title: Effects of vasoactive intestinal polypeptide (VIP) and cyclic AMP on isolated dilator pupillae muscle of albino rabbit eye.
abstract: The iris dilator muscle strips were dissected from the albino rabbit eye pretreated with 0.5% topical indomethacin and were incubated in a Krebs-Ringer solution. After pretreatment with 3 X 10(-5)M of L-phenylephrine, vasoactive intestinal polypeptide (VIP) was added to the incubation medium at final concentrations ranging from 1 X 10(-10) to 3 X 10(-7)M. The VIP effects on the tension of the dilator muscles and the cyclic AMP (c-AMP) levels in the muscles determined by a radioimmunoassay method were correlated. VIP induced a dose-dependent relaxation of the dilator muscles in the VIP concentration range between 3 X 10(-10) and 3 X 10(-8)M: the ED50 obtained from 21 muscle strips averaged 6.08 +/- 1.34 (mean +/- SEM) X 10(-9)M. The c-AMP level in the dilator muscles increased in a dose-dependent manner in the VIP concentration range from 1 X 10(-9) to 1 X 10(-7)M: the ED50 was computed to be 5.12 X 10(-9)M. The dose-response relationships both for the muscle tension and for the c-AMP level were similar. The time-courses in c-AMP change and muscle relaxation were compared. The c-AMP level increased significantly prior to the onset of muscle relaxation after VIP treatment (10(-7)M), and the level reached a maximum when the muscle relaxation was almost completed. It was concluded that the dilator muscle relaxation by VIP is mediated by an increase in the intracellular c-AMP.
mesh_terms: D000818:Animals; D000242:Cyclic AMP / Q000378:metabolism / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005260:Female; D007498:Iris / Q000187:drug effects*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects; D011817:Rabbits; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology*
chemical_list: D014660:Vasoactive Intestinal Peptide; D000242:Cyclic AMP