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(Hypertension. 1997;30:1356-1361.)
© 1997 American Heart Association, Inc.

Articles

-Adrenergic Signal Transduction in Renin Transgenic Rats

Petra Schnabel; Theo Nohr; Georg Nickenig; Martin Paul; ; Michael Böhm

From the Klinik III für Innere Medizin der Universität zu Köln (P.S., T.N., G.N., M.B.) and the Institut für Klinische Pharmakologie der Freien Universität Berlin (M.P.) (Germany).

Abstract The ₁-adrenoceptor–G protein–phosphoinositide-specific phospholipase C (PLC) signal transduction pathway is assumed to play an important role in the regulation of contractile force and in the pathophysiology of myocardial hypertrophy. In the present study, the components of this pathway were investigated in left ventricles of hearts from hypertensive transgenic rats overexpressing the mouse renin gene [TG(mREN2)27] in comparison to age- and weight-matched Sprague-Dawley control rats. Contractile force was assessed in isolated electrically driven left ventricular papillary muscle strips. ₁-adrenoceptor density was measured by radioligand binding using [³H]prazosin, steady state levels of q/11, and G protein ß-subunits by Western blotting. PLC activity was determined by a cell-free assay using exogenous phospholipid vesicles containing [³H]phosphatidylinositol (4,5)-bisphosphate as a substrate. ₁-Adrenoceptor density was significantly increased (by 80%) in transgenic rats compared with control rats, while the positive inotropic response to the ₁-adrenoceptor agonist phenylephrine was significantly reduced, suggesting a postreceptor defect in TG(mREN2)27. The expression of q and 11 was verified by reverse transcription–polymerase chain reaction, and q/11 steady state protein levels were shown to be similar in transgenic and control rats. Western blotting using a ß-common antibody revealed two bands at approximately 35 and 36 kD. The quantities of both were similar in TG(mREN2)27 compared with those in control rats. In contrast, PLC activity was significantly reduced (by 32%) in transgenic rats. In conclusion, our findings are consistent with a desensitization of the ₁-adrenergic signal transduction pathway at the level of the effector.

Key Words: signal transduction • -adrenoceptors • G proteins • phospholipase C • cardiac hypertrophy

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