The effect of histamine on microvascular permeability in the muscularis externa of rat small intestine.
Using in vivo microscopy and a fluorescent tracer, the effect of histamine on microvascular permeability was determined in the muscularis externa of the small intestine of anesthetized rats. The small intestine was exteriorized and epilluminated using a microscope equipped with a vertical illuminator and appropriate filters. Fluorescein isothiocyanate conjugated to serum albumin was injected intraarterially. Studies were monitored and videotaped using a closed-circuit television system. Topical application of histamine resulted in focal leak of the conjugate from microvessels in the muscularis externa. The extent of leakage was quantitated by determining the area of leaks through use of a grid over the face of the videomonitor. Dose response studies were performed with histamine alone and plus H1- and H2-receptor antagonists, and with H1 and H2 agonists. The findings demonstrated that histamine increased microvascular permeability to macromolecules in rat small intestine muscle in a dose-dependent manner. This effect was mediated by H1 histamine receptors.
D000818:Animals; D002199:Capillary Permeability / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D006632:Histamine / Q000494:pharmacology*; D006633:Histamine Antagonists; D007093:Imidazoles / Q000494:pharmacology; D017446:Impromidine; D007421:Intestine, Small / Q000098:blood supply*; D008297:Male; D008856:Microscopy, Fluorescence; D009130:Muscle, Smooth / Q000098:blood supply*; D011738:Pyrilamine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains
D006633:Histamine Antagonists; D007093:Imidazoles; D006632:Histamine; D017446:Impromidine; D011738:Pyrilamine