Effect of noradrenaline on tail arteries of SHR and WKY under perfusion at constant flow and constant pressure

Abstract

Vasoconstrictor effects of noradrenaline were compared in 6- to 7-month-old spontaneously hypertensive (SHR) and Wistar Kyoto (WKY) rats. A cylindrical segment was dissected from the proximal part of tail artery, cannulated at both ends and perfused alternately either at constant flow or constant pressure. Two series of experiments were performed. In the first series, vessels were perfused/superfused with Krebs-Henseleit solution. In the second one a modified salt solution was used, in which NaCl was totally replaced by an equimolar amount of KCI. Under constant flow conditions noradrenaline evoked a more prominent resistance increase in SHR compared with WKY independently of the composition of solution (normal or high-K+) used. At constant pressure perfusion with normal solution, the vasoconstrictor response to noradrenaline was more prominent in WKY. Under application of high-K+ solution, vasoconstriction at constant pressure in SHR became more pronounced than that in WKY. We suggest that there is greater wall thickness:lumen diameter ratio in SHR vessels and thus different contribution of distension-activated myogenic response is of primary importance for the data obtained.

Differences in functional and structural properties of segments of the rat tail artery

“…These arteries respond to PHE stimulation with dose-dependent pressor responses. Therefore, as previously described, the rat tail artery develops an important intrinsic tone and a large vasopressor response to PHE (5,6,24) and has been reported to be a resistance vessel (10)(11)(12)(13). Although frequently used as a proximal segment for perfusion (2,3,10-13) or as a whole isolated vascular bed (5,6,24), the diameter of this artery changes as it reaches the tail end and, to this date, there are no reports describing the characteristics of different segments of this artery.…”

“…Some studies refer to the tail artery as a resistance artery (10)(11)(12)(13); however, these studies do not define criteria for this classification. In fact, resistance vessels are arterioles and small arteries and 40 to 55% of the systemic vascular resistance resides in vessels with diameters >100 µm (14) up to a limit of 400 µm (15).…”

“…The tail artery is a suitable preparation for analysis of pressor reactivity and the perfusion technique is significantly less expensive than the measurement of pressurized arteries or isometric recordings of the 4th branch of the mesenteric artery, which is usually considered to be a resistance artery. Although frequently used as an entire isolated vascular bed (5)(6)(7)(8)(9) or as a small isolated dissected segment for pressurized artery protocols (2,(10)(11)(12)(13), the caliber of this artery changes as it reaches the tail end. There are no reports describing the characteristics of different segments of this artery.…”

Vasoconstriction reactions in tail artery in the rats with regional arterial hypotension

“…After depolarization vascular reactivity was higher in HR at both perfusion regimens [9]. To further study the effect of the vascular wall thickness on the reactivity of blood vessels we have chosen vessels with a thinner muscle wall.…”

“…Under conditions of constant-flow perfusion, the hypertensive vessels are contracted by norepinephrine (NE) stronger than the normal vessels [4][5][6]. This phenomenon is related to increased thickness of the smooth muscle wall and decreased vascular lumen in HTR [2].By contrast, the vasoconstrictor reactions were more pronounced in NTR, as compared to HTR both in the hind limb vascular system [11] and in isolated tail artery pert'used under constant pressure [9]. Different reactivity under various perfusion regimens is supposed to be determined by different distension of smooth muscle and, consequently, by various degrees of activation of the myogenic reaction [8].…”