In vitro evaluation of gut contractile response to histamine in rainbow trout (Oncorhynchus mykiss Walbaum, 1792)

The contractile response of intestinal strips in rainbow trout (Oncorhynchus mykiss Walbaum, 1792) to the administration of histaminewas assessed by means of the organ bath technique. Intestinal strips were isolated from 16 clinically healthy fish and mounted inorgan baths. Histamine was compared with the full agonist serotonin, to evaluate their contractile efficacy and potency. Serotonin eliciteda concentration-related contraction in all examined intestinal strips, whereas histamine induced the contraction only in 14 exemplars.Of these, seven exhibited a concentration-related response. A sigmoidal curve was fitted from data (R2 = 0.55) and its best fit values werecompared with those of serotonin. Interestingly, histamine exhibited the same efficacy (Emax) as serotonin (F-test, p > 0.05), but showedlower potency (by an order of magnitude) (F-test, p < 0.01). Moreover, the effect of the H1 antagonist, pyrilamine, has been tested toexclude aspecific contraction due to other agonists eventually released in situ following histamine administration. Pyrilamine showeda marked concentration-related antagonist action on the contractility induced by histamine with complete contractility antagonism at104 M. The authors suggest that the responses to histamine measured in the present study reflect a less sensitive response to an exogenoussource of histamine, possibly due to bacterial metabolism.[...]