ESTROGEN RECEPTOR CONTENT OF REGIONS OF THE HYPOTHALAMUS AND PITUITARY OF THE GILT FROM FOUR TO TWENTY-EIGHT WEEKS OF AGE

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Estradiol-17β receptors (E2R) in 100 000 × g supernatant fractions from the hypothalamus and pituitary were determined for groups of five gilts, slaughtered at 4-wk intervals from 4 to 28 wk of age. Tissue samples were separated into the anterior hypothalamus (AH), the central hypothalamus (CH), posterior hypothalamus (PH), anterior pituitary (AP) and posterior pituitary (PP). After saturation binding assays were conducted, E2R concentrations were determined by Scatchard analysis. When expressed on a fmol mg−1 protein basis there was no increase in receptor concentration with age (P > 0.05); however, AP had higher concentrations of receptors than the AH, CH or PH (10.6 ± 1.4 vs. 6.5 ± 0.9, 6.7 ± 0.7 and 6.2 ± 0.6, P < 0.01). Posterior pituitary receptor levels remained low during maturation of the gilt with affinity constant (Ka) values similar to that obtained for the AP. Affinity constant values were found not to change with age; however, AP values were greater than that of the hypothalamus samples (55.2 ± 2.7 vs. 4.8 ± 0.2, × 108M−1). On a total tissue basis AH and CH had significant increases in receptor content from 4 to 28 wk (41.4 to 138.2 and 31.6 to 163.4 fmol, P < 0.05). It was also determined that the soluble protein content per gram wet tissue decreased with age in all regions of the hypothalamus and therefore may mask increases in receptor numbers. Keywords: Estradiol, receptor, gilt, hypothalamus, pituitary, swine