UPTAKE OF LABELLED HUMAN CHORIONIC GONADOTROPHIN IN THE BRAIN OF THE ADULT FEMALE RAT

Abstract

ABSTRACT 125I, 125I-bovine serum albumin (BSA) and 125I-human chorionic gonadotrophin (HCG) were injected intravenously into adult female rats, and the radioactivity in the brain tissues was determined at 1, 2.5 and 4 h. Two and a half and 4 h after the injection of 125I-HCG, the radioactivity in the median eminence was significantly higher than in other tissues investigated, i. e. the anterior, middle and posterior hypothalamus, amygdala and cerebral cortex. Among the latter tissues no differences were found at any time. The radioactivity ratio of the median eminence to the cerebral cortex or plasma after the injection of 125I-HCG increased with time and at 4 h was significantly higher than after the injection of 125I-BSA. Following the administration of 1251 or 125I-BSA, no differences were found in radioactivity among the brain tissues at any time. A considerably higher uptake of radioactivity was observed in the ovary of the same animals 2.5 and 4 h after the injection of 125I-HCG, as compared to that after the injection of 125I or 125I-BSA. This may indicate that labelled HCG well retains its biologocal activity. Most of the radioactive materials taken up in the tissues following the injection of 125I-HCG was shown immunologically to be HCG. These results may indicate that the median eminence has a characteristic ability to take up and retain HCG. This is consistent with current evidence for the internal or short feedback of gonadotrophin to the median eminence.