Hormonal, electrolyte, and renal responses to exercise are intensity dependent

Previous work indicates that the magnitude and direction of renal responses to exercise depend on the exercise intensity. To examine mechanisms responsible for these findings, renal and hormonal responses were studied in eight healthy male subjects (29.6 +/- 1.9 yr) before and immediately after four 20-min bouts of submaximal exercise (cycle ergometry) at work loads representing 25, 40, 60, and 80% of maximal oxygen consumption. Urine flow, osmotic clearance, glomerular filtration rate, and sodium excretion (UNa+V) all tended to rise at the 25% work load but were markedly reduced at the higher work intensities. Changes in urine flow paralleled changes in glomerular filtration rate (r = 0.91). Plasma vasopressin (ADH), aldosterone, and plasma renin activity tended to increase progressively with increases in work load, with the increases for all hormones reaching statistical significance when the level of exercise reached greater than or equal to 60% of maximal oxygen consumption. However, atrial natriuretic peptide was elevated (P less than 0.05) at all work loads from greater than 1.6-fold of control levels at the 25% work load to greater than 7-fold at the 80% work load. The increase in urine flow (6 of 8 subjects) and UNa+V (7 of 8 subjects) may be due to the increase in atrial natriuretic peptide and/or a 10% suppression (P less than 0.05) of ADH at the 25% work load.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hormonal and metabolic response to physical exercise, fasting and cold exposure in the rat. Effects on ketogenesis in isolated hepatocytes

Four groups of rats were subjected to the following conditions: (1) 48 h fasting, (2) 48 h of 4 degrees C cold exposure, (3) 5 h treadmill running, (4) 48 h fasting with 4 degrees C cold exposure. The groups were compared to fed control rats in order to study hormonal and metabolic responses in blood and tissue samples. Isolated hepatocytes were used to evaluate the rate of ketogenesis. Decreases in liver glycogen and increases in blood free fatty acids (FFA) confirmed that glycogenolysis and lipolysis occur in these situations of metabolic stress. Increases in the glucagon/insulin plasma ratio were also noted. Plasma catecholamine levels were only enhanced after running and after cold exposure. Production of blood ketone bodies was stimulated more by running and by fasting than by cold exposure. The low ketone body production observed after cold exposure seems to be linked to increases liver glycogen levels and decreased FFA availability. Liver cells isolated after cold exposure exhibited higher ketogenesis than these isolated after running. This difference in ketogenic capacity could result both from the longer hormonal stimulation by high glucagon/insulin plasma ratios and from the metabolic state of the liver.     

Hormonal and ion regulatory response in three freshwater fish species following waterborne copper exposure

We evaluated effects of sublethal copper exposure in 3 different freshwater fish: rainbow trout (Oncorhynchus mykiss), common carp (Cyprinus carpio) and gibel carp (Carassius auratus gibelio). In a first experiment we exposed these fishes to an equally toxic Cu dose, a Cu level 10 times lower than their 96 h LC₅₀ value: 20, 65, and 150 µg/L Cu. In a second series we exposed them to the same Cu concentration (50 µg/L). Na⁺/K⁺-ATPase activity in gill tissue was disturbed differently in rainbow trout then in common and gibel carp. Rainbow trout showed a thorough disruption of plasma ion levels at the beginning of both exposures, whereas common carp and gibel carp displayed effects only after 3 days. Rainbow trout and common carp thyroid hormones experienced adverse effects in the beginning of the exposure. The involvement of prolactin in handling metal stress was reflected in changes of mRNA prolactin receptor concentrations in gill tissue, with an up regulation of this mRNA in rainbow trout and a down regulation in gibel carp, which was more pronounced in the latter. Overall, rainbow trout appeared more sensitive in the beginning of the exposure, however, when it overcame this first challenge, it handled copper exposure in a better manner then common and gibel carp as they showed more long term impacts of Cu exposure.     

Hormonal response to restraint in rhesus monkeys

Abstract: The purpose of this study was to characterize the hormonal responses to a restraining system in four adult male rhesus monkeys (Macaca mulatta) in preparation for a spaceflight project. After the monkeys were accustomed to food and water (Phase I), blood-volume-regulating hormones were measured during three phases: 10 days in a metabolic cage (Phase II), 16 days sitting in a restrained position in a specially designed metabolism chair (Phase III) and 10 days in metabolic cage (Phase IV). An increase of active renin (30%) and vasopressin (25%) was observed at the end of Phase III. A decrease of atrial natriuretic peptide (ANP), urodilatin, and sodium excretion occurred during the first days of Phase III. Catecholamines were unchanged. A dramatic increase (tenfold) in urinary excretion of growth hormone occurred during all of Phase III and at the beginning of Phase IV. These findings are similar to those found in man during isolation inactivity and during confinement stress.     

Hormonal response to competition among male coalitions

Previous research has shown that testosterone (T) and cortisol (C) are released in response to a wide variety of social stimuli including dyadic (one on one) competitive events, but humans also compete as groups. Here we report results from a pilot study of hormonal responses to competition between male coalitions. Salivary T and C levels were assessed in adult males from a rural Caribbean village who competed at dominoes, as two-man teams, against (a) familiar men from their own village (within coalition), and (b) strangers from another village (between coalitions). Analyses indicate that both T and C levels were higher and responses more pronounced for between-village competition than for within-village competition, but we could not compare responses to victory and defeat in the between-village case, since our subjects happened to win both such contests. Further studies of endocrine responses in the context of coalitional competition are warranted.     

Hormonal responses to exercise during moderate cold exposure in young vs. middle-age subjects.

The influence of moderate cold exposure on the hormonal responses of atrial natriuretic factor (ANF), arginine vasopressin (AVP), catecholamines, and plasma renin activity (PRA) after exhaustive exercise was studied in 9 young and 10 middle-aged subjects. Exercise tests were randomly performed in temperate (30 degrees C) and cold (10 degrees C) environments. Heart rate, oxygen consumption, and peripheral arterial blood pressure were measured at regular intervals. Blood samples were collected before and immediately after exercise at 30 or 10 degrees C. Plasma sodium and potassium concentrations as well as hemoglobin and hematocrit were measured, and the change in plasma volume was calculated. At rest and during exercise, oxygen consumption was similar during exposure to both temperate and cold temperatures. During submaximal exercise intensities, the rise in heart rate was blunted while the increase in systolic blood pressure was significantly greater at 10 than at 30 degrees C. The increases in plasma sodium and potassium concentrations after exhaustion were similar between environments, as was the decrease in plasma volume. In both groups, all plasma hormones were significantly elevated postexercise, with the AVP response similar at 10 and 30 degrees C. However, the norepinephrine and ANF responses were significantly greater while the PRA response was significantly reduced at 10 degrees C. In the middle-aged subjects the epinephrine response to exercise was higher at 10 than at 30 degrees C. The greater ANF and reduced PRA responses to exercise in the cold may have resulted from central hemodynamic changes caused by cold-induced cutaneous vasoconstriction.(ABSTRACT TRUNCATED AT 250 WORDS)     

The morphological response of Kc-H cells to ecdysteroids: Hormonal specificity

Summary Cells of the line Kc, derived fromDrosophila melanogaster embryos, extend long processes when exposed to ecdysteroid hormones. We have devised a quantitative assay for this morphological response, using the subline Kc-H. The assay was used to characterize the conditions required for the response. A halfmaximal response is elicited by approximately 10^–8M 20-hydroxyecdysone; the response is saturated by 10^–7M 20-hydroxyecdysone, which causes detectable elongation within a few hours, and a maximal response after 2–3 days. The response occurs substantially normally in the absence of serum, during growth in suspension, and in over-crowded cultures. It is not elicited by cyclic nucleotides, vertebrate growth factors, or a variety of other non-ecdysteroid reagents. Of 60 ecdysteroid compounds tested, only those which were active in other insect test systems elicited the response, and the concentrations required were approximately proportional to the concentrations active in other in vitro systems. We conclude that the response of Kc cells to 20-hydroxyecdysone retains basic features of the ecdysteroid response of intact tissues and therefore that Kc cells are a useful model system for studying ecdysteroid action.     

Effect of altitude exposure on thermoregulatory response of man to cold.

The thermoregulatory responses to 10 degrees C (for 3 h) were investigated in 1) 12 natives from sea level (lowlanders) at 150 m, and on arrival at 3,350 and 4,340 m; 2) 6 of these during a 6-wk sojourn at 4,360 m, and on return to sea level; and 3) 5 natives from each of the two altitudes (highlanders) in their respective habitat, and after descent to 150 m. The cold-induced increase in the rate of O2 consumption (Vo2) of the lowlanders was significantly smaller at both altitudes than at sea level. It did not recover substantially during the 6 wk at altitude, but was restored to its initial rate on return to sea level. By contrast, visible shivering activity was augmented on arrival at altitude. It persisted throughout the 6 wk there, but was greatly depressed on return to sea level, despite the increased Vo2. Mean skin temperatures (Tsk) stabilized in the cold at significantly higher values at altitude. Rectal temperature (Tre) decreased similarly at all altitudes. Vo2 of the highlanders in the cold was significantly greater at sea level than at their resident altitudes, although shivering activity was less intense; Tsk stabilized at significantly lower levels at 150 m than at either altitude. These results indicate that altitude exposure reduces the calorigenic response of man to cold, and that this effect is not moderated by acclimatization to altitude, yet is reversible immediately on descent to sea level. The component of cold thermogenesis which appeared to be reduced by altitude exposure was nonshivering thermogenesis rather than visible shivering.     

Recovery of acetylcholine response of denervated muscle following exposure to alpha-bungarotoxin.

Experiments were performed using denervated muscles and the irreversible cholinergic inhibitor α-Bungarotoxin. After eliminating the membrane voltage response to carbamylcholine by exposure to α-Bungarotoxin, the response was observed to recover to 30% of its original value after 5 hours. Additional experiments suggest that the dissociation of α-Bungarotoxin from the extrajunctional receptors may be responsible. It was also observed that d-tubocurarine, normally a rapidly reversible competitive inhibitor, acts as either a noncompetitive, an uncompetitive, or a slowly reversible competitive inhibitor after recovery from α-Bungarotoxin. Unlike d-tubocurarine, the rapidly reversing comeptitive effect of hexamethonium was not changed.     

Glycogenolytic response to glucagon of cultured fetal hepatocytes. Refractoriness following prior exposure to glucagon.

The glycogenolytic effect of glucagon has been studied in fetal hepatocytes cultured for 3 to 4 days in the presence of cortisol (10 muM). The hepatocytes, when transplanted from young fetuses (15-day-old), contain only minute amounts of glycogen, whereas when cultured 3 to 4 days in the presence of cortisol, they contain high levels of stored glycogen. Glucagon induced a rapid but partial mobilization of glycogen, which was maximal after 2 hours. The half-maximal response was observed with about 0.1 nM glucagon. The glycogenolytic effect of glucagon in fetal hepatocytes is probably mediated by cyclic adenosine 3':5'-monophosphate (cyclic AMP) as in adult liver. This effect was mimicked by cyclic AMP and N-6, O-2-dibutyryl cyclic AMP, (dibutyryl cyclic AMP), and potentiated by theophylline. Glucagon addition was followed by accumulation of cyclic AMP in the cells within 2 min. Glucagon produces a marked stimulation of the rate of glycogen breakdown and an inhibition of the rate of incorporation of [14-C] glucose into glycogen. The glycogeneolytic effect of a single addition of glucagon was reversed within 4 hours. A second addition of glucagon at this time was unable to induce a new glycogenolytic response. A resistance to glucagon stimulation appeared in the cells after a first exposure to the hormone. This refractoriness was also shown by the loss of glucagon-dependent cyclic AMP accumulation and was not linked to the release by the cells of a "hormone antagonist" into the medium. The hepatocytes resistant to the action of glucagon retained their response to cyclic AMP, dibutyryl cyclic AMP, and norepinephrine. Finally, glycogenolytic concentrations of cyclic AMP and of its dibutyryl derivative failed to induce a refractoriness to glucagon.     

Short exposure of polymorphonuclear leucocytes to sodium fluoride suppresses the response to fMLP.

Fluoridated dental care products are used to prevent dental decay. Up to now, there are no data available on whether the fluoride (F-) component of these products affects the bactericidal activity of salivary polymorpho-nuclear leucocytes, which are involved in the protection of the oral mucosa against infection. Therefore, after determining the concentration/time profile of F- in mixed saliva of healthy subjects after topical application of 0.5 g of a 1.25% F- containing gel, unstimulated and fMLP-stimulated polymorphonuclear leucocytes (PMNs) were shortly exposed to these F- concentrations and the generation of superoxide and hypochloric acid were measured, as well as the liberation of lysomal enzymes, and correlated with the cellular Ca2+ and cAMP-levels. The results show that F-, at concentrations as retained in saliva, did not activate the oxidative burst in unstimulated PMNs. In fMLP-activated PMNs, F-suppressed the receptor-mediated increase in the oxidative burst and the liberation of fl-glucuronidase by reduction of the availability of extracellular Ca2+ and, thus, the influx of Ca2+ necessary to couple completely the fMLP signal to effector pathways. These F- concentrations neither altered the liberation of Ca2+ from internal stores nor induced a rise in cAMP. The possible clinical consequences of these results for xerostomic patients with respect to the generation of HOSCN/OSCN/SCN in saliva an important non-immune factor for oral health, are dicussed.     

Interleukin-6 response to exercise and high-altitude exposure: influence of alpha-adrenergic blockade.

Interleukin-6 (IL-6), an important cytokine involved in a number of biological processes, is consistently elevated during periods of stress. The mechanisms responsible for the induction of IL-6 under these conditions remain uncertain. This study examined the effect of alpha-adrenergic blockade on the IL-6 response to acute and chronic high-altitude exposure in women both at rest and during exercise. Sixteen healthy, eumenorrheic women (aged 23.2 +/- 1.4 yr) participated in the study. Subjects received either alpha-adrenergic blockade (prazosin, 3 mg/day) or a placebo in a double-blinded, randomized fashion. Subjects participated in submaximal exercise tests at sea level and on days 1 and 12 at altitude (4,300 m). Resting plasma and 24-h urine samples were collected throughout the duration of the study. At sea level, no differences were found at rest for plasma IL-6 between groups (1.5 +/- 0.2 and 1.2 +/- 0.3 pg/ml for placebo and blocked groups, respectively). On acute ascent to altitude, IL-6 levels increased significantly in both groups compared with sea-level values (57 and 84% for placebo and blocked groups, respectively). After 12 days of acclimatization, IL-6 levels remained elevated for placebo subjects; however, they returned to sea-level values in the blocked group. alpha-Adrenergic blockade significantly lowered the IL-6 response to exercise both at sea level (46%) and at altitude (42%) compared with placebo. A significant correlation (P = 0.004) between resting IL-6 and urinary norepinephrine excretion rates was found over the course of time while at altitude. In conclusion, the results indicate a role for alpha-adrenergic regulation of the IL-6 response to the stress of both short-term moderate-intensity exercise and hypoxia.     

Transcriptional response of mushrooms to artificial sun exposure

Climate change causes increased tree mortality leading to canopy loss and thus sun‐exposed forest floors. Sun exposure creates extreme temperatures and radiation, with potentially more drastic effects on forest organisms than the current increase in mean temperature. Such conditions might potentially negatively affect the maturation of mushrooms of forest fungi. A failure of reaching maturation would mean no sexual spore release and, thus, entail a loss of genetic diversity. However, we currently have a limited understanding of the quality and quantity of mushroom‐specific molecular responses caused by sun exposure. Thus, to understand the short‐term responses toward enhanced sun exposure, we exposed mushrooms of the wood‐inhabiting forest species Lentinula edodes, while still attached to their mycelium and substrate, to artificial solar light (ca. 30°C and 100,000 lux) for 5, 30, and 60 min. We found significant differentially expressed genes at 30 and 60 min. Eukaryotic Orthologous Groups (KOG) class enrichment pointed to defense mechanisms. The 20 most significant differentially expressed genes showed the expression of heat‐shock proteins, an important family of proteins under heat stress. Although preliminary, our results suggest mushroom‐specific molecular responses to tolerate enhanced sun exposure as expected under climate change. Whether mushroom‐specific molecular responses are able to maintain fungal fitness under opening forest canopies remains to be tested.