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.