INVIVO INHIBITION OF THE RAT PRIMARY ANTIBODY-RESPONSE TO ANTIGENIC-STIMULATION BY SOMATOSTATIN

Somatostatin inhibits in vitro lymphocyte proliferative responses from a variety of species including human, mouse and rat. The immunoinhibi tory effects of somatostatin are thought to involve binding to specifi c cell surface somatostatin receptors on immunocompetent cells. This r eport describes an in vivo immunoinhibitory effect of somatostatin on the rat popliteal lymph node lymphocyte primary antibody response to s heep red blood cell (SRBC) stimulation. Infusion of somatostatin immed iately following SRBC injection into the hind feet of rats had a dose- related inhibitory effect. At the highest concentration used, 10 mumol /L, the level of inhibition was similar to that previously described f ollowing neonatal capsaicin treatment of rats. This suggests that neon atal capsaicin treatment may lead to decreased primary antibody respon ses to SRBC by a selective effect on tachykinin containing nerves and a lesser effect on somatostatin containing nerves. The immunoinhibitor y effect of somatostatin was reversed by co-infusion of neurokinin A b ut not substance P, both of which have been shown to stimulate this re sponse. This suggests the possibility that multiple tachykinin recepto rs are involved in the modulation of the SRBC primary antibody respons e in vivo. These results present evidence for an in vivo immunomodulat ory role of somatostatin.