Chronic intraparaventricular nuclear administration of orexin A in male rats does not alter thyroid axis or uncoupling protein-1 in brown adipose tissue.
Orexin A, synthesised in the posterolateral hypothalamus, has widespread distribution including the paraventricular nucleus (PVN), which is rich in thyrotropin-releasing hormone (TRH) neurones. Nerve fibres in the PVN synapse on neurones that send polysynaptic projections to brown adipose tissue (BAT), which is important in thermogenesis. A number of observations suggests orexin A may be involved in regulation of metabolism and thermogenesis. We investigated the effect of orexin A injected intracerebroventricularly (ICV) on thyroid-stimulating hormone (TSH) and thyroid hormones in male rats. We then examined the effect of chronic iPVN injections of orexin A on plasma TSH and uncoupling protein-1 (UCP-1) protein in BAT. Orexin A (3 nmol) administered ICV significantly suppressed plasma TSH at 10 and 90 min. Orexin A (0.3 nmol) administered into the PVN twice daily for 3 days significantly increased day-time 2-h food intake, but did not significantly alter nocturnal food intake. Though chronic iPVN orexin A altered diurnal food intake, there was no effect on 24-h food intake or body weight. Furthermore, orexin A administered chronically into the PVN did not alter UCP-1 level in BAT, or plasma hormones relative to saline injected animals. Chronic iPVN orexin A does not appear to influence thermogenesis through activation of UCP-1 or the thyroid axis.
Russell
S H
SH
ICSM Endocrine Unit, Hammersmith Hospital, Du Cane Road, W12 ONN, London, UK.
Small
C J
CJ
Sunter
D
D
Morgan
I
I
Dakin
C L
CL
Cohen
M A
MA
Bloom
S R
SR
D002001:Adipose Tissue, Brown / Q000187:drug effects* / Q000378:metabolism; D000818:Animals; D001835:Body Weight / Q000187:drug effects; D002352:Carrier Proteins / Q000008:administration & dosage / Q000378:metabolism* / Q000494:pharmacology*; D004435:Eating / Q000187:drug effects*; D007276:Injections, Intraventricular / Q000379:methods; D047908:Intracellular Signaling Peptides and Proteins; D007473:Ion Channels; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D024101:Mitochondrial Proteins; D009479:Neuropeptides / Q000008:administration & dosage / Q000494:pharmacology*; D000068797:Orexins; D010907:Pituitary Hormones / Q000097:blood; D051381:Rats; D017208:Rats, Wistar; D013961:Thyroid Gland / Q000187:drug effects*; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood; D000071256:Uncoupling Protein 1
D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D007473:Ion Channels; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D009479:Neuropeptides; D000068797:Orexins; D010907:Pituitary Hormones; C000604373:Ucp1 protein, rat; D000071256:Uncoupling Protein 1; D014284:Triiodothyronine; D013972:Thyrotropin; D013974:Thyroxine