SAT-451 Chronic Stress During Adolescence of Rats Shows Sex Dimorphism in the Thyroid Axis Response to Voluntary Exercise in Adulthood

Abstract

Exposure to chronic stress during adolescence causes long-term effects on the response of Hypothalamus-Pituitary-Adrenal (HPA) axis, affecting behavior and energy homeostasis. Voluntary exercise activates the HP-Thyroid (HPT) axis allowing efficient fluxes of substrates to active target organs. Chronic stress in adult rats blunts HPT axis response to voluntary exercise in a sex-dependent manner (Front Endocrinol 10(418):1-13, 2019). As adolescents show sex-dependent responses to stress, we sought to evaluate the effect of chronic stress at this period in the response of HPT axis to voluntary exercise in adulthood. Wistar male and female rats were divided in an undisturbed group (Control, C) and one group exposed to chronic variable stress (CVS) where the rats were daily subjected to different stressors during postnatal day (PND) 30 to 60 for females and PND 30 to 70 for males. At adulthood (PND 74 for females and PND 84 for males) rats were exposed to running wheel following published protocol (Endocrinology 155:2020-2030, 2014). As females are more susceptible to stress during adolescence than males, additional independent experiments were performed with female rats kept in group or individual housing, since PND 30 (2 per cage or isolated (Iso)). At PND 64, Iso rats were housed in pairs and exposed to CVS every 3 days until PND 80; later, rats were exercised 26 days. Hormones were quantified by ELISA or RIA; mRNA expression was determined by RT-PCR. Voluntary exercise reduced fat mass in C groups, dependent on the amount of exercise performed; stressed rats exercised did not lose fat, indicating that adolescent stress avoids an appropriate energy distribution during exercise. The expression of Crh and Avp in hypothalamic paraventricular nucleus (PVN) decreased in stressed groups mainly in females, as reported. Exercise decreased corticosterone levels only in C rats, suggesting that CVS during adolescence modifies the HPA axis response to exercise. CVS inhibited Pomc expression induced by exercise and increased Npy expression in arcuate nucleus, decreased Trh expression in PVN for both sexes and in dorsomedial hypothalamus in males. Thyroid hormones were not altered in CVS males and Iso females; however, T3 and T4 levels were high in CVS females, so different stress exposures may modify the HPT axis state in females. The response to exercise of the target organs of thyroid hormones reveals with more accuracy the activity of HPT axis, exercise stimulated the expression of Adrb3 and Dio2 in brown adipose tissue of C females, and the expression of Dio2 and Pgc1a in skeletal muscle (gastrocnemius) of both sexes, changes attenuated by CVS. These results indicate that chronic stress during adolescence blunts the response of HPT axis to voluntary exercise, strongly in females than males.