Investigations on the role of progesterone in the endocrine control of overt pseudopregnancy in the bitch: Application of an antigestagen and effects on corpus luteum function

Abstract

To test the role of progesterone in the onset and maintenance of overt pseudopregnancy, three groups of dogs were treated with the antigestagen Mifepristone (RU 38486, dose: 2 mg kg −1 body weight) commencing on Days 23.6± 1.9 (Group 1, n=5), 35.0± 1.2 (Group 2, n=5) and 42.8±3.5 (Group 3, n = 6) after onset of pro-oestrous bleeding. In all three groups, onset of overt pseudopregnancy occurred earlier in the treatment than in the control cycle ( P<0.01 − P<0.05), clinical symptoms were significantly less and duration of pseudopregnancy was shortened in Groups 1 ( P< 0.01) and 2 ( P<0.05). Treatments with RU 38486 did not affect blood cortisol levels and had no measurable effects on luteal function. The results demonstrate the role of progesterone in onset and maintenance of overt pseudopregnancy. While onset may result from a decrease in progesterone concentrations, mammary gland development and expression of other symptoms seem to depend on the continuing availability of progesterone. In contrast to other reports in the literature, RU 38486 did not affect luteal function in this study. Possible dose-related phenomena are discussed.