Experimental studies on the mechanism of reversible pressor response in pulmonary microembolism in the dog

In the present study, we examined the difference in hemodynamic responses between groups of canine lung lobes which received latex particles of different sizes (50 microns and 300 microns in diameter). We also assayed prostaglandin I2 (PGI2) and thromboxane A2 in the effluent blood of the lobes. Reversible pressor response was clear in embolization by 50 micron particles whereas it was not in that by 300 microns. No difference in PGI2 between two embolizations was seen. We conclude that a local contractile mechanism exists in the pulmonary arterial wall of about 50 microns in diameter whereas participation of the same mechanism is minimal in 300 microns, and that this difference cannot be explained from the change in PGI2.