The endocrinology of aging

Free radicals in the physiological control of cell function

At high concentrations, free radicals and radical-derived, nonradical reactive species are hazardous for living organisms and damage all major cellular constituents. At moderate concentrations, however, nitric oxide (NO), superoxide anion, and related reactive oxygen species (ROS) play an important role as regulatory mediators in signaling processes. Many of the ROS-mediated responses actually protect the cells against oxidative stress and reestablish "redox homeostasis." Higher organisms, however, have evolved the use of NO and ROS also as signaling molecules for other physiological functions. These include regulation of vascular tone, monitoring of oxygen tension in the control of ventilation and erythropoietin production, and signal transduction from membrane receptors in various physiological processes. NO and ROS are typically generated in these cases by tightly regulated enzymes such as NO synthase (NOS) and NAD(P)H oxidase isoforms, respectively. In a given signaling protein, oxidative attack induces either a loss of function, a gain of function, or a switch to a different function. Excessive amounts of ROS may arise either from excessive stimulation of NAD(P)H oxidases or from less well-regulated sources such as the mitochondrial electron-transport chain. In mitochondria, ROS are generated as undesirable side products of the oxidative energy metabolism. An excessive and/or sustained increase in ROS production has been implicated in the pathogenesis of cancer, diabetes mellitus, atherosclerosis, neurodegenerative diseases, rheumatoid arthritis, ischemia/reperfusion injury, obstructive sleep apnea, and other diseases. In addition, free radicals have been implicated in the mechanism of senescence. That the process of aging may result, at least in part, from radical-mediated oxidative damage was proposed more than 40 years ago by Harman (J Gerontol 11: 298-300, 1956). There is growing evidence that aging involves, in addition, progressive changes in free radical-mediated regulatory processes that result in altered gene expression.

The Snell dwarf mutation Pit1(dw) can increase life span in mice

Over the past 30 years, the Snell dwarf mutation (Pit1(dw)) has been reported to shorten, to have no effect on, or to increase life span in various colonies; however, few details of these disparate results have been published. We now report that mean, median, and maximum life spans are increased by 40-50% for Snell dwarf (Pit1(dw)/Pit1(dw)) DW/J females, and 25-50% for dwarf DWC3F1 males and females with the compound heterozygous Pit1(dw)/Pit1(dw-J) genotype. We previously observed aspects of delayed senescence in Snell dwarf (Pit1(dw)/Pit1(dw)) DW/J males; however, their median life span was shortened by about 25% (Genetic Effects on Aging II, 1990, The Telford Press, Caldwell, NJ, pp. 435-456). This short life span was not an intrinsic effect of the mutation, but a consequence of housing male dwarfs with normal-sized male littermates; our present results demonstrate that Snell dwarf males attain very long life spans when housed with normal-sized females. We conclude that the dwarf mutation interacts with environmental factors to alter life spans and, probably, rates of ageing, over an extremely broad range. We propose that this variation in the effect of the Snell dwarf mutation results from a tradeoff between physical vigor and life span that is mediated by pituitary hormones, and that growth hormone, thyroid hormone, and possibly prolactin regulate mechanisms that schedule mortality in mammals.

Association between menopausal state and prognosis of endometrial cancer

The purpose of our study was to examine the menopausal state as an independent prognostic variable of endometrial cancer and determine the conditions under which the menopausal state would be an independent prognostic variable of such cancer. We studied the clinical and pathologic variables of 255 patients with invasive endometrial cancer. In comparisons of the clinicopathologic variables between menopausal states, obesity and deep myometrial invasion were found more frequently in older patients than in younger ones. Multivariate analysis performed on 255 cases with complete pathologic data identified menopausal state, cervical invasion, pelvic lymph node metastasis, and tumor grade as prognostic variables. Univariate analysis revealed that survival of older patients with FIGO pathologic stage Ib disease was significantly poorer than in younger patients, while there was no significant difference in the analyses of stage Ic or advanced disease beyond stage II. We conclude that menopausal state was an independent prognostic variable for patients with early endometrial cancer, but not for patients with advanced disease.

Is the somatotropic axis related to sympathetic nerve activity in healthy ageing men?

OBJECTIVE

The mechanisms underlying the age-related increase in blood pressure and sympathetic nerve activity remain largely unknown. The decline in growth hormone (GH) secretion and insulin-like growth factor-I (IGF-I) with age has been related to several cardiovascular risk factors. Low serum IGF-I levels in severe adult GH deficiency is associated with markedly increased sympathetic nerve activity. This study evaluates whether a relationship between serum IGF-I and sympathetic nerve traffic exists in healthy aging men.

DESIGN AND METHODS

Sympathetic nerve activity to the muscle vascular bed (MSA) was recorded in 56 healthy normotensive males, and related to age (range 21-71 years), body mass index (BMI, range 18.4-32.2), serum IGF-I and plasma nitrate levels. Blood pressure, BMI and MSA increased with age, whereas IGF-I and plasma nitrate decreased. In a forward stepwise multiple regression analysis, age explained 40% of the variability in MSA and excluded other variables. Omitting age, IGF-I became the strongest independent predictor, explaining 23% of the variability in MSA. MSA was an independent predictor of diastolic blood pressure, but its influence (10%) was less than that of BMI (28%). BMI was not related to MSA or IGF-I.

CONCLUSIONS

Decreased serum IGF-I levels are coupled to increased MSA during ageing, an effect independent from the impact of increased body weight. Although MSA is a weak predictor of rising blood pressure with age, it constitutes one possible pathway for the somatotropic axis to affect cardiovascular function in ageing.

A longitudinal assessment of change in VO2max and maximal heart rate in master athletes

PURPOSE

The purpose of this study was to determine the longitudinal change in VO2max and HRmax in male and female master endurance runners and to compare these changes based upon gender, age, and change in training volume.

METHODS

Eighty-six male (53.9 +/- 1.1 yr) and 49 female (49.1 +/- 1.2 yr) master endurance runners were tested an average of 8.5 yr apart. Subjects were grouped by age at first visit, change in VO2max, and change in training volume. Measurements included body composition by hydrostatic weighing, maximal exercise testing on a treadmill, and training history by questionnaire. Data were analyzed by ANOVA and multiple regression.

RESULTS

VO2max and HRmax declined significantly regardless of gender or age group (P < 0.05). The rate of change in VO2max by age group ranged from -1% to -4.6% per year for men and -0.5% to 2.4% per year for women. Men with the greatest loss in VO2max had the greatest loss in LBM (-2.8 +/- 0.7 kg), whereas women with the greatest loss in VO2max demonstrated the greatest change in training volume (-24.1 +/- 3.0 km.wk-1). Additionally, women with the greatest loss in VO2max (-9.6 +/- 2.6 mL.kg-1.min-1) did not replace estrogen after menopause independent of age. HRmax change did not differ by VO2max change or training volume change in either gender.

CONCLUSIONS

In conclusion, these data suggest that VO2max declines in male and female master athletes at a rate similar to or greater than that expected in sedentary older adults. Additionally, these data suggest that maintenance of LBM and VO2max were associated in men, whereas in women, estrogen replacement and maintenance of training volume were associated with maintained VO2max.

GH is needed for the maturation of muscle mass and strength in adolescents

The postpubertal period and the early years of adulthood may be of importance for continuing tissue maturation of importance in adulthood and aging. An example of this is the peak bone mass. This study has evaluated the importance of GH for lean mass and muscle strength in adolescents and young adults. GH treatment was discontinued in 40 adolescents aged 16-21 yr with GH deficiency of childhood onset. Measurements of isometric and isokinetic knee-extensor and flexor strength, handgrip strength, lean body mass, fat-free mass, and total body nitrogen were performed annually for 2 yr. Two hundred fifty healthy adolescents were randomly selected for prospective measurements of lean mass and handgrip strength between the ages of 17 and 21 yr. In the adolescents with continuing GH deficiency, lean body mass decreased, compared with the patients defined as having sufficient endogenous GH. The isometric strength in knee flexors increased in the sufficient endogenous GH group and was unchanged in the GH deficiency group during the 2 yr off GH treatment (between group, P < 0.05). The mean and peak handgrip strength increased on average by 9-15% in the group with sufficient endogenous GH and was unchanged in those with GH deficiency (P < 0.05). Lean body mass and handgrip strength (both, P < 0.001) increased in both the healthy boys and girls who were followed for 4 yr with a more marked increase in the boys. The mean increase in handgrip between the age of 17 and 21 yr was 7-9%. The increased lean mass and improved muscle performance seen in healthy adolescents did not occur in adolescents with GH deficiency. These findings suggest that GH is of importance for the maturation of lean mass and muscle strength in adolescents and young adults.

The process of aging changes the interplay of the immune, endocrine and nervous systems

The immune, endocrine and nervous systems interact with each other by means of cytokines, hormones and neurotransmitters. Interaction is dependent on specific receptors and respective signaling pathways in target cells. During aging, changes occur on many levels of these global systems which depend on oxidative damage, non-enzymatic glycosylation, mitochondrial mutations, defects in cell cycle control, mitotic dysregulation, genome instability, telomere shortening and other chromosomal pathologies. An alteration of the numerical value of a parameter of one system can lead to changes of the numerical value of a variable of another system. In a non-linear dynamic process these changes can contribute to the aging phenotype. Although it is extremely difficult to dissect linear interrelations of three global systems during aging, this review attempts to identify some simple linear pathways. Furthermore, it is demonstrated that chronic inflammatory diseases may accelerate the aging process. This review also reveals that new statistical and computational methods are necessary to unravel the complexity of the aging process.

Estrogen receptor (ER)-alpha, but not ER-beta, mediates regulation of the insulin-like growth factor I gene by antiestrogens

The importance of insulin-like growth factor I (IGF-I) on maintenance of skeletal integrity has been widely recognized. Although osteoblasts secrete some IGF-I, the liver is the primary endocrine source for IGF-I. We have studied the regulation of the human IGF-I promoter in the hepatocyte cell line Hep3B, and we have shown that the IGF-I promoter, when co-transfected in Hep3B cells together with an estrogen receptor (ER)-alpha expression vector, was transcriptionally regulated by raloxifene or raloxifene-like molecules but not by 17beta-estradiol and 4(OH)-tamoxifen. The induction mediated by raloxifene is antagonized by 17beta-estradiol and mediated selectively by ER-alpha, but not by ER-beta. Transfer of IGF-I promoter sequences from -733 to -65 or from -375 to -65 to a minimal Fos promoter resulted in a comparable responsiveness to raloxifene. This region contains two CAAT/enhancer-binding protein sites and an activator protein 1 site, both of which have been shown to be involved in estrogen receptor-mediated transactivation. When the CAAT/enhancer-binding protein sites were mutated in a construct bearing the sequence from -375 to -65 in front of the minimal Fos promoter, raloxifene induction was reduced, whereas mutation of the other elements did not affect induction. In addition, using chimeric proteins, we delineated the domains of ER-alpha that confer to ER-alpha transactivation abilities on the IGF-I promoter that are not exhibited by ER-beta. These data shed new light on the mechanism of action of antiestrogens and might help explain, at least in part, the bone-protective effects observed for some antiestrogens in ovariectomized animals.

Biological ageing research in the Netherlands

After an introduction on the development of biological ageing research in the Netherlands during the past decades, 606 papers on aging published by Dutch institutes in the period 1991-2000, collected from PubMed, were analysed for their relevance to research into biological ageing. For the period 1996-2000, the total number of research papers on biological ageing amounted to 142, which accounts for 23% of all publications on ageing in that period. The number of publications per year did not change. On the basis of these papers and additional information provided by research groups a comprehensive overview of biological ageing research in the Netherlands is presented, together with an extensive literature list. Ageing of the central nervous system (CNS), of the endocrinological system and of the cardiovascular system are the topics most studied. It is concluded that general biological ageing research has not increased in the Netherlands over the last ten years, and that the infrastructure for basic biological ageing research in the Netherlands is weak.

Impaired activation of AP-1 and altered expression of constituent proteins in rat adrenal during ageing

Oxidative stress appears to be one of the primary factors contributing to an age related decline in steroidogenic response in rat adrenocortical and testicular Leydig cells. In this report we concentrate on age-related changes in the DNA binding activity of the transcription factor AP-1 which is particularly responsive to changes in cellular oxidative conditions: adrenal nuclear extracts from young mature (5 months) and old (24 months) rats treated with, and without, lipopolysaccharide (LPS) were studied. AP-1 binding activity, as measured by electrophoretic mobility shift assays (EMSA), was diminished approximately 70% with age in unstimulated adrenals. Following LPS treatment, AP-1 binding activity increased significantly in the adrenals of both young and old animals; however, the level of AP-1 binding achieved in LPS-stimulated old rats was less than that observed for LPS-stimulated young rats. There was no corresponding change in the binding activity of housekeeping transcription factors SP-1 and OCT-1. To further understand these observations, compositional changes in the members of the AP-1 DNA-binding complex were examined by a super-shift assay and Western blot analysis. In adrenals from old rats, a significant decrease in the amount of Fra2 was noted under basal conditions, whereas, substantial decreases in c-Fos, Jun D and c-Jun were observed in response to LPS treatment. In contrast, basal levels of JunB, an inhibitor of the trans-activating function of c-Jun and repressor of AP-1-dependent transcription, were significantly elevated in adrenals from old rats compared to young rats. Together, these findings suggest that ageing-induced oxidative stress may contribute to impaired functional expression of AP-1 by differentially regulating the steady state levels of AP-1 components. The observed decrease in AP-1 binding activity in ageing adrenals is most likely due to decreased expression of the AP-1 activating components (c-Fos, c-Jun, JunD, etc.) and increased expression of JunB, resulting in a switch from transcriptionally active AP-1 complexes observed in young rats to less efficient JunB containing complexes in old rats.

Activin A serum levels and aging of the pituitary-gonadal axis: a cross-sectional study in middle-aged and elderly healthy subjects

Aim of the study was to investigate activin A serum concentration in healthy adult males and post-menopausal females over a wide age-range and its correlation to gonadotropins, inhibin B and testosterone concentrations. The study included 73 males (aged 30-101 years) and 42 postmenopausal females (aged 50-104 years). Blood samples were collected after an overnight fast to measure serum activin A, inhibin B, LH, FSH, and gonadal steroid levels. A significant increase in serum activin A levels over age in both genders, especially in the oldest age-groups, was observed. Serum inhibin B and testosterone concentrations showed a sharp decrease in male subjects, reflecting the age-related decrease of testicular function and by consequence serum FSH and LH significantly increased. In female subjects LH and FSH levels were very high in subjects in their 50s and showed a continuous decline due to pituitary aging. Simple and multivariable regression analyses demonstrated the lack of correlation between activin A and FSH in both males and females. In conclusion, a steep increase in activin A levels is present during aging in both genders, especially in the last decades of life. The physiologic role and site of production of activin A in old subjects remain to be clarified.

Different modes of hippocampal plasticity in response to estrogen in young and aged female rats

Estrogen regulates hippocampal dendritic spine density and synapse number in an N-methyl-D-aspartate (NMDA) receptor-dependent manner, and these effects may be of particular importance in the context of age-related changes in endocrine status. We investigated estrogen's effects on axospinous synapse density and the synaptic distribution of the NMDA receptor subunit, NR1, within the context of aging. Although estrogen induced an increase in axospinous synapse density in young animals, it did not alter the synaptic representation of NR1, in that the amount of NR1 per synapse was equivalent across groups. Estrogen replacement in aged female rats failed to increase axospinous synapse density; however, estrogen up-regulated synaptic NR1 compared with aged animals with no estrogen. Therefore, the young and aged hippocampi react differently to estrogen replacement, with the aged animals unable to mount a plasticity response generating additional synapses, yet responsive to estrogen with respect to additional NMDA receptor content per synapse. These findings have important implications for estrogen replacement therapy in the context of aging.

The use of an antifibrosis agent to improve muscle recovery after laceration

Muscle injuries are challenging problems in traumatology and the most frequent injuries in sports medicine. Muscle injuries are capable of healing, although slowly and occasionally with incomplete functional recovery. We observed that lacerated muscle undergoes a rapid process of regeneration, which is hindered by the development of fibrosis. Biologic approaches to enhance muscle regeneration and prevent fibrosis are being investigated to improve muscle healing after injuries. We observed that growth factors can improve muscle regeneration but cannot prevent muscle fibrosis. We investigated the use of an antifibrosis substance, decorin, as an approach to prevent fibrosis and thereby improve muscle healing after injury in murine muscle. We observed that direct injection of human recombinant decorin can efficiently prevent fibrosis and enhance muscle regeneration in the lacerated muscle. More importantly, decorin can improve the recovery of strength in the injured muscle to a level similar to that observed in normal noninjured muscle. These results suggest that injection of decorin improves both the muscle structure and the function of the lacerated muscle to near complete recovery. This study will contribute significantly to the development of strategies to promote efficient muscle healing and complete functional recovery after muscle injuries.

Postmenopausal function in context: biocultural observations on Amish, neighboring non-Amish, and Ifugao household health

Ecological approaches to female post-reproductive function must consider the social context and microenvironment of the household. A model integrating these environmental factors into the analysis of late-life well-being (operationally defined as household health) is presented and explored in three settings: an Old Order Amish community, the neighboring community of non-Amish, and an Ifugao community in the Philippine highlands. Intensive interview and observation of function were completed in a sample of at least 25 households in each community. The complex interaction of social and biological factors is explored in case studies and through multiple regression analysis with household health as the dependent variable. The results emphasize the importance of social support and assessing capabilities within the household. The results also suggest the need for natural field observation of work to better understand the influence of pacing and scheduling, necessity of work, and the role of environmental modification in postmenopausal function.

Stimulation of beta-amyloid precursor protein trafficking by insulin reduces intraneuronal beta-amyloid and requires mitogen-activated protein kinase signaling

Alzheimer's Disease (AD) is characterized by cerebral accumulation of beta-amyloid peptides (Abeta), which are proteolytically derived from beta-amyloid precursor protein (betaAPP). betaAPP metabolism is highly regulated via various signal transduction systems, e.g., several serine/threonine kinases and phosphatases. Several growth factors known to act via receptor tyrosine kinases also have been demonstrated to regulate sbetaAPP secretion. Among these receptors, insulin and insulin-like growth factor-1 receptors are highly expressed in brain, especially in hippocampus and cortex. Emerging evidence indicates that insulin has important functions in brain regions involved in learning and memory. Here we present evidence that insulin significantly reduces intracellular accumulation of Abeta and that it does so by accelerating betaAPP/Abeta trafficking from the trans-Golgi network, a major cellular site for Abeta generation, to the plasma membrane. Furthermore, insulin increases the extracellular level of Abeta both by promoting its secretion and by inhibiting its degradation via insulin-degrading enzyme. The action of insulin on betaAPP metabolism is mediated via a receptor tyrosine kinase/mitogen-activated protein (MAP) kinase kinase pathway. The results suggest cell biological and signal transduction mechanisms by which insulin modulates betaAPP and Abeta trafficking in neuronal cultures.

Age-related mitochondrial genotypic and phenotypic alterations in human skeletal muscle

To have a clearer picture of how mitochondrial damages are associated to aging, a comprehensive study of phenotypic and genotypic alterations was carried out, analyzing with histochemical and molecular biology techniques the same skeletal muscle specimens of a large number of healthy subjects from 13 to 92 years old. Histochemical data showed that ragged red fibers (RRF) appear at about 40 years of age and are mostly cytochrome c oxidase (COX)-positive, whereas they are almost all COX-negative thereafter. Molecular analyses showed that the 4977 bp deletion of mitochondrial DNA (mtDNA(4977)) and the 7436 bp deletion of mtDNA (mtDNA(7436)) are already present in individuals younger than 40 years of age, but their occurrence does not change with age. After 40 years of age the number of mtDNA deleted species, as revealed by Long Extension PCR (LX-PCR), increases, the 10422 bp deletion of mtDNA (mtDNA(10422)) appears, although with a very low frequency of occurrence, and mtDNA content is more than doubled. Furthermore, mtDNA(4977) level directly correlates with that of COX-negative fibers in the same analyzed subjects. These data clearly show that, after 40 years of age, the phenotypic and genotypic mitochondrial alterations here studied appear in human skeletal muscle and that they are closely related.

Melatonin or a melatonin agonist corrects age-related changes in circadian response to environmental stimulus

The effects of a melatonin agonist, S-20098, included in the diet were tested on a specific effect of aging in hamsters: the marked decline in the phase shifting effects of a 6-h pulse of darkness on a background of constant light. In contrast to young hamsters, old hamsters fed with the control diet showed little or no phase shifts in response to a dark pulse presented in the middle of their inactive or active period. Old hamsters fed with S-20098 showed phase shifts that were ~70% of the ones in young animals and significantly greater than those in old controls. The phase advancing response to a dark pulse presented during the inactive period was dose dependent and reversed after S-20098 discontinuation. Melatonin included in the diet showed comparable restorative effects on the phase shifting response to a dark pulse in old hamsters. Replacement therapy with melatonin or melatonin-related compounds could prove useful in treating, preventing, or delaying disturbances of circadian rhythmicity and/or sleep in older people.

Delayed wound healing in aged rats is associated with increased collagen gel remodeling and contraction by skin fibroblasts, not with differences in apoptotic or myofibroblast cell populations

Aging has been anecdotally reported to result in prolonged wound healing. Measurement of punch biopsy wound closure in young (4 month old) and old (36 month old) rats indicated there was a significant delay in wound closure by old rats during the early phase of repair, after which closure rates were equivalent. The delay in granulation tissue accumulation in older animals could involve premature programmed cell death (apoptosis); however, apoptotic fibroblasts in sponge granulation tissue and tissue culture were less abundant in samples from old rats relative to young rats. Myofibroblasts express alpha-smooth muscle actin, and they are believed to be important in wound contraction. There were no significant differences in overall abundance or distribution of alpha-smooth muscle actin containing myofibroblasts in granulation tissue and in cultured granulation tissue fibroblasts regardless of the age of the donor rat. The spatial distribution of myofibroblasts and apoptotic cells was distinct. Fibroblasts from granulation tissue and skin explants were placed in a collagen gel contraction assay prior to the 5th passage to determine their in vitro contractility. While granulation tissue fibroblasts from young and old rats showed similar collagen gel contractility, skin fibroblasts from old rats displayed greater collagen gel contractile behavior than young skin fibroblasts. Greater gel contractility of fibroblasts from old rats appeared to result, in large part, from the ability of those cells to cause generalized gel degradation. Gelatin zymography indicated a greater abundance of matrix metalloproteinase-2 in supernatants from gels containing skin fibroblasts from old rats. Taken together, these results suggest that the age-associated healing delay in the rat may not be related to the appearance or abundance of distinct myofibroblast or apoptotic cell populations. Proteolysis may have a significant role in delayed wound healing in aged animals.

Metabolic disharmony and mortality

The concept of 'metabolic harmony' is introduced and conceptualized as the state in which indices of metabolic activity (i.e., serum glucose, cholesterol, systolic and diastolic blood pressure, body mass index) within an individual attain their expected values given the individual values on related variables. Its complement, 'metabolic disharmony' (i.e., the extent to which an individual's 'profile' of metabolic variables is jointly unusual in relation to their expected values) is operationalized via Mahalanbis' D(2 )statistic calculated on these indices of metabolic activity (plus age and sex). Analysis of a large (N = 5209) longitudinal (32 years) cohort study shows that, independent of the linear and quadratic effects of the aforementioned metabolic variables, the disharmony index (DI) significantly and strongly predicted hazard of death (chi(2)(1) = 20.05, P < 0.00005). That is, each 10 percentile increase in DI was associated with a 6.9% increase in the hazard rate. The association of DI to hazard rate was not materially altered when potential confounders (e.g., smoking status) were added to the model or when all subjects were included by imputing missing data. These results demonstrate that metabolic disharmony is associated with, and may cause, an increased hazard of death.

The male menopause and mood: testosterone decline and depression in the aging male--is there a link?

The objective of this study was to review the literature on the hormonal changes that occur in aging males in order to determine if testosterone declines in relation to depressed mood and if testosterone might prove useful in treatment of depression. Pertinent articles were identified through a MEDLINE search from 1966 to 1999 and by careful review of the bibliographies of articles most relevant to the topic. There is a moderate decline of total testosterone and more significant decline of bioavailable testosterone in aging males. Elderly males who are depressed appear to have the lowest testosterone levels. In eugonadal males, testosterone replacement does not have a significant effect on mood; in hypogonadal males, some studies show an effect whereas others do not. In several small studies of depressed hypogonadal males, testosterone was effective in alleviating depression. Major side effects of testosterone include increased hematocrit and potential effects on the prostate and lipid metabolism. Testosterone replacement as primary or adjuvant treatment of depression may prove useful in elderly, hypogonadal males who fail to respond to conventional antidepressants. Further studies are needed to confirm these initial impressions.

Decreased expression of voltage- and Ca(2+)-activated K(+) channels in coronary smooth muscle during aging

Aging is the main risk factor for coronary artery disease. One characteristic of aging coronary arteries is their enhanced contractile responses to endothelial vasoconstricting factors, which increase the risk of coronary vasospasm in older people. Because large-conductance voltage- and Ca(2+)-activated K(+) channels (MaxiK) are key regulators of vascular tone, we explored the possibility that this class of channels is diminished with increasing age. Using site-directed antibodies recognizing the pore-forming alpha subunit and electrophysiological methods, we demonstrate that the number of MaxiK channels is dramatically diminished in aged coronary arteries from old F344 rats. Channel density was reduced from 52+/-9 channels/pF (3 months old) to 18+/-5 channels/pF (25 to 30 months old), which represents a 65% reduction in the older population. Pixel intensity of Western blots was also diminished by approximately 50%. Moreover, the age-related decrease in the channel protein expression was also evident in humans, which showed approximately 80% reduction in 61- to 70-year-old subjects compared with 3- to 18-year-old youngsters and approximately 45% reduction compared with 19- to 56-year-old adults. In agreement with a reduction of MaxiK channel numbers in aging coronary arteries, old coronary arteries from F344 rats contract less effectively ( approximately 70% reduction) than young coronary arteries when exposed to the MaxiK channel blocker iberiotoxin. The contraction studies indicate that under physiological conditions, MaxiK channels are tonically active, serving as a hyperpolarizing force that opposes contraction. Thus, reduced expression of MaxiK channels in aged coronary arteries would lead to a decreased vasodilating capacity and increased risk of coronary spasm and myocardial ischemia in older people.

The impact of the GH-IGF-I axis on gonadotropin secretion: inferences from animal models

Given the tight, temporal coupling between growth and reproductive development, the idea that a common signal may regulate both adolescent growth and the initiation of puberty has been the focus of much research. Since the rate-limiting step for the onset of puberty is the appropriate hypothalamic secretion of gonadotropin-releasing hormone (GnRH), any factor important for the initiation of puberty must affect GnRH pulsatility. This review examines the hypothesis that GH and/or IGF-I are growth-related signals that regulate the release of GnRH, initiating puberty. By extension, this review also addresses the hypothesis that the GH axis also impacts GnRH and gonadotropin secretion in post-pubertal individuals and, thus, affects the maintenance of fertility in adults. The review examines data from a range of animal models employing a number of different strategies which directly manipulate the activity of either GH or IGF-I. The success of these strategies for producing the desired effects on the GH-IGF-I axis is somewhat variable. Although IGF-I may only play a permissive role in the maintenance of adult fertility, acting at the level of the gonad to increase sensitivity to gonadotropin stimulation, the data indicate that IGF-I is essential for reproductive maturation. However, in addition to its well-documented effects on the gonad, the specific mode of action of IGF-I on the neuroendocrine hypothalamus and GnRH pulsatility remains to be determined. Available evidence suggests that such action by IGF-I may be mediated through neurotransmitter effects on GnRH neurons, changing the availability of metabolic substrates for neuronal activity, or remodeling of synaptic input into GnRH neurons.

Translating basic aging research into geriatric health care

Aging processes are amenable to molecular genetic analyses. Two aspects of such research have been selected for discussion in this paper because of current great interest and their relevance to human aging. Studies on telomeres have revealed new insights on the control of cellular replicative senescence and provided a means to extend the cell's life span during in vitro cultivation. Emerging studies on genetic biomarkers have identified genes that appear to be associated with longevity or with risk factors for aging-related diseases, and raised considerations of ways to reduce disease expression. An interchange between basic scientists and clinicians would encourage new thoughts on the feasibility of translating these fundamental studies into interventions that promote healthier longevity.

Neuroprotection by estradiol

This review highlights recent evidence from clinical and basic science studies supporting a role for estrogen in neuroprotection. Accumulated clinical evidence suggests that estrogen exposure decreases the risk and delays the onset and progression of Alzheimer's disease and schizophrenia, and may also enhance recovery from traumatic neurological injury such as stroke. Recent basic science studies show that not only does exogenous estradiol decrease the response to various forms of insult, but the brain itself upregulates both estrogen synthesis and estrogen receptor expression at sites of injury. Thus, our view of the role of estrogen in neural function must be broadened to include not only its function in neuroendocrine regulation and reproductive behaviors, but also to include a direct protective role in response to degenerative disease or injury. Estrogen may play this protective role through several routes. Key among these are estrogen dependent alterations in cell survival, axonal sprouting, regenerative responses, enhanced synaptic transmission and enhanced neurogenesis. Some of the mechanisms underlying these effects are independent of the classically defined nuclear estrogen receptors and involve unidentified membrane receptors, direct modulation of neurotransmitter receptor function, or the known anti-oxidant activities of estrogen. Other neuroprotective effects of estrogen do depend on the classical nuclear estrogen receptor, through which estrogen alters expression of estrogen responsive genes that play a role in apoptosis, axonal regeneration, or general trophic support. Yet another possibility is that estrogen receptors in the membrane or cytoplasm alter phosphorylation cascades through direct interactions with protein kinases or that estrogen receptor signaling may converge with signaling by other trophic molecules to confer resistance to injury. Although there is clear evidence that estradiol exposure can be deleterious to some neuronal populations, the potential clinical benefits of estrogen treatment for enhancing cognitive function may outweigh the associated central and peripheral risks. Exciting and important avenues for future investigation into the protective effects of estrogen include the optimal ligand and doses that can be used clinically to confer benefit without undue risk, modulation of neurotrophin and neurotrophin receptor expression, interaction of estrogen with regulated cofactors and coactivators that couple estrogen receptors to basal transcriptional machinery, interactions of estrogen with other survival and regeneration promoting factors, potential estrogenic effects on neuronal replenishment, and modulation of phenotypic choices by neural stem cells.

Age-related changes of serum sex hormones, insulin-like growth factor-1 and sex-hormone binding globulin levels in men: cross-sectional data from a healthy male cohort

The age-dependent decline of the gonadal and somatotopic axis has been causally linked to frailty in the elderly by their effects on muscle mass and bone mineral density. However, for healthy men data on serum oestrogens and androgens, as well as IGF-1, as a common outcome measure covering the whole adult age range are scarce. We therefore studied healthy, nonobese male subjects between 20 and 80 years of age to asses their morning concentrations of total (T), free (FT), bioavailable testosterone (bT), oestradiol (E2), bioavailable oestradiol (bE2), oestrone (E1), sex-hormone binding globulin (SHBG), and insulin-like growth factor 1 (IGF-1). Five hundred and seventy-two male healthy volunteers with a BMI < 30 kg/m2 recruited from regular blood donors and senior sports clubs participated in the study. Serum samples were obtained during morning hours and T, FT, E2, E1, SHBG, albumin and IGF-1 were measured by radio-immunoassay systems. In addition, bT and bE2 were calculated. A potential relationship between sex hormones and IGF-1 was tested by multiple regression analysis including age and BMI. Ageing was negatively related to serum levels of sex steroids and IGF-1 (both P < 0.0001) with a mean decrease (youngest vs. oldest) of 51% for T, 64% for FT, 78% for bT, 32% for E2, 62% for bE2, 29% for E1 and 51% for IGF-1 starting in early adulthood whereas SHBG increased after the 5th decade of life (ANOVA P < 0.001). The decline of sex hormones and IGF-1 remained relatively unchanged after adjustment for BMI. Multiple regression analysis revealed an age-and BMI- independent association between oestradiol and IGF-1. In contrast to the female situation sex hormones in healthy, nonobese men decline continuously with age. This process has already started in the third decade, and is paralleled by a decline of IGF-1 serum levels leading to a substantial proportion of elderly men with markedly lowered serum levels of bioavailable sex hormones and IGF-1 compared to the young adult male range. With the recent demonstration of beneficial effects of androgen replacement therapy in healthy males on general well being, muscle mass and bone mineral density the present data may underline the importance of more detailed studies on the biological significance of hormonal changes in men with age.

Recent neuroendocrine facets of male reproductive aging

We recently identified consistent attenuation of LH and testosterone secretory pulse amplitude and associated disruption of their orderly patterns of release in healthy older men. These dynamic changes emerge despite young-adult concentrations of LH and total testosterone. Moreover, we could document disruption of synchrony between LH secretion and oscillations in FSH, prolactin, sleep-stage and NPT (nocturnal penile tumescence), thus pointing to loss of coordinate neurohormone outflow. Such data suggest that CNS-hypothalamically based regulatory defects may be important in aging, as inferred indirectly in the old male rat and mouse more than 15 years ago. How such alterations are related to specific hypothalamic neurotransmitter changes in aging will be critical to unravel.

The somatopause: to treat or not to treat?

There is much evidence that some aspects of ageing are similar to those observed in selective hormone deficiencies during adulthood. Replacement therapy in hypogonadism and/or growth hormone (GH) deficiency in adulthood is very successful in reversing the related clinical symptomatology. However, preliminary studies of GH treatment in the normal elderly have been largely disappointing: an increase in muscle mass is only accompanied by improved muscle strength if exercise is also increased during this period. No real benefit of GH therapy, additional to that of exercise, has been reported. Epidemiological studies indicate a relationship between high-normal insulin-like growth factor-I levels and cancer development. No definitive answers can presently be given regarding the safety of long-term GH therapy in otherwise healthy individuals during the somatopause.

Male predominance in hepatocellular carcinoma: new insight and a possible therapeutic alternative

Hepatocellular carcinoma is one of the most common cancers in the world. The male to female ratio is 3-6 to 1 in patients with hepatocellular carcinoma. Although steroid hormones and receptors have been examined extensively for their role in the growth regulation of hepatocellular carcinoma, the direct stimulation of hepatocellular carcinoma by steroid hormones still awaits elucidation. On the other hand, clinical trials using antagonists for steroid hormones to treat hepatocellular carcinoma were found to be mostly ineffective. Recently it has been found that 2-methoxyestradiol - an estrogen metabolite - is effective in growth inhibition of various tumor cells as well as in angiogenesis inhibition. Since estrogen is metabolized in the liver, it is conceivable that females with menstruation cycles have more estrogen metabolized in their liver, consequently more 2-methoxyestradiol produced which could inhibit tumor growth in situ. We propose that the low incidence and mortality of hepatocellular carcinoma found in females may have resulted from the high levels of 2-methoxyestradiol produced in the liver during their reproductive years. Consequently, the growth of hepatocellular carcinoma in females is delayed significantly as compared to males. The potential of using 2-methoxyestradiol for treatment of patients with hepatocellular carcinoma after resection of tumor should be explored.

Stereologic study of the hypothalamic infundibular nucleus in young and older women

Aging in women is associated with dramatic changes in neuronal morphology and neuropeptide gene expression in the medial basal hypothalamus. There is hypertrophy of neurons expressing substance P and neurokinin B gene transcripts in the infundibular (arcuate) nucleus, accompanied by increased tachykinin gene expression. In addition, gonadotropin-releasing hormone (GnRH) gene expression is increased in a separate subpopulation of neurons within the medial basal hypothalamus. In contrast, the number of neurons expressing proopiomelanocortin (POMC) mRNA in the infundibular nucleus of older women is decreased. To determine whether neuronal degeneration contributes to these phenomena, unbiased stereologic methods were used to compare the total number of infundibular neurons between groups of young (premenopausal) and older (postmenopausal) women. There was no significant difference in the total number of infundibular neurons between young (520,000 +/- 42,000 neurons, mean +/- SEM) and older women (505,000 +/- 51,000 neurons, mean +/- SEM). The mean volume of neuronal somata, however, was increased by 40% in the older women (young, 1,860 +/- 180 microm(3) vs. older, 2,610 +/- 230 microm(3), mean +/- SEM, P < 0.05). These data demonstrate that neuronal hypertrophy in older women is not accompanied by degeneration of the infundibular nucleus. We conclude that the loss of menstrual cyclicity in middle-aged women cannot be explained by loss of neurons within the hypothalamic control center for reproduction.

Time course of fenretinide-induced modulation of circulating insulin-like growth factor (IGF)-i, IGF-II and IGFBP-3 in a bladder cancer chemoprevention trial

The insulin-like growth factor (IGF) system is widely involved in human carcinogenesis. A significant association between high circulating IGF-I concentrations and an increased risk of lung, colon, prostate and pre-menopausal breast cancer has recently been reported. Lowering plasma IGF-I may thus represent an attractive strategy to be pursued for chemopreventive purposes. We have previously shown that the synthetic retinoid fenretinide (4-HPR) lowers plasma IGF-I in pre-menopausal breast cancer patients. We investigated the effect of fenretinide on circulating IGF-I, IGF-II and IGFBP-3 measured at yearly intervals during the 2-year treatment period and one year after treatment discontinuation in a predominantly male population of patients with superficial bladder cancer. Repeated measures analysis, after adjustment for age, body mass index (BMI) and year of study, showed a significant effect of fenretinide on IGF-I levels, which were further lowered after the second year of treatment and only partially recovered after drug discontinuation. Differently from breast cancer patients, the effect of fenretinide was not modified by age. No significant effect was evident on IGFBP-3, IGF-II and the IGF-I+IGF-II/IGFBP-3 molar ratio, expressing the tissue availability of the mitogenic peptides, although IGF-II and the molar ratio were lowered by treatment by an overall mean of 16% and 15%, respectively. Given the increasingly recognized importance of circulating IGFs in the pathogenesis of different solid tumors, our findings strengthen the rationale for studying fenretinide as a chemopreventive agent.

Dietary protein deficiency induces osteoporosis in aged male rats

Low dietary intake is common in elderly males with low femoral neck areal bone mineral density (BMD). To evaluate the selective influence of a low-protein diet in the pathogenesis of osteoporosis in males and to uncover early and late adaptation of bone cells to protein deficiency, 8-month-old male rats were pair-fed a control (15% casein) or isocaloric low-protein (2.5% casein) diet for 1 or 7 months. BMD, bone ultimate strength, stiffness, and absorbed energy were measured in tibia proximal metaphysis and diaphysis. After double-labeling, histomorphometric analysis was performed at the same sites. Serum osteocalcin, insulin-like growth factor I (IGF-I), and urinary deoxypyridinoline excretion were measured. In proximal tibia, isocaloric low-protein diet significantly decreases BMD (12%), cancellous bone mass (71%), and trabecular thickness (Tb.Th; 30%), resulting in a significant reduction in ultimate strength (27%). In cortical middiaphysis, a low-protein diet decreases BMD (9%) and enlarges the medullary cavity (36%), leading to cortical thinning and lower mechanical strength (20%). In cancellous bone, protein deficiency transiently depresses the bone formation rate (BFR; 60%), osteoid seam thickness (15%), and mineral apposition rate (MAR; 20%), indicating a decrease in osteoblast recruitment and activity. Cortical loss (15%) results from an imbalance between endosteal modeling drifts with impaired BFR (70%). From the first week of protein deficiency, osteocalcin and IGF-I levels drop significantly. Bone resorption activity and urinary deoxypyridinoline remain unchanged throughout the experiment. Protein deficiency in aged male rats induces cortical and trabecular thinning, and decreases bone strength, in association with a remodeling imbalance with a bone formation impairment and a decrease in IGF-I levels.

Evaluation of the applicability of HRT as a preservative of muscle strength in women

OBJECTIVES

To review the studies that have been undertaken on the effects of postmenopausal hormone replacement therapy (HRT); especially oestrogen (+progestin) regimens on the preservation of muscle strength. Current knowledge of the mechanisms and actions of steroid- and sex hormones on skeletal muscle tissue will be used in an attempt to clarify the mechanism of action of a possible effect. The objective is to arrive at an agreement on whether or not postmenopausal oestrogen administration has a positive influence on skeletal muscle tissue.

METHODS

Peer-reviewed publications were assessed.

RESULTS

An age-related decrement in muscle strength can be found in both men and women. However, in women, an extra decline can be observed around the time of menopause. A possible relationship between the additional diminution in muscle strength and altered hormone concentrations after the onset of menopause has been suggested. Since women nowadays spend one-third of their life postmenopausal, it is extremely important to keep the decline in muscle mass as small as possible. Besides the continuation of a physically active lifestyle, HRT was suggested to serve as a protective mechanism. Although, the usefulness of HRT as a preservative of muscle strength appeared controversial.

CONCLUSIONS

Skeletal muscle strength is sensitive to training up to a high age, though continuation of physical activity does not appear to protect skeletal muscles completely from age-related decrements. Therefore, the development of another preventive method would be useful. Considering the present knowledge it has all the hallmarks that HRT can be a useful tool in the maintenance of muscle strength in postmenopausal women. None the less, further research is necessary to endorse this theory.

Age-dependent changes in sperm production, semen quality, and testicular volume in the black-footed ferret (Mustela nigripes)

The black-footed ferret (Mustela nigripes), which was extirpated from its native North American prairie habitat during the 1980s, is being reintroduced to the wild because of a successful captive-breeding program. To enhance propagation, the reproductive biology of this endangered species is being studied intensively. The typical life span of the black-footed ferret is approximately 7 yr. Female fecundity declines after 3 yr of age, but the influence of age on male reproduction is unknown. In this study, testis volume, seminal traits, sperm morphology, and serum testosterone were compared in 116 males from 1 to 7 yr of age living in captivity. Results demonstrated that testes volume during the peak breeding season was similar (P > 0.05) among males 1 to 5 yr of age, reduced (P < 0.05) among males 6 yr of age, and further reduced (P < 0.05) among males 7 yr of age. Motile sperm/ejaculate was similar in males 1 to 6 yr of age but diminished (P < 0.05) in those 7 yr of age. Males at 6 and 7 yr of age produced fewer (P < 0.05) structurally normal sperm than younger counterparts; however, serum testosterone concentrations were not reduced (P > 0.05) in older males. Histological comparison of testicular/epididymal tissue from 5- and 7-yr-old black-footed ferrets confirmed that the interval between these two ages may represent a transitional period to reproductive senescence. In summary, functional reproductive capacity of male black-footed ferrets exceeds that of females by at least 2 yr. Testes and seminal quality are indistinguishable among males 1 to 5 yr of age, with progressive reproductive aging occurring thereafter.

Depressed mood and body mass index as predictors of muscle strength decline in old men

OBJECTIVE

To study depressed mood as a predictor of strength decline within body weight categories over a 3-year follow-up period.

DESIGN

A prospective cohort study over 3 years.

SETTING

Honolulu, Hawaii.

PARTICIPANTS

The subjects were 2275 men participating in the Honolulu Heart Program with an average age of 77.1 years (range 71-92 years), who were not cognitively impaired at baseline (Exam 4), and who participated in maximal hand grip strength measurements at baseline and 3 years later (Exam 5).

MEASUREMENTS

Hand grip strength was measured using a dynamometer. Depressive symptoms were studied using an 11-item version of Center for Epidemiologic Studies Depression Scale with 9 as a cutoff. Body weight categories were formed on the basis of body mass index (BMI) (BMI = weight/height2; underweight: BMI < 20; normal weight: BMI 20-24.99, overweight: BMI > or = 25).

MAIN RESULTS

At baseline, 9.4% of the participants were rated as having depressed mood. The mean individual strength change over 3 years was - 6.9% (standard deviation 14.0). Steep strength decline was determined as losing > or = 14% (lowest quartile). The proportions of those with steep strength decline in the groups based on combined distributions of BMI and depressed mood were: underweight/ depressed (n = 22) 41%, underweight/not depressed (n = 200) 28%, normal weight/depressed (n = 127) 30%, normal weight/not depressed (n = 1181) 25%, overweight/depressed (n = 55) 31%, overweight/not depressed (n = 675, referent) 21%. After adjusting for baseline strength, age, height, sociodemographic variables and diseases, the odds ratio for steep strength decline was more than four times greater among those who were depressed and underweight, and twice as great among people who were depressed and normal weight compared with those who were nondepressed and overweight. The risks of nondepressed under- and normal weight people and depressed overweight people did not differ from the reference group.

CONCLUSIONS

Depressed mood was associated with increased risk of steep strength decline, in particular in older men with low body weight. Low body weight in combination with depressed mood may be an indicator of frailty or severe disease status that leads to accelerated strength loss and disability.

Regulation of neurotrophin signaling in aging sensory and motoneurons: dissipation of target support?

A hallmark of senescence is sensorimotor impairment, involving locomotion and postural control as well as fine-tuned movements. Sensory and motoneurons are not lost to any significant degree with advancing age, but do show characteristic changes in gene-expression pattern, morphology, and connectivity. This review covers recent experimental findings corroborating that alterations in trophic signaling may induce several of the phenotypic changes seen in primary sensory and motoneurons during aging. Furthermore, the data suggests that target failure, and/or breakdown of neuron-target interaction, is a critical event in the aging process of sensory and motoneurons.

The roles of prolactin, growth hormone, insulin-like growth factor-I, and thyroid hormones in lymphocyte development and function: insights from genetic models of hormone and hormone receptor deficiency

An extensive literature suggesting that PRL, GH, IGF-I, and thyroid hormones play an important role in immunity has evolved. Because the use of one or more of these hormones as immunostimulants in humans is being considered, it is of critical importance to resolve their precise role in immunity. This review addresses new experimental evidence from analysis of lymphocyte development and function in mice with genetic defects in expression of these hormones or their receptors that calls into question the presumed role played by some of these hormones and reveals unexpected effects of others. These recent findings from the mutant mouse models are integrated and placed in context of the wider literature on endocrine-immune system interactions. The hypothesis that will be developed is that, with the exception of a role for thyroid hormones in B cell development, PRL, GH, and IGF-I are not obligate immunoregulators. Instead, they apparently act as anabolic and stress-modulating hormones in most cells, including those of the immune system.

An introduction to endocrine modulators

Keywords. Endocrine modulation; target sites; endocrine modulating effects; humans; reproduction; marine invertebrates; wildlife

Leptin and aging: correlation with endocrine changes in male and female healthy adult populations of different body weights

Aging is associated with changes in plasma levels of several hormones. There are conflicting reports on whether circulating leptin levels change during aging, the possible explanation for which is that alterations in adiposity and body mass index (BMI) also occur. In this study we measured plasma leptin and other hormonal parameters known to influence leptin in 150 men and 320 women of a wide age (18-77 yr) and BMI (18.5-61.1 kg/m2) range. Subjects of each gender were separated into 2 groups of similar BMI, i.e. nonobese (BMI, <30) and obese (BMI, >30), and treated separately. Statistical analysis was performed, treating each group of subjects as a whole population or divided into age groups (<30, 30-50, and >50 yr). BMI-adjusted leptin levels were progressively lower with increasing age in women, with a consistent fall after menopause (-21%; P < 0.001); in men, leptin levels also tended to be lower in subjects more than 50 yr of age, but the reduction was not significant. Multiple linear regression analysis, performed on subjects treated either as a whole population or divided into obese and nonobese, showed that in both genders BMI and age were independent contributors of leptin levels, and there was an inverse relationship between leptin and age in both obese (standardized coefficient beta = -0.25 in women and -0.23 in men; P < 0.01) and nonobese (-0.22 in women and -0.20 in men; P < 0.05) subjects. The correlation of leptin and age with plasma levels of sex and thyroid hormones, GH, insulin-like growth factor I, PRL, and insulin was also evaluated. The variables that correlated with leptin were included in a multiple regression model that included BMI and age. Testosterone in men (-0.43 in nonobese and -0.19 in obese; P < 0.05) and estradiol in women (0.22 in nonobese and 0.24 in obese; P < 0.05) were important contributors to leptin levels; also, dehydroepiandrosterone sulfate in obese women (-0.16) and sex hormone-binding globulin in obese subjects of both genders (0.15 in women and 0.19 in men) were significant determinants in the model. However, none of the hormonal parameters abolished the negative correlation between leptin and age or the gender difference in leptin levels. In conclusion, our data show that in adult humans of different body weight, serum leptin gradually declines during aging; leptin reduction is higher in women than in men, but it is independent from BMI and other age-related endocrine changes.

Endocrine modulators in the food chain and environment

Recently, considerable attention has been focused on certain environmental contaminants--"endocrine disruptors"--of industrial origin that may mimic the action of sex hormones. Natural compounds and their effects on other types of hormonal activity (eg, on adrenal or thyroid function) have for some reason not provoked similar attention. As exemplified by tributyltin and certain bioaccumulating chlorinated compounds, available evidence indicates that "endocrine disruption" caused by xenobiotics is primarily an ecotoxicologic problem. In mammals, certain phenylmethyl-substituted siloxanes have been found to be by far the most potent endocrine disrupters among various synthetic xenobiotics. On the other hand, it has not been possible to scientifically substantiate either certain alarming reports of powerful synergistic effects between chlorinated pesticides or the alleged adverse effects on the male reproductive tract in rodents (induced by alkylphenols and plasticizers at extremely low exposures). Whereas there is compelling evidence that estrogens in certain foods and herbal medicines can induce hormonal changes in women as well as overt toxicity in men, existing data are insufficient to support a causal relationship between exposure of the general human population to nonpharmaceutical industrial chemicals and adverse effects operating via the endocrine system. Moreover, in terms of magnitude and extent, all such exposures to so-called endocrine disruptors are dwarfed by the extensive use of oral contraceptives and estrogens for treatment of menopausal and postmenopausal disorders. Also, the exposure to hormonally active xenobiotics is virtually insignificant when compared with the intake of the phytoestrogens that are present in food and beverages, and it is even more insignificant when compared with certain herbal potions used in "alternative medicine." Furthermore, while there has been much concern about negligible exposures to xenobiotics with weak hormonelike activities, the potent endocrine disruptor licorice is freely given to children. Long-term exposure to this substance induces severe toxic symptoms of mineral corticoid hormone imbalance. Although exposures to xenobiotics and many natural compounds occur by identical routes of administration and may contribute to the same toxicological end point, they are, regrettably, judged by completely different standards. As is the case with all other chemicals, rational risk assessment and risk management of man-made and natural endocrine modulators must be based on the mode of action and dose-response relationships. Such end points as the induction of reproductive developmental effects, cancer, etc, relating to actual exposures must also be taken into consideration.

The question of a link between insulin-like growth factor physiology and neoplasia

The results of both population and laboratory studies suggest that the physiology of insulin-like growth factors (IGFs) has important influences on cancer biology and cancer risk. This review highlights recent laboratory and epidemiological results in this rapidly evolving area of investigation. There is no direct evidence to suggest that growth hormone (GH) treatment of GH-deficient patients increases their risk of neoplasia, but recent research reinforces the need for careful surveillance. The monitoring of serum IGF-I levels may be advisable to help avoid inadvertent over-treatment, particularly in individuals undergoing long-term GH replacement therapy.

Growth hormone and ageing

The proportion of elderly people is steadily growing in Western societies. The result is a disproportionate accumulation of the oldest and most vulnerable sector of the population, suffering from frailty-associated disorders and cardiovascular diseases. Growth hormone (GH) secretion declines progressively during adulthood. In ageing and severe GH deficiency, an individual's muscle mass, muscle strength and bone mass are decreased, and the relative proportion of total and visceral fat is increased. An association between reduced GH levels and the catabolism of ageing has been suggested. GH or GH secretagogue treatment could be of value to minimize the health-related consequences associated with the ageing process.

Insulin-Like Growth Factor–Binding Protein-3 Is Associated With the Presence and Extent of Coronary Arteriosclerosis

Abstract —Aging is associated with the progression of arteriosclerosis and the decline of several endocrine functions. We therefore investigated the association of coronary arteriosclerosis with hormones, the serum concentrations of which change during aging. Coronary angiograms of 189 men <70 years old were evaluated by 3 semiquantitative score systems to estimate the extent of focal and diffuse vessel wall alterations. Fasting sera were analyzed for levels of glucose, lipids, thyroid-stimulating hormone, insulin, insulin-like growth factor I (IGF-I), IGF-binding protein-3 (IGFBP-3), dehydroepiandrosterone sulfate (DHEAS), testosterone, and sex hormone–binding globulin (SHBG). After adjustment for age, body mass index, and waist-to-hip ratio, 92 patients with ≥1 stenoses >70% differed from 97 patients without such focal lesions by higher serum levels of glucose, total and LDL cholesterol, and apolipoprotein (apo) B, as well as by lower serum levels of IGFBP-3. Multivariate analyses revealed significant and independent correlations of all 3 coronary scores with LDL cholesterol (or apoB) and IGFBP-3; of 2 coronary scores with age, glucose, and insulin; and of 1 score with IGF-I. No significant correlations existed for waist-to-hip ratio (or body mass index) and DHEAS (or testosterone or SHBG). IGFBP-3 explained 9% to 14% and 3.5% to 10% of the variances of focal and diffuse lesions, respectively. In conclusion, IGFBP-3 and, with much less strength and consistency, insulin and IGF-I, but not markers of hypothyroidism, adrenopause, and andropause, have statistically significant and independent associations with coronary arteriosclerosis in men.