Characterization of Autonomic Receptors in the Smooth Musculature of Human Graafian Follicle

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Abstract
Various types of autonomic receptors were studied in isolated, 2 x 10 mm-size strips from the protruding part of human Graafian follicles obtained shortly before ovulation. The strip was mounted in an organ bath for recording of mechanical activity in the presence of different agonists and specific antagonists. The potency rank for sympathomimetics in their contractile effect (norepinephrine > epinephrine > penylephrine > isoproterenol) and the inhibition produced by phenoxybenzamine and piperoxan suggested the presence of a-receptors. The dissociation constant for their complex with norepinephrine (KA) was 1.68 x 10-6 M, and with piperoxan (KB) 7.90 x 10-8 M. A relaxation could be recorded from a state of active tonic contraction (achieved by carbamycholine) when the α-receptors were blocked. The potency for isoproterenol, norepinephrine, terbutaline, and epinephrine was in the order indicated, and the relaxation could be blocked in a competitive manner by propranolol (but not by the selective (β1-antagonist practolol). This shows the existence of β-receptors, and the dissociation constant in their relation with propranolol was found to be 5.42 x 10-7 M. These relaxing receptors mainly conform with the β2 subtype of receptors. Both acetylcholine and carbamylcholine produced contraction (but were without relaxing effects as tested on strips tonically contracted by prostaglandin F2α), which was competitively inhibited by atropine but not by hexamethonium. Thus, a contraction in the follicle wall is also mediated by muscarinic type of cholinergic receptors, and the dissociation constant (KB) for the receptor complex with atropine was found to be 1.17 x 10-10 M. It is suggested that local autonomic mechanisms in the follicle of the human ovary may be involved in follicular development and/or ovulation.