ABSTRACT
In addition to its role in reproduction, oxytocin [OT] has central actions modulating behavioural and hypothalamic-pituitary-adrenal axis responses during stress. This study was designed to evaluate the effect of endogenous and exogenous oxytocin administered as an intranasal inhalation on adrenocorticotrophic hormone [ACTH] and corticosterone level in the serum of male and female rats after exposure to stress; to evidence whether intranasal inhalation of oxytocin is associated with increase in its level in the cerebrospinal fluid [CSF]; and finally to assess any possible relation between the level of oxytocin and the levels of sex steroids during stress. This study was carried out on 10 male and 10 female adult rats; which were exposed to the forced swimming stress test with and without prior intranasal oxytocin inhalation. Thereafter, their anxiety behaviour was assessed by the elevated plus maze test. Blood and CSF samples were withdrawn before exposure to stress as well as after stress with and without oxytocin inhalation and were used for estimation of oxytocin level in the CSF, serum level of ACTH, corticosterone, estradiol and testosterone by enzyme immunoassay. The present study revealed a significant increase of CSF oxytocin after exposure to forced swimming stress test in both sexes; female rats however, exhibited more increase in oxytocin level. Exposure to stress was also associated with significant increase in serum level of ACTH and corticosterone in both sexes, female rats moreover, had lower level of these hormones compared to male rats. Oxytocin treatment was associated with significant increase in oxytocin level in CSF as well as reduction in the serum level of ACTH and corticosterone. With oxytocin treatment, a clear anxiolytic effect in animals was found as shown by the observations from the elevated plus-maze. A Positive significant correlation was found between serum estradiol and CSF oxytocin level in female rats, whereas, no significant correlation was noticed between serum testosterone level and CSF oxytocin level in male rats after exposure to stress. In conclusion, intranasal OT inhalation was associated with a significant increase in its CSE level; such central oxytocin can modulate hypothalamic-pituitary-adrenal [HPA] axis response in male and female rats by exerting inhibitory effect on ACTH and subsequently corticosterone secretion. Due to its anti-stress property, oxytocin can be used for psychotherapeutic intervention and treatment of numerous psychiatric illnesses. Although the central action of OT are generally inhibitory, our study suggested that circulating level of estrogen and not testosterone plays an important role modulating the effect of OT on HPA axis responsiveness to stress