TNF-alpha modulates arteriolar reactivity secondary to a change in intimal permeability

Inflammatory stimuli are often associated with marked changes in vascular reactivity. Tumor necrosis factor-alpha (TNF-alpha) is and important inflammatory cytokine with diverse effects including the ability to increase vascular endothelial cell permeability and to alter the structure of the endothelial cell glycocalyx. We have previously shown that arteriolar sensitivity to vasoactive materials is influenced by a barrier property of the arteriolar endothelium, and here we test the hypothesis that TNF-alpha might increase intimal permeability and thereby increase the access of circulating arginine-vasopressin (AVP) to vascular smooth muscle. Our objective in the current work was to show that TNF-alpha-mediated modulation of intimal cell permeability may produce both quantitative and qualitative alterations in vascular reactivity to arginine-vasopressin.

Hamster cheek pouch arterioles (approximately 65 microm, i.d.) were double-cannulated and perfused. [Arg8]-vasopressin was applied selectively to either the luminal or the adventitial surface of isolated cannulated arterioles. The reactivity of the arterioles to vasopressin was determined in the presence and absence of TNF-alpha (0.625 microg/mL; 1 hour).

Adventially applied AVP induced a concentration-dependent vasoconstriction with a threshold of approximately 1 pM, and a maximal constriction at 10 nM. In contrast, luminally applied AVP induced a biphasic response, showing a modest vasodilation in the range of 1 to 100 pM, and constrictions at doses higher than 1 nM. Maximal constrictions were not obtained with luminal doses of AVP as high as 1 microM; (i.e., at doses 100-fold higher than those that produced maximal responses with adventitial application). Dilations induced by luminal application of AVP were significantly attenuated by 10 microM Nomega-nitro-L-arginine methyl ester (L-NAME), but were not altered by 10 microM indomethacin. After treatment with TNF-alpha, the concentration-response curve for luminally applied AVP showed a more pronounced constriction and the dilator component of the agonist was eliminated. There was no change in the reactivity to adventitially applied AVP or to adventitial applications of acetylcholine. Nonspecific increases in endothelial cell permeability induced by 3-[(3-chloroamino-dopropyl)-dimethylamino]-1-propanesulfonate (CHAPS) also eliminated the potency differences between luminal and adventitial drug application. Following TNF-alpha treatment and loss of the dilator component of the response to AVP, L-NAME was still capable of reducing the arteriolar sensitivity to ACh, thus showing that the endothelial cell machinery for NO production was intact following TNF-alpha treatment.

Our findings show that the reactivity of intact resistance vessels to agonists that have both endothelial-dependent and smooth muscle cell-dependent components will be complex. Reactivity is the summation of: 1) the relative sensitivities of smooth muscle and endothelial cells to AVP, 2) the release of nitric oxide or other mediators from endothelium, and 3) the restricted access of intraluminal AVP to arteriolar smooth muscle cells. Thus, cytokines, and perhaps other materials that regulate endothelial cell permeability, can modify arteriolar reactivity by altering transendothelial cell access of luminal stimuli to the smooth muscle cells, as well as by acting directly on smooth muscle or by influencing the production of endothelial cell-derived vasoactive materials. In the case of agonists that have an endothelial cell dilator component as well as a smooth muscle constrictor component, this may result in a qualitative change in response as is shown here with AVP.