Cyclic ADP-Ribose Measurements in Rat Pancreatic Islets

Abstract

Cyclic ADP-ribose was measured by a radioimmunological procedure in rat pancreatic islets. The cyclic ADP-ribose content of the islets was much lower immediately after isolation (≤ 2.3 ± 0.2 fmol/islet) than after a further incubation of 90 min in a salt-balanced medium (26.4 ± 1.3 fmol/islet). Under the latter condition, the islet cyclic ADP-ribose content was not affected by the concentration of D-glucose and/or D-fructose in the incubation medium and, when expressed per μg protein, was 3- to 30-fold higher than that found in other biological samples such as liver, whole pancreas or tumoral islet cells. Although these findings might suggest a physiological role for cyclic ADP-ribose in islet cells, they argue against the view that the cyclic nucleotide acts as a coupling factor in the process of hexose-stimulated insulin release.