Unacylated ghrelin, leptin, and appetite display diurnal rhythmicity in lean adults.

Constant routine and forced desynchrony protocols typically remove the effects of behavioural/environmental cues to examine endogenous circadian rhythms, yet this may not reflect rhythms of appetite regulation in the real world. It is therefore important to understand these rhythms within the same subjects under controlled diurnal conditions of light, sleep and feeding. Ten healthy adults (9M/1F, Mean ±SD: age: 30 ± 10 y; BMI: 24.1 ± 2.7 kg·m-2) rested supine in the laboratory for 37 hours. All data were collected during the final 24 hours of this period (i.e. 0800 - 0800 h). Participants were fed hourly isocaloric liquid meal replacements alongside appetite assessments during waking before a sleep opportunity from 2200-0700 h. Hourly blood samples were collected throughout the 24-h period. A diurnal rhythm in mean plasma unacylated ghrelin concentration was identified (p=0.04), with the acrophase occurring shortly after waking (08:19 h), falling to a nadir in the evening with a relative amplitude of 9%. Plasma leptin concentration also exhibited a diurnal rhythm (p<0.01), with the acrophase occurring shortly after lights-out (00:32 h) and the lowest concentrations at midday. The amplitude for this rhythm was 25%. Diurnal rhythms were established in all dimensions of appetite except for sweet preference (p=0.29), with both hunger (21:03) and prospective food consumption (19:55) reaching their peak in the evening before falling to their nadir shortly after waking. Under controlled diurnal conditions, simultaneous measurement of leptin, unacylated ghrelin, and subjective appetite over a 24-hour period revealed rhythmicity in appetite regulation in lean, healthy humans.

Unacylated Ghrelin Regulates Glucose-Sensitive Neurons Activity and Glycolipid Metabolism via Orexin-A Neurons in the Lateral Hypothalamic Area

The objective of the study was to investigate the regulatory actions of unacylated ghrelin (UAG) on glucose-sensitive (GS) neurons and glycolipid metabolism in the lateral hypothalamus area (LHA) and its involvement with orexin-A-immunopositive neurons. The effects of UAG administered into the LHA on GS neurons discharges and glycolipid metabolism were detected by single neuron discharge recording, biochemical index analysis and quantitative real-time PCR; the level of c-fos protein in orexin-A-immunopositive neurons was observed using immunofluorescence staining. UAG microinjected into the LHA activated glucose-inhibited neurons, which were partially blocked by pre-administration of anti-orexin-A antibody in the LHA. Furthermore, UAG microinjected into the LHA significantly reduced serum triglycerides (TG), total cholesterol, low-density lipoprotein cholesterol, blood glucose, insulin and hepatic TG levels, while elevated serum high-density lipoprotein cholesterol levels. UAG elevated the mRNA expression of carnitine palmitoyltransferase-1 and reduced the mRNA expression of acetyl-CoA carboxylase-1 in the liver. The above-mentioned effects of UAG were partially blocked by pre-administration of anti-orexin-A antibody. The expressions of orexin-A and c-fos were observed in the LHA. After UAG injection into the LHA, some neurons showed double labeling, and the percentage of double-labeled orexin-A/c-fos neurons in orexin-A-immunopositive neurons increased significantly. UAG in the LHA regulates glycolipid metabolism by activating orexin-A-immunopositive neurons in the LHA.