Summary 1. A growing number of ecologists are turning to the enumeration of white blood cells from blood smears (leukocyte profiles) to assess stress in animals. There has been some inconsistency and controversy in the ecological literature, however, regarding their interpretation. The inconsistencies may stem partly from a lack of information regarding how stress affects leukocytes in different taxa, and partly from a failure on the part of researchers in one discipline to consult potentially informative literature from another. 2. Here, we seek to address both issues by reviewing the literature on the leukocyte response to stress, spanning the taxa of mammals (including humans), birds, amphibians, reptiles and fish. 3. We show that much of the early literature points to a close link between leukocyte profiles and glucocorticoid levels. Specifically, these hormones act to increase the number and percentage of neutrophils (heterophils in birds and reptiles), while decreasing the number and percentage of lymphocytes. This phenomenon is seen in all five vertebrate taxa in response to either natural stressors or exogenous administration of stress hormones. For the ecologist, therefore, high ratios of heterophils or neutrophils to lymphocytes (‘H : L’ or ‘N : L’ ratios) in blood samples reliably indicate high glucocorticoid levels. Furthermore, this close relationship between stress hormones and N : L or H : L ratios needs to be highlighted more prominently in haematological assessments of stress, as it aids the interpretation of results. 4. As with hormone assays, there are challenges to overcome in the use of leukocytes profiles to assess levels of stress; however, there are also advantages to this approach, and we outline each. Given the universal and consistent nature of the haematological response to stress, plus the overwhelming evidence from the veterinary, biomedical and ecological literature reviewed here, we conclude that this method can provide a reliable assessment of stress in all vertebrate taxa.

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The use of leukocyte profiles to measure stress in vertebrates: a review for ecologists

The effects of aging on the immune system are widespread and extend from hematopoietic stem cells and lymphoid progenitors in the bone marrow and thymus to mature lymphocytes in secondary lymphoid organs. These changes combine to result in a diminution of immune responsiveness in the elderly. This review aims to provide an overview of age-related changes in lymphocyte development and function and discusses current controversies in the field of aging research.

Age-related changes in lymphocyte development and function

In humans, both aging and GH deficiency are associated with reduced protein synthesis, decreased lean body and bone mass, and increased percent body fat. In healthy individuals, spontaneous and stimulated GH secretion, as well as circulating IGF-I and IGFBP-3 levels, are significantly decreased with advancing age. The extent to which these age-related changes in GH and IGF-I contribute to alterations in body composition and function remains to be elucidated. GH treatment of GH-deficient adults or old men with reduced IGF-I levels with exogenous GH increases plasma IGF-I, nitrogen retention, and lean body mass, decreases percent body fat, and exerts little effect on bone mineral density. Short-term adverse effects of GH therapy have been minimized by using low-dose regimens, but it is still uncertain whether long-term GH supplementation in adult life increases the risk of metabolic abnormalities or malignancy. Administration of GHRH, which has been shown to maintain the pattern of pulsatile GH secretion in old men, may represent another possible physiological approach to therapy. It may be justifiable initially to limit use of GH to certain elderly patients such as those suffering from catabolic illnesses, malnourishment, burns, cachexia, etc. A great deal more research will be necessary to determine whether normalization of GH and IGF-I levels in healthy older persons will lead to improvements in their physical and psychological functional capacity and quality of life.

Human Growth Hormone and Human Aging

The information available on the biological activity of hydrogen sulfide has been examined for present status of critical results pertaining to the toxicity of hydrogen sulfide. This review of the literature is intended as an evaluative report rather than an annotated bibliography of all the source material examined on hydrogen sulfide. The information was selected as it might relate to potential toxic effects of hydrogen sulfide to man and summarized, noting information gaps that may require further investigation. Several recommendations are listed for possible consideration for either toxicological research or additional short- and long-term tests. Two bibliographies have been provided to assist in locating references considered in this report: (1) literature examined but not cited and (2) reference citations. The majority of the references in the first bibliography were considered peripheral information and less appropriate for inclusion in this report.

A Critical Review of the Literature on Hydrogen Sulfide Toxicity

Levulinic acid (LA) can be produced cost effectively and in high yield from renewable feedstocks in a new industrial process. The technology is being demonstrated on a 1 ton/day scale at a facility in South Glens Falls, New York. Low cost LA can be used as a platform chemical for the production of a wide range of value-added products. This research has demonstrated that LA can be converted to methyltetrahydrofuran (MTHF), a solvent and fuel extender. MTHF is produced in >80% molar yield via a single stage catalytic hydrogenation process. A new preparation of δ-aminolevulinic acid (DALA), a broad spectrum herbicide, from LA has also been developed. Each step in this new process proceeds in high (>80%) yield and affords DALA (as the hydrochloride salt) in >90% purity, giving a process that could be commercially viable. LA is also being investigated as a starting material for the production of diphenolic acid (DPA), a direct replacement for bisphenol A.

Production of levulinic acid and use as a platform chemical for derived products

Thymic size and T-cell function decrease with age, and it has not yet been possible to totally reverse this thymic atrophy and completely restore T-cell-dependent immune functions. In this study, GH3 pituitary adenoma cells, which secrete growth hormone and prolactin, were implanted subcutaneously into 16- and 22-month-old female Wistar-Furth rats and the rats were sacrificed approximately 2 months later. Only thymic remnants were detected in aged, non-implanted rats, but thymus glands were found in both the 18- and the 24-month-old rats that had been implanted with GH3 cells. Thymus glands from the GH3-implanted 18-month-old rats contained distinct cortical thymocytes and medullary epithelial cells. Depending on the concentration of phytohemagglutinin or concanavalin A, T-cell proliferative responses of splenocytes from these implanted rats were 2- to 5-fold greater than those of 18-month-old controls. At the optimal concentration of mitogen, proliferative responses to either lectin could be restored to those levels observed in splenocytes from 3-month-old Wistar-Furth females. Thymus glands from 24-month-old GH3-implanted rats contained more cortical thymocytes and fewer fat vacuoles than controls, but they were not totally reconstituted. No significant lectin-induced T-cell proliferative responses or IL-2 secretion were detected in 24-month-old control rats, but splenocytes from GH3-implanted rats showed augmented T-cell proliferative responses and increased synthesis of IL-2. Fluorescence-activated cell-sorter analysis of thymocytes revealed that 24-month-old rats implanted with GH3 cells had a higher proportion of lymphocytes with the Thy-1.1 and helper-T-cell phenotypes. These data show that it is possible to regenerate normal thymic tissue in situ and reverse the natural loss in cell-mediated immunity that occurs with aging.

https://www.pnas.org/content/pnas/83/15/5663.full.pdf

GH3 pituitary adenoma cells can reverse thymic aging in rats

Effects of Aerial Ammonia on Growth and Health of Young Pigs

Growth hormone (GH) appears to play a major role in a reciprocal axis that has been postulated between the thymus and pituitary glands. Our previous studies showed that thymic structure, as well as T-cell proliferation and IL-2 synthesis, could be restored in aged female Wistar-Furth rats by the implantation of GH3 pituitary adenoma cells. These cells secrete GH and some prolactin. We have now used three different approaches to determine whether GH affects a variety of immune events in vivo in both old and young rodents, and whether GH3 cells can directly affect progenitor T-cells in nude rats that congenitally lack a thymus gland. To test the effects of GH in aged rats, 750 μg of pituitary-derived ovine GH was injected 2× daily into 26-month-old Fischer 344 rats for 5 weeks. This approach demonstrated that GH augments splenocyte proliferation to T-cell lectins as well as natural killer (NK) activity at low effector: target ratios even though morphologic characteristics of the thymus were not altered. To assess the effect of GH in young rodents, mice were studied that were transgenic for the rat metallothionein-GH gene. Histologic evaluation of thymus glands revealed that the amount of adipose tissue and the number of epithelial cells and Hassall's corpuscles are augmented in transgenic mice. Splenocyte proliferation at suboptimal mitogen doses is greater in transgenic than in control littermate mice, but neither IL-2 synthesis nor antibody synthesis to sheep erythrocytes is affected. The role of pituitary hormones on progenitor T-cells was then explored by implanting GH3 cells into Rowett nude rats. GH3 cells are unable to augment proliferation to T-cell lectins, IL-2 synthesis, antibody production to sheep erythrocytes, or NK activity in nude rats. Collectively, these experiments show that T-cells and NK cells from aged rats are not inherently defective because their proliferative responses to lectins and cytolytic activity can be augmented by exogenous GH. If GH affects progenitor T-cells, these effects are not apparent in nude rats. Finally, GH can also augment T-cell proliferative responses in young rodents, but the immunoenhancing effects are not as apparent as thos observed in immunocompromised aged animals.

Role of growth hormone in regulating T-dependent immune events in aged, nude, and transgenic rodents.

Macrophage responses to recombinant IFN-gamma decline during aging, as measured by two criteria of macrophage activation, O2- and TNF-alpha secretion. The production of O2- by macrophages in response to opsonized-zymosan and recombinant rat IFN-gamma is 75% lower in 23-month-old rats than in 3-month-old rats. Furthermore, the secretion of TNF-alpha in response to IFN-gamma and LPS is almost absent in macrophages from aged rats. Production of both O2- and TNF-alpha by resident peritoneal macrophages from specific pathogen-free aged rats in response to priming and triggering stimuli was partially or fully restored by implantation of syngeneic pituitary grafts from young rats. These data demonstrate that macrophages from aged rats are defective in their response to a priming signal induced by IFN-gamma, and they suggest that impaired macrophage responses during aging may be reversible.

Interferon-gamma-induced priming for secretion of superoxide anion and tumor necrosis factor-alpha declines in macrophages from aged rats.

Ammonia, hydrogen sulfide and swine-house dust at continuous aerial levels as high as or higher than those normally encountered in enclosed swine-finishing houses had little or no effect on rate of body-weight gain and respiratory-tract structure of 92 healthy pigs in seven trials. The trials were of 17 to 109 days' duration, involved air pollutants alone and in various combinations and were conducted in air-pollutant exposure chambers. (

Joseph Simon

Papers

GH3 pituitary adenoma cells can reverse thymic aging in rats

Effects of Aerial Ammonia on Growth and Health of Young Pigs

Role of growth hormone in regulating T-dependent immune events in aged, nude, and transgenic rodents.

Interferon-gamma-induced priming for secretion of superoxide anion and tumor necrosis factor-alpha declines in macrophages from aged rats.

Effects of aerial ammonia, hydrogen sulfide and swine-house dust on rate of gain and respiratory-tract structure in swine.