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The effects of V1- and V2-AVP antagonists on pressor and ANP responses to hypertonic saline infusion in conscious anephric rats
P3-18 THE EFFECTS OF V l - AND V2-AVP ANTAGONISTS ON PRESSOR AND ANP RESPONSES TO HYPERTONIC SALINE INFUSION IN CONSCIOUS ANEPHRIC RATS. K. Ota, T. Kimura, M. Inoue, T. Funyu, M. Shoji, K. Sato, M. Ohta, T. Yamamoto, K. Abe The Second Department of Internal Medicine, Tohoku University School of Medicine, Sendal, Japan It has been documented that V2-receptors of vasopressin(AVP) exist in the cardiovascular system, besides renal tubules, and elicit a vasodilation, thereby resulting in a decrease in blood pressure. However, the existence of V2-receptors in the cardiovascular system has not been clarified biochemically. Moreover, since a V2-receptor blocker gives rise to AVP-resistant diabetes insipidus, which in turn results in the contraction of body fluid affecting the cardiovascular function, the role of V2receptors in the cardiovascular system was unclear in the presence of the kidney. It remains, therefore, to be unknown whether endogenous AVP plays important roles in the cardiovascular regulation through V2- as well as Vl-receptors. In the present study, to examine the role of AVP receptors in the regulation of hemodynamics and in the release of atrial natriuretic peptide(ANP), 0.95 M hypertonic saline(HS; 0.3 ml/kg/min) was infused for 80 rain with or without a non-peptide and selective AVP antagonist(2 mg/kg + 0.167 mg/kg/min) either for the V1- (OPC-21268) or V2-receptor(OPC-31260) to conscious, bilaterally nephrectomized, Sprague-Dawiey rats(250-300g, BW). HS increased mean arterial pressure(MAP), plasma AVP and ANP, and plasma volume(PV) and osmolality(Posm). Both antagonists did not affect increases in plasma AVP, PV and Posm. However, a Vl-antagonist completely abolished an increase in MAP and a V2-antagonist attenuated it. Both antagonists attenuated increases in plasma ANP similarly. These results suggested that HS-induced pressor responses may be due mainly to the the activity of Vl-receptors of AVP and partly to that of V2-receptors, and that vasodilatory effects via V2-receptors, if any, may not have essential effect on the HSinduced hypertension. Moreover, HS-induced increases in plasma ANP may be mediated by increases in PV and blood pressure, but not be effectively modulated by the direct action through either AVP receptors.
P3-19 ROLE OF ISOPRENOIDS IN NORMAL AND PATHOLOGICAL CELL PROLIFERATION A. Corsini, M.Ralteri, M.R.Soma ,R.Fumagalll, R.Paoletti Institute of Pharmacological Sciences,University of Milan, Italy Several studies attest the role in cell growth played by the mevalonate pathway. Mevalonate is the precursor of isoprenoids that are vital for diverse cellular functions, ranging from cholesterol synthesis to growth control. While cholesterol seems to be required early in the ceil cycle (G1 phase), mevalonate itself and some of its non-steroidal derivatives (isoprenoids) are determinant for cell division and growth regulation. Based on these findings, drugs affecting mevalonate and cholesterol synthesis are now receiving increased attention as potential pharmacological tools for the control of abnormal ceil growth in pathological conditions such as vascular smooth muscle cell (SMC,myocytes) proliferation under atherogenic conditions or tumor development. In a first series of experiments the effect of inhibitors (vastatins) of 3-hydroxy-3-methyl-glutaryl CoA (HMG-CoA) reductase, the rate limiting enzyme in cholesterol biosynthesis, on the growth and on cholesterol synthesis of cultured arterial myocytes was investigated. Compounds fluvastatin (F), simvastatin (S), lovastatin (L), but not pravastatin (P), decreased the rate of growth of rat SMC. The inhibition, evaluated as cell number, was dose-dependent with an IC50 values of 2.2, 2.7 and 3.6 p.M for F,S and L, respectively; P (1-5001aM) was inactive. The inhibition of ceil growth induced by 3.5 laM S and F (70% decrease) was prevented completely by the addition of 100 p_M mevalonate, partially (70-85%) by the addition of 10p.M famesol and 51LM geranylgeraniol, but not by the addition of squalene or ubiquinone, confirming the specific role of isoprenoid metabolites in regulating cell proliferation. At least 80% inhibition of cholesterol synthesis was necessary to induce a decrease in ceil proliferation. Similar results were obtained in SMC from human femoral artery. The fact that treatment of cells with squalestatin 1(1-25 p.lVl),a potent inhibitor of squalene synthase, and NB-598(1-10), a novel squalene epoxidase inhibitor, caused a full inhibition of cholesterol synthesis without affecting SMC proliferation ruled out the importance of squalene or any distal intermediates of cholesterol synthesis in the control of cell proliferation. These results have been inte:preted to indicate the involvement of specific isoprenoid metabolites, probably geranylgeranylated proteins, in the control of ceil proliferation. Similar results were obtained when the effect of vastatins was investigated on the rate of growth of human glioma ceil. Altogether our data support the importance of the pharmacological modulation of the mevalonate pathway in order to regulate pathological accelerated cell proliferation such as in tumors and in the formation of atheroaclerotic lesions.
491
P3-19 ROLE OF ISOPRENOIDS IN NORMAL AND PATHOLOGICAL CELL PROLIFERATION A. Corsini, M.Ralteri, M.R.Soma ,R.Fumagalll, R.Paoletti Institute of Pharmacological Sciences,University of Milan, Italy Several studies attest the role in cell growth played by the mevalonate pathway. Mevalonate is the precursor of isoprenoids that are vital for diverse cellular functions, ranging from cholesterol synthesis to growth control. While cholesterol seems to be required early in the ceil cycle (G1 phase), mevalonate itself and some of its non-steroidal derivatives (isoprenoids) are determinant for cell division and growth regulation. Based on these findings, drugs affecting mevalonate and cholesterol synthesis are now receiving increased attention as potential pharmacological tools for the control of abnormal ceil growth in pathological conditions such as vascular smooth muscle cell (SMC,myocytes) proliferation under atherogenic conditions or tumor development. In a first series of experiments the effect of inhibitors (vastatins) of 3-hydroxy-3-methyl-glutaryl CoA (HMG-CoA) reductase, the rate limiting enzyme in cholesterol biosynthesis, on the growth and on cholesterol synthesis of cultured arterial myocytes was investigated. Compounds fluvastatin (F), simvastatin (S), lovastatin (L), but not pravastatin (P), decreased the rate of growth of rat SMC. The inhibition, evaluated as cell number, was dose-dependent with an IC50 values of 2.2, 2.7 and 3.6 p.M for F,S and L, respectively; P (1-5001aM) was inactive. The inhibition of ceil growth induced by 3.5 laM S and F (70% decrease) was prevented completely by the addition of 100 p_M mevalonate, partially (70-85%) by the addition of 10p.M famesol and 51LM geranylgeraniol, but not by the addition of squalene or ubiquinone, confirming the specific role of isoprenoid metabolites in regulating cell proliferation. At least 80% inhibition of cholesterol synthesis was necessary to induce a decrease in ceil proliferation. Similar results were obtained in SMC from human femoral artery. The fact that treatment of cells with squalestatin 1(1-25 p.lVl),a potent inhibitor of squalene synthase, and NB-598(1-10), a novel squalene epoxidase inhibitor, caused a full inhibition of cholesterol synthesis without affecting SMC proliferation ruled out the importance of squalene or any distal intermediates of cholesterol synthesis in the control of cell proliferation. These results have been inte:preted to indicate the involvement of specific isoprenoid metabolites, probably geranylgeranylated proteins, in the control of ceil proliferation. Similar results were obtained when the effect of vastatins was investigated on the rate of growth of human glioma ceil. Altogether our data support the importance of the pharmacological modulation of the mevalonate pathway in order to regulate pathological accelerated cell proliferation such as in tumors and in the formation of atheroaclerotic lesions.
491