The effect of pregnancy on heart size and blood pressure in renal hypertensive rats.

The main purpose of this study on rats was to examine the effect of pregnancy on experimental renal hypertension and cardiac size. Renal hypertension in the rats (RHR) was induced by standardized clamping of the left renal artery early in pregnancy (SRHR) or 4 weeks before mating (ERHR). As controls served non-pregnant RHR with the duration of hypertension matched to each above mentioned group, as well as non-pregnant and pregnant normotensive rats. Only 16% of the rats with renal artery clamping early in pregnancy (SRHR) developed hypertension in contrast to 41% of similarly operated non-pregnant rats and 56% of ERHR decreased their blood pressure to normal levels during pregnancy. Concerning left ventricular heart weight there was a slight increase in left ventricular weight during normal pregnancy in spite of a significantly reduced blood pressure. In both SRHR and ERHR an increased left ventricular heart weight was noticed during pregnancy even when arterial pressure was not increased. The present results suggest an antihypertensive effect of pregnancy and the existence of "trophic" influences and/or a volume induced adaptation of the heart causing an increased myocardial mass which is associated with pregnancy and partly independent of blood pressure influences.