Compensation for an increase in body fat caused by donor transplants into mice

Rodents tend to compensate for experimental obesity in which both adipocyte size and number are increased. In contrast, it was recently reported that Siberian hamsters do not compensate for dorsal subcutaneous transplants of fat, which increase body fat without changing the size of adipocytes. In the first experiment described here we tested whether mice changed the size of their endogenous fat stores 2 or 5 wk after donor fat was added as subcutaneous transplants. Each epididymal fat pad from donor mice was cut in half and placed ventrally in recipient mice, increasing body fat by approximately 10%. After 2 wk, there was no effect of the transplants on the size of endogenous fat depots or the size of adipocytes in epididymal fat depots. There was a substantial decrease in mass and adipocyte size in transplanted fat. Five weeks after surgery the endogenous epididymal and retroperitoneal fat depots of recipient mice were significantly decreased, serum leptin was reduced, and the size of adipocytes in endogenous epididymal fat was significantly reduced, although cell number had not changed. The size of transplanted cells was the same as at 2 wk. In a second experiment, epididymal fat was placed as either dorsal or ventral subcutaneous fat transplants. Five weeks after surgery the endogenous fat depots were decreased in all recipient mice but none of the differences reached statistical significance. These results suggest that mice have mechanisms to maintain total body fat mass that respond to an increase in the number of fat cells present.     

Transient increase of tryptophan fluorescence of enzyme caused by photoexcitation of ligand in luciferase-luciferin complex

An experiment was proposed and accomplished that was based on the hypothesis of the dissociation of the luciferase-luciferin complex in photoexcitation. A pump-probe experiment was performed with the use of picosecond laser pulses and was based on the effect of quenching of enzyme tryptophan fluorescence caused by luciferin binding. A photoinduced increase of the tryptophan fluorescence intensity was detected. Experimental results were interpreted on the basis of the assumptions on photoinduced dissociation of the luciferin-luciferase complex and Forster energy transfer from tryptophan to luciferin. Under the assumption on the photoinduced dissociation and stationary quenching of tryptophan fluorescence the rate of propagation of the conformational changes in the protein caused by the complex dissociation was estimated to be >20 m/s.     

Skin temperature increase caused by a mobile phone: a methodological infrared camera study

Mobile phone users often complain about burning sensations or a heating of the ear region. The increase in temperature may be due to thermal insulation by the phone, heating of the mobile phone resulting from its electrical power dissipation, and radio frequency (RF) exposure. The main objective of this study was to use infrared (IR) camera techniques to find how much each of these factors contributes to the increase in skin temperature resulting from the use of one GSM 900 phone. One subject, a healthy male, took part in the study. He was holding the phone in a normal position when the phone was switched off, when it was switched on but with the antenna replaced by a 50 Omega load to eliminate the RF exposure, and when it was transmitting RF fields. The output power could be fixed, and the minimal and the maximal power levels of the phone were used. The study was designed as a double blind experiment. The changes in temperature after 15 and 30 min of mobile phone use were calculated on the exposed side of the head relative to the unexposed side. The insulation and the electrical power dissipation led to statistically significant rises in the skin temperature, while the RF exposure did not.     

The increase in denaturation temperature following cross-linking of collagen is caused by dehydration of the fibres

Differential scanning calorimetry (DSC) was used to study the thermal stability of native and synthetically cross-linked rat-tail tendon at different levels of hydration, and the results compared with native rat-tail tendon. Three cross-linking agents of different length between functional groups were used: malondialdehyde (MDA), glutaraldehyde and hexamethylene diisocyanate (HMDC). Each yielded the same linear relation between the reciprocal of the denaturation temperature in Kelvin, T(max), and the water volume fraction, epsilon (1/T(max)=0.000731epsilon+0.002451) up to a critical hydration level, the volume fraction of water in the fully hydrated fibre. Thereafter, water was in excess, T(max) was constant and the fibre remained unchanged, no matter how much excess water was added. This T(max) value and the corresponding intrafibrillar volume fraction of water were as follows: 84.1 degrees C and 0.48 for glutaraldehyde treated fibres, 74.1 degrees C and 0.59 for HMDC treated fibres, 69.3 degrees C and 0.64 for MDA treated fibres, and 65.1 degrees C and 0.69 for untreated native fibres. Borohydride reduction of the native enzymic aldimines did not increase the denaturation temperature of the fibres. As all samples yielded the same temperature at the same hydration, the temperature could not be affected by the nature of the cross-link other than through its effect on hydration. Cross-linking therefore caused dehydration of the fibres by drawing the collagen molecules closer together and it was the reduced hydration that caused the increased temperature stability. The cross-linking studied here only reduced the quantity of water between the molecules and did not affect the water in intimate contact with, or bound to, the molecule itself. The enthalpy of denaturation was therefore unaffected by cross-linking. Thus, the "polymer-in-a-box" mechanism of stabilization, previously proposed to explain the effect of dehydration on the thermal properties of native tendon, explained the new data also. In this mechanism, the configurational entropy of the unfolding molecule is reduced by its confinement in the fibre lattice, which shrinks on cross-linking.     

REM sleep related increase in brain temperature: a physiologic problem

The roles of metabolic heat production, arterial blood flow and temperature in the genesis of the brain temperature increase related to REM sleep occurrence in several mammalian species are discussed on the basis of available experimental evidence. The experimental data show that only changes in arterial blood flow and temperature consistently underlie the rise in brain temperature in presence (cat) or absence (rabbit) of the carotid rete. The alteration of cardiovascular regulation in REM sleep is the remote cause of such rise. The proximate causes are decrease in carotid blood supply and increase in vertebral blood supply to the brain and related depression of systemic and selective brain cooling.     

Hemoglobin dynamics in red blood cells: correlation to body temperature

A transition in hemoglobin behavior at close to body temperature has been discovered recently by micropipette aspiration experiments on single red blood cells (RBCs) and circular dichroism spectroscopy on hemoglobin solutions. The transition temperature was directly correlated to the body temperatures of a variety of species. In an exploration of the molecular basis for the transition, we present neutron scattering measurements of the temperature dependence of hemoglobin dynamics in whole human RBCs in vivo. The data reveal a change in the geometry of internal protein motions at 36.9°C, at human body temperature. Above that temperature, amino acid side-chain motions occupy larger volumes than expected from normal temperature dependence, indicating partial unfolding of the protein. Global protein diffusion in RBCs was also measured and the findings compared favorably with theoretical predictions for short-time self-diffusion of noncharged hard-sphere colloids. The results demonstrated that changes in molecular dynamics in the picosecond time range and angstrom length scale might well be connected to a macroscopic effect on whole RBCs that occurs at body temperature.     

Protein kinase C increase in rat brain cortical membranes may be promoted by cognition enhancing drugs.

Protein Kinase C (PKC) activity was measured in soluble and particulate fractions of rat individual brain cortices after in vivo treatment with two cognition enhancers: oxiracetam and alpha-glicerylphosphorylcholine. Both drugs induced an increase (+40-50%) of PKC particulate activity at 1 hr after the treatment. The effect was transient; at 5 hours PKC activity was lower than in controls. The dose response curve to oxiracetam was bell shaped, the increase of PKC being significant at 100 mg/kg. At higher doses the drug induced a decrease in enzyme activity. The increased PKC activity may be related to the cortical effects of these compounds.     

How the body controls brain temperature: the temperature shielding effect of cerebral blood flow.

Normal brain functioning largely depends on maintaining brain temperature. However, the mechanisms protecting brain against a cooler environment are poorly understood. Reported herein is the first detailed measurement of the brain-temperature profile. It is found to be exponential, defined by a characteristic temperature shielding length, with cooler peripheral areas and a warmer brain core approaching body temperature. Direct cerebral blood flow (CBF) measurements with microspheres show that the characteristic temperature shielding length is inversely proportional to the square root of CBF in excellent agreement with a theoretical model. This "temperature shielding effect" quantifies the means by which CBF prevents "extracranial cold" from penetrating deep brain structures. The effect is crucial for research and clinical applications; the relationship between brain, body, and extracranial temperatures can now be quantitatively predicted.     

The role of liver tryptophan pyrrolase in the opposite effects of chronic administration and subsequent withdrawal of drugs of dependence on rat brain tryptophan metabolism.

1. Chronic administration of morphine, nicotine or phenobarbitone has previously been shown to inhibit rat liver tryptophan pyrrolase activity by increasing hepatic [NADPH], whereas subsequent withdrawal enhances pyrrolase activity by a hormonal-type mechanism. 2. It is now shown that this enhancement is associated with an increase in the concentration of serum corticosterone. 3. Chronic administration of the above drugs enhances, whereas subsequent withdrawal inhibits, brain 5-hydroxytryptamine synthesis. Under both conditions, tryptophan availability to the brain is altered in the appropriate direction. 4. The chronic drug-induced enhancement of brain tryptophan metabolism is reversed by phenazine methosulphate, whereas the withdrawal-induced inhibition is prevented by nicotinamide. 5. The chronic morphine-induced changes in liver [NADPH], pyrrolase activity, tryptophan availability to the brain and brain 5-hydroxytryptamine synthesis are all reversed by the opiate antagonist naloxone. 6. It is suggested that the opposite effects on brain tryptophan metabolism of chronic administration and subsequent withdrawal of the above drugs of dependence are mediated by the changes in liver tryptophan pyrrolase activity. 6. Similar conclusions based on similar findings have previously been made in relation to chronic administration and subsequent withdrawal of ethanol. These findings with all four drugs are briefly discussed in relation to previous work and the mechanism(s) of drug dependence.     

The role of an invariant tryptophan residue in alpha-bungarotoxin and cobrotoxin. Investigation of active derivatives with the invariant tryptophan replaced by kynurenine

Ozone oxidation converted the single, invariant, tryptophan residue to N2-formylkynurenine in alpha-bungarotoxin and cobrotoxin. Upon this modification, the lethal toxicity was significantly reduced in cobrotoxin but mostly retained in alpha-bungarotoxin. Each neurotoxin containing kynurenine instead of tryptophan retained the same antigenicity as the native toxin. Fluorescence and CD spectroscopy revealed that, although the environment and state of the kynurenine residue were similar, [Kyn29]cobrotoxin was much more sensitive to pH change than alpha-[Kyn28]bungarotoxin. In terms of lethal toxicity and conformational stability, the invariant tryptophan residue appears to play a more important role in cobrotoxin, imparting a higher lethal toxicity than that in alpha-bungarotoxin, which has a disulfide bond at Cys29-Cys33.     

Cholestatic jaundice caused by cloxacillin: macrophage inhibition factor test in preventing rechallenge with hepatotoxic drugs.

Severe intrahepatic cholestasis occurred in a patient after taking nitrofurantoin, ampicillin, and cloxacillin. As only nitrofurantoin was known to cause cholestasis she was given cloxacillin again two years later. The cholestasis reappeared at once. A macrophage inhibition factor test confirmed that cloxacillin was the offending drug. Cloxacillin should be added to the growing list of drugs causing cholestasis. Inadvertent rechallenge with hepatototoxic drugs might be prevented by routine use of the macrophage inhibition factor test.     

Detecting ovulation in Macaca nemestrina by correlation of vaginal cytology, body temperature and perineal tumescence with laparoscopy

Vaginal cytology, basal body temperature, and perineal tumescence were correlated with laparoscopic observations during the menstrual cycles of five pigtail monkeys (Macaca nemestrina) of known fertility. Percentages of cells obtained in vaginal smears revealed systematic variation in the presence of cell types in relation to the menstrual cycle. Measuring the percentage of exfoliate vaginal epithelial cells containing pyknotic nuclei proved to be of little value for separating the menstrual cycle into its follicular and luteal phases, nor did body temperature provide an accurate index for the occurrence of ovulation. Perineal tumescence, however, measured from the first day of menses to onset of detumescence, was a reliable indicator of the lengths of the follicular and luteal phases as correlated with laparoscopic confirmation of ovulation. Maximal perineal tumescence usually occurred within 12 hours of ovulation, although on one occasion the two events were separated by 48 hours.