Receptors for sex hormones in the skin of the amphibia

Androgen receptors in two androgen-mediated, sexually dimorphic characters of frogs

The presence/absence of androgen receptors is examined in two sexually dimorphic features of frogs: the nuptial pad and the external oblique muscle. Immunohistochemistry reveals that both males and females possess androgen receptors in these tissues. Males have a higher density of immunopositive nuclei in the oblique muscle than do females. The presence of androgen receptors in both male and female tissues is consistent with results from hormone experiments in which androgen supplements induce the expression of a nuptial pad and enlarge the external oblique muscles in castrated males and ovariectomized females.

Fine structure of nuptial pad surface of male ranid frogs

The nuptial pad, a cutaneous secondary sexual characteristic, developed on the ventrolateral aspect of the first digit (the thumb) of the male ranid frogs was observed. Under scanning electron microscopy, numerous small elevations were observed rising above the pad's surface; they were rounded in Rana brevipoda porosa and R. rugosa, conical in R. nigromaculata, and rather tall and gradually tapering in R. ornativentris. These elevations were densely crowded, and in some cases several elevations were seen to have fused to form ridges in the R. rugosa pads. Accessory microprocesses completely covered the outermost layer of cells of the elevations. Numerous pile-like microprocesses gradually shortened from the top toward the side of the elevation in R. ornativentris and R. nigromaculata. Those on the top were noticeably longer than those on the side in R. rugosa. The bundles of thick processes radically projected above the top in R. brevipoda porosa. In R. brevipoda porosa nuptial pads were observed under transmission electron microscopy, and the outermost monolayer cells of an elevation were usually keratinized, devoid of organelles and containing closely packed, fine filaments within a dense matrix. The accessory processes also contained dense fibrous matrices.

Induction of cloacal and dermal skin glands of tiger salamander larvae, (Ambystoma tigrinum): effects of testosterone and prolactin

Treatment of male and female tiger salamander larvae with testosterone (0.3 micrograms/g body weight/day) induced precocious formation of ventral cloacal glands and stimulated proliferation and differentiation of mucous and granular (serous) glands in the ventral dermis of the skin. Lower doses of testosterone produced no visible glandular effects but did cause hyperemia and edema in the cloacal region. Prolactin (0.5 micrograms/g body weight/day) enhanced the action of testosterone on the cloacal glands, increasing both the amount of gland induced and the degree of glandular secretion. There was no apparent effect of prolactin alone on cloacal glands or any effect of prolactin with or without testosterone on the dermal glands. The possible homology of the amphibian ventral cloacal gland to the mammalian prostate gland is discussed.

Prolactin receptors in the male Rana esculenta

The binding of 125I-labeled ovine prolactin (oPRL) to membrane preparations of several tissues from the male green frog, Rana esculenta, collected during the year is reported. PRL binding to kidney fractions was generally high (range 5-45%). A maximum was observed in the month of October, whereas the lowest value was found during the summer season. The binding to skin fractions was equally high (range 5-25%) and the annual profile parallels that of renal fractions. In the liver, a lower specific binding (range 3-4%) occurred consistently during the year, whereas no detectable binding was found in the muscle. The 125I-oPRL binding was inhibited by oPRL and oGH but not by oFSH or oLH. Scatchard analysis gave dissociation constants of 0.4-1 x 10(-10) M and binding capacity of about 20 fmol/mg of membrane proteins was observed in both the skin and kidney fractions. No receptor sites were detectable in 30-day hypophysectomized animals. The administration of oPRL or a crude homogenate of the frog hypophysis induced the appearance of specific PRL binding. Testosterone is able to restore prolactin binding in hypophysectomized animals, as PRL treatment does.

Androgen sensitivity of skeletal muscle: nondependence on the motor nerve in the frog forearm

The effects of castration and of subsequent androgen administration on fiber size were investigated in several frog skeletal muscles. Four months after castration, cross-sectional cell area decreased by 70% and 14%, respectively, in the flexor carpi radialis and flexor carpi centralis muscles of the forearm and only by 2% in the ileo fibularis muscle of the thigh. Injection of testosterone propionate induced a hypertrophic response that reversed the effects of androgen deprivation; after 6 weeks, complete recovery to the control value was observed in all muscles selected. This sensitivity to the exogenous androgen was not altered by denervation; a similar hypertrophic evolution was seen in the denervated right muscles and in the homologous intact left muscles of the forearms. Using the myosin ATPase reaction, the muscle histochemical patterns were unchanged in all conditions tested. These results suggest that (i) a gradient of sensitivity to androgens exists in different frog muscles; (ii) androgens control the myofiber size but not the nerve-muscle organization as can be seen from the myofibrillar ATPase pattern; and (iii) the androgen sensitivity is not dependent on the motor nerve.

Sex steroid binding proteins in non-mammalian vertebrates

High affinity cytosolic and nuclear steroid binding macromolecules have been identified in steroid target tissues of representative amphibians, reptiles and birds. In addition to these traditional "receptors" evidence exists which indicates the presence of other steroid binding proteins, varying in affinity and specificity, in the cytosol of steroid targets (liver, oviduct) of these same species. The possible relationships between cytosolic binding proteins of differing affinity and specificity and their relevance to hormone action in non-mammalian species is discussed.