Effects of nicotinamide on clonal rat insulinoma cell proliferation, polyamine content and insulin secretion.

Tumoral insulin-secreting cells (RINm5F) were cultured for 4 days with nicotinamide, a poly (ADP-ribose) synthetase inhibitor. This resulted in a dose-dependent inhibition of the cellular proliferation rate, along with a modest decrease in cell viability. Nicotinamide failed to affect the cellular insulin content, but reduced the insulin secretion into the culture medium. Nicotinamide treatment furthermore reduced the cellular content of polyamines, compounds seemingly involved in regulation of the growth and function of insulin-producing cells. Restoration of the decreased polyamine content by the concomitant addition of the polyamine precursor putrescine failed to influence the decreased proliferation rate and insulin secretion, indicating that the inhibitory effects of nicotinamide on these functions cannot be ascribed to the decrease in polyamine content.