EVIDENCE FOR AN INFLUENCE OF MAMMARY TUMOUR VIRUS ON PROLACTIN SECRETION IN THE MOUSE

Abstract

SUMMARY The mouse mammary tumour virus (MTV) is usually transmitted through milk. Foster-nursing the young of the C3H/He strain, which carries MTV in its milk, on C57BL/He dams (an MTV-negative strain) prevents infection with the milk-borne MTV and significantly alters the natural incidence of mammary tumours in the former, and vice versa. The influence of foster-nursing on prolactin secretion in C3H and C57BL mice has been examined, using two sub-strains of these mice, one maintained by Heston and the other by Strong. Prolactin levels were compared after inducing acute prolactin release with perphenazine. The MTV-positive C3H mice of both sub-strains, had prolactin levels substantially lower than those in the MTV-negative C57BL sub-strains, basally and after perphenazine administration. Foster-nursing the young of the C3H strain with dams of the C57BL strain and vice versa significantly altered this characteristic pattern of prolactin secretion. A brief pre-exposure of C3H young to the milk of their own mothers virtually abolished the effect of foster-nursing. The results showed a marked influence of the strain of the nursing mother on the adult pattern of prolactin secretion, and suggested that the milk-borne MTV may have a role in the regulation of prolactin secretion in some strains of mice. The foster-nursing-induced differences in serum prolactin patterns elicited by perphenazine were unrelated to the amount of prolactin depleted from the pituitary gland and this suggests that the metabolism of the hormone may differ in mouse strains positive and negative for certain types of MTV.