Differential effects of melatonin on adipose tissues under normoestrogenic and estrogen-deficient conditions in rats

In post-menopause, oxidative stress due to the decline of natural antioxidants increases the susceptibility to metabolic syndromes (MetS). Estrogen and melatonin (MEL) share antioxidant properties; however, few studies have reported the impact of estrogen deficiency and MEL treatment on morphology, redox status, and antioxidant defense capacity of diverse adipose tissue (AT) subtypes. To investigate this issue, MEL was administered to ovariectomized (OVX) rats and sham-operated rats for 16 weeks (10 mg/kg). The adipocyte morphology, oxidative stress parameters and antioxidant enzyme activity were evaluated in the visceral retroperitoneal adipose tissue (rVAT), subcutaneous inguinal adipose tissue (iSAT) and brown adipose tissue (BAT). In OVX rats, MEL treatment suppressed rVAT hypertrophy and increased the prevalence of small adipocytes in iSAT, suggesting a better lipid distribution among ATs. MEL treatment increased glutathione reductase and glucose-6-phosphate dehydrogenase activity in iSAT; therefore, restored the glutathione level. In rVAT, MEL increased glutathione peroxidase and glutathione reductase activity. MEL minimized the risks for the development of metabolic abnormalities due to estrogen deficiency. However, under normoestrogenic condition, MEL decreased plasma estradiol levels and uterine mass, raising the concerning of its effect on reproductive functions.