Tamura and Greenwald (13) demon-
strated that the LI of endothelial cellsin the rat corpus luteum
rose from 2.1% on day 12 to 10% on day 14 of pregnancy.
This agrees with a previous report that the total number of
luteal cells does not change throughout pregnancy in rats,
whereas the number of endothelial cells increases at mid-
pregnancy (40).