Superoxide (02-), hydrogen peroxide (H202), and lipid peroxides are generated in luteal tissue during natural and prostaglandin-induced regression in the rat, and this response is associated with reversible depletion of ascorbic acid. Reactive oxygen species immediately uncouple the luteinizing hormone receptor from adenylate cyclase and inhibit steroidogenesis by interrupting transmitochondrial cholesterol transport.7The cellular origin ofoxygen radicals in regressing corpora lutea is predominatelyfrom resident and infiltrated leukocytes, notably neutrophils. Reactive oxygen species are also produced within the follicle at ovulation and, like the corpus luteum, leukocytes are the major source of these products. Antioxidants block the resumption of meiosis, whereas the generation of reactive oxygen induces oocyte maturation in thefollicle.Although oxygen radicals may serve important physiologic roles within the ovary, the cyclic production of these damaging agents over years may lead to an increased cumulative risk of ovarian pathology that would probably be exacerbated under conditions of reduced antioxidant status.

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Free radicals and reactive oxygen species play a number of significant and diverse roles in reproductive biology. In common with other biological systems, mechanisms have evolved to minimize the damaging effects that these highly reactive molecules can have on reproductive integrity. Conversely, however, recent findings illustrate the constructive roles that oxygen radicals and reactive oxygen species play in a number of important junctures in the development of germ cells and the obligate endocrine support they receive for the successful propagation of the species. Specifically addressed in this review are some aspects of sperm development and action, the uterine environment, oocyte maturation and ovulation, and corpus luteum function and regression.

Hyperplasia of the theca-interstitial (T-I) compartment, such as observed in polycystic ovary syndrome, is associated with ovarian dysfunction. Yet the mechanisms regulating proliferation of T-I cells are virtually unknown. This study was an investigation of the effects of insulin and insulin-like growth factors (IGF-I and IGF-II) on proliferation of rat T-I cells. Purified T-I cells were incubated in chemically defined media. Insulin (1-100 nM) and both IGFs (0.3-30 nM) dose-dependently stimulated DNA synthesis as determined by radiolabeled thymidine incorporation assay. IGF-I was most potent with EC50 = 1.4 +/- 0.4 nM, while IGF-II had EC50 = 4.3 +/- 0.18 nM and insulin had EC50 = 8.4 +/- 3.9 nM. The maximal effects of all three treatments were comparable. A combination of IGF-I at 10 nM (a concentration producing a near-maximal effect) with insulin or IGF-II resulted in DNA synthesis comparable to that achieved by IGF-I alone. IGF-I mutants with decreased affinity to IGF-binding proteins (IGFBPs)-long R3-IGF-I and des(1-3)IGF-I-produced greater effects on DNA synthesis than did IGF-I. The effects of insulin and IGFs on cell proliferation were confirmed by counting the steroidogenically active cells (stained positive for 3 beta-hydroxysteroid dehydrogenase [3 beta-HSD]) and steroidogenically inactive cells (3 beta-HSD negative). The number of steroidogenically active T-I cells was increased by insulin (by 3.7-fold, p < 0.001), IGF-I (by 3.2-fold, p < 0.001), and IGF-II (by 2.1-fold, p < 0.001). The number of steroidogenically inactive cells was not significantly altered. These findings indicate that 1) insulin- and IGF-dependent synthesis of DNA by T-I cells is stimulated via a common pathway, probably via type I IGF receptors; 2) endogenous IGFBPs may modify the effects of IGF-I; and 3) the increased DNA synthesis is reflected by an increase in the number of steroidogenically active cells. Insulin and the IGFs may play a role in the regulation of proliferation and differentiation of T-I cells under physiological and pathological conditions. In particular, the present observations may explain thecal and stromal hyperplasia accompanying hyperinsulinemic conditions such as polycystic ovary syndrome or hyperthecosis.

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