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THE EFFECTS OF ICI 33828 AND PROGESTERONE ON OESTROGEN-MAINTAINED CORPORA LUTEA IN THE SOW

Exogenous oestrogens maintain the corpora lutea (CL) in the cycling gilt (Gardner, First & Casida, 1963). The pituitary is required, since oestrogen will not maintain CL in the gilt in which the pituitary stalk has been transected (Anderson, Dyck, Mori, Henricks & Melampy, 1967). Oestrogen blocks pituitary LH and FSH release, and Rothchild (1966) has therefore suggested that increased prolactin release due to oestrogen may maintain the corpora lutea in the intact gilt. Prolactin, however, will not delay CL regression in the hypo-physectomized pig (Du Buisson, Leglise, Anderson & Rombauts, 1964). Since a single oestrogen injection was found to maintain CL in the sow (Nishikawa, 1959), oestrogen may stimulate a single release of a pituitary luteotrophin, induce a constant pituitary release of a luteotrophin, or act directly at the ovarian or uterine levels to effect