PARTICULARITY OF THE PLASMA HORMONAL LEVELS DURING CYCLE, PREGNANCY AND PSEUDOPREGNANCY IN THE RAT

In the rat, the sexual cycle is short, characterised by the lack of luteal phase: which appears during pseudopregnancy. During pregnancy, plasma progesterone levels, especially high in this species, shows two successive waves: the first one is essentially dependent on the luteotropic action of prolactine, whose secretion is biphasic, semi-circadian. The LH acts also from 8th to 11th days of pregnancy: then luteotropic activity depends specifically on the placental harmones (rPL), and may be also on the rCG. Oestrogens have also a luteotropic effect during the greater part of pregnancy. Then the authors consider androgenic secretion, since the factors can influence the important variations in progresterone and prolactine levels. During pseudopregnancy, progesterone levels are the same as during pregnancy until the 11th day, and then break down: luteolysis depends on PGF2a.