Biol. Pharm. Bull. 30(7) 1324—1328 (2007)

estimate mouse hen-egg white lysozyme (HEL)-anaphylaxis, including fatal shock. This assay system monitors the decrease in blood pressure or blood flow as anaphylaxis response and makes possible investigation of the dynamics of the anaphylactic response in the same individual animals without killing them. We have also discovered a distinctive phenomenon in which the blood flow of vein microcirculation is markedly decreased by HEL-sensitization alone without the HEL-challenge. The blood flow of the HEL-sensitized mice reproducibly decreases to about 65—75% of that of normal mice. Thus, the afferent (promotion) stage of allergy caused by xenobiotics can be dynamically and easily measured by using blood flow monitoring. This blood flow decrease is considered to be due to contraction of peripheral blood vessels and increase in blood viscosity, because no relationship with blood pressure was observed. In this assay system, mice are sensitized with a mixture of HEL and adjuvant. When only HEL or only adjuvant was used, the degree of the blood flow decrease was very small compared with the case of the mixture. Although anti-HEL IgE antibody significantly increased after HEL-sensitization, there was no significant increase in the number of leukocytes. Thus, the decrease of blood flows reflects the promoter process of an allergic reaction by the cooperation action of HEL and adjuvant. Using this blood flow decrease as a guide, we developed an in vivo assay method to search for substances, which can prevent allergies. Various factors are involved in blood flow decrease, including nitric oxide (NO), cyclooxygenase (COX)-1, COX-2, thromboxane (TX) A2, endothelin (ET)-1, prostacyclin (PGI2) and granulocytic elastase (GE) from vascular endothelial cells. We also found that the plasma levels of nitrite/nitrate (NOx), metabolites of NO, together with expression of iNOS protein in the thoracoabdominal aorta synchronously increase with the blood flow decrease in HELsensitized mice. In the present study, we examined how iNOS is involved in the blood flow decrease, using an iNOS KO mouse. The relationships among iNOS and NO, COX-1, COX-2, TXA2 or ET-1 were also examined.