The binding of 3H-labelled oestradiol- and progesterone-receptor complexes to hypothalamic chromatin of male and female sheep

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Abstract
Chromatin isolated from hypothalamic nuclei of sexually mature entire male and female sheep was linked to cellulose in UV light. The saturation binding of 3H-labeled estrogen- and progesterone-receptor complexes, prepared by (NH4)2SO4 precipitation from the 105,000 g supernatant of hypothalamic cytosol, was then measured in vitro in 0.15 M KCl. Saturation binding was also measured after extraction of histones and masking acidic proteins. Salt + urea was more effective than guanidine hydrochloride in unmasking receptor acceptor sites, and the binding of labeled receptor complexes to dehistonized unmasked chromatin was largely resistant to 0.4 M KCl extraction. Whereas extents of receptor-complex binding were similar to published values for comparable preparations of hen oviduct chromatin, no sex-related difference was observed. Binding of progesterone-receptor to chromatin was greater than that of estradiol-receptor. Binding also increased more after removal of histones and masking acidic proteins, suggesting the presence of a greater number of progesterone-receptor acceptor sites in hypothalamic chromatin than of estradiol-receptor acceptor sites. The failure to demonstrate a sex-related difference in estradiol-receptor binding to hypothalamic chromatin in vitro was discussed.