|
| |
|
|
|
|
||||
| Home Help Feedback Subscriptions Archive Search Table of Contents | ||||
Journal of Experimental Biology, Vol 198, Issue 1 127-135, Copyright © 1995 by Company of Biologists
JOURNAL ARTICLES |
P Wright, A Felskie and P Anderson
The ornithine­urea cycle (OUC) is present in elasmobranch fish and many terrestrial vertebrates. Recently, a functional OUC has been reported in a few teleost species, suggesting that all teleost fish have the genes for the OUC, but expression is relatively rare. We investigated the possibility that the OUC is expressed during early development in trout as a mechanism for detoxifying ammonia produced from the catabolism of yolk protein. We followed ammonia and urea excretion rates, tissue ammonia and urea levels and OUC enzyme activities in rainbow trout up to 93 days after fertilization. Both ammonia and urea tissue concentrations increased several-fold in the first 40 days after fertilization (embryo stage), peaking at 1.7 mmol N l-1 and 2.5 mmol N l-1, respectively. Ammonia excretion could be detected in 4-day-old embryos, but urea excretion was not initiated until after hatching (day 45). Urea excretion in larval fish (days 42­93) increased several-fold and by day 93 was 14 % of total nitrogen excretion, as found in adult trout. Glutamine synthetase (GSase) and arginase activities were detected in 'whole animal' homogenates just after hatching and the levels of activity increased markedly to day 93. Carbamoyl phosphate synthetase (CPSase) and ornithine transcarbamylase (OTCase) were first detected in 40-day-old embryos; activities peaked between days 53 and 71 and then subsequently decreased. Adult liver enzyme activity for GSase was several-fold lower than in whole larval trout and OTCase and CPSase III (glutamine- and N-acetylglutamate-dependent CPSase catalysing the first step of the OUC) activities were essentially absent in adult liver. We conclude that embryonic and larval trout are primarily ammoniotelic. Urea is synthesized immediately after fertilization, but is not excreted until after the embryo is hatched. The results provide evidence for the presence of the OUC in larval rainbow trout, since four of the OUC enzymes are induced just after hatching and the levels of activity are relatively high compared with those in adult liver tissue. Furthermore, we suggest that all teleosts have retained the OUC genes, which are expressed only during certain stages of development (embryogenesis), and in a few rare species expression is maintained throughout the life cycle to cope with unusual environmental conditions (e.g. alkaline water, air exposure).
This article has been cited by other articles:
|
|
 |
|
  P. A. Essex-Fraser, S. L. Steele, N. J. Bernier, B. W. Murray, E. D. Stevens, and P. A. Wright Expression of Four Glutamine Synthetase Genes in the Early Stages of Development of Rainbow Trout (Oncorhynchus mykiss) in Relationship to Nitrogen Excretion J. Biol. Chem., May 27, 2005; 280(21): 20268 - 20273. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. L. Steele, T. D. Chadwick, and P. A. Wright Ammonia detoxification and localization of urea cycle enzyme activity in embryos of the rainbow trout (Oncorhynchus mykiss) in relation to early tolerance to high environmental ammonia levels J. Exp. Biol., March 8, 2002; 204(12): 2145 - 2154. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
B. F. Terjesen, T. D. Chadwick, J. A. J. Verreth, I. Ronnestad, and P. A. Wright Pathways for urea production during early life of an air-breathing teleost, the African catfish Clarias gariepinus Burchell J. Exp. Biol., March 8, 2002; 204(12): 2155 - 2165. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
N. T. Frick and P. A. Wright Nitrogen metabolism and excretion in the mangrove killifish Rivulus marmoratus II. Significant ammonia volatilization in a teleost during air-exposure J. Exp. Biol., January 1, 2002; 205(1): 91 - 100. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. C. Mistry, S. Honda, T. Hirata, A. Kato, and S. Hirose Eel urea transporter is localized to chloride cells and is salinity dependent Am J Physiol Regulatory Integrative Comp Physiol, November 1, 2001; 281(5): R1594 - R1604. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
K Iwata, M Kajimura, and T Sakamoto Functional ureogenesis in the gobiid fish Mugilogobius abei J. Exp. Biol., January 12, 2000; 203(24): 3703 - 3715. [Abstract] [PDF]
|
|
|
|
|
|
C. Pilley and P. Wright The mechanisms of urea transport by early life stages of rainbow trout (Oncorhynchus mykiss) J. Exp. Biol., January 10, 2000; 203(20): 3199 - 3207. [Abstract]
|
|
|
|
|
|
P. Walsh, M. Heitz, C. Campbell, G. Cooper, M Medina, Y. Wang, G. Goss, V Vincek, C. Wood, and C. Smith Molecular characterization of a urea transporter in the gill of the gulf toadfish (Opsanus beta) J. Exp. Biol., January 8, 2000; 203(15): 2357 - 2364. [Abstract] [PDF]
|
|
|
|
|
|
H Kong, N Kahatapitiya, K Kingsley, W. Salo, P. Anderson, Y. Wang, and P. Walsh Induction of carbamoyl phosphate synthetase III and glutamine synthetase mRNA during confinement stress in gulf toadfish (Opsanus beta) J. Exp. Biol., January 1, 2000; 203(2): 311 - 320. [Abstract] [PDF]
|
|
|
|
|
|
T. Chadwick and P. Wright Nitrogen excretion and expression of urea cycle enzymes in the atlantic cod (Gadus morhua l.): a comparison of early life stages with adults J. Exp. Biol., January 10, 1999; 202(19): 2653 - 2662. [Abstract] [PDF]
|
|
|
|
|
|
J. J. Korte, W. L. Salo, V. M. Cabrera, P. A. Wright, A. K. Felskie, and P. M. Anderson Expression of Carbamoyl-phosphate Synthetase III mRNA during the Early Stages of Development and in Muscle of Adult Rainbow Trout (Oncorhynchus mykiss) J. Biol. Chem., March 7, 1997; 272(10): 6270 - 6277. [Abstract] [Full Text] [PDF]
|
|
