Maternal factors modulate the increase in vasoactive substances during rat pregnancy

To explore if the changes in vasoactive substances observed during early pregnancy in the rat are modulated by maternal or fetoplacental factors.

Urinary excretion of cGMP, 6-keto-prostaglandin-F1 alpha (6-keto-PGF1 alpha), thromboxane B2 and kallikrein activity was measured in pregnant (P, n = 11), pseudopregnant (PSP, n = 12), and virgin (n = 13) rats and in ovariectomized virgin rats supplemented with slow-release pellets containing either progesterone (50 mg/pellet) or estradiol (0.5 mg/pellet) or a combination of both hormones, for 21 days.

The cGMP excretion was higher in PSP rats than in virgin rats at day 5 (virgin = 82 +/- 7, P = 93 +/- 5, PSP = 110 +/- 8 nmol/24 h, p < 0.05); at day 10, values were significantly increased in P and PSP rats. 6-keto-PGF1 alpha excretion was similarly elevated in P and PSP rats at day 5 (virgin = 120 +/- 10, P = 160 +/- 10, and PSP = 174 +/- 14 ng/24 h, p < 0.01). This trend was still present at day 10. Thromboxane B2 excretion showed a nonsignificant increase in P and PSP rats in day 5; at day 10, values were significantly elevated in both experimental groups (virgin = 23 +/- 2, P = 32 +/- 4, and PSP = 32 +/- 2 ng/24 h, p < 0.05). Kallikrein excretion was significantly increased in PSP and P rats at days 5 and 10. Estradiol or progesterone administration caused a significant decrease in serum aldosterone and an increase in urinary kallikrein activity.

These results indicate that during the first half of rat pregnancy, the increment in vasoactive substances is modulated by maternal and not by fetoplacental factors.