Compliance of Isolated Resistance Vessels from Spontaneously Hypertensive Rats

Abstract

As has now been recognized for over a century, hypertension is associated with altered vascular structure, the degree of alteration being quantitatively associated with the degree of hypertension (Folkow, 1956). Thus, under conditions of relaxation, the peripheral resistance is increased (Folkow, 1956; Takeshita and Mark, 1980), while the pressor response of the vasculature of hypertensives is also increased (Duff, 1956). Furthermore, again on the basis of in vivo measurements, the compliance of the vasculature of hypertensive individuals is abnormally high (Horwitz and Patel, 1985; Patel, 1988). The interpretation of such measurements is, however, difficult. First, it is not possible to obtain full control of the tone of the vasculature (Schulte et al., 1988). Second, the measurements do not provide information about individual vessels. The in vivo measurements do not therefore provide direct information about the mechanical properties of the components of the vascular wall, and it is necessary to perform in vitro experiments on isolated vessels (Mulvany, 1984a). This paper reviews some of the work done in the author’s laboratory over the past 10 years to assess the mechanical properties of resistance vessels taken from spontaneously hypertensive rats (SHRs) and from normotensive control Wistar-Kyoto rats (WKYs), and also points to recent work concerned with resistance vessels from patients with essential hypertension. The work includes assessment of the static mechanical properties of the vessels, under relaxed and activated conditions, as well as their dynamic mechanical properties. This information is used to provide estimates of the compliance of the vessels under these conditions. The data presented here is largely a reanalysis of data presented in part elsewhere (Mulvany, 1984b, 1986, 1988).