title: Effects of vasoactive intestinal polypeptide (VIP) and cyclic-AMP on the isolated sphincter pupillae muscles of the albino rabbit.
abstract: Iris sphincter muscle strips were dissected from the albino rabbit eye pretreated with 0.5% topical indomethacin and incubated in a Krebs-Ringer solution. Vasoactive intestinal polypeptide (VIP) was added to the incubation medium, and the effects on the tension of the sphincter pupillae muscles and the cyclic AMP (c-AMP) level in the muscles were correlated. The c-AMP level in the muscles was determined by a radioimmunoassay method. VIP induced a relaxation of the sphincter muscles and a positive correlation was found between the VIP effects and the c-AMP levels. The ED50 was calculated to be 3.72 X 10(-9)M. A significant increase in the c-AMP level occurred prior to the onset of muscle relaxation after VIP treatment (10(-7)M), and a peak level of c-AMP was reached when the relaxation was almost completed. The sphincter muscles were treated with a c-AMP phosphodiesterase inhibitor, 1-methyl-3-isobutylxanthine (MIX) (10(-5)M), 10 minutes prior to the experiment. This pretreatment enhanced the relaxation of the muscles induced by VIP.
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D000242:Cyclic AMP / Q000494:pharmacology*; D005768:Gastrointestinal Hormones / Q000494:pharmacology*; D007498:Iris / Q000187:drug effects*; D009126:Muscle Relaxation / Q000187:drug effects; D011817:Rabbits; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology*
chemical_list: D005768:Gastrointestinal Hormones; D014660:Vasoactive Intestinal Peptide; D000242:Cyclic AMP; D015056:1-Methyl-3-isobutylxanthine