Introduction: Bariatric surgery, as the only effective treatment of obesity, has strong effects on the metabolism, and nervous and endocrine systems. Thus, based on the different opinions about the efficaciousness of morbid obesity treatments, the aim of the present study was to estimate the association of serum ghrelin and Met-enkephalin (native, five amino acids and cryptic, precursor of enkephalin) concentrations with body mass index (BMI) value in bariatric patients within 30 postoperative days.

Material and methods: The study was performed on 38 female patients divided into two groups: I — BMI lower than 40 kg/m² (n = 18) and II — BMI higher than 40 kg/m² (n = 20). Blood was taken before (–24 h), and 72 h and 30 days after the sleeve gastrectomy. Routine haematological, anthropometric, and metabolic parameters as well as thyroid-stimulating hormone (TSH), ghrelin, and Met-enkephalin values were measured in all patients.

Results: There were statistically significant differences between the two groups before the surgery in terms of TSH, both forms of Metenkephalin, triglycerides concentrations, and activity of alanine transaminase (ALT), gamma glutamyltransferase (GGTP), and C-reactive protein (CRP). After 72 h, the serum levels of cryptic Met-enkephalin and CRP, and activity of enzymes varied between the two groups of patients. Thirty days after the surgery, some metabolic and immune parameters were still different in both female groups in favour of patients with lover BMI. However, significant differences were noticed in the levels of ghrelin (increase), and native (decrease) and cryptic Met-enkephalins (increase).

Conclusions: The activity of endogenous peptides in bariatric patients is connected with the degree of obesity. Ghrelin level increases are negatively correlated with native Met-enkephalin changes shortly after bariatric surgery. The interplay of ghrelin and opioids might be considered as a predictor of postoperative weight loss success.