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Postnatal development of responsiveness to adrenergic agents of longitudinal and circular smooth muscles from cat
Abstract:
The changes in the responsiveness of the isolated longitudinal and circular smooth muscles from cat terminal ileum to adrenergic agents during the postnatal period were studied by the effect of noradrenaline (0.01-100 mumol) on the smooth muscle tone and phasic contractions. Cumulatively applied noradrenaline (0.01-10 mumol) decreased the longitudinal muscle tone without age-dependent differences via inhibitory alpha 1-adrenoceptors. Noradrenaline decreased the phasic contraction amplitude of longitudinal muscle via inhibitory alpha 1-adrenoceptors. Cumulatively applied noradrenaline (0.01-10 mumol) exerted an age-dependent effect on the circular muscle tone via stimulatory alpha 1-adrenoceptors. alpha 1-adrenoceptors continue to develop functionally at 60 days postnatal. Noradrenaline decreased the phasic contraction amplitude of the circular muscle and exerted a stimulant effect on the tone which suggested an existence of two alpha 1-adrenoceptor subtypes.