Ovarian Secretion of Oestradiol, Oestrone, 20-Dihydroprogesterone and Progesterone During the Oestrous Cycle of the Guinea-Pig

The guinea-pig has an oestrous cycle of 16 to 18 days. Many original observations in reproductive endocrinology such as formation of deciduoma in response to trauma (Loeb, 1907), existence of the oestrous cycle (Stockard & Papanicolaou, 1917) and the ability of the uterus to modify luteal function (Loeb, 1923) involved the guinea-pig as the experimental animal. Several studies have delineated the pattern of progesterone secretion during the oestrous cycle of guinea-pigs (Heap, Perry & Rowlands, 1967; Feder, Resko & Goy, 1968; Challis, Heap & Illingworth, 1971; Blatchley, Donovan, Horton & Poyser, 1972) but comparative changes in the secretion of oestrogens have received very little attention. Challis et al. (1971) attempted to measure total oestrogens by radioimmunoassay in the peripheral plasma, but failed to detect any due to their very low levels. In the present study, we determined