Further Observations on the Hormonal Regulation of α-Glycerolphosphate Dehydrogenase in Rat Mammary Gland: A Possible Role for Prolactin and Thyrotropin

The roles of prolactin and thyrotropin (TSH) in the regulation of alpha-glycerolphosphate dehydrogenase (alpha-GPDH) activity in rat mammary gland were investigated by the administration of thyroid releasing hormone, bromocriptine, prolactin, TSH and triiodothyronine (T3). TRH administration failed to induce alterations in the glands from intact animals but stimulated the activity in castrated and adrenalectomized animals. Bromocriptine administration was without any effect in either group of animals. Administration of ovine prolactin to hypophysectomized rats did not affect the activity, on the other hand, treatment with either TSH or T3 resulted in a highly significant increase in the activity. Combined administration of prolactin and TSH to hypophysectomized animals showed that prolactin is capable of partially inhibiting the TSH-induced increase. It is suggested that glucocorticoids exert primary control over the enzyme's activity with the pituitary hormones only playing a permissive role in its regulation.