Histamine receptors mediate contraction of reticular groove smooth muscle of adult goats

The present study was conducted to evaluate the effect of histamine and to characterise its receptor subtypes in reticular groove (RG) smooth muscle of adult goats. The studies were done using floor and lip regions of RG. We used tension experiments on smooth muscle of RG isolated from adult goat for functional characterisation of H₁ and H₂ receptors. Western blotting and immunohistochemistry experiments were conducted for molecular characterisation of these receptors. Histamine evoked concentration-dependent contraction of isolated RG circular and longitudinal smooth muscle preparation. Pyrilamine antagonised the action of histamine. Histamine did not induce any relaxant effect on RG preparations. Additionally, cimetidine did not produce any significant effect on histamine-induced response. Non-selective histaminic receptor antagonist cyproheptadine attenuated the contraction response to histamine in the smooth muscle. Molecular characterisation and localisation of H₁ and H₂ receptor proteins confirmed the presence of these receptors in RG. It is most likely that histamine-induced contractile effect in RG smooth muscle of goats is mediated by H₁ histaminic receptors.