THE POSSIBLE INVOLVEMENT OF GALANIN IN THE MODULATION OF THE FUNCTIONOF RAT PITUITARY-ADRENOCORTICAL AXIS UNDER BASAL AND STRESSFUL CONDITIONS

The effect of a s.c. bolus injection of 2 mu g galanin on the hypothal amo-pituitary-adrenocortical (HPA) axis were investigated in both norm al and ether-stressed (2 min ether-vapor inhalation) or cold-stressed (20 min at 4 degrees C) rats. Blood concentrations of ACTH, aldosteron e (ALDO) and corticosterone (B) were measured by specific RIA, 1, 2 or 4 h after galanin injection. Galanin administration to normal rats re sulted m a marked rise in the blood levels of ACTH, ALDO and B at Ih a nd 2 h; the values returned to the baseline after 4 h. Ether and cold stresses notably raised the blood levels of ACTH, ALDO and B, and thes e rises lasted unchanged until 4 h. Galanin markedly potentiated ACTH and ALDO responses to ether stress at 1 and 2 h, but B response remain ed unchanged. ACTH response to cold stress was not affected by galanin ; however, galanin magnified ALDO response to cold stress at 4 h, and enhanced at 1 h and depressed at 2 h that of B. In light of these find ings the following conclusions can be drawn: (i) galanin exerts a stim ulatory effect on HPA axis of rats under basal conditions; (ii) under our experimental conditions. ether stress exerts a stronger stimulatio n of HPA axis than cold stress; (iii) the galaninergic mechanisms invo lved in the stimulation of ACTH release do not interfere with ether st ress-activated ones controlling ACTH secretion. and are probably simil ar to those underlying the effect of cold stress; (iv) steroidogenic c apacity of adrenal cortex, at least in term of glucocorticoid hormones , is a rate-limiting step in the response of rat HPA axis to severe st resses; and (v) galanin exerts a direct secretory action of the rat ad renal gland, that can manifest itself only in the case of submaximally cold stress-stimulated HPA axis.