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Ergocryptine (2 mg/kg) caused short- and long-term reduction of prolactin secretion in rats experiencing concurrent lactation and pregnancy. The long-term effects of the drug lasted at least 60 days and resulted in reduced milk secretion and termination of pregnancy. Prolactin replacement therapy at a low dose (5 i.u./day) was unsuccessful in overcoming these effects but a higher dose (up to 60 i.u./day) increased milk production and maintained pregnancy. One possible explanation of these results is that prolactin, rather than the suckling stimulus, was responsible for the suppression of oestrous cycles, because ergocryptine brought about a resumption of oestrous vaginal smears in all treated rats in spite of continued suckling.

Litter removal during lactation led to an increase in serum LH concentration, an effect which was completely reversed by prolactin injections. Lactating rats receiving ergocryptine also showed increased serum LH but not to the extent found during litter removal, suggesting that both prolactin and suckling are important factors in the maintenance of lactational anoestrus. The early implantation induced by removal of the litter from rats concurrently lactating and pregnant was not prevented by prolactin. Implantation occurred early in similar rats with serum prolactin levels reduced by ergocryptine treatment and the effect was reversed by prolactin. However, early implantation led to failure of the pregnancy to reach term. These results show that, although prolactin is involved, the suckling stimulus is also essential to prevent implantation in rats with concurrent lactation and pregnancy.

The pituitary of roach, Rutilus rutilus (L.), is pear-shaped and situated in the sella turcica. It is characterised by a large pars nervosa, which penetrates deep into the other regions, splitting the proximal pars distalis. Spatial localisation of nerve fibre types and glandular cell types occurs. Using a variety of staining techniques six glandular cell types have been localised and their distribution is disucssed in relation to those of the other teleost pituitaries.