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2. Mechanisms of Action of Metabolic Modifiers
Pages 5-22

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From page 5...
... anal increased milk yield of lactating goats (Asclell, 19321. In 1937, Asimov and Krouze conducted the first substantial study involving more than 500 dairy cows ant!
From page 6...
... Eff7ects of Somatotropin GROWTH PERFORMANCE Numerous studies have been conclucted to investigate the effects of different doses of pST on growth performance of pigs. Furthermore, we have a reasonable unclerstanding of the effects pST has on amino acid requirements.
From page 7...
... 6 36 19 37 28 62 ~6 Chung et al., 1985 Etherton et al., 1986 Etherton et al., 1987b Campbell et al., 1988 Evock et al., 1988 Campbell et al., 1989a Campbell et al., 1989b Bryan et al., 1989 aResponse represents a composite of percent of carcass fat, kilograms of adipose tissue, or lipid accretion rates. bResponse represents a composite of percent of carcass protein, kilograms of muscle, or protein accretion rates.
From page 8...
... aA response represents a composite of percent of carcass fat, grams adipose tissue, or lipid accretion rates. bA response represents a composite of percent of carcass protein, grams muscle, or protein accretion rates.
From page 9...
... , cattle (Heuser et al., 1990) , Increased synthesis of milk with normal composition Increased uptake of nutrients used for milk synthesis Increased activity per secretory cell Increased maintenance of secretory cells Increased blood flow consistent with change in milk synthesis Decreased glucose uptake and glucose oxidation Decreased lipid synthesis, if in positive energy balance Increased basal lipolysis, if in negative energy balance Decreased insulin stimulation of glucose metabolism and lipid synthesis Increased catecholamine stimulated lipolysis Increased ability of insulin to inhibit lipolysis Increased glucose output Decreased ability of insulin to inhibit gluconeogenesis Increased absorption of calcium and phosphorus required for milk (lactation)
From page 10...
... of, _ , As previously mentioned, changes in lipid metabolism of the bST-treated cow differ somewhat from changes observed for ST treatment of growing animals, and the differences are a function of energybalance. When bST treatment causes cows to be in negative energy balance, lipid mobiTization is increased as illustrated by decreases in body fat, chronic elevations of nonesterified fatty acids (NEFA)
From page 11...
... It is clear the ST treatment increases muscle protein deposition in growing animals and milk protein secretion in lactating cows. No studies have examined the effects of ST on the kinetics of protein metabolism during ST treatment in dairy cows.
From page 12...
... that the fractional rate of protein synthesis is increasedin skeletal muscle with bST treatment (Pell and Bates, 1987; Eisemann et al., 1989a)
From page 13...
... of glucose from glycogen stores. Catecholamines also stimulate lipolysis to cause the release of free fatty acids from adipose tissue triacy~glycerol stores.
From page 14...
... Two ,B-adrenergic agonists that dramatically enhance skeletal muscle deposition, clenbutero! and cimaterol, are purportedly specific for the ,B-2receptor subtype (O'Donnell, 1976; Kim and Sainz, 1990)
From page 15...
... on growth performance and carcass composition in finishing cattle exceed the magnitude of response seen in veal calves (Williams et al., 19871. Effects on skeletal muscle growth of 10-`lay-ol(1 lambs (15 kg BW)
From page 16...
... on specific tissues may be studied by close arterial infusion of cimaterol into specific vascular beds. No formal proof exists for a common or shared set of specific actions of these compounds on skeletal muscle growth or lipid metabolism among all species in which they have been evaluated.
From page 17...
... have subsequently been shown in further studies to be transient, and nitrogen loss was equal in control and treated sheep after a 4-(lay treatment period (Inkster et al., 19891. Indirect Effects of p-Adrenergic Agonists Despite evidence for direct, receptor-mecliate(1 influences on skeletal muscle, it is possible that some of the changes in muscle protein metabolism in viva are brought about by an indirect mechanism, that is, as a result of the changes in the circulating concentrations of some en(logenous hormones (see review by Butted and Dawson, 1987)
From page 18...
... Inadequate protein intake constrains the magnitude of improvement in growth performance, nitrogen balance, or the degree to which protein accretion rate or skeletal muscle growth is enhanced by ractopamine in pigs (Anderson et al., 1987; Acleola et al., 1990; Dunshea et al., 1991; Mitchell et al., 1991~. Anderson et al.
From page 19...
... Summary of Effects of ,B-Actrenergic Agonists on Growth and Composition Chronic dietary administration of select ,8-adrenergic agonists markedly influences protein and lipid metabolism in farm animals, leading to marked increase in skeletal muscle protein accretion rate and, in most cases, significant reduction in lipid deposition rates. Significantimprovement in carcass composition results without effect on growth of bone and with little effect on mass of visceral tissues and other organs.
From page 20...
... Growth Performance Response to Anabolic Steroids Rate of live-weight gain is increased 10 to 20 percent on average by anabolic steroids (Bradley et al. 19.57 Ohm , a-, ~ 7 -- -ear and Dyer, 1971; Griffiths, 1982; O'Lamhna and Roche, 1984, Gill et al., 1987; Keane and Drennan, 1987; Perry et al., 1991)
From page 21...
... Mechanism of Anabolic Steroid Action Few data are available that (lescribe the effects of anabolic steroids on protein metabolism, but even fewer data exist for assessment of direct effects of anabolic steroids on lipid metabolism in growing ruminants. Protein metabolism studies suggest that both fractional protein synthesis rate and protein degradation rate might be reducer]
From page 22...
... Data suggest that protein metabolism is altered toward increased rates of protein synthesis and reduced rates of amino acid oxidation and/or lesser rates of protein degradation. There may be little direct effect on lipid metabolism and associated fat deposition.


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