John C. Byatt

Growth of domesticated transgenic fish

A growth-hormone transgene boosts the size of wild but not domesticated trout.

Impact of a controlled release formulation of recombinant bovine growth hormone upon growth and seawater adaptation in coho (Oncorhynchus kisutch) and chinook (Oncorhynchus tshawytscha) salmon

Abstract Experiments were undertaken to evaluate a sustained release recombinant bovine growth hormone (rbGH) formulation (Posilac®) in salmon. The investigation was divided into two parts. The first series of studies was used to establish optimal dosages and clearance rates for the exogenous protein in size-selected coho salmon, and to examine the effect of rbGH treatment upon smoltification. The second series of studies attempted to mimic the production setting, where chinook salmon were randomly selected from a stock of animals, and taken through smoltification to grow-out. In the first experiment, coho salmon were provided with a single injection of one of three doses (420, 1260, 4200 μg/g body weight equivalent) of the rbGH preparation (n ≥30/group), or were injected with a saline solution containing the high dose equivalent of rbGH. Controls were treated with BSA, given one of three (10, 30 or 100 μl) placebo carrier preparations without rbGH, or left untreated. Animals receiving rbGH by sustained-release expressed highly significant (P

Regulation of bovine mammary growth by peptide hormones: involvement of receptors, growth factors and binding proteins

Abstract Involvement of the somatotropin (ST)/prolactin(PRL)/placental lactogen (PL) family and their mediators in regulating mammary growth in cattle was evaluated using both in vitro and in vivo models. Mitogenic activity of bovine mammary epithelial cells (BMEC) was not increased by ST, PRL or PL in vitro. Direct infusion of ST but not PRL into mammary glands of late pregnant beef cows increased mammary DNA. Exogenous treatment of steroid-primed dairy heifers with PL increased mammary DNA while PRL treatment resulted in lactogenesis but no detectable increase in mammary DNA. Insulin-like growth factor-I (IGF-I) directly increased BMEC DNA synthesis in vitro and infusion of IGF-I into mammary glands of late pregnant beef cows increased mammary growth. Epidermal growth factor and transforming growth factor-alpha increased the mitogenic response to IGF-I and are likely involved in paracrine regulation of mammary growth. IGF binding proteins are produced and secreted by BMEC and may be autocrine regulators of growth. Collectively, these data indicate that lactogenic hormone receptors are not involved in regulation of mammary growth in cattle. Increased mammary growth following ST and PL treatment was apparently mediated through local production or uptake of IGFs and/or alteration of IGF binding protein concentrations. Presently, it is not clear whether ST and PL act through local as well as distant somatotrophic receptors to alter availability and uptake of IGFs.

Recombinant bovine growth hormone treatment of tilapia: growth response, metabolic clearance, receptor binding and immunoglobulin production

Abstract Experiments were performed to examine the growth-promoting effects of recombinant bovine growth hormone (rbGH) in the euryhaline tilapia ( Oreochromis mossambicus ). A radioreceptor assay using a crude membrane preparation of tilapia liver revealed that rbGH was about 100-fold less potent than native tilapia GH (tGH) in displacing 125 I-labeled tGH. Bovine prolactin (bPRL) was equipotent to bovine GH indicating that the GH receptor of tilapia does not distinguish mammalian GH from mammalian PRL. When juvenile tilapia, weighing 1 g, were maintained at 28 °C and received intraperitoneal injection of rbGH at doses of 0.1, 1 or 10 μg/g weekly for 8 weeks, no significant effect on growth was observed. A second experiment examined weekly doses ranging from 1 to 50 μg/g for 16 weeks, using 1 g fish maintained at 23 °C. rbGH (50 μg/g) significantly increased growth after 14 and 16 weeks, although the growth rate was significantly less than those held at 28 °C. More pronounced growth-promoting effects were observed, however, when fish weighing 5 g and held at 29 °C were injected with rbGH at doses of 100 and 1000 μg/g once a week for 4 weeks. A single injection of a sustained-release formulation of rbGH (Posilac®, 100 and 1000 μg/g) also elicited growth-promoting effects in fish weighing 4 g and kept at 29 °C. Treatment with rbGH, Posilac® or bovine serum albumin (BSA) elicited significant increases in plasma levels of immunoglobulin (IgM) in a dose-dependent manner. By contrast, there was no change in plasma levels of lysozyme activity in rbGH- or Posilac®-injected fish compared with controls. An uptake and clearance study confirmed a slower decline in circulating levels of rbGH following Posilac® injection compared with rbGH in saline. There was no change in plasma concentration of tGH after rbGH treatment, indicating that GH secretion from the tilapia pituitary was unaffected by high plasma levels of rbGH. The relative refractoriness of juvenile tilapia to growth-promoting effects of rbGH compared with that of other species may be due to the specific nature of the tGH receptor in recognizing the homologous hormone.

IGF-I-Induced IGFBP-3 potentiates the mitogenic actions of IGF-I in mammary epithelial MD-IGF-I cells

Limited information is available concerning the molecular and cellular mechanisms that regulate expression of insulin-like growth factor-I (IGF-I) binding proteins (IGFBPs) in bovine mammary epithelial cells. Here, we report on the autocrine mechanisms of action of IGF-I and hormonal regulation of expression of IGFBPs in bovine mammary epithelial MD-IGF-I cells which express recombinant IGF-I under the control of the glucocorticoid-inducible mouse mammary tumor virus-long terminal repeat (MMTV-LTR). Levels of IGFBP-3 mRNA and secretion of IGFBP-3 by MD-IGF-I cells were stimulated by IGF-I, insulin (INS), and IGF-I analogs but not prolactin (PRL). Conversely, parental MAC-T cells expressed little IGF-I and secreted primarily IGFBP-2 (29-32 kDa) in response to stimulation with INS, dexamethasone (DEX), or IGF-I analogs. Secretion of recombinant IGF-I caused a 26.5-fold increase in secretion of IGFBP-3, as measured by densitometric analysis of ligand blots, which was associated with a 1.7-fold increase in total DNA. Conditioned media (CM) from MD-IGF-I cells induced with DEX stimulated a 2.8-fold increase in [3H]thymidine incorporation into DNA of parental MAC-T cells, compared with uninduced cells. Moreover, inclusion of exogenous IGF-I with CM from MD-IGF-I cells triggered an additional 3.0-fold increase in label incorporation, but only a 1.6-fold increase in the presence of IGFBP-2-containing media conditions by MAC-T cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation of Genomic Sequence Encoding a Biologically Active Bovine TGF- α Protein

AbstractGenomic clones encoding bovine TGF-α were identified by hybridization with probes derived from human TGF-α sequence. Nucleotide sequence of the clones predicts that mature bovine TGF-α is a 50 amino acid polypeptide which shares 96% and 92% homology with human and rat TGF-α, respectively. Bovine TGF-α with the predicted sequence was chemically synthesized and tested for activity. Synthetic bovine TGF-α competes in a radioreceptor assay with labelled mouse EGF with activity parallel to that of human TGF-α and mouse EGF. The mitogenic activity of bovine TGF-α is comparable to that of human EGF in causing proliferation of bovine mammary epithelial cells. An ∼ 5.0 kilobase RNA transcript is observed in polyadenylated RNA from MDBK cells by Northern blot analysis. The polymerase chain reaction detects the presence of a TGF-α transcript in many bovine tissues. These data indicate that bovine TGF-α may be a normal regulator of cell growth in the bovine animal.

The effect of bovine lactoferrin on muscle growth in vivo and in vitro.

Lactoferrin was found to be a potent stimulator of proliferation for L6 myoblasts. Both apo and holo-forms of lactoferrin were equipotent. By contrast, only the holo-form of transferrin (a structurally related iron binding protein) stimulated proliferation, apo-transferrin was without activity. Holo-transferrin was also less stimulatory than lactoferrin. Purified lactoferrin was administered to mature female rats and to neonatal rats by daily subcutaneous injection to determine if there was a measurable effect on muscle cell growth in vivo. Results from the in vivo studies suggest that lactoferrin has little or no effect on muscle cell growth in the whole animal.

Insulin-like growth factors-I and -II, somatotropin, prolactin, and placental lactogen are not acute effectors of lipolysis in ruminants☆☆☆

The acute regulation of lipolysis in the adipose tissue of ruminants was evaluated with lactating cows (n = 4) and growing ewe lambs (n = 11). Subcutaneous adipose tissue was obtained by biopsy or at slaughter and was incubated with varying concentrations of biologically active insulin-like growth factors-I and -II (IGF-I, IGF-II), somatotropin (ST), prolactin (PRL), or placental lactogen (PL) to determine the effect of these hormones on lipolysis. Complimentary studies were conducted to examine the effects of IGF-I and IGF-II on the acute regulation of lipolysis in adipose tissue from lactating ewes and wethers under a variety of incubation conditions. Isoproterenol (ISO), a beta-adrenergic agonist known to rapidly stimulate lipolysis, was used as a positive control. Incubation with ISO for 3 hr resulted in a significant increase in the rates of lipolysis. However, there was no stimulation of lipolysis over the 3-hr incubation at any concentration or under any conditions for IGF-I or IGF-II. Furthermore, ST, PRL, or PL had no acute effects on the rates of lipolysis in adipose tissue. These data demonstrate that IGF-I, IGF-II, ST, PRL, and PL are not acute effectors of the lipolytic rate in the adipose tissue of ruminants.

Dietary lipid level and growth hormone alter growth and body conformation of blue tilapia, Oreochromis aureus

Abstract Tilapia ( n =12 per treatment in duplicate) were subjected to two different dietary levels of lipid (∼8% and 17%) and injected doses of recombinant bovine growth hormone (2.5 and 5.0 μg rbGH g −1 body weight week −1 ). The effects of these treatments were examined with respect to their impact upon growth and body shape. Tilapia fed high-lipid diets expressed increased weight and length gains ( P P P P P P P P

Growth, feed utilisation, carcass composition and sensory characteristics of rainbow trout treated with recombinant bovine placental lactogen and growth hormone

The effect of treating rainbow trout (initial weight=51 g, T=10–11.5°C, fed to satiation), with recombinant bovine placental lactogen (PL, 2 μg g−1 body weight week−1) or growth hormone (GH, 2 μg g−1 body weight week−1), upon growth, feed conversion, sensory characteristics and fillet composition was investigated, with reference to three control groups. Hormone treatments were given for a period of 5–6 weeks, followed by a period of 13 weeks during which animals were left undisturbed. Differences in proximate composition of carcass (P<0.0005) and entrails (P<0.01), but not skeleton, were observed when sampled fish (PL at 5 weeks, GH at 6 weeks, and control at 7 weeks) of similar length were compared. At trial termination, eight animals from each group were randomly caught and slaughtered. The left fillet of each fish was skinned, vacuum-packed and boiled for 5 min, while the right fillet was used for compositional analyses. A trained sensory panel for flavour, odour, texture and appearance examined boiled fillets. PL-treated fish were deemed to express superior characteristics to control or GH-treated trout, particularly for juiciness (P<0.05). GH-treated animals received lower scores (P<0.05) for both sweet odour and flavour. Concurrent with a higher score for dryness, GH-treated fish returned higher fillet protein content (P<0.05) than other groups.