Cyclooxygenase products from endogenous arachidonic acid in isolated dog and rabbit lungs

We infused various doses of A23187, a calcium ionophore, into the pulmonary circulation to release endogenous arachidonic acid (AA) in salt-perfused isolated dog and rabbit lungs. Levels of prostaglandin (PG) I2 (as 6-keto-PGF1 alpha), thromboxane A2 (TXA2) as TXB2, and PGF2 alpha but not levels of PGE2 were elevated. Levels of TXA2 were similar between dog and rabbit lungs but levels of PGI2 and PGF2 alpha were higher in dog than in rabbit lungs. However, this difference was not the same at all levels of TXA2. At lower levels of TXA2, the differences were greater and narrowed at higher levels of TXA2. This led to an overlap in the ratios of PGI2/TXA2 and PGF2 alpha/TXA2 between dog and rabbit lungs. We conclude that species differences exist in formation of cyclooxygenase products between dog and rabbit lungs. With respect to products, differences may be dependent on the level of products in response to an AA-releasing agent. This suggests that rabbit lungs can be more sensitive than dog lungs to formation of relatively greater amounts of TXA2. However, the ratios of PGI2/TXA2 and PGF2 alpha/TXA2 can be similar between these species as follows: (1) if there is a sufficient dose of AA-releasing stimulus, or (2) if there is a sufficient difference in doses of the stimulus, with the lower dose being applied to rabbit lungs. Speculatively, physiologic effects of cyclooxygenase products may be similar under these conditions despite the species differences.