THE INVERSE RELATIONSHIP BETWEEN BASELINE 24-HOUR PROFILES OF PYY AND GHRELIN IN HEALTHY, NON-OBESE WOMEN

Open Access
Author:
Sato, Rino
Area of Honors:
Kinesiology
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Nancy Williams, Thesis Supervisor
  • Stephen Jacob Piazza, Honors Advisor
Keywords:
  • Ghrelin
  • PYY
  • gut hormone
Abstract:
Peptide YY (PYY) is a gut hormone believed to be involved in short-term metabolic homeostasis as a satiety signal. Studies have shown that PYY concentrations rise shortly after meal consumption [1-3] and stay elevated for several hours [4]. Ghrelin, a ligand for the growth-hormone secretagogue receptor (GHS-R), is an orexigenic peptide that rises before a meal and decreases after a meal, serving as a meal initiation signal [5]. Intravenous administration of ghrelin increases appetite and food intake [6]. Because both PYY and ghrelin have been shown to have direct access to the arcuate nucleus of the hypothalamus [7], it has been suggested that there may be a possible cross-reactivity in their regulation of energy intake. To our knowledge, no study has compared the 24-hour profiles of PYY and ghrelin. Therefore, the purpose of this study was to examine and characterize the relationship between PYY and ghrelin throughout the day in normal weight premenopausal women. We hypothesized that ghrelin would be negatively correlated with PYY throughout the day, with the correlation improving during the day when meals are consumed. In addition, we sought to shed light on the controversial argument regarding which hormone modulates the secretion of the other. It was hypothesized that PYY modulates the secretion of ghrelin throughout the day. Twelve non-obese premenopausal women completed a 24 hour repeated blood sampling procedure prior to commencing a three-month intervention that included exercise combined with caloric restriction. Repeated blood sampling occurred every 20 minutes over 24 hours, and samples were assayed every hour from 0800-1000, every 20 min from 1000 to 2000 and every hour from 2000 to 0800. Ghrelin and PYY data were expressed as percent change from baseline. A significant negative correlation was observed between the group averages of PYY and ghrelin concentrations throughout the day (r=-0.351, p=0.020). This correlation improved when only the daytime data points were considered (r=-0.431, p=0.010) and worsened when only the nighttime points were considered (r=-0.096, p=0.807). Shifting the data points of PYY forward 20 minutes improved the correlation between the group averages for the 20-min data points (r=-0.574, p=0.001), suggesting that PYY drives ghrelin. When all of the ghrelin post-meal troughs and PYY post-meal peaks of an individual were considered together, a significant correlation was observed (r=-0.474, p=0.001). This correlation was slightly greater than the correlation between ghrelin post-meal troughs and meal calories (r=-0.377, p=0.008). The ghrelin post-meal declines and PYY post-meal rises were significantly negatively correlated (r=-0.289, p=0.046) as well, but this correlation was not greater than the correlation between ghrelin post-meal decline and energy content of that meal (r=-0.542, p=0.000). There appears to be an inverse relationship between ghrelin and PYY throughout the day, with a stronger relationship during hours of meal consumption. In addition, PYY may modulate the secretion of ghrelin. The study adds valuable information to our understanding of the modulation of energy balance by gut peptides. The relationship of the two hormones may be important in developing potential therapeutic targets for obesity and other body weight related pathologies.