Postnatal changes in the amount of acetylcholine in the atrial tissue of the albino rat heart.

Changes in the acetylcholine (ACh) content and concentration in the atrial tissue of albino rats between the third day of postnatal life and adulthood were studied. The ACh content (ng in whole atria) rose during the whole of the period in question, from 5.6 ng at 3--4 days to 307.5 ng in adult rats. The ACh concentration (micrograms/g fresh tissue) rose up to the 53rd day after birth, when it attained adult values. The fastest increase in both the ACh content and concentration was observed between the 10th and the 17th postnatal day, when it amounted to over 46% of the total concentration increase between the third day of life and adulthood.