AJP - Regulatory, Integrative and Comparative Physiology, Vol 260, Issue 5 834-R838, Copyright © 1991 by American Physiological Society
Metabolism and cardiovascular effects of leukotrienes in warm- and cold-acclimated American bullfrogs (Rana catesbeiana)
C. A. Herman, G. A. Charlton and R. L. Cranfill
Department of Biology, New Mexico State University, Las Cruces 88003.
Sulfidopeptide leukotrienes are important mediators in mammals, but much
less is known of their metabolism and action in nonmammalian vertebrates.
This study examines the cardiovascular effects of leukotrienes on blood
pressure and heart rate and compares the metabolism of leukotrienes in vivo
and in vitro in warm- and cold-acclimated bullfrogs. Leukotriene C4 (LTC4)
is more potent than leukotriene D4 (LTD4) and leukotriene E4 (LTE4) in
eliciting hypotension. The leukotrienes are more potent in warm-acclimated
animals. Conversion of [3H]LTC4 to [3H]LTD4 occurs rapidly in
warm-acclimated bullfrogs, with 15.2 +/- 1.7% of the [3H]LTC4 remaining at
1.5 min. Conversion is slower in vivo in cold-acclimated frogs, with 20.2
+/- 1.7% of the [3H]LTC4 remaining by 6 min. In blood taken from
warm-acclimated frogs, conversion of [3H]LTC4 to [3H]LTD4 occurs more
rapidly at 22 than at 5 degrees C. This pattern is similar in blood taken
from cold-acclimated frogs, suggesting that no modification of
gamma-glutamyl transpeptidase occurs at low temperature. [3H]LTE4
production is not observed in vivo or in vitro during the time course of
the experiments. The rapid metabolism of LTC4 to LTD4 may represent an
inactivation mechanism in amphibians. The cardiovascular effects of LTC4 in
vivo may be much greater than current measurements indicate because of
rapid conversion of LTC4 to the less potent LTD4.
