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D J McKenzie

Publications and source records attributed to D J McKenzie.

At least 19 recordsLinked to original sources
PubMed2006

Associations between tissue fatty acid composition and physiological traits of performance and metabolism in the seabass (Dicentrarchus labrax).

Seabass were fed for 4 months with diets where the lipid was provided as either canola oil (CO), palm oil (PO) or fish oil (FO), to generate diversity in their tissue fatty acid (FA) composition and investigate how this influenced major traits of exercise performance, cardiac performance and respiratory metabolism. In particular, based upon previous observations, we investigated the hypothesis that enriching the fish tissues with oleic and linoleic acids (OA, 18:1n-9 and LA, 18:2n-6, respectively) from the CO and PO diets would improve maximum exercise and cardiac performance, and increase aerobic metabolic scope. This proved to be the case; exercise respirometry on bass fitted with cardiac flow probes revealed that those fed CO and PO diets had a significantly higher critical swimming speed (U(crit)) than those fed the FO diet. The improved swimming performance in the CO and PO groups was accompanied by a higher maximum cardiac output (Q) and net cardiac scope, and a higher active metabolic rate (AMR) and aerobic scope (AS) than in the FO group. Analysis of tissue FA composition revealed that the fish fed the CO and PO diets had accumulated significantly higher levels of OA and LA in their heart and muscle than the fish from the FO group, which had significantly higher levels of highly unsaturated FA of the n-3 series, such as EPA and DHA (20:5n-3 and 22:6n-3, respectively). Principal components analysis revealed significant positive associations between tissue OA and LA content and U(crit), maximum Q, the increase in Q during exercise, AMR and aerobic scope. There was a negative association between these physiological traits and tissue content of EPA. Therefore, diet composition is an environmental factor that can generate significant phenotypic diversity in major physiological traits of performance and metabolism in the seabass, with increased intake of FAs such as OA and LA leading to improved cardiorespiratory performance.

Acyltransferases↗
PubMed2006

Effects of oleic acid on the high threshold barium current in seabass Dicentrarchus labrax ventricular myocytes.

The present study employed a patch clamp technique in isolated seabass ventricular myocytes to investigate the hypothesis that oleic acid (OA), a mono-unsaturated fatty acid, can exert direct effects upon whole-cell barium currents. Acute application of free OA caused a dose-dependent depression of the whole-cell barium current that was evoked by a voltage step to 0 mV from a holding potential of -80 mV. The derived 50% inhibitory concentration (IC50) was 12.49+/-0.27 micromol l(-1). At a concentration of 30 micromol l(-1), OA significantly reduced the current density to about 45% of control values, but did not modify either the shape of the current-density voltage relationship or the apparent reversal potential. In addition, OA did not modify the voltage dependence of either steady state inactivation or activation curves. Taken together, these results indicate that physiological concentrations of free OA decrease the conductance of the L-type inward current, without altering its properties of selectivity and its voltage dependence. The inhibitory effect of OA upon the L-type calcium channel may translate, in vivo, into a protective effect against arrhythmias induced by Ca2+ overload.

Animals↗
PubMed2005

Reflex cardioventilatory responses to hypoxia in the flathead gray mullet (Mugil cephalus) and their behavioral modulation by perceived threat of predation and water turbidity.

In hypoxia, gray mullet surface to ventilate well-oxygenated water in contact with air, an adaptive response known as aquatic surface respiration (ASR). Reflex control of ASR and its behavioral modulation by perceived threat of aerial predation and turbid water were studied on mullet in a partly sheltered aquarium with free surface access. Injections of sodium cyanide (NaCN) into either the bloodstream (internal) or ventilatory water stream (external) revealed that ASR, hypoxic bradycardia, and branchial hyperventilation were stimulated by chemoreceptors sensitive to both systemic and water O2 levels. Sight of a model avian predator elicited bradycardia and hypoventilation, a fear response that inhibited reflex hyperventilation following external NaCN. The time lag to initiation of ASR following NaCN increased, but response intensity (number of events, time at the surface) was unchanged. Mullet, however, modified their behavior to surface under shelter or near the aquarium edges. Turbid water abolished the fear response and effects of the predator on gill ventilation and timing of ASR following external NaCN, presumably because of reduced visibility. However, in turbidity, mullet consistently performed ASR under shelter or near the aquarium edges. These adaptive modulations of ASR behavior would allow mullet to retain advantages of the chemoreflex when threatened by avian predators or when unable to perceive potential threats in turbidity.

Analysis of Variance↗
PubMed2004

The effects of sustained exercise and hypoxia upon oxygen tensions in the red muscle of rainbow trout.

Teleost fish possess discrete blocks of oxidative red muscle (RM) and glycolytic white muscle, whereas tetrapod skeletal muscles are mixed oxidative/glycolytic. It has been suggested that the anatomy of RM in teleost fish could lead to higher intramuscular O2 partial pressures (PO2) than in mammalian skeletal muscles. This study provides the first direct experimental support for this suggestion by using novel optical fibre sensors to discover a mean (+/- S.E.M., N=6) normoxic steady-state red muscle PO2 (PrmO2) of 61+/-10 mmHg (1 mmHg=133.3 Pa) in free-swimming rainbow trout Oncorhynchus mykiss. This is significantly higher than literature reports for mammalian muscles, where the PO2 never exceeds 40 mmHg. Aerobic RM powers sustained swimming in rainbow trout. During graded incremental exercise, PrmO2 declined from 62+/-5 mmHg at the lowest swim speed down to 45+/-3 mmHg at maximum rates of aerobic work, but then rose again to 51+/-5 mmHg at exhaustion. These measurements of PrmO2 during exercise indicated, therefore, that O2 supply to the RM was not a major limiting factor at exhaustion in trout. The current study found no evidence that teleost haemoglobins with a Root effect cause extremely elevated O2 tensions in aerobic tissues. Under normoxic conditions, PrmO2 was significantly lower than arterial PO2 (119+/-5 mmHg), and remained lower when the arterial to tissue PO2 gradient was reduced by exposure to mild hypoxia. When two sequential levels of mild hypoxia (30 min at a water PO2 of 100 mmHg then 30 min at 75 mmHg) caused PaO2 to fall to 84+/-2 mmHg then 61+/-3 mmHg, respectively, this elicited simultaneous reductions in PrmO2,to 51+/-6 mmHg then 41+/-5 mmHg, respectively. Although these hypoxic reductions in PrmO2 were significantly smaller than those in PaO2, the effect could be attributed to the sigmoid shape of the trout haemoglobin-O2 dissociation curve.

Analysis of Variance↗
PubMed2003

Sub-lethal plasma ammonia accumulation and the exercise performance of salmonids.

The proposal that plasma ammonia accumulation might impair the swimming performance of fish was first made over a decade ago, and has now proven to be the case for a number of salmonid species. The first experimental evidence was indirect, when a negative linear relationship between plasma ammonia concentrations and maximum sustainable swimming speed (U(crit)) was found following the exposure of brown trout (Salmo trutta) to sub-lethal concentrations of copper in soft acidic water. Since then, negative linear relationships between plasma ammonia concentration and U(crit) have been demonstrated following exposure of brown trout, rainbow trout (Oncorhynchus mykiss) and coho salmon (Oncorhynchus kisutch) to elevated water ammonia. For brown trout, the relationships between plasma ammonia and U(crit) were remarkably similar following either exposure to elevated water ammonia or to sub-lethal copper. This indicates that the impairment of swimming performance resulting from exposure to sub-lethal concentrations of heavy metals may be attributable in large part to an accumulation of endogenous ammonia. The negative relationship between plasma ammonia concentration and U(crit) was similar in size-matched rainbow and brown trout but, under similar regimes of ammonia exposure, rainbow trout were able to maintain a significantly lower plasma ammonia concentration, revealing inter-specific differences in ammonia permeability and/or transport. One primary mechanism by which ammonia accumulation may impair exercise performance is a partial depolarisation of membrane potential in tissues such as the brain and white muscle. This may prejudice the co-ordination of swimming movements and reduce or abolish the development of muscle tension, thus, compromising swimming efficiency and performance at the top end of the range.

Ammonia↗
PubMed2003

Tolerance of chronic hypercapnia by the European eel Anguilla anguilla.

European eels were exposed for 6 weeks to water CO(2) partial pressures (P(CO)(2)) from ambient (approx. 0.8 mmHg), through 15+/-1 mmHg and 30+/-1 mmHg to 45+/-1 mmHg in water with a total hardness of 240 mg l(-1) as CaCO(3), pH 8.2, at 23+/-1 degrees C. Arterial plasma P(CO)(2) equilibrated at approximately 2 mmHg above water P(CO)(2) in all groups, and plasma bicarbonate accumulated up to 72 mmol l(-1) in the group at a water P(CO)(2) of 45 mmHg. This was associated with an equimolar loss of plasma Cl(-), which declined to 71 mmol l(-1) at the highest water P(CO)(2). Despite this, extracellular acid-base compensation was incomplete; all hypercapnic groups tolerated chronic extracellular acidoses and reductions in arterial blood O(2) content (Ca(O)(2)), of progressive severity with increasing P(CO)(2). All hypercapnic eels, however, regulated the intracellular pH of heart and white muscle to the same levels as normocapnic animals. Hypercapnia had no effect on such indicators of stress as plasma catecholamine or cortisol levels, plasma osmolality or standard metabolic rate. Furthermore, although Ca(O)(2) was reduced by approximately 50% at the highest P(CO)(2), there was no effect of hypercapnia on the eels' tolerance of hypoxia, aerobic metabolic scope or sustained swimming performance. The results indicate that, at the levels tested, chronic hypercapnia was not a physiological stress for the eel, which can tolerate extracellular acidosis and extremely low Cl(-) levels while compensating tissue intracellular pH, and which can meet the O(2) requirements of routine and active metabolism despite profound hypoxaemia.

Acid-Base Equilibrium↗
PubMed2002

Tolerance of acute hypercapnic acidosis by the European eel ( Anguilla anguilla).

European eels ( Anguilla anguilla) were exposed sequentially to partial pressures of CO(2) in the water ( PwCO(2)) of 5, 10, 20, 40, 60 then 80 mm Hg (equivalent to 0.66-10.5 kPa), for 30 min at each level. This caused a profound drop in arterial plasma pH, from 7.9 to below 7.2, an increase in arterial PCO(2) from 3.0 mm Hg to 44 mm Hg, and a progressive decline in arterial blood O(2) content (caO(2)) from 10.0% to 1.97% volume. Gill ventilation rate increased significantly at water PwCO(2)s of 10, 20 and 40 mm Hg, followed by a decline at PwCO(2)s of 60 and 80 mm Hg, due to periodic breathing. Mean opercular pressure amplitude increased steadily throughout hypercapnic exposure and was significantly elevated at a PwCO(2) of 80 mm Hg. Hypercapnia caused a tachycardia between PwCO(2)s of 5 mmHg and 10 mm Hg, followed by a progressive decline in heart rate. Cardiac output (CO) remained unchanged throughout, as a consequence of a significant increase in stroke volume at PwCO(2)s of 40, 60 and 80 mm Hg. The eels maintained O(2) uptake at routine normocapnic levels throughout hypercapnic exposure. A comparison of the rates of blood O(2) delivery (calculated from CO and caO(2)) against O(2) consumption at PwCO(2)s of 60 mm Hg and 80 mm Hg indicated that a portion of O(2) uptake was due to cutaneous respiration. Thus, the European eel's exceptional tolerance of acute hypercapnia is probably a consequence of the tolerance of its heart to acidosis and hypoxia, and a contribution to O(2) uptake from cutaneous respiration.

Acid-Base Equilibrium↗
PubMed2002

Adrenergic receptors, Na+/H+ exchange and volume regulation in lungfish erythrocytes.

Aestivation in African and South American lungfish (Protopterus and Lepidosiren, respectively) is associated with elevations of extracellular osmolarity. Osmotic shrinkage of Protopterus red blood cells (RBCs) caused a small but significant stimulation of the Na influx that was amiloride-sensitive. suggesting involvement of the Na+/H+ exchanger (NHE). The associated in vitro regulatory volume increase was insignificant within a time frame of 120 min, but the shrinkage-activated Na+ influx may be sufficient for slow regulatory volume increase during aestivation in vivo. Osmotic swelling of the RBCs induced an incomplete regulatory volume decrease that was statistically significant after 180 min. The RBCs of Protopterus were very large (mean cellular volume of 6939 +/- 294 microm3) and possessed 23,066 +/- 7,326 beta-adrenoceptors cell(-1) with a Kd value of 6.1 +/- 3.2 nM. The number of receptors per unit surface area of lungfish RBCs was calculated to be twice that of trout RBCs and 70% that of cod RBCs. There was, however, no adrenergic stimulation of the NHE in either Protopterus or Lepidosiren. Acidification of the extracellular medium also failed to activate the NHE.

Animals↗
PubMed2001

Effects of dietary fatty acids on the respiratory and cardiovascular physiology of fish.

In animals, the composition of fatty acids (FAs) in body pools reflects dietary intake. This paper reviews evidence that the manipulation of tissue lipids of farmed fish, by feeding them different natural oils, can have significant effects on their respiratory and cardiovascular physiology. Sturgeon and eels with tissue lipids rich in highly unsaturated FAs of the n-3 series (n-3HUFAs, accumulated from dietary menhaden oil) had significantly lower metabolic rates than fish with tissues rich in saturated FAs (SFAs, from coconut oil), although they grew equally well. In sturgeon, the difference in metabolism influenced tolerance of hypoxia. Degrees of hypoxia that depressed oxygen uptake and spontaneous activity in fish rich in SFAs had no such effects on fish rich in n-3HUFAs. In the isolated sturgeon heart working in vitro, reduced oxygen supply depressed the performance of hearts with lipids rich in SFAs but not that of hearts rich in n-3HUFAs. In salmon fed diets with graded mixtures of menhaden and canola oils, there was no relationship between tissue n-3HUFA content (from menhaden oil) and any measured aspect of swimming performance, but a linear relationship between maximum sustainable swimming speed and muscle oleic acid levels (from canola oil). Such exploratory studies indicate that an animal's responses to its environment may be profoundly affected by the oils and FAs it consumes in its diet.

Animals↗
PubMed2001

Effects of sublethal ammonia exposure on swimming performance in rainbow trout (Oncorhynchus mykiss).

Adult trout Oncorhynchus mykiss fitted with a dorsal aortic catheter were exposed to 288+/-15 micromol l(-1) (mean +/- S.E.M.) total ammonia for 24h in water at a pH of 8.39+/-0.02, while swimming at a speed equivalent to 0.75 bodylengths s(-1) (BLs(-1)) in a Brett-type tunnel respirometer. The fish were then exposed to stepwise increments in swimming speed (0.25 BLs(-1) every 30 min) until exhaustion. Measurements of oxygen uptake (M(O2)) and plasma total ammonia levels and pH were made at each speed. Control trout were treated identically but without exposure to ammonia. Ammonia exposure caused an increase in plasma total ammonia level to 436+/-34 micromol l(-1), compared to 183+/-30 micromol l(-1)in control animals (N=6). A significant reduction in total plasma ammonia level was found in both groups during exercise, despite a large negative concentration gradient in those exposed to an elevated concentration of ammonia in water, which may indicate an active excretory process. The overall increase in plasma ammonia levels in exposed trout was associated with a significant reduction in critical swimming speed (U(crit)) to 1.61+/-0.17BL s(-1) from 2.23+/-0.15BL s(-1) in control animals. Ammonia-exposed trout had a significantly higher maintenance metabolic rate (MMR) than control fish, when estimated as the y-intercept of the relationship between swimming speed and M(O2). Active metabolic rate (AMR, maximum M(O2) as measured at U(crit)) was significantly lower in ammonia-exposed animals, leading to a profound reduction in factorial aerobic scope (AMR/MMR). Reduced U(crit) was also linked to a reduction in maximum tailbeat frequency. Calculation of membrane potentials (E(M)) in the white muscle of fish swum to U(crit) revealed a significant partial depolarisation of white muscle in ammonia-exposed fish. This may have prevented white muscle recruitment and contributed to the reduced maximum tailbeat frequency and overall impairment of swimming performance in the ammonia-exposed fish.

Ammonia↗
PubMed1997

Legal review: protecting the confidentiality and integrity of patient records.

Computerized patient records, like paper-based records, are subject to a number of security threats. In the context of health care networks, such as integrated delivery networks, special precautions are required to protect both the confidentiality and the integrity of patient records. The article discusses the principle threats to networked patient data and recommends practical steps to reduce the inherent risks.

Computer Security↗
PubMed1996

Cardioventilatory responses to hypoxia and NaCN in the neotenous axolotl.

Ventilatory and cardiac responses to hypoxia, sodium cyanide (NaCN), and intra-arterial injection of atropine, noradrenaline and DL-propranolol were investigated in the neotenous axolotl (Ambystoma mexicanum). Hypoxia elicited increased gill and lung ventilation and a tachycardia. Gill ventilation and air-breathing were stimulated by NaCN infused either into the ventilatory water stream or into the bloodstream. Cardiac responses to NaCN were complex, with an initial bradycardia followed by a tachycardia. In all animals, the tachycardia developed subsequent to lung ventilation. Atropine raised resting heart rate and abolished the bradycardia elicited by NaCN. Noradrenaline stimulated gill ventilation and heart rate but not air-breathing. These responses were not abolished by DL-propranolol, and propranolol had no effect on responses to NaCN. The results indicate that the axolotl possesses O2 chemo-sensitivity to both external and internal milieu, shows similar O2 chemo-reflexes to those of larval anurans and air-breathing fish, but does not exhibit the beta-adrenergic effects on ventilation observed in water-breathing fish.

Ambystoma↗
PubMed1996

Cardiac performance in relation to oxygen supply varies with dietary lipid composition in sturgeon.

Dietary polyunsaturated fatty acids (PUFA) of the n-3 series that have beneficial effects on mammalian heart function are typically found at high levels in fish tissues. The effects of dietary fatty acid composition on cardiac function were investigated in the sturgeon. When compared with sturgeon maintained for 1 yr on a diet enriched with saturated fatty acids (SFA) (the coconut oil-supplemented diet, COD), sturgeon maintained on a diet enriched with n-3 PUFA (the fish oil-supplemented diet, FOD) had higher myocardial 20:5(n-3) and lower 20:4(n-6) content with a consequent decrease in the n-6-to-n-3 ratio (from 0.86 to 0.25) and a lower intrinsic in vitro heart rate (22.0 +/- 1.5 vs. 29.9 +/- 1.0 beats/min) and cardiac power output (PO) (0.33 +/- 0.08 vs. 0.48 +/- 0.03 mW/g), but had a greater in vitro scope for cardiac work (almost twice the maximal-to-basal PO ratio). Reducing the oxygen supply to the hearts significantly decreased, by approximately 40%, the maximal in vitro PO in the COD group of animals but had no effect in the FOD group. These differences in performance were not reflected in heart rate or blood pressure in vivo, either in normoxia or hypoxia. Addition of vitamin E as an antioxidant to the diets reduced intrinsic heart rate by approximately 25% but did not influence the effects (dietary fatty acid composition on in vitro cardiac performance. The results indicate that dietary n-3 PUFA can have beneficial effects on the resistance of the fish heart to environmental stressors such as hypoxia.

Animals↗
PubMed1995

Aspects of cardioventilatory control in the adriatic sturgeon (Acipenser naccarii).

Cardioventilatory responses to hypoxia, the O2 chemoreceptor stimulant sodium cyanide (NaCN), and intra-arterial injection of atropine, noradrenaline and DL-propranolol were investigated in the adriatic sturgeon. Hypoxia elicited a bradycardia and hyperventilation. 1 mg NaCN added to water entering the buccal cavity stimulated a transient bradycardia but intra-arterial infusion of 150 micrograms NaCN did not, indicating that hypoxic bradycardia is controlled by chemoreceptors sensitive only to water O2 levels. NaCN stimulated hyperventilation both when added to the water and when infused intra-arterially, indicating that hypoxic hyperventilation is controlled by chemoreceptors sensitive to both internal and external milieux. Atropine abolished the hypoxic bradycardia and returned heart rate to normoxic values indicating that this species has no inhibitory vagal tone in normoxia. Noradrenaline stimulated ventilation, an effect abolished by DL-propranolol. Propranolol blocked ventilatory responses to intra-arterial infusion of NaCN whereas responses to NaCN added to the water remained unaffected, indicating that propranolol may inhibit internally-oriented O2-chemoreceptor activity or that ventilatory responses to intra-arterial NaCN are stimulated by a release of circulating catecholamines. Cardioventilatory control systems in sturgeon are similar to those of other actinopterygians but also show some characteristics of the system described for elasmobranchs.

Animals↗