Effect Of bGH Research Articles

Maternal growth hormone treatment from day 35 to 80 of gestation alters nutrient partitioning in favor of uteroplacental growth in the overnourished adolescent sheep.

Overnourishing the pregnant adolescent ewe promotes maternal tissue synthesis at the expense of placental growth and leads to a major reduction in lamb birth weight at term. Growth hormone (GH) secretion is attenuated in these overnourished dams and the maternal somatotrophic axis may play a key role in coordinating nutrient usage in the pregnant adolescent. Thus we investigated whether increasing maternal GH during the period of rapid placental proliferation alters nutrient partitioning between the maternal, placental, and fetal tissues as assessed at Day 81 of gestation. Adolescent recipient ewes were implanted with singleton embryos, derived from superovulated dams and a single sire on Day 4 postestrus. Thereafter, the ewes were offered either a high (H) or moderate intake (M) of the same complete diet. From Day 35 to 80 of gestation, ewes were either injected twice daily (s.c. at 0800 and 1800 h) with recombinant bovine GH (bGH, 0.14 mg/kg live weight/day) or remained untreated (n = 8 ewes per group). Maternal concentrations of GH, insulin, insulin-like growth factor (IGF-1), glucose, and non-esterified fatty acids (NEFAs) were higher, and leptin secretion lower, in bGH-treated dams from both nutritional groups. Maternal body weight gain was higher in H versus M groups and was independent of bGH treatment. Treatment with bGH reduced relative perirenal and carcass fat deposition and increased carcass protein content in both H and M dams. Uteroplacental mass (uterus + placentomes + fetal membranes) averaged 1099, 1069, 1112, and 1754 g in M, H, M+GH, and H+GH groups. This significant increase in uteroplacental development in the H+GH group was associated with higher fetal kidney and liver weights and elevated fetal insulin, glucose, and lactate concentrations. Treatment with bGH also induced polyhydramnios in the H group. The transplacental glucose gradient was increased twofold in the H+GH group but placental GLUT- 1 and GLUT-3 expression was unaffected. In conclusion, administration of GH during the period of rapid placental proliferation alters endocrine status and thus nutrient partitioning in the overnourished adolescent dam in favor of uteroplacental and fetal growth. It remains to be established whether these effects are due wholly to alterations in maternal metabolism or if they also reflect an effect of bGH and/or the IGF system at the level of the uteroplacenta.

Augmentation of hormonal activities with antibodies from cattle immunized with a combination of synthetic and recombinant growth Hormone Peptide

Antibodies generated against a synthetic growth hormone (GH) peptide in a number of animal species were shown to enhance the efficacy of GH. However, the ability to produce the effective antibodies diminished over time and repeated boosters failed to overcome the hurdle. Therefore, this study was designed to address the issue on the failed antibody responses by employing different GH peptide antigen preparations in cattle. Holstein steers were repeatedly immunized with a synthetic peptide corresponding to an amino acid sequence 54‐95 of porcine GH (pGH). The peptide was conjugated to ovalbumin (OVA) as a carrier. Animals initially responded to the antigen well and elicited antibodies specific to the peptide. However, the 4th challenge with the same OVA‐peptide antigen rendered animals unresponsive, resulting in a decline in antibody production. This unresponsiveness was overcome by switching the antigen at the 5th immunization from OVA‐peptide to a recombinant peptide preparation which was composed of maltose binding protein (MBP) as a carrier. Antibodies generated in cattle after the 5th immunization recognized not only the pGH(54‐95) peptide, but also bovine GH (bGH) and pGH. These antibodies were not immunoreactive with an unrelated control peptide. Hypophysectomized (hypox) rats were used for functional analysis and bGH was active in promoting the growth of these GH‐deficient rats. The growth‐promoting effect of bGH was significantly enhanced by mixing it with bovine anti‐peptide antibodies prior to administration. Therefore, the present findings suggest that peptide 54‐95 induces cattle to elicit antibodies capable of not only recognizing bGH but also augmenting the somatogenic effectiveness of bGH in hypox rats.

Augmentation of hormonal activities with antibodies from cattle immunized with a combination of synthetic and recombinant growth hormone peptide

Antibodies generated against a synthetic growth hormone (GH) peptide in a number of animal species were shown to enhance the efficacy of GH. However, the ability to produce the effective antibodies diminished over the time and repeated boosters failed to overcome the hurdle. Therefore, this study was designed to address the issue on the fallen antibody responses by employing different GH peptide antigen preparations in cattle. Holstein steers were repeatedly immunized with a synthetic peptide corresponding to an amino acid sequence 54‐95 of porcine GH (pGH). The peptide was conjugated to ovalbumin (OVA) as a carrier. Animals initially responded to the antigen well and elicited antibodies specific to the peptide. However, the 4th challenge with the same OVA‐peptide antigen rendered animals unresponsive, resulting in a decline in antibody production. This unresponsiveness was overcome by switching the antigen at the 5th immunization from OVA‐peptide to a recombinant peptide preparation which was composed of maltose binding protein (MBP) as a carrier. Antibodies generated in cattle after the 5th immunization recognized not only the pGH(54‐95) peptide, but also bovine GH (bGH) and pGH. These antibodies were not immunoreactive with an unrelated control peptide. Hypophysectomized (hypox) rats were used for functional analysis and bGH was active in promoting the growth of these GH‐deficient rats. The growth‐promoting effect of bGH was significantly enhanced by mixing with bovine anti‐peptide antibodies prior to administration. Therefore, the present findings suggest that peptide 54‐95 induces cattle to elicit antibodies capable of not only recognizing bGH but also augmenting the somatogenic effectiveness of bGH in hypox rats.

Growth hormone stimulates the proliferation of activated mouse T lymphocytes.

A modulatory role for GH on immune function has been suggested, but hormonal effects have been difficult to demonstrate with isolated cells. We have recently shown that GH receptors are present in murine hematopoietic tissues, with a lower receptor number in T lymphocytes than in B cells or macrophages. The binding of bovine GH (bGH) to murine splenocytes is increased after T cell activation with either concanavalin A or anti-CD3 antibody. In the present study, we show that bGH is able to stimulate the proliferation of activated murine T cells. Splenocytes were stimulated with either Con A or anti-CD3 antibody; addition of the mitogen resulted in increased [3H]thymidine uptake. When added together with the mitogen to the culture medium, bGH was able to further stimulate thymidine uptake. A bell-shaped dose-response curve was observed. bGH was able to increase cell proliferation by 2.5-fold over the effect of anti-CD3 alone. The amplitude of the bGH response was greater in unfractionated splenocytes than in purified T lymphocytes or thymocytes. Splenocytes were also stimulated by lipopolysaccharide, a B cell-specific mitogen; no change in the level of bGH binding was observed during activation of B cells, and no effect of bGH on the proliferative response of splenocytes to lipopolysaccharide was detected. The GH proliferative effect on T lymphocytes is probably direct and not through locally produced insulin-like growth factor I, because insulin-like growth factor I did not affect the cell proliferation when added at concentrations ranging from 10(-9)-10(-7) M. Ovine PRL was also able to stimulate [3H]thymidine uptake in splenocytes and thymocytes, and a synergistic effect was observed when bGH and ovine PRL were added together at 10(-8) M. Our findings support the biological significance of the GH receptors identified in murine T lymphocytes and confirm the role of GH in the regulation of immune functions.

The regulation of insulin-like growth factor-binding protein 1 messenger ribonucleic acid in cultured rat hepatocytes: the roles of glucagon and growth hormone.

In previous studies it was shown that bovine GH (bGH) suppressed and glucagon stimulated the level of 24- and 30- to 34-kilodalton insulin-like growth factor-binding proteins (IGFBPs) in the media of cultured rat hepatocytes. In the present study we have evaluated the regulation of IGFBP-1 gene expression in primary rat hepatocyte cultures. Glucagon produced a dose-dependent stimulation of hepatocyte IGFBP-1 messenger RNA (mRNA), attaining levels 2- to 6-fold greater than control at a glucagon concentration of 100 ng/ml. GH inhibited the accumulation of IGFBP-1 mRNA in a dose-dependent manner producing, 40-70% inhibition at 50 ng/ml. The effect of glucagon was comparable to and additive with dexamethasone (1 microM). The addition of 3-isobutyl-1-methylxanthine (100 microM) and (Bu)2cAMP (100 microM) augmented IGFBP-1 mRNA levels 5- to 6-fold. 4 beta-Phorbol 12 beta-myristate 13 alpha-acetate (300 nM) was found to inhibit IGFBP-1 mRNA levels by 40-50%. The inhibitory effect of bGH on IGFBP-1 mRNA levels was abolished after preincubation with 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (10 microM) for 24 h, whereas glucagon's stimulatory effect was unaffected. The addition of staurosporine (500 nM) and H-7 (1 mM) abolished the inhibitory effect of GH but also significantly inhibited the stimulatory effect of glucagon, a result consistent with these agents acting on both protein kinase C (PKC) and PKA. In the presence of 10 micrograms/ml cycloheximide, IGFBP-1 gene expression was superinduced by bGH, whereas the effect of glucagon was uninfluenced. Thus the inhibitory action of GH involves, in part, the activation of PKC. Glucagon's stimulatory effect seems to involve the activation of PKA. The inhibitory effect of bGH on IGFBP-1 gene expression may require the continuing synthesis of one or more labile protein(s).

Growth hormone (GH) binding and effects of GH analogs in transgenic mice.

Overexpression of human (h) or bovine (b) growth hormone (GH) in transgenic mice is associated with marked (2- to 12-fold) and significant increase in hepatic binding of GH and prolactin (PRL). This is due to an increase in the number of GH and PRL receptors (GHR, PRLR) per mg of microsomal protein without changes in binding affinity. Comparison of results obtained in transgenic animals expressing bGH with a mouse metallothionein (MT) or a rat phosphoenolpyruvate carboxykinase (PEPCK) promoter suggests that effects of bGH on hepatic GHR and PRLR do not require GH overexpression during fetal life and, within the dose range tested, the effects on PRLR are not dose dependent. The increase in hepatic GHR was accompanied by significant increases in plasma GH-binding protein (GHBP) and in mean residence time of injected GH. Thus, life-long elevation of peripheral GH levels alters the availability of both free GH and GHR. Site-directed in vitro mutagenesis was used to produce hGH and bGH analogs mutated within one of the sites involved in binding to GHR and PRLR. Mutating hGH to produce amino acid identity with bGH at Position 11, 18 (within Helix 1), 57, or 60 (within the loop between Helix 1 and 2) did not affect binding to GHR in vitro, or somatotropic activity in transgenic mice in vivo but reduced lactogenic activity in Nb2 cells by 22%-45%. Mutations of bGH designed to produce amino acid identity with hGH at one to four of the corresponding positions in the bGH molecule did not interfere with binding to GHR or somatotropic activity in vivo, and failed to produce significant binding to PRLR but resulted in alterations in the effects on the hypothalamic and anterior pituitary function in transgenic mice. Apparently region(s) outside the domains examined are essential for lactogenic activity of hGH, and different portions of the GH molecule are responsible for its diverse actions in vivo.

Glucose metabolism in transgenic mice containing a chimeric P-enolpyruvate carboxykinase/bovine growth hormone gene.

Transgenic mice, containing the chimeric gene obtained by linking the promoter-regulatory region of P-enolpyruvate carboxykinase (PEPCK) gene to the bovine growth hormone structural gene (bGH), were used to investigate the long-term effects of bGH on glucose metabolism. Expression of the PEPCK/bGH gene was markedly enhanced by feeding a diet high in protein and inhibited by a high carbohydrate diet. All transgenic mice had normal levels of blood glucose but were hyperinsulinemic, indicating that they were insulin resistant. The glycogen synthase activity ratios in the muscle and liver of transgenic mice were lower than noted for control animals, and remained unchanged in liver after feeding a standard high carbohydrate or a high protein diet. Similar effects were detected in the activity of glycogen phosphorylase, except that a high carbohydrate diet activated this enzyme in the liver. The activation of glycogen phosphorylase in both muscle and liver correlated with the expression of their genes. These animals had a significant content of glycogen and glucose 6-phosphate, which was related to the levels of glucokinase mRNA in the liver. The concentration of fructose 2,6-bisphosphate in the liver of all fed transgenic mice was lower than noted in livers from fed animals. In addition, a decrease in the hepatic expression of the endogenous genes for PEPCK, tyrosine aminotransferase (TAT), and the glucose transporter GLUT-2 was observed and directly correlated with the expression of bGH. Thus, bGH can control glucose metabolism in vivo, at least in part, by modifying the expression of several genes coding for proteins of importance in carbohydrate metabolism. Taken together, these results indicate a state of insulin resistance caused by chronic exposure of the animals to an elevated concentration of bGH.

Separate and additive stimulation of bovine milk yield by the local and systemic galactopoietic stimuli of frequent milking and growth hormone.

Lactating heifers were treated for 4 weeks with recombinant bovine growth hormone (bGH, n = 9) or were untreated (n = 9). In addition, two mammary glands of each heifer were milked four times daily rather than the normal twice daily for the same 4 weeks, and for the following 2 weeks. Over the 4 weeks, milk yield was increased 12.8% by bGH, 14.0% by frequent milking and 28.5% by the combined treatment. The effect of bGH as administered here was slower in onset than that of frequency, but eventually produced a higher peak yield. ANOVA revealed significant effects of each stimulus independently and an additive, but not synergic effect of the combined treatment. The effect of the combined treatment tended to persist beyond the end of treatment; most of this response was related to the milking frequency component rather than the bGH. Mammary differentiation was assessed in biopsies of mammary tissue obtained prior to and at the end of treatment. Mammary enzyme activities (expressed on a per cell basis) indicated minimal differentiative response to either treatment, but synthesis rates for lactose and casein determined in vitro were increased by bGH treatment. Histological examination revealed a stimulatory effect of milking frequency on epithelial cell size. The results indicate that these two galactopoietic stimuli operate through independent mechanisms, and neither stimulus alone is sufficient to maximize milk yield in dairy heifers.

The galactopoietic effect of bovine growth hormone in goats is associated with increased concentrations of insulin-like growth factor-I in milk and mammary tissue

Lactating goats exhibiting widely divergent responses to short-term (4 days) treatment with bovine GH (bGH) were retrospectively divided into two groups based on the magnitude of this response. There was no difference between groups in terms of the pretreatment milk yield, but by day 4 of treatment milk secretion had increased by 4.99 +/- 2.5 (S.E.M.) ml/h (P greater than 0.05 compared with pretreatment) for group 1 and 22.9 +/- 2.4 ml/h (P less than 0.001) for group 2. Plasma GH increased in both groups, but concentrations were significantly higher both before and during treatment in group 1 compared with group 2. Plasma concentrations of insulin-like growth factor-I (IGF-I) increased significantly during bGH treatment for both groups and there was no significant difference between the two until day 4 of treatment when levels of IGF-I in group 1 began to decline, whereas those from group 2 were maintained. Concentrations of IGF-I in milk from goats in group 1 were not significantly altered by GH administration, whereas those in goats in group 2 were increased by 40% (P less than 0.01 compared with pretreatment). Levels of IGF-I in mammary secretory tissue from four animals from group 1 were not altered by bGH (2.8 +/- 0.2 and 2.77 +/- 0.08 nmol/kg tissue before and after treatment respectively), but were significantly (P less than 0.05) increased in four animals from group 2 (2.80 +/- 0.2 and 9.9 +/- 1.1 nmol/kg tissue).(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of nutrition and bovine growth hormone (GH) on hepatic GH binding, insulin-like growth factor-I and growth of lambs

The effect on young lambs of 0.25 mg recombinant bovine GH (bGH)/kg per day on plasma concentrations of insulin-like growth factor-I (IGF-I), glucose, specific hepatic GH binding and body composition changes was examined at two levels of nutrition (lucerne pellets; 3 and 1.7% of body weight/day). Lambs on low levels of nutrition had low plasma IGF-I (P less than 0.001). Plasma concentrations of IGF-I were increased by bGH treatment at both levels of nutrition, with the high nutrition group showing the greatest IGF-I response after 3 and 40 days of bGH treatment. Plasma glucose, after 40 days, was higher overall (P less than 0.05) in lambs on high nutrition. bGH treatment increased plasma glucose, with the response being greater in the well-fed lambs. Specific binding of GH to liver membranes was highest in lambs on high nutrition and on bGH treatment; no significant interaction between nutrition and bGH treatment was detected, indicating that specific binding of GH was increased proportionally by bGH at both nutritional levels. The major change in body composition was the reduced level of fatness in lambs treated with bGH. There was no significant effect of bGH on body weight although bGH treatment tended to increase weight gain of well-fed lambs and decreased weight loss of poorly nourished lambs. The results show that, although there was a significant (P less than 0.05) bGH/nutrition interaction for IGF-I there was no such interaction for body weight/components or specific GH binding to the liver. The results indicate that an increase in plasma IGF-I does not necessarily result in increases in growth or changes in carcass composition.

Cardiovascular and metabolic responses during growth hormone treatment of lactating sheep.

Pituitary-derived bovine growth hormone (bGH) was administered to six lactating Friesland ewes for 7 d. There was no consistent galactopoietic response, with changes in milk yield varying from 0 to 33% during treatment compared with the pretreatment period. The major effect of bGH on the concentration of milk constituents was to increase fat by 14.2% (P less than 0.05). Treatment resulted in significant increases in arterial plasma concentrations of growth hormone, insulin-like growth factor I and glucose, with decreases in the plasma arterial concentrations of acetate and certain amino acids. There was a marked reduction in haematocrit and in haemoglobin concentration which took at least 3 d to recover. The arterio-venous difference across the mammary gland decreased for O2 during treatment and the veno-arterial difference for CO2 decreased after treatment. Mammary respiratory quotient therefore decreased significantly after bGH treatment. The results suggest that bGH exerts effects at a number of separate loci.

Uterine Decidual ization in Hypophysectom ized-Ovariectom ized Rats: Effects of Pituitary Hormones1

Decidualization of the endometrial stroma occurs in rats in response to implanting blastocysts or after the application of an appropriately timed artificial stimulus. It is well established that decidualization is regulated by estrogens and progesterone (P). The present study investigated the role of pituitary hormones in this response. Decidualization produced by the bilateral intrauterine injection of 100 microliter sesame oil was compared in ovariectomized (OVX) and hypophysectomized (HYPOX)-OVX rats. All animals were treated with a sequence of 17 beta-estradiol (E2) and P that in OVX rats supported decidualization. As assessed by uterine weights 5 days after uterine stimulation, decidualization was much greater in OVX than in HYPOX-OVX rats (geometric mean uterine weights of 1539 and 376 mg, respectively). To determine the ability of pituitary hormones to restore decidualization in HYPOX-OVX rats, animals were treated with ovine prolactin (oPRL, 2 x 100 micrograms daily), bovine growth hormone (bGH, 2 x 125 micrograms daily), and thyroxine (1 microgram/day, replacement for thyrotropin) in addition to E2 and P. Combined treatment with bGH + thyroxine resulted in decidualization which was not significantly different from that obtained in OVX rats; the effects of bGH and thyroxine were additive. oPRL had no significant effect. Administration of bGH + thyroxine during the prestimulation period resulted in decidualization which did not differ significantly from that obtained when the hormones were administered both pre- and poststimulation; administration during the poststimulation period only, when growth and differentiation of decidual cells occurs, resulted in much less decidualization. Because an increase in endometrial vascular permeability is a prerequiste for decidualization, [125I]-labeled bovine serum albumin was used to assess permeability 8 h after uterine stimulation. Uterine concentrations of radioactivity indicated that endometrial vascular permeability was increased to the same extent in bGH + thyroxine-treated HYPOX-OVX rats as in OVX animals; this increase was significantly reduced in vehicle-treated HYPOX-OVX rats. Because prostaglandins (PGs) are involved in decidualization, the possibility that the reduced responses in vehicle-treated HYPOX-OVX rats were a consequence of a decreased capacity of the uterus to produce PGs in response to the deciduogenic stimulus was investigated. As indicated by uterine PGE and PGF concentrations 15 min after uterine stimulation, uterine PGE and PGF production was increased by the stimulus in both vehicle-treated and bGH + thyroxine-treated HYPOX-OVX rats.(ABSTRACT TRUNCATED AT 400 WORDS)

On the hormonal regulation of lipolysis in isolated reindeer adipocytes.

The effects of insulin and bovine growth hormone (bGH) on lipolysis (basal and/or adrenaline-stimulated) were investigated in isolated adipocytes from the Norwegian reindeer. Addition of 100 nmol l-1 adrenaline to the cells increased lipolysis 20-fold above basal lipolytic rate. Insulin (0.I and I nmol l-I) depressed lipolysis significantly at submaximal adrenaline stimulation but had no effect when lipolysis was stimulated maximally. Bovine GH (25 and 100 ng ml-I) inhibited basal lipolysis during the first 2 h of incubation, whereas refractoriness to this action was induced during the third and fourth hour of incubation. These effects were not influenced by inclusion of a small amount of glucocorticoid (dexamethasone, 25 ng ml-I). Addition of 0.I and I nmol l-I insulin together with bGH (100 ng ml-I) prevented the initial antilipolytic effect of the latter and resulted in the expression of normal basal lipolytic rates. Preincubation with bGH (100 ng ml-I) for 2 h did not alter the lipolytic response of the adipocytes to adrenaline. These findings lend support to the conclusion that insulin exerts a major control of lipolysis in reindeer adipose tissue. The significance of the antilipolytic effect of bGH is difficult to evaluate since this effect was transient and was abolished during the third and fourth hour of incubation.

Epidermal growth factor and bovine growth hormone stimulate differentiation and myelination of brain cell aggregates in culture

Bovine growth hormone (bGH) and epidermal growth factor (EGF) increased the activity of ornithine decarboxylase (ODC) in brain cell aggregates cultured in a serum-free chemically defined medium. ODC is considered as a marker of cell growth and differentiation. The effect of bGH and EGF on myelination was investigated by measuring two myelin markers, 2′,3′-cyclic nucleotide 3′-phosphodiesterase (CNP) and myelin basic protein (MBP). EGF treatment at days 2 and 5 caused a dose-dependent increase of both myelin markers at culture day 12. This increase could still be observed at culture day 19, indicating a prolonged action of EGF. The continual presence of bGH in the culture medium produced a large accumulation of MBP at day 19. This effect was dose-dependent and required the presence of triiodothyronine (T 3). In contrast, the effect of bGH on CNP activity did not require the presence of T 3. This is the first report showing a direct effect of bGH on CNS myelination in vitro and of EGF on both MBP accumulation and ODC activity.

Influence of bovine growth hormone on growth rate, appetite, and food conversion of yearling coho salmon (Oncorhynchus kisutch) fed two diets of different composition.

Paired groups of yearling coho salmon at 10 °C and on a natural photoperiod were fed twice daily either Oregon moist pellets (OMP) or a diet with poultry offal (PO) as the main protein source. The fish were fed either 0.8% body weight per day (dry weight of food (g)/wet weight of fish (g)) or to satiation. Coho in one of the groups for each diet–ration combination received, by intramuscular injection, 10 μg (0.0092 IU) of bovine growth hormone (bGH) per gram body weight one time per week for 56 days. Those in the other group were not treated.Administration of bGH significantly enhanced growth and improved food and protein conversion. Ration level altered the effect of bGH on food and protein conversion as did diet formulation at satiation. The voluntary food intake of bGH-treated fish fed OMP was higher but not significantly different from that of the controls. Diet formulation differences did not significantly affect the growth rate of either bGH-treated or untreated coho at each ration level. Irrespective of the diet–ration combination, bGH administration lead to a significant decline in condition factor.At 56 days, bGH-treated fish had a significantly lower percentage of muscle protein and a significantly higher percentage of muscle water than untreated fish. At present, the use of bGH as a growth promoter for coho salmon is not economical.