AUTORADIOGRAPHIC STUDIES ON NUCLEAR DNA AND RNA SYNTHESIS IN THE ADENOHYPOPHYSIS OF CASTRATED RATS

Abstract

ABSTRACT DNA and RNA synthesis was studied autoradiographically; 5 groups of cells were observed in the adenohypophysis of rats (gonadotrophs, thyrotrophs, acidophils, small and large chromophobes) 1, 2, 4 and 8 weeks following castration and the results compared with those obtained in control animals. The proliferation of cells in the anterior lobe of the hypophysis, determined by the incorporation of isotopically labelled 3H-thymidine into the nuclei of parenchymal cells, increases by 6 fold about two weeks after castration and returns to a normal level eight weeks after the operation. The number of silver grains/μm2 nuclear area =mean silver grain density (SGD) shows a doubling of the DNA-synthesis rate (= new formation/unit of time) two weeks following castration. This result agrees with a shortening of the DNA synthesis time – and very likely also of the G2 phase and the length of mitosis – to such an extent as to be characteristic for rapidly proliferating tissues. This effect on the mode of proliferation is reversible and normalized by the end of the experiment, i. e. eight weeks following castration. After the operation there is a more marked proliferation of the gonadotrophs than the chromophobic cells. RNA synthesis as measured by the incorporation of 3H=cytidine into the cell nucleus increases continuously in the nuclei of all cell groups throughout the whole period investigated. On the other hand, the average nuclear area diminishes. This dissociation of the extent of RNA synthesis and the nuclear size is discussed.