studies on the ?venom? emission from the skin of (Bonaparte) (Amphibia Anura Discoglossidae)

Granular gland discharge from the skin of Bombina variegata pachypus was studied using a simple quantitative colorimetric method. Both acetylcholine and carbachol failed to stimulate discharge, while noradrenaline (NA) caused a dose-dependent one, which was antagonized by phentolamine, an alpha-adrenoceptor blocking agent. Beta-adrenoceptor stimulation with isoprenaline did not cause any detectable emission itself, but significantly reduced that induced by NA. Emission was dependent on extracellular calcium concentrations. It is concluded that in B. variegata the mechanism controlling the skin “venom” emission is of an adrenergic nature, i.e. is stimulated by alpha- and inhibited by beta-adrenoceptor stimulation. This mechanism represents an early step in anuran phylogenesis due to the low systematic position of Bombina.