AJP - Regulatory, Integrative and Comparative Physiology, Vol 268, Issue 3 816-R819, Copyright © 1995 by American Physiological Society
Nitric oxide responses of air-breathing and water-breathing fish
J. F. Staples, W. M. Zapol, K. D. Bloch, N. Kawai, V. M. Val and P. W. Hochachka
Department of Zoology, University of British Columbia, Vancouver, Canada.
Nitric oxide (NO), exogenously administered or endogenously produced by NO
synthase (NOS), is an important regulator of lung ventilation and perfusion
in mammals. This study attempts to investigate the evolutionary history of
this system in fish and its possible relationship to air breathing. The gas
bladder of Hoplerythrinus unitaeniatus (air-breathing teleost) and
Oncorhynchus mykiss (non-air-breathing teleost) and the lung of Lepidosiren
paradoxa (air-breathing dipnoan) all exhibited elevated guanosine
3',5'-cyclic monophosphate (cGMP) levels in response to 1 microM sodium
nitroprusside. Only the H. unitaeniatus gas bladder responded to 10 microM
acetylcholine chloride (ACh) with increased cGMP levels. The ACh response
was inhibited by N omega-nitro-L-arginine methyl ester, which inhibits NOS.
These data suggest that although tissues from each species may respond to
exogenous NO, only the gas bladder of H. unitaeniatus appears to synthesize
NO through NOS. This is the first report of constitutive NOS outside of the
central nervous system in a teleost. These results also imply that NOS did
not necessarily coevolve with air breathing in fish.
