DIFFERENTIAL-EFFECTS OF SOMATOSTATIN AND ITS ANALOG ON PROTEIN-TYROSINE KINASES ACTIVITY IN THE RAT PITUITARY AND THE MURINE COLONIC TUMORS

The effects of the native somatostatin-14 (SST-14) and of its analog o ctreotide (OCT) on the activity of protein tyrosine kinases (PTK) in t he normal rat anterior pituitary gland, diethylstilbestrol (DES)-induc ed rat pituitary tumor and murine colonic cancer Colon 38 were studied in vitro. PTK activity was estimated in tissue homogenates using gamm a-[P-32]ATP and poly (Glu(80), Tyr(20)) as a substrate. It was found t hat both SST-14 and OCT suppressed the PTK activity in all examined ti ssues. The suppressive effect was more pronounced in DES-induced pitui tary tumor than in normal anterior pituitary gland, and in the former, OCT was more effective than SST-14. In contrast, SST-14 stronger supp ressed PTK activity in colonic cancer than OCT. We hypothesize that SS T-14 acts on PTK activity in colonic cancer mainly via SSTR-1 subtype of somatostatin receptors. (C) 1998 Academic Press.