Alterations in histamine levels in the rat induced by compound 48/80

Histamine release in the rat was induced in vivo either by a single dose of compound 48/80 injected i.v. or by four repeated, daily doses of the same compound injected i.p. After i.v. injection the levels of blood histamine were determined and after i.p. injections the changes in both tele-methylhistamine and histamine levels in different tissues were investigated. I.v. injection of 48/80 induced a very rapid and marked increase of blood histamine by 7.4 to 11-fold over the control levels within the first two minutes. After repeated i.p. injections of compound 48/80 most tissues showed higher than normal tele-methylhistamine/histamine ratios. The results suggest that agents known to induce release of histamine from mast cells may exert significant changes in blood and tissue histamine levels and that liberated histamine is thereafter extensively catabolized.