Pulmonary hemodynamic reaction to foreign blood in goats and rabbits

We have found that the goat is extraordinarily sensitive to very small quantities of rabbit or rat blood. As little as 0.004 ml/kg induces transient pulmonary hypertension [maximal rise in pulmonary arterial pressure 32 +/- 10 (SD) cmH2O] in goats. We hypothesized that this reaction may be related to the presence of the resident population of intravascular macrophages that reside in the pulmonary capillaries of goats. If that is so, then rabbits or rats, which have few or no intravascular macrophages, should not be reactive to foreign blood. We compared pulmonary hemodynamics and changes in blood thromboxane B2 concentrations among goats, rabbits, and rats in response to graded doses of foreign blood. The pulmonary reaction to foreign blood was much greater in goats than in rabbits or rats, even though we injected up to 10- or 60-fold larger amounts into the latter species. In goats the pulmonary vascular pressure response to rabbit blood was dose dependent in goats and correlated well with changes in systemic arterial thromboxane B2 concentrations [change in pulmonary arterial pressure = 0.07 (thromboxane B2) + 8.3, r = 0.79]. We also tested the prostaglandin H2 endoperoxide analogue (U-46619) and found that the goats are somewhat more reactive than rabbits. We conclude that the pulmonary hemodynamic reaction to foreign blood is consistent with the concept that the foreign erythrocytes are reacting with the pulmonary intravascular macrophages in goats. The lower reactivity of the rabbit pulmonary circulation to thromboxane may also have a role.