[Seasonal changes in the acetylcholine and noradrenaline content and the sensitivity to these substances in the smooth musculature of the small intestine in the rat].

Sensitivity of the rat intestine's smooth muscle to acetylcholine (A) and noradrenaline (NA) changes in opposite directions during the year. Starting from the end of November the sensitivity to A grows gradually whereas the sensitivity to NA decreases, the maximum of the former coinciding with the minimum of the latter by the end of winter and in spring, whereas the minimum of A sensitivity coincides with the maximum of NA sensitivity in September-November. Study of the season-related changes of A and NA contents in the small intestine tissue revealed the greatest amount of A (8.0-11.5 X 10(-5) M/g) during the spring months and the least amount (3.7-5.9 X 10(-5) M/g) during the autumn and winter months. The maximal contents of NA (603-700 mg/g) occurs in autumn and the minimal that (271-390 mg/g) in spring and summer time. Like the A and NE sensitivity, the A and NA contents in the small intestine tissue changes during the year in opposite directions.