Variations in "functional" blood flow as related to corpus luteum activity in cyclic guinea pigs

Arterial blood flow to the ovary varies in proportion to luteal activity and may be involved as a mediator of ovarian function. Fifteen and 25 zm microspheres labelled with different isotopes were injected simultaneously into the left ventricle of the heart in cyclic guinea pigs and percent cardiac output to the ovary was determined. It has previously been shown that 25 m spheres do not recirculate and therefore results utilizing these were defined as representing “total ” blood flow. Since the 15 zm microspheres are trapped only in vessels 15 and smaller and have been shown to pass through arteriole-venule anastomoses, blood flow determined with the smaller microspheres was defined as “functional”. Luteolysis, as defined in these animals by a significant decline in serum progesterone concentrations, occurred between Days 12 and 14 of the cycle. On Day 12, total blood flow was apparently adequate to maintain ovarian function. However, at this time, functional blood flow was significantly less (43%) than total blood flow. Differences between functional and total blood flow at other times of the cycle ranged between 1 and 15 % and were not statistically significant. The loss of almost half the functional blood flow, presumably a result of shunting via arteriole-venule anastomoses, prior to a significant decline in progesterone concentration, supports the hypothesis that ovarian blood flow and its distribution is involved in the mediation of luteal regression in guinea pigs