Chronic central versus systemic blockade of [AT.sub.1] receptors and cardiac dysfunction in rats post-myocardial infarction

In rats, both central and systemic ANG II type 1 ([AT.sub.1]) receptor blockade attenuate sympathetic hyperactivity, but central blockade more effectively attenuates left ventricular (LV) dysfunction post-myocardial infarction (MI). In protocol 1, we examined whether functional effects on cardiac load may play a role and different cardiac effects disappear after withdrawal of the blockade. Wistar rats were infused for 4 wk post-MI intracerebroventricularly (1 mg x [kg.sup.-1] x [day.sup.-1]) or injected subcutaneously daily (100 mg x [kg.sup.-1] x [day.sup.-1]) with losartan. LV dimensions and function were assessed at 4 wk and at 6 wk post-MI, i.e., 2 wk after discontinuing treatments. At 4 and 6 wk post-MI, LV dimensions were increased and ejection fraction was decreased. Intracerebroventricular but not subcutaneous losartan significantly improved these parameters. At 6 wk, LV peak systolic pressure (LVPSP) and maximal or minimal first derivative of change in pressure over time (dP/[dt.sub.max/min]) were decreased and LV end-diastolic pressure (LVEDP) was increased. All four indexes were improved by previous intracerebroventricular losartan, whereas subcutaneous losartan improved LVEDP only. In protocol H, we evaluated effects of oral instead of subcutaneous administration of losartan for 4 wk post-MI. Losartan (~200 mg x [kg.sup.-1] x [day.sup.-1]) either via drinking water or by gavage similarly decreased [AT.sub.1] receptor binding densities in brain nuclei and improved LVEDP but further decreased LVPSP and dP/[dt.sub.max]. These results indicate that effects on cardiac load by peripheral [AT.sub.1] receptor blockade or the pharmacokinetic profile of subcutaneous versus oral dosing do not contribute to the different cardiac effects of central versus systemic [AT.sub.1] receptor blockade post-MI. losartan; cardiac remodeling; echocardiography; Millar catheter; brain; ANG II type 1