Evidence for Photoperiodic Control of Prolactin Release in Rams

Prolactin is known to increase the effect of testosterone on male accessory sex glands (Segaloff, Steelman & Flores, 1956), and to have a synergistic action with LH on spermatogenesis (Bartke, 1971) and on testicular androgen secretion (Hafiez, Bartke & Lloyd, 1972). It has been shown also that the male pituitary releases prolactin into the blood in the rat (Amenomori, Chen & Meites, 1970) and the human (Jacobs, Mariz & Daughaday, 1972). Little is known, however, about factors which regulate prolactin secretion in this sex. In the female rat, antagonism between prolactin and gonadotrophin secretion has been shown following drug treatment (Ben-David, Danon & Sulman, 1971). It is also suggested by the fact that ovariectomy produces a decrease in serum prolactin (Amenomori et al., 1970), an effect which is the reverse of the classical increase of FSH and LH