INHIBITION OF TUMOR-GROWTH INDUCED BY HISTAMINE - INVIVO AND INVITRO STUDIES

An experimental mammary carcinoma was induced in rats by the i.p. administration of N-nitroso N-methylurea (NMU) in 3 doses of 50 mg/kg. In order to study the role of histamine (Hi) and its receptors in tumor growth, in vivo and in vitro treatments were carried out. Different groups of animals received a daily s.c. injection of Hi 0.1 mg/kg, starting with the first dose of NMU. Hi significantly reduced tumor incidence and the number of tumors developed per rat. The in vitro studies, using the clonogenic agar technique, showed no difference in colony formation between control, 0.01 and 0.1 muM Hi treatment, while 1 and 10 muM Hi concentrations induced inhibition of cell growth up to 60 %. This effect was abolished by H-1 antagonists. Conversely, the action of the H-2 antagonists was a significant inhibition of colony formation. We may then conclude that in these experimental tumors, histamine exerts a regulatory function on cell growth by acting directly on specific membrane receptors.