Sensitivity and responsiveness of tracheal and bronchial tissues from young and old guinea pigs: effect of calcium antagonists.

Barium chloride contracted tracheas and bronchi from young and old guinea pigs and was equipotent in all tissues. Efficacies were significantly greater in tracheal vs. bronchial tissues within and between age groups. The effects of nitrendipine and verapamil were completely reversible with washing in tissues from young animals; in tissues from old animals the effects of the antagonists were irreversible. Nitrendipine (10, 50 and 100 nM) reduced the efficacy of barium chloride in tissues from old animals from 0 to 70%, depending upon the tissue source and the concentration of calcium channel blocker used. Verapamil (1-10 microM) reduced the contractile response of tracheal tissues from old animals to barium by 50% at the maximally effective concentration of the agonist. In contrast, in tissues from young animals, nitrendipine (50-100 nM) totally abolished the response to barium whereas 10 nM reduced efficacy by 80% without affecting tissue sensitivity. Verapamil (1 microM) reduced responses in tracheal and bronchial tissues from young animals by approximately 60%. In preparations incubated with polyethylene glycol 400 (vehicle for nitrendipine, 1 microgram/ml final bath concentration), neither efficacy nor potency of barium chloride was altered in tracheal or bronchial tissues from young animals; in bronchial and tracheal tissues from old animals, efficacy was slightly increased. Indomethacin pretreatment abolished the effects of polyethylene glycol incubation. Carbachol- and histamine-induced contractions of tracheal and bronchial tissues from young and old guinea pigs were unaffected by nitrendipine. These agents require calcium for contraction.(ABSTRACT TRUNCATED AT 250 WORDS)