EFFECT OF HYPERADRENOCORTICISM AND DIABETES-MELLITUS ON SERUM PROGESTERONE CONCENTRATIONS DURING EARLY METESTRUS OF PREGNANT AND NONPREGNANT CYCLES INDUCED BY PREGNANT MARES SERUM GONADOTROPIN IN DOMESTIC DOGS

The intramuscular (i.m.) administration of pregnant mares' serum gonad otrophin (PMSG) (20 iu kg-1 day-1 for 5 days) followed by an injection of human chorionic gonadotrophin (500 iu, i.m.) induced oestrus in 28 cross-bred bitches. These included, based on endocrine evaluations, n ine normal (N), seven insulin-deficient diabetic (ID), six insulin-res istant (IR) and six hypercortisolic (HC) bitches. The bitches were not bred but were allowed to have a non-pregnant cycle. When oestrus was induced a second time by re-treating at 35 days after the end of the n on-pregnant metoestrus of the first induced cycle, the dogs were mated . Pregnancy was obtained in five N, four ID, four IR and three HC dogs ; 15 of the 16 dogs had litters. For these 16 dogs, progesterone conce ntrations in serum were evaluated from samples that had been obtained daily during the first 30 days of the first (non-pregnant) induced cyc le and the first 11 days of metoestrus of the second induced (pregnant ) cycle. Corpus luteum development was characterized in normal bitches by a steady increase in progesterone, with highest values (33 +/- 6 n g ml-1) at day 8 of metoestrus in pregnant dogs. Progesterone averaged among the first 11 days of metoestrus (pregnant and non-pregnant) did not differ between normal and insulin-resistant bitches (20 +/- 5 ver sus 22 +/- 4 ng ml-1). Mean progesterone was lower (P < 0.01) in insul in-deficient non-pregnant (16 +/- 4 ng ml-1) and pregnant (10 +/- 3 ng ml-1) bitches, and in hypercortisolic non-pregnant (12 +/- 3 ng ml-1) and pregnant (9 +/- 2 ng ml-1) bitches. These results suggest that in sulin deficiency or hypercortisolism may decrease progesterone secreti on by corpora lutea during the early luteal phase of PMSG-induced cycl es in the bitch.