Changes in serum leptin concentrations in relation to the oestrous cycle and body fat content in female dogs - Literature review and own data

SUMMARY Background:Leptin is primarily produced by adipocytes and its serum levels reflect the amount of body fat reserves. Besides adiposity, serum leptin concen-trations are influenced by other factors, such as the levels of sexual hormones during the ovarian cycle. Objectives:We aimed to determine if serum leptin levels are influenced by sex hormone level fluctuations during the reproductive cycle in female Beagle dogs. We also investigated the relationship between body condition score (BCS) and alternative assessments of body fat percentage using morphometric calcula-tions (BF%) or bioimpedance measurements (BMI) and serum leptin levels. Materials and Methods: Seventeen non-pregnant, healthy female dogs were included in the study. For determination of leptin, progesterone, triglyceride and total cholesterol concentrations, blood samples were collected after an over-night fast three times with two-week intervals, starting in late anoestrus or in proestrus. Dogs were divided into two groups according to their body condition. Body fat percentage was determined using bioelectrical impedance analysis and morphometric measurements. Results and Discussion: Serum leptin concentrations remained unchan-ged during the reproductive cycle and were not related to serum progesterone levels. In contrast to other species, changes in serum oestrogen or progesterone concentrations during the cycle have no influence on adipose tissue leptin pro-duction, our results should be interpreted with caution due to our low sample size and frequency of blood collection. Furthermore, differences in leptin assays used between studies may also have contributed to the different results.Similarly to previous reports in dogs, we found significant differences in serum lep-tin levels between overweight animals and dogs with normal condition. We detec-ted a close positive correlation between serum leptin, BCS and BF%, which sug-gests that the latter could also be used in clinical practice to assess adiposity. BMI showed only low to moderate correlation with other measures of body condition