The influence of age on isolated tracheal responsiveness to spasmogens

The influence of animal age was examined on the responses of guinea-pig (birth-156 weeks) and rat (4-136 weeks) isolated tracheal tissue to the spasmogens histamine, 5-hydroxytryptamine (5-HT) and potassium ions (K+) using functional and biochemical techniques. Over the ages birth-12 weeks in the guinea-pig, K+ potency decreased 1.5 fold whereas histamine potency increased 2-fold between the ages of birth-2 weeks and then declined to original levels by age 20 weeks. 5-HT potency declined over the entire age range examined, resulting in a 25.1 fold decrease between the ages of 1 and 156 weeks. In the rat, 5-HT potency remained unchanged and a small but progressive increase in K+ potency was observed with respect to animal age. Significant age-related changes in inositol phosphate accumulation were observed in both unstimulated and histamine-stimulated isolated guinea-pig tracheal smooth muscle which did not correlate with the functional changes observed in response to 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.