Binding sites of muscarinic and adrenergic receptors in gastrointestinal tissues of dairy cows suffering from left displacement of the abomasum.

Muscarinic acetylcholine (M) and adrenergic (AR) receptors mediate gastrointestinal motility. Using radioligand binding assays and real-time polymerase chain reaction, the densities of binding sites and mRNA levels of M₂, M₃, α₂(AD)- and β₂-AR were compared in muscle tissues from the abomasal fundus, pylorus, duodenum, caecum, and external loop of the spiral colon of eight cows with left displacement of abomasum (LDA), and of eight healthy cows. Specific binding of the [³H]-ligands to each of the four receptors was competitive and saturable. Binding sites of M₂ (all intestinal sites), M₃ (duodenum and caecum), and of α₂(AD)-AR (abomasal fundus) were lower (P < 0.05) in cows with LDA than in healthy cows. The coefficients of correlation between binding sites and mRNA transcripts of receptors were dissimilar in cows with LDA and healthy cows. The decrease in densities of M (intestine) and of α₂(AD)-AR (abomasum) receptors suggests their implication in the impairment of motility associated with or leading to LDA.