Histology and histochemistry of androgen-stimulated nuptial pads in the leopard frog, <i>Rana pipiens</i>, with notes on nuptial gland evolution

Abstract

Nuptial pads are digital specializations of male frogs that cycle with the reproductive season and are considered to function in mating. Glandular secretions of the nuptial pads were analyzed histochemically in androgen-stimulated overwintering leopard frogs, Rana pipiens, to provide information on gland function and physiological control. In castrated and sham-operated male frogs treated with testosterone cypionate, 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, and glands of cholesterol-treated castrates and intact controls appeared to be inactive cytochemically. Nuptial glands of frogs treated with 5-α-dihydrotestosterone were histologically similar to those of frogs treated with testosterone cypionate. Nuptial glands share structural and functional characteristics with integumentary mucous glands, and may have been modified evolutionary from that parent gland population.