The physiological role of prolactin in male mammals is virtually unknown. However, in genetically sterile dwarf mice prolactin was demonstrated to promote male fertility (Bartke, 1966). The possibility of an influence of prolactin on the growth of male accessory sex organs was reported in the rat, the mouse and the guinea-pig (Meites & Nicoll, 1966; Morrison & Johnson, 1966). Seminal vesicles of the male mouse were enlarged by a 'mammotropic' tumour, probably secreting massive amounts of prolactin (Haran-Ghera, 1966). The present work was undertaken to test the effects of a relatively low dose of prolactin from a single pituitary homograft on the weight of the seminal vesicles and penis in castrated laboratory mice.
The mice were from five genetically different strains: three from our colony, Outbred strain, inbred E strain and F 1 mice from a cross of inbred strains P and E (Krzanowska, 1965) and two from strains brought