THE ROLE OF PROLACTIN IN THE REPRODUCTION OF THE DOG AND CAT

Prolactin (PRL), a pituitary hormone, exerts a significant influence o n reproductive functions in dogs and wild canids (wolf, fox, coyote an d others). Pseudopregnancy is obligatory for all non-pregnant females of these species, which assures their capability for caring for and ev en nursing a litter. This is caused by a PRL rise during the second ha lf of pregnancy, which in the dog is quantitatively equal in pregnant and overt pseudopregnant animals; in covert pseudopregnant bitches thi s rise in PRL is significantly lower. Consequently, these animals do n ot show enlargement of the mammary glands and milk secretion, and the typical distorted behavior seen in overtly pseudopregnant bitches. The use of potent PRL-inhibitors, mostly dopamine agonists like bromocrip tine, metergoline and cabergoline, has revealed that PRL is the luteot ropic hormone from day 30 of pregnancy on and that PRL is essential fo r the preparations of the mammary glands for lactation, the commenceme nt of lactation and its maintenance; and for maternal (and paternal) c are for the litter. Hence, these PRL-inhibitors are in use for inducti on of abortion after mid-gestation, for the treatment of overt pseudop regnancies and to stop unwanted lactation. Male and female dogs and wo lves show almost identical seasonal changes in PRL blood concentration s with peak levels before mid year and the nadir just before year's en d. In wild canids with one oestrus annually late in winter/early sprin g, the annual PRL-peak coincides with the need to care for the litter late in spring/early in summer: females that were pregnant or pseudopr egnant are ready to nurse and take care of whelps; simultaneously, the seasonally peaking PRL blood concentrations seem to smooth over socia l tensions between males and to assure their essential participation i n the care of the litter. In the bitch, pseudopregnancy has become an atavism and overproduction of PRL causes anoestrus. Hence, PRL inhibit ors can be used for the treatment of anoestrus and for shortening of t he oestrus interval as well. The pseudopregnant cat does not form addi tional PRL; but in the pregnant cat PRL is an essential luteotropin du ring the second half of pregnancy. Hence, in cats abortion can be indu ced during this time period with PRL-inhibitors and these compounds ar e useful to stop lactation.