Somatostatin-reduced proliferation of murine aplastic carcinoma conditioned to diabetes.

Murine mammary aplastic carcinoma, when it is passed from one alloxan-diabetic animal to another, after several passages becomes conditioned to hypoinsulinemia by secreting its own substance(s) immunologically cross-reactive with insulin (SICRI). Although not cytotoxic, the total daily dose of 2.5 mg of synthetic linear somatostatin per one kg body mass, administered in three or more portions, retards tumor growth in normoinsulinemic mice and the proliferation of tumors preconditioned by three serial passages in diabetics. After the first passage, somatostatin treatment has no effect on the already slow growth of the unconditioned tumor. Somatostatin-reduced tumor proliferation is accompanied by the strong suppression of insulin and SICRI levels, respectively; this effect is completely abolished by the administration of modest doses of crystalline insulin. It is concluded that somatostatin retards tumor growth by diminution of plasma levels of insulin and SICRI, respectively.