Effects of gender on neuroendocrine and metabolic counterregulatory responses to exercise in normal man

Differences in cardiac adaptation to exercise in male and female athletes assessed by noninvasive techniques: a state-of-the-art review

Athlete's heart is generally regarded as a physiological adaptation to regular training, with specific morphological and functional alterations in the cardiovascular system. Development of the noninvasive imaging techniques over the past several years enabled better assessment of cardiac remodeling in athletes, which may eventually mimic certain pathological conditions with the potential for sudden cardiac death, or disease progression. The current literature provides a compelling overview of the available methods that target the interrelation of prolonged exercise with cardiac structure and function. However, this data stems from scientific studies that included mostly male athletes. Despite the growing participation of females in competitive sport meetings, little is known about the long-term cardiac effects of repetitive training in this population. There are several factors-biochemical, physiological and psychological, that determine sex-dependent cardiac response. Herein, the aim of this review was to compare cardiac adaptation to endurance exercise in male and female athletes with the use of electrocardiographic, echocardiographic, and biochemical examination, to determine the sex-specific phenotypes, and to improve the healthcare providers' awareness of cardiac remodeling in athletes. Finally, we discuss the possible exercise-induced alternations that should arouse suspicion of pathology and be further evaluated.

Sexual Dimorphism in Substrate Metabolism During Exercise

During aerobic exercise, women oxidize significantly more lipids and less carbohydrates than men. This sexual dimorphism in substrate metabolism has been attributed, in part, to the observed differences in epinephrine and glucagon levels between men and women during exercise. To identify the underpinning candidate physiological mechanisms for these sex differences, we developed a sex-specific multi-scale mathematical model that relates cellular metabolism in the organs to whole-body responses during exercise. We conducted simulations to test the hypothesis that sex differences in the exercise-induced changes to epinephrine and glucagon would result in the sexual dimorphism of hepatic metabolic flux rates via the glucagon-to-insulin ratio (GIR). Indeed, model simulations indicate that the shift towards lipid metabolism in the female model is primarily driven by the liver. The female model liver exhibits resistance to GIR-mediated glycogenolysis, which helps maintain hepatic glycogen levels. This decreases arterial glucose levels and promotes the oxidation of free fatty acids. Furthermore, in the female model, skeletal muscle relies on plasma free fatty acids as the primary fuel source, rather than intramyocellular lipids, whereas the opposite holds true for the male model.

The endocrine pancreas during exercise in people with and without type 1 diabetes: Beyond the beta-cell

Although important for digestion and metabolism in repose, the healthy endocrine pancreas also plays a key role in facilitating energy transduction around physical exercise. During exercise, decrements in pancreatic β-cell mediated insulin release opposed by increments in α-cell glucagon secretion stand chief among the hierarchy of glucose-counterregulatory responses to decreasing plasma glucose levels. As a control hub for several major glucose regulatory hormones, the endogenous pancreas is therefore essential in ensuring glucose homeostasis. Type 1 diabetes (T1D) is pathophysiological condition characterised by a destruction of pancreatic β-cells resulting in pronounced aberrations in glucose control. Yet beyond the beta-cell perhaps less considered is the impact of T1D on all other pancreatic endocrine cell responses during exercise and whether they differ to those observed in healthy man. For physicians, understanding how the endocrine pancreas responds to exercise in people with and without T1D may serve as a useful model from which to identify whether there are clinically relevant adaptations that need consideration for glycaemic management. From a physiological perspective, delineating differences or indeed similarities in such responses may help inform appropriate exercise test interpretation and subsequent program prescription. With more complex advances in automated insulin delivery (AID) systems and emerging data on exercise algorithms, a timely update is warranted in our understanding of the endogenous endocrine pancreatic responses to physical exercise in people with and without T1D. By placing our focus here, we may be able to offer a nexus of better understanding between the clinical and engineering importance of AIDs requirements during physical exercise.

Analysis of sex-based differences in energy substrate utilization during moderate-intensity aerobic exercise

PURPOSE

To explore sex-based differences in energy substrate utilization during moderate-intensity aerobic exercise; to identify the underpinning candidate physiological mechanisms.

METHODS

Three databases were searched from inception to August 2020. Pertinent studies quantifying the utilization of substrates during moderate aerobic exercise in healthy men and reproductive-age women were considered. Studies conducted on sedentary/recreationally active and athletic populations were included and analyzed separately.

RESULTS

Thirty-five studies entered the meta-analysis (21 in sedentary/recreationally active, 14 in athletic populations). Compared to women, the respiratory exchange ratio was significantly higher both in sedentary (mean difference, MD: + 0.03; p < 0.00001) and athletic men (MD: + 0.02; p < 0.0001). Greater carbohydrate oxidation was observed both in sedentary (standardized MD, SMD: 0.53; p = 0.006) and athletic men (SMD: 1.24; p < 0.00001). Regarding lipid substrates, sedentary men oxidized less fat than women (SMD:  - 0.77; p = 0.0002), while no sex-based differences in fat oxidation were observed in athletes (SMD: 0.06; p = 0.77). Paucity of data prevented robust meta-analyses for protein sources. Sex hormones and different adrenergic activation were the most cited mechanisms to discuss sex-based differences.

CONCLUSIONS

Meta-analyses confirmed that men display greater reliance on carbohydrates while women rely more on lipids to sustain moderate aerobic exercise. The latter finding was not confirmed in athletes, a novel aspect of the present study. Mechanistically driven research is needed to further dissect the physiological underpinnings of sex differences in substrate utilization during aerobic exercise, especially for proteins, which are still less investigated than other substrates.

Starvation Ketosis and the Kidney

BACKGROUND

The remarkable ability of the body to adapt to long-term starvation has been critical for survival of primitive man. An appreciation of these processes can provide the clinician better insight into many clinical conditions characterized by ketoacidosis.

SUMMARY

The body adapts to long-term fasting by conserving nitrogen, as the brain increasingly utilizes keto acids, sparing the need for glucose. This shift in fuel utilization decreases the need for mobilization of amino acids from the muscle for purposes of gluconeogenesis. Loss of urinary nitrogen is initially in the form of urea when hepatic gluconeogenesis is dominant and later as ammonia reflecting increased glutamine uptake by the kidney. The carbon skeleton of glutamine is utilized for glucose production and regeneration of consumed HCO3-. The replacement of urea with NH4+ provides the osmoles needed for urine flow and waste product excretion. Over time, the urinary loss of nitrogen is minimized as kidney uptake of filtered ketone bodies becomes more complete. Adjustments in urine Na+ serve to minimize kidney K+ wasting and, along with changes in urine pH, minimize the likelihood of uric acid precipitation. There is a sexual dimorphism in response to starvation. Key Message: Ketoacidosis is a major feature of common clinical conditions to include diabetic ketoacidosis, alcoholic ketoacidosis, salicylate intoxication, SGLT2 inhibitor therapy, and calorie sufficient but carbohydrate-restricted diets. Familiarity with the pathophysiology and metabolic consequences of ketogenesis is critical, given the potential for the clinician to encounter one of these conditions.

The presence of 3-hydroxypropionate and 1,3-propanediol suggests an alternative path for conversion of glycerol to Acetyl-CoA

BACKGROUND

In our recent study using [U-13C3]glycerol, a small subset of hamsters showed an unusual profile of glycerol metabolism: negligible gluconeogenesis from glycerol plus conversion of glycerol to 1,3-propanediol (1,3PDO) and 3-hydroxypropionate (3HP) which were detected in the liver and blood. The purpose of the current study is to evaluate the association of these unusual glycerol products with other biochemical processes in the liver.

METHODS

Fasted hamsters received acetaminophen (400 mg/kg; n = 16) or saline (n = 10) intraperitoneally. After waiting 2 h, all the animals received [U-13C3]glycerol intraperitoneally. Liver and blood were harvested 1 h after the glycerol injection for NMR analysis and gene expression assays.

RESULTS

1,3PDO and 3HP derived from [U-13C3]glycerol were detected in the liver and plasma of eight hamsters (two controls and six hamsters with acetaminophen treatment). Glycerol metabolism in the liver of these animals differed substantially from conventional metabolic pathways. [U-13C3]glycerol was metabolized to acetyl-CoA as evidenced with downstream products detected in glutamate and β-hydroxybutyrate, yet 13C labeling in pyruvate and glucose was minimal (p < 0.001, 13C labeling difference in each metabolite). Expression of aldehyde dehydrogenases was enhanced in hamster livers with 1,3PDO and 3HP (p < 0.05).

CONCLUSION

Detection of 1,3PDO and 3HP in the hamster liver was associated with unorthodox metabolism of glycerol characterized by conversion of 3HP to acetyl-CoA followed by ketogenesis and oxidative metabolism through the TCA cycle. Additional mechanistic studies are needed to determine the causes of unusual glycerol metabolism in a subset of these hamsters.

Muscle fiber size in healthy children and adults in relation to sex and fiber types

BACKGROUND

In adult males, cross-sectional area (CSA) for type II muscle fibers is generally larger than for type I fibers. In this cross-sectional study the aim was to compare sex-related CSAs of various muscle fiber types during childhood-to-adulthood transition.

METHODS

Percutaneous biopsy samples were obtained from vastus lateralis in 10-y-old children (10 males and 5 females) and in young adults (9 males and 7 females). Fiber types were classified by myofibrillar ATPase and CSAs from NADH-dehydrogenase staining.

RESULTS

Type IIA were larger than type I fibers in adult males, but not in adult females or children (age x sex x fiber type, P < .002). When including all participants, body weight and sex explained 78% of the variation in type IIA CSA but only body weight contributed for type I.

CONCLUSIONS

Sex-specific patterns in CSA of the muscle fiber types appears to develop during the transition from childhood to adulthood.

REM sleep loss-induced elevated noradrenaline could predispose an individual to psychosomatic disorders: a review focused on proposal for prediction, prevention, and personalized treatment

Historically and traditionally, it is known that sleep helps in maintaining healthy living. Its duration varies not only among individuals but also in the same individual depending on circumstances, suggesting it is a dynamic and personalized physiological process. It has been divided into rapid eye movement sleep (REMS) and non-REMS (NREMS). The former is unique that adult humans spend the least time in this stage, when although one is physically asleep, the brain behaves as if awake, the dream state. As NREMS is a pre-requisite for appearance of REMS, the latter can be considered a predictive readout of sleep quality and health. It plays a protective role against oxidative, stressful, and psychopathological insults. Several modern lifestyle activities compromise quality and quantity of sleep (including REMS) affecting fundamental physiological and psychopathosomatic processes in a personalized manner. REMS loss-induced elevated brain noradrenaline (NA) causes many associated symptoms, which are ameliorated by preventing NA action. Therefore, we propose that awareness about personalized sleep hygiene (including REMS) and maintaining optimum brain NA level should be of paramount significance for leading physical and mental well-being as well as healthy living. As sleep is a dynamic, multifactorial, homeostatically regulated process, for healthy living, we recommend addressing and treating sleep dysfunctions in a personalized manner by the health professionals, caregivers, family, and other supporting members in the society. We also recommend that maintaining sleep profile, optimum level of NA, and/or prevention of elevation of NA or its action in the brain must be seriously considered for ameliorating lifestyle and REMS disturbance-associated dysfunctions.

GLP-1 Receptor in Pancreatic α-Cells Regulates Glucagon Secretion in a Glucose-Dependent Bidirectional Manner

Glucagon-like peptide 1 (GLP-1) is known to suppress glucagon secretion, but the mechanism by which GLP-1 exerts this effect is unclear. In this study, we demonstrated GLP-1 receptor (GLP-1R) expression in α-cells using both antibody-dependent and antibody-independent strategies. A novel α-cell-specific GLP-1R knockout (αGLP-1R^-/-) mouse model was created and used to investigate its effects on glucagon secretion and glucose metabolism. Male and female αGLP-1R^-/- mice both showed higher nonfasting glucagon levels than their wild-type littermates, whereas insulin and GLP-1 levels remained similar. Female αGLP-1R^-/- mice exhibited mild glucose intolerance after an intraperitoneal glucose administration and showed increased glucagon secretion in response to a glucose injection compared with the wild-type animals. Furthermore, using isolated islets, we confirmed that αGLP-1R deletion did not interfere with β-cell function but affected glucagon secretion in a glucose-dependent bidirectional manner: the αGLP-1R^-/- islets failed to inhibit glucagon secretion at high glucose and failed to stimulate glucagon secretion at very low glucose condition. More interestingly, the same phenomenon was recapitulated in vivo under hypoglycemic and postprandial (fed) conditions. Taken together, this study demonstrates that GLP-1 (via GLP-1R in α-cells) plays a bidirectional role, either stimulatory or inhibitory, in glucagon secretion depending on glucose levels.

New Zealand blackcurrant extract enhances fat oxidation during prolonged cycling in endurance-trained females

PURPOSE

New Zealand blackcurrant (NZBC) extract has previously been shown to increase fat oxidation during prolonged exercise, but this observation is limited to males. We examined whether NZBC intake also increases fat oxidation during prolonged exercise in females, and whether this was related to greater concentrations of circulating fatty acids.

METHODS

In a randomised, crossover, double-blind design, 16 endurance-trained females (age: 28 ± 8 years, BMI: 21.3 ± 2.1 kg·m-2, VO2max: 43.7 ± 1.1 ml·kg-1·min-1) ingested 600 mg·day-1 NZBC extract (CurraNZ™) or placebo (600 mg·day-1 microcrystalline cellulose) for 7 days. On day 7, participants performed 120 min cycling at 65% VO2max, using online expired air sampling with blood samples collected at baseline and at 15 min intervals throughout exercise for analysis of glucose, NEFA and glycerol.

RESULTS

NZBC extract increased mean fat oxidation by 27% during 120 min moderate-intensity cycling compared to placebo (P = 0.042), and mean carbohydrate oxidation tended to be lower (P = 0.063). Pre-exercise, plasma NEFA (P = 0.034) and glycerol (P = 0.051) concentrations were greater following NZBC intake, although there was no difference between conditions in the exercise-induced increase in plasma NEFA and glycerol concentrations (P > 0.05). Mean fat oxidation during exercise was moderately associated with pre-exercise plasma NEFA concentrations (r = 0.45, P = 0.016).

CONCLUSIONS

Intake of NZBC extract for 7 days elevated resting concentrations of plasma NEFA and glycerol, indicative of higher lipolytic rates, and this may underpin the observed increase in fat oxidation during prolonged cycling in endurance-trained females.

Sex-related differences in fuel utilization and hormonal response to exercise: implications for individuals with type 1 diabetes

Sex-related differences in metabolic and neuroendocrine response to exercise in individuals without diabetes have been well established. Men and women differ in fuel selection during exercise, in which women rely to a greater extent on fat oxidation, whereas males rely mostly on carbohydrate oxidation for energy production. The difference in fuel selection appears to be mediated by sex-related differences in hormonal (including catecholamines, growth hormone, and estrogen) response to different types and intensities of exercise. In general, men exhibit an amplified counter-regulatory response to exercise, with elevated levels of catecholamines compared with women. However, women exhibit greater sensitivity to the lipolytic action of the catecholamines and deplete less of their glycogen stores than men during exercise, which suggests that women may experience a greater defense in blood glucose control after exercise than men. Conversely, little is known about sex-related differences in response to exercise in individuals with type 1 diabetes (T1D). A single study investigating sex-related differences in response to moderate aerobic exercise in individuals with T1D found sex-related differences in catecholamine response and fuel selection, but changes in blood glucose were not measured. To our knowledge, there are no studies investigating sex-related differences in blood glucose responses to different types and intensities of exercise in individuals with T1D. This review summarizes sex-related differences in exercise responses that could potentially impact blood glucose levels during exercise in individuals with T1D and highlights the need for further research.

Could Age, Sex and Physical Fitness Affect Blood Glucose Responses to Exercise in Type 1 Diabetes?

Closed-loop systems for patients with type 1 diabetes are progressing rapidly. Despite these advances, current systems may struggle in dealing with the acute stress of exercise. Algorithms to predict exercise-induced blood glucose changes in current systems are mostly derived from data involving relatively young, fit males. Little is known about the magnitude of confounding variables such as sex, age, and fitness level-underlying, uncontrollable factors that might influence blood glucose control during exercise. Sex-related differences in hormonal responses to physical exercise exist in studies involving individuals without diabetes, and result in altered fuel metabolism during exercise. Increasing age is associated with attenuated catecholamine responses and lower carbohydrate oxidation during activity. Furthermore, higher fitness levels can alter hormonal and fuel selection responses to exercise. Compounding the limited research on these factors in the metabolic response to exercise in type 1 diabetes is a limited understanding of how these variables affect blood glucose levels during different types, timing and intensities of activity in individuals with type 1 diabetes (T1D). Thus, there is currently insufficient information to model a closed-loop system that can predict them accurately and consistently prevent hypoglycemia. Further, studies involving both sexes, along with a range of ages and fitness levels, are needed to create a closed-loop system that will be more precise in regulating blood glucose during exercise in a wide variety of individuals with T1D.

Exercise Lowers Plasma Angiopoietin-Like 2 in Men with Post-Acute Coronary Syndrome

Pro-inflammatory angiopoietin-like 2 (angptl2) promotes endothelial dysfunction in mice and circulating angptl2 is higher in patients with cardiovascular diseases. We previously reported that a single bout of physical exercise was able to reduce angptl2 levels in coronary patients. We hypothesized that chronic exercise would reduce angptl2 in patients with post-acute coronary syndrome (ACS) and endothelial dysfunction. Post-ACS patients (n = 40, 10 women) were enrolled in a 3-month exercise-based prevention program. Plasma angptl2, hs-CRP, and endothelial function assessed by scintigraphic forearm blood flow, were measured before and at the end of the study. Exercise increased VO₂peak by 10% (p<0.05), but did not significantly affect endothelial function, in both men and women. In contrast, exercise reduced angptl2 levels only in men (-26±7%, p<0.05), but unexpectedly not in women (+30±16%), despite similar initial levels in both groups. Exercise reduced hs-CRP levels in men but not in women. In men, levels of angptl2, but not of hs-CRP, reached at the end of the training program were negatively correlated with VO₂peak (r = -0.462, p = 0.012) and with endothelial function (r = -0.419, p = 0.033) measured at baseline: better initial cardiopulmonary fitness and endothelial function correlated with lower angptl2 levels after exercise. Pre-exercise angptl2 levels were lower if left ventricular ejection time was long (p<0.05) and the drop in angptl2 induced by exercise was greater if the cardiac output was high (p<0.05). In conclusion, in post-ACS men, angptl2 levels are sensitive to chronic exercise training. Low circulating angptl2 reached after training may reflect good endothelial and cardiopulmonary functions.

Strategies and methods to study female-specific cardiovascular health and disease: a guide for clinical scientists

BACKGROUND

In 2001, the Institute of Medicine's (IOM) report, "Exploring the Biological Contributions to Human Health: Does Sex Matter?" advocated for better understanding of the differences in human diseases between the sexes, with translation of these differences into clinical practice. Sex differences are well documented in the prevalence of cardiovascular (CV) risk factors, the clinical manifestation and incidence of cardiovascular disease (CVD), and the impact of risk factors on outcomes. There are also physiologic and psychosocial factors unique to women that may affect CVD risk, such as issues related to reproduction.

METHODS

The Society for Women's Health Research (SWHR) CV Network compiled an inventory of sex-specific strategies and methods for the study of women and CV health and disease across the lifespan. References for methods and strategy details are provided to gather and evaluate this information. Some items comprise robust measures; others are in development.

RESULTS

To address female-specific CV health and disease in population, physiology, and clinical trial research, data should be collected on reproductive history, psychosocial variables, and other factors that disproportionately affect CVD in women. Variables related to reproductive health include the following: age of menarche, menstrual cycle regularity, hormone levels, oral contraceptive use, pregnancy history/complications, polycystic ovary syndrome (PCOS) components, menopause age, and use and type of menopausal hormone therapy. Other factors that differentially affect women's CV risk include diabetes mellitus, autoimmune inflammatory disease, and autonomic vasomotor control. Sex differences in aging as well as psychosocial variables such as depression and stress should also be considered. Women are frequently not included/enrolled in mixed-sex CVD studies; when they are included, information on these variables is generally not collected. These omissions limit the ability to determine the role of sex-specific contributors to CV health and disease. Lack of sex-specific knowledge contributes to the CVD health disparities that women face.

CONCLUSIONS

The purpose of this review is to encourage investigators to consider ways to increase the usefulness of physiological and psychosocial data obtained from clinical populations, in an effort to improve the understanding of sex differences in clinical CVD research and health-care delivery for women and men.

Sex hormones and macronutrient metabolism

The biological differences between males and females are determined by a different set of genes and by a different reactivity to environmental stimuli, including the diet, in general. These differences are further emphasized and driven by the exposure to a different hormone flux throughout the life.

These differences have not been taken into appropriate consideration by the scientific community. Nutritional sciences are not immune from this “bias” and when nutritional needs are concerned, females are considered only when pregnant, lactating or when their hormonal profile is returning back to “normal,” i.e., to the male-like profile.

The authors highlight some of the most evident differences in aspects of biology that are associated with nutrition.

This review presents and describes available data addressing differences and similarities of the “reference man” vs. the “reference woman” in term of metabolic activity and nutritional needs. According to this assumption, available evidences of sex-associated differences of specific biochemical pathways involved in substrate metabolism are reported and discussed. The modulation by sexual hormones affecting glucose, amino acid and protein metabolism and the metabolization of nutritional fats and the distribution of fat depots, is considered targeting a tentative starting up background for a gender concerned nutritional science.

Effect of antecedent moderate-intensity exercise on the glycemia-increasing effect of a 30-sec maximal sprint: a sex comparison

This study investigated whether a prior bout of moderate-intensity exercise attenuates the glycemia-increasing effect of a maximal 30-sec sprint. A secondary aim was to determine whether the effect of antecedent exercise on the glucoregulatory response to sprinting is affected by sex. Participants (men n = 8; women n = 7) were tested on two occasions during which they either rested (CON) or cycled for 60-min at a moderate intensity of ~65% (EX) before performing a 30-sec maximal cycling effort 195 min later. In response to the sprint, blood glucose increased to a similar extent between EX and CON trials, peaking at 10 min of recovery, with no difference between sexes (P > 0.05). Blood glucose then declined at a faster rate in EX, and this was associated with a glucose rate of disappearance (R_d) that exceeded the glucose rate of appearance (R_a) earlier in EX compared with CON, although the overall glucose R_a and R_d profile was higher in men compared with women (P < 0.05). The response of growth hormone was attenuated during recovery from EX compared with CON (P < 0.05), with a lower absolute response in women compared with men (P < 0.05). The response of epinephrine and norepinephrine was also lower in women compared with men (P < 0.05) but similar between trials. In summary, a prior bout of moderate-intensity exercise does not affect the magnitude of the glycemia-increasing response to a 30-sec sprint; however, the subsequent decline in blood glucose is more rapid. This blood glucose response is similar between men and women, despite less pronounced changes in glucose R_a and R_d, and a lower response of plasma catecholamines and growth hormone to sprinting in women.

Sexual Dimorphism in Glucose and Lipid Metabolism during Fasting, Hypoglycemia, and Exercise

Sexually dimorphic physiologic responses occur during fasting, hypoglycemia, and exercise. The areas covered in this mini review include studies that have used isotopic tracer methods and/or euglycemic clamp studies to investigate substrate metabolism during the above common physiologic stress. Women have greater reliance on lipid metabolism during fasting, hypoglycemia, and exercise while men exhibit preference of carbohydrate utilization. Plasma glucose concentrations were shown to be lower, while free fatty acids (FFA) and lipolysis higher in women compared to men after fasting. Hypoglycemia resulted in significantly reduced epinephrine, norepinephrine, glucagon, growth hormone, pancreatic polypeptide, and hepatic glucose production responses in females as compared to males. Sexual dimorphism during exercise was demonstrated by higher glycerol and FFA responses in women compared to men and higher carbohydrate oxidation rate in men. Mechanisms that can increase lipolytic rates in women include higher total fat mass, enhanced lipolytic sensitivity to epinephrine, and increased activation of β adrenergic receptors.

Menstrual cycle phase and carbohydrate ingestion alter immune response following endurance exercise and high intensity time trial performance test under hot conditions

Background

Sex hormones are known to regulate some responses during exercise. Evaluation of the differences in exercise response with regard to menstrual cycle will help understand the menstrual cycle phase specific adaptations to exercise and athletic performance.

Methods

We investigated the effects of menstrual cycle phase and carbohydrate (CHO) ingestion on immune response during endurance exercise at 30°C. Six healthy women completed 4 trials comprising 90 min of cycling at 50% peak aerobic power V˙O2peak and a high intensity time trial performance test (POST). They ingested a placebo- or CHO-containing beverage during the trials, which were performed during both the follicular and luteal phases of the menstrual cycle. In all trials, thermoregulatory, cardiorespiratory, and immune responses were measured during exercise and after POST.

Results

Although the thermoregulatory responses differed between the menstrual cycle phases, the cardiorespiratory responses were not different. After placebo ingestion, leukocyte concentration (cells/μL) at POST (15.9 × 10³) in the luteal phase was significantly higher than that in the follicular phase (12.9 × 10³). The rise in leukocyte concentration was attenuated upon CHO ingestion, and the difference between menstrual cycle phases disappeared. A significant positive correlation was found between leukocyte concentration and serum free fatty acid concentrations. Interleukin-6, calprotectin, and myeloperoxidase concentrations significantly increased at POST in all trials, but no significant differences were observed between menstrual cycle phase or beverage type. Concentrations of other cytokines did not change during exercise in any of the 4 trials. Menstrual cycle phase and beverage type had no significant effect on the POST outcome. Thus, differences in leukocyte mobilization between menstrual cycle phases could result from the effect of sex hormones on substrate utilization.

Conclusions

The menstrual cycle affected circulating leukocyte concentrations during endurance exercise with POST when a placebo was ingested. Therefore, we recommend ingesting CHO beverages to attenuate immune disturbances, especially in the luteal phase, even though they are unlikely to enhance test performance.

Prevalence and clinical characteristics of mental stress-induced myocardial ischemia in patients with coronary heart disease

OBJECTIVES

The goal of this study was to evaluate the prevalence and clinical characteristics of mental stress-induced myocardial ischemia.

BACKGROUND

Mental stress-induced myocardial ischemia is prevalent and a risk factor for poor prognosis in patients with coronary heart disease, but past studies mainly studied patients with exercise-induced myocardial ischemia.

METHODS

Eligible patients with clinically stable coronary heart disease, regardless of exercise stress testing status, underwent a battery of 3 mental stress tests followed by a treadmill test. Stress-induced ischemia, assessed by echocardiography and electrocardiography, was defined as: 1) development or worsening of regional wall motion abnormality; 2) left ventricular ejection fraction reduction ≥ 8%; and/or 3) horizontal or downsloping ST-segment depression ≥ 1 mm in 2 or more leads lasting for ≥ 3 consecutive beats during at least 1 mental test or during the exercise test.

RESULTS

Mental stress-induced ischemia occurred in 43.45%, whereas exercise-induced ischemia occurred in 33.79% (p = 0.002) of the study population (N = 310). Women (odds ratio [OR]: 1.88), patients who were not married (OR: 1.99), and patients who lived alone (OR: 2.24) were more likely to have mental stress-induced ischemia (all p < 0.05). Multivariate analysis showed that compared with married men or men living with someone, unmarried men (OR: 2.57) and married women (OR: 3.18), or living alone (male OR: 2.25 and female OR: 2.72, respectively) had higher risk for mental stress-induced ischemia (all p < 0.05).

CONCLUSIONS

Mental stress-induced ischemia is more common than exercise-induced ischemia in patients with clinically stable coronary heart disease. Women, unmarried men, and individuals living alone are at higher risk for mental stress-induced ischemia. (Responses of Myocardial Ischemia to Escitalopram Treatment [REMIT]; NCT00574847).

Evidence for transaldolase activity in the isolated heart supplied with [U-13C3]glycerol

Studies of glycerol metabolism in the heart have largely emphasized its role in triglyceride synthesis. However, glycerol may also be oxidized in the citric acid cycle, and glycogen synthesis from glycerol has been reported in the nonmammalian myocardium. The intent of this study was to test the hypothesis that glycerol may be metabolized to glycogen in mammalian heart. Isolated rat hearts were supplied with a mixture of substrates including glucose, lactate, pyruvate, octanoate, [U-(13)C(3)]glycerol, and (2)H(2)O to probe various metabolic pathways including glycerol oxidation, glycolysis, the pentose phosphate pathway, and carbon sources of stored glycogen. NMR analysis confirmed that glycogen production from the level of the citric acid cycle did not occur and that the glycerol contribution to oxidation in the citric acid cycle was negligible in the presence of alternative substrates. Quite unexpectedly, (13)C from [U-(13)C(3)]glycerol appeared in glycogen in carbon positions 4-6 of glucosyl units but none in positions 1-3. The extent of [4,5,6-(13)C(3)]glucosyl unit enrichment in glycogen was enhanced by insulin but decreased by H(2)O(2). Given that triose phosphate isomerase is generally assumed to fully equilibrate carbon tracers in the triose pool, the marked (13)C asymmetry in glycogen can only be attributed to conversion of [U-(13)C(3)]glycerol to [U-(13)C(3)]dihydroxyacetone phosphate and [U-(13)C(3)]glyceraldehyde 3-phosphate followed by rearrangements in the nonoxidative branch of the pentose phosphate pathway involving transaldolase that places this (13)C-enriched 3-carbon unit only in the bottom half of hexose phosphate molecules contributing to glycogen.

Exercise training improves hemodynamic recovery to isometric exercise in obese men with type 2 diabetes but not in obese women

OBJECTIVES

Women with type 2 diabetes (T2D) show greater rates of mortality due to ischemic heart disease than men with T2D. We aimed to examine cardiovascular and autonomic function responses to isometric handgrip (IHG) exercise between men and women with T2D, before and after an exercise training program.

MATERIALS/METHODS

Hemodynamic responses were measured in 22 men and women with T2D during and following a 3-min IHG test, and before and after 16 wks of aerobic exercise training.

RESULTS

Women had a smaller decrease in mean arterial pressure (MAP) and systolic blood pressure (BP) during recovery from IHG (ΔMAP(REC)) than men pre- and post-training (P<0.05). Men showed a greater reduction in diastolic BP during recovery from IHG (P<0.05), and exercise training improved this response in men but not in women (men, pre-training: -13.9±1.8, post-training: -20.5±5.3 mmHg vs. women, pre-training: -10.7±1.7, post-training: -4.1±4.9 mmHg; P<0.05). Men had a greater reduction in sympathetic modulation of vasomotor tone (P<0.05), as estimated by blood pressure variability, following IHG. This response was accentuated after training, while this training effect was not seen in women. Post-training ΔMAP(REC) was correlated with recovery of low frequency component of the BP spectrum (ΔLF(SBPrec), r=0.52, P<0.05).

CONCLUSIONS

Differences in BP recovery immediately following IHG may be attributed to gender differences in cardiovascular autonomic modulation. An improvement in these responses occurs following aerobic exercise training in obese men, but not in obese women with T2D which reflects a better adaptive autonomic response to exercise training.

Left ventricular twisting mechanics and exercise in healthy individuals: a systematic review

The aim of this study was to review systematically the effects of exercise on left ventricular (LV) twisting mechanics in healthy individuals. Literature searches were conducted in electronic databases for articles reporting measures of LV twisting mechanics in healthy individuals before and during/after exercise. Upon review, 18 articles were analyzed. Studies were separated by exercise type into the following four categories to allow for detailed comparisons: submaximal, prolonged endurance, maximal, and chronic endurance. Despite an overall methodological quality of low to moderate and within-group variations in exercise intensity, duration, and subject characteristics, important trends in the literature emerged. Most important, the coupling of LV systolic twisting and diastolic untwisting was present in all exercise types, as both were either improved or impaired concomitantly, highlighting the linkage between systole and diastole provided through LV twist. In addition, trends regarding the effects of age, training status, and cardiac loading also became apparent within different exercise types. Furthermore, a potential dose-response relationship between exercise duration and the degree of impairment to LV twisting mechanics was found. Although some disagreement existed in results, the observed trends provide important directions for future research. Future investigations should be of higher methodological quality and should include consistent exercise protocols and subject populations in order to minimize the variability between investigations.

Using biofeedback while immersed in a stressful videogame increases the effectiveness of stress management skills in soldiers

This study assessed the efficacy of using visual and auditory biofeedback while immersed in a tridimensional videogame to practice a stress management skill (tactical breathing). All 41 participants were soldiers who had previously received basic stress management training and first aid training in combat. On the first day, they received a 15-minute refresher briefing and were randomly assigned to either: (a) no additional stress management training (SMT) for three days, or (b) 30-minute sessions (one per day for three days) of biofeedback-assisted SMT while immersed in a horror/first-person shooter game. The training was performed in a dark and enclosed environment using a 50-inch television with active stereoscopic display and loudspeakers. On the last day, all participants underwent a live simulated ambush with an improvised explosive device, where they had to provide first aid to a wounded soldier. Stress levels were measured with salivary cortisol collected when waking-up, before and after the live simulation. Stress was also measured with heart rate at baseline, during an apprehension phase, and during the live simulation. Repeated-measure ANOVAs and ANCOVAs confirmed that practicing SMT was effective in reducing stress. Results are discussed in terms of the advantages of the proposed program for military personnel and the need to practice SMT.

Female rats are relatively more sensitive to reduced lipid versus reduced carbohydrate availability

Objectives:

Because females have blunted counterregulatory responses to hypoglycemia relative to males, we hypothesized that females would have greater sensitivity to changes in lipid availability.

Design and subjects:

To assess this, we examined the feeding response to glucoprivation (2-deoxyglucose; 2DG) and lipoprivation (mercaptoacetate; MA) in age-matched male and female Long-Evans rats.

Results:

Males versus females had significantly greater food intake after 250 mg kg⁻¹ of 2DG, but there were no sex differences with the 750 mg kg⁻¹ dose of 2DG. Glucose responses to 250 mg kg⁻¹ of 2DG were also significantly greater in males versus females. In contrast, females had a significant increase in food intake with all doses of MA versus saline, and had significantly greater food intake compared with males at the lowest and highest doses of MA with a trend towards significance with the intermediate dose. To determine whether estradiol (E2) is the mechanism underlying this sexual dimorphism, ovariectomized females were injected with vehicle or 2 μg of E2 every fourth day to mimic the variations in across the estrous cycle. Ovariectomized females significantly increased feeding and glucose after 250 mg kg⁻¹ of 2DG over intact females and E2 had no effect on these responses. Although the feeding response to 2DG was not different, the glucose response to 2DG was still significantly greater in males versus ovariectomies females. However, ovariectomized females also did not increase food intake after MA, regardless of E2 treatment.

Conclusions:

These data collectively suggest that males are relatively more sensitive to glucose deprivation and females are relatively more sensitive to lipid deprivation. Further, these data rule out a role for cyclic changes in E2 in these sex differences.

Skeletal muscle signaling response to sprint exercise in men and women

To determine if there is a sex dimorphism in the skeletal muscle signaling response to sprint exercise, 17 men and ten women performed a 30-s Wingate test. Muscle biopsies were taken before, immediately after the exercise and at 30 and 120 min during the recovery period. Thr(172)-AMPKα, Ser(221)-ACCβ, Thy(705)-STAT3, Thr(202)/Thy(204)-ERK1/2 and Thr(180)/Thy(182)-p38MAPK phosphorylation responses to sprint exercise were not statistically different between men and women. AMPKα phosphorylation was enhanced fourfold 30 min after the sprint exercise in males and females (P < 0.01). ACCβ phosphorylation was enhanced by about threefold just after the sprint test exercise and 30 min into the recovery period in males and females (P < 0.01). STAT3 phosphorylation was increased 2 h after the Wingate test compared to the value observed right after the end of the exercise (P < 0.05), and 30 min after the Wingate test there was a 2.5-fold increase in ERK1/2 phosphorylation, compared to both the pre-exercise and to the value observed right after the Wingate test (both, P < 0.05). In conclusion, the skeletal muscle signaling response to a single bout of sprint exercise mediated by AMPK, ACC, STAT3, ERK and p38MAPK is not statistically different between men and women. Marked increases in AMPKα, ACCβ, STAT3 and ERK phosphorylation were observed after a single 30-s all-out sprint (Wingate test) in the vastus lateralis.

Relationship of sleep quantity and quality with 24-hour urinary catecholamines and salivary awakening cortisol in healthy middle-aged adults

OBJECTIVES

a. Explore the stability in sleep/wake patterns of middle-aged adults over a 3-year follow-up period. b. Explore the relationship between objectively measured sleep indices, urinary catecholamines, and salivary cortisol.

DESIGN

Naturalistic follow-up for sleep/wake patterns (n = 114) by 2-week sleep log and cross-sectional design for objective sleep assessments and hormonal measures (n = 96) at follow-up period nearly 3 years after baseline measurements.

SETTING

Community

PARTICIPANTS

Healthy middle-aged adults

INTERVENTIONS

N/A.

MEASUREMENTS AND RESULTS

There were high correlations between baseline and follow-up period (2.6 ± 0.5 years) on sleep/wake patterns (r = 0.6-0.79) as measured by 2-week sleep log. For wave 2 cross-sectional study, objective poor sleepers (3-day actigraphy sleep efficiency < 85%) had a higher 24-h urinary norepinephrine (NE) level (205.7 ± 105 nmol/d vs 162.1 ± 55.6 nmol/d, P = 0.03) and a nearly significantly higher 24-h urinary epinephrine (E) level (P = 0.12) than good sleepers. There were no differences in 3-day mean salivary awakening cortisol and 24-h urinary catecholamines (NE and E) between short and normal/long sleepers. Linear regression results, however, showed that shorter time in bed and actual sleep time, longer sleep onset latency, and lower sleep efficiency were correlated with higher 24-h urinary E and NE (all P < 0.05) but not salivary cortisol. The effect of poor sleep quality on 24-h urinary catecholamines was stronger in males than females.

CONCLUSIONS

Increased sympathetic activity as measured by 24-h urinary catecholamines might play a critical role in the pathogenesis mediating the relationship of insufficient sleep (quantity and quality) with subsequent cardiovascular and metabolic complications. Salivary awakening cortisol was not associated with sleep quantity and quality in healthy middle-aged adults.

Blood glucose regulation during prolonged, submaximal, continuous exercise: a guide for clinicians

Management of many chronic diseases now includes regular exercise as part of a viable treatment plan. Exercise in the form of prolonged, submaximal, continuous exercise (SUBEX; i.e., approximately 30 min to 1 h, approximately 40-70% of maximal oxygen uptake) is often prescribed due to its relatively low risk, the willingness of patients to undertake, its efficacy, its affordability, and its ease of prescription. Specifically, patients who are insulin resistant or that have type 2 diabetes mellitus may benefit from regular exercise of this type. During this type of exercise, muscles dramatically increase glucose uptake as the liver increases both glycogenolysis and gluco-neogenesis. While a redundancy of mechanisms is at work to maintain blood glucose concentration ([glucose]) during this type of exercise, the major regulator of blood glucose is the insulin/glucagon response. At exercise onset, blood [glucose] transiently rises before beginning to decline after approximately 30 min, causing a subsequent decline in blood [insulin] and rise in blood glucagon. This leads to many downstream effects, including an increase in glucose output from the liver to maintain adequate glucose in the blood to fuel both the muscles and the brain. Finally, when analyzing blood [glucose], consideration should be given to nutritional status (postabsorptive versus postprandial) as well as both what the analyzer measures and the type of sample used (plasma versus whole blood). In view of both prescribing exercise to patients as well as designing studies that perturb glucose homeostasis, it is imperative that clinicians and researchers alike understand the controls of blood glucose homeostasis during SUBEX.

Greater systemic lipolysis in women compared with men during moderate-dose infusion of epinephrine and/or norepinephrine

Women have lower circulating catecholamine levels during metabolic perturbations, such as exercise or hypoglycemia, but similar rates of systemic lipolysis. This suggests women may be more sensitive to the lipolytic action of catecholamines, while maintaining similar glucoregulatory effects. The aim of the present study, therefore, was to determine whether women have higher rates of systemic lipolysis compared with men in response to matched peripheral infusion of catecholamines, but similar rates of glucose turnover. Healthy, nonobese women (n = 11) and men (n = 10) were recruited and studied on 3 separate days with the following infusions: epinephrine (Epi), norepinephrine (NE), or the two combined. Tracer infusions of glycerol and glucose were used to determine systemic lipolysis and glucose turnover, respectively. Following basal measurements of substrate kinetics, the catecholamine infusion commenced, and measures of substrate kinetics continued for 60 min. Catecholamine concentrations were similarly elevated in women and men during each infusion: Epi, 182-197 pg/ml and NE, 417-507 pg/ml. There was a significant sex difference in glycerol rate of appearance and rate of disappearance with the catecholamine infusions (P < 0.0001), mainly due to a significantly greater glycerol turnover during the first 30 min of each infusion: glycerol rate of appearance during Epi was only 268 +/- 18 vs. 206 +/- 21 micromol/min in women and men, respectively; during NE, only 173 +/- 13 vs. 153 +/- 17 micromol/min, and during Epi+NE, 303 +/- 24 vs. 257 +/- 21 micromol/min. No sex differences were observed in glucose kinetics under any condition. In conclusion, these data suggest that women are more sensitive to the lipolytic action of catecholamines, but have no difference in their glucoregulatory response. Thus the lower catcholamine levels observed in women vs. men during exercise and other metabolic perturbations may allow women to maintain a similar or greater level of lipid mobilization while minimizing changes in glucose turnover.

Gender impacts the post-exercise substrate and endocrine response in trained runners

BACKGROUND

Although several studies have investigated gender differences in the substrate and endocrine responses during and following endurance exercise, few have studied sex differences during a more prolonged recovery period post endurance exercise. The purpose of this study was to compare and characterize the endocrine and substrate profiles of trained male and female adult runners during the three-and-a-half hour recovery period from an endurance run.

METHODS

After consuming a euenergetic diet (1.8 g.kg-1.d-1 protein, 26% fat, 58% carbohydrates, 42.8 +/- 1.2 kcal/kg body weight) for 8 days, blood was collected from trained male (n = 6, 21 yrs, 70 kg, 180 cm, 9% body fat, VO(2peak) 78.0 +/- 3.4 mL.kg FFM-1.min-1) and female (n = 6, 23 y, 66 kg, 170 cm, 29% body fat, VO(2peak) 71.6 +/- 4.5 mL.kg FFM-1.min-1) endurance runners at rest and during recovery from a 75 min run at 70% VO(2peak). Circulating levels of glucose, lactate, free fatty acids (FFAs), insulin, cortisol, growth hormone (GH), and free insulin-like growth factor I (IGF-I) were measured.

RESULTS

During the recovery period, females experienced increases in glucose, lactate and insulin while no changes were noted in men (P < 0.05). Males experienced increases in GH and decreases in IGF-I levels respectively (P < 0.05) while no changes were observed in females. FFA levels increased during recovery from endurance exercise, but changes were not different between genders.

CONCLUSION

These data further document gender differences in substrate and endocrine changes during a prolonged recovery period following endurance exercise. Future studies are needed to evaluate the effect of differing diets and nutritional supplements on these gender-specific post-exercise substrate and endocrine differences.

Influence of sex and active muscle mass on renal vascular responses during static exercise

During exercise, reflex renal vasoconstriction helps maintain blood pressure and redistributes blood flow to the contracting muscle. Sex and muscle mass have been shown to influence certain cardiovascular responses to exercise. Whether sex and/or muscle mass influence renal vasoconstrictor responses to exercise is unknown. We studied healthy men (n = 10) and women (n = 10) matched for age and body mass index during handgrip (HG, small muscle mass) and quadriceps contraction (QC, large muscle mass) as beat-to-beat changes in renal blood flow velocity (RBV; duplex ultrasound), mean arterial pressure (MAP; Finapres), and heart rate (ECG) were monitored. Renal vascular resistance (RVR) index was calculated as MAP / RBV. Responses to HG vs. QC were compared in 13 subjects. We found that 1) RVR responses to short (15-s) bouts and fatiguing HG were similar in men and women (change in RVR during 15-s HG at 70% of maximum voluntary contraction = 23 +/- 4 and 31 +/- 4% in men and women, respectively, P = not significant); 2) post-HG circulatory responses were similar in men and women; and 3) HG and QC were similar during short (15-s) bouts (change in RVR during HG at 50% of maximum voluntary contraction = 19 +/- 3 and 18 +/- 5% for arm and leg, respectively, P = not significant). Our findings suggest that muscle reflex-mediated renal vasoconstriction is similar in men and women during static exercise. Moreover, muscle mass does not contribute to the magnitude of the reflex renal vasoconstrictor response seen with muscle contraction.

Influence of gender, menstrual phase, and oral contraceptive use on immunological changes in response to prolonged cycling

This study determined the influence of gender, menstrual phase (MP), and oral contraceptive (OC) use on immunological changes in response to endurance exercise. Twelve women and 11 men similar in age, aerobic power, and activity level cycled for 90 min at 65% maximal aerobic power. Women were OC users (n = 6) or nonusers (NOC) and cycled during the follicular (Fol) and the luteal (Lut) phases. Venous blood was collected before and after exercise to determine leukocyte counts, IL-6 concentrations, and cortisol. Higher resting levels of neutrophils (approximately 1.5-fold) and cortisol (approximately 2.5-fold) were found in OC vs. NOC and men. Exercise-induced immune cell count and IL-6 changes were similar between men and NOC, except for an approximately 38% greater lymphocyte response in NOC vs. men (P = 0.07). Neutrophil, monocyte, and lymphocyte responses to exercise during Lut in OC were greater than during Fol and also greater than the responses in men (P < or = 0.003). Changes in immune cell counts were consistently greater during Lut in OC vs. NOC, regardless of MP, but only neutrophil responses reached statistical significance (P = 0.01). The exercise-induced change in IL-6 was approximately 80% greater in NOC vs. OC during Fol (P = 0.06), but it was similar between these groups during Lut. Cortisol changes with exercise were not different between groups or MP. These results highlight the necessity to control for gender, and in particular OC use, when designing studies evaluating exercise and immunology.

Effects of training period on haemorheological variables in regularly trained footballers

OBJECTIVE

To investigate the effects of one football training period on haemorheological variables in regularly trained footballers.

METHOD

Ten subjects were randomly selected from the reserve team of a football club in the Turkish Premier League. During the last week of the football season, one day before a standard training session and two days after the previous league match, venous blood samples were taken (pre-exercise). After 90 minutes of standard training, further blood samples were taken (post-exercise). Blood lactate, blood viscosity, plasma fibrinogen, blood clotting time, acid-base variables, and plasma Na+, K+, and Ca2+ were determined.

RESULTS

Haemoglobin, packed cell volume, and mean corpuscular volume were all significantly decreased, whereas white blood cells and platelets were both increased after training. Blood viscosity decreased but the reduction was not significant. Blood lactate, plasma glucose, and Na+ content were significantly increased, but standard bicarbonate, actual bicarbonate, and Ca2+ were significantly decreased. Blood clotting time had shortened significantly after training. Blood viscosity was inversely correlated with plasma glucose concentration (r = -0.48 and p = 0.032).

CONCLUSIONS

The results show that blood viscosity tends to decrease as the result of this type of training. This is due to a reduction in packed cell volume and mean corpuscular volume. The increased blood lactate does not have an adverse effect on the blood viscosity of these subjects because protective mechanisms develop with regular training throughout the season.

The I1-imidazoline agonist moxonidine decreases sympathetic tone under physical and mental stress

AIMS

Moxonidine is an I1-imidazoline receptor agonist that reduces blood pressure by inhibition of central sympathetic activity. The effects of the drug under physical and mental stress have not been studied in detail.

METHODS

We investigated the effects of 0.4 mg moxonidine orally on sympathetic activity, blood pressure and heart rate in a double-blind, placebo-controlled crossover study in 12 healthy volunteers. The subjects underwent physical exercise test using bicycle ergometry and a mental stress test using an adaptive reaction test device. Potential association of parameters with the GNB3 C825T polymorphism was also assessed.

RESULTS

Under resting conditions, moxonidine decreased plasma noradrenaline (NA: -66.1 +/- 12 pg ml(-1); P < 0.01 vs placebo) and adrenaline (A: -18.8 +/- 6 pg ml(-1); P < 0.05 vs placebo). Physical exercise evoked a significant increase in plasma NA and A (NA: 760 +/- 98 pg ml(-1); A: 97 +/- 9 pg ml(-1); P < 0.001 vs baseline), which was significantly reduced after pretreatment with moxonidine (NA: 627 +/- 68 pg ml(-1); P < 0.05 vs placebo; A: 42.8 +/- 4 pg ml(-1); P < 0.01 vs placebo). Maximal physical exercise capacity was not limited by moxonidine (NS). During the mental stress test, increases in NA (placebo: 146 +/- 24 pg ml(-1), moxonidine: 84 +/- 26 pg ml(-1); P < 0.01 vs placebo) and A (placebo: 22.8 +/- 9 pg ml(-1), moxonidine: 8.0 +/- 8 pg ml(-1); P < 0.01 vs placebo) were significantly reduced after pretreatment with moxonidine. Increases in blood pressure during mental stress were significantly lower after pretreatment with moxonidine (P < 0.05 vs placebo). There was no association of the response to moxonidine with GNB3 genotypes (NS).

CONCLUSIONS

Moxonidine decreases total sympathetic tone under basal conditions as well as during physical exercise and mental stress without limiting absolute exercise capacity. Thus, moxonidine appears suitable for the treatment of patients with high SNS activity and hypertension induced by physical or mental stress. As the drug does not reduce exercise capacity, it may be considered as an alternative to beta-adrenoceptor blockers in selected patients.

Development of diabetes mellitus in aging transgenic mice following suppression of pancreatic homeoprotein IDX-1

Monogenic forms of diabetes can result from mutations in genes encoding transcription factors. Mutations in the homeodomain transcription factor IDX-1, a critical regulator of pancreas development and insulin gene transcription, confer a strong predisposition to the development of diabetes mellitus in humans. To investigate the role of IDX-1 expression in the pathogenesis of diabetes, we developed a model for the inducible impairment of IDX-1 expression in pancreatic beta cells in vivo by engineering an antisense ribozyme specific for mouse IDX-1 mRNA under control of the reverse tetracycline transactivator (rtTA). Doxycycline-induced impairment of IDX-1 expression reduced activation of the Insulin promoter but activated the Idx-1 promoter, suggesting that pancreatic beta cells regulate IDX-1 transcription to maintain IDX-1 levels within a narrow range. In transgenic mice that express both rtTA and the antisense ribozyme construct, impaired IDX-1 expression elevated glycated hemoglobin levels, diminished glucose tolerance, and decreased insulin/glucose ratios. Metabolic phenotypes induced by IDX-1 deficiency were observed predominantly in male mice over 18 months of age, suggesting that cellular mechanisms to protect IDX-1 levels in pancreatic beta cells decline with aging. We propose that even in the absence of Idx-1 gene mutations, pathophysiological processes that decrease IDX-1 levels are likely to impair glucose tolerance. Therapeutic strategies to attain normal glucose homeostasis by restoring normal IDX-1 levels may be of particular importance for older individuals with diabetes mellitus.