IS SUB-MAXILLARY GLAND IMMUNOREACTIVE GLUCAGON IMPORTANT IN CARBOHYDRATE HOMEOSTASIS

Previous investigators have shown rat submaxillary gland extracts to contain large amounts of material immunologically similar to pancreatic glucagon (SM-IRG). The present studies were designed to assess any physiologic contribution of this material to plasma immunoreactive glucagon (IRG) levels and to overall carbohydrate homeostasis in the rat. Bilateral submaxillary glandectomy or sham surgery was performed on adult male rats. After 2-4 wk, these animals were subjected to arginine or epinephrine infusion, fasting, insulin-induced hypoglycemia, or oral glucose loads. No measurable differences could be found between animals with or without submaxillary glands with respect to basal plasma levels of IRG, immunoreactive insulin (IRI), blood glucose (BG), or to the response of these parameters to any of the conditions tested. Furthermore, when eviscerated animals (without gastrointestinal tract or pancreas, but with intact liver and kidneys) were studied with or without submaxillary glands, no significant differences were found in either basal or stimulated levels of plasma IRG and BG. We conclude that SM-IRG makes no significant contribution to either plasma IRG or the metabolism of carbohydrates in the rat, even when other known sources of IRG have been surgically removed. While being unable to document any apparent role for SM-IRG in the maintenance of carbohydrate homestasis, we did observe dynamic changes in the glandular content of SM-IRG that occurred with the onset of puberty in both male and female weanling rats. The possibility, thus, remains that SM-IRG may be physiologically important, but in areas not necessarily related to carbohydrate metabolism. © 1979.