Histamine tachyphylaxis in young dog airway--compared with adult dog

The phenomenon of histamine tachyphylaxis in vitro previously observed in the airway smooth muscle from adult dogs was investigated in airway smooth muscle from young dogs (age 72-96 days; mean: 91 days). Tachyphylaxis was demonstrated by repetitive exposure to 10(-4) M histamine (4th contractile response was 53.0 +/- 4.9% of the initial histamine contraction; n = 6, P less than 0.01). This result was similar to that previously reported (Anderson et al., 1979) in adult canine tracheal smooth muscle. Tachyphylaxis to histamine was demonstrated also by repetitive exposure to histamine (10(-4) M) in the small airway smooth muscle (2 mm diameter), (4th contractile response was 59.6 +/- 7.2% of the initial histamine contraction; n = 6, P less than 0.01). This tachyphylaxic response is not present in the small airways from adult animals. The development of histamine tachyphylaxis in both tracheal and small airway smooth muscle could be prevented or reversed by preincubation of the tissue with indomethacin (2.8 x 10(-6) M). The composite information thus implicates prostaglandins as the most probable mediators of the process. These results suggest that the variable phenomenon of histamine tachyphylaxis is dependent on the maturity of the animal and on the size of the airway.