Amphibian pheromones and endocrine control of their secretion

Amphibian sex pheromones of 3 urodele (Cynops pyrrhogaster, C. ensicauda, and Plethodon jordani) and 1 anuran (Litoria splendida) species have been isolated and characterized and found to be either small peptides or larger proteins. Each pheromone secreted by the male acts on conspecific females. Endocrine control of pheromone secretion has been best studied in Cynops. The C. pyrrhogaster pheromone, sodefrin, and the C. ensicauda pheromone, silefrin, are generated from their precursor proteins. The sodefrin and silefrin precursor mRNA levels in the abdominal gland of the cloaca are elevated by prolactin and androgen. An increase in the level of both immunoassayable pheromones caused by treatment with these hormones has also been demonstrated. Receptors for both of these hormones have been localized in the abdominal gland. The discharge of sodefrin into the water is elicited by arginine vasotocin. The responsiveness of the female vomeronasal epithelial cells to sodefrin, as estimated by electro-olfactography, is enhanced markedly by a combination of prolactin and estrogen. Sodefrin elevates intracellular calcium levels in vomeronasal epithelial cells. The population of the sodefrin-responsive cells increases during the breeding period.