Progestin receptors in dispersed rat anterior pituitary cells: Enriched binding in lactotrope fractions

Cytosolic progesterone and R5020 binding activities were demonstrated in Pronase-dispersed anterior pituitary cells from estrogenprimed ovariectomized and adrenalectomized rats. Pronase-dispersed pituitary cells were also separated into six cellular fractions on the basis of size and density by sedimentation velocity at unit gravity 1n a BSA gradient. Fractions enriched in lactotropes or gonadotropes were identified by the cellular contents of radioimmunoassayable prolactin and LH, respectively. Cytosollc progestin receptors appeared to be predominantly associated with lactotrope-rich fractions. Since there was some cross-over between the LH and prolactin enriched fractions, progestin receptors may also be associated with a subpopulation of gonadotropes, as well.