Regulation of progesterone during pregnancy in the cat: studies on the roles of corpora lutea, placenta and prolactin secretion.

The regulation of progesterone secretion and release by the corpus luteum and/or by the placenta in cats during pregnancy has been poorly studied and the relative roles of the corpus luteum and the placenta in the release of progesterone into the plasma is not well defined. It is generally assumed that after 40-45 days of pregnancy, circulating progesterone is mainly produced by the placenta and that after 45-50 days the corpus luteum is no longer necessary to maintain pregnancy, even if remnants of corpora lutea are detected in the ovaries during the following interoestrous period. In this study, the relative roles of the placenta and ovary in progesterone production after 30 days of pregnancy have been analysed in an attempt to define the role of progesterone in pregnant cats. Different experiments involved (1) analysis of the effects of an ovariectomy performed at 30 days of pregnancy, and of megestrol acetate supplementation on plasma progesterone during the second half of pregnancy, (2) analysis of the effects of an ovariectomy performed at 45 days on plasma progesterone production and on pregnancy and (3) analysis of the effects of an antiprolactin agent (cabergoline) at days 30 and 40 of pregnancy on progesterone secretion and pregnancy. These results were all compared with the normal plasma progesterone profiles during (a) pseudopregnancy and (b) pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)