The effect of eight weeks of high-intensity interval swimming on hepatic shbg protein levels and glycemic control variables in high-fat diet-fed male rats

Document Type : Original Article

Authors

1 Assistant Professor at Department of Sports Sciences, Faculty of Humanities, University of Hormozgan, Bandar Abbas, Iran.

2 PhD in Exercise Physiology, Faculty of Psychology and Educational Sciences, Shiraz University, Shiraz, Iran.

Abstract

Extended Abstract 
Background and Aim: Non-alcoholic fatty liver disease (NAFLD) and its advanced form, non-alcoholic steatohepatitis (NASH), have been rapidly increased in prevalence worldwide, including in Iran. These hepatic metabolic disorders are associated with an elevated risk of cardiovascular mortality, type 2 diabetes, and other metabolic comorbidities. Hepatokines such as sex hormone-binding globulin (SHBG), beyond their hormonal regulatory functions, have been identified as sensitive biomarkers for the diagnosis of NASH and glycemic disturbances. Recent studies suggest that SHBG concentrations are inversely related to steatosis severity and insulin resistance, lifestyle modifications and physical activity—particularly high-intensity interval training (HIIT)- can enhance SHBG levels. Therefore, the aim of this study was to evaluate the effects of eight weeks of HIIT swimming on hepatic SHBG protein levels and selected glycemic control variables in a rat model of NASH induced by a high-fat diet.
Materials and Methods: This experimental study was conducted on 40 male Sprague-Dawley rats (6-8 weeks old, weighing 230±20 g). The animals were randomly assigned to four groups: healthy-control, exercise-healthy, control-patient, and exercise-patient. To induce NASH, the patient groups were fed a high-fat diet for eight weeks. Following confirmation the induction of the disease through macroscopic, microscopic, and biochemical assessments, the exercise intervention was initiated. The exercise groups underwent a HIIT swimming protocol consisting of 20 × 30-second swim bouts, each followed by 30 seconds of rest, with a weight attached to the tail. The HIIT was conducted three times per week for eight weeks. Exercise intensity progressed from 7% of body weight in the first week to 14% by the eighth week.
Forty-eight hours after the final exercise session, blood and liver tissue samples were collected. SHBG protein levels were measured via Western blot, serum insulin was assessed using ELISA, and fasting blood glucose was determined using a photometric method. Insulin resistance was calculated using the HOMA-IR formula.
During the study, animal housing conditions (temperature 22-24°C, humidity 45%, dark-light cycle 12:12) and free access to water and food were observed. To reduce animal stress, a familiarization phase with the pool and training environment was performed two weeks prior to the intervention. Data were analyzed using one-way analysis of variance and Bonferroni post hoc test at a significance level of p<0.05.
Findings: Pathological, biochemical, and macroscopic changes characteristic of NASH were observed in rats. Macroscopically, the livers of the diseased groups appeared pale and swollen compared to the smooth, reddish livers of the healthy groups. Microscopic observations with H&E and Oil Red O staining revealed marked steatosis, inflammation, and extensive fat accumulation in the livers of the diseased animals, consistent with established NASH pathology and previous studies. Biochemical assays showed significantly increased levels of alanine aminotransferase (ALT) and aspartate transaminase (AST) enzymes in diseased groups versus healthy controls, confirming hepatocellular injury and successful disease induction. Hepatic sex hormone-binding globulin (SHBG) protein was highest in the healthy -control group, while significantly reduced in control-patient (p=0.001) and exercise-patient (p=0.002) groups when compared to healthy controls. Still, the exercise-patient group showed a non-significant upward trend in SHBG compared to control-patient. Fasting blood glucose was significantly reduced in the exercise-patient group compared to control-patient (p=0.001), indicating improved glycemic regulation through HIIT swimming. Although insulin and HOMA-IR values were lower in the NASH exercise group compared to the NASH control group, the differences were not statistically significant (p=0.14).
In terms of body weight, the healthy exercise group exhibited a significant reduction compared to both the healthy control (p=0.003) and NASH control (p=0.002) groups. The NASH exercise group also showed a non-significant downward trend in body weight compared to the NASH control group (Table 1).
Conclusion: The findings of this study clearly demonstrate that eight weeks of HIIT swimming significantly reduced fasting blood glucose and prevented further declines in hepatic SHBG levels in a diet-induced NASH rat model. Although changes in insulin resistance were not statistically significant, a downward trend was observed, reflecting the exercise’s potential for beneficial impact. Given the prognostic value of SHBG in liver pathology and type 2 diabetes, the present results underscore the capacity of HIIT to modulate metabolic disorders and possibly exert direct regulative effects on hepatic molecular dynamics. Additionally, aquatic environments may minimize injury risk and inflammation, making swimming particularly suitable for metabolically impaired subjects. In summary, sustained high-intensity exercise—even in the absence of dietary restriction—can play a crucial role in managing NAFLD/NASH. Further research is warranted to explore the underlying mechanisms and long-term effects of such interventions.
Ethical Considerations: This study was approved by the Research Ethics Committee of Shiraz University of Medical Sciences (Code: IR.SUMS.REHAB.REC.1400.008). All experimental procedures were conducted in accordance with institutional guidelines for the care and use of laboratory animals.
Compliance with Ethical Guidelines: The research adhered to the ethical standards of the Declaration of Helsinki and institutional guidelines. Participation was voluntary, and confidentiality of data was maintained at all stages.
Funding: This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors. 
Conflicts of Interest: The authors declare no conflicts of interest regarding the publication of this study.

Keywords

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Journal of Practical Studies of Biosciences in Sport
Volume 13, Issue 35
2025
Pages 24-41

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