PROLACTIN RECEPTOR CONCENTRATIONS IN THE SKIN OF MINK DURING THE WINTER FUR GROWTH-CYCLE

The objectives of this study were to determine: 1) if the skin of mink might be a target organ for prolactin (PRL) by establishing if PRL bi nding sites (receptors) exist in the cell membranes of skin, and 2) if PRL receptor concentrations change during the onset and progression o f the winter fur growth cycle. Skin was collected on October 6, 1992 f or characterization of PRL receptors and from July through December 19 92 (N = 3 mink/month) to evaluate possible changes in PRL receptor con centrations during the fur growth cycle. PRL receptors were quantified using I-125- oPRL in a validated radioreceptor assay. Scatchard analy sis of saturation data revealed a single class of high-affinity (K-d = 5.21 x 10(-11) +/- .84 M), low capacity (B-max = 27.03 +/- 3.37 fmole s/mg) binding sites. Only oPRL (40% displacement) and to a lesser exte nt oGH (3% displacement) inhibited the binding of I-125-oPRL to mink s kin cell membranes. No inhibition of I-125-oPRL binding to membranes o ccurred in the presence of a 500-fold excess of bTSH or oLH, indicatin g that the receptors were hormone specific. Concentrations of I-125-oP RL receptors during the onset and development of winter fur growth (Ju ly through November) exhibited no significant change. However, followi ng completion of the winter fur growth cycle (December 1) PRL receptor concentration was significantly higher than all preceding months. The greater binding observed at that time may reflect a change in tissue sensitivity, in preparation for growth of the summer pelage. These dat a suggest to us that the skin of mink is a target organ for PRL and ar e consistent with the hypothesis that part of the affects of PRL on fu r growth occur directly at the level of the skin. (C) 1995 Wiley-Liss, Inc.