Cyproheptadine-induced alterations in clonal insulin-producing cell lines

Abstract

Cyproheptadine (CPH) inhibits glucose-stimulated insulin synthesis and secretion, and reversibly depletes pancreatic insulin content in the rat. To examine whether the inhibitory actions of CPH on insulin cell function are linked to the ability of glucose to stimulate insulin synthesis and secretion, studies were performed in two different insulin-producing cell lines. CPH effects were compared in HIT-T15 cells, which respond to glucose with increased insulin synthesis and secretion, and in glucoseunresponsive RINm5F cells. CPH produced similar alterations in both cells lines. After a 48-hr culture period in the presence of 0, 0.1, 1.0 or 10.0μM CPH, cellular insulin stores and media insulin levels were decreased in a concentration-dependent manner. At 10.0 μM CPH, RIN and HIT cell insulin content declined to 34 and 33% of controls respectively. Cellular insulin returned to control levels 48 hr after removal of CPH. In experiments designed to test a direct inhibitory effect on stimulated insulin secretion, 1 and 10.0 /smM concentrations of CPH were found to inhibit glucose-stimulated insulin release from HIT cells, and K +, alanine and glyceraldehyde-stimulated release from RIN cells. CPH was also shown to inhibit insulin biosynthesis in both cell lines at concentrations that did not alter the synthesis of total cellular proteins. All of these alterations in cellular function were shown to occur at CPH concentrations that did not affect cell growth or viability. The results show that the actions of CPH do not appear to be dependent upon the existence of operational glucose signalling mechanisms for insulin synthesis and secretion.