Abstract
The effects of drugs on the tonus changes of ovarian smooth muscles of tilapia Sarotherodon niloticus were studied on isolated preparations. Excitatory action of acetylcholine was abolished by atropine and enhanced by neostigmine, indicating the presence of muscarinic acetylcholine receptors on smooth muscle cells. The cholinergic contractions of the ovary were inhibited by the beta adrenergic action of sympathomimetic amines (isoprenaline, adrenaline and noradrenaline), since their inhibitory action was abolished by a beta adrenoceptor antagonist, propranolol. After an application of propranolol, the excitatory alpha adrenergic action of the amines, except isoprenaline, was uncovered, indicating that alpha adrenoceptors are also located on them. Both field and paravascular nerve stimulations activated cholinergic excitatory nerves and caused ovarian contractions, since the contraction was blocked by atropine and tetrodotoxin. From the present results, excitatory cholinergic innervation of the tilapia ovary was confirmed. However, no conclusive evidence to show inhibitory adrenergic innervation was obtained.
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