Angiogenesis in the developing corpus luteum of pregnant rats: a stereologic and autoradiographic study

Within the adult mammalian ovary, angiogenesis is associated with development of the corpus luteum (CL). In this study, developing luteal tissue was examined to determine whether its vascularization involves endothelial cell replication and to what extent this proliferation contributes to forming new capillaries. Five rats each at 12, 24, 36, 48, 60, 72, 84, and 96 hr of gestation were given a subcutaneous injection of tritiated thymidine (specific activity 5 Ci/mM; 1 uCi/g body weight). One hour later they were anesthetised with sodium pentobarbitone, and the left ovary was processed for light microscopy. Sections were cut through each ovary until three newly formed CL were recognized; a 1-micron section was taken from the maximum diameter of each CL and processed for autoradiographic demonstration of thymidine labeling in endothelial cell nuclei. The same sections were also examined with stereological techniques to quantitate growth of the vascular compartment. The results show that 36.1 +/- 5.7% of endothelial cells of invading capillary sprouts divide within 12 hr of ovulation; at 24 hr, 29.0 +/- 2.8% are dividing. Within 12 hr after ovulation, blood vessels occupied 5.9 +/- 1.4% of the peripheral space of the ruptured follicle but only 1.6 +/- 0.5% in the center. However, by 36 hr these respective values were 9.3 +/- 1.6% and 8.4 +/- 1.9%. A further peak in endothelial-cell replication (31.2 +/- 5.4%), early on the 3rd day of gestation, corresponded to the very extensive anastomoses within the capillary bed established between this time (13.6% vascularity) and late on the 4th day (about 23%).(ABSTRACT TRUNCATED AT 250 WORDS)