[Investigation of biomechanics and of neural regulation of the sphincter ani internus (author's transl)].

Abstract

The contraction capability of the sphincter ani internus corresponds to that of the other sphincters, the muscle itself being twice as expandable. Acetylcholine creates slight relaxation. The transmitters of the inhibiting purinergic system have a semi-maximal effectivity of 123 +/- 30 microgram/ml. The purinergic system is therefore probably of minor importance for the regulation of muscle tone. On the other hand, an adrenergic stimulation leads primarily, by means of beta-receptors, to a strong relaxation followed by a powerful alpha-adrenergic contraction.