PROLACTIN IN CANINE AND FELINE REPRODUCTION

Prolactin (PRL), a pituitary hormone, exerts a significant influence o n reproductive functions in dogs and non-domestic canines (wolf, fox, coyote et al.). Pseudopregnancy is obligatory for all non-pregnant fem ales in these species, which ensures their capability of caring for an d even nursing a litter. This is caused by a PRL rise during the secon d half of pregnancy, which in the dog is quantitatively equal in pregn ant and overt pseudopregnant animals; in covert pseudopregnant bitches this rise in PRL is significantly lower. Consequently, these animals do not show the enlargement of the mammary glands and their secretions , and the typical distorted behaviour seen in overtly-pseudopregnant b itches. The use of potent PRL-inhibitors, mostly dopamine agonists lik e bromocriptine, metergoline and cabergoline, has revealed that PRL is the luteotropic hormone from day 30 of pregnancy onward and that PRL is essential for the preparation of the mammary glands for lactation, the commencement of lactation and its maintenance, and for the materna l (and paternal) care of the litter. Hence, these PRL-inhibitors are i n use for induction of abortion after mid-gestation, for the treatment of overt pseudopregnancies and to stop unwanted lactation. Male and f emale dogs and wolves show almost identical seasonal changes in PRL bl ood concentrations with peak levels before mid-year and the nadir just before the year's end. In non-domestic canines with one oestrus annua lly in late winter/early spring the annual PRL peak coincides with the need to care for the litter late in spring/early in summer. Females t hat were pregnant or pseudopregnant are ready to nurse and take care o f whelps and simultaneously, the seasonally peaking PRL blood concentr ations seem to smooth over social tensions between males and ensure th eir essential participation in the care of the litter. In the bitch, p seudopregnancy has become an atavism and overproduction of PRL causes anoestrus. Hence, PRL-inhibitors can be used for the treatment of anoe strus and for shortening the oestrous interval as well. The pseudopreg nant cat does not form additional PRL, but in the pregnant cat, PRL is an essential luteotropin during the second half of pregnancy. Hence, cats can be aborted during this time period with PRL-inhibitors and th ese compounds are useful in order to stop lactation.