Effect of social stress on COX-1 and COX-2-induced alterations in the adrenergic agonists-evoked hypothalamic-pituitary-adrenal responses

The purpose of the present study was to investigate the contribution of prostaglandins (PGs) synthesized by constitutive (COX-1) and inducible (COX-2) cyclooxygenase to stimulation of the hypothalamic-pituitary-adrenal (HPA) axis by adrenergic receptor agonists in rats under social crowing stress 3 days, (21 per a cage for 6) animals. The effects of phenylephrine, clonidine and isoprenaline, an alpha1-, alpha2- and beta-adrenergic agonist, respectively, in the presence and absence of COX-1 inhibitor, piroxicam, and COX-2 inhibitor, compound NS-398, on ACTH and corticosterone secretion in stressed rats were compared with these effects in non-stressed animals. All drugs were given intracerebroventricularly (i.c.v.), COX inhibitors 15 min before adrenergic agonists. Piroxicam (0.02 microg) and NS-398 (0.1 microg) significantly reduced the phenylephrine (30 microg) -induced ACTH and corticosterone secretion in both stressed and non-stressed rats. Piroxicam (0.02 microg) and NS-398 (0.01 microg) moderately decreased the clonidine (10 microg) -evoked hormone responses in control rats but did not alter these responses in stressed rats. Piroxicam (0.2 microg) and NS-398 (0.1 microg) moderately diminished the isoprenaline (20 microg) -evoked ACTH and corticosterone response in control rats, while in stressed rats these inhibitors did not significantly alter the isoprenaline-induced rise in ACTH and corticosterone secretion. These results indicate that in hypothalamic structures involved in the regulation of adrenergic agonists-induced HPA stimulation COX-2 is expressed under physiological synaptic activity. Social crowding stress does not alter the significant involvement of prostaglandins in the HPA response induced by stimulation of central alpha1-adrenergic receptors. Prostaglandins are of lesser importance in activation of the HPA axis by alpha2- and beta-adrenergic receptors under basal and social stress conditions.