Steroid Hormone Uptake by Anterior Pituitary Cell Suspensions11

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Abstract
Anterior pituitary glands from 7–day ovariectomized rats were serrated and digested with 0.05% pronase in calcium—magnesium free Hanks' medium (CMFH). Cells dispersed in CMFH contained characteristic secretory granules and had RNA/DNA and protein DNA ratios similar to those of intact pituitary tissue. When a constant number of cells was incubated with increasing concentrations of 3H-estradiol, uptake and retention of 3H-estradiol resulted from specific and nonspecific binding processes. The specific component had a high affinity (KA = 2.3 X 109M-1) and low capacity for estradiol (0.0029 pmole/Mg DNA). The nonspecific component had a lower affinity for 3H-estradiol and was not saturable using concentrations of estradiol up to 1.55 X 10-8M. Nonspecific uptake was greatly reduced when 3H-estradiol was bound to BSA before incubation with cells. Scatchard plot data for specific binding indicated there are ∼19000 binding sites per cell (10.8 pg DNA). Pituitary cells concentrated 3H-estradiol rapidly at 37 C, and peak uptake occurred by 20 min. Nuclear uptake and retention increased gradually and peaked at 30 min when 66% of the cellular radioactivity was localized in the nuclear fraction. Nonestrogenic hormones (3H-progesterone, 3H-testosterone and 3H-corticosterone) were not retained by cells to the extent that 3H-estradiol was, and only a small fraction of the nonestrogenic hormones was bound by the nuclear fraction. All 3H-hormones were metabolized to some extent by cells, with 3Hprogesterone being most actively metabolized. Thus, cell suspensions have confirmed the presence of an estrogen—binding system in the anterior pituitary gland which functions to transport and concentrate estradiol in the nuclear fraction. (Endocrinology92: 94, 1973)

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