AJP - Regulatory, Integrative and Comparative Physiology, Vol 249, Issue 1 23-R30, Copyright © 1985 by American Physiological Society
Time-dependent effect of insulin in suprachiasmatic nucleus on blood glucose
T. Mori, K. Nagai, M. Hara and H. Nakagawa
Studies were made on the effects of insulin (30 or 300 microU) injected
into the suprachiasmatic nucleus (SCN) of the hypothalamus on the plasma
glucose and insulin concentrations in pentobarbital-anesthetized rats,
which had been kept under 12:12 light-dark conditions. Insulin injection
caused a decrease in the plasma glucose concentration in the light period
but an increase in the dark period, these changes being significant within
2 min after injection. Insulin injection also caused a decrease in plasma
insulin concentration in the light period but a tendency for its increase
in the dark period. Intraperitoneal injection of insulin at the same dose
did not affect the plasma glucose or insulin concentration in either the
light or dark period. Insulin injection into the SCN decreased glycogen
phosphorylase a activity but increased glycogen synthase I activity in the
liver in the light period, but the insulin injection did not affect the
activities of these enzymes in the dark period. Lesions including bilateral
SCN completely eliminated the responses of the plasma glucose and insulin
concentrations to insulin injection both in the light and dark periods.
These findings suggest that insulin injection into the SCN causes
time-dependent changes in plasma glucose through changes in activities of
glycogen metabolizing enzymes in the liver in the light period but through
other mechanisms in the dark period.
