Progestin Receptors in the Brain and Pituitary of the Bonnet Monkey (Macaca radiata): Differences between the Monkey and the Rat in the Distribution of Progestin Receptors*

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Abstract
Using the radiolabeled synthetic progestin [3H] R5020, putative progestin receptors have been identified by Sephadex LH-20 gel filtration and density gradient centrifugation in soluble cytosol fractions of uterus, pituitary gland, and brain of the bonnet monkey (Macaca radiata). These receptors had a high affinity for [3H]R5020 (Kd = 0.3 nm) and sedimented at 6–7S in 10% glycerol, 5–20% sucrose gradients. [3H]R5020 binding was inhibited more than 70% by 25-fold molar excesses of progesterone or other physiologically active synthetic progestins but was unaffected by estradiol, corticosterone, dexamethasone, or testosterone. In ovariectomized monkeys, the progestin receptors were restricted to the hypothalamus and preoptic area; no receptors were detected in cingulate or parietal cortex, amygdala, midbrain, brainstem, or cerebellum. When ovariectomized monkeys were implanted with estradiol-containing Silastic capsules to generate serum levels of this hormone in the physiological range, cytosol progestin receptor levels were elevated by 10-fold in the uterus and pituitary gland and by 3-fold in the hypothalamus. However, there was no effect of the estrogen treatment on receptor levels in any other brain region studied. In the rat, on the other hand, physicochemically similar progestin receptors are present not only in the uterus, pituitary, hypothalamus, and preoptic area but also in cortex, amygdala and midbrain. Furthermore, estradiol replacement to ovariectomized rats induces a 2- to 3-fold elevation in receptor levels in both the hypothalamus and preoptic area. These results indicate that, although physicochemically similar, progestin receptors may have strikingly different distribution profiles in the primate and rodent brain. These differences may reflect a divergence between rodents and primates in the sites of ovarian steroid hormone feedback on brain and pituitary function. (Endocrinology 106: 185, 1980)