Endothelial role in ouabain-induced contractions in guinea pig carotid arteries.

Abstract

The influence of endothelium on the direct contractile effects of ouabain in vascular smooth muscle was analyzed in isolated perfused guinea pig carotid arteries. After blocking the neurogenic component of the giycoside contraction with or-adrenergic receptor blocking drugs or treating the animals with reserpine, ouabain-induced contractions were markedly reduced in vessels with intact endothelium. However, removal of the vascular endothelium from reserpinized carotid arteries resulted in ouabain-induced contractions similar to those observed in control arteries. These effects were not mimicked by the inhibitor of nitric oxide A fG -monomethyl L-arginine or by the cyclooxygenase blocker indomethacin. Bioassay experiments suggested that these endothelial effects are mediated by diffusible factors. Uptake of M Rb to measure sodium pump activity was significantly reduced by removal of the endothelium. These results suggest the existence of an inhibitory modulation by the endothelium of contractions induced by ouabain, likely mediated by a diffusible factor (or factors) released from these cells. The nature of this substance is unknown, but it is neither related to prostaglandins nor a nitric oxide-related compound. Its mechanism of action could be the stimulation of vascular sodium pump activity, the antagonism of the pump's inhibition by ouabain, or both. 1 -7 These contractions can be produced by a direct effect on vascular smooth muscle (myogenic component) or are mediated by the release of norepinephrine (NE) from perivascular adrenergic nerve endings (neurogenic component); the predominant component depends on the animal and the vessel studied. 5 -7 -9 On the other hand, ouabain or potassium-free solutions inhibit endothelium-dependent relaxations. 10 -12 This action can be mediated by the blockade of endothelium-derived relaxing factor (EDRF) or nitric oxide (NO) released from endothelial cells 1314 or by the impairment of endothelium-dependent hyperpolarization of smooth muscle cells.12 ' 1315Both endothelium and the sodium pump have been involved in the pathogenesis of hypertension.16 -20 However, in spite of the above discussed results, little is known concerning effects of the endothelium on the vascular actions of cardiac glycosides. Therefore, the present work was undertaken to analyze the possible endothelial influence on contractile responses to ouabain in perfused guinea pig carotid arteries. To simplify the experimental model, only the direct effects of the giycoside on vascular smooth muscle (the myogenic component) were analyzed. For this purpose, the possible ouabain-induced vasoconstrictions due to NE release were avoided by using o-adrenergic receptor antagonists or by pretreating the animals with reserpine. Methods Perfusion of Arterial SegmentsGuinea pigs of either sex weighing about 500 g (DunkinHarthey, IFFA-CREDO, Domaine des Oncins, France) housed at the facilities of Facultad de Medicina de la Universidad Aut6noma, Madrid, Spain, were anesthetized with 35 mg/kg i.p. sodium pentobar...

Endothelial Modulation of Ouabain-lnduced Contraction and Sodium Pump Activity in Aortas of Normotensive Wystar-Kyoto and Spontaneously Hypertensive Rats

“…Thus, an increase or a decrease in the contractions were observed in WKY and SHR aortas, respectively, which suggests endothelial modulation of ouabain con tractions, negative in WKY and positive in SHR. The negative endothelial modulation of ouabain response ob tained in normotensive WKY aortas agrees with the results described in human chorionic vessels [6] and guin ea pig carotid arteries [7] and with those observed in WKY mesenteric arteries with a K+-free solution [5,23]. However, there is, to our knowledge, no report concerning the positive endothelial modulation of ouabain-induced contractions in hypertensive SHR vessels.…”

“…Indeed, the contractions evoked by a K+-free solution in rat mesenteric arteries [5] and those produced by ouabain in human placental arteries [6] and guinea pig carotid arteries [7] are attenuated when the endothelium is present. The endothelial factor in volved in these effects appears to be nitric oxide (NO) in rat mesenteric arteries [5], but a still unknown factor in human placental and guinea pig carotid arteries [6,7], An increase in the response to ouabain has been reported in the vasculature of spontaneously hypertensive rats (SHR) when compared with that obtained in normotensive Wistar-Kyoto rats (WKY) [8][9][10], These higher responses can be due to enhanced sodium pump activity, higher Na+-Ca2+ exchange or other alterations in mem brane permeability to Na+ and Ca2+ [8][9][10][11]. However, the possible involvement of vascular endothelium has not yet been elucidated although an important endothelial dys function associated with hypertensive disease has been reported [12], Therefore, the aim of the present work was to investi gate any involvement of vascular endothelium in the responses to ouabain in vessels from WKY and SHR, as well as the possible mechanisms involved.…”

Neurogenic component of ouabain-evoked contractions is modulated by the endothelium.

“…Taken together with our previous observations concerning the endothelial modulation of a myogenic component involved in the contraction induced by the glycoside, 18 the endothelium of guinea pig carotid arteries possesses opposite effects on the neurogenic and myogenic actions of the glycoside: neurogenic contractions are facilitated by endothelial cells, whereas myogenic contractions are inhibited. Both effects seem to be due to released factor (or factors) from endothelium, the nature of which is unknown, although cyclooxygenase products or NO-related substances do not appear to be implicated.…”

“…However, when we used well sympathetically innervated vessels (guinea pig carotid arteries), this potentiating effect was not observed, as the responses in vessels with and without endothelium were similar. 18 This fact suggests that endothelium may modulate not only the myogenic but also the neurogenic component of ouabain-induced contractions. Phentolamine (a nonselective a-adrenergic blocker) and prazosin (a selective a,-adrenergic receptor antagonist) but not yohimbine (an a 2 -adrenergic blocker) induced concentration-dependent inhibition of ouabain-evoked contractions.…”

“…18 These latter results suggested that the endothelium also could have a positive influence on the neurogenic component of ouabain-evoked responses. 18 The ability of the endothelium to modulate the vascular response induced by sympathetic nerve activity already has been proposed; thus, endothelium removal increases contractions caused by nerve stimulation. 1925 However, to our knowledge there are no studies analyzing whether the norepinephrine release caused by sodium pump inhibition can be affected by the endothelium.…”