Novel ghrelin assays provide evidence for independent regulation of ghrelin acylation and secretion in healthy young men.
BACKGROUND
Ghrelin, an acylated peptide hormone secreted from the gut, regulates appetite and metabolism. Elucidating its pattern of secretion in the fed and fasted states is important in the face of the obesity epidemic.


OBJECTIVE
Our objective was to examine changes in circulating ghrelin and des-acyl ghrelin in response to meals and fasting using newly developed two-site sandwich assays and sample preservation protocols to allow specific detection of full-length forms.


METHODS
Ten-minute sampling was done for 26.5 h during a fed admission with standardized meals and on a separate admission during the final 24 h of a 61.5-h fast and continuing for 2.5 h after terminating the fast.


METHODS
The study was conducted at the University Hospital General Clinical Research Center.


METHODS
Eight male volunteers participated, mean +/- sd age 24.5 +/- 3.7 yr and body mass index 24 +/- 2.1 kg/m(2).


METHODS
Ten-minute sampling profiles were assessed for ghrelin and des-acyl ghrelin, fed and fasting.


RESULTS
In the fed state, ghrelin and des-acyl ghrelin showed similar dynamics; both were sharply inhibited by meals and increased at night. During fasting, ghrelin decreased to nadir levels seen postprandially, and des-acyl ghrelin remained near peak levels seen preprandially. Total full-length ghrelin (acyl plus des-acyl) levels remained unchanged.


CONCLUSIONS
Meals inhibited secretion of both ghrelin and des-acyl ghrelin, yet long-term fasting inhibited acylation but not total secretion. Acylation may be regulated independently of secretion by nutrient availability in the gut or by esterases that cleave the acyl group. These studies highlight the importance of stringent conditions for sample collection and evaluation of full-length ghrelin and des-acyl ghrelin using specific two-site assays.
Liu
Jianhua
J
Department of Medicine, University of Virginia Health System, Charlottesville, VA 22908, USA.
Prudom
Catherine E
CE
Nass
Ralf
R
Pezzoli
Suzan S
SS
Oliveri
Mary C
MC
Johnson
Michael L
ML
Veldhuis
Paula
P
Gordon
David A
DA
Howard
Andrew D
AD
Witcher
Derrick R
DR
Geysen
H Mario
HM
Gaylinn
Bruce D
BD
Thorner
Michael O
MO
D000215:Acylation; D000328:Adult; D002091:Butyrylcholinesterase / Q000097:blood; D004797:Enzyme-Linked Immunosorbent Assay; D005215:Fasting / Q000097:blood; D054439:Ghrelin / Q000097:blood*; D006801:Humans; D007106:Immune Sera / Q000276:immunology; D008297:Male; D012680:Sensitivity and Specificity
D054439:Ghrelin; D007106:Immune Sera; C422650:ghrelin, des-n-octanoyl; D002091:Butyrylcholinesterase