The effect of Vasoactive Intestinal Peptide (VIP) on muscle strips from the reticular groove, the reticulo-omasal orifice (ROO) and the omasal canal was studied. VIP caused a concentrationdependent (10-8-5 .10-7 mol/l) reduction of the acetylcholine-induced (55 . mol/l) contraction of the reticular groove muscle preparations from calves and adult cattle. VIP was more effective in the muscle strips from calves than in those from adult cattle. Moreover, the circular muscle strips from the reticular groove were more sensitive to VIP than the longitudinal muscle strips.VIP also induced a concentration-related (10+-5 . io-'mol/l) relaxation of muscle strips from the calf ROO. Furthermore, both circular and longitudinal muscle strips from the omasal canal of the calf were relaxed by VIP (10-'-5~10-7m0l/l). The relaxing effect of VIP on the circular muscle strips from the reticular groove of the calf was not significantly affected during incubation with 5 . 10dmoVl tetrodotoxin. The relaxing effect of VIP therefore seems to be mediated by VIP receptors of smooth muscle cells.These properties of VIP in conjunction with its presence in nerve fibres located in the wall of the reticular groove and ROO are consistent with a role of VIP as inhibitory transmitter in this region of the bovine stomach.

Summary The effect of noradrenaline (NA) on smooth muscle strips from the reticular groove of adult cattle was studied. The mechanical activity of the muscle strips was recorded isometrically. Noradrenaline caused concentration dependent (1.1 · 10−6 ‐ 55 · 10−6mol/l) contractions of both the transversal muscle strips from the floor and the longitudinal muscle strips from the lips of the reticular groove. This excitatory effect of noradrenaline was antagonized by the α‐receptor antagonist prazosine (10−8 mol/1) and by higher concentrations of the α2‐receptor antagonist yohimbine (10−6 mol/1) and atropine (10−5 mol/1). Tetrodotoxin (5 ·10−6 mol/1) and latrotoxin did not affect the contractile response of the muscle strips to noradrenaline (55 · 10−6 mol/l). Furthermore, strips stored for 24 hours in Tyrode's solution at 4 °C without oxygen supply maintained their full sensitivity to noradrenaline. Propranolol (10−4 mol/1), a β‐receptor antagonist, led to a significant increase of the contractions induced by noradrenaline (55 · 10−6 mol/l). These results suggest that noradrenaline increases the tone of the smooth muscle of the reticular groove via α‐adrenergic receptors and decreases its tone via β‐adrenergic receptors. Both receptor types are located on the smooth muscle cells. The α1‐receptor mediated effect appears to be predominant.

The effect of electrical field stimulation (EFS) on smooth muscle strips from the chicken crop was investigated. The EFS (5 Hz, 2 ms, 400 mA; 10 Hz, 2 ms, 400 mA; 5 Hz, 2 ms, 500 mA; 10 Hz, 2 ms, 500 mA) produced contractions in all preparations. Atropine (10(−5) mol l−1) diminished muscle contraction in response to EFS. Tetrodotoxin (5 X 10(−6) mol l−1) fully suppressed the contractile responses to EFS. A serotonin antagonist (methysergide, 10(−4) mol l−1) did not alter contractions elicited by EFS. Propranolol (10(−5) mol l−1) led to an increase of contractions induced by EFS. Noradrenaline (10(−6)−10(−4) mol l−1) reduced acetylcholine‐induced (1.1 X 10(−6) mol l−1) contraction of the crop smooth muscle strips. Propranolol (10(−5) mol l−1) abolished noradrenaline‐induced relaxation almost fully. Tetrodotoxin (5 X 10(−6) mol l−1) did not change the relaxing effect of noradrenaline. These results suggested that the responses of crop smooth muscle to EFS involve excitatory cholinergic and non‐cholinergic (probably peptidergic) as well as inhibitory adrenergic nerves.