Differential alterations in sympathetic neurotransmission in mesenteric arteries and veins in DOCA-salt hypertensive rats

Abstract

Sympathetic control of arteries and veins may be altered in hypertension. To test this hypothesis, constrictions of mesenteric arteries and veins caused by nerve stimulation and by norepinephrine (NE) and ATP were studied in vitro in tissues from deoxycorticosterone acetate (DOCA)-salt hypertensive and sham normotensive rats. In DOCA-salt arteries, the maximum neurogenic response was greater than that in sham arteries. The P2 receptor antagonist, pyridoxal-phosphate-6-azophenyl-2',4'-disulfonic acid (PPADS, 10 microM), greatly reduced neurogenic responses in sham but not DOCA-salt arteries. The alpha1-adrenergic receptor antagonist, prazosin (0.1 microM), inhibited responses in DOCA-salt but not sham arteries. Concentration-response curves for norepinephrine and ATP were similar in sham and DOCA-salt arteries, indicating that reactivity to sympathetic vasoconstrictor transmitters was not changed in DOCA-salt arteries. Neurogenic constrictions in sham and DOCA-salt veins were similar in amplitude, and they were completely blocked by prazosin. However, concentration-response curves for norepinephrine in DOCA-salt veins were right-shifted compared to those in sham veins. Cocaine (10 microM) and corticosterone (10 microM) caused a leftward shift in norepinephrine concentration-response curves in DOCA-salt but not sham veins. Norepinephrine content was decreased in DOCA-salt arteries and veins, and there was an increased norepinephrine transporter (NET) level in DOCA-salt veins. These data indicate that, in DOCA-salt hypertension, there is an increased norepinephrine release from sympathetic nerves associated with mesenteric arteries and veins. In arteries, this results in an increase in the amplitude of neurogenic constrictions. In veins, increased norepinephrine release maintains neurogenic constrictions in the presence of increased NET levels.