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The modulation of dopamine DA1 receptors of cultured rat renal arterial smooth muscle cells by glucocorticoid and sodium chloride was studied. At a concentration of 10 nM, the synthetic glucocorticoid dexamethasone increased maximum receptor binding but had no effect on the dissociation constant. However, the maximum binding of [3H]Sch-23390 in cells treated with 100 mM sodium chloride did not change. However, the dissociation constant for DA1 receptor was increased by adding sodium chloride. The glucocorticoid effect on DA1 of arterial smooth muscle cells became apparent after hours of incubation in the presence of the steroid and was significantly inhibited by cycloheximide (10 micrograms/ml) or by the glucocorticoid receptor antagonist RU-38486, indicating that the effect required protein synthesis through glucocorticoid receptors. Treatment of cells with 1 microM dexamethasone for 24 h increased basal and DA1-stimulated adenylate cyclase activity. Basal adenylate cyclase was decreased by sodium chloride in a dose-dependent manner. These results suggest differential control of DA1 receptors on vascular smooth muscle cells by glucocorticoid or sodium chloride.

Endothelin (ET) B-type receptor-mediated signal transduction after stimulation with ET-3 was examined in cultured aortic endothelial cells obtained from spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats. The purpose of this study was to elucidate ETB receptor-mediated response in endothelial cells from hypertensive rat models. Non-isopeptide-selective displacement and affinity in these binding experiments suggest that aortic endothelial cell receptors for ET-3 correspond to ETB receptor subtypes. These receptors for ET-3 were similar in WKY and SHR endothelial cells. ETB receptor mRNA expression in cultured endothelial cells was also similar in WKY and SHR. However, the cytosolic free Ca2+ level in the absence of extracellular Ca2+ as well as the inositol 1,4,5-trisphosphate level in response to ET-3 were greater in endothelial cells from SHR than in those from WKY. Phospholipase C and protein kinase C activities after stimulation with ET-3 were also greater in SHR than in WKY. The 6-ketoprostaglandin F1 alpha production was also augmented in SHR, although nitric oxide formation and guanosine 3',5'-cyclic monophosphate production after stimulation with ET-3 were similar in WKY and SHR. We conclude that the phosphoinositide turnover signaling stimulated by ET-3 is augmented in cultured aortic endothelial cells from SHR compared with those from WKY.

The blood pressure was decreased after chronic treatment with enalapril, MK-954, and hydralazine in deoxycorticosterone acetate (DOCA)-salt-induced malignant hypertension of spontaneously hypertensive rats (SHR); however, ventricular weight and plasma brain natriuretic peptide (BNP) concentration were decreased after enalapril and MK-954 but not after hydralazine. The BNP secretory rates from the ventricle in enalapril- and MK-954-treated DOCA-salt SHR were decreased to approximately 50% of those in untreated DOCA-salt SHR. The BNP secretory rate from the ventricle was positively correlated with ventricular weight in untreated and treated DOCA-salt SHR. In contrast, acute administration of captopril or MK-954 did not decrease the BNP secretory rate from the heart. Results suggest that the decrease in plasma BNP after enalapril and MK-954 is attributed to a decline in the secretion from the ventricle but not from the atrium. The reduction in ventricular mass appeared to be related to this decline.

The present study examined the possible interaction of platelet-derived growth factor (PDGF) and atrial or brain natriuretic peptides (ANP and BNP, respectively) on cellular proliferation and secretion of endothelin-1 in cultured rat mesangial cells. PDGF increased cellular proliferation and endothelin-1 secretion. The protein kinase C (PKC) inhibitors, 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine, staurosporine, and PKC inhibitor peptide, inhibited such stimulation. Rat ANP-(1-28) and rat BNP-45 exhibited clearly dose-related inhibition of PDGF-stimulated cellular proliferation and endothelin-1 secretion. This inhibition by ANP and BNP was paralleled by an increase in the cellular level of guanosine 3',5'-cyclic monophosphate (cGMP). Results indicate that PDGF stimulates cellular proliferation and endothelin-1 secretion in cultured rat mesangial cells by a mechanism probably involving activation of PKC and that ANP and BNP inhibit such stimulation through a cGMP-dependent process.

The interaction between dopamine DA1 receptors and a phorbol ester was studied to elucidate the role of protein kinase C in the response of this receptor. The in vitro binding of [3H]Sch 23390 to DA1 receptor sites on vascular smooth muscle cells was saturable. The extent of [3H]Sch 23390 binding to phorbol ester-treated cells was increased without any change in the dissociation constant. The production of adenosine 3',5'-cyclic monophosphate (cAMP) in response to DA1 receptor stimulation was enhanced by preincubation of vascular smooth muscle cells with the phorbol ester for 4 h. However, no enhancement was observed when the medium used for preincubation was supplemented with a protein kinase C inhibitor. Direct stimulation of stimulatory guanine nucleotide-binding regulatory protein with 5-guanylylimidodiphosphate and direct stimulation of adenylate cyclase with forskolin produced no significant differences in cyclase levels between phorbol ester-treated and untreated cells. These results suggest that activation of protein kinase C triggers an increase in the membrane expression of DA1 receptors, thereby enhancing receptor-coupled cAMP generation.

Previous studies have shown that chronic subcutaneous administration of heparin significantly reduces blood pressure in hypertensive rats. The intracellular mechanisms of how heparin prevents smooth muscle cell proliferation remain unclear. This study was designed to examine whether heparin affects endothelin-1 action and production, to further elucidate the mechanism of the antihypertensive effect of heparin. Four-week treatment with heparin (300 U/day sc) significantly decreased blood pressure in spontaneously hypertensive rats (SHR; 199 +/- 8 vs. 164 +/- 9 mmHg; P < 0.001) and completely blunted pressor response to endothelin-1 in SHR. Heparin treatment did not decrease blood pressure response nor did it attenuate blood pressure responses to endothelin-1 in Wistar-Kyoto rats (WKY). Heparin significantly suppressed endothelin-1-induced increase in intracellular calcium concentration and inositol 1,4,5-trisphosphate level in cultured vascular smooth muscle cells in a dose-dependent manner and endothelin-1 release from cultured endothelial cells. These inhibitions were significantly more pronounced in SHR than in WKY. In conclusion, our findings indicate that the antihypertensive effect of heparin is mediated, at least in part, by the inhibition of endothelin-1 action on vascular smooth muscle cells and endothelin-1 production from endothelial cells.