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Endocrinology, doi:10.1210/endo-115-3-959
Endocrinology Vol. 115, No. 3 959-961
Copyright © 1984 by the Endocrine Society.
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Nitrendipine Prolongs Rat Parturition: No Changes Occur in Progesterone Withdrawal

HIDEKI SAKAMOTO and GABOR HUSZAR

Uterine Physiology Unit, Department of Obstetrics and Gynecology, Yale University School of Medicine New Haven Connecticut 06510

Address all correspondence and requests for reprints to: Dr. Gabor Huszar, Department of Obstetrics and Gynecology, Yale University School of Medicine, 333 Cedar Street, New Haven Connecticut 06510.

Abstract

The mechanism of tocolytic action of the calcium channel-blocking agent nitrendipine [3-ethyl-5-methyl-1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl) 3,5-pyridinedicarboxylate; BAYER E 5009] has been examined. Pregnant rats (duration of pregnancy, 22 days) were treated with nitrendipine (12.5 mg/kg, sc) on days 18–21 of gestation (group I) or on days 20–21 of gestation (group II) and with vehicle only (control group). Serum levels of progesterone from the three experimental groups were determined on days 20 and 22, and the course of labor was monitored on days 22–23 in the individually caged dams. The duration of labor, delivery times, and other labor parameters were significantly delayed in the treated groups vs. the control group, while there was no difference in serum progesterone levels among the three experimental groups on day 20 or 22 of gestation 136.0 ± 5.6 (mean ± SEM; (n = 6) and 43.8 ± 7.2 (n = 17) ng progesterone/ml serum, respectively. We can conclude that progesterone withdrawal, the primary event in the initiation of rat labor, is not altered by nitrendipine treatment. The delay of labor is apparently related to a decrease in the contractile state of myometrium due to the inhibition of calcium influx by nitrendipine. (Endocrinology 115: 959–961, 1984)

Received January 25, 1984.






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Copyright © 1984 by The Endocrine Society