In vivo functional implications of isoproterenol-mediated relaxation of isolated human iris sphincter.
The isolated human iris sphincter contracted with carbachol produced relaxation with an average ED50 of 1.30 x 10(-7) M for (-)-isoproterenol. The effect is sensitive to block by (-)-timolol with KB 3 x 10(-9) M. The magnitude of the average relaxation mediated by the beta-adrenoceptor agonist was only 31%. Lowering of the temperature did not potentiate the effect of (-)-isoproterenol to a significant extent. Thus, in contrast to bovine iris sphincter, where the beta-adrenoceptor mediated response of (-)-isoproterenol produces a maximum relaxation or complete mydriasis, the maximum beta-adrenoceptor mediated mydriasis of human iris may not be more than 1/3 of the maximum pupillary dilatation achieved by physiologic or pharmacologic procedures.
Patil
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PN
College of Pharmacy, Ohio State University, Columbus.
Weber
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PA
D000368:Aged; D000369:Aged, 80 and over; D002217:Carbachol / Q000494:pharmacology; D002924:Ciliary Body / Q000503:physiopathology; D006801:Humans; D007498:Iris / Q000503:physiopathology*; D007545:Isoproterenol / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D009126:Muscle Relaxation / Q000187:drug effects; D011680:Pupil / Q000187:drug effects; D013696:Temperature; D013999:Timolol / Q000494:pharmacology
D013999:Timolol; D002217:Carbachol; D007545:Isoproterenol