Melanophore stimulating hormone (MSH) release: inhibition by cytochalasin B and "stimulation" by dimethyl sulfoxide.

Incubation of rat or frog pituitaries in cytochalasin B (10-4 minus 10-8 g/ml) for 2, 4 or 6 hr produces a time-dependent inhibition of MSH release. This inhibition is reversible and, again, time-dependent since longer incubations of pituitaries returned to normal media result in greater hormone secretion. Cytochalasin B inhibits MSH release even at a high concentration (10%) of dimethylsulfoxide (DMSO) which, itself, is "stimulatory" to hormone release. MSH release in high DMSO concentration is also inhibited by ouabain or by the absence of Ca2+ from the medium. In amphibian Ringer enriched with glucose, and in Medium 199, cytochalasin B fails to inhibit the release of MSH from the frog pituitary. Colchicine, vinblastine, and vincristine (10-3 minus 10-6 g/ml) were without effect on MSH release. These data suggest a possible role for microfilaments in the control of MSH release but fail to provide information on the exact nature of the mechanisms involved.