Tetrahydropapaveroline (
THP), a condensation product of
ethanol-derived
acetaldehyde, potentiates cardiac function through a beta-
adrenergic mechanism. It is well established that beta-
adrenergic activity is markedly depressed in
hypertension. However, little is known about the myocardial action of THP in
hypertension. In this study, the effect of THP was examined using left ventricular papillary muscles and ventricular myocytes from 10-week-old normotensive (WKY) and spontaneously hypertensive (SHR) rats. The mechanical parameters evaluated include: peak tension developed (PTD), peak twitch amplitude (PTA), time-to-PTD/PTA (
TPT/TPS), time-to-90% relaxation/relengthening (RT(90)/TR(90)), and the maximal velocities of contraction/shortening and relaxation/relengthening (+/-VT/+/-dL/dt). Intracellular Ca(2+) transients were measured as
fura-2 fluorescence intensity changes (delta FFI). THP (0.01-100 microM) produced a concentration-dependent increase in myocardial contraction on muscles and myocytes from both groups of animals. However, preparations from the SHR group were generally less responsive to THP than their normotensive counterparts. The increase in contractility by THP was associated with increases in delta FFI and +/-VT, and shortening of
TPT/TPS and RT(90)/TR(90). The role of beta-
adrenoceptor(s) in the mechanism of action of THP was explored using specific beta-receptor subtype antagonists CGP 207.12A (beta(1)) and
ICI 118,551 (beta(2)). In preparations from both WKY and SHR hearts, the THP-induced increase in cardiac contractility was either attenuated or blocked by CGP 207. 12A and
ICI 118,551. These results indicate that THP exhibits a positive action on myocardial contraction that is mediated, in part, through both beta(1) and
beta(2) adrenergic receptors. This cardiac inotropic response, however, is markedly diminished in
hypertension, which is due possibly to alterations in beta-
adrenergic signal transduction.