Thyrotropin receptor messenger ribonucleic acid is expressed in most brown and white adipose tissues in the guinea pig

High affinity TSH binding has been reported in a variety of tissues other than the thyroid, most commonly in adipocytes and lymphocytes. This extrathyroidal binding of TSH has been documented most carefully in the guinea pig epididymal fat pad, where it has been postulated to be due to the presence of the TSH receptor (TSH-R). Extrathyroidal TSH-R expression has also been theorized to account for the associated dermopathy and ophthalmopathy seen in some patients with Graves' disease. We have isolated a cDNA encoding a fragment of the guinea pig TSH-R and have used this as a probe to study the distribution of TSH-R mRNA in the guinea pig. We show here that TSH-R mRNA is expressed in most white adipose tissues and in all brown adipose tissues tested. However, no expression was detectable by Northern analysis or in most polymerase chain reaction experiments using guinea pig retroorbital tissues, bringing into question the proposed role of the TSH-R as an autoantigen in autoimmune ophthalmopathy. The presence of significant amounts of TSH-R mRNA in most adipose tissues suggests a more important role for TSH in lipolysis and thermogenesis than previously thought.

Convertible adipose tissue in mice

Ability to express uncoupling protein (UCP) and establish UCP-dependent thermogenesis was analyzed in anatomical areas of mice that are generally considered to be white adipose tissue: mesenterial, perimetral, epididymal, inguinal, and superficial layer of interscapular white adipose tissue. The mice were acclimatized for 1 week to 4 degrees C; the following week they were exposed to cold stress (1 h at -20 degrees C, 2-3 times daily). In such conditions in inguinal adipose tissue, slot-blot analysis detected significant amount of UCP mRNA and lipoprotein lipase mRNA. Immuno-electron-microscopic localization of UCP showed that developed mitochondria of cold-stressed inguinal adipocytes contained UCP in the same amount as uncoupled (UC)-mitochondria of brown adipocytes. Morphological and morphometrical analysis showed that such inguinal adipose tissue appeared as brown adipose tissue. Since in control mice, inguinal adipose tissue was UCP-negative and tissue appeared as white adipose tissue, the duration of this white-to-brown adipose tissue conversion was analyzed. Mice, cold stressed for 1 week, were rewarmed at 28 degrees C and their inguinal adipose tissue was analyzed in comparison with interscapular brown adipose tissue and epididymal white adipose tissue for another 37 days. During that time inguinal adipocytes ceased expressing UCP mRNA; UC-mitochondria in inguinal adipocytes were destroyed and replaced with common, C-mitochondria; and UCP was undetectable immunohistochemically. Adipocytes accumulated lipids, and the tissue morphologically once again resembled white adipose tissue. Described changes showed that besides typical brown and white adipose tissue in mice, there existed a third type of adipose tissue described as convertible adipose tissue.

Serotonin content of the interscapular brown adipose tissue of growing rats

In brown fat of newborn rats the serotonin (5HT) content is high during the first five days of life. This may play a part in the lipid repletion of the tissue, lipids being the main fuel for nonshivering thermogenesis. Subsequently 5HT increases more in young rats reared at 16 degrees C than in those reared at 28 degrees C but to a lesser extent than norepinephrine (NE) content. A possible role of 5HT in thermoregulation of the rat during the early postnatal period is discussed.

Steroid profiles of brown adipose tissue

In brown adipose tissue of alp-marmot (Marmota marmota), badger (Meles meles) and Wistar rats steroids of C21- and C19-type are identified and quantified. The detection of 3 alpha-hydroxy-5 alpha-pregnan-20-one, 3 alpha-hydroxy-5 beta-pregnan-20-one, 3 alpha,21-dihydroxy-5 alpha-pregnan-20-one, 3 alpha,21-dihydroxy-5 beta-pregnan-20-one and 3 beta,21-dihydroxy-5 alpha-pregnan-20-one is of special interest since sleep-inducing properties have been described with these steroids.

Brown adipose tissue mitochondria are cytochrome c-subsaturated

The oxidative activity of mitochondria freshly isolated from brown adipose tissue of rats was stimulated two-fold on the addition of small concentrations of exogenous cytochrome c to the reaction medium. Loss of membrane-bound cytochrome c did not occur during isolation of mitochondria. Estimation of the high-affinity binding sites on the organelle membrane indicated that less than a third of these sites remained saturated with cytochrome c. The pigment is thus shown to be a functionally limiting electron transport component in brown adipose tissue.

Measurement of brown adipose tissue uncoupling protein by enzyme linked immunosorbent assay

Antibody to uncoupling protein (UCP) purified from rat brown adipose tissue (BAT) was raised in rabbits and an enzyme linked immunosorbent assay was developed. The antiserum did not cross-react with other mitochondrial proteins from BAT and from other tissues but cross-reacted with UCP from hamster, guinea pig and mouse. The assay is capable of detecting 5 ng of UCP. Using this assay and a crude mitochondrial preparation, UCP content of BAT was shown to increase during cold adaptation.

The correlation between magnetic resonance imaging and ultrastructural patterns of brown adipose tissue

The present paper reports on magnetic resonance imaging (MRI) at high spatial resolution of the brown adipose tissue (BAT) in laboratory rodents, in comparison with light and electron microscopy findings. Our aim was to assess whether MRI correlates with the expected ultrastructural differences between newborn and adult BAT. The study was performed on the cervical and the interscapular BAT deposits by means of a nuclear magnetic resonance (NMR)-spectrometer equipped with a high resolution imaging system. Ultrastructural examination of BAT at different ages showed three different patterns of adipocyte ultrastructure in BAT which were associated with different MRI patterns. In BAT, MRI identifies the prevalent type of adipocyte in the tissue providing information consistent with ultrastructural results. Results presented here show that MRI represents a precise and reliable tool to investigate the morphology of tissues in living animals. The safe, non-invasive MRI technique represents a very useful tool in morphological research.

Adipose tissues and vitamin E

1. Vitamin E content in the adipose tissue was examined in rats with and without vitamin E deficiency. With the progression of vitamin E depletion, the more rapid decrease in tocopherol concentration was observed in brown adipose tissue (BAT) than in white adipose tissue (WAT), and the rate of decrease of tocopherol was approximately three times faster in BAT than in WAT. After the intramuscular administration of 10 mg/kg of all-rac-tocopheryl acetate twice a week for two weeks to vitamin E-deficient rats, a similar pattern of increase was observed in the tocopherol concentrations of BAT and WAT, although the rate of increase was slower in WAT than in BAT. 2. Changes of tocopherol concentration in BAT and WAT were investigated in normo-nourished rats with hyperlipemia produced by the intramuscular injection of Triton WR-1339 for 7 days. A marked increase in tocopherol concentration was observed in both BAT and WAT in the late period of hyperlipemia, with the increase being greater in WAT. 3. The fatty acid composition of adipose tissue was compared between rats with and without vitamin E deficiency. No significant differences were observed in BAT and WAT between the two groups. 4. The glucose uptake of WAT was not altered in vitamin E-deficient rats when compared with control rats.