Sympathetic Control of Rhythmically Active Vascular Smooth Muscle as Studied by a Nerve‐muscle Preparation of Portal Vein

Techniques are described for recording directly the contractile responses elicited in the longitudinal smooth muscle of cat or rabbit portal vein by vasomotor nerve stimulation in situ or in vitro. This vascular smooth muscle, which shows a spontaneous rhythmic activity of 3 to 8 contractions per minute, responded to splanchnic or postganglionic nerve stimulation by an increase in the mean level of tension associated with an increased frequency of contractions. Guanethidine abolished these neurogenic responses indicating that they were due to adrenergic sympathetic fibre activation. Effects of vagal nerve stimulation were weak and inconsistent. The quantitative tension responses produced by splanchnic or postganglionic nerve stimulation at graded impulse rates increased steeply in the low frequency range and reached a maximum at 8 to 16 imp/sec. These frequency‐response curves, obtained by direct recording of vascular smooth muscle contractions, are in conformity with those found in previous investigations studying blood flow or regional blood volume in intact vascular beds. The mechanisms by which the sympathetic innervation controls activity in rhythmically active vascular smooth muscle and the quantitative aspects of this influence are discussed in the light of the present results