Excitatory neurotransmission in the mammalian bladder and the effects of suramin

To compare the electrical and mechanical activity, and assess the effect of suramin on strips of detrusor from various species.

Bladder muscle strips from guinea-pigs, rabbits, monkeys and sheep and detrusor strips from humans (obtained at operation) were studied. The mechanical responses to nerve stimulation were recorded with a force transducer and electrical activity was recorded with the double sucrose gap.

In all species acetylcholine was released from the nerves and a prolonged contraction was produced. A second transmitter, possibly adenosine triphosphate, produced a rapid transient contraction, the amplitude of which varied with the species. In the rabbit and guinea-pig the phasic contraction and accompanying depolarization were large, whereas in primates they were small and in sheep were intermediate. At high concentrations, suramin reduced the contraction and accompanying depolarization in rabbit and guinea-pig muscle but not in sheep. Suramin enhanced the late cholinergic responses and increased spontaneous mechanical activity in all species. These latter effects were not seen after desensitization of the receptors with the ATP analogue alpha, beta- methylene ATP.

Although suramin reduces the excitatory effect of nerve activity in some species, it would produce little beneficial effect in the human hyperexcitable bladder as any inhibitory effect might be offset by the increase in spontaneous activity.