Abstract
Monoamine-depleting drugs (reserpine; α-methyl- m-tyrosine) were administered to normal “bleached” Bufo arenarum toads and appreciable increases in the melanophore index (MI) were observed. These drugs failed to increase the MI of hypophysectomized animals. Monoamine-increasing drugs (nialamide and dihydroxyphenyl-alanine) produced marked decrease in the MI of normal “darkened” toads as well as in animals darkened by adrenalectomy, hypothalamic transection, and both adrenalectomy and hypothalamic transection. No bleaching action of these drugs was observed when administered in hypophysectomized toads darkened with ACTH. Guanethidine produced an initial decrease in the MI followed by an increase to pre-injection values. The importance of monoamines (specially adrenal and nervous catecholamines) in the regulation of the activity of the pars intermedia of the pituitary is emphasized. Evidence is discussed indicating that the control exerted by the hypothalamus on the intermediate lobe is achieved through monoamines released into the pars intermedia instead of by other neurosceretory products.
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