Luteal function of induced corpora lutea in the bitch

Nineteen anestrous bitches with a mean of 22 kg body weight and ranging from 2 to 4 years of age were induced to exhibit estrus and ovulate using PMSG and HCG. Twelve days after the first day of estrus, bitches were assigned to four treatment groups. Group (A) consisted of six bitches, Group (B) of five bitches and Groups (C) and (D) of four bitches each. At this time, bitches in Groups (A), (B) and (C) were laparotomized and those assigned to Groups (A) and (B) were bilaterally hysterectomized leaving the cervix and oviducts intact. Although bitches in Group (C) were laparotomized, they were not hysterectomized. Group (D) bitches were not subjected to any surgical procedures. Homologous uterine extract was prepared from each bitch in Group (A) and administered intramuscularly beginning on day 25 (day 0 = first day of estrus) and continued every other day for 61 days post-estrus. Bitches in Group (B) were similarly injected with equal volumes of 0.9% saline. Blood samples, obtained prior to laparotomy and every other day for 85 days thereafter, were assayed for plasma progesterone concentrations using radioimmunoassay. One bitch in each of Groups (A) and (D) did not form luteal tissue following treatment with PMSG and HCG although both bitches exhibited estrus following treatment. All other bitches showed an increase in progesterone levels (4 to 19 ng/ml) between the first day of estrus and 10 days post-estrus. Thereafter, progesterone levels progressively declined in all groups with levels below 1 ng/ml between 38 to 40 days post-estrus. Results of this study suggested that CL formed in the bitch following PMSG and HCG treatment have a reduced function compared to non-induced CL of a normal, non-fertile estrous cycle. Such premature CL regression appears to be independent of the presence or absence of the uterus.