Adrenergic and novel non-adrenergic neuronal mechanisms in the control of smooth muscle activity in the human oviduct.

The isthmic portion of human Fallopian tubes was excised during surgery and the ampullary-isthmic junction was identified. The external, longitudinal and the inner, circular muscle layers of this structure were then mechanically separated. The contractile activity of thin strips from these layers was studied isometrically in organ bath experiments. Administration of various adrenoceptor agonists and antagonists revealed that the responses of the longitudinal smooth muscle are primarily mediated by alpha-adrenoceptors while there is a marked dominance of beta-adrenoceptor-mediated effects in the circular layer. Transmural nerve stimulation to those caused by exogenous noradrenaline, although nerve-mediated inhibition of circular muscle activity was not abolished entirely by propranolol, atropine or guanethidine, but by tetradotoxine, indicating the existence of a hitherto unknown non-adrenergic, non-cholinergic, inhibitory neurogenic mechanism. The results support the concept of a specific sphincter-like function controlling ovum transport at the human oviductal isthmus, and that this sphincter may be controlled by both adrenergic nerves and nerves liberating an unidentified transmitter substance.