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.