Renal response to atrial stretch during pregnancy in conscious rats.

Chronic indwelling balloons were placed at the junction of the right atrium and the right superior vena cava of virgin female rats. The renal response to discrete standardized atrial stretch was tested in the conscious animals. The rats were then mated, and the renal response was retested at days 7, 14, and 20 of pregnancy. On day 21, the rats were killed, and the pressure-volume relationship of the right atria was measured. In response to atrial stretch, there was an increase in urine volume, urine sodium output, and urine potassium output and a decrease in free water clearance in the virgin rats. Subsequent to mating, these responses were completely abolished at all stages of pregnancy. The renal responses to atrial stretch were also abolished during pseudopregnancy. Central venous pressure did not change when the intracardiac balloons were inflated; there were also no changes in resting central venous pressure during pregnancy. There were no significant changes in unstressed atrial volume or in atrial compliance during pregnancy.