Leukotriene C4-stimulated contractions in bullfrog lung are affected by cold acclimation and calcium antagonists.

Leukotriene C4 (LTC4) contracts isolated bullfrog lung. This study examined effects of cold-acclimation and the involvement of extracellular and intracellular Ca++ on the contractile response to LTC4. The response to LTC4 was greater in lungs from warm-acclimated (22 degrees C) frogs compared with cold-acclimated (5 degrees C) frogs at incubation temperatures of both 22 degrees C and 5 degrees C. LTC4, LTC5, and N-methyl LTC4 were equally effective in stimulating lung contraction at concentrations from 1-100 nM. Nicardipine (3 microM) partially antagonized the response to LTC4, but verapamil, nifedipine, or nitrendipine at the same concentration was ineffective. Ethylene glycol tetraacetic acid (EGTA, 0.3 mM) prevented the response to 30 nM LTC4, but the response was restored when the lung was retested in EGTA-free medium containing Ca++, suggesting that extracellular Ca++ was involved in the response. Caffeine (10 mM) or thapsigargin (1 mM) inhibited the responses to LTC4, suggesting a role for intracellular Ca++ in the contraction.

Eicosanoid synthesis by warm- and cold-acclimated American bullfrog (Rana catesbeiana) brain.

Previous studies in bullfrogs have demonstrated the presence of leukotriene (LT)C4 binding sites in the brain. However, synthesis of eicosanoids by brain tissue has not been examined. Because prostaglandin (PG) synthesis differs in warm- and cold-acclimated bullfrog lung tissue, this study compared the synthesis of prostaglandins and leukotrienes in brains from warm-(22 degrees C) and cold-acclimated (5 degrees C) animals. Initial experiments determined that leukotriene and prostaglandin production rates were greatest during the initial 30 min time period. Therefore, tissues were incubated in Munsick's solution and gassed with 95% O2, 5% CO2 for 30 min. Media were analyzed by radioimmunoassay for LTC4, LTB4, PGE2, PGF2 alpha, TXB2, and 6-keto PGF1 alpha. In warm-acclimated bullfrog brains, production was as follows: LTC4 > PGE2 > 6-keto PGF1 alpha, thromboxane (TX)B2, LTB4, and PGF2 alpha. Brain tissues from cold-acclimated animals incubated at 22 degrees C produced significantly greater quantities of PGE2 and 6-keto PGF1 alpha than did brains from warm-acclimated animals. Stimulation of TXB2 levels was observed when the animal was stunned with a blow to the head prior to decapitation. Indomethacin, a cyclooxygenase inhibitor, decreased prostaglandin but not leukotriene synthesis. Epinephrine (4 x 10(-8) M), the amphibian sympathetic postganglionic neurotransmitter, stimulated leukotriene synthesis by brains from warm-acclimated bullfrogs, and the effect was blocked with the 5-lipoxygenase inhibitor MK-886 (5 x 10(-5) M). These results clearly indicate that the bullfrog brain synthesized both leukotrienes and prostaglandins. Further studies are necessary to determine their function in the amphibian central nervous system.