Peripheral plasma levels of oestradiol-17 and progesterone in the bitch during the oestrous cycle, in normal pregnancy and after dexamethasone treatment

Abstract

Plasma estradiol-17.beta. [E2] concentrations in Labradors increased during proestrus to an average maximal concentration of 79.7 .+-. 10.9 (SD) pg/ml, and then fell rapidly. In 6/7 bitches the peak occurred within 1 day of estrus. No consistent changes in plasma E2 levels were observed during pregnancy and at parturition, and the values were similar to those in late anestrus. Plasma progest erone [P4] levels did not increase markedly during proestrus. At estrus, P4 values rose and maximal concentrations, which varied from about 20 to about 55 ng/ml, were reached within a few days of the E2 peak. Plasma P4 decreased in late pregnancy and in 1 of the 3 bitches studied in detail low or undetectable levels were reached 10 days before parturition. In the other 2 bitches an abrupt decrease in P4 occurred just before parturition. Dexamethasone treatment (2 .times. 5 mg daily for 10 days) from day 30 of pregnancy resulted in intrauterine death and resorption of the fetuses in the 2 bitches studied. Treatment from about day 45 resulted in the birth of dead fetuses at days 55 and 59 of pregnancy. The changes in plasma E2 levels were very small. No changes in plasma P4 levels were seen when dexamethasone was given in late pregnancy, but an accelerated decline occurred after treatment in mid-pregnancy.