The effect of lactation on protein synthesis in ovine skeletal muscle

Abstract

SUMMARYProtein synthesis was measured in non-breeding sheep and in sheep at two stages of lactation by constant intravenous infusion of [3H] tyrosine. In early lactation plasma tyrosine flux was 50% higher than in non-breeding ewes and it remained somewhat higher in late lactation. Estimates of protein synthesis per day in the whole body showed similar changes.In early lactation the weights of the longissimus dorsi and semitendinosus muscles were respectively 37 and 28% lower than those for non-breeding ewes, but both muscles regained weight in late lactation. There were corresponding changes in the total protein, total RNA and total lipid contents of both muscles.The fractional rates of protein synthesis in the longissimus dorsi and the semitendinosus were between 2 and 3% per day, but it was higher in heart muscle. At both stages of lactation the synthesis rate in the longissimus dorsi was similar to that in nonbreeding ewes, but in the semitendinosus and in the heart synthesis rates were lower in lactating animals. In both skeletal muscles the total protein synthesized per day was lower in early lactation because their total protein contents were lower at this time. It is concluded that the maternal skeletal muscles may undergo a controlled depletion during lactation.

Metabolism of Valine and the Exchange of Amino Acids across the Hind-limb Muscles of Fed and Starved Sheep

“…Comparison of values for fractional rate of protein synthesis (FRS) in this and other studies (Lobley et al 1980;Bryant and Smith 1982) reveals similar values for animals of the same age, and indeed FRS values for the semitendinosus and gastrocnemius muscles reported by Bryant and Smith (1982) are similar to the values obtained in the present studies. Differences in FRS between types of skeletal muscle imply that extrapolation from a single muscle type to whole-body skeletal muscle should be undertaken with caution.…”

“…However, as has been pointed out by Bryant and Smith (1982), it is unlikely that they cancel out exactly and caution in the interpretation of results should be exercised. Furthermore, in fed sheep net splanchnic valine utilization would be expected to be high, and would not contribute to the measur~d valine entry rate, whereas, in fasted sheep, little net valine utilization would be expected by the splanchnic bed.…”

Relationship of Lactation Energy Intake and Occurence of Postweaning Estrus to Body and Backfat Composition in Sows

“…Also, Duee and Desmoulin (1982) noted that weight loss in lactating sows was associated with mobilization of muscle tissue; however, the relationship with estrous activity after weaning was not reported. Bryant and Smith (1982) concluded that skeletal muscles of lactating ewes may undergo a controlled depletion.…”

Metabolic responses to euglycaemic hyperinsulinaemia in lactating and non-lactating sheep in vivo

“…To accommodate these require¬ ments extramammary tissues of lactating animals show considerable modifications in their normal metabolism. Hepatic gluconeogenesis in ruminants is stimulated two-to threefold (Bergman & Hogue, 1967;Baird, Symonds & Ash, 1975;Aiello, Kenna & Herbien, 1984), in adipose tissue rates of lipogenesis are low while lipolysis is stimulated (Chilliard, Durand, Sauvant & Morand-Fehr, 1978;Vernon, Clegg & Flint, 1981) and protein turnover, especially protein degradation, is increased (Bryant & Smith, 1982;Vincent & Lindsay, 1984). The sensitivity of tissues to hormonal stimulation is also modified during lactation (Burnol, Leturque, Ferré & Girard, 1983;Vernon, 1985;Vernon & Taylor, 1988).…”