Thyrotropin-releasing hormone as a mediator of the central autonomic pathway controlling ovarian function

We studied the effect of thyrotropin-releasing hormone (TRH) applied centrally on the sympathetic activity of the ovary in female rats. Intracerebroventricular (i.c.v.) administration of a dose of 25 ng/kg weight produced an increase in noradrenaline (NA) content at the ovary after 5 days of hormone administration. However, higher doses in a range up to 500 ng/kg weight decreased NA content at the ovary. At the celiac ganglia (where the cell bodies of sympathetic neurons projecting to the ovary originate) there was an accumulation of NA in spite of a decrease in tyrosine hydroxylase activity (T-OH). After cold exposure, opposite effects on T-OH activity and no effects on NA in ganglia and in ovary were obtained. Besides, i.v. injection of TRH only induced a decrease in ovarian NA. In contrast to the increase in T(3) plasma levels obtained after the cold-stress procedure, none of the i.c.v. doses of TRH used produced changes in T(3) plasma levels, strongly suggesting that the effect on sympathetic activity is mediated by a central effect of TRH acting as a putative activator of ovarian sympathetic nerves.