[Effects of cooling on cholinergically-mediated contractions of tracheal muscle taken from immature and mature guinea pigs].

The tracheal strip-chain preparations taken from immature (less than 2 weeks old) and mature (greater than 16 weeks old) guinea pigs were used to study the cooling effects of bathing temperature on cholinergically-mediated contractions. In the tracheal muscles from immature animals, cooling of the bathing temperature from 37 degrees C to 20 degrees C augmented both the contractions induced by electrical stimulation (0.05-2 Hz, 0.6 msec, 150 mA) of intramural cholinergic nerves and contractions in response to acetylcholine (0.01-3 microM), while the cooling inhibited the carbachol (0.01-3 microM)-induced contractions. The pretreatment of the tissue with physostigmine (0.05 microM) also augmented both contractions induced by cholinergic nerve stimulation and those in response to acetylcholine (0.01-3 microM), but the cooling did not produce further augmentation of the responses. On the other hand, the tracheal muscles from mature animals showed a reduced contraction in response to cholinergic nerve stimulation by cooling, although the response was potentiated by the physostigmine pretreatment. Histochemical distributions of acetylcholinesterase activities were more marked in the tracheal muscles of immature guinea pigs than in mature ones. From these results, we conclude that increased responsiveness by cooling of the isolated immature guinea pig tracheal muscle to cholinergic nerve stimulation or exogenous acetylcholine may involve the decrease of intramural acetylcholinesterase activities which might be decreased age-dependently.