Fructose 1,6-bisphosphatase and aldolase B location in organs of sheep supplemented with nonprotein nitrogen

Abstract

In ruminants, ammonia interferes in gluconeogenesis, reducing conversion of propionate to glucose. The importance of renal and hepatic gluconeogenesis in ruminants is well established, but cellular localization of the key gluconeogenic enzymes liver fructose-1,6-bisphosphatase (FBPase, EC.3.1.3.11) and aldolase B (AldoB, EC.4.1.2.13) in these organs and the potential contribution of other tissues in this process have not been investigated. The objective of this study was to determine the effect of nonprotein nitrogen (NPN) diets on the cellular localization of FBPase and AldoB in sheep organs. Eighteen sheep, allotted to three groups, were supplemented with NPN in the diet every 8 h for 18 days: Control (no NPN, 16.8 % crude protein (CP)), moderate NPN = 182 mg N/kg0.75 (22.9 % CP), and high NPN = 425 mg N/kg0.75 (30.7 % CP). Animals were slaughtered and pieces of organs were collected. Immunostaining for FBPase and AldoB expressions were examined by light microscopy, and co-localizations of these enzymes were examined with a confocal microscope. FBPase and AldoB were expressed in the cytoplasm of periportal hepatocytes, proximal tubular cells of the kidney, columnar absorptive cells of the duodenum, submucosa of the rumen, and β cells of Langerhans’ islets in the pancreas. Moreover, AldoB revealed to be located in the nucleus of hepatocytes. The localizations of both enzymes were not modified by NPN supplementation. In conclusion, FBPase and AldoB were detected in sheep tissues other than the liver and kidney, suggesting their potential contribution to gluconeogenesis or other functions in these tissues and their expressions were not changed by the inclusion of NPN in the diet.