CIRCULATING APELIN LEVELS AND METABOLIC PARAMETERS IN RESPONSE TO EXERCISE IN NORMAL AND DIABETIC RATS

Abstract

Background: Apelin is a peptide hormone recently identified as an endogenous ligand for the Gi proteincoupled,
receptor named APJ. Apelin and APJ have a widespread distribution in the body; apelin is
considered a beneficial adipokine related to glucose and lipid metabolism. Exercise was proved to increase
apelin expression in cardiac myocytes, but its effect on circulating apelin levels is not known up to the
date.
Aim: This work was done to explore the effect of continuous and intermittent exercise on circulating
apelin levels and some metabolic parameters in normal and Streptozotocine induced diabetic rats. Design:
A total number 60 adult, healthy, male albino rats. The rats were divided into 2 main groups Group I lean
group:( n= 24) it was further subdivided into 3equal subgroups (n= 8): Group I A: lean control group.
Group I B: Rats were exposed to continuous exercise. Group I C: Rats were exposed to intermittent
exercise. Group II Streptozotocine- induced (STZ) diabetic group: 36 rats were used. After induction
of diabetes, it was further subdivided into 3equal subgroups (n= 12): Group III A: control STZ diabetic
group. Group III B: Rats were exposed to continuous exercise Group III C: Rats were exposed to
intermittent exercise. The animals were maintained for 4 weeks and then blood samples were collected for
measurement of: Serum apelin, insulin, glucose, total cholesterol (TC), triglycerides (TG), low density
lipoproteins (LDL), high density lipoproteins (HDL); body mass index (BMI) and HOMA-IR were
calculated. Results: STZ induced diabetic control group showed significantly lower serum apelin (p <
0.001) serum insulin (p < 0.001), calculated HOMA-IR (p < 0.01) and serum HDL (p < 0.001) with serum
glucose, total cholesterol, triglycerides and LDL levels significantly higher(p < 0.001) than control lean
group. In lean groups exercise caused significant increase in serum apelin and HDL levels, with
significant decrease (P < 0.05) in serum LDL, calculated HOMA-IR (intermittent) and BMI (intermittent).
In STZ induced diabetic groups exercise caused significant (P< 0.05) elevation of serum apelin, insulin,
HOMA-IR and HDL with significant decrease (P< 0.05) in total cholesterol, triglycerides and LDL.
Conclusion: STZ induced diabetes results in decrease serum apelin levels and disturbed glucolipid
metabolism, but exercise was able to elevate serum apelin levels nearly toward normal values, also it was
able to correct partially the disturbed glucolipid metabolism and the effect of intermittent pattern was
more profound than that of continuous pattern. Further studies in both animals and humans are needed to
explore the related mechanisms.
Keywords: Apelin; exercise; STZ diabetes; adipokines