Dietary exposure to ergot alkaloids decreases contractility of bovine mesenteric vasculature.

Ergot alkaloids are hypothesized to cause vasoconstriction in the midgut, and prior exposure may affect the vasoactivity of these compounds. The objectives of this study were to profile vasoactivity of ergot alkaloids in bovine mesenteric artery (MA) and vein (MV) and determine if previous exposure to endophyte-infected tall fescue seed affected vasoactivity of ergocryptine (ERP), ergotamine (ERT), ergocristine (ERS), ergocornine (ERO), ergonovine (ERN), lysergic acid (LSA), ergovaline-containing tall fescue seed extract (EXT), and 5-hydroxytryptamine (5HT; serotonin). Ruminally cannulated Angus steers (n = 12; BW = 547 ± 31 kg) were paired by weight and randomly assigned to 6 blocks. Steers were ruminally dosed daily with 1 kg of either endophyte-infected (E+; 4.45 mg ergovaline/kg DM) or endophyte-free (E-; 0 mg ergovaline/kg DM) tall fescue seed for 21 d before slaughter. Branches of MA and MV supporting the cranial portion of the ileum were collected after slaughter on d 22, placed in a modified Krebs-Henseleit buffer on ice, cleaned, sectioned, and mounted in a multimyograph chamber. Contractile response was normalized to a maximum KCl response. Inner diameter (P = 0.04) and outer diameter (P = 0.02) of MA were smaller for E+ steers than E- steers. Maximum contractile responses to 120 mM KCl were not different between seed treatments in MA (P = 0.33; E-: 2.67 ± 0.43 g; E+: 3.33 ± 0.43 g) or MV (P = 0.26; E-: 2.01 ± 0.18 g; E+: 1.81 ± 0.18 g). Steers receiving E+ had a smaller (P < 0.01) MA contractile response than E- steers to ERP, ERT, ERS, ERO, ERN, EXT, and 5HT. Steers receiving E+ had a smaller (P < 0.05) MV contractile response than E- steers to ERP, ERT, ERS, ERN, EXT, and 5HT. Lysergic acid failed to induce a contractile response in MA and MV. The contractile response in MA and MV of E- steers produced by 5HT was very large. The EXT was the most potent (P < 0.05) agonist in MV and MA of E+ steers. These data showed that ergot alkaloids were vasoactive in the bovine midgut, and steers exposed to E+ had diminished contractility to some ergot alkaloids in small intestinal vasculature. The findings of this study suggest that dietary exposure to ergot alkaloids has the potential to alter nutrient absorption from the midgut by decreasing blood flow to and from the midgut due to vasoconstriction.

Cage-like complexes formed by DOTAP, Quil-A and cholesterol.

In this note we describe the substitution of the phospholipid component in classical ISCOMs (immune-stimulating complexes) with the cationic lipid dioleoyl-trimethyl-ammonium-propane (DOTAP). The self-assembled colloidal structures formed by DOTAP, Quil-A and cholesterol were characterised using transmission electron microscopy and laser Doppler velocimetry. Samples were prepared using the lipid-film hydration and dialysis techniques. Cage-like structures containing DOTAP were obtained in high numbers using dialysis, but not lipid-film hydration on day 4 post-preparation. The formation of cage-like structures was however only observed at compositions with low weight proportions of DOTAP (less than 25%) resulting in neutral to negative zeta-potentials of the colloidal particles. Compositions with high weight proportions of DOTAP displayed phase separation phenomena. Thus, whilst DOTAP can be incorporated with Quil-A and cholesterol to form cage-like particles, it appears to be unsuitable to prepare cationic equivalents of ISCOMs.

On the dilution behaviour of immuno-stimulating complexes (ISCOMs).

Immunostimulating complexes (ISCOMs) are used as potent vaccine delivery systems. However, the mechanisms by which ISCOMs work are mostly unknown. The immunological potency of ISCOMs has often been associated with their characteristic cage-like structure. Since ISCOMs can be regarded as composite mixed micelles that contain Quillaja saponin as the surfactant, we postulated a micelle to vesicle transition of the particles upon dilution with aqueous solutions. The dilution behaviour of ISCOMs is not only an important preparative aspect, but may also be of high relevance for both cell culture and in vivo applications in which dilutions occur. Crude and purified preparations of ISCOM matrices were prepared by dialysis. Methods used to analyse the micelle to vesicle transitions were transmission electron microscopy and dynamic light scattering. Significant morphological changes occurred upon dilution with TRIS buffered saline and non-buffered saline, and a step-wise transition from the typical cage-like structure via both less well defined ISCOM-like structures and helical micelles to small lipidic particles was observed. Aggregation of the resulting small lipidic particles was noted. The results obtained by dynamic light scattering complemented these findings. With increasing dilution factors, increase in particle size and polydispersity was observed. Zeta-potentials showed a trend towards less negative values upon dilution, indicating that saponins were not retained within the lipid matrix. The results indicated that at least partial separation of Quillaja saponins from the remaining colloidal species occurred upon dilution with aqueous solutions. The release of saponins upon dilution may be an important aspect of how ISCOMs work.