The hormones of the hypothalamic-pituitary-thyroid axis and their receptors in the immune system

The role of protein restriction and interaction with antibiotics in the regulation of compensatory growth in pigs: growth performance, serum hormone concentrations, and messenger RNA levels in component tissues of the endocrine growth axis

The present study investigated the effects of protein restriction and antibiotics on the hypothalamus-pituitary-liver growth axis during the compensatory growth of growing and finishing pigs. Growth performance, serum hormones, and messenger RNA (mRNA) levels of hormones and their receptors in growth axis tissues were recorded for analyses. A total of 64 piglets (large white × Landrace × Duroc cross) with an initial weight of 10.07 ± 0.14 kg were randomly divided into 4 treatment groups of 16 piglets per group. The dietary treatments consisted of 2 protein levels (14% and 20%) and 2 antibiotic levels (no antibiotics and 20 mg/kg colistin sulfate with 50 mg/kg kitasamycin) in a 2 × 2 factorial arrangement. The study was performed over 30 d for the first stage (S1, restriction phase) and 74 d for the second stage (S2, realimentation phase). The 4 treatment diets were maintained throughout the duration in the restriction phase. The 4 groups were fed the same diet in the realimentation phase. The trial period totaled 104 d. Protein restriction decreased BW, average daily food intake, and ADG in weaning pigs (P < 0.01) and induced compensatory growth after feeding a normal diet during the growth of finishing pigs. Average daily gain increased during the last phase of compensatory growth (P < 0.01). Protein restriction increased serum GH and leptin (LEP) and the mRNA levels of liver IGF-1 receptor (IGF-1-R; P < 0.01) but decreased serum IGF-1 (P < 0.01) and the mRNA levels of liver GH receptor (GH-R; P < 0.01) and IGF-1 (P < 0.05) in weaning piglets. Serum GH was increased, but serum IGF-1 was decreased during the realimentation phase (P < 0.05). Antibiotics increased the mRNA levels of GHRH (P < 0.05) and decreased somatostatin (P < 0.01) in the hypothalamus of weaning pigs. Protein restriction and antibiotics had no interactions across the entire trial. In conclusion, the slowing of growth caused by early protein restriction may be compensated for in the later stages of pig raising, and the mechanism of compensation is related to the regulation of GH, IGF-1, GH-R, and IGF-1-R.

Neuroendocrine-immune interactions in the neonate

Cytokine responses to lipopolysaccharides in neuroendocrine tissues are age- and tissue-dependent in neonatal pigs. Developmental differences in serum and tissue-specific responses are not necessarily equivalent. Lower levels of cytokine gene expression in neuroendocrine tissues of early neonates potentially could influence neuroendocrine and immune responses to infection. The limited information on neuroendocrine-immune responses and interactions in neonatal farm animals presents significant challenges, as well as opportunities for new discoveries and improvements of livestock production.

Lactotroph and somatotroph function in piglets reared in a constant hot environment

The present study evaluated the effect of rearing in a constant hot (32 degrees C) or cool (21 degrees C) thermal environment (TE) on lactotroph and somatotroph secretory activity in 5-wk-old barrows (castrate males) and gilts (female). Pituitary cells from seven gilts and seven barrows from each TE were cultured at a density of 250,000 cells/1 ml well and exposed to vehicle (culture medium); .1, 1, 10, or 100 nM thyrotropin-releasing hormone (TRH); or .1, 1, or 10 nM growth hormone-releasing hormone (GHRH). Post-receptor cellular stimulation was induced pharmacologically with 2 mM 8-Br-cAMP (cAMP); 100 nM phorbol myristate acetate (PMA); or 59 mM KCl. Prolactin secretion in culture was stimulated by TRH and by pharmacological compounds (p < .0001). In vitro PRL secretion was increased approximately two-fold in the hot environment (p < .02). Similarly, cellular PRL content in the hot TE was twice that in the cool TE (p < .01). The in vitro secretion of growth hormone (GH) was increased by GHRH and by pharmacological compounds (p < .0001), but was unaffected by TE (p > .5). No effects of sex (p > .3) or sex x TE interactions (p > .2) were detected in any endpoint. The results of this study demonstrate that lactotroph, but not somatotroph, secretory activity is enhanced by a constant hot TE in early postweaning pigs. This increase in secretory activity does not appear to be dependent on receptor-mediated cellular activation, but may reflect enhanced levels of cellular PRL available for release.

Somatostatin (SRIF) stimulates the release of interleukin-6 (IL-6) from human peripheral blood monocytes (PBM) in vitro

Recent evidence has revealed that various neuropeptides appear to have distinct roles as immunomodulators. The aim of this study was to evaluate the role of hypothalamic neuropeptides (thyreoliberin [TRH], somatostatin [SRIF], and gonadoliberin [LH-RH]) on the secretion of interleukin-1 beta (IL-1 beta) and interleukin-6 (IL-6) from lipopolysaccharide (LPS) activated human peripheral blood monocytes (PM) cultured in vitro. LPS in concentration 1.5 micrograms/ml stimulated PBM to release IL-1 beta or IL-6 into the supernatants. SRIF in concentrations from 10(-8)M to 10(-10)M (but neither RH nor LH-RH in the same concentrations) potentiated the release of IL-6 from PBM. None of the tested neuropeptides stimulated the release of IL-1 beta from LPS activated human monocytes. These data indicate that SRIF in physiological or pharmacological concentrations which activate the release of IL-6 from PBM may be one of the regulators of immune response in humans.

Visible light induced changes in the immune response through an eye-brain mechanism (photoneuroimmunology)

The immune system is susceptible to a variety of stresses. Recent work in neuroimmunology has begun to define how mood alteration, stress, the seasons, and daily rhythms can have a profound effect on immune response through hormonal modifications. Central to these factors may be light through an eye-brain hormonal modulation. In adult primates, only visible light (400-700 nm) is received by the retina. This photic energy is then transduced and delivered to the visual cortex and by an alternative pathway to the suprachiasmatic nucleus (SCN). The SCN is a part of the hypothalamic region in the brain believed to direct circadian rhythm. Visible light exposure also modulates the pituitary and pineal gland which leads to neuroendocrine changes. Melatonin, norepinephrine and acetylcholine decrease with light activation, while cortisol, serotonin, gaba and dopamine levels increase. The synthesis of vasoactive intestinal polypeptide (VIP), gastrin releasing peptide (GRP) and neuropeptide Y (NPY) in rat SCN has been shown to be modified by light. These induced neuroendocrine changes can lead to alterations in mood and circadian rhythm. All of these neuroendocrine changes can lead to immune modulation. An alternative pathway for immune modulation by light is through the skin. Visible light (400-700 nm) can penetrate epidermal and dermal layers of the skin and may directly interact with circulating lymphocytes to modulate immune function. However, even in the presence of phototoxic agents such as eosin and rose bengal, visible light did not produce suppression of contact hypersensitivity with suppresser cells. In contrast to visible light, in vivo exposure to UV-B (280-320 nm) and UV-A (320-400 nm) radiation can only alter normal human immune function by a skin mediated response. Each UV subgroup (B, A) induces an immunosuppressive response but by differing mechanisms involving the regulation of differing interleukins and growth factors. Some effects observed in humans are: inhibition of allergic contact dermatitis; inhibition of delayed hypersensitivity to an injected antigen; prolongation of skin-graft survival and induction of a tumor-susceptible state. The following article will review much of the progress in this field and explore possible areas of future research.

Increased interleukin-2 levels during standard TRH test in man

Interleukin-2 (IL-2) is a pluripotential cytokine that, besides its role in the regulation of immunocompetent cells function, also stimulates hormone secretion. On the other hand, several factors, including cytokines (interleukin-1, IL-1; interleukin-6, IL-6) and pituitary hormones (thyrotropin, TSH; prolactin, PRL), exert stimulatory effects on T-cell connected IL-2 production. In order to evaluate the role of both pituitary hormones in the activation of the immune system, the following two standard diagnostic tests were performed: TRH test (0.2 mg) in 8 healthy human subjects (4F/4M) aged 18-50 years, and oral metoclopramide (MCP) test (10 mg) in 8 females with galactorrhea and regular menstruation aged 18-52 years. The mobilization (peak response) of PRL, TSH, triiodothyronine (T3), thyroxin (T4), IL-1 beta, IL-2, IL-6 in TRH test, and PRL, IL-1 beta, IL-2, IL-6 for MCP test were evaluated. The responses of TSH (2.0 +/- 0.3 vs 12.3 +/- 2.2 microlU/ml, p < 0.01), PRL (15.3 +/- 2.3 vs 46.4 +/- 8.8 ng/ml, p < 0.01), T3 (178.0 +/- 16.4 vs 248.7 +/- 21.1 ng/dl, p < 0.001), T4 (7.9 +/- 0.4 vs 9.6 +/- 0.5 micrograms/dl, p < 0.001), and IL-2 (45.6 +/- 7.8 vs 79.9 +/- 16.4 fmol/ml, p < 0.05) in TRH test were noted. The peak response of PRL (16.3 +2- 2.6 vs 107.7 +/- 22.4 ng/ml, p < 0.01) in MCP test was also observed, but without any changes in interleukin concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Somatotroph, lactotroph and thyrotroph function in three-week-old gilts reared in a hot or cool environment

The influence of the thermal environment on the ability of the pituitary gland to secrete growth hormone (GH), prolactin (PRL), and thyroid-stimulating hormone (TSH) was examined in gilts reared under hot (H: 27-32 degrees C, 50-90% RH, n = 6) or cool (C: 20 degrees C, 50% RH, n = 6) conditions. Piglets were sacrificed at 3 wks of age. Pituitary cells from each animal were cultured and exposed to vehicle (culture medium); 1, 1, and 10 nM thyrotropin-releasing hormone (TRH); .1, 1, and 10 nM growth hormone-releasing hormone (GHRH); 59 mM KCl; 2 mM 8-Br-cAMP; and 100 nM phorbol myristate acetate. Rearing in the H, compared to the C, environment increased plasma PRL concentrations (p < .001), in vitro PRL secretion subsequent to all secretagogue treatments (p < .001), and cellular PRL content (p < .001). The stimulated release of TSH in culture was reduced (p < .001), but cellular TSH content was increased (p < .05) by exposure to the H environment. The total amount of TSH in culture (secreted + cellular) was not affected by thermal environment. The release of GH in vitro, cellular GH content, total GH in culture, and plasma GH concentrations were similar between H and C groups. The only dose-response curves that differed in slope between thermal groups were those produced by the TSH response to TRH (p < .001). The results of this study suggest that chronic exposure to a hot environment can 1) enhance PRL secretion by a mechanism which affects the quantity of releasable PRL rather than lactotroph sensitivity to secretagogues and 2) reduce TSH secretion by inhibiting thyrotroph secretory response to stimulation.