Within-breath electromyographic changes during loaded breathing in adult sheep

To investigate the changes in diaphragm electromyogram (EMG) during the course of severe loaded breathing, we subjected five conscious adult sheep to inspiratory flow resistive breathing (resistance greater than 150 cmH2O X l-1 X s) for up to 2-3 h and studied the total EMG power per breath (iEMG) and the EMG power per unit time after dividing the duration of EMG activity within each breath into three equal parts (iEMG1, iEMG2, and iEMG3). Both total breath iEMG and transdiaphragmatic pressure (Pdi) increased, remained at a high level for a certain period of time, and then started to fall. A change in the pattern of iEMG within a breath was observed during loaded breathing. The increase in total-breath iEMG was associated mostly with an increase in iEMG3, or the last part of the EMG power within each inspiration. Similarly, the decrease in total breath iEMG was primarily due to a decrease in iEMG3. We conclude that, in sheep subjected to severe IFR loads for prolonged periods the marked increase in total-breath iEMG at the beginning of loaded breathing and the marked decrease in this iEMG at the time of decrease in Pdi are largely due to changes in iEMG that occur during the latter third of each breath. We speculate that during loaded breathing the recruitment pattern of diaphragmatic muscle fibers changes during the course of an inspiratory effort.     

Mice lacking the proton channel Hv1 exhibit sex-specific differences in glucose homeostasis

Sex as a physiologic factor has a strong association with the features of metabolic syndrome. Our previous study showed that loss of the voltage-gated proton channel Hv1 inhibits insulin secretion and leads to hyperglycemia and glucose intolerance in male mice. However, there are significant differences in blood glucose between male and female Hv1-knockout (KO) mice. Here, we investigated the differences in glucose metabolism and insulin sensitivity between male and female KO mice and how sex steroids contribute to these differences. We found that the fasting blood glucose in female KO mice was visibly lower than that in male KO mice, which was accompanied by hypotestosteronemia. KO mice in both sexes exhibited higher expression of gluconeogenesis-related genes in liver compared with WT mice. Also, the livers from KO males displayed a decrease in glycolysis-related gene expression and an increase in gluconeogenesis-related gene expression compared with KO females. Furthermore, exogenous testosterone supplementation decreased blood glucose levels in male KO mice, as well as enhancing insulin signaling. Taken together, our data demonstrate that knockout of Hv1 results in higher blood glucose levels in male than female mice, despite a decreased insulin secretion in both sexes. This sex-related difference in glucose homeostasis is associated with the glucose metabolism in liver tissue, likely due to the physiological levels of testosterone in KO male mice.     

Postnatal ontogeny of glucose homeostasis and insulin action in sheep

Glucose tolerance declines with maturation and aging in several species, but the time of onset and extent of changes in insulin sensitivity and insulin secretion and their contribution to changes in glucose tolerance are unclear. We therefore determined the effect of maturation on glucose tolerance, insulin secretion, and insulin sensitivity in a longitudinal study of male and female sheep from preweaning to adulthood, and whether these measures were related across age. Glucose tolerance was assessed by intravenous glucose tolerance test (IVGTT, 0.25 g glucose/kg), insulin secretion as the integrated insulin concentration during IVGTT, and insulin sensitivity by hyperinsulinemic-euglycemic clamp (2 mU insulin.kg(-1).min(-1)). Glucose tolerance, relative insulin secretion, and insulin sensitivity each decreased with age (P < 0.001). The disposition index, the product of insulin sensitivity, and various measures of insulin secretion during fasting or IVGTT also decreased with age (P < 0.001). Glucose tolerance in young adult sheep was independently predicted by insulin sensitivity (P = 0.012) and by insulin secretion relative to integrated glucose during IVGTT (P = 0.005). Relative insulin secretion before weaning was correlated positively with that in the adult (P = 0.023), whereas glucose tolerance, insulin sensitivity, and disposition indexes in the adult did not correlate with those at earlier ages. We conclude that glucose tolerance declines between the first month of life and early adulthood in the sheep, reflecting decreasing insulin sensitivity and absence of compensatory insulin secretion. Nevertheless, the capacity for insulin secretion in the adult reflects that early in life, suggesting that it is determined genetically or by persistent influences of the perinatal environment.     

The role of diet during development on the regulation of adult cholesterol homeostasis

Atherosclerosis is believed to begin early in life and to develop over several decades. Elevated plasma cholesterol is a major contributing factor. Studies in animals have shown that manipulation of cholesterol metabolism during its development in pre- and early post-natal life can permanently alter cholesterol synthesis and catabolism to favour lower plasma cholesterol levels in the adult faced with a high dietary cholesterol intake. Although the mechanisms and pathways involved are likely to be different, "metabolic training" can occur as a result of both the diet fed to the mother during gestation and lactation and from the diet fed to the animal itself in early life. The presence of cholesterol itself in the suckling diet does not appear to confer any lasting improvement to cholesterol handling in either man or animals. Although much research is still required to define the time in development for effective training of specific steps in cholesterol metabolism and the primary site and mechanism of permanently altered metabolism, significant progress has been made. These studies will form the basis of this review.     

Maternal flaxseed oil intake during lactation changes body fat,inflammatory markers and glucose homeostasis in the adult progeny: role of gender dimorphism

We evaluated maternal flaxseed oil intake during lactation on body composition, lipid profile, glucose homeostasis and adipose tissue inflammation in male and female progeny at adulthood. Lactating rats were divided into the following: control 7% soybean oil (C), hyper 19% soybean oil (HS) and hyper 17% flaxseed oil + 2% soybean oil (HF). Weaned pups received a standard diet. Offspring were killed in PN180. Male HF presented higher visceral adipose tissue (VAT) and triacylglycerol, and female HF showed insulin resistance. Both male and female HF had hyperleptinemia, and only male HF had hyperprolactinemia. In VAT, male HF presented lower PPAR-γ expressions and higher TNF-α, IL-6, IL-1β and IL-10 expressions; in subcutaneous adipose tissue (SAT), they presented lower PPAR-γ and TNF-α expressions. Female HF presented higher leptin, as well as lower adiponectin, TNF-α, IL-6 and IL-1β expressions in VAT and lower TNF-α in SAT. Flaxseed oil during lactation leads to gender-specific effects with more adiposity and dyslipidemia in male and insulin resistance in female. Higher prolactin and inflammatory cytokines in male could play a role in these gender differences. We suggest that the use of flaxseed oil during lactation increases metabolic syndrome risk in the adult progeny.     

Maternal exposure to dexamethasone or cortisol in early pregnancy differentially alters insulin secretion and glucose homeostasis in adult male sheep offspring

An adverse intrauterine environment increases the risk of developing various adult-onset diseases, whose nature varies with the timing of exposure. Maternal undernutrition in humans can increase adiposity, and the risk of coronary heart disease and impaired glucose tolerance in adult life, which may be partly mediated by maternal or fetal endocrine stress responses. In sheep, dexamethasone in early pregnancy impairs cardiovascular function, but not glucose homeostasis in adult female offspring. However, male offspring are often more susceptible to early life "programming". Pregnant sheep were infused intravenously with saline (0.19 ml/h), dexamethasone (0.48 mg/h), or cortisol (5 mg/h), for 2 days from 26 to 28 days of gestation. In male offspring, size at birth and postnatal growth were measured, and glucose tolerance [intravenous glucose tolerance test (IVGTT)], insulin secretion, and insulin sensitivity of glucose, alpha-amino nitrogen, and free fatty acid metabolism were assessed at 4 yr of age. We show that cortisol, but not dexamethasone, treatment of mothers causes fasting hyperglycemia in adult male offspring. Maternal cortisol induced a second-phase hyperinsulinemia during IVGTT, whereas maternal dexamethasone induced a first-phase hyperinsulinemia. Dexamethasone improved glucose tolerance, while cortisol had no impact, and neither affected insulin sensitivity. This suggests that maternal glucocorticoid exposure in early pregnancy alters glucose homeostasis and induces hyperinsulinemia in adult male offspring, but in a glucocorticoid-specific manner. These consequences of glucocorticoid exposure in early pregnancy may lead to pancreatic exhaustion and diabetes longer term and are consistent with stress during early pregnancy contributing to such outcomes in humans.     

Ontogeny of the insulin response to glucose in fetal and adult sheep

The purpose of the present experiments was to examine in sheep whether the fetal insulin response to glucose was present by day 110 (d110) of pregnancy and whether the magnitude of the fetal insulin response changed between d110 and d145 (term). We also compared the responses observed in fetuses to those of adult nonpregnant sheep. Basal concentrations of glucose measured in plasma collected from the fetal femoral artery rose progressively between d110 and d145 of gestation, but did not attain the plasma glucose concentrations measured in adult sheep. Peak glucose concentrations in fetuses were achieved 10 min following the bolus injection of glucose (0.8 g/kg estimated fetal body weight) into the fetal femoral vein, and peak values increased with gestational age. Significantly higher peak glucose concentrations were achieved in adult sheep. The concentration of insulin rose rapidly in fetuses at d110, and a similar time course of insulin release in plasma was seen at all gestational ages. The peak plasma insulin concentrations were achieved at 20 min and were significantly greater in older (d140-145) than younger (d125-130) fetuses (p less than 0.05). Peak insulin values in fetuses were much less than in adult sheep. In adult sheep glucose and insulin concentrations remained elevated at 120 min following the injection of glucose, whereas in the fetus the concentration of insulin had returned to preinjection values by 60 min. The insulin/glucose ratio did not change in fetal lambs over the last one third of gestation and was not different from the adult sheep.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regulation of blood glucose homeostasis during prolonged exercise

The maintenance of normal blood glucose levels at rest and during exercise is critical. The maintenance of blood glucose homeostasis depends on the coordination and integration of several physiological systems, including the sympathetic nervous system and the endocrine system. During prolonged exercise increased demand for glucose by contracting muscle causes to increase glucose uptake to working skeletal muscle. Increase in glucose uptake by working skeletal muscle during prolonged exercise is due to an increase in the translocation of insulin and contraction sensitive glucose transporter-4 (GLUT4) proteins to the plasma membrane. However, normal blood glucose level can be maintained by the augmentation of glucose production and release through the stimulation of liver glycogen breakdown, and the stimulation of the synthesis of glucose from other substances, and by the mobilization of other fuels that may serve as alternatives. Both feedback and feedforward mechanisms allow glycemia to be controlled during exercise. This review focuses on factors that control blood glucose homeostasis during prolonged exercise.     

Abnormal glucose homeostasis in adult female rat offspring after intrauterine ethanol exposure

Adverse events during pregnancy, including prenatal ethanol (EtOH) exposure, are associated with insulin-resistant diabetes in male rat offspring, but it is unclear whether this is true for female offspring. We investigated whether prenatal EtOH exposure alters glucose metabolism in adult female rat offspring and whether this is associated with reduced in vivo insulin signaling in skeletal muscle. Female Sprague-Dawley rats were given EtOH, 4 g.kg(-1).day(-1) by gavage throughout pregnancy. Glucose tolerance test and hyperinsulinemic euglycemic clamp were performed, and insulin signaling was investigated in skeletal muscle, in adult female offspring. We gave insulin intravenously to these rats and determined the association of glucose transporter-4 with plasma membranes, as well as the phosphorylation of phosphoinositide-dependent protein kinase-1 (PDK1), Akt, and PKCzeta. Although EtOH offspring had normal birth weight, they were overweight as adults and had fasting hyperglycemia, hyperinsulinemia, and reduced insulin-stimulated glucose uptake. After insulin treatment, EtOH-exposed rats had decreased membrane glucose transporter-4, PDK1, Akt, and PKCzeta in the gastrocnemius muscle, compared with control rats. Insulin stimulation of PDK1, Akt, and PKCzeta phosphorylation was also reduced. In addition, the expression of the protein tribbles-3 and the phosphatase enzyme activity of phosphatase and tensin homolog deleted on chromosome 10 (PTEN), which prevent Akt activation, were increased in muscle from EtOH-exposed rats. Female rat offspring exposed to EtOH in utero develop insulin-resistant diabetes in association with excessive PTEN and tribbles-3 signaling downstream of the phosphatidylinositol 3-kinase pathway in skeletal muscle, which may be a mechanism for the abnormal glucose tolerance.     

The influence of parathyroidectomy upon calcium and phosphate homeostasis in adult sheep.

The absorption and secretion of Ca and PO4 were measured with the use of radioactive isotopes in 4 adult sheep before and after parathyroidectomy. Secretion of Ca and PO4 into the stomach and intestines was measured separately. Parathyroidectomy resulted in a negative balance for Ca and PO4 and an accompanying fall in plasma Ca and PO4 concentrations. In the case of PO4 this response was attributed primarily to a reduced intestinal absorption, but for Ca increases in urinary excretion and intestinal secretion also contributed significantly. Secretion of PO4 to the stomach was reduced but endogenous PO4 excretion in the faeces was unchanged which indicated a reduced reabsorption of secreted PO4 by the intestines.     

Nutritional dynamics during the development of xylophagous beetles related to changes in the stoichiometry of 11 elements

The present study examines the adaptive strategy used by wood‐boring beetles to compensate for the lack of nutrients in dead wood. The contents of nutritional elements in growing wood‐boring beetles (Stictoleptura rubra L. and Chalcophora mariana Dejean) are compared with the elemental composition of decaying dead wood (pine stumps), showing changes during the beetles' ontogenetic (i.e. larval) development. The stoichiometric ratios of C and other nutritional elements (N, P, K, Na, Ca, Mg, Fe, Zn, Mn and Cu) are investigated to identify the most important nutrients for larval development. The degree of nutritional mismatch that is encountered by the beetle larvae changes dramatically over 3–4 years of simultaneous larval growth and wood decay. Excluding C, the relative contents of nutritional elements increase substantially in decaying wood, whereas the opposite tendency is found in larvae, most likely because of carbon deposition in fat. The elements limiting larval development because of their scarcity in dead wood are N, P, K, Na, Mg, Zn and Cu. Fungal activity (i.e. the transport of nutrients from the surrounding environment to decaying stumps) can explain the observed mitigation of the original mismatch, although prolongation of the larval development time is still necessary to compensate for the scarcity of some of the required elements in food.     

Calcium homeostasis during oral glucose load in healthy women.

It has been demonstrated that in healthy subjects during oral glucose tolerance test, serum calcium declines, while urinary calcium excretion increases, even if there is not a general agreement in this regard. The study was carried out in order to evaluate the effects of glucose oral load on calcium homeostasis in eight healthy adult women, also considering ionized calcium, plasma insulin and parathyroid hormone changes. The results showed a decline of total and ionized serum calcium (p < 0.05 and p < 0.01, respectively; maximum of the decrease at time 120'), in parallel with the increase of urinary calcium/ creatinine ratio (p < 0.05). Serum glucose and insulin increase (p < 0.0001 and p < 0.0005 respectively; maximum value at time 60'), while the parathyroid hormone level decreases (maximum decline at time 120', p < 0.01). No changes were observed in fasting control subjects for all parameters considered. The changes of these parameters with time suggest that the effects of glucose oral load on calcium metabolism in healthy adult women may be the consequence of parathyroid hormone suppression induced by acute hyperglycemia/hyperinsulinemia. The results confirm in vivo the PTH behaviour in vitro, on cultured bovine parathyroid cells, with high glucose concentration.     

Sequential changes in propionate metabolism during the development of cobalt/vitamin B12 deficiency in sheep

The changes in propionate metabolism that accompany cobalt deficiency in sheep are described. Two groups of sheep, fed either a cobalt sufficient or deficient diet, were given an iv propionate load at intervals during a 14 w experiment. There was a tendency towards increased propionate half-life as the animals became cobalt deficient. However, significant changes in the area under the plasma methylmalonic acid-time curve occurred very early, indicating significant impairment of propionate metabolism. Despite this, the area under the plasma glucose-time curve was unaffected by cobalt deficiency, suggesting that the impairment of propionate metabolism, although significant, is not extensive.     

Seasonal changes in cell proliferation in the adult sheep brain and pars tuberalis

To adapt to seasonal variations in the environment, most mammalian species exhibit seasonal cycles in their physiology and behavior. Seasonal plasticity in the structure and function of the central nervous system contributes to the adaptation of this physiology in seasonal mammals. As part of these plasticity mechanisms, seasonal variations in proliferation rate and neuron production have been extensively studied in songbirds. In this report, we investigated whether this type of brain plasticity also occurs in sheep, a seasonal species, by assessing variations in cell proliferation in the sheep diencephalon. We administered the cell birth marker 5'-bromodeoxyuridine (BrdU) to adult female sheep in July and December, during long and short photoperiod, respectively. The BrdU incorporation was analyzed and quantified in the hypothalamus, a key center for neuroendocrine regulations, as well as in other structures involved in relaying neuroendocrine and sensory information, including the median eminence, the pars tuberalis of the pituitary gland, and the thalamus. In December, 2-fold and 6-fold increases in the number of BrdU+ nuclei were observed in the hypothalamus and thalamus, respectively, when compared with July. This variation is independent of the influence of peripheral gonadal estradiol variations. An inverse seasonal regulation of cell proliferation was observed in the pars tuberalis. In contrast, no seasonal variation in cell proliferation was seen in the subventricular zone of the lateral ventricle. Many of the newborn cells in the adult ovine hypothalamus and thalamus differentiate into neurons and glial cells, as assessed by the expression of neuronal (DCX, NeuN) and glial (GFAP, S100B) fate markers. In summary, we show that the estimated cell proliferation rates in the sheep hypothalamus, thalamus, and pars tuberalis are different between seasons. These variations are independent of the seasonal fluctuations of peripheral estradiol levels, unlike the results described in the brain nuclei involved in song control of avian species.