Intranasal insulin enhances postprandial thermogenesis and lowers postprandial serum insulin levels in healthy men.
OBJECTIVE
Animal studies indicate a prominent role of brain insulin signaling in the regulation of peripheral energy metabolism. We determined the effect of intranasal insulin, which directly targets the brain, on glucose metabolism and energy expenditure in humans.


METHODS
In a double-blind, placebo-controlled, balanced within-subject comparison, 19 healthy normal-weight men (18-26 years old) were intranasally administered 160 IU human insulin after an overnight fast. Energy expenditure assessed via indirect calorimetry and blood concentrations of glucose, insulin, C-peptide, and free fatty acids (FFAs) were measured before and after insulin administration and the subsequent consumption of a high-calorie liquid meal of 900 kcal.


RESULTS
Intranasal insulin, compared with placebo, increased postprandial energy expenditure, i.e., diet-induced thermogenesis, and decreased postprandial concentrations of circulating insulin and C-peptide, whereas postprandial plasma glucose concentrations did not differ from placebo values. Intranasal insulin also induced a transient decrease in prandial serum FFA levels.


CONCLUSIONS
Enhancing brain insulin signaling by means of intranasal insulin administration enhances the acute thermoregulatory and glucoregulatory response to food intake, suggesting that central nervous insulin contributes to the control of whole-body energy homeostasis in humans.
Benedict
Christian
C
Department of Neuroendocrinology, University of Lübeck, Germany. benedict@kfg.uni-luebeck.de
Brede
Swantje
S
Schiöth
Helgi B
HB
Lehnert
Hendrik
H
Schultes
Bernd
B
Born
Jan
J
Hallschmid
Manfred
M
D000281:Administration, Intranasal; D000293:Adolescent; D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D002149:Energy Intake; D004734:Energy Metabolism / Q000187:drug effects*; D005230:Fatty Acids, Nonesterified / Q000097:blood; D006801:Humans; D007328:Insulin / Q000008:administration & dosage / Q000097:blood* / Q000494:pharmacology; D061389:Insulin, Regular, Pork; D008297:Male; D019518:Postprandial Period; D012016:Reference Values; D022722:Thermogenesis / Q000187:drug effects / Q000502:physiology*; D055815:Young Adult
D001786:Blood Glucose; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D061389:Insulin, Regular, Pork; C000006:insulin, neutral