Localisation of receptors for prolactin in ovine skin

Abstract

Abstract Although prolactin (PRL) receptors are found in many mammalian tissues, specific PRL binding to mammalian skin has not been demonstrated. In view of the temporal relationships observed between photoperiod, circulating PRL and pelage replacement in seasonally responsive mammals, we sought to provide evidence of PRL receptors in ovine skin. Cryosections of skin from New Zealand Wiltshire ewes were incubated with radiolabelled human GH (125I-hGH) and ovine PRL (125I-oPRL) in the presence and absence of excess unlabelled hormones (hGH, oPRL or ovine GH (oGH)). Binding was inhibited by unlabelled oPRL and hGH but not by oGH. In microautoradiographs, both radioligands were localised most strongly in the dermal papillae of wool follicles in the anagen (growth) phase of the hair cycle and in apocrine sweat glands. Higher levels of specific binding to dermal papilla cells, compared with the follicle epithelial matrix and the surrounding dermis, were confirmed by measurement of microautoradiograph silver grain density (respectively, 34·±3·0, 11·4±1·0 and 5·5±0·5 grains per 100 μm2 (mean±s.e.m., n=10)). Total binding for 125IhGH and 125I-oPRL radioligands to follicle dermal papilla was not significantly different (34·1±3·0 vs 43·6±2·5 grains per 100 μm2, n=10) but the level of non-specific binding of 125I-oPRL was higher than for 125I-hGH (18·9±1·4 vs 6·1±0·6 grains per 100 μm2, n=10; (P<0·001). Binding assays of receptors in crude microsomal membranes extracted from ovine skin were used to ascertain binding capacity and specificity. Scatchard analysis yielded a dissociation constant (3·9 nm) and receptor concentration (2·22 pmol/mg protein) similar to that reported for ovine mammary gland. These results provide evidence for the presence of PRL receptors in ovine skin and are consistent with the hypothesis that PRL has a direct role in mediating wool follicle activity. Journal of Endocrinology (1995) 144, 143–151