Somatolactogens, somatomedins, and immunity

Perspectives on ruminant nutrition and metabolism. II. Metabolism in ruminant tissues

The discovery of the dominance of short-chain fatty acids as energy sources in the 1940s and 1950s, as discussed in part I of this review (Annison & Bryden, 1998) led to uncertainties concerning the interrelationships of glucose and acetate in ruminant metabolism. These were resolved in the following decade largely by use of14C-labelled substrates. Although only small amounts of glucose are absorbed in most dietary situations, glucose availability to ruminant tissues as measured by isotope dilution was shown to be substantial, indicating that gluconeogenesis is a major metabolic activity in both fed and fasted states. Studies with14C-labelled glucose and acetate revealed that in contrast to non-ruminants, acetate and not glucose is the major precursor of long-chain fatty acids in ruminant tissues. Interest in the measurement of energy metabolism in livestock grew rapidly from the 1950s. Most laboratories adopted indirect calorimetry and precise measurements of the energy expenditure of ruminants contributed to the development of new feeding systems. More recently, alternative approaches to the measurement of energy expenditure have included the use of NMR spectroscopy, isotope dilution and the application of the Fick principle to measure O2consumption in the whole animal and in defined tissues. The refinement of the classical arterio-venous difference procedure in the study of mammary gland metabolism in the 1960s, particularly when combined with isotope dilution, encouraged the use of these methods to generate quantitative data on the metabolism of a range of defined tissues. The recent introduction of new methods for the continuous monitoring of both blood flow and blood O2content has greatly increased the precision and scope of arterio-venous difference measurements. The impact of data produced by these and other quantitative procedures on current knowledge of the metabolism of glucose, short-chain fatty acids and lipids, and on N metabolism, is outlined. The role of the portal-drained viscera and liver in N metabolism is discussed in relation to data obtained by the use of multi-catheterized animals. Protein turnover, and the impact of stress (physical, social and disease related) on protein metabolism have been reviewed. The growth of knowledge of mammary gland metabolism and milk synthesis since the first quantitative studies in the 1960s has been charted. Recent findings on the regulation of amino acid uptake and utilization by the mammary gland, and on the control of milk secretion, are of particular interest and importance.

Pain, psychological variables, sleep quality, and natural killer cell activity in midlife women with and without fibromyalgia

In women with fibromyalgia (FM), central nervous system (CNS) dysfunction in pain, mood, and sleep processes could be associated with changes in immune system indicators. The primary purpose of this study was to compare pain, psychological variables, subjective and objective sleep quality, lymphocyte phenotypes and activation markers, and natural killer activity (NKA) in midlife women with and without FM. A secondary purpose was to explore relationships among these variables in a step-wise regression. Subjects had pain pressure tender points assessed, completed a psychiatric interview and questionnaires (Beck Depression Inventory, SCL-90, Profile of Mood States, subjective sleep), and underwent polysomnograhic assessment for two consecutive nights. Lymphocyte phenotypes, activation markers, and NKA were assessed from blood drawn the morning after sleep laboratory night 2. Compared to controls, women with FM had lower pain thresholds, more psychological distress, higher depression scores, and reduced subjective and objective sleep quality. They also had fewer NK cells (p <.009) and more NK cells that expressed the IL-2 receptor (p <.04), but these differences were not statistically significant after correction for multiple comparisons. NKA was not statistically significantly lower in the women with FM compared to controls. In a multiple regression of age, tender point threshold, depression, psychological distress, and sleep efficiency, only the effect of group was significant (F = 5.479, p <.03) on NKA. In conclusion, we found little evidence to support the hypothesis that pain, mood, and sleep symptoms are associated with changes in the enumeration of peripheral lymphocytes or function in FM.

Effects of prolactin administered to a perfused area of the skin of Angora goats

It is suspected that prolactin may affect mohair growth; therefore, effects of infusing prolactin on mohair growth were investigated using a skin perfusion technique. Seven Angora wethers (average body weight, 30 +/- 3 kg) were implanted bilaterally with silicon catheters into the superficial branches of the deep circumflex iliac artery and vein. For the first 14 d of the experiment, animals were infused (2.4 mL/h) with prolactin (one side) or control (other side) into the deep circumflex iliac arteries. The infusion rate of prolactin was 2.21 mg/d and was calculated to triple prolactin blood concentration in the perfused region. The area of skin supplied by the deep circumflex iliac artery was approximately 240 cm2. Two weeks after the cessation of infusions, 100-cm2 areas within the perfused regions were shorn to determine mohair growth. Greasy and clean mohair production was decreased (P < 0.05) by prolactin compared with control (3.79 vs 4.62 and 3.02 vs 3.67 g/[100 cm2 x 28 d], respectively). Oxygen satura tion in blood hemoglobin from the deep circumflex iliac veins was greater (P < 0.02) on the side infused with prolactin than on the control side (75.1 vs 68.2%). Higher concentrations of methionine, lysine, valine, isoleucine, and leucine were observed in blood of the deep circumflex iliac vein on the side infused with prolactin vs that infused with control (P < 0.05). In conclusion, direct skin infusion with prolactin decreased mohair fiber synthesis by the skin and may have concomitantly lessened oxygen consumption. Thus, effects of increasing prolactin concentration approximately two-fold in the skin on mohair fiber growth may not be limited to simple competition for nutrients between skin and other tissues such as the mammary gland.

The production of nitric oxide in EL4 lymphoma cells overexpressing growth hormone

Growth hormone (GH) is produced by immunocompetent cells and has been implicated in the regulation of a multiplicity of functions in the immune system involved in growth and activation. However, the actions of endogenous or lymphocyte GH and its contribution to immune reactivity when compared with those of serum or exogenous GH are still unclear. In the present study, we overexpressed lymphocyte GH in EL4 lymphoma cells, which lack the GH receptor (GHR), to determine the role of endogenous GH in nitric oxide (NO) production and response to genotoxic stress. Western blot analysis demonstrated that the levels of GH increased approximately 40% in cells overexpressing GH (GHo) when compared with cells with vector alone. The results also show a substantial increase in NO production in cells overexpressing GH that could be blocked by N(G)-monomethyl-L-arginine (L-NMMA), an L-arginine analogue that competitively inhibits all three isoforms of nitric oxide synthase (NOS). No evidence was obtained to support an increase in peroxynitrite in cells overexpressing GH. Overexpression of GH increased NOS activity, inducible nitric oxide synthase (iNOS) promoter activity, and iNOS protein expression, whereas endothelial nitric oxide synthase and neuronal nitric oxide synthase protein levels were essentially unchanged. In addition, cells overexpressing GH showed increased arginine transport ability and intracellular arginase activity when compared with control cells. GH overexpression appeared to protect cells from the toxic effects of the DNA alkylating agent methyl methanesulfonate. This possibility was suggested by maintenance of the mitochondrial transmembrane potential in cells overexpressing GH when compared with control cells that could be blocked by L-NMMA. Taken together, the data support the notion that lymphocyte GH, independently of the GH receptor, may play a key role in the survival of lymphocytes exposed to stressful stimuli via the production of NO.

The beneficial effects of recombinant human insulin-like growth factor-I (IGF-I) on wound healing in severely wounded senescent mice

The effects of recombinant insulin-like growth factor I (rIGF-I) on wound healing were tested using senescent and young BDF-1 mice, aged 108 weeks and 10 weeks, respectively. After inflicting a full thickness dermal burn encompassing 15% of the body surface, a skin incision, 2 cm in length, was made in the back. A silicone tube containing a piece of polyvinyl sponge was then implanted into a subcutaneous pocket in the flank to collect body fluid. An osmotic pump was buried in the abdominal subcutaneous tissue for the continuous infusion of rIGF-I, the control being treated with the solvent of IGF-I, physiological saline, only. The administration of IGF-I produced favorable effects on wound healing in the senescent mice, shown by enhanced tensile strength and an elevated concentration in the hydroxyproline of the polyvinyl sponge content. The IGF-I-treated severely wounded senescent mice healed better than their counterparts and their skeletal muscles contained more glutamine. Furthermore, they showed more enhanced cutaneous hypersensitivity towards dinitrofluorobenzene than the controls, suggesting an enhanced grade of cellular immunity. There were no conspicuous differences between the two groups of young mice. These data may suggest the beneficial effects of rIGF-I on wound healing, especially in geriatric surgery.

Pituitary function in the acute phase response in domestic farm animals: cytokines, prostaglandins, and secretion of ACTH

Contained in this report is a review of available data on pituitary cytokines in domestic species of agricultural importance. The concept is advanced that the pituitary gland is essential to appropriate generation of host defense mechanisms and thus should be considered among other tissues contributing to innate immunity. The functions of these intrapituitary cytokines, principally IL-6, are discussed in the context of potential regulation of the pituitary-adrenal axis (ACTH secretion) via intrapituitary PGE2 generation during the acute-phase response to infectious/inflammatory stimuli. Data from other species are cited as appropriate for comparative purposes and elaboration of proposed mechanisms. However, the scope of the review is not intended to comprehensively cover the vast literature on proinflammatory cytokines and prostaglandins generated peripherally and centrally during host responses to inflammatory stimuli.

Effects of growth hormone and insulin-like growth factor I on opsonin receptor expression on local and systemic phagocytes in a lethal peritonitis model

OBJECTIVE

To investigate the effects of pretreatment with growth hormone (GH) and insulin-like growth factor I (IGF-I) on phagocyte exudation and bacterial clearance, focusing on CD11b and CD32/CD16 expression on local and systemic phagocytes, in a lethal peritonitis model.

DESIGN

Prospective randomized experimental study.

SETTING

Research laboratory in a university hospital.

SUBJECTS

Balb/c mice (n = 21).

INTERVENTIONS

Mice were challenged intraperitoneally with 1 x 10(8) Escherichia coli, after 6 days of pretreatment with saline (control), GH (4.8 mg/kg/day), or IGF-I (24 mg/kg/day). Samples were harvested at 4 hrs after the challenge.

MEASUREMENTS AND MAIN RESULTS

Viable bacterial counts in peritoneal lavage fluid (PLF) and blood were determined. Peritoneal exudative cells and peripheral blood leukocytes were counted and analyzed for receptor expressions by flow cytometry. GH reduced viable bacterial counts in PLF, as compared with the saline control. GH (three-fold) and IGF-I (two-fold) increased the number of peritoneal exudative neutrophils (PENs), as compared with the saline control. The number of PENs showed an inverse correlation with PLF viable bacterial counts. By contrast, there were no differences in peripheral blood neutrophil (PN) counts among the three groups, nor was there a correlation between PN and PEN counts. CD11b expression was greater on PENs than on PNs in all three groups. CD11b expression on PNs did not differ among the three groups. However, GH increased CD11b expression on PENs, as compared with saline and IGF-I, and this expression showed a positive correlation with PEN numbers and an inverse correlation with PLF viable bacterial counts. CD11b expression on peritoneal macrophages and peripheral blood monocytes did not differ among the three groups. There were no differences in phagocyte CD32/CD16 expression among the three groups.

CONCLUSIONS

GH pretreatment enhanced CD11b expression on PENs, but not PNs, possibly in association with enhanced neutrophil recruitment, phagocytosis, and bacterial elimination by PENs, without activation of PNs. GH prophylaxis may be useful for reducing the frequency rate and severity of septic complications, via modulation of CD11b expression on local and systemic neutrophils.

Effects of peripartum stress and health on circulating bovine lymphocyte subsets

Alterations in the proportions of peripheral blood lymphocyte subsets was monitored using flow cytometry, before, during and after the peripartum period (week-8 to week (wk) 16) of dairy cows, when pregnancy and lactational stresses prevail and disease incidence is highest. A health code was assigned to each animal at each sampling time, and a subset of non-pregnant, non-lactating (NPNL) cows were sampled for comparisons, and to examine the effect of pregnancy and lactation only, on lymphocyte subset proportions. Results were expressed as the percentage of positive stained cells expressing CD2, CD4, CD8, WC1(gamma delta), IgM and class II major histocompatibility complex (MHC-II) molecules, as determined by flow cytometry. Comparisons of subset proportions were made across time and between health status categories. Mean fluorescence intensity (MFI) values were also examined across the periparturient period for CD2, CD4, CD8 and gamma delta T cell subsets. All T cell subsets varied significantly during the perparturient period in healthy cows, especially around parturition. B cell and MHC-II+ populations remained relatively constant until after calving and then significantly (P < or = 0.06) decreased. Compared to NPNL cows, all T cell subsets were significantly lower in healthy cows at most time points, whereas B cell and MHC-II+ cells were comparable to the NPNL values. CD2, CD4, and CD8 subsets decreased significantly at wk-3 and returned to initial subset proportions by wk 16. Conversely, the WC1 population increased at wk-3 relative to calving but declined to approximate initial proportions at calving. Health status had no significant overall effect on any subset unless it was separated by weeks in which case there were interactions between health and week for CD2 and CD8. Results indicate that variations in T lymphocyte subsets and in the concentrations of surface marker molecules (MFI) occur more as a result of pregnancy and lactation than health status in the dairy cow and that these factors have the least influence upon B cell and MHC-II+ populations during the periparturient period.

Hormones, lymphohemopoietic cytokines and the neuroimmune axis

The classical distinction between hormones and cytokines has become increasingly obscure with the realization that homeostatic responses to infection involve coordinated changes in both the neuroendocrine and immune systems. The hypothesis that these systems communicate with one another is supported by the ever-accruing demonstrations of a shared molecular network of ligands and receptors. For instance, leukocytes express receptors for hormones and these receptors modulate diverse biological activities such as the growth, differentiation and effector functions. Leukocyte lineages also synthesize and secrete hormones, such as insulin-like growth factor-I (IGF-I), in response to both growth hormone (GH) and also to cytokines such as tumor necrosis factor-alpha (TNF-alpha). Since hormones share intracellular signaling substrates and biological activities with classical lymphohemopoietic cytokines, neuroendocrine and immune tissues share a common molecular language. The physiological significance of this shared molecular framework is that these homeostatic systems can intercommunicate. One important example of this interaction is the mechanism by which bacterial lipopolysaccharide, by eliciting a pro-inflammatory cytokine cascade from activated leukocytes, modulate pituitary GH secretion as well as other CNS-controlled behavioral and metabolic events. This article reviews the cellular and molecular basis for this communication system and proposes novel mechanisms by which neuroendocrine-immune interactions converge to modulate disease resistance, metabolism and growth.

Nutritional modulation of somatotropic axis-cytokine relationships in cattle: a brief review

The objective of this review is to summarize data on the interrelationships that exist between nutrition, the endocrine system and their modulation of plasma tumor necrosis factor-alpha responses to endotoxin in cattle. During stress, intake of nutrients often is compromised and a percentage of available nutrients are diverted away from growth processes to stabilize other physiological processes of a higher survival priority. Management practices that minimize the magnitude and duration of disease stress will aid in speeding the return to homeostatic equilibrium. However, the shift away from growth during stress is almost inevitable as a mechanism to survive. Some degree of control and management of the metabolic cost of disease stress involves understanding the integration of nutritional, endocrine and immune signals by cells and working with the natural homeostatic processes. Endocrine hormones and immune system cytokine signals participate in redirecting nutrient use during disease stress. In an intricate interplay, hormones and cytokines regulate, modify and modulate each other's production and tissue interactions to alter metabolic priorities. Levels of dietary protein and energy intake affect patterns of hormones and cytokines in the blood after endotoxin challenge and further modulate the biological actions of many of these regulatory effectors. In vivo, administration of growth hormone to young calves has significant effects to decrease the many specific physiological responses to endotoxemia. Many aspects of nutrition can attenuate or facilitate this effect.

Experimental approaches to therapy and prophylaxis for heat stress and heatstroke

New developments in the fields of biochemistry, physiology, sepsis, cancer therapy, and molecular genetics have led to opportunities for the development of new therapies and prophylaxes for heat illnesses and for improving human performance during conditions of environmental stress. These include antilipopolysaccharide agents, anticytokines, potassium channel agents, a diet rich in omega-3 fatty acids, and psychological conditioning. This review summarizes the backgrounds and recent findings in the above fields and provides specific suggestions for potential therapy and prophylaxis for classic and exertional heatstroke and for improving athletic performance.

Effects of Freund's complete adjuvant on the diurnal rhythms of neuroendocrine processes and ornithine decarboxylase activity in various tissues of male rats

The aim of this study was to investigate the effects of Freund's complete adjuvant (FCA) on the diurnal rhythms of hormonal parameters in serum and ornithine decarboxylase (ODC) activity in various tissues of male rats. On days 1-2 after FCA, increase of ODC activity (used to evaluate the level of activation) was observed in the hypothalamus, pituitary gland, adrenal medulla, adrenal cortex, liver and lymphoid tissues, while the ODC activity in the kidney was reduced. This was accompanied by an increase in serum corticosterone. On days 3-4 after FCA, ODC activity remained elevated in the pituitary gland, liver and lymphoid tissues, while the ODC activity in the testes and pancreas was reduced; kidney ODC activity returned to baseline. This was associated with increased serum levels of prolactin (Prl) and luteinizing hormone, but decreased growth hormone, testosterone and insulin. The increase in ODC activity in the thymus, as well as the reduced ODC activity in the testes and kidney, can be obtained with paraffin. Furthermore, bromocryptine microcapsules (CBLA) reduced the FCA-induced increase of ODC activity in the pituitary gland, liver and lymphoid tissues (days 3-4) but did not affect the changes in other tissues. The increase in ODC activity in the pituitary gland, liver and lymphoid tissues is specific for FCA. A role for Prl in the induction of ODC in liver and lymphoid tissues is suggested by the fact that CBLA suppresses this enhancement.

Immunoregulatory properties of growth hormone and prolactin

Reciprocal communication between the neuroendocrine and immune systems is critical to the establishment of host homeostatic and defence mechanisms. The production and utilisation of common ligands and their receptors by cells of the immune and neuroendocrine systems constitutes a biochemical information circuit between and within the immune and neuroendocrine systems. Although the structures of the various signalling components appear to be similar in both systems, the regulation of their synthesis may be different. Growth hormone and prolactin have similar and marked influences on the function/activity of each of the major immune cell types, both in vitro and in vivo. The underlying molecular mechanisms are just beginning to be unravelled, and it is anticipated that further work in this rapidly developing field will establish abnormal pituitary and/or lymphocyte growth hormone and prolactin synthesis and function as a contributory factor to a number of pathologic situations, including leukaemia and autoimmunity.

Prolactin as an immunoreactive agent

Prolactin (PRL), an endocrine hormone from the anterior pituitary, is also synthesized and secreted by activated immunocytes, mostly T cells and thymocytes. In vitro PRL acts as an autocrine or paracrine growth factor which regulates the proliferation of previously stimulated immunocompetent cells. PRL acts through its specific cell surface receptors expressed on different immunocytes including T cells, B cells, monocytes, NK cells and neutrophils. In vivo the immunoregulatory role of PRL is still the subject of intense investigation, especially in the conditions of stress and reproduction. The conflicting results suggest that PRL concentration, sex hormones and some other factors influence the immunomodulatory role of PRL.

The influence of season, photoperiod, and pineal melatonin on immune function

In addition to the well-documented seasonal cycles of mating and birth, there are also significant seasonal cycles of illness and death among many animal populations. Challenging winter conditions (i.e., low ambient temperature and decreased food availability) can directly induce death via hypothermia, starvation, or shock. Coping with these challenges can also indirectly increase morbidity and mortality by increasing glucocorticoid secretion, which can compromise immune function. Many environmental challenges are recurrent and thus predictable; animals could enhance survival, and presumably increase fitness, if they could anticipate immunologically challenging conditions in order to cope with these seasonal threats to health. The annual cycle of changing photoperiod provides an accurate indicator of time of year and thus allows immunological adjustments prior to the deterioration of conditions. Pineal melatonin codes day length information. Short day lengths enhance several aspects of immune function in laboratory studies, and melatonin appears to mediate many of the enhanced immunological effects of photoperiod. Generally, field studies report compromised immune function during the short days of autumn and winter. The conflict between laboratory and field data is addressed with a multifactor approach. The evidence for seasonal fluctuations in lymphatic tissue size and structure, as well as immune function and disease processes, is reviewed. The role of pineal melatonin and the hormones regulated by melatonin is discussed from an evolutionary and adaptive functional perspective. Finally, the clinically significance of seasonal fluctuations in immune function is presented. Taken together, it appears that seasonal fluctuations in immune parameters, mediated by melatonin, could have profound effects on the etiology and progression of diseases in humans and nonhuman animals. An adaptive functional perspective is critical to gain insights into the interaction among melatonin, immune function, and disease processes.

Differential expression of type I insulin-like growth factor receptors in different stages of human T cells

Insulin-like growth factor I (IGF-I) has been implicated to play a regulatory role in T cell development and in T cell function. We investigated the expression of type I IGF receptors on human peripheral T cells related to the maturation and activation stage using the type I IGF receptor-specific monoclonal antibody alpha IR3. It appeared that 87% of the CD4+CD45RA+ cells and 66% of the CD8+CD45RA+ cells were alpha IR3+, whereas only 37% of the CD4+CD45R0+ cells and 38% of the CD8+CD45R0+ cells bound alpha IR3. We also found that the fraction of alpha IR3+ cells within in vivo or in vitro activated (HLA-DR+) T cells is markedly lower than in nonactivated (HLA-DR-) cells. In vitro phytohemagglutinin-activated T cells and CD4+CD45R0+ cells activated with recall antigens also contained less alpha IR3+ cells (1-6%) than nonactivated cells (30-54%).