CARDIOVASCULAR EFFECTS OF 5HT(2) AND 5HT(3) RECEPTOR STIMULATION IN THE NUCLEUS-TRACTUS-SOLITARIUS OF SPONTANEOUSLY HYPERTENSIVE RATS

The effects of local application of 5-HT2- and 5-HT3-receptor agonists in the nucleus tractus solitarius (NTS) on the cardiovascular parameters were investigated in anaesthetized spontaneously hypertensive (SH) rats and their genetically normotensive precursors (WKY). Unilateral microinjection of picomolar doses of a 5HT(2) receptor agonist, 2,5-dimethoxy-3-bromo-amphetamine (DOE, 0.025-0.5 pmol), produced a dose-dependent hypotension and bradycardia in both SH and WKY rats. These effects could be prevented by prior local microinjection of a 5-HT2 receptor antagonist, ketanserin (10 pmol). However, for both cardiovascular parameters, DOE was more potent in SH than in WKY rats. Thus, the dose-related responses to DOE were shifted to the left in SH as compared to WKY rats. Bilateral microinjection of the 5-HT3 receptor agonist, phenylbiguanide (1.7-5 nmol), produced an increase in blood pressure and reduced the cardiovagal component of the baroreflex. These effects were not significantly different in SH and WKY rats. These data suggest that 5-HT2 receptors, but not 5-HT3 receptors, are supersensitive in the NTS of SH rats.