Contrast-enhanced MRI of brown adipose tissue after pharmacological stimulation.

A non-invasive method for studying the modifications induced in lipid depots by hormonal stimulation could extend knowledge of adipose tissues. We studied the effect of adrenergic stimulation on interscapular brown adipose tissue (IBAT) of rats using contrast-enhanced MRI. Controls and rats pre-treated with adrenaline 40 s before the acquisition of pre-contrast images were used. In the control group, IBAT showed an enhancement of 56 +/- 29%, whereas adrenaline pre-treatment resulted in a significantly higher value (83 +/- 49%, P < 0.05). In the control group, the skeletal muscle of the anterior limb showed an enhancement of 24 +/- 12%, while adrenaline pre-treatment led to a higher value (26 +/- 10%), although the difference was not significant. In the control group, the skeletal muscle adjacent to the IBAT showed an enhancement of 30 +/- 13%, while adrenaline pre-treatment resulted in a non-significantly higher value (33 +/- 10%). In both groups, enhancement values in the muscle adjacent to the IBAT were significantly higher than the values in the muscle of the anterior limb (P < 0.05). This study demonstrates the feasibility of detecting the effect of hormonal stimulation on small fat depots. The demonstration of greater blood flow in the muscles surrounding the IBAT than in the muscles of the anterior limb suggests that the muscles of the back operate in synergy with the IBAT.

The hydrolipidic ratio in age-related maturation of adipose tissues.

The hydrolipidic ratio (HLR) expresses the amount of water and fat in a tissue. HLR can be studied non-invasively in the living organism and can be mapped in different areas of the body with high spatial and temporal resolution. In the present work we have evaluated the HLR in different adipose tissue depots in young or adult rats using tissue arrays of fat fragments by 1H-spectroscopy. In young animals, the highest percentage of water (33%) was found in the interscapular brown adipose tissue (iBAT). Mesenteric fat (mWAT) also appeared highly hydrated (24%). The deposits composed of epididymal, retroperitoneal and pelvic white adipose tissue (eWAT, rWAT and pWAT, respectively) contained an amount of water ranging from 14% to 17%. In adult animals, a reduction of the water content was found in all the depots. In e/r/pWAT, the age-related maturation was characterized by large changes in adipocyte diameter accompanied by a small change in HLR. In the iBAT, the maturation was accompanied by small change in adipocyte diameter and a greater diminution of HLR. mWAT showed an intermediate pattern between e/r/pWAT and iBAT. In all the studied depots, an age-related increase in leptin expression was found. This increase was relatively low in iBAT (40%) and high in the e/r/pWAT (204-273%). The work expand the knowledge about the physiological significance of the HLR by 1H-spectroscopy.