Epstein, M.S. and D.G. Blackburn (1997). Histochemistry of androgen-induced secretions of nuptial pads in the leopard frog, Rana pipiens, with notes on nuptial gland function and evolution. Canadian Journal of Zoology 75: 472-477.
Abstract: Nuptial pads are digital specializations of male frogs that cycle with the reproductive season, and that are thought to function in mating. Glandular secretions of the nuptial pads were analyzed histochemically in androgen- stimulated, overwintering Rana pipiens, to provide information on gland function and physiological control. In male frogs treated with testosterone cypionate (TC), the secretory product of the nuptial gland epithelium stained positive for carbohydrates and proteins, yet negative for lipids and glycogen. Secretions also stained positive for tyrosine residues, and negative for acidic mucosubstances, sulphated mucosubstances, tryptophan, and cystine. Castration prior to hormone treatment had no effect on gland staining properties, but glands of cholesterol-treated castrates and intact controls appeared to be inactive histochemically. Nuptial glands of frogs treated with 5 alpha- dihydrotestosterone (DHT) were histologically similar to those of TC-treated frogs. Nuptial glands share a variety of structural and functional characteristics with mucous glands of the skin, and probably have been modified evolutionarily from that parent gland population.