The effects of thyroidectomy on androgen and prolactin receptors in the dorsal skin and caudal fin of Triturus cristatus carnifex

Targeted expression of androgen receptors in tooth-forming tissues of a neotropical salamander (Bolitoglossa schizodactyla) enables region-specific formation of dimorphic types of teeth in the male

Bicuspid teeth are a morphological characteristic in adult metamorphosed urodeles. However, during the mating season the males of many species of plethodontid salamanders (Urodela, Plethodontidae) from northern America bear large monocuspid teeth on their jaws. Since androgen levels are elevated during the mating season, it is likely that the formation of monocuspid teeth is controlled by androgens. However, many plethodontid salamanders from southern Central America live in habitats which lack significant seasonal changes and therefore are no seasonal breeders. These males constantly bear monocuspid teeth, however their presence is restricted to the premaxillary bone, which forms the most frontal element of the upper jaw. Teeth of all other dentigerous bones are bicuspid. This study is based on an immunohistochemical localisation of androgen receptors and reveals a differential expression of androgen receptors in the three separate dental laminae of the upper jaw of Bolitoglossa schizodactyla (Urodela, Plethodontidae) from western Panama. Our findings suggest that the restriction of androgen receptor expression to the premaxillary dental lamina of the male and its absence in all other tooth-forming tissues leads to the differences in tooth morphogenesis. In conclusion, a differential and cell-specific expression of androgen receptors in urodeles-similar to the situation in mammalian species-allows a selective response of differentiating tissues to the hormonal status of the animal.

Effect of hypophysectomy, replacement therapy with ovine prolactin, and cortisol and triiodothyronine treatment on prolactin receptors of the tilapia (Oreochromis mossambicus)

The effects of hypophysectomy and subsequent replacement therapy with ovine prolactin (oPRL) on specific binding of 125I-oPRL to gill, kidney, and liver membranes of male tilapia were examined. The possible control of prolactin receptors by cortisol (F) and triiodothyronine (T3) was also studied using intact animals. In gill and kidney, hypophysectomy resulted in a significant decrease in specific binding that was partially restored (threefold increase) by three injections of oPRL, suggesting a role of the pituitary in the control of prolactin receptors. However, removal of the pituitary and replacement therapy with oPRL had no effect on binding by liver membranes. Cortisol and T3 treatment, alone or in combination, did not significantly affect prolactin binding by any of the tissues tested.

Prolactin receptors in liver, kidney, and gill of the tilapia (Oreochromis mossambicus): characterization and effect of salinity on specific binding of iodinated ovine prolactin

Specific binding of 125I-ovine prolactin (oPRL) to microsomal fractions from gill, kidney, and liver of adult tilapia was determined. Specific binding varied among tissues, the highest values being displayed by kidney membranes. In the liver, the binding of oPRL was not strongly displaced by tilapia prolactins (tPRL177 and tPRL188), although tPRL177 was six times more potent than tPRL188. On the other hand, in kidney and gill membranes, the two tPRLs were equipotent. Tilapia PRLs showed low potency in competing for oPRL-binding sites when pregnant rat liver membranes were utilized. Tilapia growth hormone (tGH) and human growth hormone (hGH) displaced 125I-oPRL from liver as well as did tPRL177 but were not recognized well by renal or branchial receptors. Two 125I-oPRL-binding sites were detected in every tissue tested. These binding sites are subject to physiological regulation since adaptation to seawater resulted in a significant decrease in specific binding.

Seasonal variations in the effect of prolactin on the short-circuit current across bullfrog skin

The effect of serosal application of ovine prolactin (PRL) on the short-circuit current (SCC) across the abdominal skin of larval or adult Rana catesbeiana was compared between two seasons, spring-summer and autumn-winter. Prolactin induced a transient increase in SCC in Cl-Ringer's solution, to a greater extent in spring-summer than in autumn-winter. The skin of stage XXV frogs was more sensitive to PRL than the skin of adult frogs. On the other hand, PRL had no effect on SCC in SO4-Ringer's solution either in summer or in autumn.

Androgen binding in the skin of mature male brown trout, Salmo trutta L

Specific, saturable binding of [3H]testosterone (Kd = 12.5 nM, Nmax = 1.1 pmol mg-1 protein) has been identified in skin cytosol of mature male brown trout. Binding with this affinity and capacity resembles more closely that observed in the plasma of mature male brown trout (Kd = 20.6 nM, Nmax = 6.6 pmol mg-1 protein) than that expected of a specific steroid receptor. However, the fraction of skin cytosol precipitating with 30% ammonium sulphate has a higher affinity for testosterone (Kd = 1.9 nM) and a lower capacity (Nmax = 96.3 fmol mg-1 protein) than does whole cytosol. Furthermore, the high-salt extract of crude skin nuclear pellet binds [3H]testosterone with affinity (Kd = 1.3 nM) and capacity (Nmax = 69.4 fmol mg-1 protein) similar to those of ammonium sulphate-precipitated cytosol. Specific binding in all three fractions of skin is abolished by treatment with proteolytic enzymes and a component of both cytosol and nuclear extract, which binds [3H]testosterone specifically, is retained on DNA-cellulose columns, eluting with high-salt buffer. Specifically bound [3H]testosterone is displaced most efficiently by testosterone. 5 alpha-dihydrotestosterone, estradiol-17 beta, and 11-ketotestosterone also compete but are 5- to 10-fold less potent. Consistent and reproducible binding of [3H]11-ketotestosterone to skin cytosol fractions or nuclear extract could not be demonstrated. It is concluded that testosterone binding with the above characteristics partially fulfills the criteria required of a putative steroid hormone receptor. The results are discussed with reference to the relative roles of testosterone and 11-ketotestosterone during sexual maturation.

Prolactin binding sites in Xenopus laevis tissues: comparison between normal and dehydrated animals

The binding of 125I-labeled ovine prolactin (125I-oPRL) to membranes from the kidney, epidermis, liver, and testis of Xenopus laevis adult specimens either kept in an aquatic environment or exposed for 2 weeks to dehydrating conditions was studied. Prolactin binding specificity was assayed through competition with several unlabeled hormones (oPRL, hGH, rGH, rLH, and porcine insulin). In the animal exposed to dehydrating conditions a statistically highly significant reduction in prolactin binding to the membranes from the kidney and epidermis was recorded. No significant variations were revealed by the membranes from the liver and testis. The reduction detected in the binding of 125I-oPRL is not related to the dissociation constant, but to the number of PRL binding sites. Since PRL ranks among the few peptide hormones whose rise in the bloodstream promotes an increase in the number of their own receptors, the reduction of its binding sites in Xenopus specimens exposed to dehydration might lend some support to our earlier hypothesis that transfer to a dehydrating environment may bring about, in this totally aquatic species, some decrease in the blood PRL levels.