Ghrelin a peptide which is mainly derived from the stomach, is present in plasma in an active (acylated) and inactive (des-acylated) form. The major active form of ghrelin contains 28 amino acids with a unique post-translational modification: the hydroxyl group of ser3 is esterified by octanoic acid. The n-octanoyl group is essential for the GH (growth hormone) releasing activity. Plasma ghrelin plays a role in energy homeostasis, food intake, and possibly in GH release and obesity. To date it is unclear how circulating ghrelin levels are regulated. The overall hypothesis of this grant is that glucose, insulin as well as insulin sensitivity play a role in the acute regulation of ghrelin. The influence of age and BMI on the response of circulating ghrelin to these factors will also be examined.
Specific Aim 1. To determine to what extent the short-term regulation of ghrelin is mediated through glucose (peripheral or luminal) and/or peripheral insulin. In man, circulating ghrelin levels decrease after glucose administration. It is unclear to what extent the route of glucose administration plays a role in its effects on circulating ghrelin. Studies of insulin effects on ghrelin levels under euglycemic conditions have yielded inconsistent results, i.e., a decrease in circulating ghrelin vs. no change. It is also unclear to what extent the route of glucose administration plays a role in its effects on circulating ghrelin and whether differences in insulin resistance have an impact on the effects of insulin and/or glucose on circulating ghrelin. In two groups of BMI matched young adults with different insulin resistance, we will examine the effects of insulin under euglycemic conditions on peripheral ghrelin and compare them with the effects of oral and IV glucose. We will also compare the effects of oral and IV glucose on peripheral ghrelin with each other. The glucose levels reached after IV administration will match those reached during the oral glucose test. The effects of insulin and glucose on bioactive ghrelin have not been reported. Using assays developed in our laboratory, both bioactive and inactive ghrelin will be measured Specific Aim 2. To determine whether the insulin-mediated decrease in circulating ghrelin levels is age dependent. Insulin sensitivity decreases with age. This is partially a result of the age-dependent increase in abdominal visceral fat. The studies proposed will investigate whether there are differences between young and older adults regarding the acute insulin mediated decrease in circulating ghrelin (bioactive, inactive form) levels.

Agency
National Institute of Health (NIH)
Institute
National Center for Research Resources (NCRR)
Type
Mentored Patient-Oriented Research Career Development Award (K23)
Project #
5K23RR018770-05
Application #
7649412
Study Section
National Center for Research Resources Initial Review Group (RIRG)
Program Officer
Wilde, David B
Project Start
2005-09-22
Project End
2012-07-31
Budget Start
2009-08-01
Budget End
2012-07-31
Support Year
5
Fiscal Year
2009
Total Cost
$131,323
Indirect Cost
Name
University of Virginia
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
065391526
City
Charlottesville
State
VA
Country
United States
Zip Code
22904
Nass, Ralf; Nikolayev, Alexander; Liu, Jianhua et al. (2015) The level of circulating octanoate does not predict ghrelin O-acyl transferase (GOAT)-mediated acylation of ghrelin during fasting. J Clin Endocrinol Metab 100:E110-3
Nass, Ralf; Farhy, Leon S; Liu, Jianhua et al. (2014) Age-dependent decline in acyl-ghrelin concentrations and reduced association of acyl-ghrelin and growth hormone in healthy older adults. J Clin Endocrinol Metab 99:602-8
Nass, Ralf; Liu, Jianhua; Patrie, James et al. (2014) Four-hour infusion of hydrocortisone does not suppress the nocturnal increase of circulating acyl- or desacyl-ghrelin concentrations in healthy young adults. J Clin Endocrinol Metab 99:E1696-700
Nass, Ralf; Farhy, Leon S; Liu, Jianhua et al. (2008) Evidence for acyl-ghrelin modulation of growth hormone release in the fed state. J Clin Endocrinol Metab 93:1988-94
Liu, Jianhua; Prudom, Catherine E; Nass, Ralf et al. (2008) Novel ghrelin assays provide evidence for independent regulation of ghrelin acylation and secretion in healthy young men. J Clin Endocrinol Metab 93:1980-7