EFFECTS OF ACETYLCHOLINE AND NITROPRUSSIDE ON SYSTEMIC AND REGIONAL HEMODYNAMICS IN HYPERTENSIVE RATS

This study was performed to investigate the in vivo effects of acetylc holine, a stimulator of endogenous NO production, and nitroprusside, a n exogenous NO-donor, on hemodynamics in the normotensive (WKY) and th e hypertensive (SHR) rat. Anesthetized rats were given microspheres fo r the measurement of cardiac index (CI), total vascular resistance (TP RI), regional blood flow and vascular resistance. Infusion of acetylch oline (2 mu g/kg/min) caused a marked decrease in TPRI by (-35+/-5%, /-SEM) in the WKY (n=8), whereas in the SKR (n=8) a less pronounced re duction was seen (-14+/-3%, p<0.01 between groups). CI increased by 27 +/-9% in the WKY, but was unaltered in the SHR. Blood pressure decreas ed similarily (17-20%). Acetylcholine significantly increased blood fl ow by about 40% in the kidneys and the heart in the WKY, but had no si gnificant effect in the SHR. Other tissues, such as skeletal muscle an d cerebral tissues, showed no major changes. Infusion of nitroprusside (1 mu g/kg/min) reduced blood pressure by 5 to 10% in the strains. Th e regional effects of nitroprusside did not differ between the strains . In conclusion, the acetylcholine-induced vasodilation in the kidney and the heart was attenuated in the SHR compared to the WKY. These fin dings might suggest a difference in the endothelial response between t he SHR and the WKY in some, but not in all, tissues.