R. Vasilatos-Younken

Effect of pattern of administration on the response to exogenous pituitary-derived chicken growth hormone by broiler-strain pullets.

The effect of pulsatile versus continuous intravenous administration of exogenous, pituitary-derived chicken growth hormone (cGH) on growth performance and endocrine/metabolite status of broiler-strain pullets was determined. In a first study, 8-week-old pullets, surgically prepared with intravenous catheters and maintained via a fluid swivel/spring tether/harness system, were administered cGH or vehicle (control) over a 10-min period every 90 min (i.e., 90-min pulse pattern) for 21 consecutive days. Feed intake, body weight gain, and carcass yield and composition were determined in conjunction with plasma concentrations of several hormones and metabolites. In a second study, 8-week-old pullets were intravenously administered cGH or vehicle continuously for 21 consecutive days under the same conditions as for Study I. Pulsatile cGH administration improved feed efficiency (P less than 0.02), increased longitudinal bone growth (P less than 0.02) and mass (P less than 0.01), and reduced abdominal fat pad size (P less than 0.05) and total carcass lipid (P less than 0.09) over the 21-day treatment period in comparison to vehicle infusion. Pulsatile cGH administration also resulted in hepatomegaly, a marked elevation in plasma IGF-I (P less than 0.003) and T3 (P less than 0.005) concentrations, and a reduction in plasma T4 levels (P less than 0.04). In contrast to the above responses to pulsatile cGH, continuous intravenous cGH administration significantly impaired feed efficiency (P less than 0.01) and had no significant effect on abdominal fat pad or liver size or on total carcass lipid, but did result in widening of the epiphyseal growth plate (P less than 0.06) and increased bone mass (P less than 0.01) in comparison to vehicle infused controls. These studies demonstrate that in the broiler chicken, for which endogenous plasma GH concentrations are pulsatile at early ages in conjunction with rapid growth, the pattern of exogenous GH administration is clearly a factor influencing the nature of response to the hormone.

Effect of exogenous chicken growth hormone (cGH) administration on insulin-like growth factor-I (IGF-I) gene expression in domestic fowl

The effects of chicken growth hormone (cGH) infusion on insulin-like growth factor (IGF-I) gene expression in rapidly-growing, meat-type chickens was investigated. Chicken GH was infused either continuously or in a pulsatile fashion to 8-week-old birds during a 7-day period. Following cGH infusion, both IGF-I peptide and IGF-I mRNA content were measured in selected tissues. Steady-state IGF-I mRNA abundance was determined by a solution hybridization nuclease protection assay using total cellular RNA obtained from liver, heart, kidney, spleen, epiphyseal growth plate cartilage, gastrocnemius and pectoralis muscles. Continuous infusion of cGH elicited a two-fold increase in IGF-I peptide concentration in the kidney (P < 0.05), while all other tissues remained unchanged by cGH treatment under this infusion pattern. Pulsatile cGH infusion produced a two-fold increase in IGF-I peptide content in the liver, gastrocnemius, and pectoralis muscles (P < 0.05). In contrast with the levels of IGI-I peptide, relative steady-state IGF-I mRNA content was two-fold higher in liver and spleen of birds treated continuously with cGH, but was decreased to 35 and 55% of control birds in heart and pectoralis muscle. Pulsatile cGH infusion resulted in a 64% increase in IGF-I mRNA in the liver and remained unchanged in other tissues. Under both patterns of administration, changes in IGF-I mRNA were not reflected by changes in tissue IGF-I peptide levels. Overall correlations between tissue IGF-I mRNA and peptide levels were low and not significant in the tissues studied, except for liver under pulsatile infusion, in which IGF-I peptide levels paralleled changes in IGF-I mRNA. We conclude that, in chickens, exogenous cGH treatment stimulates hepatic IGF-I transcription and translation only when the pattern of infusion mimics the natural episodic pattern of GH secretion. The low correlation between IGF-I peptide and mRNA levels in extra-hepatic tissues may indicate differential responsiveness to GH in birds, and that in some tissues IGF-I levels are under GH-independent transcriptional controls.

Effects of growth hormone and pair-feeding on leptin mRNA expression in liver and adipose tissue

Previous research has reported that elevations in circulating growth hormone (GH) levels in meat-type chickens depresses feed intake (FI) more than 30%. It is known that the product of the obese gene, leptin, functions to regulate FI and energy expenditure. To investigate the effect of GH on leptin gene expression, broiler chickens were infused with recombinant chicken GH. To separate any secondary effects of a GH-induced reduction in FI on leptin expression, groups of birds were pair-fed to an average level of voluntary intake similar to GH-treated birds, but received no GH treatment. GH treatment induced a dose-dependent increase in liver leptin gene expression, as measured by reverse transcriptase-polymerase chain reaction, whereas leptin expression in adipose tissue was unchanged. Conversely, in chickens pair-fed (feed-restricted) there was a decrease in leptin gene expression in both tissues. These results provide evidence of a direct effect of GH on leptin gene expression, which is independent of any effects on intake attributable to GH-treatment, and suggest differential regulation of leptin expression between adipose tissue and liver. The results of these experiments provide the first evidence of a relationship between GH and leptin in domestic birds.

The distribution of neuropeptide Y gene expression in the chicken brain

Neuropeptide Y (NPY) is demonstrated to play an important role in central control of voluntary feed intake (FI) of a variety of species. The commercial broiler chicken has been intensively selected over generations for increased body weight, achieved largely through increased FI. This has resulted in a contemporary animal that does not regulate FI to maintain energy balance, and represents a model for hyperphagia and obesity if allowed unrestricted access to feed. In the present study, the distribution of NPY mRNA was mapped in the brain of juvenile, broiler-strain chicken, and results interpreted in the context of previous data for strains that do not exhibit hyperphagia. NPY mRNA was widely distributed in the broiler brain, and highly expressed in the hippocampus, nucleus commissurae pallii, infundibular hypothalamic nucleus, nucleus pretectalis pars ventralis and neurons around the nucleus rotundus. Moderately labeled neurons were found in the lateral septal organ, nucleus periventricularis hypothalamus and nucleus paraventricularis magnocellularis. The pallium exhibited only sparse labeling. Generally, the distribution of cell groups expressing NPY mRNA was consistent with those regions exhibiting NPY immunoreactivity, and also matches the distribution of receptor binding sites reported in the literature for the chicken brain. This suggests that NPY may be involved in functions controlled by these regions. The observation of NPY gene expression in brain regions involved in appetite regulation is consistent with the recognized importance of NPY in FI regulation in a variety of species, and with the chronic hyperphagia, characteristic of the broiler.

Effect of pulsatile or continuous administration of pituitary-derived chicken growth hormone (p-cGH) on lipid metabolism in broiler pullets.

1. The effects of pulsatile and continuous intravenous administration of exogenous, pituitary-derived chicken growth hormone (p-cGH) on lipid metabolism and endocrine/metabolite levels of broiler-strain pullets were studied. 2. Eight-week-old pullets were administered p-cGH or vehicle over a 10 min period every 90 min for 7 days. 3. Pullets were also administered the same daily amount (123 micrograms/kg of body weight/day) continuously for 7 days. 4. Feed intake, body weight gain, in vitro lipogenesis and hepatic enzyme activities were determined with certain hormones identified with the control of growth. 5. Pulsatile p-cGH administration for 7 days lacked effect on weight gain, feed efficiency, muscle or bone development. 6. Abdominal fat pad size was decreased (P less than 0.05) by pulsatile but not continuous administration of p-cGH. Pulsatile p-cGH administration also decreased (P less than 0.05) in vitro lipogenesis. Liver malic enzyme and isocitrate dehydrogenase activities were increased (P less than 0.05) by pulsatile but not continuous administration of p-cGH. In contrast, glutamic oxaloacetic transaminase activity was increased by a continuous infusion of p-cGH. 7. Plasma concentrations of T4 corticosterone and triglycerides were decreased (P less than 0.05) by a pulsatile but not a constant infusion of p-cGH. 8. Plasma T3 and GH were increased (P less than 0.05) by pulsatile p-cGH compared to both a continuous infusion of p-cGH and the saline controls. 9. This study is the first to prove that in the broiler chicken, the pattern of exogenous p-cGH administration is a factor influencing in vitro responses to the hormone.

Preparation and culture of dispersed avian pituitary cells, and age-related changes in donor pituitary weight and growth hormone content☆

Techniques were perfected for the enzymatic dissociation of chicken pituitary glands and a number of factors evaluated for their effects upon growth hormone (GH) production by dispersed chicken pituitary cells in culture. Age-related changes in donor pituitary weight and GH content were also determined. A procedure involving digestion of minced glands with a solution of 0.1% trypsin in S-MEM tissue culture medium (0.1% BSA) for 1 hr at 37 degrees under an atmosphere of 5% CO2-95% air yielded greater than 2.0 X 10(6) cells per gland with 80-90% viability. Five tissue culture media (D-MEM, alpha-MEM, RPMI 1640, Med-199, Earles salts), two serum sources (calf serum (CS), horse serum (HS), and two levels of serum (5, 20%) were tested for their ability to support GH synthesis over 4 days in culture. Additionally, two culture regimes (continuous culture vs daily media changes) were evaluated for their effects on GH production. alpha-MEM resulted in the numerically highest net GH synthesis (over starting cell content), although not statistically different from RPMI 1640 or Earles salts. Neither serum type nor percentage was significant; therefore the lower serum percentage (5) was adopted for future studies. Culture regime significantly altered the proportion of secreted vs stored hormone harvested at the end of the culture period. Changing media daily resulted in a 40% reduction in final cell GH content compared to continuous culture, whereas total cumulative media GH was approximately 39% greater (P less than 0.01). Pituitary weight increased with age until approximately 9 weeks, whereas GH content plateaued earlier, at 5 weeks of age.(ABSTRACT TRUNCATED AT 250 WORDS)

Unique Profile of Chicken Adiponectin, a Predominantly Heavy Molecular Weight Multimer, and Relationship to Visceral Adiposity

Adiponectin, a 30-kDa adipokine hormone, circulates as heavy, medium, and light molecular weight isoforms in mammals. Plasma heavy molecular weight (HMW) adiponectin isoform levels are inversely correlated with the incidence of type 2 diabetes in humans. The objectives of the present study were to characterize adiponectin protein and quantify plasma adiponectin levels in chickens, which are naturally hyperglycemic relative to mammals. Using gel filtration column chromatography and Western blot analysis under nonreducing and non-heat-denaturing native conditions, adiponectin in chicken plasma, and adipose tissue is predominantly a multimeric HMW isoform that is larger than 669 kDa mass. Under reducing conditions and heating to 70-100 C, however, a majority of the multimeric adiponectin in chicken plasma and adipose tissue was reduced to oligomeric and/or monomeric forms. Immunoprecipitation and elution under neutral pH preserved the HMW adiponectin multimer, whereas brief exposure to acidic pH led to dissociation of HMW multimer into multiple oligomers. Mass spectrometric analysis of chicken adiponectin revealed the presence of hydroxyproline and differential glycosylation of hydroxylysine residues in the collagenous domain. An enzyme immunoassay was developed and validated for quantifying plasma adiponectin in chickens. Plasma adiponectin levels were found to be significantly lower in 8- compared with 4-wk-old male chickens and inversely related to abdominal fat pad mass. Collectively, our results provide novel evidence that adiponectin in chicken plasma and tissues is predominantly a HMW multimer, suggesting the presence of unique multimerization and stabilization mechanisms in the chicken that favors preponderance of HMW adiponectin over other oligomers.

In vitro lipid metabolism, growth and metabolic hormone concentrations in hyperthyroid chickens

Indian River male broiler chickens growing from 7 to 28 d of age were fed on diets containing energy:protein values varying from 43 to 106 MJ/kg protein and containing 0 or 1 mg triiodothyronine (T3)/kg diet to study effects on growth, metabolic hormone concentrations and in vitro lipogenesis. In vitro lipid synthesis was determined in liver explants in the presence and absence of ouabain (Na+, K(+)-transporting ATPase (EC 3.6.1.37) inhibitor) to estimate the role of enzyme activity in explants synthesizing lipid. Growth and feed consumption increased (P < 0.01) when the energy:protein value decreased from 106 to 71 MJ/kg protein; however, both variables decreased as the value was further decreased from 53 to 43 MJ/kg protein. Triiodothyronine depressed (P < 0.01) growth, but not food intake. Large energy:protein diets (> 53 MJ/kg protein) and dietary T3 lowered (P < 0.01) plasma growth hormone. Large energy:protein diets (> 53 MJ/kg protein) increased (P < 0.01) lipogenesis, plasma growth hormone (GH) and decreased plasma insulin-like growth factor 1 (IGF-1). Also, T3 decreased plasma GH, IGF-1 in vitro lipogenesis. Ouabain inhibited a greater proportion of in vitro lipogenesis in those explants synthesizing fat at a high rate. Both dietary T3 and in vitro ouabain decrease lipogenesis, but, when combined, the effects are not cumulative.

Circulating IGF-I in plasma of growing male and female turkeys of medium and heavy weight lines

Plasma concentrations of insulin-like growth factor-I (IGF-I) were determined in male and female turkeys from a medium weight (RBC2) and a related heavy weight line (F) from 1 to 28 wks of age. At hatch, the concentrations of IGF-I were relatively low and not different between lines or sexes. During the neonatal period (1 to 7 wks), the concentrations of IGF-I increased and were higher in the faster growing F line and in males. During the juvenile period (8 to 15 wks) the concentrations of IGF-I were higher in males but not different between lines. During the preadolescent period (16 to 21 wks), the concentrations of IGF-I were higher in males but was not different between lines in males while the females of the RBC2 line had higher concentrations than females of the F line. During the adolescent period (22 to 28 wks) the concentrations of IGF-I were higher in males but was not different between lines in males while the females of the RBC2 line had higher concentrations than females of the F line. A phenotypic correlation (+.25) between plasma IGF-I and growth rate was present after statistical absorption of model effects during the neonatal period but not at the later ages. We conclude that IGF-I concentration was positively correlated with growth rate during the neonatal period, but that this relationship changed during the preadolescent and adolescent periods so that IGF-I concentrations were not related to growth rate in males but were negatively related to growth rate in females.

Expression of adiponectin and its receptors in avian species.

Adipose tissue is a dynamic endocrine organ secreting a variety of hormones that affect physiological functions within the central nervous system, cardiovascular system, reproductive, and immune systems. The endocrine role of avian adipose tissue remains enigmatic as many of the classical hormones found in mammalian adipose tissue have not been found in avians. This mini-review summarizes our current knowledge on avian adiponectin, one of the most abundant adipose tissue hormones, and its receptors. We cloned the genes encoding chicken adiponectin and its receptors, AdipoR1 and AdipoR2. Using anti-chicken adiponectin antibody, we found that chicken adipose tissue and plasma predominantly contain a unique polymer of adiponectin with a mass greater than 669kDa, unlike mammalian adiponectin which is found as three distinct oligomers. Mass spectrometric analyses of chicken adiponectin revealed certain post-translational modifications that are likely to favor the unique multimerization of adiponectin in chickens. Unlike adiponectin, the nucleotide sequences of chicken AdipoR1- and AdipoR2 cDNA are highly similar to that of mammalian adiponectin receptors. Both adiponectin and adiponectin receptors are widely expressed in several tissues in the chicken. Herein, we review the unique biochemistry of adiponectin as well as expression of adiponectin and its receptors in the chicken. Future studies should focus on elucidating the role of adiponectin, AdipoR1, and AdipoR2 on metabolism, steroidogenesis, and adipose tissue remodeling during growth and reproduction in birds.