Comparative studies of colon reactivity of healthy and ionization-radiated guinea-pigs to some spasmogens and their antagonists.

Comparative studies were carried out of the contractile effects of acetylcholine (1 X 10(-6) M), histamine (1 X 10(-6) M), serotonin (1 X 10(-5) M), nicotine (1 X 10(-5) M), BaCl2 (1 X 10(-3) M) and of the influence on the induced contractions caused by the antagonists of these spasmogens, namely: atropin (1 X 10(-6) M), dipenhydramine (1 X 10(-6) M), benzyloxygramine (1 X 10(-5) M), hexamethonium (1 X 10(-5) M) and papaverine (1 x 10(-5) M) on isolated segment of guinea-pig colon. Experimental acute radiation sickness is found to induce considerable changes in the reactivity of the intestinal smooth-muscle preparation used to the spasmogens applied and to their antagonists. Depending on the nature of the pharmacological agents, the degree of development of the experimental acute radiation sickness, and on other factors, the changes in the reactivity to the drugs tested revealed very great qualitative and quantitative differences. The following more definite changes could be pointed out. The spastic effects of serotonin and BaCl2 were potentiated, while the spastic effects of histamine and nicotine showed a tendency toward decrease. Under conditions of acute radiation sickness tha antagonistic effect of atropine to acetylcholine was intensified, while the antagonistic effects of benzyloxygramine to serotonin, of hexamethonium to nicotine and of papaverine to BaCl2, grew weaker. Diphenhydramine showed potentiated antagonistic effect to histamine on the 72nd h after radiation. Certain possibilities are discussed concerning the mechanisms underlying the changes in the reactivity of the intestinal smooth muscle to pharmacological agents, induced by acute radiation sickness.