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Mediator-induced changes in macromolecular permeability in the rat mesenteric microcirculation
Abstract:
An intravital fluorescence microscopic method for measurement of changes in macromolecular permeability has been established in the mesenterial microcirculation of the rat. After exteriorization of the fat-free distal part of the ileal mesentery, a 1-hr period of stabilization was followed by the injection of FITC-labeled macromolecules. Five minutes later, histamine, leukotriene B4, or leukotriene C4 was topically applied to the tissue by means of a micromanipulator. Areas of 1 mm2 were videotaped with a SIT camera. The fluorescence intensity of these areas was measured by an analogous video image processing system and displayed as gray value histograms. The shift of the frequency of gray levels from lower to upper regions could be attributed to an increase in light intensity in the mesentery, indicating an increase in vessel wall permeability. The sites of action of histamine and leukotriene C4 were very similar. Both mediators affected mainly the larger collecting venules. In contrast, leukotriene B4 exerted its effect at postcapillary venules. Moreover, leukotriene B4-induced extravasation was inhibited by superoxide dismutase, suggesting an involvement of oxygen radicals. The studies with histamine alone and with H1- and H2-antagonists demonstrated that histamine-induced extravasation in the rat mesentery was mediated by H1-histamine receptors. The present study introduces an experimental model for the measurement of changes in macromolecular permeability, which is useful for studying mediator effects and their pharmacological inhibition in the microcirculation of the rat mesentery.
Insights
Researchers developed a new intravital microscopy method to measure changes in macromolecular permeability in rat mesentery. This technique helps study how mediators like histamine and leukotrienes affect microcirculation and allows for testing drug inhibition.
Area of Science:
- Physiology
- Pharmacology
- Microcirculation Research
Background:
- Assessing macromolecular permeability is crucial for understanding inflammatory and immune responses.
- Existing methods for measuring microvascular permeability have limitations in real-time dynamic analysis.
Purpose of the Study:
- To establish and validate an intravital fluorescence microscopic method for quantifying changes in macromolecular permeability.
- To investigate the effects of histamine, leukotriene B4, and leukotriene C4 on rat mesenteric microcirculation.
- To elucidate the specific venule targets and underlying mechanisms of these inflammatory mediators.
Main Methods:
- Intravital fluorescence microscopy of rat ileal mesentery.
- Topical application of FITC-labeled macromolecules, histamine, leukotriene B4, and leukotriene C4.
- Video image processing to measure fluorescence intensity and assess vessel wall permeability.
- Pharmacological inhibition studies using antagonists and superoxide dismutase.
Main Results:
- Histamine and leukotriene C4 primarily affected larger collecting venules.
- Leukotriene B4 acted on postcapillary venules and its effects involved oxygen radicals.
- Histamine-induced extravasation was mediated by H1-histamine receptors.
Conclusions:
- The developed intravital microscopy method is effective for measuring dynamic changes in macromolecular permeability.
- Different inflammatory mediators exhibit distinct patterns of action within the mesenteric microvasculature.
- This model provides a valuable tool for studying mediator effects and evaluating pharmacological interventions in microcirculation.