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  • Title: Induction and inhibition of implantation in lactating rats.
    Author: Maneckjee R, Moudgal NR.
    Journal: J Reprod Fertil; 1975 Apr; 43(1):33-40. PubMed ID: 1127638.
    Abstract:
    The interrelationship between prolactin and LH in the maintenance of pregnancy during lactation was studied. The reduction of suckled young from eight to two or less, as late as on the morning of Day 4 of pregnancy, resulted in normal implantation. Reintroduction of eight young on Day 4 to lactating pregnant rats deprived of their litters on Day 1 resulted in an inhibition of implantation, but reintroduction on Days 5 or 6 did not inhibit implantation. If oestrogen, HCG or PMSG was given on Day 4 of pregnancy, implantation was induced at the normal time in rats suckling large litters. When LH antiserum was given on the morning of Day 4 or Day 8 to pregnant rats suckling two young each, it blocked implantation and postimplantation survival of blasto-cysts, respectively. When the number of suckling young was increased from two to eight on Day 6, however, LH antiserum blocked pregnancy only to the extent of 70%. Prolactin administered during the preimplantation phase inhibited implantation in pregnant rats suckling a minimum number of young, but had no effect when given during the postimplantation phase. Progesterone failed to block implantation. Prolactin had no inhibitory effect on implantation in the absence of the suckling stimulus or in non-lactating pregnant rats. The inhibition of implantation by prolactin in rats suckling two young could be effectively reversed by the administration of oestrogen, PMSG or HCG on Day 4 of pregnancy. The relationship between prolactin and LH in the maintenance of pregnancy during lactation was studied in rats. The reduction of sucklings from 8 to 2 or less as late as the 4th day of pregnancy resulted in normal implantation. Reintroduction of 8 young on Day 4 to lactating pregnant rats deprived of sucklings on Day 1 resulted in inhibition of implantation, but reintroduction on Days 5 or 6 did not inhibit implantation. If estrogen, HCG or pregnant mares serum gonadotrophin PMSG was given on Day 4 of pregnancy, implantation was induced at the normal time in rats nursing large litters. When LH antiserum was given on the morning of Day 4 or Day 8 to pregnant rats nursing 2 young each it blocked implantation and postimplantation survival of balstocysts, respectively. When the number of suckling young was increased from 2 to 8 on Day 6, however, LH antiserum blocked pregnancy only to the extent of 70%. Prolactin administered during the preimplantation phase inhibited implantation in pregnant rats suckling a minimum number of young, but had no effect when given during the postimplantation phase. Progesterone failed to block implantation. Prolactin had no inhibitory effect on implantation in the absence of the suckling stimulus or in nonlactating pregnant rats. The inhibition of implantation by prolactin in rats suckling 2 young could be effectively reversed by the administration of estrogen, PMSG, or HCG on Day 4 of pregnancy. The inhibition of lactation on implantation appears to be an easily reversible process in rats. The observation that LH antiserum also inhibits implantation in lactating pregnant animals shows that the hormonal requirement for implantation is the same as in normal pregnancy. More work needs to be done on the nature of the vehicle and the dosage before the amount of LH necessary to bring about implantation can be determined.
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