Histamine response in developing chick oesophagus

Developmental changes in response to histamine were investigated in the oesophagus isolated from the chick between 15 days of incubation and 15 days after hatching. The contraction could be already caused by histamine (20 μM) in the chick oesophagus from 15 days of incubation. The pD₂ values for histamine and acetylcholine did not change during the period between 17 days of incubation and 5 days after hatching. The response to histamine (20 μM) was extremely resistant to tetrodotoxin (0.78 μM), procaine (0.2 mM) and atropine (1 μM) during the period between 17 days of incubation and 20 days of incubation. The tetrodotoxin-resistant response was replaced by a tetrodotoxin-sensitive response after hatching. On the other hand, the neuronal response induced by transmural electrical stimulation (20 Hz) or dimethylphenylpiperazinium (20 μM) was uniformly sensitive to tetrodotoxin throughout the periods. Mepyramine (2 μM), but not metiamide (20 μM), inhibited the histamine-induced responses in every age tested. These results suggest that the myogenic receptivity of histamine transiently increases during the terminal period of embryonic development and declines after hatching.