AJP - Endocrinology and Metabolism, Vol 256, Issue 1 E159-E166, Copyright © 1989 by American Physiological Society
Fasting and postabsorptive hepatic glucose and insulin metabolism in hyperthyroidism
N. Raboudi, R. Arem, R. H. Jones, Z. Chap, J. Pena, J. Chou and J. B. Field
Department of Medicine, Baylor College of Medicine, Houston, Texas.
The effect of thyroid hormone excess on hepatic glucose balances and
fractional hepatic extraction of insulin and glucagon was examined in six
conscious dogs with catheters in the portal vein, hepatic vein, and femoral
artery and Doppler flow probes on the portal vein and hepatic artery. An
oral glucose tolerance test was performed before and after the animals were
made hyperthyroid by intramuscular thyroxine administration (100
micrograms.kg-1.day-1) for 10 days. In the basal state and after oral
glucose, insulin and glucagon levels in the three vessels and the basal
fractional hepatic extraction of insulin and glucagon were not
significantly modified by thyroid hormone. These results suggest that in
short-term thyrotoxicosis insulin secretion is not impaired, and the rise
in fasting plasma glucose and increased hepatic glucose production could
reflect hepatic insulin resistance, increased availability of precursors
for gluconeogenesis, or increased glycogenolysis. Hyperthyroidism
significantly increased basal flows in the portal vein (14.7 +/- 0.6 vs.
12.9 +/- 0.5 ml.kg-1.min-1), the hepatic artery (4.8 +/- 0.3 vs. 3.9 +/-
0.2 ml.kg-1.min-1) and vein (19.6 +/- 0.7 vs. 16.9 +/- 0.4 ml.kg-1.min-1),
the fasting plasma glucose concentration (104 +/- 3 vs. 92 +/- 2 mg/dl),
and basal hepatic glucose output (2.1 +/- 0.2 vs. 1.5 +/- 0.2
mg.kg-1.min-1). It did not alter the nonhepatic splanchnic uptake of
glucose, the percent of orally administered glucose that appeared in the
portal vein (47 +/- 2 vs. 45 +/- 11%), the percent of hepatic uptake of
glucose (59 +/- 11 vs. 74 +/- 22%), or the shape of the glucose tolerance
test.
