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Am J Physiol Endocrinol Metab 288: E534-E540, 2005. First published November 9, 2004; doi:10.1152/ajpendo.00451.2004
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Hepatic glycogen breakdown is implicated in the maintenance of plasma mannose concentration

T. Taguchi,1 E. Yamashita,1 T. Mizutani,1 H. Nakajima,2 M. Yabuuchi,3 N. Asano,4 and I. Miwa1

1Department of Pathobiochemistry, Faculty of Pharmacy, Meijo University, Nagoya; 2Department of Clinical Laboratory, Osaka Medical Center for Cancer and Cardiovascular Diseases, Osaka; 3Research and Development Division, Pharmaceutical Group, Nippon Kayaku Co., Ltd., Tokyo; and 4Department of Biochemistry, Faculty of Pharmaceutical Sciences, Hokuriku University, Kanazawa, Japan

Submitted 24 September 2004 ; accepted in final form 5 November 2004

D-Mannose is an essential monosaccharide constituent of glycoproteins and glycolipids. However, it is unknown how plasma mannose is supplied. The aim of this study was to explore the source of plasma mannose. Oral administration of glucose resulted in a significant decrease of plasma mannose concentration after 20 min in fasted normal rats. However, in fasted type 2 diabetes model rats, plasma mannose concentrations that were higher compared with normal rats did not change after the administration of glucose. When insulin was administered intravenously to fed rats, it took longer for plasma mannose concentrations to decrease significantly in diabetic rats than in normal rats (20 and 5 min, respectively). Intravenous administration of epinephrine to fed normal rats increased the plasma mannose concentration, but this effect was negated by fasting or by administration of a glycogen phosphorylase inhibitor. Epinephrine increased mannose output from the perfused liver of fed rats, but this effect was negated in the presence of a glucose-6-phosphatase inhibitor. Epinephrine also increased the hepatic levels of hexose 6-phosphates, including mannose 6-phosphate. When either lactate alone or lactate plus alanine were administered as gluconeogenic substrates to fasted rats, the concentration of plasma mannose did not increase. When lactate was used to perfuse the liver of fasted rats, a decrease, rather than an increase, in mannose output was observed. These findings indicate that hepatic glycogen is a source of plasma mannose.

Goto-Kakizaki rat; hepatic mannose output; glycogen phosphorylase inhibitor; glucose-6-phosphatase inhibitor


Address for reprint requests and other correspondence: I. Miwa, Dept. of Pathobiochemistry, Faculty of Pharmacy, Meijo Univ., 150 Yagotoyama, Tempaku-ku, Nagoya 468-8503, Japan (E-mail: miwaichi{at}ccmfs.meijo-u.ac.jp)






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