Maintenance of the Mammary Lobulo-Alveolar System in Rats After Adreno-Orchidectomy by Prolactin and Growth Hormone1

Four groups of mature male rats were adreno-orchidectomized and were injected subcutaneously, 4 times daily, for 10 days with .9 % saline, 15 IU prolactin (60 IU total) and 1 mg growth hormone (4 mg total), or with both hormones. An intact group and an orchidectomized group were given .9% saline. On the day after the last injection, the rats were killed and the mammary glands were removed, fixed, stained and examined for degree of development. The adreno-orchidectomized or orchidectomized rats given saline only showed complete disappearance of the mammary lobulo-alveolar system and atrophy of the ducts, when compared to the intact animals. Injections of either prolactin or growth hormone resulted mainly in maintenance of the mammary duct system in the adrenogonadectomized rats, whereas injections of prolactin and growth hormone together maintained the mammary lobulo-alveolar system in a state equal to that of the intact controls. These results indicate that the combination of prolactin and growth hormone can maintain mammary lobulo-alveolar development in male rats in the absence of gonadal or adrenal cortical hormones. (Endocrinology 76: 1220, 1965) R we reported that frequent injections of relatively large doses of prolactin and growth hormone could induce lobulo-alveolar mammary growth in adrenoovariectomized or adreno-ovariectomized, hypophysectomized rats (1). This followed a report (2), since confirmed by us (3), that pituitary "mammotropic" tumors (MtT.F4), could elicit mammary lobulo-alveolar growth in adreno-gonadectomized rats. These observations suggested, contrary to a widely held concept (4), that estrogen and progesterone are not essential for mammary lobulo-alveolar growth in rats, and that such growth can be elicited by prolactin and growth hormone alone. The mammary glands of mature male rats are characterized by the presence of dense clusters of alveoli and thickened ducts with relatively little branching (5); in contrast, the mammary glands of mature virgin female rats have a more extensively deReceived December 21, 1964. 1 This work was supported in part by grants from the NIH (AM 4784-05), the Michigan Cancer Foundation, and by an Institutional Research Grant from the American Cancer Society. Published with approval of the Michigan Agricultural Experiment Station as Journal Article No. 3540. veloped duct system, but there are usually few or no alveoli present. The mammary glands of male rats have been reported to undergo marked regression after orchidectomy (6). It was of interest to determine whether frequent injections of relatively large doses of prolactin and growth hormone could maintain lobulo-alveolar development in male rats after adreno-orchidectomy. Materials and Methods Carworth CFN male rats, 4-6 months old, were divided into 6 groups of 8-17 each. Four groups were adrenalectomized and orchidectomized on the same day, 1 group was orchidectomized only and 1 group was permitted to remain intact. Beginning on the day after surgery, the rats were each injected subcutaneously, 4 times daily for 10 days, with .9% saline, 15 IU prolactin (60 IU total), 1 mg growth hormone (4 mg total), or with both 15 IU prolactin and 1 mg growth hormone. The injections were given each day at 8 AM, 1 PM, 5 PM, and 10 PM. All rats were fed ad lib. on Wayne Lab-Blox pellets, and the adreno-orchidectomized rats were given 1% saline in their drinking water. The rats were maintained in an air-conditioned room at a temperature of 75 +1 C. 2 Prolactin (22.5 IU/mg) was kindly provided by Dr. A. Borman, E. R. Squibb and Son, New Brunswick, N. J.; and STH by the Endocrinology Study Section, NIH.