The degradation of histamine in some animal species.

The aim of this work was 1. determine the major [3H]-metabolites of histamine in vivo by using the musculus gracilis of the dog, and in vitro in different tissues of the cat, 2. determine the endogenous levels of histamine and N tau-methylhistamine in some tissues of the cat and the rat. [3H] histamine injection into arterial supply of the muscle of the dog: after 60 minutes the content of [3H] histamine in the muscle was 1.9 +/- 0.6% and the content of [3H] N tau-methylhistamine and [3H] 'Acid metabolites' was 47 +/- 6.7% and 51.0 +/- 6.5%. The cat tissues in vitro showed the following t1/2 for exogenous histamine: submandibular gland, 95.9 min, parotid gland, 36.1 min, stomach pylorus, 39.5 min, thyroid gland, 28.3 min, liver, 23.7 min. Endogenous levels of histamine and N tau-methylhistamine were determined in the cat and the rat. In general, the contents of endogenous histamine and N tau-methylhistamine were similar to the data obtained with labelled [3H] histamine. In both species submandibular gland was among the richest tissues in N tau-methylhistamine content. The provenience of N tau-methylhistamine in mast cells is discussed.