The natriuretic actions of vasopressin in the female rat: variations during the 4 days of the oestrous cycle.

The renal actions of vasopressin were studied in the conscious female rat. Vasopressin caused a dose-dependent increase in sodium excretion when administered at 40-160 pmol/min. The highest dose, which increased sodium excretion from 10.4 +/- 0.3 mumol/min (n = 32) to 18.3 +/- 0.8 mumol/min (n = 8, P < 0.001), also caused a significant rise in glomerular filtration rate (GFR). The antidiuretic and natriuretic responses to vasopressin varied significantly over the 4 days of the oestrous cycle. Both responses were greatest on pro-oestrus, being -57 +/- 3 and 52 +/- 3% above the control values with 80 pmol vasopressin/min. Responses of similar magnitude were also seen on dioestrus day 1. On these two cycle days the effects on urine flow and sodium excretion were accompanied by a significant increase in GFR. Smaller antidiuretic and natriuretic responses were seen on oestrus and dioestrus day 2, without concomitant changes in GFR. As the plasma vasopressin concentrations produced by hormone infusion were similar on each day of the cycle, the renal responsiveness to vasopressin appears to vary over the 4 days of the oestrous cycle. This may be important in terms of alteration and possible disturbances of fluid balance which may occur during reproductive cycles and pregnancy.