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F C Leung

Publications and source records attributed to F C Leung.

At least 37 records · Page 2Linked to original sources
PubMed1991

Circadian rhythms of melatonin release from chicken pineal in vitro: modified melatonin radioimmunoassay.

An improved and simplified radioimmunoassay for measuring pineal, serum, and in vitro cultured medium melatonin is described. Using 2-[125I]iodomelatonin as radiolabeled ligand and a polyclonal rabbit antimelatonin antiserum, melatonin concentrations were determined in all three types of samples by a 2-day direct equilibrium double-antibody assay method without prior extraction. Serial dilutions of pineal homogenates, serum, and cultured medium all gave parallel displacement curves. Cross-reactivity of the antisera with other indoles was negligible. Intraassay coefficients of variation (n = 3) were 5.09, 3.32, and 5.05% at 7.81, 62.5, and 500 pg/tube, respectively, and the interassay coefficients of variation (n = 20) were 12.18% at 62.5 pg/tube. A characteristic diurnal rhythm of melatonin was observed using this direct assay for measuring daytime and nighttime chicken pineal and serum samples. An in vitro incubation of chicken pineal glands with a lighting cycle of 12-hr light:12-hr dark showed that the diurnal rhythm of melatonin secretion into the cultured medium was maintained. The direct assay method described in this report for measuring chicken melatonin using 2-[125I]iodomelatonin as radiolabeled ligand coupled with the in vitro cultured chicken pineal gland clearly offers great potential for studying the chicken pineal circadian oscillator and its underlying mechanism.

Animals↗
PubMed1988

A comparison of bovine growth-hormone gene expression in mouse L cells directed by the Moloney murine-leukemia virus long terminal repeat, simian virus-40 early promoter or cytomegalovirus immediate-early promoter.

Three transcriptional regulatory regions including a human cytomegalovirus immediate-early region (CMVIE) promoter, the simian virus-40 early region (SV40E) promoter, and Moloney murine leukemia virus (MoMLV) long terminal repeat (LTR) were ligated to the bovine growth hormone (bGH)-coding gene. Using a bGH transient expression system, the CMVIE and SV40E gene transcriptional regulatory regions were found to be approximately two-fold more efficient than the MoMLV LTR in directing expression of bGH in mouse L cells.

Animals↗
PubMed1987

Ontogenesis of immunocytochemically demonstrable somatotrophs in the adenohypophyseal pars distalis of the developing chick embryo.

Growth hormone (GH)-containing cells in the hypophyseal pars distalis of the chick embryo were identified immunohistochemically using anti-chicken GH sera. GH cells are first demonstrable in Rathke's Pouch as early as Day 4.5 of incubation. By Day 9.5, when the two lobes (rostral and caudal) of the pars distalis are easily recognized, GH cells are confined exclusively to the caudal lobe. Although the number of GH cells increases gradually during embryonic development, there is a statistically significant difference between Days 10.5 and 12.5 in both the cellular density and the percentage of somatotrophs. GH cells, which contain coarse granules evenly distributed throughout the cytoplasm, varied in diameter from 9.3 micron on Day 4.5 to 11.8 micron on Day 20.5, while the nuclear diameter of these cells increased from 2.8 micron on Day 4.5 to 4.9 micron on Day 20.5. There was a statistically significant difference in the nuclear/cytoplasmic ratio between Days 4.5 and 13.5 and between Days 13.5 and 20.5 of incubation. Aspects of the regulation of growth hormone synthesis and secretion in the chick embryo are discussed.

Animals↗
PubMed1987

Diminished hepatic growth hormone receptor binding in sex-linked dwarf broiler and leghorn chickens.

Hepatic growth hormone (GH) receptor binding was compared in normal and sex-linked dwarfs (SLD) from both Hubbard and Cornell strain chickens. At 6, 8, and 20 weeks of age, hepatic GH receptor binding in the Hubbard SLD chickens was significantly lower than that of normal fast-growing birds. At 20 weeks of age, only 2 of 22 SLD chickens in the Hubbard broiler strain showed positive binding at a high enough level to allow for Scatchard analysis. The affinity constants and binding capacities of these two SLD chickens were numerically (but not significantly) lower than those of the normal fast-growing birds. We further examined hepatic GH receptor binding in two closely related White Leghorn strains of chickens that have been maintained as closed breeding populations for many years. We observed no detectable hepatic GH binding in the Cornell SLD chickens (N = 20), as compared to the normal-growing control strain (K strain). In both SLD strains, pretreatment with 4 M MgCl2 did not enhance GH binding, suggesting that there was no endogenous GH binding to the receptor. Based on these data, we suggest that the lack, or greatly reduced number, of GH receptors may be a major contributing factor to the dwarfism observed in these strains.

Animals↗
PubMed1986

Avian hormones.

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Animals↗
PubMed1986

Purified chicken growth hormone (GH) and a human pancreatic GH-releasing hormone increase body weight gain in chickens.

Purified chicken GH (cGH) and a synthetic human GH-releasing hormone (hpGRF) were tested for the ability to improve growth performance in chickens. Purified cGH was given to 4-week-old cockerels at 5, 10, and 50 micrograms/day for 14 days via daily iv injection. Body weights of chickens receiving 5 and 10 micrograms/day cGH were significantly increased at 6 days by 13.5% and 11.2%, respectively, relative to control values. At 14 days, body weights averaged 8.1% and 7.7% greater than controls, but these values were not statistically significant. There was a slight stimulation of body weight gain in chickens receiving 50 micrograms/day cGH. In general, cGH produces a transient stimulation of body weight gain in chickens. hpGRF was also given to 4-week-old cockerels for 14 days via daily iv injection at 0.1, 1.0, and 10.0 micrograms/day. hpGRF at 0.1 microgram/bird daily increased body weight on day 14 (9.1% over the control value). The stimulating effects of hpGRF on body weight are also transient. The effects of cGH on serum somatomedin-C (SM-C) were examined. Serum SM-C concentrations were significantly elevated 24 and 36 h after injection of cGH. In conclusion, purified cGH and hpGRF appear to have some growth-promoting activity. The stimulatory effect of hpGRF on weight gain may be mediated via GH, and the stimulatory effect of cGH could be mediated through SM-C.

Animals↗
PubMed1986

Purification and physiochemical properties of a recombinant bovine growth hormone produced by cultured murine fibroblasts.

Mouse fibroblast cell lines which secrete bovine (b) GH have been generated. This was accomplished by cotransforming mouse L cells (thymidine kinase-negative [TK-] and adenine phosphoribosyl transferase-negative [APRT-]) with DNA molecules encoding the Rous sarcoma virus-long-terminal repeat and bGH genes along with the herpes viral TK gene and the hamster APRT gene. One stable cell line, Pd lambda-pbGH 4-13, was found to secrete approximately 75 micrograms bGH per 24 h/5.0 X 10(6) cells. Media from this cell line were collected for purification of recombinant bGH (rbGH). Purification involved (NH4)2SO4 fractionation, ion-exchange chromatography, and gel filtration on Sephacryl S-200. The rbGH was characterized by bioassay, RIA, radioreceptor assay, and sodium dodecyl sulfate gel electrophoresis. Results of these analyses were compared with those obtained with a highly purified pituitary bGH. In the rat tibia bioassay, rbGH was found to be as potent as pituitary bGH. Results from the RIA, radioreceptor assay, and sodium dodecyl sulfate gel electrophoresis and Western blot analysis also suggested that the rbGH was similar to that of pituitary origin. Amino acid composition, partial (amino-terminal) sequence, and tryptic peptide maps were also found to be similar between the rbGH and pituitary bGH preparations. The amino terminus of the rbGH showed similar heterogeneity to that of the bGH of pituitary origin. We conclude that rbGH which was synthesized, processed, and secreted from transformed mouse fibroblasts possessed almost exactly the same physiochemical properties as pituitary bGH.

Amino Acids↗
PubMed1986

The relationship between age and genotype and the growth of commercial meat strain chickens.

Sex-linked dwarf male (dw/dw) and female (dw/-) chickens from a commercial meat strain, grew significantly slower than genetically normal broilers (Dw/Dw). The differences were evident at 2 weeks of age and they remained constant with age, at least through 8 weeks. The dwarfs in turn grew significantly faster than genetically normal (Dw/Dw) but slow-growing roaster strain chicks. Heterozygous (Dw/dw) normal, fast-growing male broilers grew significantly faster than the normal and roaster chicks but weighed 8% less than the normal broilers at 8 weeks. Abdominal fat accretion was greatest in the dwarf chicks and least in the slow-growing roaster strain when comparisons were made at the same age and the same body weight. Pectoralis muscle growth was greater in the broiler strain when equal age and weight comparisons were made. Gastrocnemius muscle growth, however, was greatest in the slow-growing roaster chicks.

Adipose Tissue↗
PubMed1986

The relationship between age and genotype and circulating concentrations of triiodothyronine (T3), thyroxine (T4), and growth hormone in commercial meat strain chickens.

The presence of the sex-linked dwarf gene (dw) in homozygous male (dw/dw) and female (dw/-) meat strain chickens is associated with a significant reduction in circulating levels of triiodothyronine (T3). Heterozygous (Dw/dw) male broiler strain chickens have T3 concentrations similar to those in homozygous (Dw/Dw) male broilers. Genetically normal (Dw/Dw) but significantly slower growing roaster strain male meat chickens had consistently higher T3 than the faster growing broilers at all ages in one experiment but only at 8 weeks in a second experiment. Age and not growth rate appears to have a greater influence on serum T3 concentrations in the slow- and fast-growing normal strains. Growth hormone levels were significantly higher in the dwarf chickens at all ages and in all three experiments. The heterozygous and homozygous broilers had similar GH levels and the slow-growing, genetically normal roasters had intermediate concentrations between the broiler and dwarf lines. GH was influenced to a greater extent by the rate of body weight gain than by increasing age in the genetically normal fast and slow growing strains.

Aging↗
PubMed1986

Interaction of human pancreatic growth hormone-releasing factor, thyrotropin-releasing hormone, and somatostatin on growth hormone release in chickens.

The effects of synthetic somatostatin (SRIF) on serum growth hormone (GH) concentrations stimulated by exogenous administration of synthetic thyrotropin-releasing hormone (TRH) and/or human pancreatic GH-releasing factor (hpGRF) were investigated in 4-week-old cockerels. In addition, the additive effects of TRH and hpGRF on serum GH were examined. TRH and hpGRF, when given in combination intravenously, produced an additive effect on serum GH concentration that peaked 10 min after the injection. The somatostatin did not significantly affect basal GH concentrations when given alone, but did significantly decrease the magnitude of the GH response to hpGRF. In contrast, SRIF did not significantly decrease the stimulatory effects of TRH on GH release. These results suggest that TRH and hpGRF are potent GH releasers in vivo and that their stimulating effects on GH release are additive, suggesting different mechanisms for their stimulation. The results obtained from the combination studies suggest that the main site of the stimulatory action of hpGRF is at the pituitary, and that SRIF significantly inhibited the rise in serum GH induced by a synthetic hpGRF, but not that induced by TRH.

Animals↗
PubMed1985

Effects of dietary thyroid hormones on growth, plasma T3 and T4, and growth hormone in normal and hypothyroid chickens.

Cockerels and pullets fed with T3 or T4 for 2 weeks showed a decrease in both body weight gain and feed efficiency. The reduction in body weight gain and feed efficiency was dose related in cockerels where T3 or T4 were fed at 0.1, 1.0, and 10.0 ppm levels. T3 and T4 at 0.1 and 1.0 ppm had no significant effects on growth or feed efficiency in pullets, but the 10.0-ppm level of T3 and T4 caused a reduction of -55.24 and -28.18%, respectively, in body weight gain as compared with control birds. T3 was more active than T4 in reducing growth and was toxic when fed at 10.0 ppm both in cockerels and pullets. Both propylthiouracil (PTU)- and methimazole-treated cockerels showed a decrease in rates of gain. T3 and T4 at a dietary level of 0.1 ppm were equipotent in promoting growth in these PTU- and methimazole-treated cockerels, but 10.0 ppm caused a further reduction in body weight gain. Plasma T3 levels were found to be significantly higher in birds that were fed either T3 or T4. Plasma T4 levels were higher in T4-fed birds, but significantly lower in T3-fed birds as compared with controls. Both PTU- and methimazole-treated cockerels had significantly lower plasma T3 and T4 concentrations, but elevated plasma GH concentrations. Dietary T3 and T4 at 1.0 and 10.0 ppm significantly lowered plasma GH concentrations. In summary, these results indicated that T3 was more active than T4 in reducing body weight gain in intact normal birds, but that they were equally potent in promoting growth in PTU- and methimazole-treated hypothyroid birds.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Use of avian retroviral-bovine growth hormone DNA recombinants to direct expression of biologically active growth hormone by cultured fibroblasts.

A variety of recombinant DNA molecules were constructed in which an avian retroviral long terminal repeat (LTR) was ligated to the bovine growth hormone (bGH) gene. The retroviral LTR was derived from a plasmid clone of a Schmidt Ruppin B strain of Rous sarcoma virus while the bGH gene was subcloned from a lambda bacteriophage genomic library. Using a transient eukaryotic expression assay system, recombinant plasmid constructs were screened for their ability to direct expression and secretion of bGH. One such plasmid DNA construct, termed pBGH-4, was found to be active in the production of bGH. Stable mouse fibroblast cell lines were generated containing pBGH-4 DNA integrated into the mouse cell genome. Many of these mouse cell lines express and secrete bGH. One line, L-Pd lambda-BGH4-13, was found to secrete bGH at a rate of 75 micrograms per 5 X 10(6) cells per 24 hr. Bovine growth hormone derived from this cell line is biologically active.

Animals↗
PubMed1985

Homologous and heterologous growth hormones fail to stimulate avian cartilage growth in vitro.

Recent reports that GH has a direct effect on growing cartilage have raised questions as to the role of somatomedins (Sm) in cartilage growth. To test the hypothesis that GH directly stimulates cartilage growth, we added homologous and heterologous GHs to organ cultures of embryonic chick pelvic cartilage. Pelvic rudiments from 9-day-old chick embryos were incubated in serum-free medium for 3 days in medium alone or medium containing chicken GH, turkey GH, bovine GH, human GH, and bovine GH produced by recombinant DNA methodology. None of the GH preparations studied stimulated avian cartilage growth in vitro. However, cartilage wet weight increased in response to sera from normal and growth hormone-treated hypophysectomized rats. In addition, 20 ng/ml purified Sm-C caused a 78% increase in cartilage weight above that of cartilage incubated in medium alone. Insulin also caused an increase in cartilage weight, but in concentrations 50,000-100,000 times that of Sm-C. Our studies demonstrate that homologous and heterologous GH have no effect on growing avian cartilage and support the hypothesis that Sm directly mediate cartilage growth.

Animals↗
PubMed1984

Purification and properties of chicken growth hormone and the development of a homologous radioimmunoassay.

Highly purified growth hormone (GH) has been isolated from pituitary glands of chicken (Gallus domesticus), and a specific homologous radioimmunoassay (RIA) has also been developed. The purified chicken GH was active in the rat tibia bioassay and it gave a dose-dependent response which paralleled that of the bovine GH standard. High pressure liquid chromatography revealed that the purified chicken GH was homogenous. Chicken GH had an Rf value of 0.2 in disc electrophoresis, and a MW of 26,000 from sodium dodecyl sulfate-gel electrophoresis. The isoelectric point was estimated to be 7.6 by gel isoelectric focusing. The amino acid composition of chicken GH was found to be similar to that of mammalian GH, and the NH2-terminal amino acid was threonine. Partial sequencing (114 amino acids) of the chicken GH showed 79% homology with bovine GH. An antiserum was developed to the purified chicken GH in a rabbit, and it was used to develop a homologous RIA using 125I-labeled chicken GH as the ligand. The purified chicken GH was iodinated via the lactoperoxidase method to a specific activity of approximately 100 microCi/micrograms. Plasma from chickens, medium from incubation of pituitary glands, and homogenates of pituitary glands gave parallel dilution-response curves with the chicken GH standard. Mammalian GH, prolactin (PRL), follicle-stimulating hormone (FSH), and luteinizing hormone (LH) showed no cross-reaction with the 125I-labeled chicken GH. Purified turkey GH showed parallel dose response with the chicken GH, but purified turkey PRL did not cross-react. Chicken FSH and LH also showed no inhibition of binding. The minimum detectable concentration of the assay was 0.93 ng/tube, and the intraassay and interassay coefficients of variation were 9 and 16%, respectively. The specific binding of 125I-labeled chicken GH to a microsomal fraction isolated from chicken liver was identified, and the specific binding was generally low (1-4%). Turkey PRL, and chicken LH and FSH showed no inhibition of the 125I-labeled chicken GH hepatic binding and the ontogeny of the hepatic GH receptor binding sites in male and female chickens was examined.

Aging↗
PubMed1984

Thyrotropin-releasing hormone stimulates body weight gain and increases thyroid hormones and growth hormone in plasma of cockerels.

The effect of TRH on growth in 4-week-old cockerels was examined in two separate experiments. Daily injection of TRH via the brachial vein stimulated growth in 4-week-old cockerels over 17 days of treatment in the first experiment and over 25 days in the second. In the first experiment, TRH at 1.0 micrograms and 10.0 micrograms/bird caused significant (P less than 0.05) increases of 12.0% and 12.4%, respectively, in growth rate, whereas in the second experiment, only the 1.0 micrograms/bird level of TRH caused an increase (P less than 0.05). In each experiment, the increase in body weight gain was not TRH dose dependent, and neither feed consumption nor feed efficiency was affected. Possible involvement of pituitary hormones in TRH-stimulated growth in cockerels was studied in a separate experiment, and the effects of TRH on plasma T3, T4, and GH were examined. TRH was given iv at 0.1, 1.0, and 10.0 micrograms/bird daily for 5 days, and plasma T3, T4, and GH concentrations were measured 15, 60, and 180 min postinjection by RIA on days 1, 3, and 5. The responses of T3 and T4 to TRH were greatest on day 1, were diminished by days 3 and 5, and were not dose-related. Significant, not dose-related, elevations of plasma GH concentrations were obtained at all doses of TRH. Based on these results, we suggest that TRH has the ability to promote a significant increase in body weight gain in 4-week-old cockerels, and the stimulatory effects may be mediated through GH and/or thyroid hormones.

Animals↗