Physiological responses to glycerol ingestion during exercise

To study selected cardiovascular, thermoregulatory, and hormonal responses to the consumption of glycerol solutions during exercise, nine subjects cycled for 90 min at 50% peak O2 uptake in a 30 degree C, 45% relative humidity environment. Beverages tested included a 10% glycerol solution (G), a 6% carbohydrate-electrolyte beverage (CE), the 6% carbohydrate-electrolyte beverage plus 4% glycerol (CEG), and a water placebo (WP) ingested at regular intervals during the first 60 min of exercise. The beverages were administered in counterbalanced order with subjects serving as their own controls. Ingestion of the glycerol solutions resulted in an increase in plasma osmolality and attenuation of the decrease in plasma volume associated with the WP treatment (P less than 0.05). Plasma renin activity was highest with WP (P less than 0.05), and G was associated with increased antidiuretic hormone levels (P less than 0.05). Ratings of perceived thirst were lowest for CEG and G, and the frequency of gastrointestinal distress was greatest for G (P less than 0.05). However, no differences among beverage treatments were observed for heart rate, esophageal temperature, sweat rate, ratings of perceived exertion, or changes in cortisol and aldosterone levels. These data indicate that there are no substantial metabolic, hormonal, cardiovascular, or thermoregulatory advantages to the consumption of solutions containing 4 or 10% glycerol during exercise.     

Incretin and islet hormonal responses to fat and protein ingestion in healthy men

Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) regulate islet function after carbohydrate ingestion. Whether incretin hormones are of importance for islet function after ingestion of noncarbohydrate macronutrients is not known. This study therefore examined integrated incretin and islet hormone responses to ingestion of pure fat (oleic acid; 0.88 g/kg) or protein (milk and egg protein; 2 g/kg) over 5 h in healthy men, aged 20-25 yr (n=12); plain water ingestion served as control. Both intact (active) and total GLP-1 and GIP levels were determined as was plasma activity of dipeptidyl peptidase-4 (DPP-4). Following water ingestion, glucose, insulin, glucagon, GLP-1, and GIP levels and DPP-4 activity were stable during the 5-h study period. Both fat and protein ingestion increased insulin, glucagon, GIP, and GLP-1 levels without affecting glucose levels or DPP-4 activity. The GLP-1 responses were similar after protein and fat, whereas the early (30 min) GIP response was higher after protein than after fat ingestion (P<0.001). This was associated with sevenfold higher insulin and glucagon responses compared with fat ingestion (both P<0.001). After protein, the early GIP, but not GLP-1, responses correlated to insulin (r(2)=0.86; P=0.0001) but not glucagon responses. In contrast, after fat ingestion, GLP-1 and GIP did not correlate to islet hormones. We conclude that, whereas protein and fat release both incretin and islet hormones, the early GIP secretion after protein ingestion may be of primary importance to islet hormone secretion.     

Circulatory and hormonal changes induced by microgravity

The absence (or decrease) of the hydrostatic pressure during space flights (microgravity state) or simulations of weightlessness (by immersion, bed rest or head-down tilt) result in a body fluid shift and an engorgement of the central circulation where mechanoreceptors involved in plasma volume regulation are located. Their activation induces the initial (first hours) hormonal response with a decrease in plasma vasopressin, renin and aldosterone and probably an increase in a natriuretic factor (Gauer reflex). Prolonged exposure to microgravity leads to more complex and often hypothetical responses: cardiovascular deconditioning, modifications in secretion and circadian rhythms of above cited hormones. After 24 years of studies on approximately 200 astronauts our knowledge of cardiovascular and hormonal adaptation to space flight is still at the beginning.     

Arterial wall neovascularization induced by glycerol

An intense and significant neovascularization, with numerous capillaries growing into the media layer of the rat femoral artery, was demonstrated when glycerol was administered into the interstitium between the femoral vein and the femoral artery. The maximum microvascularization was observed at days 7 and 9 after glycerol administration. Afterwards, involution of the majority of the newly-formed microvessels in the arterial wall occurred. Other substances containing glycerol in their molecules, such as triacetyl-glycerol and tributyril-glycerol, failed to produce significant neovascularization in the media layer of the femoral artery. Neovascularization of the arterial wall was preceded by a considerable decrease in the number of the smooth muscle cells, which experienced apoptosis and necrobiosis, disappearing in extense areas of the arterial segment affected by glycerol. Coinciding with neovascularization and microvascular involution, repopulation of the media layer by smooth muscle cells was observed.     

Effect of carbohydrate ingestion and hormonal responses on ratings of perceived exertion during prolonged cycling and running

This randomized, double-blind, placebo-controlled study was designed to determine the influence of exercise mode, and 6% carbohydrate (C) versus placebo (P) beverage ingestion, on ratings of perceived exertion (RPE) and hormonal regulation to 2.5 h of high-intensity running and cycling (approximately 75% maximum oxygen uptake) by ten triathletes who acted as their own controls. Statistical significance was set at P < or = 0.05. The pattern of change in RPE over time was significantly different between C and P ingestion (P < 0.001) and between running and cycling modes (P = 0.001). The lowest RPE values were seen in the C-cycling sessions and the highest in the P-running sessions. The pattern of change in the respiratory exchange ratio and fat and carbohydrate oxidation rates were significantly different between the C and P conditions but not between the running and cycling modes. C relative to P ingestion (but not exercise mode) was associated with higher plasma levels of glucose and insulin and lower plasma cortisol and growth hormone levels. The pattern of change in plasma levels of catecholamines and lactate did not differ between the C and P conditions. These data indicate that a lower RPE was associated with a higher level of carbohydrate oxidation, higher plasma glucose and insulin levels, and lower plasma cortisol and growth hormone levels during cycle exercise following C supplementation as compared to P feeding. These findings support a physiological link between RPE and carbohydrate substrate availability as well as selected hormonal regulation during cycle exercise.     

Effect of propranolol on glycerol induced acute renal failure in rats

The effect produced by propranolol, administered for a prolonged period of time and in large doses, on renal function in rats has been studied, as well as the modifications induced by this treatment in an experimental model of acute renal failure, and the effects of a single dose of propranolol given 1 hour before provoking failure. Propranolol, administered chronically, causes sodium and water retention and increases creatinine clearance. Acute renal failure induced by glycerol in rats treated for 7 days with propranolol is less severe than the one produced in untreated animals. In this ARF model, a single dose of propranolol does not seem to have a protective effect.     

Protection of heat induced cytoxicity by glycerol

Glycerol, at concentrations of 2–10% is a potent hyperthermic (43°–45°C) protector of cultured Chinese hamster cells, V79. Furthermore, the sensitization effect of low pH on heat death is also drastically reduced by the addition of glycerol into the culture medium. Together with the known cellular effects of heat and the role of glycerol in various cellular structures and functions, the data suggest that microtubules and membranes may be involved in the expression of heat-induced cell death.     

Estrogen receptor stereochemistry: receptor binding and hormonal responses

Estrogen stimulation of the uterus elicits a spectrum of biochemical responses which are customarily linked together. DES and certain structural analogs, indenestrol A (IA), indenestrol B (IB), indanestrol (I), and pseudo DES (PD), were used as probes to segregate various genomic responses previously considered interrelated, most notably the events of specific protein synthesis, DNA synthesis, and mitosis. These compounds have poor uterotrophic activity; except for I, they interact specifically with mouse uterine estrogen receptors (ER) with high affinity. All translocate stoichiometrically similar amounts of ER complex to the nucleus. IA and IB possess a single chiral carbon atom and exist as a mixture of enantiomers (ENT). We investigated whether the poor biological activity of IA could be explained by differential activity of the enantiomers. The IA ENT were separated to greater than 98% purity using a chirally active HPLC column. Competitive binding assays to cytosolic ER demonstrated a stereochemical chiral preference. This preference was also evident from nuclear ER translocation experiments. IB was as active as DES to induce mouse uterine glucose 6-phosphate dehydrogenase (G-6-PD), while the other compounds had weak activity. Induction of cytosolic progesterone receptor (PR) was stimulated by all the DES compounds. Ornithine decarboxylase (ODC) was stimulated 600% by DES and 180% by IB; the other compounds had no significant activity. Uterine DNA synthesis was increased by DES and IB. Thymidine autoradiography indicated nuclear labeling was occurring primarily in luminal epithelium. Treatment with PD increased uterine cell height but not cell numbers, suggesting the two responses are not necessarily interdependent as previously thought and may require two separate receptor interactions. Such a probe should be useful in studying the individual events involved in estrogen-induced uterine growth. These data also indicate that induction of ER, PR and G-6-PD are not coupled. Therefore, stimulation of a certain uterine response may depend on the structure of the particular ligand receptor complex formed, and its interaction may be regulated by specificity at the genomic acceptor site.     

Metabolic and hormonal responses during squash

The metabolic and hormonal response during squash was observed in eight normal men. Significant increases from resting were found for blood glucose, lactate, pyruvate, alanine and glycerol while total ketone bodies and plasma nonesterified fatty acids rose after play stopped. Insulin and C-peptide decreased significantly and catecholamines, ACTH, prolactin and growth hormone increased.     

Effects of hydration state on hormonal and renal responses during moderate exercise in the heat

The effects of hydromineral hormones and catecholamines on renal concentrating ability at different hydration states were examined in five male volunteers while they performed three trials. Each of these trials comprised a 60-min exercise bout on a treadmill (at 50% of maximal oxygen uptake) in a warm environment (dry bulb temperature, 35°C; relative humidity, 20–30%). In one session, subjects were euhydrated before exercise (C). In the two other sessions, after thermal dehydration (loss of 3% body mass) which markedly reduced plasma volume (PV) and increased plasma osmolality (osm_pl), the subjects exercised either not rehydrated (Dh) or rehydrated (Rh) by drinking 600 ml of mineral water before and 40 min after the onset of exercise. During exercise in the Dh compared to C state, plasma renin, aldosterone, arginine vasopressin (AVP), noradrenaline and adrenaline concentrations were increased (P < 0.05). A reduction in creatinine clearance and urine flow was also observed (P < 0.05) together with a decrease in urine osmolality, osmolar clearance and sodium excretion, while free water clearance increased (P < 0.05). However, compared to Dh, Rh partially restored PV and osm_pl and induced a marked reduction in the time courses of both the plasma AVP and catecholamine responses (P < 0.05). Values for renal water and electrolyte excretion were intermediate between those of Dh and C. Plasma atrial natriuretic peptide presented similar changes whatever the hydration state. These results demonstrate that during moderate exercise in the heat, renal concentrating ability is paradoxically reduced by prior dehydration in spite of high plasma AVP levels, and might be the result of marked activation of the sympatho-adrenal system. Rehydration, by reducing this activation, could partially restore the renal concentrating ability despite the lowered plasma AVP. Accepted: 23 April 1997     

Acute renal insufficiency in the rabbit by glycerol.

The appearance of an acute renal insufficiency in the rabbit, after glycerol injection (10, 13 or 15 ml/kg of a 50% solution) is investigated. After a 24 hours of intoxication, especially in the ten following days, cylinders, erythrocytes and renal cells appear in the urine sediment. Proteinuria appears after 24 hours and practically disappears after 72 h. Glucosuria persists from 24 hours to 6 days. Haemoglobinuria is intense after 24 and 48 hours and persists slightly about 6 days. Na, K and Cl elimination in urine diminishes clearly in all animals. Plasma K increases in non-surviving animals and does not change in those surviving. Plasma Na does not change in the dying ones, and decreases in those surviving. In non-surviving animals, pH, pCO2 and CO3H minus decrease sharply. In the surviving ones pCO2 decreases clearly after 24 hours, increasing afterwards slowly to normal values. pH increases, slightly during the first 48 hours, and then neatly during approximately 6 days. Standard CO2H minus does not change during the first 48 hours, increasing afterwards during 6 to 7 days. Histologically, the chief lesion is a vacuolar degeneration of the proximal tubule. The possible mechanisms of such alterations are discussed.     

Hyperhydration: tolerance and cardiovascular effects during uncompensable exercise-heat stress

This study examined the efficacy of glycerol andwater hyperhydration (1 h before exercise) on tolerance andcardiovascular strain during uncompensable exercise-heat stress. Theapproach was to determine whether 1-h preexercise hyperhydration (29.1 ml H₂O/kg lean body mass with orwithout 1.2 g/kg lean body mass of glycerol) provided a physiologicaladvantage over euhydration. Eight heat-acclimated men completed threetrials (control euhydration before exercise, and glycerol and waterhyperhydrations) consisting of treadmill exercise-heat stress (ratio ofevaporative heat loss required to maximal capacity of climate = 416).During exercise (~55% maximalO₂ uptake), there was nodifference between glycerol and water hyperhydration methods forincreasing (P < 0.05) total bodywater. Glycerol hyperhydration endurance time (33.8 ± 3.0 min) waslonger (P < 0.05) than for control(29.5 ± 3.5 min), but was not different(P > 0.05) from that of waterhyperhydration (31.3 ± 3.1 min). Hyperhydration didnot alter (P > 0.05) core temperature, whole body sweating rate, cardiac output, blood pressure, total peripheral resistance, or core temperature tolerance. Exhaustion from heat strain occurred at similar core and skin temperatures andheart rates in each trial. Symptoms at exhaustion included syncope andataxia, fatigue, dyspnea, and muscle cramps(n = 11, 10, 2, and 1 cases,respectively). We conclude that 1-h preexercise glycerolhyperhydration provides no meaningful physiological advantage overwater hyperhydration and that hyperhydration per se only provides theadvantage (over euhydration) of delaying hypohydration duringuncompensble exercise-heat stress.

     

Aneuploidy in male germ cells induced by alcohol ingestion

The effects of ethyl alcohol ingestion, at levels comparable to human drinking, have been evaluated by cytogenetic analysis of mouse spermatogonia and primary spermatocytes. The alcohol was administered intragastrically at different doses and for various periods of time. An increase in mitotic and first division meiotic aneuploidy was observed in direct proportion to the alcohol dose. Approximately a three-fold increase in mitotic and meiotic aneuploidy over control levels was observed in animals exposed to a daily 3 gm/kg bw dose for 6 to 28 days. The level of aneuploidy was found to return to control levels by 14 days after cessation of alcohol ingestion. Analysis of the kinetics of decrease in aneuploidy following cessation of alcohol suggests that the primal event resulting in altered chromosome numbers occurs at a stage of the cell cycle other than anaphase and therefore is not due to nondisjunction nor to anaphase lagging.     

Plant responses induced by herbivores

Physiological and chemical traits of many plant species change in response to real or simulated herbivory. These changes often have significant impacts on behavior, growth, survivorship, feeding and oviposition of insects. However, evidence that plants gain direct or indirect protection from insect enemies thereby is equivocal at present. Evidence is lacking for an impact of induced defenses on insect population dynamics, but few studies have sought it. More detailed studies of plant physiology, biochemistry, genetics and net benefit to individual plants are needed to identify the adaptive significance of induced defenses.     

Serotonergic mechanisms of the lateral parabrachial nucleus in renal and hormonal responses to isotonic blood volume expansion

This study investigated the involvement of serotonergic mechanisms of the lateral parabrachial nucleus (LPBN) in the control of sodium (Na+) excretion, potassium (K+) excretion, and urinary volume in unanesthetized rats subjected to acute isotonic blood volume expansion (0.15 M NaCl, 2 ml/100 g of body wt over 1 min) or control rats. Plasma oxytocin (OT), vasopressin (VP), and atrial natriuretic peptide (ANP) levels were also determined in the same protocol. Male Wistar rats with stainless steel cannulas implanted bilaterally into the LPBN were used. In rats treated with vehicle in the LPBN, blood volume expansion increased urinary volume, Na+ and K+ excretion, and also plasma ANP and OT. Bilateral injections of serotonergic receptor antagonist methysergide (1 or 4 microg/200 etal) into the LPBN reduced the effects of blood volume expansion on increased Na+ and K+ excretion and urinary volume, while LPBN injections of serotonergic 5-HT(2a)/HT(2c) receptor agonist, 2.5-dimetoxi-4-iodoamphetamine hydrobromide (DOI; 1 or 5 microg/200 etal) enhanced the effects of blood volume expansion on Na+ and K+ excretion and urinary volume. Methysergide (4 microg) into the LPBN decreased the effects of blood volume expansion on plasma ANP and OT, while DOI (5 microg) increased them. The present results suggest the involvement of LPBN serotonergic mechanisms in the regulation of urinary sodium, potassium and water excretion, and hormonal responses to acute isotonic blood volume expansion.     

Structural modifications of oxidized insulin B-chain induced by glycerol addition

H-NMR studies of the bovine insulin S-sulfonatedB-chain are reported in H₂O/D₂O (9/1) and inglycerol-d₅ (5 M) using two-dimensional NMRspectroscopy. The first results show that the oxidizedinsulin B-chain secondary structure differs from thatof native insulin by a loss of the -helixbetween the two disulfide bridges and that theglycerol favours the structuring of the peptide.     

Structural modifications of oxidized insulin B-chain induced by glycerol addition

Summary ¹H-NMR studies of the bovine insulin S-sulfonated B-chain are reported in H₂O/D₂O (9/1) and in glycerol-d ₅ (5 M) using two-dimensional NMR spectroscopy. The first results show that the oxidized insulin B-chain secondary structure differs from that of native insulin by a loss of the α-helix between the two disulfide bridges and that the glycerol favours the structuring of the peptide.