Complete suppression of protein synthesis during anoxia with no post-anoxia protein synthesis debt in the red-eared slider turtle Trachemys scripta elegans.

Two previous studies of the effects of anoxia on protein synthesis in anoxia-tolerant turtles (Trachemys scripta elegans, Chrysemys picta bellii) have generated opposing results. Using the flooding-dose method, we measured the rate of protein synthesis following injection and incorporation of a large dose of radiolabelled phenylalanine to resolve the question of whether anoxia results in a downregulation of protein synthesis. After 1 h of anoxia, levels of protein-incorporated radiolabel indicated that protein synthesis rates in the intestine, heart, liver, brain, muscle and lungs were not significantly different from those of normoxic controls. However, from 1 to 6 h of anoxia, quantities of protein-incorporated radiolabel did not increase, suggesting that protein synthesis had ceased or had decreased below a measurable level. There was also no significant post-anoxia increase in protein synthesis rates above normoxic control levels during 3 h of recovery from anoxia. RNA-to-protein ratios did not change significantly in any tissue except the heart, in which RNA levels decreased below normoxic control levels after 6 h of anoxia. Except in the heart, downregulation of protein synthesis during anoxia does not appear to be mediated by changes in tissue RNA concentration.

Estradiol stimulates growth hormone production in female goldfish.

The effects of estradiol (E2) on growth hormone (GH) production was investigated in gonad-intact female goldfish. It was first necessary to generate a specific antibody for use in immunocytochemistry, Western, and dot-blot analyses of GH production. To accomplish this, grass carp GH (gcGH) cDNA was cloned by the reverse transcription polymerase chain reaction (RT-PCR) and expressed in Echerichia coli and a specific polyclonal antibody to recombinant gcGH was generated in the rabbit. In Western blot, the anti-gcGH antibody specifically immunoreacted with recombinant gcGH, purified natural common carp GH, and with a single 21.5-kDa GH form from pituitary extracts of grass carp, common carp, goldfish, and zebrafish but not salmon, trout, or tilapia. Intraperitoneal injection of the recombinant gcGH enhanced the growth rates of juvenile common carp demonstrating biological activity of this GH preparation. Electron microscopic studies showed that the anti-gcGH-I antibody specifically reacted with GH localized in the secretory granules of the goldfish somatotroph. Using anti-gcGH-I in a dot-blot assay, it was found that in vivo implantation of solid silastic pellets containing E2, (100 micrograms/g body weight for 5 days) increased pituitary GH content by 150% in female goldfish. In a second, independent study employing a previously characterized anticommon carp GH antibody for radioimmunoassay, it was found that E2 increased pituitary GH content by 170% and serum GH levels by approximately 350%. The E2-induced hypersecretion of GH and increase in pituitary GH levels was not associated with changes in steady-state pituitary GH mRNA levels, suggesting that this sex steroid may enhance GH synthesis at the posttranscriptional or translational level. Previous observations indicate that GH can stimulate ovarian E2 production. The present results show that E2 can in turn stimulate GH production, indicating the existence of a novel pituitary GH-ovarian feedback system in goldfish.

Tissue-specific changes in protein synthesis rates in vivo during anoxia in crucian carp.

Mechanisms of anoxia tolerance were investigated in crucian carp. Rates of protein synthesis were calculated in selected tissues of normoxic and anoxic animals. Exposure to 48 h of anoxia resulted in a significant reduction in protein synthesis in the liver (> 95%), heart (53%), and red and white muscle (52 and 56%, respectively), whereas brain protein synthesis rates were unaffected. Seven days of anoxia produced similar results. After 24 h of recovery from a 48-h anoxic period, protein synthesis rates had virtually returned to normoxic values. The effect of anoxia on the amount of RNA (relative to protein) varied depending on the tissue and also the length of exposure (except in the brain, where it was consistently reduced). However, the effect on RNA translational efficiency was purely tissue specific (i.e., independent of exposure time) and was unaffected in the heart, reduced in the liver and red and white muscle, and increased in the brain. Downregulation of protein synthesis on a tissue-specific basis appears to be a significant mechanism for energy conservation as well as maintaining neural function, thus promoting survival during anoxia.

Protein synthesis, growth and energetics in larval herring (Clupea harengus) at different feeding regimes.

Rates of growth, protein synthesis and oxygen consumption were measured in herring larvae, Clupea harengus, in order to estimate the contribution that protein synthesis makes to oxygen consumption during rapid growth at 8°C. Protein synthesis rates were determined in larvae 9 to 17 d after hatching. Larvae were bathed in (3)H phenylalanine for several hours and the free pool and protein-bound phenylalanine specific radioactivities were determined.Fractional rates of protein synthesis increased 5 to 11 fold with feeding after a period of fasting. Efficiencies of retention of synthesized protein were approximately 50% during rapid growth. Rapid growth in herring larvae thus appears to be characterized by moderate levels of protein turnover similar to those obtained for larger fish. Increases in growth rate occurred without changes in RNA concentration, i.e., the larvae increased the efficiency of RNA rapidly. Oxygen consumption rates were not correlated with growth rates. Protein synthesis was estimated to account for 79% of the oxygen consumption, and energy costs of protein synthesis were high, i.e., about 98 mmole O2 g(-1) protein synthesized.