Low dihydrotestosterone and weight loss in the AIDS wasting syndrome.

24 consecutive AIDS patients with wasting, and who had never received anabolic therapies, were evaluated to determine their profile of sex hormones and whether transformation of testosterone (T) to the nuclear androgen, dihydrotestosterone (DHT), was impaired. Eleven (46%) patients had normal testosterone and DHT (group I), 10 (42%) had normal testosterone but low DHT (group II), and 3 (12%) had low testosterone and low DHT (group III). Age, prior opportunistic complications, symptoms, serum albumin, hemoglobin levels, and CD4 lymphocyte counts were similar in the groups. DHT was significantly lower (22.2 +/- 6.8 microg/dl) in group II compared with group I (50.8 +/- 15.3 microg/dl). The ratio of T/DHT, a measure of the conversion of testosterone to DHT, in group I was 15.1 +/- 3.5, which was within the range for eugonadal young men. In group II, the ratio was 22.3 +/- 1.5, indicating a defect in generation of DHT. Patients in group II had lost 9.2 +/- 3.5 kg compared with 5.6 +/- 2.6 kg in group I (p = .015). Thus, a syndrome of low DHT with normal testosterone was associated with significantly greater weight loss than in patients with normal testosterone and DHT. Further studies are needed to clarify whether low DHT is a result of AIDS wasting or is causally related to weight loss and whether androgen therapy in the form of DHT could reverse some of the metabolic changes associated with AIDS wasting.

Magnesium modulates ouabain action on angiotensin II-induced aldosterone synthesis in vitro.

Ouabain can block the action of angiotensin II (AII on aldosterone secretion in both rat and human adrenal tissue although its action is much more potent on human zona glomerulosa cells (ZG). Since magnesium can antagonize digitalis action in vivo, we have examined the interaction of both agents on aldosterone secretion in both rat and human adrenal cells. Ouabain itself at high concentration (10(-5) M) in Mg++ buffer blocks AII action on aldosterone secretion on rat ZG cells and at 1000-fold lower concentrations inhibits AII-action in human cells as previously reported by us. When buffer Mg++ is higher (4mM) than normal (0.7 mM) in cultured human adrenal cells it decreases both basal aldosterone secretion (8.6 +/- 0.4 vs. 6.8 +/- 0.2, p < 0.001) and AII action on aldosterone (13.9 +/- 0.6 vs. 9.7 +/- 0.7 ng/10(6) cells/h, p < 0.01). High Mg++ buffer had this effect at both 10(-8) and 10(-7) M concentrations of ouabain (control 8.6 +/- 0.4, AII [10(-9) M] 13.9 +/- 0.7, AII + Ouabain [5 x 10(-8) M] 10.9 +/- 0.6, AII + ouabain [10(-7) M] 7.8 +/- 0.3 ng/10(6) cells/h, both p < 0.01 vs. AII). In contrast, a low Mg++ buffer stimulated both basal (6.9 +/- 0.2 vs. 8.3 +/- 0.4 ng/10(6) cells/h, p < 0.01) and AII stimulation of aldosterone secretion (8.4 +/- 0.2 vs. 9.8 +/- 0.4 ng/10(6) cells/h, p < 0.01). When ouabain was added to low Mg++ buffer there was further inhibition of AII induced aldosterone secretion than with normal Mg++ buffer. However, the effect of ACTH on aldosterone was not altered by changes in Mg++. We conclude that ouabain actions and the effect of angiotensin II on aldosterone is inhibited by an increased level of Mg++ while low levels of Mg++ are stimulatory to both basal and AII action on aldosterone.

Ouabain is a potent inhibitor of aldosterone secretion and angiotensin action in the human adrenal.

Digitalis glycosides and a putative ouabain-like substance act by inhibiting Na,K-adenosine triphosphatases and could regulate aldosterone secretion. We studied the effects of ouabain on basal and angiotensin II (AII)-induced aldosterone in rat and human adrenal glomerulosa cells. In the rat, ouabain at doses as high as 10(-4) mol/L had no effect on basal aldosterone secretion, but caused a dose-related inhibition of AII and ACTH secretion. In human glomerulosa cells, ouabain was 1000 times more potent on both basal and AII stimulation, with action at 10(-8) mol/L. The effect of ACTH was also blunted by 10(-8)-10(-7) mol/L ouabain. However, the effect of potassium (8.7 mmol/L) on aldosterone was not altered by these doses of ouabain. These results suggest that nanomolar levels of ouabain can reduce aldosterone secretion from human zona glomerulosa cells.

A 12-lipoxygenase product, 12-hydroxyeicosatetraenoic acid, is increased in diabetics with incipient and early renal disease.

Earlier studies in diabetic animal models or ex vivo from diabetics suggest a deficiency in prostacyclin (PGI2) production and an increase in an alternate arachidonic acid metabolite, 12-hydroxyeicosatetraenoic acid (12-HETE), which stimulates angiogenesis, mitogenesis, and inhibits renin secretion. We studied the urinary excretion rate of 6-keto-PGF1 alpha (a stable metabolite of PGI2) and 12-HETE in controls and 42 noninsulin-dependent diabetes mellitus (NIDDM) patients with normal renal function and those with micro- or macroalbuminuria/hyporeninemic hypoaldosteronism (HH). The 2 eicosanoids were measured in urine using previously described high pressure liquid chromatography and RIA methods. Normal subjects and patients with NIDDM and microalbuminuria were infused with low dose calcium infusions that stimulate prostacyclin production in normal subjects. The PGI2 excretion rate of NIDDM patients with normal renal function was not different from that of controls (143 +/- 17 vs. 118 +/- 34 ng/g creatinine), but was reduced in those with microalbuminuria (75 +/- 10) and in macroalbuminuria patients (48 +/- 7; P < 0.01). In contrast, 12-HETE was increased in diabetics with normal renal function as well as in those with micro- or macroalbuminuria patients (69 +/- 18 vs. 250 +/- 62 vs. 226 +/- 60 and 404 +/- 131 ng/g creatinine; P < 0.01). Calcium did not stimulate PGI2, but increased 12-HETE in diabetics with microalbuminuria in contrast to levels in normal subjects. HH patients excreted less PGI2 (as previously reported), but had increased 12-HETE. HETE/PGI2 ratios further demonstrated these changes in the various groups. In a nondiabetic hypertensive microalbuminuria group, 12-HETE excretion was normal (73 +/- 28 ng/g creatinine). We conclude that the lipoxygenase product 12-HETE is increased early in the diabetic process, whereas PGI2 production is progressively impaired in NIDDM. These changes may play a role in the vascular disease of diabetes and partially explain the HH syndrome.

Renin response to 12-hydroxyeicosatetraenoic acid is increased in diabetic rats.

Eicosanoids (prostaglandins) can alter renin secretion and angiotensin (ANG) II action. We have studied the effects of both prostacyclin and a lipoxygenase (LO) product, 12-hydroxyeicosatetraenoic acid (12-HETE), on renin in normal and streptozotocin-induced diabetic rats. 12-HETE is not only a potent inhibitor of basal renin secretion but also a key mediator of ANG II-induced renin inhibition. We have also examined the effects of ANG II on 12-HETE formation in normal and diabetic animals. Both plasma (3.9 +/- 0.9 vs. 0.8 +/- 0.1 ng ANG I.ml-1.h-1, P < 0.01) and tissue (38 +/- 6 vs. 21 +/- 2 ng ANG I.mg tissue-1.h-1, P < 0.05) renin activity levels were markedly reduced in diabetic animals. Iloprost (10(-6) mol/l), a stable analog of prostacyclin, had similar stimulatory effects on renin secretion in both normal and diabetic tissues, but the response was enhanced by LO inhibition in diabetic tissue. 12-HETE (10(-7) mol/l) had an exaggerated effect on renin inhibition in diabetic tissue (78 +/- 2% normal vs. 65 +/- 4% diabetic, P < 0.05). Similarly, ANG II (10(-8) mol/l) inhibition of renin was significantly enhanced in diabetic rats (P < 0.001). However, ANG II did not produce an exaggerated increase in 12-HETE in diabetic renal tissue. Insulin reversed the inhibitory effects of ANG II on renin in normal rats, but it blunted the effect of ANG II in diabetic rats. These studies suggest that, while the capacity of renal cortical tissue to synthesize 12-HETE in response to ANG II is not altered, 12-HETE and ANG II actions are exaggerated in diabetes, and this may contribute to reduced renin production.

Activin and inhibin have opposite effects on steroid 5 alpha-reductase activity in genital skin fibroblasts.

The transforming growth factor beta (TGF-beta) superfamily includes several closely related peptides including the activins and inhibins. Since we recently reported that TGF-beta 1 and beta 2 are potent inducers of steroid 5 alpha-reductase (5 alpha R), we have now studied the effects of these other peptides using primary cultures of human scrotal skin fibroblasts. Recombinant human activin A or inhibin A were added to cultured cells (2 x 10(5) cells) for 2 days in a serum free media and 5 alpha R activity was measured by the %-conversion of tracer [3H]-testosterone to dihydrotestosterone (DHT) over a 4-h period. Activin significantly stimulated 5 alpha R activity in a dose related manner (control 3.0 +/- 0.4%, activin (1.2 x 10(-9) M) 6 +/- 0.7%, P < 0.01, (2.4 x 10(-9) M) 8.5 +/- 0.6%, P < 0.001). In comparison, androgen (DHT 10(-7) M) induction of 5 alpha R was 4.7 +/- 0.2%, P < 0.05. Combined exposure of fibroblasts to activin (1.2 x 10(-9) M) and androgen (10(-7) M) did not result in additive or synergistic effect on 5 alpha R activity. In contrast, exposure of cells to an androgen (10(-7) M) and TGF-beta (2 x 10(-10) M) led to synergistic effects on 5 alpha R activity (control 1.5 +/- 0.1%, DHT 2.6 +/- 0.2% TGF-beta 1 4.8 +/- 0.5, TGF-beta 1 + DHT 9.2 +/- 1.2%).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of dopamine2 blockade on renal function under varied sodium intake.

This study explored the role of the dopamine-2 receptor (DA2) in the control of renal blood flow (RBF) and the influence of variations in sodium intake. These relationships have not been previously defined in man. Seven normotensive male subjects underwent a low dose dopamine (DA) infusion (1 microgram/kg.min) for 3 h, known to activate both DA1 and DA2 receptors. The effect of DA2 receptor on renal hemodynamics was studied using a relatively specific DA2 blocker [domperidone (DOM); 60 mg, orally] alone and with a DA infusion. Systemic and renal hemodynamics parameters were measured noninvasively. Urinary prostacyclin was measured in 3-h urine specimens, obtained during the DA infusion. The DA infusion increased RBF and prostacyclin during both normal and high salt diets, but this effect was attenuated on a low salt diet. DOM alone significantly reduced basal RBF during normal (1304 +/- 48 vs. 1175 +/- 45 mL/min.1.73 m2; P < 0.01) and low salt diets (1402 +/- 80 vs. 1220 +/- 101 mL/min.1.73 m2; P < 0.02), but was without effect during high sodium intake. DOM had no effect on prostacyclin excretion at any level of salt intake. These results suggest that both DA1 and DA2 are activated in renal vessels by DA, and that DA2 receptors play a role in the renal vasodilating action of DA. Changes in sodium balance alter the actions of the two receptors (DA1 and DA2) in a coordinated fashion in the regulation of RBF.

Effects of transforming growth factor beta and epidermal growth factor on steroid 5 alpha-reductase activity in genital skin fibroblasts.

Regulation of steroid 5 alpha-reductase (5 alpha R) activity and dihydrotestosterone (DHT) formation is central to prostate and sexual skin (hair) growth and cell function. Transforming growth factor-beta 1 (TGF-beta 1) is a ubiquitous peptide present in skin and scrotal tissue and its receptor is universally expressed. We have explored the role of TGF-beta 1 and -beta 2 on androgen formation in skin. Rat or human sexual skin fibroblasts were grown in primary cultures (passage 3-7). 5 alpha-Reductase activity was measured by the %-conversion of tracer 3H-testosterone to dihydrotestosterone over a 4 h period. Incubation of scrotal fibroblasts (2 x 10(5) cells) in serum and growth factor free media with androgen, such as DHT for two days significantly stimulates 5 alpha R in these cells (1.6-fold, p < 0.05 vs control). TGF-beta 1 alone at picomolar concentrations (2 x 10(-11) M to 2 x 10(-10) M) was a potent inducer of 5 alpha R activity in both rat (1.8-fold and 2.8-fold, respectively, p < 0.001 vs control at both doses) and human cells (TGF-beta 1 2 x 10(-10) M 3.3-fold, p < 0.001 vs control). Combined exposure of these fibroblasts to TGF-beta 1 (2 x 10(-10) M) and androgen (10(-7) M) further potentiated 5 alpha R activity (rat cells 6.5-fold, human cells 6.4-fold, p < 0.001 vs DHT or TGF-beta 1 alone).(ABSTRACT TRUNCATED AT 250 WORDS)

Transforming growth factor-beta is a renin secretagogue at picomolar concentrations.

Transforming growth factor-beta s (TGF-beta s), a family of peptides, have many actions including modulating cellular growth, differentiation, and influencing steroidogenesis. Because both TGF-beta and renin are present in renal juxtaglomerular cells, we have examined the effects of these peptides on renin secretion using static incubations of rat renal cortical slices. We report here an effect of both TGF-beta 1 and -beta 2 on renin secretion. At low concentrations, both TGF-beta 1 (4 x 10(-12) M) and -beta 2 (8 x 10(-12) M) stimulate basal renin secretion (control, 100 +/- 4%; TGF-beta 1, 123 +/- 4%; TGF-beta 2, 124 +/- 5%; both P < 0.02 compared with control). However, at higher concentrations (2 x 10(-10) M), both peptides do not alter basal renin release. Our previous studies show that both prostaglandins and lipoxygenase (LO) products of arachidonic acid play an important dual regulatory role in renin secretion; therefore, we have examined the effects of both cyclooxygenase (CO) and LO inhibition in TGF-beta action.(ABSTRACT TRUNCATED AT 250 WORDS)

Androgen induction of steroid 5 alpha-reductase may be mediated via insulin-like growth factor-I.

The action of added insulin-like growth factor-I (IGF-I) and dihydrotestosterone (DHT) on steroid 5 alpha-reductase (5 alpha R) activity was studied using primary cultures of rat or human scrotal skin fibroblasts. Agents were added to cultured cells (2 x 10(5) cells) for 2 days, and enzyme activity was measured by the percent conversion of [3H] testosterone to DHT over a 4-h period in the absence of fetal calf serum or other growth factors. DHT, but not testosterone, at 10(-7) M significantly increased 5 alpha R activity (rat, 1.5 +/- 0.3% to 3.0 +/- 0.4%; human, 7.6 +/- 1.7% to 11.4 +/- 2.9%; P < 0.01). IGF-I (10(-9)-6.4 x 10(-9) M), but not IGF-II (10(-9)-10(-8) M) or insulin (10(-9)-10(-7) M), increased enzyme activity in a dose-related fashion [i.e. 1.5 +/- 0.5 to 10 +/- 2 in rat and 6.0 +/- 1.1 to 9.8 +/- 1.6% (P < 0.01) in human cells]. No change in cell numbers was observed in any experiment. Since the effect of IGF-I was about 100 times that of androgen, we studied the possibility that androgen induction of the enzyme activity could be via IGF-I production. Addition of a monoclonal antibody against IGF-I significantly reduced the effect of DHT, and simultaneous addition of a specific IGF-I receptor antibody blocked the expected induction of 5 alpha R activity (control, 4.9 +/- 0.5; DHT, 8.0 +/- 1.9; DHT plus IGF-I receptor antibody, 3.7 +/- 0.4%). No effect on 3 alpha-reduction of [3H]DHT to 3 alpha-androstanediol was detected in separate experiments. These studies indicate that IGF-I may be an important regulator of skin 5 alpha R activity and, thus, may influence DHT formation. The previously known androgen induction of this peripheral steroidogenic enzyme may be via paracrine/autocrine production of an IGF-I-type growth factor.

Magnesium deficiency produces insulin resistance and increased thromboxane synthesis.

Evidence suggests that magnesium deficiency may play an important role in cardiovascular disease. In this study, we evaluated the effects of a magnesium infusion and dietary-induced isolated magnesium deficiency on the production of thromboxane and on angiotensin II-mediated aldosterone synthesis in normal human subjects. Because insulin resistance may be associated with altered blood pressure, we also measured insulin sensitivity using an intravenous glucose tolerance test with minimal model analysis in six subjects. The magnesium infusion reduced urinary thromboxane concentration and angiotensin II-induced plasma aldosterone levels. The low magnesium diet reduced both serum magnesium and intracellular free magnesium in red blood cells as determined by nuclear magnetic resonance (186 +/- 10 [SEM] to 127 +/- 9 mM, p < 0.01). Urinary thromboxane concentration measured by radioimmunoassay increased after magnesium deficiency. Similarly, angiotensin II-induced plasma aldosterone concentration increased after magnesium deficiency. Analysis showed that all subjects studied had a decrease in insulin sensitivity after magnesium deficiency (3.69 +/- 0.6 to 2.75 +/- 0.5 min-1 per microunit per milliliter x 10(-4), p < 0.03). We conclude that dietary-induced magnesium deficiency 1) increases thromboxane urinary concentration and 2) enhances angiotensin-induced aldosterone synthesis. These effects are associated with a decrease in insulin action, suggesting that magnesium deficiency may be a common factor associated with insulin resistance and vascular disease.

Epidermal growth factor is a potent inhibitor of renin secretion.

Epidermal growth factor (EGF) is not only a cell mitogen but a potent vasoconstrictor that shares many properties with angiotensin II. Because EGF is localized in the kidney, we have studied the direct effects of EGF on renin secretion using both static incubations and perifusions of rat renal cortical slices. EGF at 5 x 10(-9) M significantly inhibited renin secretion in static incubations (control, 100 +/- 3%; EGF, 72 +/- 3%; p < 0.001). When added to perifusions, EGF acted rapidly, reducing renin secretion at the earliest time period (10 minutes). Similarly, transforming growth factor-alpha, which can bind to the EGF receptor, also inhibited renin secretion (control, 92 +/- 8%; transforming growth factor-alpha [2 x 10(-9) M], 63 +/- 4%; p < 0.02). Because both prostaglandins and lipoxygenase products of arachidonic acid have been shown to play a role in some EGF-mediated actions, we examined these possible mechanisms of EGF action. Meclofenamate, a cyclooxygenase blocker, and BW755c and baicalein, both lipoxygenase blockers, were studied. None of these agents altered EGF-mediated renin inhibition. EGF action has also been coupled to the stimulation of tyrosine kinase activity; therefore, we examined the effects of the tyrosine kinase inhibitors genistein and quercetin. Both genistein (10(-5) M) and quercetin (10(-5) M) abolished the inhibition of renin by EGF (control, 100 +/- 3%; EGF, 82 +/- 4%; EGF plus genistein, 110 +/- 7%; p < 0.01; EGF, 75 +/- 4%; EGF plus quercetin, 92 +/- 4%; p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Paracrine regulation of the renin-aldosterone system.

A number of clinical states have been described where there are derangements or discrepancies between renin-angiotensin and aldosterone secretion. We have studied the potential effect of some cytokines or growth factors (peptide regulatory factors) on this system in vitro. Both tumor necrosis factor/cachectin and interleukin I are potent regulators acting as renin secretagogues and inhibitors of aldosterone synthesis. These actions are mediated by prostaglandin cyclooxygenase products and their actions mimic the syndrome of hyperreninemic hypoaldosteronism in critical illness. Insulin and insulin-like growth factor I are also renin secretagogues in vitro However in a diabetic model (streptozotocin rat), there is resistance to both agonists as well as enhanced feedback suppression to angiotensin. A third peptide, transforming growth factor (TGF beta) has even more complex actions, acting as a secretagogue at low doses (10(-12) M) but inhibiting renin at higher doses. TGF beta production is increased in the diabetic state so that this peptide as well as the insulin family may be involved in hyporeninemic hypoaldosteronism.

Altered regulation of renin secretion by insulinlike growth factors and angiotensin II in diabetic rats.

The etiology of the low renin state in DM is not clear. To assess the role of certain growth and regulatory factors in this process, we studied the effects of insulin, IGF-I, and IGF-II on the renin-angiotensin system in normal and 8-wk STZ-induced diabetic rats. Renin secretion was studied both in static incubations and by perifusion of rat renal cortical slices. In diabetic rats, both plasma renin activity (0.65 +/- 1.6 vs. 4.0 +/- 1.2 ng ANG I.ml-1.h-1) and tissue renin concentrations (27 +/- 5 vs. 51 +/- 8 ng ANG I.mg tissue-1.h-1) were reduced. Insulin (0.1-1.0 mu/ml) and IGF-I (10(-9) to 4 x 10(-9) M) stimulated renin secretion in normal tissue (control, 95 +/- 3%; insulin [0.5 mu/ml], 134 +/- 7%; IGF-I [4 x 10(-9) M], 149 +/- 7%). IGF-I stimulated renin secretion in perifusions as early as 30 min, whereas IGF-II had no effect. However, in diabetic renal tissue, neither insulin (0.1-1.0 mu/ml) nor IGF-I (10(-9) to 4 x 10(-9) M) had an effect on renin. This lack of effect was overcome by adding up to 100-fold higher concentrations of these growth factors. ANG II (10(-10) M-10(-8) M) had an exaggerated inhibitory effect on renin secretion in diabetic tissue. This study suggests that the low renin state in DM may be explained by the enhanced inhibitory effect of ANG II and the resistance to the secretogogue actions of insulin and IGF-I.

12-lipoxygenase products are potent inhibitors of prostacyclin-induced renin release.

In isolated human or rat glomeruli, arachidonic acid can be metabolized by the cyclooxygenase pathway to prostaglandins or by the lipoxygenase pathway to hydroxyeicosatetraenoic acids (HETES). We have recently shown that 12-lipoxygenase products are potent inhibitors of renin release. Since prostacyclin (PGI2) is a potential renin secretagogue, we studied the direct effects of 12-lipoxygenase products on prostacyclin-induced renin secretion. Treatment of rat renal cortical slices with picomolar concentrations of 12-hydroperoxyeicosatetraenoic acid (12-HPETE) and 12-HETE blocked the prostacyclin- or iloprost (an analog of PGI2)-induced renin secretion. The inhibitory effects of 12-lipoxygenase products were not exhibited by the 5-lipoxygenase-derived products, leukotriene B4 and 5-HPETE. These results suggest that HETES are not only potent modulators of prostacyclin actions on renin, but that the concerted actions of these compounds in cells may be critical determinants of the juxtaglomerular cell secretion of renin.

Effect of dopamine on renal blood flow, prostaglandins, renin and electrolyte excretion in normal and hypertensive humans.

A low dose of dopamine (1 microgram/min/kg) infused for 3 h, which is without systemic hemodynamic effects in normal subjects, increased the renal blood flow and renal production of prostacyclin (PGI2). This action was blocked by metoclopramide as well as by either of two cyclooxygenase (CO) blockers, but effects were not altered by administration of the alpha 1 blocker prazosin. Much of the effect of dopamine (DA) is apparently via the DA1 receptor, since fenoldopam (0.1 microgram/min/kg) reproduced these actions. However, although fenoldopam increased glomerular filtration rate and urinary Na+, CO blockers were without effect. In contrast neither DA or fenoldopam infusions changed either renal blood flow or PGI2 in a group of patients with essential hypertension. Renin secretion was shown to be increased via DA1 receptor activation both in humans and rat renal tissue. The DA2 receptor may also play a role since domperidone can reduce renal blood flow.

Tumor necrosis factor and interleukin-1 may regulate renin secretion.

Cytokines such as tumor necrosis factor (TNF) and interleukin-1 (IL-1) are not only immunoregulatory polypeptides, but may have endocrine functions. We have studied the direct effects of recombinant and purified TNF and IL-1 on renin secretion using both static incubations and perifusions of rat renal cortical slices. Ultrapure human IL-1 (hIL-1) at concentrations as low as 5 U/ml (3 X 10(-12) M) significantly stimulated renin secretion (control, 98 +/- 4%; hIL-1, 153 +/- 13%; P less than 0.01). TNF similarly induced renin release [control, 97 +/- 6%; TNF (10 U/ml), 151 +/- 13%; P less than 0.005]. TNF and recombinant human IL-1 beta (rhIL-i beta) also blocked the inhibitory actions of angiotensin-II (AII) on renin release [control, 100 +/- 3%; AII (2 X 10(-7) M), 80 +/- 5%; AII plus TNF (20 U/ml), 102 +/- 7%; AII plus rhIL beta (10 U/ml), 106 +/- 6%; both P less than 0.02 vs. AII]. A cyclooxygenase (CO) blocker, meclofenamate (M), which does not significantly alter basal renin release, attenuated the TNF- and rhIL-1 beta-induced renin secretion [TNF (20 U/ml), 132 +/- 11%; TNF plus M (5 X 10(-5) M), 100 +/- 3% (P less than 0.01); rhIL-1 beta (10 U/ml), 135 +/- 9%; rhIL-1 beta plus M, 105 +/- 10% (P less than 0.05)]. The stimulatory effects of TNF and IL-1 on renin were reversible. These results suggest that IL-1 and TNF are renin secretagogues and can also block the inhibitory actions of AII on renin. Since the effect of TNF and IL-1 on renin can be blocked by a (CO) inhibitor, the studies indicate a role of prostaglandins in their action. Therefore, locally produced TNF and IL-1 may play an important paracrine role in regulation of the renin-angiotensin system.

Comparison of dopamine and fenoldopam effects on renal blood flow and prostacyclin excretion in normal and essential hypertensive subjects.

We recently reported that a low dose dopamine (DA) infusion in normal subjects increased renal blood flow (RBF) via prostacyclin (PGI2) formation without changes in PGE2 levels. The present study explores whether this mechanism is mediated by the DA1 receptor and evaluates the effect of DA on RBF and PGs in subjects with essential hypertension (EH). A low dose of DA (1 microgram/kg.min), which previously did not alter hemodynamics in normal subjects was infused into eight patient with EH to determine the role of DA stimulation in hypertensives. To assess the effect of DA1 stimulation, fenoldopam, a selective DA1 agonist, was infused (0.1 microgram/kg.min) into 10 normal and 10 hypertensive patients. Fenoldopam, unlike DA, significantly decreased diastolic blood pressure in hypertensives (96 +/- 3 to 85 +/- 2 mm Hg; P less than 0.01) along with a significant increase in pulse rate (68 +/- 2 vs. 73 +/- 2 beats/min; P less than 0.01). RBF measured by para-aminohippurate clearance increased only in normals during fenoldopam infusion from 1185 +/- 71 to 1533 +/- 84 L/min.m2 (PGI(2)01), and this was associated with an increase in PGI2 (6-keto-PGF1) excretion (149 +/- 19 vs. 214 +/- 32 ng/g creatinine; P less than 0.02). These effects of fenoldopam were similar to DA effects on RBF and PGI2 excretion in normals. In contrast, in hypertensive subjects, neither fenoldopam (867 +/- 113 vs. 1054 +/- 177 L/min.m2; P greater than 0.1) nor DA (1098 +/- 85 vs. 1061 +/- 101 L/min.m2; P greater than 0.1) increased RBF. Similarly, neither the DA nor the fenoldopam infusion stimulated PGI2 excretion in the hypertensives. The fenoldopam infusion in the hypertensives produced a significant natriuresis (22 +/- 3 to 49 +/- 9 mmol/3 h; P less than 0.05). Similar effects on Na+ excretion in this group were noted during DA infusion (17 +/- 3 to 36 +/- 3 mmol/3 h; P less than 0.05), suggesting that DA-induced natriuresis is not directly linked to DA-induced changes in RBF or PG excretion. The present study shows that in normal subjects, fenoldopam, a specific DA1 agonist, like DA, stimulates renal PGI2 release and RBF. In contrast, neither DA nor fenoldopam alters PGI2 or RBF in patients with EH, suggesting an alteration of dopaminergic tone in some hypertensives that is characterized by a defect in DA1 receptor sensitivity.

A 12-lipoxygenase product of arachidonate metabolism is involved in angiotensin action on renin release.

Angiotensin II (AII) action is coupled to the hydrolysis of phospholipids resulting in the formation of arachidonic acid, the precursor of both prostaglandins, and hydroxyeicosatetraenoic acids (HETEs). Since 12-HETE is not only a major arachidonate lipoxygenase (LO) product in the kidney, but is also a potent inhibitor of renin release, we studied the role of AII on renin inhibition and 12-HETE formation using rat renal cortical slices and isolated juxtaglomerular-like cells. In both preparations, 12-HETE was produced in a basal state. AII significantly inhibited renin release (control 100 +/- 3%, AII (10(8) M) 79 + 4%, P less than 0.01) and stimulated 12-HETE formation in slices (control 106 +/- 6%, AII 10(-8) M 177 +/- 18%, P less than 0.01) and in an enriched juxtaglomular cell preparation (control 96 +/- 3%, AII 10(-8) M 130 +/- 6%, P less than 0.001). A specific cyclooxygenase blocker, meclofenomate, or 5-LO blocker, U60,257, did not alter basal or AII-induced renin inhibition or 12-HETE formation by slices. The LO blockers BW755c, at 10(-5) M, or baicalein, 10(-6) M, did not significantly alter basal renin or 12-HETE levels, but BW755c at 10(-4) M, significantly stimulated basal renin (131 +/- 4%) and decreased basal 12-HETE levels (72 +/- 5%). However, both BW755c and baicalein blunted AII-induced renin inhibition (AII, 10(-8) M 70 +/- 3%, AII + BW755c, 10(-5) M 85 +/- 4%, P less than 0.02, AII + baicalein, 10(-6) M, 90 +/- 4%, P less than 0.005) and AII mediated 12-HETE formation (AII, 10(-8) M 150 +/- 5%, AII + BW755c, 10(-5) M 117 +/- 8%, P less than 0.02, AII + baicalein, 10(-6) M 110 +/- 3%, P less than 0.005). These results suggest that AII inhibition of renin is not mediated by the cyclooxygenase or 5-LO pathway, but rather by the 12-LO pathway. These findings reveal a new action for 12-LO products which may play a pivotal role in stimulus secretion coupling of renin secretion.

Evidence that specific dopamine-1 receptor activation is involved in dopamine-induced renin release.

Direct effects of dopamine on renin release were examined using static incubations and perifusions of rat renal cortical slices. Dopamine (10(-5)M) significantly stimulated renin release compared with control. To determine which receptors are involved in dopamine-elicited renin release, studies were performed with specific dopamine-1 and dopamine-2 receptor agonists and antagonists, as well as with alpha- and beta-adrenergic antagonists. Fenoldopam, a dopamine-1 receptor agonist, dose dependently stimulated renin secretion both in static incubations and perifusions; whereas quinpirole (10(-7)-10(-5)M), a dopamine-2 receptor agonist, was ineffective. Phentolamine (10(-4)M), an alpha-adrenergic antagonist, did not alter dopamine- or fenoldopam-induced renin release. Similarly, propranolol, a beta-blocker, did not interfere with the renin stimulation of dopamine (10(-5)M) or fenoldopam (10(-6)M) incubations or perifusion experiments; whereas propranolol significantly blocked isoproterenol action. SCH 23390 (10(-5)M), a specific dopamine-1 antagonist, blocked dopamine- and fenoldopam-induced renin. In contrast, pimozide, a dopamine-2 receptor antagonist, was ineffective. These studies indicate that dopamine is a direct renin secretogogue, and its effects seem to be mediated by specific dopamine-1 receptor activation, as neither alpha- nor beta-adrenergic blockers nor dopamine-2 receptor antagonists altered dopamine actions. The results suggest that dopamine produced locally in the kidney may stimulate renin secretion directly by dopamine-1 receptor activation.