Neuropeptide Y suppressed the T3-induced rise in brown fat mitochondrial respiration in hypothyroid rats.
It has been postulated that a cold-induced decrease in hypothalamic neuropeptide Y (NPY) might disinhibit the sympathetic outflow that activates brown adipose tissue (BAT) thermogenesis. The present work has assessed the interscapular BAT NPY and norepinephrine (NE) concentrations 7 days after surgical excision of the sympathetic nerves (Sx) of each BAT lobe in rats exposed to 4 degrees C or 24 degrees C during 24 h. In addition, the effects of NPY treatment on BAT oxygen (O2) consumption in normal and T3-treated hypothyroid rats was determined. Sprague-Dawley rats weighing 220-240 g were used. BAT was removed and homogenized in 0.1 M HCl. BAT NPY content at 24 degrees C was 109 +/- 19 pg/mg protein. Sx decreased this value significantly (P < 0.001) and cold increased it by two-fold (P < 0.001). Neither cold nor Sx altered hypothalamic NPY. BAT O2 consumption was depressed by NPY treatment (P < 0.001) and increased by NE (P < 0.001). In euthyroid Sx rats, NPY decreased O2 consumption (P < 0.001). NPY failed to alter O2 consumption in hypothyroid rats and sharply decreased it in T3-treated rats. The results show that NPY blocked the effects of T3 on BAT O2 consumption, and that cold-induced activation of the thermogenic process did not produce measurable changes in hypothalamic NPY.
Rebagliati
I
I
Hospital de Clinicas, University of Buenos Aires, Argentina.
Ricci
C
C
Zaninovich
A
A
Tang
F
F
D002001:Adipose Tissue, Brown / Q000737:chemistry / Q000294:innervation / Q000648:ultrastructure*; D000818:Animals; D003080:Cold Temperature; D007037:Hypothyroidism / Q000209:etiology / Q000378:metabolism*; D007457:Iodine Radioisotopes / Q000494:pharmacology; D008928:Mitochondria / Q000378:metabolism*; D009478:Neuropeptide Y / Q000032:analysis / Q000502:physiology*; D009638:Norepinephrine / Q000032:analysis / Q000494:pharmacology; D010101:Oxygen Consumption / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013564:Sympathetic Nervous System / Q000502:physiology / Q000601:surgery; D014284:Triiodothyronine / Q000494:pharmacology*
D007457:Iodine Radioisotopes; D009478:Neuropeptide Y; D014284:Triiodothyronine; D009638:Norepinephrine