The Influence of Coitus, Suckling, and Prolactin Injections on Pregnancy in Pelvic Neurectomized Rats

Bilateral resection of the pelvic nerve (PN) in female rats had no effect on the estrous cycle, but prevented pregnancy when performed prior to mating. Pelvic neurectomy performed 30 min postmating did not affect the interim pregnancy, but blocked parturition. Twice daily sc injections of 7.0 to 28 IU of prolactin (NIH-S-8) into PN females beginning on the a.m. after mating (day 1) maintained normal pregnancy until sacrifice at day 16. Lower doses of 1.4 and 3.5 IU of prolactin twice daily were partially effective; whereas a single injection of 280 IU on day 1 was ineffective. Injections of 7.0 IU of prolactin on days 1-3 maintained pregnancy in 60% of the PN females. Following parturition, lactating females suckling six young were bilaterally pelvic neurectomized and mated to a fertile male. Pregnancy occurred and was maintained in 7 of 10 females, sacrificed at day 16 postpartum. Removal of the entire litter at day 1, 3, or 6 postpartum, resulted in maintenance of pregnancy in two of eight, three of nine, and two of eight PN females, respectively.