ATRIAL-NATRIURETIC-FACTOR RELEASE DURING PREGNANCY IN RATS

1. We investigated the control of atrial natriuretic factor (ANF) secretion during pregnancy. 2. Plasma ANF levels were measured in conscious virgin female rats under basal conditions, and after atrial distension with an indwelling balloon catheter. The rats were then mated, and the measurements repeated at 7, 14 and 21 days of pregnancy, and at 1 week postpartum. Plasma ANF levels were also measured in ovariectomized rats injected with progesterone, oestradiol, or oestradiol plus progesterone. 3. Basal plasma ANF levels were elevated at 7 and 14 days of pregnancy but returned to pre-pregnant levels by 21 days. At 1 week postpartum, they were again elevated. 4. In response to atrial stretch, plasma ANF increased significantly in virgin rats (from 100 +/- 10 to 148 +/- 13 pg ml(-1), P < 0.001, n = 20). In contrast, there was no such secretory response observed in the pregnant and postpartum animals i.e. stretch-induced secretion of ANP was markedly attenuated. 5. Treatment with exogenous oestradiol caused a significant increase in plasma ANP levels in acyclic rats. However, neither progesterone nor a combination of oestradiol plus progesterone had any effect. 6. It is concluded that basal and stretch-induced ANF secretion are differentially influenced by pregnancy; oestradiol is identified as a potential stimulatory factor.