Influence of hyperosmotic shrinkage and β-adrenergic stimulation on red blood cell volume regulation and oxygen binding properties in rainbow trout and carp

Whole blood from rainbow trout and carp was subjected to hyperosmotic shock and subsequent beta-adrenergic stimulation (isoprenaline) at different oxygen tension ( PO(2)) and carbon dioxide tension ( PCO(2)) levels with the aim to evaluate changes in red blood cell (RBC) volume, pH and ion concentrations and their ultimate effect on blood O(2) transport characteristics. Hyperosmolality (addition of NaCl) induced RBC shrinkage, which was followed by a regulatory volume increase (RVI) that was larger at low than at high PO(2)and more complete in carp than in trout. Carp RBC showed practically full volume recovery within 140 min at low PO(2)and partial recovery at high PO(2), whereas RVI was partial under all PO(2)and PCO(2)conditions in trout. The RVI increased intracellular [Na(+)], water content, and, in carp, also pH (pHi), suggesting activation of Na(+)/H(+) exchange. In trout RBCs, activation of RVI was rapid but succeeded by deactivation. In carp RBCs, activation of Na(+) influx was slower but it continued, allowing full volume recovery. Shrinkage of the RBCs was associated with only minor decreases in blood oxygen saturation and oxygen affinity in both species. Thus, the oxygen affinity decrease expected on the basis of the increased concentration of intracellular haemoglobin and organic phosphates was small, and it appeared to some extent countered during RVI by an oxygen affinity increase via increased pHi. Addition of isoprenaline increased RBC volume and pHi and increased Hb oxygen saturation. The beta-adrenergic response was stronger at low compared to high PO(2) and at high compared to low PCO(2). The PO(2) dependency was largest in carp, whereas the PCO(2) (pH) dependency was more expressed in trout. The adrenergic response of trout RBCs was similar under isoosmotic and hyperosmotic conditions. In carp RBCs, the response was absent at high PO(2) under isoosmotic conditions, but interestingly it could be induced under hyperosmotic conditions. The data suggest that the RBC shrinkage occurring in fish moving from freshwater to seawater has minimal impact on blood O(2) binding properties.     

The physiological response of diploid and triploid brook trout to exhaustive exercise

Using triploidy as an experimental model, we examined whether cell size limits the post-exercise recovery process in fish. Because triploids generally possess larger cells, which could affect many physiological and biochemical processes, we hypothesized that triploids would take longer to recover from exhaustive exercise compared to diploids. To test this, we measured plasma lactate, glucose and osmolality, and white muscle energy stores (glycogen, phosphocreatine and ATP) and lactate before and immediately following exhaustive exercise and during recovery at 2 and 4 h post-exercise. In addition, oxygen consumption and ammonia excretion rates were determined before and after exhaustive exercise. Overall, diploid and triploid brook trout showed similar metabolic responses exercise, but plasma osmolality, white muscle lactate, white muscle ATP and post-exercise oxygen consumption rates recovered earlier in triploids compared to diploids. The results of this study suggest that the characteristic larger cell size of triploidy does not limit the physiological response to, or recovery from, exhaustive exercise.     

Why do fish die after severe exercise?

Trout fitted with dorsal aortic cannulae were subjected to 6 min of intensive exercise and monitored over the following 12 h recovery period. Delayed mortality was 40%; the majority of deaths occurred 4–8 h post-exercise. Surviving fish exhibited a short-lived haemoconcentration reflected in increased haematocrit, haemoglobin, plasma protein, Na⁺ and Ch^- levels; an extended rise in plasma [K⁺]; a quickly corrected respiratory acidosis; and a more prolonged metabolic acidosis in concert with a rise in blood lactate. Dying fish exhibited very similar trends except for a significantly greater metabolic acidosis, lower plasma [Cl^-], and the apparent accumulation of an unknown anion in the blood prior to death. Cardiac failure did not occur. Blood metabolic acid levels, while elevated, were only ∼ 50% of peak lactate anion levels and well within the normal range of tolerance, as were all other changes observed in the blood of non-survivors. The hypothesis that post-exercise mortality is due to excessive 'lactic acid' accumulation in the blood is discounted. It is suggested that intracellular acidosis may be the proximate cause of death.     

Linking physiological and cellular responses to thermal stress: β-adrenergic blockade reduces the heat shock response in fish

When faced with stress, animals use physiological and cellular strategies to preserve homeostasis. We were interested in how these high-level stress responses are integrated at the level of the whole animal. Here, we investigated the capacity of the physiological stress response, and specifically the β-adrenergic response, to affect the induction of the cellular heat shock proteins, HSPs, following a thermal stress in vivo. We predicted that blocking β-adrenergic stimulation during an acute heat stress in the whole animal would result in reduced levels of HSPs in red blood cells (RBCs) of rainbow trout compared to animals where adrenergic signaling remained intact. We first determined that a 1 h heat shock at 25 °C in trout acclimated to 13 °C resulted in RBC adrenergic stimulation as determined by a significant increase in cell swelling, a hallmark of the β-adrenergic response. A whole animal injection with the β₂-adrenergic antagonist, ICI-118,551, successfully reduced this heat-induced RBC swelling. The acute heat shock caused a significant induction of HSP70 in RBCs of 13 °C-acclimated trout as well as a significant increase in plasma catecholamines. When heat-shocked fish were treated with ICI-118,551, we observed a significant attenuation of the HSP70 response. We conclude that circulating catecholamines influence the cellular heat shock response in rainbow trout RBCs, demonstrating physiological/hormonal control of the cellular stress response.     

Proenkephalin peptide F immunoreactivity in different circulatory biocompartments after exercise

This study was the first study to examine the three circulatory biocompartments (plasma, white blood cell layer (WBC) and red blood cell layer (RBC)) and determine PF concentrations before and after exercise. Proenkephalin peptide F (PF) is an enkephalin-containing peptide found predominantly within the adrenal medulla. PF is co-packaged with epinephrine, and both can be co-secreted in response to similar stimuli. PF and epinephrine have shown immunomodulating properties. Ten healthy resistance trained men performed six sets of 10 RM squats with 2 min rest periods between sets and 10 healthy active men were matched and served as resting controls. Blood samples were obtained pre-exercise, immediately post-exercise and 15 min post-exercise and were analyzed for lactate, cortisol, epinephrine and biocompartmentalized PF. There was no change in resting control values measured across time within respective PF biocompartments and endocrine profile, indicating stability and technique validity of peptide F across the time period measured. As expected, the acute resistance exercise protocol caused an increase in lactate at 15 min post-exercise. Circulating epinephrine increased immediately post-exercise and returned to baseline during 15 min into recovery. Plasma PF increased immediate post-exercise and 15 min post-exercise, while WBC-PF and RBC-PF only increased at 15 min into recovery. For all time points tested, resting and exercise WBC-PF and RBC-PF concentrations were lower than plasma PF thus indicating a concentration difference across the three different biocompartments within the same blood sample. The presence of PF within all three biocompartments of whole blood may indicate the potential for biological transport and interactions with other cells in other biocompartments of the blood.     

Isolation and preliminary characteristics of β-N-acetylglucosaminidase in the sperm of Siberian sturgeon (Acipenser baerii) and rainbow trout (Oncorhynchus mykiss)

The aim of this study was to characterize the enzyme β- N -acetyglucosaminidase (β-NAGase) in the milt and spermatozoa extracts from Siberian sturgeon and rainbow trout. After ion exchange chromatography one protein peak showed β-NAGase activity in sturgeon milt plasma and sperm extracts of both species. Surprisingly, two protein peaks showing β-NAGase activity were found in rainbow trout milt plasma. The molecular mass of β-NAGase was estimated by gel filtration as 127 kDa for rainbow trout spermatozoa, 271 kDa for sturgeon spermatozoa, and 74 kDa for milt plasma from both species. The kinetic parameters were determined for milt plasma and sperm extracts. The optimum pH of the β-NAGases was 3.8 for sturgeon milt plasma, 4.4 for sturgeon sperm extract, and 4.4–4.8 for milt plasma and sperm extract from rainbow trout. K _m value of the β-NAGases was 0.212, 0.563, 0.779 m m for sturgeon milt plasma, sturgeon sperm extract or rainbow trout extract, respectively. The β-NAGase from sperm extracts in both species showed 100% activity even after incubation at 56°C by 20 min, whereas its activity was decreased to 23% in sturgeon milt plasma and to 2% in trout milt plasma.     

Increase in kinins on post-exercise hypotension in normotensive and hypertensive volunteers

Post-exercise hypotension is an important event for blood pressure regulation, especially in hypertensive individuals. Although post-exercise hypotension is a well-known phenomenon, the mechanism responsible is still unclear. The kallikrein-kinin system is involved in blood pressure control, but its role in post-exercise hypotension has not yet been investigated. Thus, the purpose of this study was to investigate the involvement of the vasodilators bradykinin and des-Arg(9)-BK and kallikrein activity in post-exercise hypotension promoted by 35 min of cycle ergometer (CE) or circuit weight-training (CWT) bouts in normotensive and hypertensive individuals. A significant decrease in mean arterial pressure at 45 and 60 min after CE and 45 min after CWT was observed in normotensive individuals. Hypertensive values of mean arterial pressure were significantly reduced at 45 and 60 min after CE and at 60 min after CWT. Before exercise, plasma bradykinin concentrations and kallikrein activity were higher in hypertensive compared to normotensive volunteers. Kinin levels increased in the groups evaluated at the end of the training period and 60 min post-exercise. These data suggest that the kallikrein-kinin system may be involved in post-exercise hypotension in normotensive and hypertensive individuals subjected to CE and CWT bouts.     

Alpha 2-adrenergic receptors accelerate Na+/H+ exchange in neuroblastoma X glioma cells

The regulation of cytoplasmic pH (pHi) was examined in neuroblastoma X glioma hybrid cell-line cells (NG108-15 cells) using 2,7-biscarboxyethyl-5(6)-carboxyfluorescein. The pHi of NG108-15 cells suspended in nominally HCO-3-free, Na+-containing buffer could be reduced by the external application of acetate. The recovery of pHi to its resting value was blocked by the removal of extracellular Na+, by the addition of extra-cellular H+, and by the addition of analogs of amiloride selective for inhibition of Na+/H+ exchange. The rate of recovery of pHi from acid load exhibited an ionic selectivity of Na+ greater than Li+ much greater than K+, and no recovery was observed in N-methyl-D-glucamine+. Tetrodotoxin and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid had no effect on early pHi recovery. These data suggest that Na+/H+ exchange accounts primarily for the recovery of pHi in NG108-15 cells under our experimental conditions. Na+/H+ exchange in NG108-15 cells was accelerated by alpha 2-adrenergic receptors. Thus, (-)epinephrine, but not (+)epinephrine, elicited an intracellular alkalinization which was blocked by the alpha 2-adrenergic receptor selective antagonist yohimbine but not by the alpha 1-adrenergic receptor antagonist, prazosin, nor the beta-adrenergic antagonist, propranolol. Norepinephrine, clonidine, and the clonidine analog, UK-14304, also caused alkalinization of NG108-15 cells, whereas isoproterenol, a beta-adrenergic receptor agonist, and phenylephrine, a selective alpha 1-adrenergic receptor agonist, did not. Manipulations that blocked Na+/H+ exchange blocked the ability of alpha 2-adrenergic agonists to alkalinize the interior of NG108-15 cells without blocking the ability of these agonists to attenuate cAMP accumulation. These findings provide the first direct evidence of modulation of Na+/H+ exchange activity by a receptor linked to inhibition of adenylate cyclase and offer a possible mechanism whereby alpha 2-adrenergic receptors might influence cellular activity apart from changes in cyclic nucleotide metabolism.     

The effects of high-intensity intermittent exercise on the plasma concentrations of glutamine and organic acids

Glutamine is an essential substrate for the proper functioning of cells of the immune system. Falls in plasma glutamine concentration after exercise may have deleterious consequences for immune cell function and render the individual more susceptible to infection. The purpose of the present study was to examine changes in plasma glutamine concentration (measured using a validated enzymatic spectrophotometric method) following an acute bout of intermittent high-intensity exercise. Eight well-trained male games players took part in the study. Subjects reported to the laboratory following an overnight fast and performed a 1-h cycle exercise task consisting of 20 1-min periods at 100% maximal O₂ consumption (V˙O_2max) each separated by 2 min of recovery at 30% V˙O_2max. Venous blood samples were taken before exercise and at 5 min, 1 h, 2.5 h, 5 h and 24 h post-exercise. Glutamine was measured by enzymatic spectrophotometric determination of the ammonia concentration before and after treatment of the plasma with glutaminase (EC 3.5.1.2). Plasma glutamine concentration did not fall in the immediate post-exercise period [pre-exercise 681 (23) μM compared with 663 (46) μM at 5 min post-exercise, mean (SEM)], but fell to 572 (35) μM at 5 h post-exercise (P < 0.05 compared with pre-exercise). Plasma lactate concentration rose to 8.8 (1.0) mM at the end of exercise and fell to 1.8 (0.4) mM at 1 h post-exercise, but plasma concentrations of free fatty acids and β-hydroxybutyrate both rose substantially in the post-exercise period (to 240% and 400% of pre-exercise levels, respectively). The circulating leucocyte count increased significantly during exercise (P < 0.01), continued to increase in the hours following exercise and peaked at 2.5 h post-exercise (mainly due to a neutrophilia). The fall in the plasma glutamine concentration at 5 h post-exercise could be due to increased renal uptake of glutamine, which generally occurs in conditions of metabolic acidosis or due to a greater removal of glutamine from the plasma resulting from the elevated circulating leucocyte count. Accepted: 22 October 1997     

Adrenergic involvement in blood oxygen transport and acid-base balance during hypercapnic acidosis in the Rainbow Trout,Salmo gairdneri

Summary Rainbow trout (Salmo gairdneri) were subjected to 12 h of external hypercapnia (1% CO₂ in air) during - and/or -adrenoceptor blockade in order to assess the importance of adrenergic responses in modulating blood oxygen transport and acid-base balance during an acute acidotic stress. External hypercapnia caused an elevation of blood carbon dioxide tension and a reciprocal decrease in whole blood pH. A gradual elevation of blood bicarbonate levels caused whole blood pH to increase toward pre-hypercapnic values throughout the hypercapnic period. Pre-treatment of fish with propranolol (a -adrenoceptor antagonist) or phentolamine (an -adrenoceptor antagonist) did not affect their ability to regulate extracellular acid-base status during hypercapnia. On the other hand, adrenergic responses were essential in the maintenance of arterial blood oxygen content during hypercapnia despite the severe extracellular acidosis and a marked Root effect in trout blood, in vitro. Important adrenergic responses included pronounced increases in haematocrit (an -adrenergic effect) and arterial oxygen tension (- and -adrenergic effects) as well as partial regulation of red blood cell pH (a -adrenergic effect). Although pre-treatment of fish with either propranolol or phentolamine caused a reduction in blood oxygen content during hypercapnia, fish died only during complete adrenoceptor blockade, presumably due to severe hypoxemia.Symbols and abbreviations total concentration of oxygen or carbon dioxide, respectively - hct haemotocrit - rbc red blood cell     

The effect of pre-fasting diet and water temperature on liver glycogen and liver weight in rainbow trout, Salmo gairdneri Richardson, during fasting

The effect of feeding an isocaloric and isonitrogenous trout diet that contained different levels of digestible carbohydrate (cerelose) to rainbow trout at either 10 or 15° C on liver glycogen and liver weight was determined in two fasting studies of 12 and 41 days duration. Trout fed diets with increased levels of digestible carbohydrate (HC) had significantly higher liver-body weight ratios (LW) and liver glycogen (LG) than trout reared on low digestible carbohydrate diets (HF). Both LW and LG declined in fasting trout previously fed HC diets but declined little in fasting trout previously fed HF diets. Trout reared at 10° C had higher LW and LG than trout reared at 15° C on either the HC or HF diets. During fasting, the trout reared on HC diets at 10° C required a longer period of time for the LG and LW to decline to the levels of trout reared on the low carbohydrate diets, than did trout reared on the HC diets at 15° C. The results indicate that both pre-fasting diet and water temperature can affect liver glycogen utilization and liver weight in fasting trout. Prolonged elevation of LW and LG in fasting trout could jeopardize the survival rate of stocked trout, particularly at low water temperatures.     

Exercise in a hot environment influences plasma anti-inflammatory and antioxidant status in well-trained athletes

Exercise in thermally stressful environmental conditions can enhance oxidative stress. We sought to measure the plasma antioxidant defenses and cytokine response together with oxidative damage post-exercise in a temperate versus a hot environment. The plasma concentrations of vasoactive endothelin-1 and vascular angiogenic growth factor were also evaluated. Male athletes (n=9) volunteered to participate. The athletes randomly performed two bouts of treadmill exercise of 45 min at 75–80% of maximal oxygen uptake in a climatic-controlled chamber under two different conditions: temperate environment (10–12 °C, 40–55% humidity) and hot, humid environment (30–32 °C, 75–78% humidity). Venous blood samples were obtained immediately pre- and post-bout and on recovery after 2 h. Serum glucose, malondialdehyde and lactate concentrations were significantly increased post-exercise in hot but maintained in the temperate environment; these post-exercise values were significantly higher after exercise in hot than in temperate. Urinary 8-hydroxy-2′-deoxyguanosine concentration, plasma phosphocreatine kinase and catalase activities, creatinine and monocyte chemoattractant protein-1, and interleukin-6 significantly increased post-exercise in hot but maintained in temperate environment. The post-exercise circulating values of antioxidant enzyme paraoxonase-1 and endothelin were significantly higher in the hot than in temperate environment. Exercise in a hot and humid environment resulted in mild hyperthermia with elevated perceived exertion and thermal stress. Hyperthermic environment induced hyperglycemia, lactatecidemia and more cellular and oxidative damage than exercise in a temperate environment but also induced a post-exercise antioxidant and anti-inflammatory response in plasma. These results suggest that environmental temperature needs to be taken into account when evaluating exercise-related oxidative stress and inflammation.     

Cardiovascular adjustments to rhythmic handgrip exercise: relationship to electromyographic activity and post-exercise hyperemia

The purpose of this study was to examine the association among electromyographic (EMG) activity, recovery blood flow, and the magnitude of the autonomic adjustments to rhythmic exercise in humans. To accomplish this, 10 healthy subjects (aged 23-37 y) performed rhythmic handgrip exercise for 2 min at 5, 15, 25, 40, and 60% of maximal voluntary force. Heart rate and arterial blood pressure were measured at rest (control), during each level of exercise, and for 2 min following exercise (recovery). The rectified, filtered EMG activity of the exercising forearm was measured continuously during each level of exercise and was used as an index of the level of central command. Post-exercise hyperemia was calculated as the difference between the control and the average recovery (2 min) forearm blood flows (venous occlusion plethysmography) and was examined as a possible index of the stimulus for muscle chemoreflex activation. Heart rate, arterial pressure, forearm EMG activity, and post-exercise hyperemia all increased progressively with increasing exercise intensity. The magnitudes of the increases in heart rate and arterial pressure from control to exercise were directly related to both the level of EMG activity and the degree of post-exercise hyperemia across the five exercise intensities (delta heart rate vs EMG activity: r = 0.99; delta arterial pressure vs EMG activity: r = 0.99; delta heart rate vs hyperemia: r = 0.99; and delta arterial pressure vs hyperemia: r = 0.98; all p less than 0.01). Furthermore, the level of EMG activity was directly related (r = 0.99) to the corresponding degree of hyperemia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Use of trout serum to prepare primary attached monolayer cultures of hepatocytes from rainbow trout (Salmo gairdneri)

Summary The influence of trout serum on the attachment and spreading of isolated trout hepatocytes maintained in primary culture at different temperatures was evaluated. Hepatocytes were obtained from young rainbow trout (Salmo gairdneri) by collagenase dissociation and maintained in modified Leibowitz L15 medium at 10° or 27° C for 24 h in plastic dishes previously coated with type I bovine collagen. In the absence of serum, fewer than 10% of hepatocytes attached and none of them spread on the collagen substrate. Trout serum at concentrations as low as 1.25% in the medium resulted in a pronounced concentration-dependent increase in hepatocyte attachment, as determined by direct counts by phase contrast microscopy, or by percentage of lactate dehydrogenase activity attached to the dishes after washing away unattached cells. Attachment rates were greater at the lower temperature (10° C). Trout serum also substantially increased the proportion of attached hepatocytes that spread as monolayers on the collagen substrate, especially at 10° C. By comparison, fetal bovine serum had little influence on the attachment or spreading of trout hepatocytes. These studies demonstrate a simple inexpensive method for preparing attached monolayer trout hepatocyte cultures. This procedure may be useful in toxicologic or functional studies in which fish hepatocyte attachment is an operational requirement.     

Depletion of high energy phosphates implicates post-exercise mortality in carp and trout; an in vivo 31P-NMR study.

As in vivo 31P-Nuclear Magnetic Resonance spectroscopy is currently the state of the art method to measure continuously intracellular pH (pH(i)) and energy status of muscle tissue, we used this method to study the recovery from exhaustive exercise. The biochemical changes during recovery are not well understood and it was suggested that post-exercise mortality could be caused by low pH(i); other studies however indicate that energy depletion might be more important. To analyse the mechanism of post-exercise recovery pH(i), ATP, P(i), and PCr must be measured at the same time, which is possible using in vivo 31P-NMR. Common carp and rainbow trout of about 100 g were exercised to exhaustion in a swim tunnel. After swimming 10 h at 1.5 body lengths (BL)/s (aerobic control), 50% of the fish were forced to swim at 6 BL/s until exhaustion. Recovery of energy rich phosphates was found to be faster in carp (1.2-1.9 h) than in trout (1.5-2.3 h). The same applied for the recovery from acidosis, which took 1.75 h in carp and 5.75 h in trout. In parallel experiments the energy phosphates and lactate levels were measured in liver, red muscle, and white muscle. Exhaustion caused a significant drop in the energy status of red and white muscle tissue of trout and carp (corroborates NMR data), while no change at all was observed in liver tissue. The lactate levels were increased in the muscle but not in liver and blood. While all experimental animals looked healthy after exhaustion, 40-50% of the carp as well as trout died during the recovery phase. The energy status of those individuals measured by 31P-NMR was much lower than that of the survivors, while in contrast there was no difference in pH(i). Thus, it appears that not acidosis but depletion of high energy phosphates disabled muscle function and therefore may have been the cause of death of the non-survivors.     

Depletion of high energy phosphates implicates post-exercise mortality in carp and trout; an in vivo 31P-NMR study

As in vivo 31P-Nuclear Magnetic Resonance spectroscopy is currently the state of the art method to measure continuously intracellular pH (pH(i)) and energy status of muscle tissue, we used this method to study the recovery from exhaustive exercise. The biochemical changes during recovery are not well understood and it was suggested that post-exercise mortality could be caused by low pH(i); other studies however indicate that energy depletion might be more important. To analyse the mechanism of post-exercise recovery pH(i), ATP, P(i), and PCr must be measured at the same time, which is possible using in vivo 31P-NMR. Common carp and rainbow trout of about 100 g were exercised to exhaustion in a swim tunnel. After swimming 10 h at 1.5 body lengths (BL)/s (aerobic control), 50% of the fish were forced to swim at 6 BL/s until exhaustion. Recovery of energy rich phosphates was found to be faster in carp (1.2-1.9 h) than in trout (1.5-2.3 h). The same applied for the recovery from acidosis, which took 1.75 h in carp and 5.75 h in trout. In parallel experiments the energy phosphates and lactate levels were measured in liver, red muscle, and white muscle. Exhaustion caused a significant drop in the energy status of red and white muscle tissue of trout and carp (corroborates NMR data), while no change at all was observed in liver tissue. The lactate levels were increased in the muscle but not in liver and blood. While all experimental animals looked healthy after exhaustion, 40-50% of the carp as well as trout died during the recovery phase. The energy status of those individuals measured by 31P-NMR was much lower than that of the survivors, while in contrast there was no difference in pH(i). Thus, it appears that not acidosis but depletion of high energy phosphates disabled muscle function and therefore may have been the cause of death of the non-survivors.     

ADRENERGIC α- AND β-RECEPTORS EXPRESSED BY THE SAME CELL TYPE IN PRIMARY CULTURE OF PERINATAL MOUSE BRAIN

Abstract— The β-adrenergic agonist, isoproterenol and the α- and β-adrenergic agonist. NA. raise the intracellular concentration of cyclic AMP in cultures of dissociated perinatal mouse brain. This rise is prevented by a β- but not by an α-adrenergic antagonist. The maximal level of cyclic AMP reached in the presence of isoproterenol is markedly higher than that found after exposure to NA. However, if NA is used along with an α-adrenergic antagonist, cyclic AMP levels as high as those after isoproterenol are measured. Agonists with α-adrenergic activity including NA decrease the response to isoproterenol. The decrease is blocked by α-adrenergic antagonists. From this and additional evidence it is concluded: (1) The increase in the level of cyclic AMP caused by β-adrenergic agonists is due to β-receptor-mediated stimulation of adenylate cyclase; (2) the inhibition of this effect by α-adrenergic agonists is mediated by adrenergic α-receptors; (3) the α- and β-adrenergic receptors are likely to be located on the same cells, probably the most abundant putative glial precursor cells. The simultaneous stimulation of α- and β-adrenergic receptors on the same cell may be of significance in the regulation of the response to NA.     

Differences in metabolic response to Loma salmonae infection in juvenile rainbow trout Oncorhynchus mykiss and brook trout Salvelinus fontinalis

Routine and post-exercise metabolic rates were measured for juvenile rainbow trout Oncorhynchus mykiss and brook trout Salvelinus fontinalis infected with the microsporidium gill parasite Loma salmonae under laboratory conditions. Rainbow trout increased routine and post-exercise metabolic rate in response to infection compared with controls. Brook trout, on the other hand, lowered routine metabolic rate without effecting post-exercise metabolic rate compared to controls. The result of these 2 different strategies may either reflect defense of metabolic scope or a difference in the rate of recovery of the excess post-exercise oxygen consumption between the 2 species in response to the same infection.     

Endothelial nitric oxide synthase activation contributes to post-exercise hypotension in spontaneously hypertensive rats

We investigated the role that endothelial nitric oxide synthase plays in post-exercise hypotension in spontaneously hypertensive rats. To accomplish this, rats were subjected to a single bout of dynamic exercise on a treadmill at 15 m/min for 20 min. l-Nitroarginine methyl ester (l-NAME, 40 mg/kg, i.p.) significantly inhibited post-exercise hypotension (25 ± 11 and 5 ± 3 mm Hg, respectively; P < 0.05). In addition, the superoxide anion generation was decreased, while the plasma nitrite production and serine phosphorylation of endothelial nitric oxide synthase were significantly elevated in spontaneously hypertensive rats at 30 min after the termination of exercise. Taken together, these data demonstrate that the increased phosphorylation of endothelial nitric oxide synthase plays a crucial role in the reduction of arterial pressure following a single bout of dynamic exercise in spontaneously hypertensive rats.     

Exercise and recovery metabolism in the pacific spiny dogfish (<Emphasis Type="Italic">Squalus acanthias</Emphasis>)

We examined the effects of exhaustive exercise and post-exercise recovery on white muscle substrate depletion and metabolite distribution between white muscle and blood plasma in the Pacific spiny dogfish, both in vivo and in an electrically stimulated perfused tail-trunk preparation. Measurements of arterial-venous lactate, total ammonia, -hydroxybutyrate, glucose, and l-alanine concentrations in the perfused tail-trunk assessed white muscle metabolite fluxes. Exhaustive exercise was fuelled primarily by creatine phosphate hydrolysis and glycolysis as indicated by 62, 71, and 85% decreases in ATP, creatine phosphate, and glycogen, respectively. White muscle lactate production during exercise caused a sustained increase (~12 h post-exercise) in plasma lactate load and a short-lived increase (~4 h post-exercise) in plasma metabolic acid load during recovery. Exhaustive exercise and recovery did not affect arterial PO₂, PCO₂, or PNH₃ but the metabolic acidosis caused a decrease in arterial HCO₃^– immediately after exercise and during the first 8 h recovery. During recovery, lactate was retained in the white muscle at higher concentrations than in the plasma despite increased lactate efflux from the muscle. Pyruvate dehydrogenase activity was very low in dogfish white muscle at rest and during recovery (0.53±0.15 nmol g wet tissue^–1 min^–1; n=40) indicating that lactate oxidation is not the major fate of lactate during post-exercise recovery. The lack of change in white muscle free-carnitine and variable changes in short-chain fatty acyl-carnitine suggest that dogfish white muscle does not rely on lipid oxidation to fuel exhaustive exercise or recovery. These findings support the notion that extrahepatic tissues cannot utilize fatty acids as an oxidative fuel. Furthermore, our data strongly suggest that ketone body oxidation is important in fuelling recovery metabolism in dogfish white muscle and at least 20% of the ATP required for recovery could be supplied by uptake and oxidation of -hydroxybutyrate from the plasma.Abbreviations CoA-SH free coenzyme A - CPT-1 carnitine palmitoyltransferase-1 - CrP creatine phosphate - H⁺_m metabolic proton load - Lac lactate load - PDH pyruvate dehydrogenase - PVP polyvinylpyrrolidone - SCFA-carnitine short-chain fatty acyl-carnitine - TAG triacylglycerol - TENS trancutaneous electrical nerve stimulator Communicated by: L.C.-H. Wang