TY - JOUR T1 - THE PHARMACOLOGICAL ACTION OF RYANODINE ON RHYTHMICALLY CONTRACTING MAMMALIAN SMOOTH MUSCLE JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 140 LP - 144 VL - 123 IS - 2 AU - Ira W. Hillyard AU - Leonard Procita Y1 - 1958/06/01 UR - http://jpet.aspetjournals.org/content/123/2/140.abstract N2 - The purified South American plant alkaloid, ryanodine, in concentrations extending to 10-7M, produces a progressive increase in the longitudinal muscle tonus of rhythmically active isolated duodenal strips from the rabbit. The rate of onset and the degree of the ryanodine effect is dependent on the degree of existing activity in the muscle. Alteratiomi of the environment by such methods as decreasing the ionic calcium strength, increasing the ionic magnesium stremigth, the addition of such metabolic inhibitors as DNP or cyanide, all changes which decrease the activity of the muscle, will either slow the rate of onset of the ryanodine contracture or inhibit it. The ryanodine-induced contracture of intestinal smooth muscle is irreversible. Temporary antagonism or prevention is possible with agents capable of producing a relaxation of smooth muscle. Removal of the antagonist, however, brings about a prompt return of the contracted state. ER -