Vasopressin secretion after stimulation of abdominal vagus in rabbit: role of A1 norepinephrine neurons.

We determined whether electrical stimulation of the abdominal vagus nerve causes secretion of vasopressin in the rabbit and whether inhibition of neuronal function in the A1 region of the medulla oblongata impairs this secretion. In urethan-anesthetized rabbits, electrical stimulation of the abdominal vagus (5-min train of cathodal pulses, 0.5 ms duration, 20 Hz, 0.5-1 mA) increased plasma vasopressin from 37 +/- 8 to 133 +/- 19 pg/ml (P < 0.01, n = 11). Prior section of the cervical vagus completely prevented the increase seen with stimulation of the abdominal vagus. Injecting the inhibitory agent muscimol (1 nmol) 2 mm dorsal to the A1 area did not significantly reduce the vasopressin response to abdominal vagal stimulation. However, when muscimol was injected into the A1 area, the vagally mediated increase in plasma vasopressin was completely prevented. Our results show that stimulation of abdominal vagal afferents causes secretion of vasopressin in the rabbit via a central pathway that includes neurons in the A1 area.