An investigation of the role of circulating catecholamines in the control of ventilation during acute moderate hypoxia in rainbow trout (Oncorhynchus mykiss)

Summary Gill ventilation volume ( w), arterial blood oxygen tension (PaO₂) and arterial blood oxygen content (CaO₂) of rainbow trout (Oncorhyncus mykiss) were monitored during normoxia [waterPO₂ (PwO₂) 155 Torr], hypoxia (PwO₂=72±5.8 Torr), or hyperoxia (PwO₂=643±32 Torr). Fish hyperventilated during acute (30 min) hypoxia and hypoventilagted during acute hyperoxia. Plasma catecholamine levels were unchanged after 30 min of hypoxia or hyperoxia. In addition, selective adrenoceptor blockade with either propranolol (-adrenoceptor antagonist) or phentolamine (-adrenoceptor antagonist) did not modify the hyperventilatory response during hypoxia. These results indicate that circulating catecholamines are not involved in the control of ventilation in moderately hypoxic rainbow trout. In the summer, intra-arterial infusion of catecholamine in normoxic trout caused transient (adrenaline) or persistent (noradrenaline) hypoventilation. These observations also do not support a role for catecholamines in the stimulation of ventilation.During hypoxia,PwO₂,PaO₂ andCaO₂ were depressed whereas during hyperoxia, onlyPwO₂ andPaO₂ was elevated significantly. Thus, it is suggested that the hypoventilatory response to hyperoxia is mediated by a direct effect of elevatedPwO₂/PaO₂, whereas the hyperventilatory response to hypoxia is mediated by changes inPwO₂/PaO₂, and/orCaO₂.     

The effects of endogenous or exogenous catecholamines on blood respiratory status during acute hypoxia in rainbow trout (Oncorhynchus mykiss)

Summary An extracorporeal circulation of rainbow trout (Oncorhynchus mykiss) was utilized to continuously monitor the rapid and progressive effects of endogenous or exogenous catecholamines on blood respiratory/acid-base status, and to provide in vivo evidence for adrenergic retention of carbon dioxide (CO₂) in fish blood (cf. Wood and Perry 1985). Exposure of fish to severe aquatic hypoxia (final P _wO₂=40–60 torr; reached within 10–20 min) elicited an initial respiratory alkalosis resulting from hypoxia-induced hyperventilation. However, at a critical arterial oxygen tension (P _aO₂) between 15 and 25 torr, fish became agitated for approximately 5 s and a marked (0.2–0.4 pH unit) but transient arterial blood acidosis ensued. This response is characteristic of abrupt catecholamine mobilization into the circulation and subsequent adrenergic activation of red blood cell (RBC) Na⁺/H⁺ exchange (Fievet et al. 1987). Within approximately 1–2 min after the activation of RBC Na⁺/H⁺ exchange by endogenous catecholamines, there was a significant rise in arterial PCO₂ (P _aCO₂) whereas arterial PO₂ was unaltered; the elevation of P _aCO₂ could not be explained by changes in gill ventilation. Pre-treatment of fish with the -adrenoceptor antagonist phentolamine did not prevent the apparent catecholamine-mediated increase of P _aCO₂. Conversely, pre-treatment with the -adrenoceptor antagonist sotalol abolished both the activation of the RBC Na⁺/H⁺ antiporter and the associated rise in P _aCO₂, suggesting a causal relationship between the stimulation of RBC Na⁺/H⁺ exchange and the elevation of P _aCO₂. To more clearly establish that elevation of plasma catecholamine levels during severe hypoxia was indeed responsible for causing the elevation of P _aCO₂, fish were exposed to moderate hypoxia (final P _wO₂=60–80 torr) and then injected intraarterially with a bolus of adrenaline to elicit an estimated circulating level of 400 nmol·l^-1 immediately after the injection. This protocol activated RBC Na⁺/H⁺ exchange as indicated by abrupt changes in arterial pH (pHa). In all fish examined, P _aCO₂ increased after injection of exogenous adrenaline. The effects on P _aO₂ were inconsistent, although a reduction in this variable was the most frequent response. Gill ventilation frequency and amplitude were unaffected by exogenous adrenaline. Therefore, it is unlikely that ventilatory changes contributed to the consistently observed rise in P _aCO₂. Pretreatment of fish with sotalol did not alter the ventilatory response to adrenaline injection but did prevent the stimulation of RBC Na⁺/H⁺ exchange and the accompanying increases and decreases in P _aCO₂ and P _aO₂, respectively. These results suggest that adrenergic elevation of P _aCO₂, in addition to the frequently observed reduction of P _aO₂ are linked to activation of RBC Na⁺/H⁺ exchange. The physiological significance and the potential mechanisms underlying the changes in blood respiratory status after addition of endogenous or exogenous catecholamines to the circulation of hypoxic rainbow trout are discussed.Abbreviations P _aCO₂ arterial carbon dioxide tension - P _aO₂ arterial oxygen tension - P _da dorsal aortic pressure - pHa arterial pH - P _wO₂ water oxygen tension - RBC red blood cell - V _f breathing frequency     

Evidence for multiple adrenoceptor sites in rainbow trout vasculature

The importance of neuronal and lumenal vascular adrenoceptors in the regulation of vascular reactivity was examined in rainbow trout (Oncorhynchus mykiss), in vivo and in vitro. In vivo, ganglionic blockade with hexamethonium or -adrenoceptor blockade, with either phentolamine or prazosin, produced similar (7 mmHg) decreases in dorsal aortic blood pressure. The drop in dorsal aortic pressure produced by phentolamine or prazosin was due to reduced systemic vascular resistance. Neither the -adrenoceptor antagonist, phenoxybenzamine nor chemical sympathectomy with 6-hydroxy-dopamine affected dorsal aortic pressure. However, after chemical sympathectomy, phenoxybenzamine lowered dorsal aortic pressure to levels similar to that produced by either phentolamine or prazosin. Plasma epinephrine and norepinephrine concentrations increased four- and twofold, respectively, in sympathectomized fish. Sympathectomy also produced a leftward shift in the epinephrine dose/response curve of the in vitro perfused splanchnic vasculature, placing the effective catecholamine concentration well within the in vivo plasma levels. These results indicate that following chemical sympathectomy arterial blood pressure is stabilized by circulating catecholamines through the combined effect of increased plasma catecholamine concentrations and increased sensitivity of vascular adrenoceptors. Phenoxybenzamine is incapable of blocking neuronal vascular adrenoceptors but is a potent antagonist of the up-regulated adrenoceptors, suggesting that the latter are localized on the lumenal side of the vessel.Abbreviations 6OH-DA 6-hydroxy dopamine - EC ₅₀ half-maximal response - EDTA ethylenediaminetetra-acetate - PE polyethylene - PBS phosphate-buffered saline - P _da dorsal aortic pressure - USP United States Pharmacopeia     

Oxygen transport and cardiovascular responses in skipjack tuna (Katsuwonus pelamis) and yellowfin tuna (Thunnus albacares) exposed to acute hypoxia

Summary Responses to acute hypoxia were measured in skipjack tuna (Katsuwonus pelamis) and yellowfin tuna (Thunnus albacares) (1–3 kg body weight). Fish were prevented from making swimming movements by a spinal injection of lidocaine and were placed in front of a seawater delivery pipe to provide ram ventilation of the gills. Fish could set their own ventilation volumes by adjusting mouth gape. Heart rate, dorsal and ventral aortic blood pressures, and cardiac output were continuously monitored during normoxia (inhalant water (PO ₂>150 mmHg) and three levels of hypoxia (inhalant water PO ₂130, 90, and 50 mmHg). Water and blood samples were taken for oxygen measurements in fluids afferent and efferent to the gills. From these data, various measures of the effectiveness of oxygen transfer, and branchial and systemic vascular resistance were calculated. Despite high ventilation volumes (4–71·min^-1·kg^-1), tunas extract approximately 50% of the oxygen from the inhalant water, in part because high cardiac outputs (115–132 ml·min^-1·kg^-1) result in ventilation/perfusion conductance ratios (0.75–1.1) close to the theoretically ideal value of 1.0. Therefore, tunas have oxygen transfer factors (ml O₂·min^-1·mmHg^-1·kg^-1) that are 10–50 times greater than those of other fishes. The efficiency of oxygen transfer from water in tunas (65%) matches that measured in teleosts with ventilation volumes and order of magnitude lower. The high oxygen transfer factors of tunas are made possible, in part, by a large gill surface area; however, this appears to carry a considerable osmoregulatory cost as the metabolic rate of gills may account for up 70% of the total metabolism in spinally blocked (i.e., non-swimming) fish. During hypoxia, skipjack and yellowfin tunas show a decrease in heart rate and increase in ventilation volume, as do other teleosts. However, in tunas hypoxic bradycardia is not accompanied by equivalent increases, in stroke volume, and cardiac output falls as HR decreases. In both tuna species, oxygen consumption eventually must be maintained by drawing on substantial venous oxygen reserves. This occurs at a higher inhalant water PO₂ (between 130 and 90 mmHg) in skipjack tuna than in yellowfin tuna (between 90 and 50 mmHg). The need to draw on venous oxygen reserves would make it difficult to meet the oxygen demand of increasing swimming speed, which is a common response to hypoxia in both species. Because yellowfin tuna can maintain oxygen consumption at a seawater oxygen tension of 90 mmHg without drawing on venous oxygen reserves, they could probably survive for extended periods at this level of hypoxia.Abbreviations BP_da, BP_va dorsal, ventral aortic blood pressure - C _aO₂, C _vO₂ oxygen content of arterial, venous blood - DO₂ diffusion capacity - E_b, E_w effectiveness of O₂ uptake by blood, and from water, respectively - Hct hematocrit - HR heart rate - PCO₂ carbon dioxide tension - P _aCO₂, P _vCO₂ carbon dioxide tension of arterial and venous blood, respectively - PO₂ oxygen tension - P _aO₂, P _vO₂, P _iO₂, P _cO₂ oxygen tension of arterial blood, venous blood, and inspired and expired water, respectively - pHa, pHv pH of arterial and venous blood, respectively - P_w—b effective water to blood oxygen partial pressure difference - Pg partial pressure (tension) gradient - cardiac output - R vascular resistance - SV stroke volume - SEM standard error of mean - TO₂ transfer factor - U utilization - _g ventilation volume - O₂ oxygen consumption     

Absence of adrenergic red cell pH and oxygen content regulation in American eel (Anguilla rostrata) during hypercapnic acidosis in vivo and in vitro

Summary American eels (Anguilla rostrata) were exposed to acute (30 min) external hypercapnia (1% CO₂ or 5% CO₂ in air) in order to assess the involvement of circulating catecholamines in regulating red blood cell (RBC) pH and oxygen content during whole blood acidosis. Plasma adrenaline levels increased approximately 5-fold during severe hypercapnia yet absolute levels remained below 1.0 nM; plasma noradrenaline levels were unchanged. Both RBC pH and oxygen bound to haemoglobin ([O₂]/[Hb]) conformed to in vitro relationships with whole blood pH (pHe) indicating absence of regulation during hypercapnia in vivo. Pre-treatment of eels with - or -adrenoceptor antagonists, phentolamine or propranolol was without effect on RBC pH or [O₂]/[Hb] during hypercapnia. Further, intra-arterial injection of adrenaline (final plasma concentration=134 nM) or noradrenaline (final plasma concentration = 34 nM) into hypercapnic eels 5 min prior to blood sampling did not modify any measured blood variable RBC nucleoside triphosphate (NTP) levels, RBC pH and [O₂]/[Hb]. In vitro, the application of adrenaline or noradrenaline to eel RBC's during graded normoxic hypercapnia or hypoxic hypercapnia (noradrenaline only) did not affect RBC pH significantly. RBC NTP levels were depressed by noradrenaline in vitro but only during hypoxic hypercapnia.The results demonstrate adrenergic insensitivity of eel RBC's in vivo even under conditions (acidosis, hypoxemia) known to enhance catecholamine-mediated RBC responses in other species. We conclude that the American eel has no capacity to regulate RBC pH during hypercapnia and consequently [O₂]/[Hb] is reduced in accordance with the in vitro Root effect.     

Sympathetic nervous control of the iris sphincter of the atlantic cod,Gadus morhua

Summary The autonomic nervous control of the cod iris has been studied. The pharmacological properties of the smooth muscles of the iris have been elucidated by agonist/antagonist studies on isolated strip preparations. Electrical stimulation of parasympathetic and sympathetic pathways to the eye have been carried out, with recordings of the movements of the iris margin. Additions of cholinergic and adrenergic antagonists in selective concentrations were made to investigate the nature of the autonomic nerve fibres controlling the iris.Isolated strip preparations of the iris sphincter contracted in response to cholinergic or-adrenoceptor agonists. There appear to be no radial muscular elements in the cod iris. The effect of carbachol on the iris sphincter could be competitively antagonized by atropine, suggesting the presence of muscarinic receptors of the smooth muscles. The effect of adrenaline was similarly antagonized by phentolamine. The effect of phentolamine, and the order of potency for the adrenergic agonists, shows the presence of-adrenoceptors in the iris sphincter.-adrenoceptors of minor importance are also suggested by the inhibitory effects of isoprenaline on preparations pre-contracted by carbachol.The indirectly acting adrenergic agonist tyramine also contracts the isolated sphincter preparations. This effect is probably due to release of nervously stored catecholamines, since tyramine lacks effect on preparations from animals pre-treated with 6-hydroxydopamine. Preparations from 6-hydroxydopamine pre-treated animals also show a 10-fold increase in the affinity for adrenaline, demonstrating the development of a pre-synaptic supersensitivity due to the destruction of adrenergic nerve terminals of the iris. Stimulation of the sympathetic chain or ciliary nerves produces a constriction of the pupil of the same side. Application of selective concentrations of the antagonists atropine and phentolamine shows that the sympathetic constrictory innervation is solely adrenergic. In some preparations a small pupillo-dilatory effect of nerve stimulation is evident after the constrictory effect has been abolished by phentolamine. This inhibitory effect can be abolished by propranolol, indicating the presence of a-adrenoceptor mediated inhibitory control of minor importance. Stimulation of the oculomotor nerve produces no consistent responses of the cod iris.Illumination of one eye produces a pupilloconstriction comparable to that seen after sympathetic nerve stimulation. The light induced response is insensitive to atropine, phentolamine and tetrodotoxin, showing a direct effect on the smooth muscles of the sphincter. There is no consensual reflex in the cod.I wish to thank Dr. Susanne Holmgren for critically examining the original draft of this paper, and Mrs. Lena Utter for skilled assistance with isolated strip preparations and processing of concentration-response data. The fish was kindly supplied by Mr. Ingmar Hakemar. This work has been supported by grants from the Swedish Natural Science Research Council, the M. Bergvall Foundation and the Adlerbert Foundation.     

Multiple vital functions of the daughterless (da) gene in Drosophila melanogaster and factors influencing its expression

Multiple sub-vital effects, here designated as reductions in fitness S₁–S₅, for the second chromosome gene daughterless (da) of Drosophila melanogaster were described as (S₁) a recessive maternal lethality for daughters, (S₂) a reduced fertility of da/da females, (S₃) a recessive sub-vital zygotic effect, (S₄) a recessive female-specific zygotic effect and (S₅) a recessive maternal interaction effect on sons. (For S_1–3 see also: Bell, 1954; Sandler, 1972; Cline, 1976). These five distinct effects were initially quantified from estimates of viability in single generation crossing experiments. Dynamic estimates of these fitness parameters were obtained by fitting the elimination rate of da from a series of large random mating cage populations to a recurrence equation by the method of minimum chi-square. The stability of these estimates discerns those effects which are truly pleiotropic versus those due to linked genes.The dynamic estimates supported only S₁ and S₄ effects. Evidence for S₂ and S₅ was indeterminate, but the S₃ effect was rejected (P<0.01). The observed reduction in fitness, supposedly due to this recessive zygotic effect for da, was most likely the result of linked deleterious genes. These results indicate that pleiotropic vital effects observed in single generation test-cross matings may be caused by linked genes rather than the specific mutant per se. This problem is of particular importance when the mutant allele has been maintained with a balancer chromosome.Experiments on the rescue of daughters from da/da mothers with low temperatures during embryogenesis and with dechorionation of eggs were described in which the findings failed to confirm previously reported actions of the da gene. Modifying genes rather than environmental variables were cited as the probable cause for these conflicting results.Journal paper number 8000 of the Purdue University Agricultural Experiment Station. This study was supported by a research grant from the Comite Conjunto Hispano-Norteamericano para Asuntas Educativos y Culturales, Madrid.     

The effect of exogenous catecholamines on the ventilatory and cardiac responses of normoxic and hyperoxic rainbow trout,Oncorhynchus mykiss

Ventilation frequency, opercular pressure amplitude, heart rate, dorsal aortic pressure, arterial pH, arterial O₂ tension, and plasma catecholamine levels were recorded in rainbow trout, Oncorhynchus mykiss, during normoxia (19.7 kPa, 148 mmHg) or hyperoxia (51.2 kPa, 384 mmHg) after injection of various concentrations of catecholamines. In normoxic fish, adrenaline injection resulted in a depression of arterial O₂ tension, hypoventilation due to a drop in ventilation frequency, and a drop in heart rate, while dorsal aortic pressure increased. Noradrenaline depressed ventilation frequency, but opercular pressure amplitude increased to a far greater extent, and dorsal aortic pressure increased. During hyperoxia, adrenaline injection lowered ventilation frequency, opercular amplitude and heart rate, but dorsal aortic pressure increased. The stimulatory effects of noradrenaline on ventilation were abolished during hyperoxia, but the cardiac responses were similar to those seen during normoxia. These results indicate that catecholamines can modify the ventilatory output from the respiratory centre, and modification of ventilation frequency can occur independently of opercular pressure amplitude.Abbreviations f _g ventilation frequency - HPLC high performance liquid chromatography - P _op opercular pressure amplitude - f _h heart rate - P _DA dorsal aortic pressure - pH_a arterial pH - P _aO₂ arterial oxygen tension - PO₂ oxygen tension     

Nitrogen isotope discrimination in white spruce fed with low concentrations of ammonium and nitrate

Differences in ¹⁵N among ten white spruce [Picea glauca (Moench) Voss] families were examined in hydroponic experiments testing (1) three N sources [100 M N as (i) NH₄⁺, (ii) NO₃^– or (iii) NH₄NO₃] and (2) two supply regimes [200 M NH₄⁺ (i) maintained steadily or (ii) recurrently drawn-down]. In the N-source experiment, the NH₄⁺ treatment resulted in superior growth and lower C/N ratios. Whole plant ¹⁵N was higher on NH₄⁺ and NH₄NO₃, reflecting higher NH₄⁺ removal rates from the media. Families expressed differences in biomass, C/N, ¹⁵N and ¹³C. Family ¹⁵N and ¹³C were positively correlated in the NH₄NO₃ treatment and the steady-state regime. Supply regime did not affect total biomass, but higher root/shoot ratios implied N was more limiting under the draw-down regime. Family rank changed with supply regime, but not with N source. Analysis of media isotope enrichment during substrate depletion revealed relationships between net discrimination and external N concentration. Discrimination against ¹⁵NH₄⁺ was about twice that of ¹⁵NO₃^–. A simple model relating isotope discrimination to relative rates of ion efflux and influx predicted efflux/influx ratios consistent with published values for white spruce. We propose that genetic differences in discrimination are caused by different demands on assimilation and in uptake capacity which interact, influencing the balance between N influx and efflux.     

Seasonal Stable Isotope Records of Otoliths from Ocean-pen Reared and Wild Cod, Gadus morhua

Otoliths of ocean-pen reared cod, Gadus morhua, provide a unique opportunity to examine the lifetime history of the fish. Here we report 18 analyses of such otoliths on seasonal (winter and summer) stable oxygen and carbon isotope ratios. The calculated isotopic temperatures from otoliths of reared cod were essentially in agreement with the temperature record during rearing, suggesting that temperature is a dominant factor in the precipitation of otolith aragonite. Carbon isotope ratios increased with age and leveled off at 4 years old, presumed to correlate with sexual maturity of cod. As compared with otoliths of wild-caught cod, significant differences were found in isotope variation and the correlation between ¹³C and ¹⁸O. These differences were probably attributable to the different environmental constraints and food supply.     

Sympathetic nervous control of the vasculature in the tail of the Atlantic cod,Gadus morhua

Summary The effects of some drugs and electrical stimulation of the sympathetic chain on the vasculature of the isolated perfused tail of the cod has been studied. Adrenaline, phenylephrine and isoprenaline all constricted the tail vasculature, isoprenaline also producing dilation in some preparations at lower concentrations (10^–9–10^–6M). Electrical stimulation of the sympathetic chain produces vasoconstriction, which can be abolished by phentolamine in concentrations expected to be selective for -adrenoceptor blockade in the cod. A small dilatory response to nerve stimulation was seen in some preparations after phentolamine. Carbachol produced weak and irregular effects, and a contribution by cholinergic fibres therefore seems unlikely. It is concluded that the excitatory nervous control of the cod tail vasculature is solely by adrenergic sympathetic fibres, which act via an -adrenoceptor mechanism.     

Renal response to hypoxia in carp,Cyprinus carpio: Changes in glomerular filtration rate,urine and blood properties and plasma catecholamines of carp exposed to hypoxic conditions

• 1.1. Changes in glomerular nitration rate (GFR), urine and blood properties and plasma catecholamines of carp were investigated during and following hypoxia.
• 2.2. GFR and urine flow decreased with increased urinary concentrations of bio-components, except protein, in the course of hypoxia.
• 3.3. Decreases in blood pH, and increases in haematocrit value and plasma K⁺, Ca²⁺, Mg²⁺, inorganic phosphate (P_i), ammonia, lactic acid and catecholamines (CAs) were observed as hypoxia progressed.
• 4.4. Increased GFR and urine flow, and higher values for urinary components, except protein, compared with those of the control were found in the initial post-stress stage.
• 5.5. The possible significance of increased plasma CAs in relation to changes in renal function in hypoxic carp is discussed.

     

PO2 and pH changes in the retina of the crab Ocypode ryderi: evidence for aerobic glycolysis

Summary The isolated retina of the terrestrial crab Ocypode ryderi exhibits a pronounced lactate production in spite of being supplied with sufficient O₂ (140 torr). To determine whether this lactate production is caused by hypoxic areas in the tissue or represents aerobic glycolysis, oxygen partial pressure and pH measurements with two-channel glass microelectrodes and additional biochemical analyses were carried out on this organ. Distinct profiles were obtained for O₂ partial pressure and pH inside the tissue. At a depth of 200 m different O₂ partial pressure levels could be observed depending on the O₂ partial pressure in the medium (85 torr at 280 torr and 36 torr at 130 torr, respectively). The extracellular pH displays a similar pattern; it reaches a stable value of 7.15 at 100 m inside the tissue. Lowering bath O₂ partial pressure from 280 torr to about 15 torr (hypoxia) induces a decrease of the O₂ partial pressure in the tissue with different time-courses for different tissue depths. However, hypoxia did not change the extracellular pH. Addition of antimycin A (100 mol · 1^-1) to the medium abolishes the O₂ partial pressure gradient and the delayed recovery of the tissue O₂ partial pressure after hypoxia. These results and the biochemical data suggest that in the crab retina a high glycolytic activity occurs simultaneously with oxydative carbohydrate degradation (aerobic glycolysis).Abbreviations AEC Atkinson energy charge - DC bioelectric potential - dw dry weight - HEPES N-[2-Hydroxyethyl]piperazine-N-[2-ethanesulphonic acid] - PCO₂ carbon dioxide partial pressure - PO₂ oxygen partial pressure - P _tO₂ oxygen partial pressure inside the tissue - P _mO₂ oxygen partial pressure in the medium - pH_t pH inside the tissue - pH_m pH in the superfusion medium     

Uptake of the Herbicidal Glyphosate by Escherichia coli K-12

The uptake of the aminoacid biosynthesis inhibitor, used as the broad-spectrum herbicide ingredient, glyphosate (N-[phosphonomethyl]-glycine) was investigated in E. coli as a model to study mechanisms of cell resistance to antimetabolites as drugs and pesticides. Unlike the glyphosate-degrading Arthrobacter sp. strain for which the first successful measurement of glyphosate uptake and its inhibition by orthophosphate was reported [15], E. coli K-12 cannot take up this inhibitor either in the presence of orthophosphate, or after a prolonged starvation for it. However, cells made competent after an overnight cold CaCl₂ exposure followed by dimethyl sulfoxide (DMSO) treatment could take up this compound (K _m for glyphosate uptake, 274 M). Neither amino acids, belonging to a single transport system, nor orthophosphate gave essential inhibition of glyphosate uptake by these cells.     

The role of the vagus nerve in the generation of cardiorespiratory interactions in a neotropical fish,the pacu, <Emphasis Type="Italic">Piaractus mesopotamicus</Emphasis>

The role of the vagus nerve in determining heart rate (f _H) and cardiorespiratory interactions was investigated in a neotropical fish, Piaractus mesopotamicus. During progressive hypoxia f _H initially increased, establishing a 1:1 ratio with ventilation rate (f _R). Subsequently there was a hypoxic bradycardia. Injection of atropine abolished a normoxic inhibitory tonus on the heart and the f _H adjustments during progressive hypoxia, confirming that they are imposed by efferent parasympathetic inputs via the vagus nerve. Efferent activity recorded from the cardiac vagus in lightly anesthetized normoxic fish included occasional bursts of activity related to spontaneous changes in ventilation amplitude, which increased the cardiac interval. Restricting the flow of aerated water irrigating the gills resulted in increased respiratory effort and bursts of respiration-related activity in the cardiac vagus that seemed to cause f _H to couple with f _R. Cell bodies of cardiac vagal pre-ganglionic neurons were located in two distinct groups within the dorsal vagal motor column having an overlapping distribution with respiratory motor-neurons. A small proportion of cardiac vagal pre-ganglionic neurons (2%) was in scattered positions in the ventrolateral medulla. This division of cardiac vagal pre-ganglionic neurons into distinct motor groups may relate to their functional roles in determining cardiorespiratory interactions.     

Sympathetic nervous control of blood flow in the gills of the Atlantic cod,Gadus morhua

Summary The effects of sympathetic nerve stimulation, adrenaline and isoprenaline on the inflow pressure and efferent arterial and venous flow rates were studied in a cod gill preparation perfused at constant flow rate.The dominant effect of adrenaline was a reduced inflow pressure, accompanied by an increase in arterial flow and a decrease in venous flow. Isoprenaline also decreased the inflow pressure, but the changes in both outflow rates were small or absent.Sympathetic nerve stimulation gave arterial and venous flow changes comparable to the adrenaline effects, but the inflow pressure increased during nerve stimulation. Propranolol has little effect on the nerve responses, but phentolamine abolished or reversed the increase in inflow pressure, and also decreased or abolished the changes in outflow rates.The possible sites of action of the sympathetic fibres, and the distribution of adrenoceptors in the effector tissue is discussed. It is concluded that the main effect of sympathetic nerve stimulation is -adrenoceptor mediated, involving constriction of the arterio-venous pathway. The-adrenoceptor mediated control of total branchial vascular resistance may largely depend on circulating catecholamines.     

Gas exchange and habitat selection in the aquatic salamanders Necturus maculosus and Cryptobranchus alleganiensis

Summary The standard metabolic rate (SMR) and critical O₂ tension (P_c) of water-breathing mudpuppies and hellbenders were determined at 20° C using open-system respirometry. Both species are metabolic O₂ regulators, although the P_c of hellbenders (90 mmHg) is much higher than that of mudpuppies (40 mmHg). The SMR of the two species in water saturated with air was similar (19.5 and 20.0 l O₂/g·h for Cryptobranchus and Necturus, respectively) and not different from that of salamanders in general. Both species were able to survive for at least 5–11 days in severely hypoxic water (9–10 mmHg) by breathing air, indicating that the lungs are functional accessory respiratory structures.We conclude that hellbenders are restricted to relatively cool and flowing waters because of their limited gas exchange capabilities, particularly with regard to their limited aerobic scope for activity and slow recovery from exercise. Necturus maculosus is much more tolerant of hypoxia, but it is not known if they can inhabit areas were hypoxia is combined with hypercarbia.     

Dependence of oxygen uptake on ambient PO 2 in isolated perfused frog skin

Summary Rates of O₂ uptake across isolated perfused skin of bullfrogs (Rana catesbeiana) were measured in relation to blood flow at three levels of ambient O₂ tension: normoxia (O₂ tension=152 torr), hypoxia (12% O₂, 87 torr) and hyperoxia (42% O₂, 306 torr). At bulk perfusion rates ranging from 3.4 to 10.1 l·cm^-2·min^-1, O₂ uptake was positively correlated with hemoglobin delivery rate in both normoxia and hyperoxia, but was independent of delivery rate in hypoxia. Mean O₂ uptake in normoxia was 3.8 nmol O₂·cm^-2·min^-1 at a delivery rate of 9.8 nmol·cm^-2·min^-1 and 6.5 nmol O₂·cm^-2·min^-1 at a delivery rate of 28.3 nmol·cm^-2·min^-1. At any given bulk perfusion rate, oxygen uptake averaged about 49% lower in hypoxia than in normoxia, decreasing in proportion to the reduction of O₂ tension difference between medium and blood. In hyperoxia, O₂ uptake did not increase proportionally with the difference in O₂ tension between blood and medium, averaging only 50% higher at a 2.4-fold greater O₂ tension difference. Cutaneous diffusing capacity for O₂ averaged 0.041 nmol O₂·cm^-2·torr^-1·min^-1 during the first hour of perfusion in normoxia, and was not affected by reduction of ambient O₂ tension. The results indicate that cutaneous O₂ uptake in hypoxia is highly diffusion limited, and consequently, increases in cutaneous perfusion can not effectively compensate for reduction of ambient O₂ tension. In hyperoxia, O₂ uptake may be substantially perfusion limited because of reduced blood O₂ capacitance at high O₂ saturations.Abbreviations O₂ capacitance - C _Hb hemoglobin concentration - D diffusing capacity - PO₂ medium-blood PO₂ difference - Hb flow, hemoglobin delivery rate - Hepes N-[2-Hydroxyethyl]piperacine-N-[2 ethanesulfonic acid] - L _diff extent of diffusion limitation - MO₂ oxygen uptake rate - PO₂ oxygen tension - S O₂ saturation     

Pre-and post-branchial blood respiratory status during acute hypercapnia or hypoxia in rainbow trout,Oncorhynchus mykiss

Simultaneous venous (pre-branchial) and arterial (post-branchial) extracorporeal blood circulations were utilized to monitor continuously the rapid and progressive effects of acute environmental hypercapnia (water partial pressure of CO₂ 4.8±0.2 torr) or hypoxia (water partial pressure of O₂ 25±2 torr) on oxygen and carbon dioxide tensions and pH in the blood of rainbow trout (Oncorhynchus mykiss). During hypercapnia, the CO₂ tension in the arterial blood increased from 1.7±0.1 to 6.2±0.2 torr within 20 min and this was associated with a decrease of arterial extracellular pH from 7.95±0.03 to 7.38±0.03; the acid-base status of the mixed venous blood changed in a similar fashion. The decrease in blood pH in vivo was greater than in blood equilibrated in vitro with a similar CO₂ tension indicating a significant metabolic component to the acidosis in vivo. Under normocapnic conditions, venous blood CO₂ tension was slightly higher than arterial blood CO₂ tension difference was abolished or reversed during the initial 25 min of hypercapnia indicating that CO₂ was absorbed from the water during this period. Arterial O₂ tension remained constant during hypercapnia; however, venous blood O₂ tension decreased significantly (from 22.0±2.6 to 9.0±1.0 torr) during the initial 10 min. Hypercapnia elicited the release of catecholamines (adrenaline and noradrenaline) into the blood. The adrenaline concentration increased from 6±3 to 418±141 nmol · l^-1 within 25 min; noradrenaline concentration increased from 3±0.5 to 50±21 nmol · l^-1 within 15 min. During hypoxia arterial blood O₂ tension declined progressively from 108.4±9.9 to 12.8±1.7 torr within 30 min. Venous blood O₂ tension initially was stable but then decreased abruptly as catecholamines were released into the circulation. The release of catecholamines occurred concomitantly with a sudden metabolic acidosis in both blood compartments and a rise in CO₂ tension in the mixed venous blood only.Abbreviations CCO₂ plasmatotal carbondioxide - CtO₂ blood oxygen content - PO₂ partial pressure of oxygen - PCO₂ partial pressure of carbon dioxide - PaO₂ arterial bloodPO₂ - PaCO₂ arterial bloodPCO₂ - PvCO₂ venous bloodPCO₂ - PwO₂ waterPO₂ - PwCO₂ waterPCO₂ - Hb haemoglobin - SHbO₂ haemoglobin oxygen saturation - HPLC high-performance liquid chromatography - rbc red blood cell(s) - Hct haematocrit     

Catecholaminergic nerves in the embryonic chick ovary: co-localization with β2-adrenoceptor-bearing steroidogenic cells

Summary The present study investigates the innervation of the embryonic chick ovary with regard to (i) development and compartmentalization of catecholaminergic nerves, and (ii) presence of adrenoceptors on steroidogenic target cells of catecholaminergic nerve terminals. Catecholaminergic nerve fibers visualized by glyoxylic acid-induced histofluorescence first appeared at embryonic day (E) 13. From E15 through E21 the density of fluorescent aminergic nerves increased markedly in parallel with the concentration of catecholamines and numbers of nerve bundles and single axons seen at the electron-microscopic level. Catecholaminergic nerves were confined to the ovarian medulla and closely associated with interstitial cells. Nerve terminals approached interstitial cells up to a distance of 20 nm and, in their majority, exhibited uptake of the false adrenergic transmitter 5-hydroxydopamine. Although adrenaline amounted to 14% of the total catecholamine content at E21, adrenaline immunoreactivity was only detected in adrenal chromaffin cells, but not in nerve fibers or cell bodies within the ovary. Interstitial cells structurally matured between E15 and E21 as documented by an increase of smooth endoplasmic reticulum and tubular mitochondria. Monoclonal antibodies mAB 120 and BRK 2 raised against avian ₁ and mammalian ₂-adrenergic receptors revealed the presence of ₂-adrenoceptor-like immunoreactivity on the surface of interstitial cells, but not on any other cell type.The results are consistent with the notion of a dense adrenergic innervation of the embryonic chick ovarian medulla and its steroidogenic interstitial cells, and suggest the chick ovary as an excellent model for elucidating the functional role of a neural input to steroidogenic cells during development.