Lesions involving the suprachiasmatic nucleus eliminate the glucagon response to intracranial injection of 2-deoxy-D-glucose.

The role of the suprachiasmatic nucleus (SCN) of the hypothalamus in the glucagon response to intracranial injection of 2-deoxy-D-glucose (2DG) was examined using rats with lesions involving the SCN under 12-h light (0800-2000 h), 12-h dark (2000-0800 h) illumination. In sham-operated rats, 2DG injection into the lateral cerebral ventricle caused rapid increase in the plasma glucagon level, which was associated with increase in the plasma glucose concentration in both the light and dark period. The glucagon responses to 2DG injection in the light and dark periods were similar. In contrast, lesions involving the SCN not only reduced the plasma glucagon level before 2DG injection but also completely eliminated the glucagon response to 2DG injection, which was not associated with a rise in plasma glucose concentration. Under free feeding conditions, plasma insulin level was higher and lower in rats with the lesions involving the SCN than that in controls at 1400 h and 0200 h, respectively, but the glucagon level was lower in rats with the lesions than that in controls both at 1400 h and 0200 h. These findings suggest that the area including bilateral SCN has a regulatory (stimulatory) action on glucagon secretion from the pancreas and is involved in the glucagon response to 2DG injection into the lateral cerebral ventricle.