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1. The relative rates of synthesis of fatty acid synthetase and the pyruvate dehydrogenase complex were measured in adipose tissue in virgin, late pregnant and early lactating rats after injection of l -[2,3- 3 H]alanine. The relative rate of synthesis of fatty acid synthetase decreased approximately 4-fold between 2 days prepartum and 2 days postpartum. The relative rate of synthesis of the pyruvate dehydrogenase complex did not change. 2. The fractional rate of total adipose tissue protein synthesis was measured by constant infusion with l -[U- 14 C]tyrosine. Total protein synthesis did not differ in virgin and 2-day lactating rats. The half-life of adipose tissue protein in virginn rats determined by decay of 14 C label from protein after injection of NaH 14 CO 3 was 86.9 ± 6.7 h. This is in close agreement witht the half-life (82.5 ± 20 h) calculated from the fractional rate of protein synthesis determined by the constant infusion method.

1. The specific activities of fatty acid synthetase, acetyl-CoA carboxylase and pyruvate dehydrogenase were measured in rat adipose-tissue extracts in pregnancy and lactation. Fatty acid synthetase specific activity correlates very closely with the rate of fatty acid synthesis, the enzyme specific activity decreasing after mid-pregnancy in a manner very similar to the rate of fatty acid synthesis. Acetyl-CoA carboxylase specific activity also decreases dramatically after mid-pregnancy. Initial pyruvate dehydrogenase specific activity shows a decrease between 2 days pre partum and 2 days post partum, but total enzyme activity shows no significant change in the same period. 2. Immunotitrations of fatty acid synthetase and pyruvate dehydrogenase activities were carried out; the titrations showed that the change in the fatty acid synthetase activity is due to a change in the enzyme amount; the amount of pyruvate dyhydrogenase does not change. Therefore the decrease in fatty acid biosynthesis in subcutaneous and parametrial adipose tissue in late pregnancy and early lactation is associated with a decrease in the amount of at least one of the enzymes involved in fatty acid biosynthesis. The correlation of these events with known hormonal changes is discussed.

Anabolic preparations which act at the tissue level can often be classified into those with androgenic properties and those with oestrogenic properties, however, it may not be these properties which are responsible for their growth promoting ability. The mode of action of the anabolic agent trenbolone, with androgenic properties, and the anabolic agent zeranol, with oestrogenic properties, is discussed. It is considered unlikely that trenbolone is acting as a classical androgen, at least as far as its action on muscle is concerned. Zeranol is considered unlikely to be acting solely via growth hormone. The question is posed: is it possible that these two agents just cause slight changes in the total endogenous hormone pattern which is sufficient to account for their growth promoting properties.

The degree of coordination between protein synthesis and degradation during protein accretion or diminution in three different types of development transition is examined. Protein turnover patterns in postnatally developing liver, terminally differentiating mammary gland, and in maternal adipose tissue in the perinatal period are presented. Studies on turnover of specific enzymes and resolved protein populations from morphologically (biosynthetically) defined organelle subcompartments are presented. Data are given on the turnover characteristics of monoamine oxidase, pyruvate dehydrogenase, and cytochrome oxidase, as well as proteins in defined mitochondrial subcompartments from rat liver. The turnover characteristics of fatty acid synthetase, casein, and cytosol proteins in rabbit mammary explants in organ culture arc presented. Changes in turnover characteristics of lipogenic enzymes, mitochondrial proteins, and cytosol proteins in maternal rat subcutaneous and parametrial adipose tissue around parturit...

1. Tissue composition and skeletal muscle cathepsin D (EC3.4.23.5) activity weremeasured in wether lambs treated with trenbolone acetate (TBA) and oestradiol-17β (Oe) in combination and female lambs treated with TBA or zeranol. Muscle and liver protein fractional synthesis rates and plasma leucine flux were measured in the female lambs.2. Male castrate lambs treated with TBA plus Oe showed increased growth rate, improvedfood conversion efficiency, decreased muscle RNA concentration and decreased total cathepsin D activity in muscle.3. Female lambs treated with TBA or zeranol showed increased weight gain, improved food conversion efficiency, decreased muscle RNA and DNA concentrations and decreased free cathepsin D activity in muscle. Mixed muscle protein fractional synthesis rate was decreasedafter TBA treatment. Plasma leucine flux, not corrected for oxidation or food intake, wasnot increased by TBA or zeranol treatment.4. Treatment of female lambs with TBA or zeranol caused increased growth rate. This increased growth rate is probably due in part to decreased muscle protein degradation, since evidence was obtained that muscle protein synthesis is decreased by TBA and zeranol treatment.