Catecholaminergic control of plasma growth hormone and thyrotropin levels in hypophysectomized rats bearing ectopic pituitary transplants

Transplantation of the anterior pituitary to an ectopic site leads to stimulation of PRL secretion and suppression of the release of other adenohypophyseal hormones. We have previously reported that precursors and blockers of catecholamine synthesis can affect PRL release from the ectopic pituitary. In the present study we have measured the effects of L-3,4-dihydroxyphenylalanine (DOPA), DL-threo-dihydroxyphenylserine (DOPS), alpha-methyl-para-tyrosine (alpha-mpt) and diethyldithiocarbamate (ddc) on plasma growth hormone (GH) and thyrotropin (TSH) levels in hypophysectomized rats with pituitary transplants under the renal capsule. In these animals, peripheral plasma GH levels were elevated by a precursor (DOPA) and reduced by a blocker (alpha-mpt) of catecholamine synthesis. Plasma TSH levels were increased by a precursor (DOPS) and reduced by a blocker (ddc) of norepinephrine synthesis. We suspect that GH and TSH present in the circulation of pituitary-grafted animals were derived, in part, from the ectopic pituitary tissue and suggest that the small but detectable secretion of hormones other than PRL in this animal model is under the control of endogenous catecholamines.