Maternal factors modulate the increase in vasoactive substances during ratpregnancy

Objective: To explore if the changes in vasoactive substances observed duri ng early pregnancy in the rat are modulated by maternal or fetoplacental fa ctors. Methods: Urinary excretion of cGMP, 6-keto-prostagladin-F1 alpha (6-keto-PG F1 alpha), thromboxane B-2 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 containi ng either progesterone (50 mg/pellet) or estradiol (0.5 mg/pellet) or a com bination of both hormones, for 21 days. Results: The cGMP excretion was higher in PSP rats than in virgin rats at d ay 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 (vir gin = 120 +/- LO, P = 160 +/- 10, and PSP = 174 +/- 14 ng/24 h, p < 0.01). This trend was still present at day 10. Thromboxane B-2 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 pr ogesterone administration caused a significant decrease in serum aldosteron e and an increase in urinary kallikrein activity. Conclusions: These results indicate that during the first half of rat pregn ancy, the increment in vasoactive substances is modulated by maternal and n ot by fetoplacental factors.