Methoxychlor-Induced Alterations in the Histological Expression of Angiogenic Factors in Pituitary and Uterus

Abstract

Within the reproductive system, oestrogenic stimulation of uterine and pituitary tissue typically causes a proliferative response accompanied by an angiogenic induction of new blood vessels from existing ones, thereby providing nutrients and oxygen to the growing tissue. The pro-oestrogenic pesticide methoxychlor (MXC), however, has shown a differential effect on proliferative activity. An increase in uterine growth is present, while the pituitary undergoes a decrease in size, even though the effect is accompanied by a characteristic oestrogen-induced elevation in pituitary prolactin concentration. The focus of the current study was whether the observed differences in tissue growth between uterus and pituitary in response to MXC administration were paralleled by a corresponding disparity in the expression of those growth factors (members of the vascular endothelial growth factor (VEGF) and angiopoietin families and their receptors) that are involved in the angiogenic cascade. Ovariectomized adult Sprague-Dawley female rats were administered MXC (0-200 mg/kg, oral) for 1 or 3 weeks. Immunohistochemical staining of uteri and pituitaries was performed under strictly controlled conditions for VEGF and its receptor VEGFR2, Angiopoietin-1 (Ang1) and angiopoietin-2 and their tyrosine kinase receptor Tie2, and platelet endothelial adhesion factor (as an index of vascularity). Image acquisition and densitometric assessments of staining intensity were conducted under blind conditions. The results showed uterine MXC-induced increases in the expression of VEGFR2 and Ang1, changes consistent with a normal proliferative response to oestrogenic stimulation. For VEGF, staining tended to be most pronounced in the stromal region, although there did not appear to be a progressive increase with dose. VEGFR2 expression showed significant dose-related trends in luminal and glandular epithelia by 1 week. Similar effects at 1 week were evident for Ang1 in glandular epithelium. In the anterior pituitary, a dose-related increase in VEGF was present for the 1 and 3 week treatments, and the number of pituitary vessels per unit area was also increased after 3 weeks. The effects indicate that even though the insecticide has not been found to cause an augmentation in pituitary growth, a dose-related rise in the expression of at least one principal angiogenic factor is present that may be associated with an increase in vascular density.