Regulation of Corpus Luteum Function in the Domestic Dog (Canis familiaris) and Comparative Aspects of Luteal Function in the Domestic Cat (Felis catus)

Abstract

The domestic dog (Canis familiaris) and the cat (Felis catus), although sharing the same goal of ensuring maximal fertility, have developed different reproductive strategies. Significant differences can be found in the mechanisms regulating luteal function. In the dog, the lack of an acute luteolytic mechanism in the absence of pregnancy results in prolonged regression of the corpus luteum (CL), extended luteal progesterone secretion, and CL lifespan, features that are similar in pregnant and nonpregnant bitches until the acute prepartum luteolysis. This observation emphasizes the differences between pregnant and nonpregnant dogs in mechanisms regulating the termination of CL function and further highlights the interspecies differences. In the domestic cat, successful mating results in pregnancy and a luteal lifespan that extends until parturition, and after a nonfertile mating ovulation is followed by pseudo-pregnancy. However, differing from the dog, the duration of pseudo-pregnancy is approximately half the gestation length observed during pregnancy. The persistence of luteal function in pregnant queens over the duration of pseudo-pregnancy is, most probably, caused by the supportive role of placental steroidogenesis, which is lacking in the dog. Interestingly, in both species luteal function, at least in the absence of pregnancy, is independent of a uterine luteolysin, as it remains unaffected by hysterectomy. Consequently, in both species the luteal regression/luteolysis during pseudo-pregnancy appears to be a passive degenerative process in the absence of a luteolytic principle of uterine origin; however, the inherent luteal lifespan is much shorter in the feline than in the canine species, facilitating and hastening reproduction in cats.