Protein synthesis and degradation in the mammary gland of lactating goats

SummaryLactating goats were given a close arterial infusion of [1-14C]leucine and [4,5-3H]4-methyl-2-oxopentanoic acid into one half of the mammary gland at 2–3 weeks and 34–39 weeks after kidding. Rates of protein synthesis, degradation and net output were determined from measurements of arteriovenous difference and blood flow using a model of leucine metabolism previously developed for muscle (Oddy & Lindsay, 1986). Protein leucine output in milk (Y μmol/min) correlated well with the difference between synthesis and degradation (X μmol/min) derived from the model:There was substantial synthesis and degradation of protein within the mammary gland. Although only an approximate value could be obtained for the partitioning of protein synthesis and degradation between tissue and milk proteins, there was evidence of appreciable turnover of both. There was no significant difference between mammary leucine and protein metabolism in early and late lactation other than that imparted by a greater mass of mammary tissue in early lactation, although there was a tendency for greater oxidation of leucine in late lactation.

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Cardiac protein synthesis and degradation during thyroxine-induced left ventricular hypertrophy

AJP Cell Physiology ◽

10.1152/ajpcell.1986.251.5.c727 ◽

1986 ◽

Vol 251 (5) ◽

pp. C727-C736 ◽

Cited By ~ 65

Author(s):

M. S. Parmacek ◽

N. M. Magid ◽

M. Lesch ◽

R. S. Decker ◽

A. M. Samarel

Keyword(s):

Protein Synthesis ◽

Left Ventricular Hypertrophy ◽

Total Protein ◽

Ventricular Hypertrophy ◽

Left Ventricular ◽

Protein Accumulation ◽

The Difference ◽

Protein Synthesis And Degradation ◽

Synthesis And Degradation

Assessment of cardiac protein metabolism in thyroxine-induced left ventricular hypertrophy requires measurements of both protein synthesis and degradation. In vivo protein degradative rates can best be measured as the difference between rates of protein synthesis and growth. Accordingly, rates of left ventricular protein accumulation were determined in growing rabbits, and in animals administered intravenous L-thyroxine (200 micrograms X kg-1 X day-1) for up to 15 days. Left ventricular protein fractional synthetic rates in euthyroid and thyroxine-treated rabbits were measured by continuous infusion of [3H]leucine (200 mu Ci/h X 6 h), and results converted to milligrams protein synthesized and degraded per day. Thyroxine administration produced left ventricular hypertrophy by increasing the rate of total protein synthesis (35.7 +/- 2.0, 71.0 +/- 7.0, and 62.6 +/- 4.0 mg of left ventricular protein synthesized per day for 0-, 3-, and 9-day, thyroxine-treated rabbits, respectively). However, the increased rate of total protein synthesis was greater than the measured rate of total protein accumulation (8.1 vs. 15.9 mg protein/day for euthyroid and thyroxine-treated animals), indicating that left ventricular protein degradative rates were increased as well. These studies indicate that accelerated proteolysis may be important in the molecular and architectural remodeling of the rapidly hypertrophying heart during thyrotoxicosis.

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Effects of Exercise Training on the Performance, Growth, and Protein Turnover of Rainbow Trout (Salmo gairdneri)

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f87-195 ◽

1987 ◽

Vol 44 (9) ◽

pp. 1614-1621 ◽

Cited By ~ 121

Author(s):

D. F. Houlihan ◽

P. Laurent

Keyword(s):

Protein Synthesis ◽

Rainbow Trout ◽

Control Fish ◽

Salmo Gairdneri ◽

Degradation Rates ◽

The Difference ◽

Net Protein ◽

Protein Synthesis And Degradation ◽

Synthesis And Degradation ◽

Better Than

Rainbow trout (Salmo gairdneri) that were made to swim continuously at 1 body length/s for 6 wk had double the growth rate of tank-rested control fish. The endurance to fatigue at a range of swimming velocities of these trained animals was significantly better than that of the controls. Measurement of the rate of protein synthesis in the tissues was carried out by the free pool flooding technique. Protein degradation rates were calculated from the difference between synthesis and net protein accretion. In controls and trained animals the fractional rates of protein synthesis and degradation were ranked gills > ventricle > red muscle > white muscle whereas the efficiencies of conversion of protein synthetised into protein retained as growth were in the reverse sequence. Synthesis rates in three of the four tissues of the trained animals were approximately double those of the control animals. Calculated degradation rates of proteins also increased in the trained animals; the increased growth rates resulted from the proportionately greater increase in the rate of synthesis. The rate of synthesis decreased to control levels once the trained animals ceased swimming.

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Effect of insulin on protein synthesis and degradation in skeletal muscle after exercise

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1990.258.1.e92 ◽

1990 ◽

Vol 258 (1) ◽

pp. E92-E97 ◽

Cited By ~ 6

Author(s):

T. W. Balon ◽

A. Zorzano ◽

J. L. Treadway ◽

M. N. Goodman ◽

N. B. Ruderman

Keyword(s):

Protein Synthesis ◽

Protein Degradation ◽

Moderate Intensity ◽

Control Group ◽

Intense Exercise ◽

Rat Muscle ◽

The Difference ◽

Protein Synthesis And Degradation ◽

Synthesis And Degradation ◽

Stimulation Of

This study examined whether insulin stimulation of protein synthesis and inhibition of protein degradation is enhanced after exercise. The isolated perfused rat hindquarter preparation was used to evaluate net protein breakdown, myofibrillar protein degradation, and protein synthesis. Thirty minutes after treadmill exercise of high and moderate intensity, rates of tyrosine release were increased by 58 and 25%, respectively. Insulin at 75 microU/ml had no effect on these increases after intense exercise; however, 20,000 microU/ml of insulin totally inhibited this increase. Cycloheximide increased the tyrosine release in both control and exercised rat muscle. It also abolished the difference between them, suggesting that the increase in tyrosine release after exercise is caused by an inhibition of protein synthesis. Phenylalanine incorporation into protein was marginally depressed (22%, P = NS) in the white gastrocnemius muscle after intense exercise. Insulin at 200 microU/ml stimulated protein synthesis in these rats, but no more than it did in a nonexercised control group. Failure to observe a greater effect of insulin on protein metabolism was also noted when rat muscle was studied 150 min after intense exercise and after contractions induced by electrical stimulation of the sciatic nerve. These findings suggest that after exercise or electrically induced contractions the enhanced ability of insulin to stimulate hexose and amino acid transport is not paralleled by an increase in its ability to stimulate protein synthesis or inhibit protein degradation.

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