AGE AND REGION-DEPENDENT CONTRACTION TO ALPHA-ADRENOCEPTOR AGONISTS IN RAT AND GUINEA-PIG ISOLATED TRACHEA

1 The influence of age and of region on alpha-adrenoceptor-mediated co ntraction to (-)-adrenaline and (-)-noradrenaline was examined in rat (4-136 weeks) and guinea-pig (2-156 weeks) isolated tracheal ring prep arations with particular emphasis on the early (up to 12 weeks) matura tion phase. 2 In rat tracheal rings, significant regional variation wa s observed with respect to maximal (-)adrenaline-induced contraction, such that the greatest activity was seen in ring preparations from the laryngeal end of the trachea. Tracheal rings from the carinal end res ponded very poorly or were unresponsive to (-)-adrenaline, depending o n animal age. These regional differences were seen across the age rang e. The potencies of (-)-adrenaline and (-)-noradrenaline remained unch anged with respect to animal age, but the maximum contractile tension that developed in response to these agonists increased with increasing animal age in all regions of the trachea. 3 In guinea-pig isolated tr acheal tissue, maximum contractile responses (E-max) to (-)-adrenaline and (-)-noradrenaline remained unchanged with increasing animal age. In addition, there was no evidence for a region-dependence in the resp onsiveness of tracheal tissue to alpha-adrenoceptor-mediated contracti on in this species. 4 In both guinea-pig and rat isolated tracheal tis sue, alpha-adrenoceptor-mediated contraction appeared to involve the a ctivation of alpha(1)-adrenoceptors.