Acute Effect of Leptin and Ghrelin Injection on Postprandial Glycogen and Lipid Synthesis in Rats

Acyl ghrelin, desacyl ghrelin and their ratio affect hepatic steatosis via PPARγ signaling pathway

BACKGROUND AND STUDY AIMS

Ghrelin is an appetite hormone-containing 28-amino acid and has 4 different forms in the body. Ghrelin forms have different physiological functions in the body. This study aims to analyze the effect of acyl and desacyl ghrelin hormone on hepatic steatosis and biochemical findings in 36 male Wistar rats.

MATERIALS AND METHODS

Rats were split into 6 equal groups, consisting of control, acyl ghrelin, desacyl ghrelin, acyl/desacyl 3:1, acyl/desacyl 1:1, and acyl/desacyl 1:3 groups, and administered placebo or 200 ng/kg hormone subcutaneous twice a day for 14 days. Oral Glucose Tolerance Test (OGTT) was performed on Day 15, Insulin Tolerance Test (ITT) on Day 16, and scarification procedure on Day 17. Certain biochemical data and liver diacylglycerol (DAG), glycogen, protein kinase C and PPAR-γ levels were detected in the blood. Histological analyses were also conducted on the liver tissues.

RESULTS

The highest plasma total cholesterol and VLDL-K levels were found in the acyl/desacyl 1:3 group, and lower insulin, and HOMA-IR levels were found in groups where acyl and desacyl were administered together (p < 0.05). PPAR-γ gene expression level increased in acyl ghrelin and acyl/desacyl 1:3 groups compared to the control group. Protein kinase C gene expression was highest in the acyl/desacyl 1:3 group. The most severe degenerative findings compliant with steatosis in the liver were observed in the acyl ghrelin group (p < 0.05).

CONCLUSION

It was determined that administering rats acyl alone and acyl/desacyl by 1:3 caused the highest PPAR-γ gene expression, serum total cholesterol, HDL-K, and VLDL-K levels in the body. Besides, it is shown that desacyl ghrelin effectively regulates the blood glucose level when administered alone.

Food-Restriction Lowers the Acoustic Startle Response in both Male and Female Rats, and, in Combination with Acute Ghrelin Injection, Abolishes the Expression of Fear-Potentiated Startle in Male Rats

Food restriction has been reported to reduce anxiety-like behaviour in male rats, whereas the effects of food restriction on anxiety in female rats are less clear. Ghrelin is a peptide hormone produced and secreted in the stomach that stimulates food intake and is considered to play a role in reward and emotional responses such as fear expression. Under food restriction, endogenous ghrelin levels increase. In the present study, we examined the effect of moderate food restriction (80% of ad libitum fed weight), with or without an acute application of a small dose of exogenous ghrelin intended to cause an immediate hunger response, on the expression of the acoustic startle reflex (ASR). This was carried out under basal conditions (baseline ASR to 90- and 95-dB noise bursts), and in the presence of a light cue associated with a mild foot-shock, as measured by fear-potentiated startle, which compares the proportional change in ASR in the presence of the conditioned stimulus. The results obtained show that food-restriction reduces basal ASR in both male and female rats, apart from any concomitant change in motor activity, suggesting that food-restriction reduces anxiety levels in both sexes. In addition, the data show that food-restriction reduces fear-potentiated startle in male but not female rats. Acute ghrelin injection, prior to fear-potentiated startle testing, eliminates the expression of fear-potentiated startle in food-restricted male rats alone, suggesting a role for ghrelin in the reduction of fear expression in food-restricted male rats. These data imply that, although food-restriction decreases anxiety in both sexes, learned fear responses remain intact after food-restriction in female but not male rats.

Detrimental and protective fat: body fat distribution and its relation to metabolic disease

Obesity is linked to numerous comorbidities that include, but are not limited to, glucose intolerance, insulin resistance, dyslipidemia, and cardiovascular disease. Current evidence suggests, however, obesity itself is not an exclusive predictor of metabolic dysregulation but rather adipose tissue distribution. Obesity-related adverse health consequences occur predominately in individuals with upper body fat accumulation, the detrimental distribution, commonly associated with visceral obesity. Increased lower body subcutaneous adipose tissue, however, is associated with a reduced risk of obesity-induced metabolic dysregulation and even enhanced insulin sensitivity, thus, storage in this region is considered protective. The proposed mechanisms that causally relate the differential outcomes of adipose tissue distribution are often attributed to location and/or adipocyte regulation. Visceral adipose tissue effluent to the portal vein drains into the liver where hepatocytes are directly exposed to its metabolites and secretory products, whereas the subcutaneous adipose tissue drains systemically. Adipose depots are also inherently different in numerous ways such as adipokine release, immunity response and regulation, lipid turnover, rate of cell growth and death, and response to stress and sex hormones. Proximal extrinsic factors also play a role in the differential drive between adipose tissue depots. This review focuses on the deleterious mechanisms postulated to drive the differential metabolic response between central and lower body adipose tissue distribution.