The effects of angiotensin II, endothelin-1, and protein kinase C inhibitor on DNA synthesis and intracellular calcium mobilization in vascular smooth muscle cells from young normotensive and spontaneously hypertensive rats

Angiotensin II (Ang-II) and endothelin 1 (ET-1) are important peptides that induce a prolonged vasoconstriction and enhance proliferation of vascular smooth muscle cells (VSMC). These substances may have an important role in the development of hypertension and atherosclerosis. Our objectives were to determine whether there are inborn differences in the proliferation patter ns of VSMC obtained from spontaneously hypertensive (SHR) and Wistar-Kyoto rats (WKY) by studying the effects of Ang-II and ET-1 on VSMC from those st rains before the onset of hypertension, and to evaluate the roles of protei n kinase C (PKC) and intracellular Ca2+ in the mechanism of action of ET-1 and Ang-II. VSMC from aortas of young (1- to 2-week-old) SHR and WKY rats were grown as primary cultures in plates for 48 h. The cells were incubated with Ang-II (0.1 to 1000 nmol/L) or ET-1 (0.1 to 100 nmol/L). VSMC were also incubated in the presence of various concentrations of a PKC inhibitor, chelerythrine (0.1-10 nmol/L). Thymidine incorporation into DNA was measured as an indic ator of DNA synthesis. Intracellular free Ca2+ was determined by using FURA -2AM. ET-1 and Ang-II caused a marked dose-dependent enhancement of thymidine inc orporation into DNA. The responses of VSMC from WKY and SHR to Ang-II and E T-1 were similar. In both strains, chelerythrine caused a dose-dependent su ppression in the activity of ET-1 and Ang-II. However, VSMC from SHR incuba ted in the presence of ET-1 were more susceptible tea the inhibitory effect of chelerythrine. Both Ang-II and ET-1 induced an increase of intracellula r free Ca2+. ET-1 induced a larger increase than Ang-II (190% and 100% grea ter than baseline free Ca2+ levels, respectively), in spite of a lower conc entration of ET-1 (ET-1 = 30 nmol/L; Ang-II 100 nmol/L). Ang-II and ET-1 exerted a similar mitogenic effect on primary cultures of V SMC obtained from young SHR before the development of hypertension, compare d with WKY. The mitogenic activity of Ang-II and ET-1 was accompanied by an increase of intracellular free Ca2+. The effect of ET-1 upon intracellular Ca2+ was stronger than that of Ang-II. VSMC cultures of SHR stimulated wit h ET-1 were more susceptible to PMC inhibition than those of WKY. The simil arity of the effects of Ang-II and ET-1 on SHR and WKY does not exclude the ir role in the pathogenesis of hypertension and atherosclerosis, and furthe r studies should be carried out to determine their role. Am J Hypertens 199 9;12:1243-1251 (C) 1999 American Journal of Hypertension, Ltd.