Saturable binding of [3H]-promegestone in sheep liver cytosol is not to receptors for progesterone or glucocorticoids.

Saturable, high affinity binding of [3H]-promegestone has been observed in sheep liver cytosol. In two tissues specimens the Kd values were 5.9 and 6.3 nmol/l, and the concentrations of binding sites were 84.5 and 66.2 pmol/g wet tissue respectively. The synthetic steroids methyltrienolone and ORG 2058 were capable of some degree of competition. Progesterone was a weak competitor; cortisol, dexamethasone and testosterone were ineffective. Bound promegestone in liver cytosol was taken up by liver nuclei, but not by sheep uterine nuclei. These promegestone-binding sites are neither progesterone or glucocorticoid receptors.