ONTOGENY OF FAD-LINKED GLYCEROPHOSPHATE DEHYDROGENASE IN RAT PANCREATIC-ISLETS

The activities of the mitochondrial FAD-linked glycerophosphate dehydr ogenase (m-GDH), glutamate dehydrogenase, alpha-ketoglutarate dehydrog enase, glutamate-pyruvate transaminase (GPT) and glutamate-oxaloacetat e transaminase were measured in islet and liver homogenates from fetal , neonatal, adult male, adult female, pregnant and lactating rats. Eit her parallel or dissociated ontogenic changes were observed in islet a nd liver homogenates. The activity of islet m-GDH was slightly, albeit not significantly, lower in neonates than in adult rats, comparable i n male and female adult animals, unaffected by pregnancy, and increase d during lactation. It was much higher in fetal or adult islets cultur ed for 7 days than in freshly isolated islets from adult rats. In cult ured islets from adult rats, the increase in m-GDH activity coincided with a dramatic decrease of GPT activity, a situation the mirror image of that found in several animal models of non-insulin-dependent diabe tes mellitus. The intrinsic properties of m-GDH, as judged by comparis on of measurements made by either a radioisotopic or a colorimetric pr ocedure, were not identical in islet and liver homogenates and differe d between fetal and adult islets, suggesting the existence of distinct iso-enzymes. These findings illustrate adaptive changes of islet enzy mes, with exclusive or partial mitochondrial location, in ontogenic si tuations characterized by a remodelling of fuel homeostasis.