Progressive and concurrent deterioration of vagus-stimulated and hypoglycemia-induced glucagon secretion in streptozotocin-diabetic rats

Abstract

The effects of left cervical vagus nerve stimulation on glucagon secretion were studied in streptozotocin-diabetic and age-matched control adult male rats. At two-week intervals, after the induction of streptozotocin-diabetes, streptozotocin-diabetic and age-matched control rats were anesthetized with chloral hydrate (350 mg/kg, ip). Left cervical vagus nerves were electrically stimulated via a Grass stimulator with 5-volt monophasic pulses of 3 msec duration at a frequency of 20 Hz for 1, 2, and 4 min. Arginine-induced glucagon secretion was also determined. Vagus nerve-stimulated (2 and 4 min) glucagon secretion deteriorated as the duration of streptozotocin-diabetes increased. Glucagon secretion in response to vagus nerve stimulation was virtually absent by 12 weeks of streptozotocin-diabetes. However, arginine-induced glucagon secretion was unaffected. Subsequent experiments showed that the defect in glucagon secretion from vagal stimulation occurred concurrently with that seen from insulin-induced hypoglycemia. These results indicate that the impaired hypoglycemia-induced glucagon secretion in long-term streptozotocin-diabetic rats may be correlated with the deterioration of the parasympathetic nervous system transmission in streptozotocin-diabetes.