Nicotine Does Not Affect Vascularization But Inhibits Growth of Freely Transplanted Ovarian Follicles by Inducing Granulosa Cell Apoptosis

Abstract

Smoking clearly is associated with decreased female fertility and fecundity. An estimated 30% of women of reproductive age in the United States are cigarette smokers. An effect of smoking on angiogenesis has been invoked to explain why smoking compromises fertility. Studies in hamsters have found a significant reduction in blood vessels within corpora lutea after exposure to smoke. Furthermore, nicotine-the major active component of cigarette smoke-reportedly stimulates angiogenesis in diverse pathologic conditions. The investigators transplanted ovarian follicles into a dorsal skinfold chamber of pregnant hamsters treated with nicotine and used in vivo fluorescence microscopy to examine the growth and vascularization of the follicle grafts. The animals received daily subcutaneous nicotine doses of 0.2 or 1.0 mg/kg, mimicking the exposure of low-rate and high-rate smokers, respectively. Control animals received saline in place of nicotine. Proliferating cell nuclear antigen (PCNA) and cleaved caspase-3 were estimated immunohistochemically in the follicle grafts, and angiogenesis was assessed using an aortic ring sprouting assay. Rates of revascularization of ovarian follicles were similar in the nicotine-treated and control animals. Within a week after follicle transplantation, nicotine was associated with a dose-dependent inhibition of follicular growth, but neither the vascularized area nor the density of microvessels was affected. Studies using the in vitro aortic ring assay confirmed that nicotine did not influence sprouting or microvessel formation. Immunohistochemical studies of cleaved caspase-3 showed considerable granulosa cell apoptosis within the transplanted follicles of animals given the higher dose of nicotine. There were no group differences in PCNA staining. These findings suggest that nicotine in cigarette smoke alters the growth of ovarian follicles, presumably by increasing cellular apoptosis. It did not adversely affect follicle vascularization in the present study. Retardation or inhibition of follicle growth might help explain the association observed between smoking and impaired fertility.