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ORIGINAL RESEARCH ARTICLE

Involvement of the Peripheral Cholinergic Muscarinic System in the Compensatory Ovarian Hypertrophy in the Rat

Vladimir Trkulja^*,1, Vladiana Crljen-Manestar, Hrvoje Banfic and Zdravko Lackovic^*

^* Department of Pharmacology and Department of Physiology, Croatian Brain Research Institute, Zagreb University School of Medicine, 10000 Zagreb, Croatia

To whom requests for reprints should be addressed at ¹ Department of Pharmacology and Croatian Brain Research Institute, Zagreb University School of Medicine, Salata 11, Zagreb, Croatia. E-mail: vladimir.trkulja{at}zg.htnet.hr

In the present experiments, unilateral ovariectomy (ULO) induced compensatory hypertrophy (COH) of the remaining rat ovary (60%–85% increase in ovarian weight, total proteins, and total RNA and DNA). An increased thymidine uptake preceded the organ enlargement. COH was inhibited by ip-administered muscarinic antagonist propantheline (dose-dependently) or botulinum toxin delivered locally to the ovary. The effects were reversed by bethanecol ip (a muscarinic agonist). In sham ULO animals, [³H]-scopolamine binding to ovarian membranes indicated the existence of muscarinic receptors (K_d 2.5 nM, B_max 12 fmol/mg proteins, Hill 1.0). The ovarian 1,2-diacylglycerol (DAG) was 120–150 pmol/mg tissue and did not react to carbachol in vitro (50 µM). At 15 minutes after ULO, the [³H]-scopolamine binding was unchanged (K_d 2.6 nM, B_max 12.6 fmol/mg tissue, Hill 1.0), but the ovarian DAG was increased (280–350 pmol/mg tissue) and increased further in response to carbachol (460–550 pmol/mg tissue). After ULO, ovarian DAG remained continuously responsive to carbachol. The ULO-induced DAG increase and enhanced susceptibility to carbachol were inhibited by the botulinum toxin or atropine pretreatments. Abdominal vagotomy done immediately before ULO also inhibited the ULO-induced DAG increase and DAG responsiveness to carbachol. However, when the vagotomy was performed 10 mins after ULO, the ovarian DAG remained responsive to carbachol in vitro. The data suggest that the peripheral cholinergic system, including the ovarian muscarinic receptors, stimulates COH. This is apparently associated with the ULO-induced coupling of the ovarian muscarinic receptors to phosphoinositide (PI) breakdown. Vagus plays a role in the occurrence of the changed muscarinic receptor-PI breakdown relationship in the remaining ovary.

Key Words: compensatory ovarian hypertrophy • muscarinic receptors • vagus