Recombinant porcine IFN-gamma potentiates the secondary IgG and IgA responses to an inactivated suid herpesvirus-1 vaccine and reduces postchallenge weight loss and fever in pigs.

The effect of recombinant porcine interferon-gamma (IFN-gamma) on the immunogenicity in vivo of inactivated suid herpesvirus-1 (SHV-1, Phylaxia strain) was studied applying two successive i.m. immunizations. The animals were injected with inactivated virus alone or inactivated virus supplemented with 10(4) or 10(6) U IFN-gamma. After the first immunization, none of the animals responded with measurable virus-neutralizing antibody (VNAb), virus-specific IgG or IgA. Following a second immunization 4 weeks later, a significantly increased VNAb response was noted in animals that had received vaccine doses containing 10(4) U IFN-gamma (p < 0.05). These animals also had significantly augmented serum levels of IgG (p < 0.01) and IgA (p < 0.05). Inclusion of 10(6) U IFN-gamma in the vaccine preparation did not affect the antibody response. In one experiment, the pigs were challenged oronasally with 10(5) TCID50 of the 75V19 strain of SHV-1, 7 weeks after administration of the second vaccine dose. Those that had received 10(4) U IFN-gamma in the vaccination developed less fever during the postchallenge period (p < 0.004). In all challenged pigs, growth performance was compromised during the first week after challenge. However, the only animals retaining an average net increase in body mass were those covaccinated with 10(4) U IFN-gamma (p < 0.05). Nasal excretion of virus was not significantly different between groups that had been vaccinated with or without IFN-gamma. Multiple linear regression analysis of variables from individual vaccinated animals revealed the VNAb response to be correlated with serum IgG levels (p < 0.025) and with postchallenge growth performance (p < 0.0001) but not with serum IgA levels (p > 0.5). On the other hand, serum IgA appeared to be inversely correlated with early nasal virus excretion after challenge (p < 0.006). Taken together, our data suggest that addition of IFN-gamma to inactivated SHV-1 vaccine may be a useful tool for enhancement of both mucosal and systemic immune responses in pigs.

Myocardial beta-adrenergic receptor characteristics in T(3)-induced ascites and in broiler lines differing in ascites susceptibility.

The present study was designed to investigate the myocardial beta-adrenergic receptor characteristics in T3-induced ascites in two genetic lines of broilers, in order to look for possible involvement of myocardial beta-adrenergic receptors in the development of broiler ascites syndrome. Myocardial membrane fractions were prepared from 6 and 8 week old chickens fed a 1.5 parts/10(6) T(3) supplemented diet from day 1 in order to increase ascites incidence. Also, a similar assay was performed on myocardial cells of ascites sensitive and ascites resistant chickens at 5 weeks of age. The binding capacity and binding affinity of the myocardial beta-adrenergic receptor of the two genetic lines of birds did not differ significantly, but the tendency of beta-adrenergic receptor binding capacity and affinity constants in ascites-sensitive birds was slightly higher compared to ascites-resistant birds. In commercial broilers, although dietary T(3) significantly increased ascites mortality and the RV/TV ratio compared to control, it did not affect significantly beta-adrenergic receptor characteristics.

Evaluation of parenteral vaccination methods with glycoproteins against Aujeszky's disease in pigs.

A comparative evaluation of vaccination methods with glycoproteins for the induction of immune responses and protection of the pig against Aujeszky's disease virus (ADV) was performed. Different vaccination routes (intradermal (i.d.) versus intramuscular (i.m.)), inoculation sites (the neck versus the back) and number of inoculation points (2 versus 6) per site were compared. Body weight (BW) changes and viral excretion after challenge were compared with virus-neutralizing titers, antigen-specific IgG and IgA responses in serum and virus-specific lymphoproliferative responses in peripheral blood during the immunisation period. According to BW changes better protection was obtained with six-point than two-point i.d. injections. i.d. vaccination in the back at six points gave similar results as i.m. vaccination in the neck but appeared inferior in the reduction of virus excretion. Regarding the immunological parameters, the virus-specific IgA response in serum gave the best indication for protection. It can be concluded that according to BW changes, six-point i.d. immunisation in the back and i.m. immunisation in the neck provided the best protection and that six-point i.d. injections resulted in a better vaccination than two-point i.d. injections.

Pulsatility of plasma growth hormone and hepatic growth hormone receptor characteristics of broiler chickens divergently selected for abdominal fat content.

1. Plasma growth hormone (GH) pulsatility and hepatic GH receptor characteristics were compared in experimental lines of meat-type chickens selected for high (HF) or low (LF) abdominal fat content. 2. Mean GH concentration, baseline and amplitude of pulses were slightly, but not significantly, greater in LF chickens. Length and frequency of pulses were similar. 3. LF chickens exhibited higher plasma triiodothyronine (T3) concentrations. This difference between genotypes disappeared when the diet was supplemented with 1 mg/kg T3. 4. Specific binding of GH to liver membranes was higher for the fat line but was depressed by T3 supplementation to the same level in both lines. No difference was observed between lines for affinity constants. 5. It is concluded that direct selection for leanness has a less pronounced, if any, effect on GH pulsatility as compared with selection for food conversion efficiency; therefore, different physiological mechanisms are triggered to achieve leanness.

Study of the hepatic growth hormone (GH) receptor at different ages in chickens selected for a good feed conversion (FC) and a fast weight gain (GL).

The influence of genetic selection for improved feed conversion (FC) and fast growth (GL) in broiler chickens, on the hepatic growth hormone receptor was investigated as a function of age. Selection for improved feed conversion resulted in lean chickens, whereas selection for fast growth resulted in fat chickens. Growth hormone receptor characteristics were determined in liver microsomal fractions and plasma GH concentrations were measured by radioimmunoassay. Embryos from the FC line showed higher specific GH binding than GL embryos at day 16 of embryonic development only (P < 0.05). On day 18 of embryonic development, the FC line had slightly more GH receptors than the GL line (P < 0.05), whereas simultaneous plasma GH concentrations were greater in the GL line. The effect of selection on hepatic growth hormone binding was greatest in 4 week old growing chicks at which age the GL line showed a 2- to 3-fold higher % of specific binding than the FC line (P < 0.001). The difference at this stage is probably due to down regulation of the receptor by the significantly higher GH concentrations in the FC line. The adult GL chickens also showed higher specific binding than FC, but the difference was less pronounced than in the growing stage (P < 0.05). This was due to a higher number of GH receptors, while receptor affinity was unchanged. Because no line difference in plasma GH concentrations was found in adult hens, other unknown mechanisms probably play a role in determining differences in GH receptor binding between these selected lines at older ages.

Endogenous growth hormone controls high plasma levels of 3,3',5-triiodothyronine (T3) in growing chickens by decreasing the T3-degrading type III deiodinase activity.

The influence of endogenous GH levels on peripheral monodeiodination activity has been investigated in growing chickens at the age of 4 weeks, when they normally show no T3 increase after GH injection. Injection of anti-GH serum decreased plasma T3 and increased plasma T4. Three d and 1 week after hypophysectomy, plasma T3 was also markedly decreased, while T4 was only slightly affected, hepatic 5'D-I activity showed a transient decrease, but 5D-III activity was highly increased, as were the number of hepatic GH receptor sites. Injection of GH in hypophysectomized chickens decreased 5D-III activity and increased plasma T3. GH receptor-deficient dwarf chickens had decreased plasma T3 and increased plasma T4 and hepatic 5'D-I and 5D-III activities compared to their normally-growing siblings. GH administration could only affect T3 and 5D-III in the non-dwarf siblings, which showed higher basal 5D-III activity compared to the non-responsive age-matched chickens of the Hisex strain used in the other experiments. It can be concluded that endogenous GH is an important factor in the control of plasma T3 levels in growing chickens due to its influence on the activity of the T3-degrading type III deiodinase. The effectiveness of exogenous GH administration to acutely increase plasma T3 probably depends on the balance between the injected dose and the endogenous GH concentration, the hepatic GH receptor availability and the hepatic type III deiodinase level.

Growth hormone acutely decreases type III iodothyronine deiodinase in chicken liver.

Growth hormone (GH) increases plasma T3 and decreases plasma T4 in 18-day old chicken embryos, in newly hatched chicks and in adult chickens within 2 h after injection. The in vivo increase in T3 can be linked to an increased in vitro T3 recovery from liver homogenates incubated with T4. Specific type I and type III deiodinase tests (5'D-I and 5D-III), however, show that GH has no effect at all on the amount of hepatic type I enzyme (catalyzing T4 deiodination to T3) but acutely decreases the amount of type III enzyme (catalyzing T3 deiodination). This suggests that the GH-induced increase in plasma T3 is not due to an increased T3 production, but is the result of a decreased T3 breakdown. The lack of a stimulatory effect of GH injection in 3-day-old fed chicks might be the combined result of a low hepatic type III enzyme level and a low GH receptor availability at that stage.

Food intake after hatching inhibits the growth hormone induced stimulation of the thyroxine to triiodothyronine conversion in the chicken.

The effect of a single injection of 10 micrograms chicken GH on circulating thyroid hormones as well as in vitro liver 5'-monodeiodination (5'-D) activity was studied in posthatch chicks submitted to different feeding conditions. One group was normally fed after hatching, a second group was only fed after three days and a third group was food deprived after 2 days of feeding. Combination of all results indicates that the start of food intake abolishes the stimulatory effect of a GH injection on circulating T3 and liver 5'-D activity. Food deprivation after a period of food intake restores the GH effect on plasma T3 but not on liver 5'-D.

Effect of hypophysectomy and acute administration of growth hormone (GH) on GH-receptor binding in chick liver membranes.

The effects of hypophysectomy on GH binding to liver membranes of young chicks were studied 3 days and 1 week after surgery. Specific binding of 125I-labelled chicken GH (cGH) to MgCl2-treated liver microsomal fractions of hypophysectomized animals was two- to fivefold greater than to those of sham-operated or control (non-operated) birds. This effect was due to a rise in binding capacity rather than a change in binding affinity of the GH receptor. Two daily injections of cGH (20 micrograms/animal) returned the number of hepatic GH receptors from hypophysectomized chicks to the level of the sham-operated ones. Administration of GH to the latter group did not cause a significant lowering of specific binding or number of receptors. No positive correlation between GH binding and plasma concentrations of insulin-like growth factor-I (IGF-I) was observed; although GH binding increased, IGF-I levels were lower for the hypophysectomized group. Since the number of hepatic GH receptors and the plasma GH levels were inversely correlated, it was concluded that the GH receptors in the liver of the chicken can be down-regulated by GH. This possibly explains why GH binding is low in posthatch and young chicks, because circulating GH concentrations are high during this period.

Differences in hepatic growth hormone receptor binding during development of normal and dwarf chickens.

The aim of this study was to compare the growth hormone (GH) receptor in liver microsomal fractions of normal chickens (Dw) and chickens carrying the dwarf gene (dw). Specific binding of GH to its hepatic receptor was significantly higher for Dw embryos from d 14 till d 20 of incubation than for dw embryos. The difference in binding was due to a decreased binding capacity but not affinity in the livers of the dwarf embryos. The same binding pattern was found in livers of adult chickens: lower binding was again caused by a lower number of GH receptors and at this stage the difference was even clearer than during embryonic development. Binding studies on livers of growing chicks demonstrated that binding was low for both genotypes, but a small though significant difference between them remained. The cause of this decrease in number of GH receptors in dwarf birds has yet to be determined but may be due to the primary action of the dwarf gene.

Thyrotropin-releasing hormone (TRH) is not thyrotropic but somatotropic in fed and starved adult chickens.

Adult fed and starved Warren chickens, 2 yr of age, and approaching the end of the second laying year, were injected iv with 1 of the following products: 10 micrograms of thyrotropin releasing hormone (TRH); 100 micrograms of bovine thyrotropin (bTSH); 100 micrograms of ovine growth hormone (oGH); saline. The influence on plasma concentrations of thyroxine (T4), triiodothyronine (T3) or chicken GH (cGH) were followed. Prior to injection, it was clear from the control values that starvation for 3 d decreased plasma levels of T3 and increased cGH, whereas 7 d of fasting increased T4 and cGH. The plasma levels of cGH were elevated greater than 10-fold at 15 min following the TRH challenge in food-deprived chickens compared to a less than 4-fold increase in normal fed hens. This increase was followed by a rise in T3 after 1 h, which was also more pronounced in the starved animals, whereas T4 decreased or remained unaffected. Increases in T4 can, however, be obtained with 100 micrograms TSH in normal fed (2-fold) or starved animals (greater than 3-fold). Following injection of 100 micrograms oGH, a significant increase in T3 levels was observed which in fed animals was already present at 30 min, but the higher levels persisted for 1 and 2 h in fed and starved hens. At the same time, a decrease in T4 was observed in both groups of GH-treated chickens. It is concluded that TRH at the dose used is not thyrotropic but has a somatotropic effect and is responsible for the peripheral conversion of T4 into T3.

A decreased capacity of hepatic growth hormone (GH) receptors and failure of thyrotrophin-releasing hormone to stimulate the peripheral conversion of thyroxine into triiodothyronine in sex-linked dwarf broiler hens.

The effect of two different doses of thyrotrophic releasing hormone (TRH) upon the plasma levels of growth (GH) and thyroid hormones in both sex-linked dwarf (dw) and normal (Dw) broiler hens was determined. In normal hens, 1.5 and 24 microg TRH/kg increased the GH plasma concentrations after 15 min. Plasma concentrations of T3 increased significantly 1 h after TRH injection, whereas T4 concentration decreased after 2 following injection of 24 microg/kg TRH. In dwarf hens both doses of TRH increased the plasma concentrations of GH and the GH response lasted longer. However, TRH was ineffective in raising T3 and T4 levels. Saline-injected dwarf birds showed no differences in plasma T4 and T3 levels in comparison with normal hens. A smaller number of hepatic cGH receptors was found in dwarf hens, whereas the affinity of the hepatic GH receptor was not influenced by the genotype. It is concluded that the sex-linked dwarf broiler hen is unable to respond to a TRH-induced GH stimulus probably because of a deficiency in hepatic GH receptors resulting in a failure to stimulate the T4 to T3 converting activity.

Hypothalamic hormones that release growth hormone stimulate hepatic 5'-monodeiodination activity in the chick embryo.

Plasma GH, tri-iodothyronine (T3), thyroxine (T4) and liver 5'-monodeiodination (5'-D) activity were measured in 18-day-old chick embryos injected with thyrotrophin-releasing hormone (TRH) and human pancreatic growth hormone releasing factor (hpGRF). Injections of 0.1 and 1 microgram TRH and 1.5 micrograms hpGRF increased the concentration of plasma GH while injection of 15 micrograms hpGRF had no effect. Concentrations of plasma T3 were raised after injection of TRH or hpGRF. Injections of TRH but not of hpGRF raised the concentration of plasma T4. The increases in concentration of plasma T3 after injection of TRH or hpGRF were parallelled by increases in liver 5'-D activity. An injection of 0.25 micrograms T4 significantly raised the concentration of T4 in plasma but had no effect on plasma T3 or liver 5'-D activity. It is concluded that the release of chicken GH by TRH or hpGRF is responsible for the observed increase in plasma concentration of T3 and liver 5'-D activity.