Status of Current Strategies for Growth Regulation

400

311

The beta-adrenergic receptors (beta-AR) are present on the surface of almost every type of mammalian cell. These receptors are stimulated physiologically by the neurotransmitter, norepinephrine and the adrenal medullary hormone, epinephrine. There are three subtypes of beta-AR, namely, beta1-AR, beta2-AR, and beta3-AR; the pharmacological and physiological responses of an individual cell result from the particular mixture of the three beta-AR subtypes present on that cell. Species-specific structure (amino acid sequence) also causes modification of the function of a given beta-AR subtype. Knowledge of the beta-AR subtypes present in various cell types, coupled with knowledge of receptor structure (sequence), will allow an understanding of the complexity of physiological function regulated by beta-AR. Oral administration of some beta-AR agonists increases muscle and decreases fat accretion in cattle, pigs, poultry, and sheep. The large number of physiological functions controlled by beta-AR suggests that the mechanism(s) for the observed changes in carcass composition may be extremely complex. Any proposed mechanism must begin with the possibility of direct effects of the agonist on skeletal muscle and adipocyte beta-AR. However, many other mechanisms, such as modification of blood flow, release of hormones, or central nervous system control of feed intake may contribute to the overall effects observed with a given beta-AR agonist in a given species. Furthermore, the pharmacodynamic properties of a particular agonist are complex and expected to vary among species as well as within the same species at different ages or when fed different diets.

Section: Use Of β-Adrenergic Receptor Agonists In Growing Animalsmentioning

confidence: 99%

Overview of the effects of beta-adrenergic receptor agonists on animal growth including mechanisms of action.

Mersmann

1998

400

311

“…Exogenous administration of porcine somatotropin ( pST) alters carcass composition and visceral organ mass of growing swine (see Beermann, 1989;Boyd and Bauman, 1989;Brier and Gluckman, 1991). Etherton et al (1987) demonstrated linear increases in serum growth hormone ( GH) , insulin, and IGF-I with increasing pST dosage, whereas pST caused only minor changes in glucose and NEFA.…”

Section: Introductionmentioning

confidence: 99%

Effects of somatotropin and salbutamol in three genotypes of finishing barrows: blood hormones and metabolites and muscle characteristics.

Hansen

Yen

Klindt

et al. 1997

We evaluated the effects of recombinant porcine somatotropin (pST) and the beta-adrenergic agonist salbutamol on plasam endocrine and metabolite profiles and muscle chemistry in three genotypes of growing barrows (n = 96, 139 d old). Treatments were in a 2 x 2 x 3 factorial arrangement, and main effects were pST (0 or 4 mg/d) and salbutamol (0 or 2.75 ppm); the three genotypes including purebred Meishan (M), 1/4 Duroc, 3/4 White composite (D x Wc), and 1/4 Meishan, 3/4 White composite (M x Wc). Individual pigs were injected daily with buffer or pST at 0700 and allowed ad libitum access to a corn-soybean meal diet (1.2% lysine) and water for 33 d. Plasma was obtained 4 h after injection and 3 h postprandially on d 0, 14, and 28 for determination of growth hormone (GH), insulin, IGF-I, glucose, urea N (PUN), NEFA, triglycerides, and cholesterol. Longissimus and semitendinosus samples were obtained, and protein, RNA, and DNA were quantified and loin chop shear force was measured. In general, plasma hormones and metabolites on d 14 and 28 were not affected by salbutamol in the absence of pST, although salbutamol tended to increase d 14 and 28 GH concentrations. Salbutamol lowered plasma IGF-I (d 14 and 28, P < .05), insulin (d 14, P < .01), and NEFA (d 28, P = .07) when pST was administered, although concentrations still exceeded those for control pigs. Salbutamol reduced (P < .05) IGF-I in M and M x Wc pigs, and GH was not changed in M pigs. Meishan pigs had a greater increase in glucose with pST than M x Wc or D x Wc pigs, although the effect was not consistent over time. Individual treatment with pST caused GH, insulin, IGF-I, glucose, NEFA, and triglycerides to be increased and PUN to be decreased on d 14 and 28. Cholesterol on d 14 and 28 was decreased by pST in M pigs, whereas no effects were found in the other genotypes. Muscle protein and RNA were increased by salbutamol and were consistently lowest for M pigs. Furthermore, pST did not affect muscle protein, but it increased RNA more in M pigs than in the others. Overall, pST and salbutamol seemed to act separately and by different mechanisms to alter muscle composition, but blood criteria generally representing fat metabolism (insulin, glucose, NEFA, triglycerides) were interactively affected. Meishan pigs tended to have greater changes in muscle and plasma composition with pST treatment than did M x Wc or D x Wc pigs.

“…In our consumer-driven economy, livestock producers need to be using a variety of techniques to produce red meat products that meet current human dietary guidelines. Feeding high-forage diets to ruminants (Westerling and Hedrick, 1979;Marmer et al, 1984;Solomon et al, 1986) implanted with anabolic steroids (Beermann, 1989) should be used to produce high-leadow-fat carcasses. Anabolic steroids are known to increase muscle protein accretion J. h i m .…”

Section: Introductionmentioning

confidence: 99%

The effect of trenbolone acetate on performance, plasma lipids, and carcass characteristics of growing ram and ewe lambs1

Lough

Kahl

Solomon

et al. 1993

The purpose of the study was to determine the effect of trenbolone acetate (TBA) on performance, plasma lipid metabolites, and carcass characteristics of growing ram and ewe lambs in two separate experiments. Treatments consisted of 1) a control, no implants, and 2) a TBA implant (60 mg of Finaplix; Hoechst-Roussel Agri-Vet). Twelve Rambouillet cross ram lambs (average 19.9 kg BW; Exp. 1) and 18 Suffolk-Hampshire ewe lambs (average 37.2 kg BW; Exp. 2) were given ad libitum access to a 77% forage/23% concentrate diet (15.5% CP and 2.14 Mcal of ME/kg). On d 0, six rams and nine ewes received TBA as an ear implant and six rams and nine ewes were designated as controls. Blood samples were collected via jugular venipuncture on d 0, 28, 56, and 84 and plasma was separated and analyzed for lipid metabolites. Rams (30.5 kg BW) and ewes (50.0 kg BW) were slaughtered after 93 and 91 d, respectively. Average daily gain was not affected by TBA in rams (117 g/d) or ewes (159 g/d). Nutrient intake restricted normal BW gains in the rams. Plasma concentrations of total cholesterol, high-density lipoprotein cholesterol, triglycerides, and nonesterified fatty acids were not affected by TBA in either rams or ewes. Trenbolone acetate had no effect on subcutaneous fat measurements in either rams or ewes. Lamb chops from rams implanted with TBA were less (P < .04) tender (5.58 vs 4.26 kg/1.27-cm core) than lamb chops from control rams. Additional studies examining growth and carcass composition are needed in ruminants implanted with anabolic steroids and fed high-forage diets.