An environment for development.

-The influence of some biogenic amines and amine-receptor-blocking drugs in the growth rate of human colorectal carcinomas propagated as s.c. xenografts in immune-deprived mice was studied. In mice treated with adrenaline, a /3-adrenergic agonist, the growth of xenografts was suppressed for 2 days, after which growth was resumed at a rate similar to that in control animals. Treatment with the phosphodiesterase inhibitor theophylline prolonged the adrenaline-induced inhibition of growth. Treatment with the /-adrenergic antagonist sotalol or practolol increased the rate of tumour growth. Treatment with either serotonin or the histamine H2-receptor agonist Dimiprit had no effect on tumour growth rate. However, the antiserotoninergic drug BW 501C and the histamine H2-receptor antagonist cimetidine each caused short-term suppression of tumour growth.