ABSTRACT
We have investigated the effects of beta-lactam antibiotics on isolated preparations of rat fundus, ileum, and the body of feline stomach. Isotonic changes of isolated preparations were recorded. Benzylpenicillin (EC50 = 1.31 +/- 0.13 x 10(-5) M), ampicillin (EC50 = 2.16 +/- 0.15 x 10(-5) M), cefotaxime (EC50 = 1.33 +/- 0.15 x 10(-5) M), ceftriaxone (EC50 = 4.39 +/- 0.13 x 10(-5) M) and ceftazidime (EC50 = 1.42 +/- 0.01 x 10(-3) M) produced concentration-dependent tonic contractions of rat fundus. Rat ileum and feline stomach did not respond on these substances. Lidocaine (2.3 x 10(-5) M) and physostigmine (1.0 x 10(-8) M) significantly potentiated contractions produced by benzylpenicillin. On the other hand, methysergide (1.4 x 10(-7) M) and atropine (9.6 x 10(-9) M) significantly blocked tonic contractions produced by benzylpenicillin. Effects of beta-lactam antibiotics on smooth muscle isolated preparations were tissue and species dependent, indicating selectivity of their action.