PROGESTIN-INDUCED HYPERSECRETION OF GROWTH-HORMONE - AN INTRODUCTORY REVIEW

In the 1970s acromegalic features were reported in some dogs used in l ong-term toxicity studies of progestins. In 1980 confirmation that pro gestagen administration can lead to increased circulating growth hormo ne (GH) concentrations was obtained. This phenomenon appeared not to b e confined to exogenous progestins, for an excess of GH was also found in bitches during the luteal phase of the oestrous cycle. In bitches with a progestin-induced excess of GH, GH secretion could neither be i nhibited nor stimulated by well-known regulatory neurohormones, indica ting autonomous secretion. Because it could not be attributed to a neo plasm and was reversible, an extra-pituitary site of GH production was investigated. The progestin-induced GH was found to originate from th e mammary gland. This phenomenon seems to play a role in the mammary d evelopment that occurs during the luteal phase of the oestrous cycle. The increase in cell proliferative activity may also be responsible fo r the susceptibility of the mammary gland to neoplastic transformation . The discovery of mammary GH in the dog has recently become of wider importance now that expression of the GH gene has also been demonstrat ed in other species, namely, humans and cats.