Effects of the vagus nerves on gastric motility and release of vasoactive intestinal polypeptide in the anaesthetized lamb.

1. Effects of the vagus nerves on the activity of the reticulo-omasal orifice (ROO) and the abomasum and the concentration of vasoactive intestinal polypeptide (VIP) in gastric and intestinal venous effluent were studied in anaesthetized lambs. 2. Both excitatory and inhibitory effects of the vagus on the ROO and abomasum were demonstrated. Excitation of activity of the ROO was dominant with stimulation at lower frequencies (less than or equal to 20 Hz) whereas higher frequencies (50-70 Hz) caused inhibition. 3. Inhibition but not stimulation of the ROO and abomasum were obtained with vagal stimulation after administration of atropine (200-500 micrograms kg-1 I.V.). 4. The concentration of VIP in gastric venous effluent blood rose by 41 +/- 10 pmol l-1 (n = 13) within 90 s of the start of stimulation (10 Hz, 5 ms pulse duration, 10 V for 180 s) of a vagus nerve and fell within 60 s of its cessation to or near basal levels. The effects of vagal stimulation in changing the concentration of VIP were not altered by administration of atropine. 5. The concentration of VIP in the intestinal venous effluent increased during stimulation (10 Hz, 5 ms pulse duration, 10 V, for 180 s) of a vagus nerve by 15 +/- 5 pmol l-1 (n = 11) and remained elevated for more than 10 min after the stimulus had ceased. 6. The changes in gastric motility and in concentration of VIP in gastric and intestinal venous blood with stimulation of the vagus nerves have been discussed in relation to similar alterations which occur in lambs during sucking of milk.