INTERSTITIAL GLAND TISSUE OF MAMMALIAN OVARY

ABSTRACT The interstitial gland cells of the mammalian ovary originate from the theca interna and surrounding stromal elements of degenerating follicles and are simultaneously vascularized, and hypertrophied (or luteinized). They form a specific feature of the mammalian ovary, and are invariably present in the ovaries of young and adult mammals. The interstitial gland cells show several variations in their amount and distribution in different mammals. They also show cycles of abundance and differentiation correlated with the reproductive age and ovarian cycles. The interstitial gland cells possess the cytological, histochemical and biochemical features of well-established steroid-secreting cells. These features are: a) abundant diffuse lipids (lipoproteins) in the cytoplasm, which apparently derive from the abundant ultrastructural agranular endoplasmic reticulum; b) well-developed cell organelles, especially the pleomorphic mitochondria with complex system of internal cristae that are predominantly tubular; c) the development of diffuse lipoproteins (or membranes of smooth reticulum), closely accompanied by the appearance of enzyme activities indicative of the biosynthesis of steroid hormones; d) under certain physiological situations, stored lipid droplets in the cytoplasm, which consist of phospholipids, triglycerides, and cholesterol and/or its esters; and e) the capacity to form steroid hormones in biochemical experiments in vitro and in vivo. The physiological significance of these various features, which do not show any appreciable development in the compressed, relatively embryonic stromal elements of the general ovarian stroma, has been discussed in relation to steroid hormone synthesis in the interstitial gland cells. In general, the results of the cytological, histochemical and biochemical studies agree well with each other and are compatible with their endocrine function. After stimulation with endogenous gonadotrophins, the interstitial gland cells undergo conspicuous cytological, histochemical and biochemical changes, which have been correlated to the accelerated production of steroid hormones. The formation of androgenic steroids seems to be the principal product of interstitial gland cells; in some mammalian species, oestrogens and progestins are also formed. Further comparative studies on the interstitial gland cells in different mammalian species are suggested to determine the nature and physiological significance of their steroid secretions under different physiological situations. Interstitial gland cells of different mammals show several variations with regard to their permanency, apparently depending on some gonadotrophic stimulation. After persisting for some time, they gradually lose their cytoplasm and lipids, and ultimately revert to the relatively embryonic, compressed stromal tissue from which they are originally derived. This cytoplasmic change is closely accompanied by the loss of blood vascularity, which may be providing the gonadotrophic hormone and other nutrient substances to the functional interstitial gland cells. Some interstitial gland cells show degenerative cytoplasmic changes, and ultimately become refractory to gonadotrophic stimulation.