THE INFLUENCE OF AGE ON ISOLATED TRACHEAL RESPONSIVENESS TO SPASMOGENS

The influence of animal age was examined on the responses of guinea-pi g (birth-156 weeks) and rat (4-136 weeks) isolated tracheal tissue to the spasmogens histamine, 5-hydroxytryptamine (5-HT) and potassium ion s (K+) using functional and biochemical techniques. Over the ages birt h-12 weeks in the guinea-pig, K+ potency decreased 1.5 fold whereas hi stamine potency increased 2-fold between the ages of birth-2 weeks and then declined to original levels by age 20 weeks. 5-HT potency declin ed over the entire age range examined, resulting in a 25.1 fold decrea se between the ages of 1 and 156 weeks. In the rat, 5-HT potency remai ned unchanged and a small but progressive increase in K+ potency was o bserved with respect to animal age. Significant age-related changes in inositol phosphate accumulation were observed in both unstimulated an d histamine-stimulated isolated guinea-pig tracheal smooth muscle whic h did not correlate with the functional changes observed in response t o spasmogenic stimulation. The results describe disparate age-related changes between two species of different spasmogenic agonists with the majority of age-related changes occurring during the maturation phase of growth of the guinea-pig. (C) 1998 Elsevier Science B.V.