Comparison of four magnetic resonance methods for mapping small temperature changes

Non-invasive detection of small temperature changes (< 1 degree C) is pivotal to the further advance of regional hyperthermia as a treatment modality for deep-seated tumours. Magnetic resonance (MR) thermography methods are considered to be a promising approach. Four methods exploiting temperature-dependent parameters were evaluated in phantom experiments. The investigated temperature indicators were spin-lattice relaxation time T1, diffusion coefficient D, shift of water proton resonance frequency (water PRF) and resonance frequency shift of the methoxy group of the praseodymium complex (Pr probe). The respective pulse sequences employed to detect temperature-dependent signal changes were the multiple readout single inversion recovery (T One by Multiple Read Out Pulses; TOMROP), the pulsed gradient spin echo (PGSE), the fast low-angle shot (FLASH) with phase difference reconstruction, and the classical chemical shift imaging (CSI). Applying these sequences, experiments were performed in two separate and consecutive steps. In the first step, calibration curves were recorded for all four methods. In the second step, applying these calibration data, maps of temperature changes were generated and verified. With the equal total acquisition time of approximately 4 min for all four methods, the uncertainties of temperature changes derived from the calibration curves were less than 1 degree C (Pr probe 0.11 degrees C, water PRF 0.22 degrees C, D 0.48 degrees C and T1 0.93 degrees C). The corresponding maps of temperature changes exhibited slightly higher errors but still in the range or less than 1 degree C (0.97 degrees C, 0.41 degrees C, 0.70 degrees C, 1.06 degrees C respectively). The calibration results indicate the Pr probe method to be most sensitive and accurate. However, this advantage could only be partially transferred to the thermographic maps because of the coarse 16 x 16 matrix of the classical CSI sequence. Therefore, at present the water PRF method appears to be most suitable for MR monitoring of small temperature changes during hyperthermia treatment.     

Harmonic motion imaging for focused ultrasound (HMIFU): a fully integrated technique for sonication and monitoring of thermal ablation in tissues

FUS (focused ultrasound), or HIFU (high-intensity-focused ultrasound) therapy, a minimally or non-invasive procedure that uses ultrasound to generate thermal necrosis, has been proven successful in several clinical applications. This paper discusses a method for monitoring thermal treatment at different sonication durations (10 s, 20 s and 30 s) using the amplitude-modulated (AM) harmonic motion imaging for focused ultrasound (HMIFU) technique in bovine liver samples in vitro. The feasibility of HMI for characterizing mechanical tissue properties has previously been demonstrated. Here, a confocal transducer, combining a 4.68 MHz therapy (FUS) and a 7.5 MHz diagnostic (pulse-echo) transducer, was used. The therapy transducer was driven by a low-frequency AM continuous signal at 25 Hz, producing a stable harmonic radiation force oscillating at the modulation frequency. A pulser/receiver was used to drive the pulse-echo transducer at a pulse repetition frequency (PRF) of 5.4 kHz. Radio-frequency (RF) signals were acquired using a standard pulse-echo technique. The temperature near the ablation region was simultaneously monitored. Both RF signals and temperature measurements were obtained before, during and after sonication. The resulting axial tissue displacement was estimated using one-dimensional cross correlation. When temperature at the focal zone was above 48 degrees C during heating, the coagulation necrosis occurred and tissue damage was irreversible. The HMI displacement profiles in relation to the temperature and sonication durations were analyzed. At the beginning of heating, the temperature at the focus increased sharply, while the tissue stiffness decreased resulting in higher HMI displacements. This was confirmed by an increase of 0.8 microm degrees C(-1)(r=0.93, p<.005). After sustained heating, the tissue became irreversibly stiffer, followed by an associated decrease in the HMI displacement (-0.79 microm degrees C(-1), r=-0.92, p<0.001). Repeated experiments showed a reproducible pattern of the HMI displacement changes with a temperature at a slope equal to 0.8+/-0.11 and -0.79+/-0.14 microm degrees C(-1), prior to and after lesion formation in seven bovine liver samples, respectively. This technique was thus capable of following the protein-denatured lesion formation based on the variation of the HMI displacements. This method could, therefore, be applied for real-time monitoring of temperature-related stiffness changes of tissues during FUS, HIFU or other thermal therapies.     

Properties of heat-treated calcium phosphate coatings deposited by high-velocity oxy-fuel (HVOF) spray

The influence of crystallization, upon heat treatment, on the properties of high-velocity oxy-fuel (HVOF) sprayed hydroxyapatite (HA) coatings was investigated. The characterization of the HA coating was performed by X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). Differential Scanning Calorimeter (DSC) was employed to determine the crystallization temperature of the amorphous phase in an as-sprayed HA coating. The study demonstrated the effect of crystallization on the coating properties by considering the changes in materials chemistry, crystallinity level, and mechanical performance. Results showed that complete crystallization of the amorphous phase occurred at approximately 700 degrees C and the crystallization temperature was dependent on sample heating rate in the DSC test. The changes of ion groups were detected by FTIR, before and after the phase transformation. The crystallization of the coating after annealing at 750 degrees C resulted in a significant increase of the coatings' adhesive strength and shear strength, which attained maximum values 34 +/- 3 and 14.1 -/+ 0.8 MPa, respectively. Young's modulus increased from 21 +/- 1 to 25 +/- 2 GPa. Microhardness measurements confirmed the changes in coating properties. It is also found that the transformation from the amorphous phase has crystalline HA as the only resultant phase detected by XRD.     

Effect of skin temperature on the cholinergic sensitivity of the human eccrine sweat gland

Although sweat gland activity is directly controlled by the central nervous system, which detects changes in core body temperature, sweat glands can also be influenced by local cutaneous thermal conditions. OBJECTIVE: The present study sought to determine the effect of local skin temperature on pilocarpine-induced sweating within a range of typical skin temperatures. METHODS: Thirteen subjects (30 +/- 6 years; 172 +/- 11 cm; 72.8 +/- 11.0 kg) had forearm sweat rates measured at rest following pilocarpine iontophoresis at each of three skin temperatures in randomized order: warm (T(warm) = 37.1 +/- 0.9 degrees C), control (T(con) = 32.3 +/- 1.4 degrees C), and cool (T(cool) = 26.6 +/- 1.3 degrees C). T(skin) was raised and lowered with an electric heating pad and gel ice pack, respectively. Forearm T(skin) was measured with a skin temperature probe. Pilocarpine iontophoresis was used on an approximately 7 cm(2) area of the anterior forearm to stimulate localized sweating. Following stimulation, sweat was collected from the area for 15 min with a Macroduct Sweat Collection System. RESULTS: There was a higher sweat rate at T(warm) (p = 0.001) and T(con) (p = 0.006) compared to that at T(cool). However, there was no difference between the sweat rate at T(warm) and that at T(con) (p = 0.127). CONCLUSION: These results indicated that skin temperatures below approximately 32 degrees C affect local sweat production primarily by altering glandular sensitivity to the neurotransmitter, whereas skin temperatures above approximately 32 degrees C predominantly affect neurotransmitter release. Furthermore, sweat glands display maximal or near maximal cholinergic sensitivity at resting skin temperature in a thermoneutral environment.     

Enhanced heat loss responses induced by short-term endurance training in exercising women

We investigated the effects of short-term endurance training and detraining on sweating and cutaneous vasodilatation during exercise in young women, taking into account changes in maximal oxygen uptake (VO2max) and the phase of the menstrual cycle. Eleven untrained women participated in endurance training; cycle exercise at approximately 60% VO2max for 60 min day(-1), 4-5 days week(-1) (30 degrees C, 45% relative humidity) for three complete menstrual cycles. The standard exercise test consisted of exercise at 50% VO2max for 30 min (25 degrees C, 45% relative humidity), and was conducted before training (Pre), during training sessions (T1, T2 and T3) and after cessation of training (D1 and D2). Values of VO2max increased significantly from 32.7 +/- 1.2 to 37.8 +/- 1.2 ml min(-1) kg(-1) at the end of the training. Local sweat rate in the chest and thigh, but not in the back and forearm, were significantly greater during T1 and T2 only in women who started training from the midfollicular phase. Cutaneous blood flow did not change with training. The threshold oesophageal temperatures for heat loss responses were significantly decreased during T1 versus Pre (averaged values for each body site: sweating, 37.49 +/- 0.08 versus 37.22 +/- 0.12 degrees C; and cutaneous vasodilatation, 37.40 +/- 0.07 versus 37.17 +/- 0.10 degrees C) and maintained through T3; the sensitivities of heat loss responses were not altered. These changes returned to the Pre level by D1. Our data indicate that physical training improves heat loss responses by decreasing the threshold temperatures and that these effects occur within a month of training and disappear within a month after cessation of training. The degree of increase in sweating with training differs among body sites and might be affected by the phase of the menstrual cycle.     

Preliminary assessment of one-dimensional MR elastography for use in monitoring focused ultrasound therapy

The purpose of this work is to assess a fast technique that measures tissue stiffness and temperature during focused ultrasound thermal therapy (FUS). A one-dimensional (1D) MR elastography (MRE) pulse sequence was evaluated for the purpose of obtaining rapid measurements of thermally induced changes in tissue stiffness and temperature for monitoring FUS treatments. The accuracy of the 1D measurement was studied by comparing tissue displacements measured by 1D MRE with those measured by the well-established 2D MRE pulse sequence. The reproducibility of the 1D MRE measurement was assessed, in gel phantoms and ex vivo porcine tissue, for varied FUS intensity levels (31.5-199.9 W cm(-2)) and over a range of displacements at the focus (0.1-1 microm). Temperature elevations in agarose gel phantoms were measured using 1D MRE and calibrated using fiberoptic-thermometer-based measurements. The 1D MRE displacement measurements are highly correlated with those obtained with the 2D technique (R(2) = 0.88-0.93), indicating that 1D MRE can successfully measure tissue displacement. Ten repeated trials at each FUS power level yielded a minimum detectable displacement change of 0.2 microm in phantoms and 0.4 microm in tissue (at 95% confidence level). The 1D MRE temperature measurements correlated well with temperature changes measured simultaneously with fiberoptic thermometers (R(2) = 0.97). The 1D MRE technique is capable of detecting tissue displacements as low as 0.4 microm, which is an order of magnitude smaller than 5 microm displacements expected during FUS therapy (Le et al 2005 AIP Conf. Proc.: Ther. Ultrasound 829 186-90). Additionally, 1D MRE was shown to provide adequate measurements of temperature elevations in tissue. These findings indicate that 1D MRE may be an effective tool for monitoring FUS treatments.     

Effects of concanavalin A on glutamate operated postsynaptic channels in crayfish muscle

Small crayfish muscle fibres were voltage clamped, and synaptic current noise induced by bath application of glutamate was measured. Desensitization of the glutamate receptors was blocked by preincubating the fibres with 0.3-1.0 mumol/l concanavalin A (Con A) for at least 30 min. The power density spectra of the glutamate current noise could be fitted by single component Lorentz curves. The lectin Con A did not influence significantly the conductance gamma of the glutamate channels but increased their mean open time, tau noise. The respective mean values found at T = 8 degrees C and E = -60 mV were gamma = 23.5 +/- 7.0 pS and tau noise = 1.5 +/- 0.2 ms. Both the conductance gamma and the closing rate alpha = tau -1 noise increased with temperature (Q10 approximately 1.9). This temperature dependence was characterized by the activation energies E gamma = 35.2 +/- 7.1 kJ/mol and E alpha = 46.9 +/- 2.1 kJ/mol. The potential dependence of tau noise was almost completely abolished by Con A.     

Feasibility of fast MR-thermometry during cardiac radiofrequency ablation

Online MR temperature monitoring during radiofrequency (RF) ablation of cardiac arrhythmias may improve the efficacy and safety of the treatment. MR thermometry at 1.5 T using the proton resonance frequency (PRF) method was assessed in 10 healthy volunteers under normal breathing conditions, using a multi-slice, ECG-gated, echo planar imaging (EPI) sequence in combination with slice tracking. Temperature images were post-processed to remove residual motion-related artifacts. Using an MR-compatible steerable catheter and electromagnetic noise filter, RF ablation was performed in the ventricles of two sheep in vivo. The standard deviation of the temperature evolution in time (TSD) was computed. Temperature mapping of the left ventricle was achieved at an update rate of approximately 1 Hz with a mean TSD of 3.6 ± 0.9 °C. TSD measurements at the septum showed a higher precision (2.8 ± 0.9 °C) than at the myocardial regions at the heart-lung and heart-liver interfaces (4.1 ± 0.9 °C). Temperature rose maximally by 9 °C and 16 °C during 5 W and 10 W RF applications, respectively, for 60 s each. Tissue temperature can be monitored at an update rate of approximately 1 Hz in five slices. Typical temperature changes observed during clinical RF application can be monitored with an acceptable level of precision.     

Changes in dielectric properties of ex vivo bovine liver at 915 MHz during heating

We have developed a coaxial measurement system for determining the time and temperature dependence of the dielectric properties of bovine liver at 915 MHz during heating. Our data suggest that changes in dielectric properties due to heating are dominated by the relaxation response of two tissue components: tissue water and proteins. At temperatures above 60 degrees C, the effects of these two components contribute to increases of up to 100% and 5% in the values of conductivity and permittivity respectively. Changes due to tissue water content were found to be reversible with temperature, while changes due to protein denaturation were found to be permanent. The temperature coefficients for reversible changes were found to be 1.82 +/- 0.28% degrees C(-1) and -0.130 +/- (5.9 x 10(-2))% degrees C(-1) for conductivity and permittivity respectively. The critical temperatures and activation energies leading to irreversible changes in conductivity and permittivity were determined using Arrhenius analysis. Frequency factors of (1.14 +/- 0.27) x 10(43) s(-1) and (1.95 +/- 0.49) x 10(36) s(-1) were determined for permittivity and conductivity respectively. The activation energies were calculated to be 70.7 +/- 15.8 kcal mol(-1) for permittivity and 60.1 +/- 14.0 kcal mol(-1) for conductivity.     

Impact of climate on thermal rhythm in pastoral sheep.

The effects of environmental conditions on temperature rhythms were investigated in ewe lambs at pasture. Two groups of 20 lambs had heart rate (HR), vaginal temperature (T(v)), ear-canal temperature (T(c)) and ear-pinna temperature (T(p)) monitored continuously for 3 days. Climatic conditions were recorded at the same time and Temperature Humidity Index (THI) calculated. One group experienced fine clear weather for the 3 days, the other group experienced 2 days of heavy rain. During periods of fine weather, the daily rhythm for T(v) and T(c) was monophasic. However, heavy rain and a constant THI reduced the amplitude of the recorded temperature rhythms. Daily T(v) and T(c) patterns correlated strongly with THI, with a phase lag of 2 h. Peak T(v) and T(c) were at approximately 17:00 h each day. Mean maximum daily amplitudes were approximately 1.3 degrees C for T(v) and T(c). Mean T(v) was 39.3+/-0.1 and 39.6+/-0.1 for weeks 1 and 2, respectively, while mean T(c) was 38.9+/-0.1 and 39.2+/-0.1. Changes in T(v) and T(c) were closely correlated. We conclude that climate has a major effect on body temperature rhythms.     

Thermal modulation of the toxicokinetics of benzo[a]pyrene in isolated hepatocytes of sablefish (Anoplopoma fimbria), black rockfish (Sebastes melanops), and chub mackerel (Scomber japonicus)

Hepatocytes from sablefish (Anoplopoma fimbria), black rockfish (Sebastes melanops) and chub mackerel (Scomber japonicus) were isolated from 11 degrees C acclimated animals. The uptake, metabolism, and excretion of benzo[a]pyrene (B[a]P) in hepatocytes was measured at 6, 11 and 19 degrees C. Chub mackerel hepatocyte uptake rates were significantly lower (0.012 +/- 0.003 microg/s per g cell) at 11 degrees C than black rockfish (0.028 +/- 0.009 microg/s per g cell) or sablefish (0.032 +/- 0.012 microg/s per g cell) hepatocytes at all temperatures. Hepatocytes metabolized B[a]P to phase I (1-8%) and phase II (92-99%) metabolites. Accumulation of phase II metabolites was lower in chub mackerel hepatocytes (0.016 +/- 0.004 microg/h per g cell), than black rockfish (0.052 +/- 0.012 microg/h per g cell), or sablefish hepatocytes (0.060 +/- 0.015 microg/h per g cell). Phase II metabolite accumulation increased greatest with temperature in chub mackerel hepatocytes (Q10 = 1.94 +/- 0.30), followed by sablefish (Q10 = 1.65 +/- 0.30), and rockfish (Q10 = 1.38 +/- 0.30). Sablefish hepatocytes had higher excretion rates of phase II metabolites (0.010 +/- 0.0023 microg/h per g cell), than mackerel (0.0046 +/- 0.0009 microg/h per g cell) or rockfish hepatocytes (0.0029 +/- 0.0008 microg/h per g cell). Phase II metabolite excretion rates increased with temperature only in sablefish hepatocytes (Q1O = 1.67 +/- 0.76). These differences in toxicokinetics may indicate distinct consequences for various species exposed to xenobiotics.     

Time course and nature of temperature-induced changes in sodium-glucose interactions of the goldfish intestine

1. Glucose-evoked potentials measured at low incubation temperatures were found to be highly temperature dependent (phase 1), but less so at high incubation temperatures (phase 2) and acclimatization of an 8 degrees C fish to 25 degrees C resulted in the extension of phase 1 up to the environmental temperature of the fish. This change was only part of the mechanism controlling the acclimatization of sodium transport across the intestine.2. The temperature at which the glucose-evoked potential changed from phase 1 to phase 2 was approximately equal to the temperature at which glucose began to raise the steady transmural potential of the intestine.3. No changes in intestinal electrical parameters could be detected when fish, acclimatized to 8 degrees C, were heated at 25 degrees C for 15 hr, but after 20 hr at the higher temperature, acclimatization to the new temperature was complete.4. Intestines from fish acclimatized to 8 degrees C, but which had first spent 15 hr at 25 degrees C and then 10 hr at 8 degrees C, still behaved qualitatively like 8 degrees C - intestines but the magnitude of the glucose-evoked potentials was slightly reduced.5. It is suggested as a working hypothesis that acclimatization of the sodium-glucose interaction to different environmental temperatures involves the synthesis of new carrier molecules, qualitatively different from the old ones.     

Effects of heat removal through the hand on metabolism and performance during cycling exercise in the heat.

OBJECTIVE: This two-part study tested the hypotheses that the use of a new cooling device, purported to extract heat from the body core through the palm of the hand, would (a) attenuate core temperature rise during submaximal exercise in the heat, thereby suppressing exercise-associated metabolic changes, and (b) facilitate a higher sustained workload, thus shortening the completion time of a time-trial performance test. METHODS: In Study 1, 8 male triathletes (age 27.9 +/- 2.0 yrs, mass 77.2 +/- 3.1 kg, VO2peak 59.0 +/- 4.1 ml x min(-1) x kg(-1)) cycled for 1 hr at the same absolute workload (approximately 60% VO2peak) in a heated room (31.9 +/- 0.1 degrees C, 24 +/- 1% humidity) on two occasions counterbalanced for cooling (C) or noncooling (NC). In Study 2, 8 similar subjects (age 26.9 +/- 2.0 yrs, mass 75.2 +/- 3.7 kg, VO2peak 54.1 +/- 3.1 ml x min(-1) x kg(-1)) performed two 30-km cycling time-trial performance tests under the same conditions (C(T), NC(T)). RESULTS: In Study 1, cooling attenuated the rise in tympanic temperature (T(TY)) (1.2 +/- 0.2 vs. 1.8 +/- 0.2 degrees C; p < 0.01) and lowered mean oxygen consumption (VO2, 2.4 +/- 0.1 vs. 2.7 +/- 0.1 L x min(-1); p < 0.05) and blood lactate (1.7 +/- 0.2 vs. 2.2 +/- 0.2 mmol x L(-1); p < 0.01) during exercise. There were no significant differences in respiratory exchange ratio (RER), blood glucose, heart rate (HR), face temperature (T(F)), or back temperature (T(B)) between NC and C. In Study 2, time to complete 30 km was 6 +/- 1% less with cooling than without cooling (60.9 +/- 2.0 vs. 64.9 +/- 2.6 min; p < 0.01). During the last 20% of C(T), subjects sustained a workload that was 14 +/- 5% (p = 0.06) higher than NC(T) at the same T(TY) and HR. CONCLUSIONS: Heat extraction through the hand during cycle ergometer exercise in the heat can (a) lower T(TY), lactate concentration, and VO2 during a submaximal set-workload test and (b) reduce the time it takes to complete a 30-km time-trial test.     

Reduced xenon diffusion for quantitative lung study--the role of SF(6)

The large diffusion coefficients of gases result in significant spin motion during the application of gradient pulses that typically last a few milliseconds in most NMR experiments. In restricted environments, such as the lung, this rapid gas diffusion can lead to violations of the narrow pulse approximation, a basic assumption of the standard Stejskal-Tanner NMR method of diffusion measurement. We therefore investigated the effect of a common, biologically inert buffer gas, sulfur hexafluoride (SF(6)), on (129)Xe NMR and diffusion. We found that the contribution of SF(6) to (129)Xe T(1) relaxation in a 1:1 xenon/oxygen mixture is negligible up to 2 bar of SF(6) at standard temperature. We also measured the contribution of SF(6) gas to (129)Xe T(2) relaxation, and found it to scale inversely with pressure, with this contribution approximately equal to 1 s for 1 bar SF(6) pressure and standard temperature. Finally, we found the coefficient of (129)Xe diffusion through SF(6) to be approximately 4.6 x 10(-6) m(2)s(-1) for 1 bar pressure of SF(6) and standard temperature, which is only 1.2 times smaller than the (129)Xe self diffusion coefficient for 1 bar (129)Xe pressure and standard temperature. From these measurements we conclude that SF(6) will not sufficiently reduce (129)Xe diffusion to allow accurate surface-area/volume ratio measurements in human alveoli using time-dependent gas diffusion NMR.     

Fast spectroscopic imaging for non-invasive thermometry using the Pr[MOE-DO3A] complex.

The praseodymium complex of 10-(2-methoxyethyl)-1,4,7,10-tetraaza-cyclododecane-1,4,7-tr iacetate) was evaluated as a temperature-sensitive contrast agent using the temperature dependence (approximately 0.12 ppm degrees C(-1)) of the chemical shift of its methoxy side group signal. Pr[MOE-DO3A] was employed in combination with spectroscopic imaging (SI) methods for the determination of spatially resolved 2D and 3D temperature distributions in phantoms. Conventional SI and fast echo planar SI sequences (EPSI) were implemented on a 4.7 T MR imaging system fulfilling the demands for non-invasive thermometry (NIT) with respect to thermal and temporal resolution, being <1 degree C and <20 s total measuring time, respectively. The sequences are based on a fast spin echo SI method taking into account the very short relaxation times of the Pr complex methoxy group (T1 = 28 ms, T2 = 13 ms) and its chemical shift difference (-24 ppm) from water. Calibration curves were measured in a uniformly heated water phantom and 2D SI methods were applied to dynamic heating experiments. The average differences between the temperatures measured via fibreoptic thermometer and those derived from the spectroscopic methods were < or =0.2 degrees C. Furthermore, 3D EPSI experiments with a 16 x 16 x 16 matrix size yielded temperature measurements within 17 s from voxels of size 3 x 3 x 3 mm3.     

Growth hormone and prolactin responses during partial and whole body warm-water immersions

AIM: To elucidate the role of core and skin thermoreceptors in the release of growth hormone (GH) and prolactin (PRL), a sequence of two experiments using whole-body (head-out) and partial (one forearm) hot water immersions was performed. METHODS: Experiment 1: Nine healthy men were exposed to head-out and partial water immersions (25 min, 38-39 degrees C). RESULTS: Head-out immersion increased the core temperature (38.0 +/- 0.1 vs. 36.7 +/- 0.1 degrees C, P < 0.001) and plasma concentration of the hormones (GH, 16.1 +/- 4.5 vs. 1.2 +/- 0.4 ng mL(-1), P < 0.01; PRL, 9.1 +/- 1.0 vs. 6.4 +/- 0.4 ng mL(-1), P < 0.05). During the partial immersion the core temperature was slightly elevated (36.8 +/- 0.1 vs. 36.6 +/- 0.1, P < 0.001), the concentration of GH increased (4.8 +/- 1.7 vs. 0.6 +/- 0.3, P < 0.05), while plasma PRL decreased (7.6 +/- 0.8, 6.0 +/- 0.6, 5.2 +/- 0.6, P < 0.01). Experiment 2: Seven volunteers immersed one forearm once in 39 degrees C and once in 38 degrees C water. The measurements were performed in 5-min intervals. The GH concentration increased gradually from the beginning of the immersions (min 10; 39 degrees C: 1.9 +/- 1.0 vs. 0.6 +/- 0.3 ng mL(-1), P < 0.01; 38 degrees C: 0.19 +/- 0.03 vs. 0.14 +/- 0.03, P < 0.05) and peaked after their completion (39 degrees C: +10 min, 3.7 +/- 2.0, P < 0.001; 38 degrees C: +15 min, 0.86 +/- 0.61, P < 0.01). The core temperature was unchanged until min 15 of the 39 degrees C bath. Thereafter, it increased about 0.15 degrees C above the baseline (P < 0.01). Immersion in 38 degrees C water did not induce core temperature changes. CONCLUSIONS: Peripheral thermoreceptors are involved in GH release when the body is exposed to elevated environmental temperature while a substantial elevation of core temperature is a precondition of PRL release.     

The relationship between serum water proton T1 and protein content in the P388 leukemic mouse and the effect of chemotherapy by cis-diamminedichloroplatinum(II)

Proton NMR longitudinal relaxation times (T1; 10.7 MHz; 37 degrees C) were measured in the kidneys and blood serum of mice inoculated with P388 leukemia, and/or treated with the chemotherapeutic drug cis-diamminedichloroplatinum(II) (cis-Pt). In parallel, serum total protein content, urea and creatinine levels were determined and protein fractions were separated electrophoretically. Serum T1 was found to be 1518 +/- 73 ms (1 SD) in control mice, 1670 +/- 69 ms in leukemic mice, and 1380 +/- 71 ms in the healthy and the leukemic cis-Pt treated mice. The T1 increase in leukemic serum and T1 decrease in the serum of cis-Pt injected mice are attributed to decreased and increased protein contents respectively. A detailed analysis in terms of electrophoretic fractions of serum proteins reveals that the serum relaxation rate 1/T1 is a multilinear function of the mass concentrations of the main serum protein fractions, explaining all serum T1 effects. This makes T1 a non-specific blood parameter. The kidney T1 was found to be 311 +/- 12 ms in normal mice and 334 +/- 20 ms in leukemic mice. A dramatic T1 increase is observed when the mice are injected with cis-Pt; the values are 400 +/- 38 ms and 407 +/- 39 ms for healthy and leukemic mice, respectively. This effect is related to the nephrotoxicity of the drug, as evidenced by serum urea and creatinine levels and protein content being higher than normal.     

A comparison of thermoregulatory responses in the Japanese macaque (Macca fuscata) and the crab-eating macaque (Macaca irus) during cold exposure.

Thermoregulatory responses in four male adult Japanese macaques and four male adult crab-eating macaques, weighing 6-12 kg and 6.2-8 kg, respectively, were compared at ambient temperatures (Ta) ranging from 5 degrees C to 25 degrees C. The average values +/- S.E. for some physiological measurements made at Ta of 25 degrees C in the Japanese macaque and the crab-eating macaque, respectively, were as follows: resting metabolic rate; 47.6 +/- 5.0 and 42.5 +/- 1.7 W/M2; tissue conductance; 11.9 +/- 0.8 and 8.9 +/- 0.8 W/M2/degrees C; respiratory evaporative heat loss; 4.1 +/- 0.3 and 3.2 +/- 0.5 W/M2; rectal temperature; 38.6 +/- 0.1 and 37.4 +/- 0.2 degrees C; mean skin temperature; 34.0 +/- 0.3 and 31.2 +/- 0.1 degrees C. When Ta was lowered stepwise from 25 degrees C to 20, 15, 10, and 5 degrees C successively, and maintained constant at each temperature level for 1 hr, metabolic heat production graudually increased in both species. Whe Ta was lowered from 10 degrees C to 5 degrees C, the crab-eating macaque did not show further increase in heat production and the result was a loss of thermal equilibrium with rectal temperature continuing to fall. On the other hand, the Japanese macaque maintained thermal balance even at Ta of 5 degrees C. Tissue conductance, which was significantly higher in the Japanese macaque than in the crab-eating macaque at Ta of 5, 15, and 25 degrees C, decreased in both species at Ta was lowered from 25 degrees C to 15 and 5 degrees C. The specific differences in thermo-regulatory responses are considered to be adaptational, relative to the natural habitat of thw two species studied.     

Temperature-dependence of rod photoresponses from the aspartate-treated retina of the frog (Rana temporaria)

The effects of temperature changes on rod photoresponses were studied by recording the aspartate-isolated mass receptor potential in the dark-adapted retina of the frog Rana temporaria. The amplitude of saturating responses, indicating the magnitude of the dark current, increased linearly with temperature in the measured range 6-26 degrees C, extrapolating to zero dark current at 0 degrees C. Sensitivity was maximal around 18 degrees C but the decrease towards lower temperatures was shallow. The results show that rod phototransduction in the frog Rana temporaria is adapted to lower temperatures than in the tropical toad Bufo marinus. Responses to dim flashes were, approximately up to peak, well fitted by the same 'independent activation' model with four delay stages as have been found to best describe current responses from single toad rods. The kinetics (reciprocal time-to-peak) showed Arrhenius-type temperature-dependence with apparent activation energy 12.4 kcal mol-1 and Q10 = 2.1.     

Carotid-sinus baroreflex modulation of core and skin temperatures in rats: an open-loop approach

The neural mechanisms of the thermoregulatory control of core and skin temperatures in response to heat and cold stresses have been well clarified. However, it has been unclear whether baroreceptor reflexes are involved in the control of core and skin temperatures. To investigate how the arterial baroreceptor reflex modulates the body temperatures, we examined the effect of pressure changes of carotid sinus baroreceptors on core and skin temperatures in halothane-anesthetized rats. To open the baroreflex loop and control arterial baroreceptor pressure (BRP), we cut vagal and aortic depressor nerves and isolated carotid sinuses. We sequentially altered BRP in 20-mmHg increments from 60 to 180 mmHg and then in 20-mmHg decrements from 180 to 60 mmHg while measuring systemic arterial pressure (SAP), heart rate (HR), and core blood temperature (T(core)) at the aortic arch and skin temperature (T(skin)) at the tail. In response to the incremental change in BRP by 120 mmHg, SAP, HR, and T(core) fell by 90.3 +/- 5.1 mmHg, 60.3 +/- 10.5 beats min(-1), and 0.18 +/- 0.01 degrees C, respectively. T(skin) rose by 0.84 +/- 0.10 degrees C. The maximum rate of change per unit BRP change was -2.1 +/- 0.2 for SAP, -1.5 +/- 0.4 beats min(-1) mmHg(-1) for HR, -0.003 +/- 0.001 degrees C mmHg(-1) for T(core), and 0.011 +/- 0.002 degrees C mmHg(-1) for T(skin). After the administration of hexamethonium or bretylium, these baroreflexogenic responses were completely abolished. We concluded that T(core) and T(skin) are modulated by the arterial baroreceptor reflex.