Presynaptic Serotonin Receptors on Peripheral Noradrenergic and Central Serotoninergic Neurons of Spontaneously Hypertensive and Wistar‐Kyoto Rats

In spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats it was examined whether the effects mediated by presynaptic 5-HT1 receptors on noradrenergic and serotoninergic neurons are altered in hypertension. Vascular strips (arteria iliaca, vena cava) as well as brain slices (nucleus tractus solitarii, hypothalamus, cortex) were prepared from 5–7-, 9–11-, and 19–22-week-old SHR and WKY rats (mean systolic blood pressure: 111, 183, and 212 and 105, 113, and 106 mm Hg, respectively). Subsequent to incubation with [3H]noradrenaline ([3H]NA; vascular strips) and [3H]serotonin ([3H]5-HT; brain slices), the tissues were superfused and the effects of 5-HT on the electrically evoked [3H]monoamine overflow were studied. The inhibitory effect of 5-HT on the evoked [3H]NA release in the arterial strips did not differ between both strains (at any age). In strips of the vena cava, the maximum inhibitory effect of 5-HT on evoked release was, at any age, more pronounced in SHR than in WKY rats. In slices of the three brain regions, the evoked [JH]5-HT release was similar in SHR and WKY rats. Likewise, the inhibitory effect of 5-HT on the evoked release did not differ in both strains at any age. The present results indicate that the inhibitory effect mediated by presynaptic 5-HT1 receptors is more pronounced in the vein, but is identical in the artery, of SHR rats compared to WKY rats. 5-HT release in the brain and its modulation via inhibitory presynaptic 5-HT1 autoreceptors do not differ in both strains. In conclusion, the effect of 5-HT1 receptor agonists is not attenuated in hypertension; this is of importance, because their inhibitory action on (peripheral) NA and (central) 5-HT release and their direct vasodilatory action may lower blood pressure.