Time course of the inflammatory response to histamine and allergen skin prick test in guinea-pigs

Plasma exudation and vasodilatation are key microvascular features of acute inflammation. Exudation and vasodilatation responses in the weal area afte r skin prick testing with histamine are essentially completed within 30 min . There is evidence to suggest that vasodilatation lasts considerably longe r after provocation with allergen, but there is no information on the durat ion of plasma exudation. The purpose of this study was to measure the time course of the microvascular inflammatory response in the skin after histami ne and allergen provocation. Skin prick tests were performed with histamine , allergen (ovalbumin) or saline (control) on guinea-pigs which were shaved on their backs. Radioactive (113m)ln was used to label transferrin as a pl asma tracer. Radioactivity was recorded from the superficial part of the sk in by external detection of conversion electrons from the decay of (113m)ln . The increase in count rate, corresponding to tracer accumulation by vasod ilatation and/or plasma exudation, was used as a measure of the microvascul ar inflammatory response to skin prick test. The microvascular response was studied immediately and up to 30 min after provocation. The largest respon se to histamine and allergen occurred immediately after provocation. The ex udative response then gradually declined to be absent after 25-30 min. Skin prick test with saline resulted in a small response of shorter duration. W e conclude that the microvascular reaction to histamine as well as allergen provocation in guinea-pig skin has a rapid onset and a duration of approxi mate to 39 min.