Effects of enalaprilat on circadian profiles in blood pressure and heart rate of spontaneously and transgenic hypertensive rats.

We investigated the dose-dependent cardiovascular effects of enalaprilat at different dosing times in two animal models of hypertension. Blood pressure (BP) and heart rate (HR) were measured telemetrically in 5 spontaneously hypertensive rats (SHR) and in 5 transgenic hypertensive rats (TGR) after intraperitoneal (i.p.) injection of enalaprilat either at 700 h or at 1900 h. In SHR, dosing of enalaprilat at the beginning of the resting period, i.e., at 700 h, significantly reduced BP but did not influence HR. After dosing at 1900 h, BP was unchanged, whereas HR increased, which might have resulted from reflexly increased sympathetic tone. In TGR, enalaprilat at either dosing time decreased BP dose dependently and to a higher extent than in SHR, but the effects were more pronounced after morning than after evening dosing. These findings demonstrate that in two animal models of hypertension the antihypertensive effects of enalaprilat depended on the time of drug dosing.