Neurogenic and Myogenic Responses in Isolated Smooth Muscle of The Bovine Teat

Strips of bovine teat smooth muscle were studied. Their innervation was investigated with analytical pharmacology on field stimulated preparations. The content of noradrenaline in the teat wall and the sphincter region was determined. The main results were: teat smooth muscle has properties of single unit smooth muscle i.e. automaticity and active response to stretch. Especially the sphincter region is inclined to rapid phasic rhythmicity. The teat smooth muscle receives excitatory adrenergic innervation. The noradrenaline released from the nerves preferentially activates α-adrenoceptors, while β-adrenoceptors essentially are noninnervated and humoral. The sphincter region has a higher concentration of noradrenaline and a more intimate neuro-effector arrangement. This is probably of functional significance. Moderate chilling increases the response to adrenergic nerve stimulation while it is decreased at higher temperatures. This has most likely physiological importance. The results are discussed with respect to in vivo findings and it is concluded that the bovine teat smooth muscle with its excitatory adrenergic nerves forms a normally very efficient neuro-effector system with a particular strength in the sphincter around the streak canal.