Differential effects of central leptin, insulin, or glucose administration during fasting on the hypothalamic-pituitary-thyroid axis and feeding-related neurons in the arcuate nucleus.
The reductions in circulating levels of leptin, insulin, and glucose with fasting serve as important homeostasis signals to neurons of the hypothalamic arcuate nucleus that synthesize neuropeptide Y (NPY)/agouti-related protein (AGRP) and alpha-MSH/cocaine and amphetamine-regulated transcript. Because the central administration of leptin is capable of preventing the inhibitory effects of fasting on TRH mRNA in hypophysiotropic neurons primarily through effects on the arcuate nucleus, we determined whether the continuous administration of 30 mU/d insulin or 648 microg/d glucose into the cerebrospinal fluid by osmotic minipump might also have similar effects on the hypothalamic-pituitary-thyroid axis. As anticipated, the intracerebroventricular infusion of leptin reduced fasting-induced elevations in NPY and AGRP mRNA and increased proopiomelanocortin and cocaine and amphetamine-regulated transcript mRNA in the arcuate nucleus. In addition, leptin prevented fasting-induced reduction in pro-TRH mRNA levels in the paraventricular nucleus and in circulating thyroid hormone levels. In contrast, whereas insulin increased proopiomelanocortin mRNA and both insulin and glucose reduced NPY mRNA in arcuate nucleus neurons, neither prevented the fasting-induced suppression in hypophysiotropic TRH mRNA or circulating thyroid hormone levels. We conclude that insulin and glucose only partially replicate the central effects of leptin and may not be essential components of the hypothalamic-pituitary-thyroid regulatory system during fasting.
Fekete
Csaba
C
Tupper Research Institute and Department of Medicine, Division of Endocrinology, Diabetes, Metabolism, and Molecular Medicine, New England Medical Center, Boston, Massachusetts 02111, USA.
Singru
Praful S
PS
Sanchez
Edith
E
Sarkar
Sumit
S
Christoffolete
Marcelo A
MA
Riberio
Rogerio S
RS
Rand
William M
WM
Emerson
Charles H
CH
Bianco
Antonio C
AC
Lechan
Ronald M
RM
D054366:Agouti Signaling Protein; D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000187:drug effects / Q000502:physiology*; D003042:Cocaine / Q000494:pharmacology; D005215:Fasting / Q000502:physiology*; D005247:Feeding Behavior / Q000187:drug effects / Q000502:physiology*; D005947:Glucose / Q000008:administration & dosage / Q000494:pharmacology*; D007030:Hypothalamo-Hypophyseal System / Q000187:drug effects / Q000502:physiology*; D007328:Insulin / Q000008:administration & dosage / Q000494:pharmacology*; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics; D020738:Leptin / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009478:Neuropeptide Y / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D013961:Thyroid Gland / Q000187:drug effects / Q000502:physiology*; D013972:Thyrotropin / Q000235:genetics; D014158:Transcription, Genetic / Q000187:drug effects
D054366:Agouti Signaling Protein; D007328:Insulin; D036341:Intercellular Signaling Peptides and Proteins; D020738:Leptin; D009478:Neuropeptide Y; D012333:RNA, Messenger; D013972:Thyrotropin; D003042:Cocaine; D005947:Glucose