Abstract
Sulfidopeptide leukotrienes (LTs) include LTC4, LTD4, and LTE4. They contract airway smooth muscle and reduce heart contractility in mammals. In this study, LTC4, LTD4, and LTE4 were compared for their effects on bullfrog heart and lung contractility in vitro. LTC4, LTD4, and LTE4 all stimulated lung contraction and increased heart contractility, but LTC4 was more potent than the other two leukotrienes. LY 171883, a mammalian LTD4 receptor antagonist, failed to block the heart and lung responses to LTC4 but did blunt the responses to LTD4 and LTE4. Metabolism studies carried out with 3H-LTC4 demonstrated conversion to LTD4 and small amounts of LTE4 by heart, but not by lung. Thus, bullfrogs respond to leukotrienes in ways which may be similar to (increase in lung contractility) or different from (increase in heart contractility) mammals. Leukotriene receptors appear to be highly conserved, despite the fact that tissue responsiveness to leukotrienes has changed over evolutionary time.
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