The CRF-related peptide sauvagine stimulates and the GABA B receptor agonist baclofen inhibits cyclic-AMP production in melanotrope cells of Xenopus laevis

Abstract

Release of α-MSH from the pars intermedia melanotrope cells of Xenopus laevis is regulated by various classical neurotransmitters and neuropeptides. We have examined the effect of two of these regulatory substances, the neurotransmitter GABA and the CRF-related peptide sauvagine, on the adenylate cyclase system of the melanotrope cells. Sauvagine treatment, which stimulates α-MSH release, lead to an elevation in the level of cyclic-AMP, an effect which was potentiated by cholera toxin. Treatment with baclofen, a GABA B receptor agonist, gave a pertussis toxin-sensitive decrease in the cyclic-AMP level and an inhibition of α-MSH release. We conclude that sauvagine stimulates α-MSH secretion through activation of adenylate cyclase and that GABA B receptor activation inhibits secretion through inhibition of cyclic-AMP production. Baclofen treatment sensitized melanotrope cells to the stimulatory action of 8-bromo-cyclic-AMP on the secretion of α-MSH. This observation supports the conclusion that GABA B receptor activation inhibits cyclic-AMP production.