Integrated nature of chromatophore responses in the in vitro frog skin bioassay.

Abstract

A cytological analysis of the in vitro response of frog skin chromatophores to hormonal and pharmacological agents is presented. The significance of the diverse chromatophore responses to stimulation is discussed in light of interpretations that might erroneously be drawn from objective photometric measurements as in the frog skin bioassay. Melanophorestimulating hormone (MSH) disperses melanin granules within both dermal and epidermal melanophores; the previously dispersed reflecting platelets within iridophores become aggregated. Acetylcholine lightens MSH-darkened skin to a near pre-MSH level by reversing the action of MSH on all chromatophores. Melatonin and norepinephrine only weakly reverse the darkening action of MSH on frog skin as not all chromatophores respond to these agents. Melatonin causes melanin granule aggregation within only a small number of localized dermal melanophores and is without effect on iridophores. Norepinephrine, unlike melatonin, but like acetylcholine, redisperses the refle...