The Effect of Muscle Contraction on the Blood Flow and on the Vascular Responses to Adrenaline, Noradrenaline and Isoprenaline in Individual Skeletal Muscles of the Cat

Abstract

Abstract The effect of muscle contraction on the rate of venous outflow and on the vascular responses to adrenaline, noradrenaline and isoprenaline was studied in individual muscles of the hind limbs of cats under chloralose anaesthesia. The maximum hyperaemia arising from contraction was produced when maximal twitches were elicited at frequencies which varied in different experiments from 1 to 8 per second, that is, frequencies well below those required to produce tetanus. During prolonged tetanic contractions the tension in the muscles soon fell to become constant at a lower level. This fall in tension reduced the mechanical impedance to flow and allowed vasodilatation to occur. In the tibialis anterior muscle the maximum hyperaemia was reached during the constant tension phase of the tetanus but in the soleus, the tension of which is maintained at a higher level, mechanical compression impeded the flow throughout the contraction. Both local vasodilator and vasoconstrictor actions of the sympathomimetic amines were reduced during the hyperaemia of muscle contraction. During contraction the muscle blood flow was markedly influenced by changes in mean arterial pressure. Thus isoprenaline, although a dilator substance in resting muscle, often passively reduced the blood flow through a contracting muscle, when injected intravenously, because of its hypotensive action. The reverse occurred with intravenously administered adrenaline and noradrenaline. The rise in blood pressure produced by these amines often forced more blood through the contracting muscle despite a weak local constrictor action.