Intra-arterial infusions of vasoactive intestinal polypeptide (VIP) were made in anaesthetized lambs in which activity of the reticulo-omasal orifice (ROO) was recorded manometrically and in conscious lambs in which activity of the reticulum, ROO and abomasum were recorded by electromyographic (EMG) techniques. 2. Spontaneous rhythmic opening and closing movements of the ROO occurred in anaesthetized lambs at 3-5 min-1. Infusions of VIP into the left gastric artery at rates of 0.5-3.0 nmol min-1 produced changes in activity of the ROO. Within 120 s of commencement of the infusions there was an increase in frequency and magnitude of the movements of the ROO for up to 120 s. This was followed with infusion of VIP at the lower levels (0.5-1.0 nmol min-1), by a marked reduction and sometimes complete loss of the rhythmic movements. There was always complete cessation of activity of the ROO with infusion of VIP at 1.5-3.0 nmol min-1. 3. In conscious lambs the frequency of the diphasic reticular EMG bursts which recur at intervals of ca. 1 min was not affected by infusions of VIP at 3.0 nmol min-1 for 10 min. 4. Between each diphasic reticular EMG burst in the conscious lamb there was normally phasic activity of the ROO consisting of EMG bursts of long (ca. 4 s) and short (ca. 1 s) duration. Within 90 s of commencement of infusion of VIP at 3.0 nmol min-1 short-burst EMG activity disappeared with the remaining long bursts being of greater duration (5.4 +/- 1.2 s) than before infusion. After a series of four to fifteen such more prolonged long bursts there was quiescence of the EMG of the ROO. After infusion of VIP EMG activity recommenced first as a series of eight to fourteen long bursts which was followed by the reappearance also of short-burst activity. Infusions of VIP at 8-10 nmol min-1 produced a more prompt cessation of EMG activity of the ROO. Of other peptides which were infused only PHI (a peptide with N-terminal histidine and C-terminal isoleucine amide) produced cessation of the EMG activity of the ROO. However, on a molar basis VIP was 2-3 times more potent than PHI in causing cessation of activity of the ROO. 5. Infusion of VIP at 3.0 nmol min-1 produced a cessation or diminution of EMG activity of the body, antrum and pylorus of the abomasum.(ABSTRACT TRUNCATED AT 400 WORDS)
