Abstract
Thyrotropin-releasing hormone (TRH) is a potent stimulator of melanotropin (α-MSH) release from pituitary melanotrophs in pig, frog, and fish. Concurrently, it has recently been shown that injection of TRH induces skin darkening in the lizard Anolis carolinensis ( Licht and Denver, 1988). In the present study, we have thus investigated in vitro the possible effect of TRH on α-MSH release from the lizard ( Lacerta vivipara) neurointermediate lobe, by means of the perifusion technique. Using our radioimmunoassay procedure, we found that serial dilutions of L. vivipara NIL extracts and synthetic α-MSH gave parallel binding curves. Administration of graded doses of TRH (10 −8–10 −6 M) did not cause any modification of α-MSH release. In contrast, infusion of a depolarizing concentration of K + induced a robust stimulation of α-MSH secretion. These results indicate that, in the lizard L. vivipara, the neuropeptide TRH does not stimulate pituitary melanotrophs.
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