Muscarinic Stimulation of Arachidonic Acid Release and Prostaglandin Synthesis in Bovine Ciliary Muscle: Prostaglandins Induce Cyclic AMP Formation and Muscle Relaxation

• Published in: Experimental eye research Vol. 58; no. 5; pp. 513 - 522
• Main Authors: Yousufzai, S.Y.K., Zheng, P., Abdel-Latif, A.A.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.05.1994
• Subjects: Animals; arachidonate release; Arachidonic Acid - metabolism; Atropine - pharmacology; bovine; Cattle; Cholinergic Agents - pharmacology; Ciliary Body - drug effects; Ciliary Body - metabolism; ciliary muscle; Culture Techniques; cyclic AMP; Cyclic AMP - biosynthesis; Dinoprost - biosynthesis; Dose-Response Relationship, Drug; Kinetics; Lipid Metabolism; muscarinic agonists; Muscle Contraction - drug effects; Phospholipids - metabolism; prostaglandins; Prostaglandins - biosynthesis; Prostaglandins - pharmacology; relaxation; ciliary muscle; relaxation; bovine; prostaglandins; cyclic AMP; arachidonate release; muscarinic agonists
• ISSN: 0014-4835; 1096-0007
• DOI: 10.1006/exer.1994.1045

In the present study it is demonstrated that in bovine ciliary muscle, muscarinic stimulation results in; (a) release of 14C-arachidonic acid (14C-AA) and 14C-labeled prostaglandins (PGs) from muscle prelabeled with 14C-AA; (b) release of endogenous PGs, measured by means of radioimmunoassay; (c) enhanced IP3 production and (d) muscle contraction. In addition, PGs, such as PGE2 and PGD2, increased cAMP formation and induced muscle relaxation. The studies on the kinetics of 14C-AA metabolism revealed that incorporation of 14C-AA into glycerolipids and its conversion into PGs by the ciliary muscle were rapid and time-dependent. The amounts of 14 C-radioactivity recovered in the major PGs decreased in the following order: PGD2 > PGE2 < PGF2α > 6-keto-PGF1a. The rate of endogenous PGF2α synthesis by iris-ciliary body tissues from different mammalian species was found to be in the following order: ciliary muscle < ciliary processes < sphincter muscle. The EC50s for muscarinic-stimulated release of 14C-AA, 14C-labeled PGs, and endogenous PGF2α and PGE2, and for IP3 production and contraction of the ciliary muscle indicate that CCh is 2-16 times as potent as pilocarpine in eliciting these responses, with the greatest difference being for contraction. The maximal increase in ciliary muscle tension due to CCh was 48% greater than that evoked by pilocarpine. All PGs tested, including PGE2, 17-phenyl trinor PGE2, 11-deoxy PGE1, PGF2α and PGD2 had no effect on IP3 production and contraction in the ciliary muscle. However, PGE2 and PGD2 stimulated cAMP formation and inhibited CCh-induced IP3 production in a dose-dependent manner. In addition, PGE2 and PGD2 induced relaxation in ciliary muscle precontracted by CCh. In presence of indomethacin (1 μM), the CCh-induced contraction was greater than that observed in absence of the cyclo-oxygenase inhibitor. It is suggested that in the ciliary muscle certain PGs, such as PGE2 and PGD2, may function to modulate, via cAMP, the responses to muscarinic stimulation in this tissue.