Effects of aminobenzyl penicillin (AB-PC), methylchlorophenyl isoxazolyl penicillin (MCI-PC) and 6-aminopenicillanic acid (6-APA) on the contractile response of guinea-pig urinary bladder.

The present study was undertaken to investigate the effects of aminobenzyl penicillin (AB-PC), methylchlorophenyl isoxazolyl penicillin (MCI-PC), and 6-aminopenicillanic acid (6-APA) on the contractile response of guinea-pig urinary bladder. AB-PC, MCI-PC, and 6-APA, respectively, diminished the intramural electrical stimulation-induced contractile response. AB-PC had almost no effect on the contractile response to exogenous acetylcholine, while MCI-PC remarkably reduced it. The reducing effect of MCI-PC was greater on the intramural electrical stimulation-induced contractile response than it is on the exogenous acetylcholine-induced contractile response. 6-APA slightly reduced the exogenous acetylcholine-induced contractile response. The reducing effect of 6-APA was a little weaker on the exogenous acetylcholine-induced contractile response than it is on the intramural electrical stimulation-induced contractile response. By the addition of AB-PC, the amplitude of spontaneous contractile response of the tissue was reduced gradually with light lowering of the tonus level of the tissue was almost prevented with a little lowering of the tonus level of the tissue. The effects of AB-PC and MCI-PC on the spontaneous contractile response of the tissue mentioned above were also observed in the presence of tetrodotoxin. On the other hand, by the addition of 6-APA, the reducing effect on the amplitude of spontaneous contractile response of the tissue and increasing effect on its frequency were recognized with remarkable raise of the tonus level of the tissue. These phenomena which were induced by 6-APA were also observed in the presence of tetrodotoxin. From these results, the conclusion comes as follows: 1) AB-PC may affect not only on the muscle but also on the intramural cholinergic nerves. 2) MCI-PC may affect on the muscle, but its effect on the intramural nerves is also not likely to be negligible at this time. 3) 6-APA may affect mainly on the muscle.