibition is specific--some acids like stearic are inactive, and the adrenal fasciculata is relatively resistant to inhibition. Oleic acid rapidly and reversibly inhibits aldosterone secretion by perfused dog adrenals. Observations in vivo suggest a reciprocal relationship between plasma levels of FA and aldosterone: insulin infusion into dogs lowers plasma FA and increases adrenal responsiveness to All; salt infusions into humans increase plasma FA as aldosterone falls; plasma FA are low in low-renin essential hypertension where adrenal responsiveness to All is high; plasma FA are inversely correlated with ratios of aldosterone to renin in black hypertensives; and plasma FA are high in some seriously ill patients whose aldosterone levels are inexplicably low. All receptors and the final step of aldosterone biosynthesis, oxidation at the 18 position, are the adrenal sites most sensitive to FA. Insulin's antinatriuresis may be mediated in part by its ability to lower plasma FA and thereby enhance adrenal response to secretagogues.

Effect of omega-3 fatty acids on the vascular response to angiotensin in normotensive men

There is a widespread interest in fish oil as a dietary supplement and possible nonpharmacologic adjunct in the treatment of hypertension. The effect of dietary fish oil on blood pressure is controversial and the effect on systemic hemodynamics and regional vascular reactivity in humans is unknown. To address these questions, a double-blind, placebo-controlled, crossover study on the effect of dietary fish oil substitution was performed during a carefully controlled diet in 8 normotensive men. Systemic hemodynamics and the forearm vascular response to intrabrachial artery infusions of norepinephrine, phentolamine and angiotensin II were obtained. Compared with a safflower oil placebo, dietary fish oil had no effect on cardiac output (6.42 +/- 0.38 vs 6.87 +/- 0.28 liters/min, p = not significant) or 24-hour blood pressure (122/68 +/- 3/3 vs 122/68 +/- 3/2 mm Hg, p = not significant). The vascular response to norepinephrine and phentolamine was unchanged. Fish oil, however, significantly (p < 0.05) reduced forearm vascular resistance responses to angiotensin II. These changes were associated with a reduction in plasma triglycerides (64 +/- 9 vs 39 +/- 4 mg/dl, p = 0.02) and an increase in plasma eicosapentaenoic acid levels (0.51 +/- 0.25 vs 1.72 +/- 0.35 microM, p < 0.05). Substitution of a moderate dose of fish oil for fat in a "Western diet" selectively attenuates the vascular response to angiotensin independently of changes in alpha-adrenergic vasoconstriction or systemic hemodynamics.

Salt loads raise plasma fatty acids and lower insulin

Some fatty acids are potent inhibitors of angiotensin binding and aldosterone production in adrenal glomerulosa cells and thereby may be involved in regulating salt and water balance. To study the possible regulation of fatty acids by salt, we measured the levels of unesterified fatty acids in plasma from patients subjected to extremes of dietary salt intake and saline infusion. Insulin and catecholamines, two known regulators of plasma fatty acids, also were measured. Infusion of 2 l saline over 4 hours caused the levels of most unesterified fatty acids to rise. Total unesterified fatty acids rose 60-100%. A high salt diet caused a smaller rise in total unesterified fatty acids (approximately 33%). In both instances, oleic and palmitoleic acids showed the greatest proportionate increases, whereas stearic acid was relatively unaffected. When salt loads were administered by either intravenous or dietary routes, plasma insulin levels fell by approximately 50%. Plasma norepinephrine increased after saline infusion but not during a high salt diet. Postsaline levels of fatty acids correlated inversely with postsaline levels of aldosterone, supporting a possible role for fatty acids as physiological regulators of the adrenal glomerulosa. A rise in plasma fatty acids and fall in insulin in response to salt loads could act in concert to increase sodium excretion, constituting a physiological mechanism contributing to salt and water balance.

Fatty acids are potential endogenous regulators of aldosterone secretion

Adrenal glomerulosa cells washed with delipidated albumin produced increased amounts of aldosterone in response to angiotensin-II (AII) or (Bu)2cAMP. Albumin treatment also increased binding of 125I-labeled AII to high affinity binding sites on adrenal cells. Lipid extracts of albumin solutions that were used to wash cells inhibited AII binding and aldosterone responses by washed glomerulosa cells. Chromatographic fractionation and mass spectroscopic analysis indicated that the inhibitors removed from cells by albumin were long chain fatty acids. Exogenous fatty acids not only inhibited AII binding, but they inhibited basal aldosterone production and increments in aldosterone caused by AII or dbcAMP, suggesting an effect on postreceptor steps in aldosteronogenesis. The most potent and most abundant fatty acids removed from adrenal cells were oleic, linoleic, and arachidonic. These fatty acids inhibited at micromolar concentrations in the absence of albumin and at somewhat higher concentrations in its presence. Cells that had been washed, then inhibited by exogenous oleic acid in vitro, were restored to their enhanced responsiveness by a second albumin wash, making it unlikely that cell damage is the mechanism of inhibition by fatty acids. Responses of fasciculata cells were not potentiated by albumin washes, and cortisol production was less sensitive than aldosterone production to exogenous fatty acids. Binding of ANP to glomerulosa cells was not affected by albumin or fatty acids. These results combined with clinical correlations make it plausible that unesterified fatty acids are naturally occurring regulators of the adrenal glomerulosa. Insulin's ability to lower plasma levels of fatty acids may be one way that it causes sodium retention.

Sphingosine inhibits angiotensin-stimulated aldosterone synthesis

Sphingosine and other protein kinase C inhibitors were tested for their ability to inhibit aldosterone synthesis by bovine adrenal glomerulosa cells. Sphingosine inhibited angiotensin (AII)-stimulated aldosterone synthesis (IC50 of 5 microM). At doses that totally blocked steroidogenesis, sphingosine did not affect protein synthesis or [125I]AII binding to cells. Sphingosine also inhibited dibutyryl cyclic AMP (dbcAMP)-stimulated aldosterone synthesis. Sphingosine inhibited pregnenolone synthesis from cholesterol, but not the conversion of progesterone or 20 alpha-hydroxycholesterol to aldosterone. These results suggest that sphingosine inhibits steroidogenesis at a locus close to that where stimulation occurs by AII and dbcAMP. Other protein kinase C inhibitors were tested. Retinal, 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7), and staurosporine inhibited aldosterone synthesis stimulated by AII and dbcAMP. Retinal and H-7 also inhibited progesterone conversion to aldosterone, and retinal blocked [125I]AII binding. Staurosporine was more specific, inhibiting AII-stimulated aldosteronogenesis at concentrations which had little effect on conversion of progesterone to aldosterone. Because they inhibited dbcAMP stimulation, none of the inhibitors was sufficiently specific to use as a probe of the role of protein kinase C. The IC50 of sphingosine suggests that this or related products of lipid hydrolysis could act as endogenous regulators of adrenal cell function.

Cost of switching hypertensive patients from enalapril maleate to lisinopril

The costs and potential savings associated with switching patients in a hypertension clinic from enalapril maleate to lisinopril were analyzed. Patients taking enalapril were randomized to receive lisinopril or to continue taking enalapril. For the 47 patients randomized, data were collected for 25 patients switched to an equal milligram dosage of lisinopril and for 21 patients who continued to receive a constant dosage of enalapril. To maintain blood pressure control, it was necessary to double the dosage of lisinopril in five patients (20%) and have it in one patient (4%), while the enalapril dosage was doubled in two patients (9.5%). The total direct cost of switching patients to lisinopril was $66.33 per patient. The annual drug cost savings per patient for switching to lisinopril would be $52.08, $46.80, and $120.24 for therapy with one 5-, 10-, and 20-mg tablet per day, respectively. A patient would have to receive 15, 17, or 7 months of therapy with 5-, 10-, or 20-mg tablets of lisinopril, respectively, before a net cost savings would be realized. In the evaluation of a less expensive therapeutic alternative, the total cost of switching must be considered.

Hyperinsulinemia and the aldosterone and pressor responses to angiotensin II

To determine whether hyperinsulinemia alters angiotensin II-mediated aldosterone secretion, the increase in plasma aldosterone after intravenous angiotensin II (5, 10, and 20 ng/kg/min for 15 minutes each) was measured before and after euglycemic hyperinsulinemia in seven chronically instrumented dogs. In a random sequence on 4 successive days, dogs received either 0, 2, 4, or 8 milliunits/kg/min insulin. Euglycemic hyperinsulinemia, at all insulin doses, resulted in a significantly greater (p less than 0.01) change in the angiotensin II-stimulated increments of plasma aldosterone than was observed when angiotensin II was administered alone. However, there was no dose-dependence of insulin's effect on angiotensin II-stimulated aldosterone. The effect of weight gain on the angiotensin II response was also evaluated in five dogs. After weight gain, euglycemic hyperinsulinemia augmented angiotensin II-stimulated aldosterone to the same magnitude that was observed before weight gain. Possible mechanisms whereby insulin could increase angiotensin II-stimulated aldosterone production include: increased intracellular potassium, reduced plasma free fatty acids, and a direct action of insulin to induce increased adrenal steroidogenesis. In addition to altering the angiotensin II-aldosterone dose-response curve, hyperinsulinemia also increased the pressor action of angiotensin II. In contrast to the angiotensin II-aldosterone response, progressive hyperinsulinemia resulted in a progressive increase in the pressor response to angiotensin II. The increased pressor response is probably due to an increased activation of the sympathetic nervous system by insulin.

Analysis of angiotensin II binding to human platelets: differences in young and old subjects

We examined the binding of radiolabeled angiotensin II (AII) to human platelets to characterize the apparent increase in AII receptors observed in older subjects. At 22 degrees C, the amount of radioactivity associated with platelets from older subjects increased continuously for more than 2 hours. The same amount of radioactivity was displaced by addition of unlabeled AII at 30 min and 60 min. In the presence of phenylarsine oxide, in the cold, or when labeled antagonist was the ligand, binding came to equilibrium by 30 min. High pressure liquid chromatography demonstrated that 125I-AII was the major radioactive compound in the supernatant and platelets after incubation, but the platelets also contained radiolabeled AII fragments. Thus, some degradation accompanied interaction of AII and platelets. Phenylarsine oxide did not prevent degradation of bound AII, suggesting that degradation precedes internalization. On average, maximum binding was greater in older subjects whether platelets were incubated with 125I-AII alone, with 125I-AII and phenylarsine oxide to prevent internalization, or when the competitive inhibitor 125I-sar1,ile8-AII was the radioligand. Variability of binding among subjects also increased with age. Thus, platelets bind, degrade, and internalize AII, and the three processes occur to a greater extent in platelets from some, but not all older subjects.

Ionophores for monovalent cations inhibit angiotensin-stimulated aldosteronogenesis

We examined the effects of monensin (a sodium ionophore), valinomycin (a potassium ionophore), and nigericin (a nonspecific ionophore) on steroid production and its stimulation in bovine adrenal glomerulosa and fasciculata cells. All three ionophores at nanomolar concentrations inhibited angiotensin (AII)-stimulated aldosterone production; potassium-stimulated aldosteronogenesis was more sensitive, and cortisol synthesis by fasciculata cells was much less sensitive. Ionophores completely inhibited the early pathway of aldosteronogenesis and partially inhibited conversion of progesterone to aldosterone. Ionophores had no effect on pregnenolone production by isolated glomerulosa mitochondria. Monensin had no effect on AII binding, calcium flux, calcium transient, protein phosphorylation, or protein synthesis; valinomycin slightly inhibited these processes. Valinomycin lowered cell potassium and raised cell sodium, but its inhibition of aldosteronogenesis was not overcome by increasing extracellular potassium. Monensin and nigericin had no effect on cell potassium or sodium. Cellular ATP was decreased by valinomycin, but not by monensin or nigericin. Our results show that stimulation of aldosteronogenesis by AII and potassium is highly sensitive to ionophores of monovalent cations. Monensin and nigericin inhibit steroidogenesis at concentrations that have no other observed deleterious effects on glomeulosa cells. These results identify a distinguishing characteristic of adrenal glomerulosa cells and suggest a new pharmacologic approach to inhibition of aldosteronogenesis.

Lack of interaction between sulindac or naproxen and propranolol in hypertensive patients

Seventeen patients with hypertension and osteoarthritis participated in a single-blind crossover study comparing the effects of sulindac 200 mg twice daily, naproxen 500 mg twice daily, and placebo on blood pressure. All patients were treated for hypertension with propranolol monotherapy. Blood pressures were back-titrated to achieve a baseline diastolic blood pressure of 90 to 100 mm Hg while taking naproxen. There were no significant differences in mean sitting or standing blood pressures among the patients receiving naproxen, sulindac, or placebo treatments. There was no change in pulse, weight, or any of the laboratory measurements at the end of each treatment phase. These results suggest that neither sulindac nor naproxen interferes with propranolol therapy for uncomplicated hypertension.

Low oxygen selectively inhibits aldosterone secretion from bovine adrenocortical cells in vitro

Systemic hypoxia has been reported to inhibit selectively aldosterone secretion in vivo. The mechanism of this inhibition has not been elucidated. We hypothesized that decreased tissue PO2 directly inhibited aldosteronogenesis. To test this hypothesis, we exposed dispersed adrenocortical cells (90% glomerulosa/10% fasciculata) to decreased PO2 in vitro while simultaneously stimulating aldosterone secretion with angiotensin II, N6,2'-O-dibutyryladenosine 3',5'-cyclic monophosphate (dibutyryl cAMP) adrenocorticotropic hormone (ACTH)-(1-24), or progesterone. Decreasing buffer PO2 from approximately 150 to approximately 85 Torr significantly inhibited basal and angiotensin II, cAMP, progesterone, and ACTH-stimulated aldosterone secretion at all doses of secretagogue. Inhibition was largest for angiotensin II (55 +/- 9% inhibition at 1 microM) and cAMP (54 +/- 8% at 3 mM) and lowest for ACTH (24% at 100 nM) and basal aldosterone secretion (31 +/- 7%). This inhibition was reversed by returning the buffer PO2 to 150 Torr. Cortisol secretion was not significantly inhibited by decreased buffer PO2. We conclude that decreased buffer PO2 significantly inhibits aldosterone secretion in vitro, and this inhibition is reversible and specific. Hypoxia-induced inhibition of aldosterone secretion in vivo may be caused, at least in part, by a direct effect of low tissue PO2 within the adrenal cortex.

Transdermal clonidine compared with hydrochlorothiazide as monotherapy in elderly hypertensive males

Sixteen of 22 elderly male patients (aged 60-74 years) who had previously taken only hydrochlorothiazide 50 mg completed a study evaluating the safety, efficacy, and tolerability of 12-20 weeks of transdermal clonidine (Catapres TTS) as monotherapy for mild hypertension. Thirteen of the sixteen patients (81%) responded to transdermal clonidine which was begun after 28 days of placebo. Five patients discontinued transdermal clonidine therapy because of intolerable skin irritation, and one because of daytime fatigue. Clonidine caused none of the metabolic effects we observed with hydrochlorothiazide: no change in serum potassium, uric acid, cholesterol, or triglyceride. Eleven of the 22 patients (50%) who began the study experienced a skin reaction under the transdermal clonidine patch. The incidence of dry mouth and fatigue in patients using transdermal clonidine was dose-related and similar to reports of dry mouth and fatigue in patients taking oral clonidine tablets. Rebound hypertension occurred in one patient upon withdrawal of transdermal clonidine. There was no effect of transdermal clonidine or hydrochlorothiazide on cognitive function or emotional state tested with three questionnaires. Overall, transdermal clonidine, in various doses, was as effective as hydrochlorothiazide in elderly male hypertensive patients. The effectiveness of both was inversely proportional to the level of untreated blood pressure. The high incidence of skin reactions limited prolonged use of transdermal clonidine in our patients.

Effects of atrial natriuretic factor on maternal ovine vascular resistance

Atrial natriuretic factor (ANF) is a potent endogenous vaso-dilator and diuretic peptide of uncertain physiologic relevance. In this study, the effects of ANF on normal and angiotensin II constricted placental, uterine and renal vessels were examined in pregnant sheep. Ewes were equipped with catheters to monitor vascular pressures, infuse drugs and measure blood flow by the microsphere technique. An electromagnetic flow sensor was placed around the middle uterine artery and electromyogram electrodes were attached to the uterus. ANF was administered into a branch of the uterine artery to minimize its systemic effects. The experiment included two protocols. First, blood flows and pressures were measured after a 5-min period of saline infusion into the uterine artery. These measurements were repeated at the end of a 5-min infusion of ANF (6.25 micrograms.min-1) into the uterine artery. During the second protocol, angiotensin II (AII) was infused via the jugular vein at 5 micrograms.min-1 for 10 min and ANF (6.25 micrograms.min-1) was infused through the uterine artery during the second half of the AII infusion. In the absence of AII, ANF lowered blood pressure from 97 +/- 6 to 90 +/- 6 mmHg (P less than 0.05); and placental resistance from 67.8 +/- 11.3 to 57.3 +/- 10.4 mmHg.min.ml-1 per g (P less than 0.01). Uterine resistance did not change.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of atrial natriuretic peptide, angiotensin, cyclic AMP, and potassium on protein phosphorylation in adrenal glomerulosa cells

Bovine adrenal glomerulosa cells were incubated with 32PO4 and angiotensin II (AII), atrial natriuretic peptide (ANP) (rat[8-33]), N6,O2'-dibutyryl cyclic AMP, or elevated potassium (7.2 mM). Solubilized cells were analyzed by one-dimensional polyacrylamide gel electrophoresis, autoradiography, and laser densitometry. AII and dibutyryl cyclic AMP increased labeling of a 17.6 kd protein. Elevated potassium did not alter labeling of this protein. ANP inhibited labeling, whether basal or stimulated by AII, and to a lesser extent that stimulated by dibutyryl cyclic AMP. Similar dose-response curves were obtained for the effect of AII on labeling of the 17.6 Kd band and on aldosterone synthesis; ANP had a similar inhibitory effect on AII-stimulated phosphorylation and aldosterone synthesis. Effects of AII and ANP were apparent after 15 minutes of hormone treatment. Fractionation of labeled cells showed that the 17.6 Kd protein was not in cytosol, mitochondria, or endoplasmic reticulum, but was enriched in a crude nuclear fraction. These results suggest that AII and ANP affect aldosterone synthesis at the level of protein phosphorylation.