Skeletal-muscle growth and protein turnover

Abstract

Because of turnover, protein synthesis and breakdown can each be involved in the regulation of the growth of tissue protein. To investigate the regulation of skeletal-muscle-protein growth we measured rates of protein synthesis and breakdown in growing rats during development on a good diet, during development on a marginally low-protein diet and during rehabilitation on a good diet after a period of severe protein deficiency. Rates of protein synthesis were measured in vivo with a constant intravenous infusion of [14C]tyrosine. The growth rate of muscle protein was measured and the rate of breakdown calculated as breakdown rate=synthesis rate-growth rate. These measurements showed that during development on a good diet there was a fall with age in the rate of protein synthesis resulting from a fall in capacity (RNA concentration) and activity (synthesis rate per unit of RNA). There was a fall with age in the breakdown rate so that the rate was highest in the weaning rats, with a half-life of 3 days. There was a direct correlation between the fractional growth and breakdown rates. During rehabilitation on the good diet, rapid growth was also accompanied by high rates of protein breakdown. During growth on the inadequate diet protein synthesis rates were lesss than in controls, but growth occurred because of decreased rates of protein breakdown. This compression was not complete, however, since ultimate muscle size was only one-half that of controls. It is suggested that increased rates of protein breakdown are a necessary accompaniment to muscle growth and may result from the way in which myofibrils proliferate.

The effects of ovine growth hormone on protein turnover in rainbow trout

“…In a growing animal, increased protein accretion rates are generally the result of both increased protein synthesis and, to a lesser degree, increased protein degradation rates (Millward et al, 1975;Houlihan and Laurent, 1987;Houlihan et al, 1988). However, in the present study, higher whole-body protein accretion rates were not accompanied by significantly increased protein synthesis or degradation rates.…”

Effect of litter size and bacitracin administration on tissue protein synthesis of lactating rabbit does

“…Higher values (5 and 10%/day, respectively) have been observed for young males of either up to 1.4 kg (Palmer et al, 1980) or 2 to 2.5 kg BW (Laurent, 1982). FSR is known to be closely related to animal development (Laurent, 1982) and decreases with age (Millward et al, 1975;Lobley, 1993) and the multiparous does used in this study are considered adult animals. Lactation has a clear effect on mammary and liver tissues (Sampson et al, 1986), but effects on muscle are not yet confirmed.…”

Protein Synthesis, Degradation, and Retention: Mechanisms of Indeterminate Growth in Cephalopods

“…Pron p 8 r p 0.41 P 1 0.05 tein concentration was determined using a modification of the folin-phenol method (Lowry et al 1951), and RNA concentration was estimated using dual-wavelength absorbance with an internal RNA standard, with blanks to confirm that the protocol was working (Ashford and Pain 1986). Fractional rates of protein degradation (k d , in percent per d) were calculated as (Millward et al 1975). RNA was expressed as…”