The influence of a simulated digest of an equine dietary feed additive G's formula on contractile activity of gastric smooth muscle in vitro.

G's Formula is a novel equine feed additive formulated to promote optimal GI function. The objective of this study was to determine whether the addition of a simulated digest of the composite feed additive G's Formula (FA) would alter the contractile response of gastric smooth muscle to acetylcholine (Ach). Smooth muscle strips from porcine stomachs were excised and attached to an isometric force transducer. An experiment was run to compare tissue contraction between tissue exposed to FA (FA; n = 8, simulated digest of FA was added to the bath) and control tissue (CO; n = 8, no additions made). Increasing concentrations of Ach were added into the bath such that the concentration increased from 10-8 -10-3  M. Based on the analysis of these data, a difference between FA and CO was observed. Therefore, another trial was run which included a blank group (BL n = 6) in which the tissue was exposed to the simulated digest without FA. More CO (n = 5) and FA (n = 4) tissue was also run. Force was compared to baseline and between groups. In FA group, mean force for 1-min following all Ach additions was higher than baseline (p < .05) and by 2-min the integral-under-force/time curve (AUC) was higher than baseline from 10-7 -10-3  M compared to lower concentrations of Ach in both CO (10-6  M for both) and BL (10-5  M and 10-6  M, respectively). By 8-min AUC of all Ach concentrations were higher than baseline in FA compared to an Ach of 10-6  M in both CO and BL. A simulated digest of FA appears to sensitize gastric smooth muscle to Ach in vitro. FA may increase GI contractility, and the functional effect of this should be studied further in vivo.