Histamine-n-methyltransferase activity of the nervous system of the chick during development.

The developmental course of histamine-N-methyltransferase activity was determined in the chick pineal gland, thalamus, cerebral hemispheres, cerebellum and sciatic nerve from the 13-day embryo to 1-week post-hatching. In each tissue, low levels of enzyme activities were detectable in the 13-day embryo. Thereafter, to the stage of hatching activity rose rapidly in the pineals, thalamus and peripheral nerve. Enzyme activity in the pineals decreased after hatching and remined at a relatively low pre-hatch level in the 7-day chick. In the sciatic nerve and thalamus activity also dropped slightly after hatching. The increase of enzyme activity in the cerebellum and cerebellum hemispheres was very gradual after the 13th day of embryonic stage and maximum activities were obtained only 2 days after hatching. Highest specific activities of the enzyme were detected in the sciatic nerve, pineals and thalamus at each developmental stage. The Km values for histamine and S-adenosyl-l-methionine and the behavior towards certain drugs of the enzyme in the pineals and sciatic nerve did not change significantly during development.