Investigation of the pruritogenic effects of histamine, serotonin, tryptase, substance P and interleukin‐2 in healthy dogs

Abstract

There are numerous studies of the pruritus-producing effects of histamine, serotonin, tryptase, substance P and interleukin-2 in humans and mice, but very little reported in dogs even though a common reason dogs are presented to veterinarians is pruritus. The aim of this study was to determine whether substances known to cause pruritus in humans also cause pruritus in dogs. Twenty-five clinically healthy research beagle dogs were included in the study. All dogs first received an intradermal injection of 0.05 mL saline as a control substance and were video-recorded for 20 min before and after the injection. Twenty-four hours later the dogs were randomly divided into five groups of five dogs each and randomly assigned to receive histamine, serotonin, tryptase, substance P or interleukin-2 injected intradermally each at the volume of 0.05 mL. On subsequent days, increasing concentrations of each substance were used. Before (baseline) and after the injection of each concentration of the substances, the dogs were video-recorded for 20 min. The frequency and character of pruritus episodes (scratching, licking, chewing, rubbing or rolling) were noted and these data were used for statistical analysis. The number of pruritus episodes was compared among baseline, saline and the different concentrations of each substance. The results showed that dogs did not have a significant increase in pruritic behaviour above baseline or saline after injection of any of the investigated substances (generalized linear model; P = 0.23).

Dose‐dependent pruritogenic and inflammatory effects of intradermal injections of histamine, compound 48/80 and anti‐canine IgE in healthy dogs

“…In contrast to humans and mice, dogs develop wheal and erythema reactions after i.d. injections of histamine at 50 μg/site; however, none of the dogs demonstrated strong pruritic behaviour in previous studies when a single histamine concentration was tested . In our study, there was mild acute pruritic behaviour with increasing i.d.…”

“…buffered saline as a negative control; buffered saline was used to determine if the i.d. injection of a known nonpruritogenic substance would elicit a pruritic response . The order of injections was randomized using statistical computer software ( Prism 8.0; GraphPad Software, La Jolla, CA, USA).…”

“…The order of injections was randomized using statistical computer software ( Prism 8.0; GraphPad Software, La Jolla, CA, USA). Each injection was given as a single intervention, and a washout period between 72 h and 7 days was utilized between injections . To avoid residual inflammation from the previous injection, injections were rotated to alternate side between the left and right sides of the thorax; the injection site was moved cranial and caudal as well as dorsal and ventral on the thorax .…”

“…Behaviours were defined in the written definition and with video example for observers to objectively quantify the presence of pruritic behaviour. Behaviours quantified included licking, biting/chewing, scratching, head shaking, scooting, rolling, pawing and rubbing, whereas flinching from the site of injection or vocalization was considered to be indicative of pain . Two trained investigators reviewed all video recordings and were blinded to the substances administered until all data were analysed.…”

Cowhage can induce itch in the atopic dog

“…Whereas localized atopic skin lesions can be reproduced experimentally in dogs by allergen painting (3,4), attempts to experimentally induce itch in dogs with non-allergenic substances have been unsuccessful. Indeed, intradermal injections of histamine, serotonin, tryptase, substance P, interleukin-2 (5) or mast cell degranulating anti-IgE antibodies (6) all failed to induce itch in dogs.…”