The Uptake of Tritiated Uridine and Phenylalanine by the Ovaries of Rats and Monkeys

Abstract

Rats and monkeys (Macaca mulatta, M. irus) were injected with tritiated uridine or phenylalanine and ovarian tissue was recovered at intervals from 15 min to 24 h later. Autoradiographs were prepared and studied by light microscopy; in addition some specimens which received uridine were examined using the electron microscope. The two isotopes are taken up by the ovaries of both species. The trace obtained with phenylalanine shows a very general distribution, whereas uridine seems to be more selectively incorporated by the various components of the ovary. The nuclei of primordial and growing oocytes are labelled with uridine, and so are the granulosa cells in follicles at all stages of development. The theca surrounding multilayered and vesicular follicles also shows a trace which appears heavier than that over the ovarian stroma. In the neonatal rat, the nuclei of oocytes at the pachytene and diplotene stages take up uridine. Autoradiographs prepared from ovaries fixed from 30 min to 4 h after injection and examined under the electron microscope show silver grains associated with the nucleoli and electron-dense chromosomal cores which are characteristic of these stages in meiotic prophase. Oocytes in primordial follicles, in immature and mature rats, are also labelled, showing that nuclear uptake continues as oocytes enter the ‘resting’ or dictyate stage. Since the chromosomes lose their morphological identity at this time, however, silver grains appear to be randomly distributed over the nuclear matrix. Primordial oocytes in the monkey also have a heavy nuclear label, seen under the light microscope to be associated with chromosomes and nucleoli. At the ultrastructural level, most of the extra-nucleolar silver grains are associated with condensed fibrillar material thought to represent part of the lateral component of chromosomes which are of the ‘lampbrush’ type. The synthetic activity of germinal and somatic elements in the ovary is discussed, and possible differences in the structure and metabolic activity of oocyte chromosomes are considered in relation to intra- and inter-specific variations in radiosensitivity.