Release of serotonin in the locus coeruleus of normotensive and spontaneously hypertensive rats (SHR)

The aim of the present work was to clarify whether differences exist betwee n the release of endogenous serotonin in the locus coeruleus of normotensiv e and hypertensive rats, The locus coeruleus was superfused with artificial cerebrospinal fluid (aCSF) through a push-pull cannula and serotonin and i ts metabolite 5-hydroxyindoleacetic acid (5-HIAA) were determined in the su perfusate by HPLC combined with electrochemical detection. Compared with no rmotensive Wistar-Kyoto (WKY) rats, the basal release rate of serotonin in the locus coeruleus of spontaneously hypertensive rats (SHR) was increased more than twofold. Intravenous infusion of noradrenaline (4 mu g/kg min) in creased mean arterial blood pressure to the same extent in hypertensive and normotensive mts. The presser response was associated with an increased se rotonin release, In WKY rats, the release of serotonin in the locus coerule us evoked by noradrenaline infusion was more pronounced than in SHR. In WKY mts, intravenous infusion of sodium nitroprusside (150 mu g/kg min) led to a fall in blood pressure which was less pronounced and lasted shorter than in SHR. The depressor response was associated with decreased serotonin rel ease. In WKY rats, the decrease in serotonin release evoked by sodium nitro prusside was more pronounced and lasted longer than in SHR. Neither noradre naline nor sodium ni troprusside influenced the outflow of 5-HIAA. The sens ory stimuli noise and tail pinch led to a slight rise in arterial blood pre ssure which was similar in WKY rats and SHR. These stimuli enhanced the rel ease rate of serotonin and the outflow of 5-HIAA to the same extent in the locus coeruleus of normotensive and hypertensive rats. The findings suggest that the enhanced release of serotonin in the locus coeruleus of genetical ly hypertensive rats reflects a mechanism counteracting the disturbed blood pressure homeostasis. Stressors influence blood pressure and release of se rotonin in the locus coeruleus of SHR and WKY rats to the same extent.