Progressive Adaptation of the Endocrine Pancreas during Long-Term Protein Deficiency in Rats: Effects on Blood Glucose Homeostasis and on Pancreatic Insulin, Glucagon and Somatostatin Concentrations

Abstract

Blood glucose, plasma insulin and glucagon, as well as pancreatic insulin, glucagon and somatostatin contents, were measured in control (C group, 18% casein), deprived (D group, 5% casein) and pair-fed (PF) rats at seven intervals during 23 wk after weaning (wk 0). In C rats, plasma and pancreatic insulin showed parallel variations, in D rats, plasma insulin increased normally until wk 3 after weaning, dropped from wk 3 to 8 and was higher in wk 16 and 23 than in wk 8, while pancreatic insulin increased linearly after a significant drop between wk 0 and 1. Insulin variations in D rats were related to protein deficiency until wk 5, but only to energy deficiency thereafter. Circulating and pancreatic glucagon dropped identically for the three groups until wk 5: its role in adaptation to malnutrition is quite irrelevant, although a dysregulation of its secretion was noted. Protein-energy malnutrition induced an increase of pancreatic somatostatin content that was due to the energy deficiency. On the basis of the insulin-to-glucagon ratio, three phases of adaptation to protein-energy malnutrition appeared. From wk 0 to 3, the metabolic priority was growth, whereas glucose homeostasis was secondary, accounting for the early hypoglycemia. From wk 3 to 8 survival was the main priority. After wk 8, the various biochemical parameters stabilized, and growth was parallel to that of normal animals. Protein-energy malnutrition was responsible for a dissociated adaptation of pancreatic hormones.