RESUMEN
The effects of pretreatment with selective histamine receptor antagonists on changes in sympathoadrenal activity and haemodynamics, induced by 60-min immobilization stress, were studied in conscious rats. Using adrenomedullary microdialysis, it was shown that ranitidine (5 mg/kg, i.v.), a histamine H2 receptor antagonist, selectively suppressed stress-stimulated noradrenaline secretion without affecting adrenaline response, whereas triprolidine (10 mg/kg, i.v.), a histamine H1 receptor antagonist, had little effect on stress-induced secretion of both catecholamines. Neither triprolidine nor ranitidine changed the pressor response to 60-min stress. The stress-induced increase in heart rate was not altered by triprolidine, whereas ranitidine reduced it after 30 min of stress. To test whether the anti-secretory effect of ranitidine could be of peripheral origin, in a separate experimental series, a local catecholamine secretion was stimulated by histamine (0.5 mM) perfused through the adrenomedullary dialysis probe. It appeared that triprolidine, but not ranitidine, reduced this effect of histamine. Thus, the present results suggest that during stress, the activity of the central histaminergic system, via histamine H2-receptors, may selectively modulate noradrenaline secretion by the adrenal gland.