The distal colon of the guinea pig is relaxed by noradrenaline, by isoprenaline and by the stimulation of fibres running with the colonic nerves or intramurally. The relaxations in response to stimulation of the colonic nerves have a guanethidine sensitive (adrenergic) and a guanethidine insensitive (non adrenergic) component. Cocaine causes a three fold sensitization of the muscle to noradrenaline but no sensitization to isoprenaline. Cocaine increases the duration, but does not affect the amplitude, of the relaxation observed when adrenergic nerves are stimulated, and affects neither duration nor amplitude of the non adrenergic response. The adrenergic nerve terminals lie in Auerbach's plexus, not in the longitudinal muscle. It is concluded that the sensitization to noradrenaline and the increases in durations of responses to adrenergic nerve stimulation are due to inhibition of catecholamine uptake into adrenergic nerves by cocaine. It appears that, even where the neuromuscular separation is large, as it is in the colon, the concentration of exogenous noradrenaline at the receptors can be decreased by neuronal uptake, and the uptake mechanism can modify responses to nerve stimulation in vitro.
|Number of pages||10|
|Journal||Australian Journal of Experimental Biology and Medical Science|
|Publication status||Published - 1 Jun 1975|