The present study investigated the effects of
Hachimi-jio-gan (HJ) on diabetic
hyperglycemia in
streptozotocin (STZ)-induced diabetic rats. After STZ administration, rats had free access to pellets containing 1% HJ extract
powder for four weeks. HJ markedly suppressed
hyperglycemia in STZ-induced diabetic rats at three and four weeks after the start of administration. There were also significant increases in serum and pancreatic immunoreactive
insulin levels in STZ and HJ co-administering rats. However, in the present study, the number of beta cells in the pancreatic Langerhans' islets did not increase. Next, in order to investigate the action mechanism besides the
glycemic control action of
insulin, the expression of
glucose transporter 2 (
GLUT2) protein, which is involved in
glucose uptake and release in the liver, was investigated.
GLUT2 protein expression was increased by STZ administration but was normalized after four weeks of HJ administration. Therefore, irrespective of the structural changes in pancreatic beta-cells due to STZ, HJ increased
insulin production and secretion by the pancreas and significantly suppressed GLUT2 synthesis in the liver.
Amylase secretion from the pancreas was measured to assess pancreatic secretion.
Amylase activity was decreased by STZ but was increased by HJ. Therefore, the effects of HJ on STZ-induced
hyperglycemia in rats could be summarized as follows: besides increasing
insulin synthesis and release, HJ normalizes
GLUT2 protein expression in the liver to suppress
hyperglycemia. Hence, the results of the present study suggest for the first time that HJ affects not only the production and secretion of
insulin, but also the release of
glucose from the liver.