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McClure JM, Rossi NF, Chen H, O'Leary DS, Scislo TJ: Vasopressin is a major vasoconstrictor involved in hindlimb vascular responses to stimulation of adenosine A (1) receptors in the nucleus of the solitary tract. Am J Physiol Heart Circ Physiol. 2009 Nov;297(5):H1661-72. Epub 2009 Sep 11.
Our previous study showed that stimulation of adenosine A (1) receptors located in the nucleus of the solitary tract (NTS) exerts counteracting effects on the iliac vascular bed: activation of the adrenal medulla and beta-adrenergic vasodilation versus vasoconstriction mediated by neural and unknown humoral factors. In the present study we investigated the relative contribution of three major potential humoral vasoconstrictors: vasopressin, angiotensin II, and norepinephrine in this response. In urethane-chloralose anesthetized rats we compared the integral changes in iliac vascular conductance evoked by microinjections into the NTS of the selective A (1) receptor agonist N (6)-cyclopentyladenosine (CPA; 330 pmol in 50 nl) in intact (Int) animals and following: V (1) vasopressin receptor blockade (VX), angiotensin II AT (1) receptor blockade (ATX), bilateral adrenalectomy + ganglionic blockade (ADX + GX; which eliminated the potential increases in circulating norepinephrine and epinephrine), ADX + GX + VX and ADX + GX + VX + ATX. In Int animals, stimulation of NTS A (1) adenosine receptors evoked typical variable responses with prevailing pressor and vasoconstrictor effects. VX reversed the responses to depressor ones. ATX did not significantly alter the responses. ADX + GX accentuated pressor and vasoconstrictor responses, whereas ADX + GX + VX and ADX + GX + VX + ATX virtually abolished the responses. Stimulation of NTS A (1) adenosine receptors increased circulating vasopressin over fourfold (26.4 + or - 10.4 vs. 117.0 + or - 19 pg/ml). These data strongly suggest that vasopressin is a major vasoconstrictor factor opposing beta-adrenergic vasodilation in iliac vascular responses triggered by stimulation of NTS A (1) adenosine receptors, whereas angiotensin II and norepinephrine do not contribute significantly to the vasoconstrictor responses. |
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