This thesis involves laser flash photolysis studies of the kinetic behaviour of photochemical reactions in heterogeneous media with the emphasis on the effects of magnetic fields on the reactions involving triplet radical pairs. Chapters 3 and 4 present results of the effects of magnetic fields on the behaviour of radical pairs in organized systems. Free radicals are known to be involved in many biological processes and are thought to be a major initiator of some types of cancer. As a result, we have determined how free radical behaviour is modified in the presence of a 60 Hz oscillating magnetic field superimposed over a static magnetic field of comparable magnitude. We showed that the effect of an oscillating magnetic field on radical behaviour is identical to that exerted by a static magnetic field of the same strength provided the frequency is low in comparison with radical pair dynamics. We have used a test system involving radical pairs generated in micellar solutions by photolysis of benzophenone in the presence of 1,4-cyclohexadiene. Our results show that radical pair reactions in micellar solutions exhibit the same behaviour under 60 Hz oscillating fields as under static field conditions at any point in time. Given that (a) radicals play an important role in metabolic processes, and (b) that radical behaviour is strongly influenced by magnetic fields, it was clearly necessary to undertake experiments that better mimic in vivo systems. Laser flash photolysis of probe molecules, such as benzophenone and some of its derivatives, leads to a triplet spin-correlated radical pair due to the hydrogen abstraction of the triplet from Bovine and/or Human Serum Albumin. The analysis of the kinetics of the radical pair, where one of them is derived from the protein, in the presence and in the absence of a magnetic field, shows that the protein-probe radical pair is subject to a magnetic field effect. In Chapter 5, the photophysical properties of microheterogeneous systems have been characterized using the triplet state of an appropriate probe. (Abstract shortened by UMI.)

Even though lipids are thought to be a major metabolic fuel in fish during aerobic activity, little is known about their mobilization. Therefore, the goal of my thesis was to quantify lipid mobilization in fish. By analogy with mammals, I hypothesized that when fish are subjected to submaximal exercise, they mobilize their triacylglycerol (TAG) reserves above resting levels, which would result in: (1) increases in fatty acid (NEFA) and glycerol appearance rates (also termed fluxes), and (2) a decrease in the percent of NEFA reesterified by the TAG:FA substrate cycle. To test this hypothesis, I measured NEFA and glycerol rates of appearance, and I calculated the intracellular TAG:FA cycling rate in rainbow trout swimming for 1 h at either 1.0 or 1.5 bl s$\sp{-1},$ and 4 days at 1.0 bl s$\sp{-1}.$ This study is the first to measure glycerol appearance rate and TAG:FA cycling in fish. This thesis demonstrates that during submaximal exercise fish do not mobilize their triacylglycerol reserves above their resting levels. This result contrasts with what was expected by analogy to the mammalian situation or from body composition studies in exercising fish. (Abstract shortened by UMI.)

PGE$\sb2$ attenuates AVP-dependent solute transport in the medullary thick ascending limb of Henle (mTAL) and like the PGI$\sb2$ I-prostanoid (IP) receptor inhibits AVP-dependent water flow in the collecting duct. PGI$\sb2$ may play a role similar to PGE$\sb2$ in the mTAL. We therefore further characterize E-prostanoid (EP) receptor subtypes and the IP receptor in a freshly isolated suspension of rat mTAL. Using 10 nM PGE$\sb2,$ we confirmed previous work showing a Gi coupled EP$\sb3$ receptor subtype in rat mTAL that attenuates AVP-dependent cAMP by 70.7%. Pertussis toxin reversed this inhibitory response by 73.2%. In the absence of AVP, micromolar concentrations of PGE$\sb2$ and the EP$\sb2$ receptor subtype specific agonist butaprost produced significant elevations in cAMP levels, indicating the existence of the G$\rm\sb{s}$-coupled EP$\sb2$ receptor subtype. This response was insensitive to the EP$\sb4$ receptor subtype antagonist AH-23848B. Using the PGI$\sb2$ analogs iloprost (ILP) and cicaprost (CCP), we have demonstrated the presence of a Gi-coupled PGI$\sb2$ receptor. AVP-dependent cAMP was reduced 80% and 68.9% by 0.1uM ILP and 1 uM CCP respectively. Pertussis toxin reversed these inhibitory actions by 73%. Neither the EP$\sb3$ receptor subtype nor IP receptor inhibitory responses on AVP-dependent cAMP were sensitive to the EP$\sb1$ receptor subtype specific antagonist AH-6809 and the protein kinase C (PKC) inhibitors bisindolylmaleimide 1 and calphostin C. By associating in situ hybridization for receptor mRNA with TAL-specific Tamm-Horsfall glycoprotein immunostaining on serial sections from rat kidney, we have clearly shown EP$\sb3$ receptor subtype and IP receptor expression in the rat mTAL. These results suggest that a Gi-coupled IP receptor and the EP$\sb3$ receptor subtype play a role in attenuating the AVP-dependent cAMP in the rat mTAL.

The goal of this thesis was to examine the pathophysiological effects of chloramine-T exposure on the respiratory, acid-base and ionoregulatory physiology of the rainbow trout gill. In particular, chloramine-T was used as a tool to probe the fundamental physiological processes of gas transfer, acid-base and ion regulation in response to branchial irritation. Exposure of rainbow trout (Oncorhynchus mykiss) to therapeutic and subtherapeutic concentrations of chloramine-T (9 mg.L$\sp{-1}$ and 2 mg.L$\sp{-1}$, respectively) caused acute respiratory and acid-base disturbances. These consisted of an increase in ventilation frequency and arterial blood PCO$\sb2$ (PaCO$\sb2$); arterial PO$\sb2$ (PaO$\sb2$) was unaffected. Exposure of fish to chloramine-T under hyperoxic and moderately hypoxic conditions suggested that CO$\sb2$ excretion was being impaired due to the secretion of mucus in response to irritation by hypochlorite. To verify that the apparent impediment to excretion was diffusional and not due to a reduced functional surface area for gas exchange, direct measurements of cardiac output, O$\sb2$ uptake, CO$\sb2$ excretion, dorsal and ventral aortic blood pressures were made. There were no changes in dorsal or ventral aortic pressures or in branchial or systemic vascular resistance. The perfusion convection requirement for CO$\sb2$, but not O$\sb2$, increased during exposure to chloramine-T even though there were consistent increases in cardiac output. Thus a greater blood flow than was achieved would be required to excrete an equivalent amount of CO$\sb2$ during chloramine-T exposure as under non-exposed (control) conditions. However, there was sufficient blood flow to maintain and even increase O$\sb2$ uptake. Repeated intermittent exposure of fish to chloramine-T resulted in a reduction in the thickness of the gill epithelial diffusion barrier and a mucous cell hyperlasia. The consequences of these morphological changes on gas exchange were assessed using a graded hypoxic challenge. There was no effect of chloramine-T treatment on oxygen uptake rates but fish which had been pre-treated with chloramine-T maintained their PaO$\sb2$ at higher levels at 70-80 mmHg water PO$\sb2$ compared with controls. PaCO$\sb2$ levels were not significantly different between control and experimental animals even though chloramine-T treated animals had higher ventilation frequencies under pre-hypoxic conditions. Acute acid-base disturbances during chloramine-T exposure consisted of a metabolic alkalosis superimposed over a respiratory acidosis. A study of the net and unidirectional ionic and acid-base fluxes across the gill confirmed that chloramine-T exposure caused a reduction in the uptake of acidic equivalents. Acute Na$\sp+$ and Cl$\sp-$ losses were also observed with chloramine-T exposure and were attributed to an increase in a transcellular rather than paracellular ionic efflux. Chloramine-T did not effect urine flow rate, glomerular filtration rate, renal Na$\sp+$ and Cl$\sp-$ effluxes or renal clearance of Na$\sp+$ and Cl$\sp-$. Exposure of soft-water acclimated fish to chloramine-T did not cause increased ionic losses, consistent with the theory of transcellular rather than paracellular ionic losses. Ionic losses in both normal tap water and artificial soft water acclimated trout were eliminated by the addition of 0.1% (w/v) NaCl to the water. (Abstract shortened by UMI.)

The purpose of this study was to evaluate the relationships between heart rate (HR), oxygen consumption (VO$\sb2$) and mechanical Peak crank torque (PCT) and Average crank torque (ACT$\sb{60}$) variables in response to submaximal exercise employing a cycling race ergometer (RE), treadmill cycling (TC) and cycling in the field (FC). The work intensities identified as sub LT, LT and supra LT were equated on the basis of HR. Voltage signals from the crank arm were recorded as FM signals for subsequent representation of peak crank force (PCT) and average crank torque (ACT$\sb{60}$). Field VO$\sb2$ measures were done by Douglas bag procedure while an open circuit method was used for all laboratory testing. Heart rates were recorded with a Polar Electro Sport Tester PE3000. The observed results of field cycling demonstrated that laboratory conditions would overestimate the oxygen consumption in the field while force measurements suggested that laboratory conditions would underestimate mechanical work expenditures in the field. These differences become reduced at work intensities approximating VO$\sb{\rm 2max}$. It was concluded that HR can not always be used as an indicator of work stress when attempting to equate similar work loads performed under different conditions. (Abstract shortened by UMI.)

The primary purpose of this research was to study esophageal temperature elevation and quadriceps and triceps intra-muscular temperature gradients during resting recovery from exercise. Eight physically active male participants and 24 +/- 4 years of age, rested in a buttocks supported upright posture for a 50 +/- 12.5 minutes in ambient conditions of 24.7 +/- 1.17°C and 24 +/- 4.6% relative humidity. Participants then performed a steady state cycle ergometry exercise at 70% VO2 max, until they reached until heat produced by exercise above metabolic rate accumulated to 1000 kJ. This was followed by 120 minutes of resting recovery. Active intra-muscular temperature was measured in the vastus medialis at four depths, with the tip of the probe being at 10 mm from the femur and deep femoral artery and the others sensor at 15, 30 and 45 mm from the tip of the probe. Pre-exercise resting esophageal temperature and quadriceps intra-muscular temperatures were 36.95 +/- 0.22°C (Tes), 36.31 +/- 0.39°C (Tmuq1), 36.10 +/- 0.50°C (Tmuq2), 35.75 +/- 0.84°C (Tmuq3) and 35.33 +/- 0.88°C (Tmuq4) respectively. Exercise resulted in a 0.94 +/- 0.32°C increase in esophageal temperature above pre-exercise resting values. End of exercise intra-muscular quadriceps temperatures were 38.81 +/- 0.42°C (T muq1), 38.61 +/- 0.60°C (Tmuq2), 38.13 +/- 0.75°C (Tmuq3) and 37.71 +/- 0.96°C (Tmuq4 ). Esophageal temperature remained significantly elevated from pre-exercise resting values for 10 minutes following exercise. These results indicate that post-exercise esophageal temperature elevation, following cycle ergometry exercise, is not dependent on a temperature gradient between esophageal temperature and deep muscle temperature from the previously active muscle. Further, a prolonged and sustained post-exercise esophageal temperature was not demonstrated following this cycle ergometry exercise.

Recent published work showed post-exercise (PostEx) esophageal temperature (Tes) recovered rapidly to a persistent plateau that was significantly elevated (0.5$\sp\circ$C or more) above pre-exercise (PreEx) values. Non-acral skin temperatures, except over exercised muscle, returned rapidly to PreEx levels. Rectal temperatures (Tre) fell gradually during recovery reaching a plateau late in recovery (45 min) equal in magnitude of difference from Tes to PreEx values. Surface temperatures over the quadriceps remained high, indicating that heat was trapped in muscle. A similarity between the exercise Tes at which skin surface dilation occurred (Tdil) and the PostEx Tes was identified. These observations contradict the widely accepted "load-error" prinicple of thermoregulation which predicts that displacement of core temperature (Tco) from a hypothalamic set point (SPhy) will induce defense reflexes until the displacement is reversed. These data lead to the hypothesis that there was some residual influence related to exercise that retained the modulation of thermal reflex thresholds during recovery. Testing of the hypothesis was conducted with experiments to establish if: (1) the PostEx Tes was related to PreEx temperature; (2) exogenous thermal loading would produce the same post treatment elevation; (3) PostEx Tes elevation followed by exogenous thermal loading would result in an increase in the Tes elevation and (4) a 5 min exercise generating Tes below Tdil would result in a PostEx elevation of Tes. It was demonstrated that repeated running-recovery cycles produced patterns of rise and then fall of Tes to an elevated PostEx plateau that was equal to Tdil. This was similar to previous results except that the second exercise was begun at an elevated Tes and produced further elevation of Tdil with a comparable effect on PostEx Tes. Similarly, the third exercise further increased Tes following which it recovered to an even higher plateau equal in magnitude to Tdil. We observed that exogenous heat loading, by immersion of subjects in a bath of water at 44$\sp\circ$C to produce a rate of increase and peak elevation of Tes equal to exercise, did not result in a post-treatment elevation in Tes. Similarly, the PostEx Tes elevated plateau, equal to Tdil, remained unchanged following water immersion at 44$\sp\circ$C despite a larger total heat gain during the immersion. These observations eliminate whole body heat content changes as the primary cause of the Tes elevation and support the hypothesis that the homeothermic defense mechanisms become inoperative during recovery at a temperature above resting values as defined by Tdil. The physiological importance of Tdil in defining upper limits of resting temperature cannot be determined at this point. However, the physiological relationship of Tdil with PostEx Tes suggests that neuro-muscular activity significantly influences thermolytic controls which persist in recovery. That Tdil may represent the upper limit of a range of "normal temperatures" is supported by data from a 5 min exercise performed to a Tes elevation below Tdil. Within minutes of exercise termination Tes achieved a stable elevated PostEx Tes (0.3$\sp\circ$C or greater) which was maintained with no change over 65 min of recovery. The data suggest the possibility of: (1) a metabolically induced change in SPhy thermosensitivity, (2) a decreased sensitivity to an increase LE, or (3) a range of temperature regulation defined by an upper threshold control for thermolytic temperature defense reflexes.

The role of baroreceptor modulation on the post-exercise esophageal temperature threshold for cutaneous vasodilation (ThVD) and sweating (Th SW) was investigated. Six subjects were randomly exposed to lower body positive pressure (LBPP) and to no lower body positive pressure (NoLBPP) following a No-Exercise (NoEx) and Exercise (Ex) treatment protocol. The Exercise treatment consisted of 15 min of cycling at 70% VO2max and the No-Exercise treatment consisted of 15 min upright resting. Immediately following either treatment, subjects were positioned within a LBPP box after which a whole body water perfused suit was used to regulate mean skin temperature to assess ThVD and ThSW. ThVD increased 0.34°C post-exercise from the NoEx/NoLBPP condition to the Ex/NoLBPP condition (P < 0.05). However, the post-exercise increase in ThVD was abolished in the Ex/LBPP condition. No differences in ThSW were measured among the 4 conditions. These data support the hypothesis that the observed elevated post-exercise ThVD is the result of baroreceptor unloading. The similarity in threshold responses for sweating onset suggests that the post-exercise ThSW is not sensitive to baroreceptor loading or unloading.

No description available.

No description available.