Adrenergic Transmission at Vasoconstrictor Nerve Terminals Partially Depleted of Noradrenaline1

Publisher Website
Google Scholar
Abstract
Sedvall, G. and J. Thorson. Adrenergic transmission at vasoconstrictor nerve terminals partially depleted of noradrenaline. Acta physiol. scand. 1965. 64. 251–258. – The circulatory responses to activation of the vasoconstrictor nerves in skeletal muscle of the cat were studied after partial depletion of their transmitter stores by the action of reserpine and nerve impulses. In spite of the presence of 30 per cent of the noradrenaline store, practically no responses to vasoconstrictor nerve stimulation were obtained provided that the physiological impulse discharge had been impinging on the stores for 2.5 hrs after reserpine administration (5 mg/kg i. v.). If the impulse flow had been interrupted during this time, 40 per cent of the store was present and normal vasoconstrictor responses were obtained. At 10 hrs after reserpine, only a 10 per cent fraction of the noradrenaline store was left but normal responses were still produced – provided that no impulses had reached the nerve endings after the administration of reserpine. About 80 per cent of this small fraction could be depleted by electrical stimulation of the vasoconstrictor nerves. No difference in the sensitivity of the blood vessels to injected noradrenaline could be found as a result of decentralization or differences in the duration of reserpine treatment. The results suggest that a large part of the noradrenaline store in vasoconstrictor nerves is not directly available for release by nerve impulses in the reserpinized cat. The ability of the nerves to transmit vasoconstrictor impulses appears to be dependent on the presence of a small noradrenaline fraction, constituting 10–15 per cent of the total store.