Some relevance of presynaptic beta-adrenoceptors to development of hypertension in spontaneously hypertensive rats.

The effect of cumulatively applied carteolol alone 10(-8) M to 10(-6) M on [3H] release evoked by transmural field stimulation at 5 Hz was studied in renal and mesenteric arteries preloaded with [3H]-norepinephrine, from prehypertensive 4 weeks old and hypertensive 14 weeks old spontaneously hypertensive rats (SHR) and age-matched Wistar Kyoto rats (WKY). The [3H] release in renal and mesenteric arteries from young SHR was greater than that from age-matched WKY, whereas there was no difference of the parameter in both arteries from adult rats of both strains. In renal arteries, carteolol 10(-6) M inhibited [3H] release in young SHR and the inhibition differed from no effect in age-matched WKY, but the inhibition was not seen in adult SHR and WKY. In mesenteric arteries, carteolol 10(-7) M and 10(-6) M concentration-dependently inhibited [3H] release in young SHR and WKY, the antagonist 10(-6) M inhibited the parameter in adult SHR and WKY and the inhibition in young SHR was greater than that in age-matched WKY, whereas the inhibition in adult SHR was smaller than that in age-matched WKY. Presynaptic beta-adrenoceptors may function tonically to facilitate the release of norepinephrine in renal arteries from young SHR and in mesenteric arteries from young and adult SHR and WKY. The modifications of these adrenoceptors in young SHR appear to have causal relevance to development of the hypertension.