Histamine 2 receptor-mediated immunomodulation in the mouse. I. Immunomodulation by the H2 agonist tolazoline.

Tolazoline, a drug used in the treatment of hypertension, has been described as a typical H2 agonist. In this study possible immunomodulating properties of tolazoline were investigated. A single injection of tolazoline 1 day before immunization caused an effect on delayed hypersensitivity that depended on the antigen dose. The response to 10(5) and 10(6) sheep red blood cells (SRBC) was decreased, whereas the response to 10(9) SRBC was enhanced. Administration of tolazoline 4 days after immunization predominantly affected the humoral response. The IgM response was inhibited in favour of the IgG response. Low doses of tolazoline, given to animals simultaneously with the elicitation for delayed hypersensitivity, lead to a more severe inflammation. The possible involvement of suppressor cells and vessels in tolazoline action is discussed. The application of tolazoline in the immunotherapy of human cancer is suggested.