EFFECTS OF SINGLE AND REPEATED ELECTROCONVULSIVE SHOCK ON ISOPROTERENOL-STIMULATED PINEAL N-ACETYLTRANSFERASE ACTIVITY AND MELATONIN PRODUCTION IN RATS

The response of the pineal gland to acute isoproterenol administration represents a useful tool to investigate beta(1)-adrenoceptor function , because the production of melatonin and the activity of its main syn thesizing enzyme, N-acetyltransferase (NAT), are regulated by beta(1)- adrenergic receptors. In the present study, rats underwent single elec troconvulsive shock (ECS) administration (0.80 mA, 0.5 s, at midday), chronic ECS treatment (0.80 mA, 0.5 s, once daily for 8 days), or sham treatments. On the day after the last ECS or sham ECS, animals were i njected with isoproterenol hydrochloride (1 mg.kg(-1) SC) or volume-ma tched saline at 1600 h. After single ECS, isoproterenol injection indu ced a clear-cut increase in both pineal NAT activity and melatonin lev els with no significant differences between ECS-treated rats and the s ham-treated ones. In rats chronically treated with ECS, the isoprotere nol-induced increases in both pineal NAT activity and melatonin conten t were significantly lower than in sham-treated animals (p < 0.001 for NAT activity; p < 0.005 for melatonin levels; Tukey's test). These da ta show that the pinealocyte beta-adrenoceptor function is reduced by chronic, but not acute ECS administration, and that this change is not due to the nonspecific stress effect of animal handling or to the acu te effects of the last of a series of ECS.