Effects of unilateral ovariectomy with compensatory hypertrophy on ovarian blood flow, oxygen consumption and progestin secretion in the 16-day pregnant rat.

Stimulated ovulation with resultant multiple corpora lutea (CL) can result in lower progesterone levels than expected from the increased luteal tissue mass. Unilateral ovariectomy (ULO) was used to increase CL number in rats and determine whether this would compromise luteal tissue blood flow, oxygen consumption and progestin secretion. All investigations were performed in vivo, using a venous outflow technique on Day 16 of gestation, when progesterone secretion is maximal. ULO, performed before pregnancy, doubled CL number and total CL mass in the remaining ovary of six treated compared to five control rats. Growth of CL was not affected. The rate of ovarian blood flow (microL min(-1) mg CL(-1)) fell to 47% of control levels in ULO animals and progesterone secretion (microg h(-1) mg CL(-1)) to 68%. Secretion of the minor progestin, 20alpha-hydroxypregn-4-en-one was not affected. Tissue oxygen consumption was maintained despite the reduction in blood flow by an increase in oxygen extraction from arterial blood. These results suggest that overcrowding of CL in ULO-stimulated rat ovaries compromises luteal tissue blood flow and subsequently progesterone secretion.

Direction of blood flow and changes in resistance of major arteries supplying the ovary of the pregnant rat.

In this study, we examined changes in vascular resistance contributing to increased ovarian blood flow in the pregnant rat. Ovarian blood flow was monitored in vivo using a venous outflow cannulation technique in nonpregnant rats and in pregnant rats at Day 16 and Day 22, and increased from 0.18 +/- 0.02 to 0.81 +/- 0.09 and 1.02 +/- 0.08 ml min(-1) ovary(-1) (mean +/- SEM; n = 7, 7, 6), respectively. Intrinsic vessels within the ovarian complex accounted for 81%, 73%, and 70% of total resistance to ovarian blood flow. Of the two major extrinsic supply vessels, from one-half to two-thirds of the ovarian blood was derived from the uterine artery, and the ovarian artery never contributed to uterine blood flow. These results indicate that the major supply vessels are unlikely to limit ovarian blood flow, even near term when competing demand by the gravid uterus reaches a peak. The finding that ovarian blood flow is derived predominantly from the uterine artery may relate to local mechanisms that influence ovarian function and fetal growth.

Effects of noradrenaline on blood flow, progesterone secretion and oxygen consumption in the intact ovary of rats on day 16 of pregnancy.

The effects of noradrenaline on the rates of secretion of ovarian progesterone and 20 alpha-hydroxypregn-4-en-3-one (20 alpha-OHP), blood flow and oxygen consumption were examined in rats on day 16 of pregnancy. A modified venous outflow technique was used to infuse noradrenaline directly into the ovary, without recirculation, and to monitor subsequent changes in the ovary. Noradrenaline was infused for periods of 10 min at a low and a high concentration, which achieved effective blood concentrations of about 6.25 and 25 ng ml-1, respectively. Each period of noradrenaline infusion was interspersed by a 10 min period of infusion of its ascorbic acid carrier. Two series of infusions of low and high concentrations of noradrenaline were carried out on each rat. Neither the infusion of the ascorbic acid carrier nor of the low concentration of noradrenaline had any effect on ovarian progestin secretion. The high concentration of noradrenaline reduced blood flow by 30% but had no apparent effect on progestin secretion or oxygen consumption. Collectively, these findings question the generally accepted view that noradrenaline has a physiological role in the regulation of progesterone secretion. Further, putative luteotrophins need to be examined in the intact ovary as well as under in vitro and indirect in vivo conditions to determine their physiological role.