Morphological and histochemical studies on the foetal and postnatal ovaries of the field rat (Millardia meltada).

A morphological and histochemical study has been made of the development of the field rat (Millaridia meltada) ovary with special reference to follicular and interstitial gland tissue development. On day 17 of foetal life, the developing ovary consists of surface epithelium, clusters of germ cells associated with pregranulosa cells, undifferentiated stromal cells and blood vessels. The primordial follicles first appear on foetal day 19. The primary follicles develop on postnatal days 1 and 3, small secondary follicles on days 5 and large ones on day 10; the antral follicles appear on day 17. Zona pellucida material first appears in primary follicles on postnatal day 3. The thecal layer of stromal origin begins to be formed on postnatal day 5. Some lipid bodies consisting of phospholipids are present in the granutosa cells of healthy follicles. Lipids of hypertrophied theca interna cells, which develop on postnatal days 16 and 17, consist of triglycerides and phospholipids; cholesterol and/or its esters also store later on during the postnatal period. Atresia affects follicles of all sizes. The granulosa of atretic large secondary and antral follicles stores triglycerides, cholesterol and/or its esters and some phospholipids. Their hypertrophied theca interna cells form patches of interstitial gland cells in the ovarian stroma, which develop diffuse lipoproteins and lipid bodies composed of cholesterol and/or its esters, triglycerides and phospholipids. Two types of interstitial cells are identified in the developing ovary of the field rat. The primary interstitial cells start developing from the interfollicular fibroblast-like stromal cells on postnatal day 10. The secondary interstitial cells originate by the hypertrophy of the theca interna and surrounding stroma of the atretic follicles and they start accumulating from postnatal day 17 onwards. The lipids of both types of interstitial cells consist of diffusely distributed lipoproteins and lipid droplets composed of triglycerides, phospholipids and cholesterol and/or its esters. The functional meaning of interstitial gland cells is discussed in relation to steroid hormone synthesis.