Showing papers by "Hamish N. Munro published in 1982"

Nutritional requirements in the elderly.

Abstract: Do the nutritional needs of the elderly differ significantly from those of younger adults, and if so, how? This and other fundamental questions are addressed in the light of recent experimental and clinical findings.

Quantitation of muscle-specific mRNAs by using cDNA probes during chicken embryonic muscle development in ovo

Abstract: The emergence of abundant-class mRNAs specific for contractile muscle proteins and their distribution between polysomal and free mRNP fractions were studied in skeletal muscle excised from chicken embryos during the transition from myoblasts (day 9) to myotubes (day 18). Muscle-specific cDNA was selectively prepared by hybridizing cDNA to template RNA (polysomal poly(A)+ mRNA) from day-14 embryos followed by isolation of the abundant class, which represents approximately 20% of total mRNA. The specificity of the cDNA probe for this class was confirmed by the differential degree of hybridization to cytoplasmic RNA from cultured myotube and myoblast cells and by its inability to hybridize with mRNA from nonmuscle cells such as liver. Except for muscle from day-9 embryos, the concentrations of the abundant-class muscle-specific mRNAs were higher in polysomes than in free mRNP fractions. Furthermore, the levels of these mRNAs in polysomes increased 12-fold from day 9 (myoblast) to day 14 (intermediate) with a further 3.6-fold increase from day 14 to day 18 (myotube). In contrast to this 45-fold net increase in the polysomal level of these mRNAs from day 9 to day 18, the levels in the free mRNP fraction showed only a 3-fold decrease during this period. Because the amount of mRNA lost from the mRNP fraction is much less than the net increase in the polysome fraction, mRNP does not serve as a reservoir of untranslated muscle-specific mRNA for transfer to polysomes. Consequently, the emergence of muscle-specific polysomal mRNA for contractile proteins during myogenesis in ovo appears to be regulated primarily by transcriptional control.

Effect of testosterone on the rate of myofibrillar protein breakdown in castrated and adrenalectomized male rats measured by the urinary excretion of 3-methylhistidine.

Abstract: Urinary output in N tau-methylhistidine (3-MeHis) was used to evaluate changes in myofibrillar protein breakdown rate in the skeletal muscles of castrated and adrenalectomized-castrated young male rats, and the response of breakdown to testosterone and corticosterone replacement. The castrated rats grew less well than intact control rats and excreted significantly less 3-MeHis. Administration of low and high doses of testosterone restored the weight of the levator ani of the castrated animals but failed to affect growth rate or 3-MeHis output. Although this might suggest that testosterone has an indirect effect on muscle turnover through changes in growth rate, this parallelism was not confirmed by studies on adrenalectomized-castrated rats. Adrenalectomy of castrated rats caused a further reduction in growth rate and in output of 3-MeHis, but administration of testosterone now reduced 3-MeHis output still further while stimulating growth. Treatment of the adrenalectomized-castrated rats with low doses of corticosterone increased growth modestly, while depressing 3-MeHis output, and again output of this metabolite was further reduced when testosterone was added to the treatment, although growth rate was unaffected. Finally, large doses of testosterone given to adrenalectomized-castrated rats receiving excessive amounts of corticosterone did not prevent the growth failure or the increased output of 3-MeHis due to the corticosteroid, though it appeared to reduce the magnitude of the response to corticosterone alone. It is concluded that the effects of testosterone on growth and on 3-MeHis output are not necessarily associated and that the functional status of the adrenal cortex modifies the response of myofibrillar breakdown rate to testosterone treatment.