Cell proliferation and vascular morphology in the marmoset corpus luteum.

Luteal formation is associated with angiogenesis and low progesterone production. Maximal mid-luteal phase progesterone production is concurrent with extensive vascularization, and luteolysis occurs when steroidogenesis decreases. Angiogenic cell proliferation and vascular changes have not been examined in the marmoset. The aim of this study was to examine vascular morphology throughout the luteal phase by identifying: (i) von Willebrand factor VIII antigen (vW)-immunopositive endothelial cells; (ii) Ki67-positive proliferating cells; and (iii) bromodeoxyuridine-positive proliferating cells. Marmoset corpora lutea were examined throughout the cycle, and natural regression was compared with induced luteolysis after administration of a prostaglandin F(2alpha) analogue or gonadotrophin-releasing hormone (GnRH) antagonist. Steroidogenic and endothelial cells were positive for proliferation markers. Endothelial cell proliferation was highest during luteal formation, then decreased and remained low during the luteal phase and functional regression, however endothelial cell proliferation increased during structural regression. Endothelial cell proliferation was unchanged by induced regression. The area of vW immunostaining was highest during luteal formation, decreased thereafter and remained constant during the luteal phase and regression. Distribution of immunostaining indicated the presence of an extensive capillary network, but during structural regression the numbers of capillaries decreased and numbers of microvessels increased. These results suggest that vascular changes are concurrent with changes in the functional status of the marmoset corpus luteum.