The elastic modulus of conductance coronary arteries from spontaneously hypertensive rats is increased

To assess the alterations of morphological and functional properties of conductance coronary and mesenteric resistance arteries in spontaneously hypertensive rats (SHR).

The in-vitro intrinsic elastic properties of the wall material in SHR coronary arteries were determined in comparison with those of Wistar-Kyoto (WKY) rats. Mesenteric resistance arteries from rats of both strains were also studied.

Arterial segments were cannulated at both ends using an arteriograph system and subjected to pressure increments with simultaneous measurements of the wall thickness and internal diameter. The strain, stress and incremental elastic modulus (Einc) were calculated from diameter-pressure curves.

Over the full range of pressures tested (10-160 mmHg), the internal diameters of SHR coronary arteries were not significantly different from those of WKY rat arteries, whereas we observed that SHR mesenteric resistance arteries had a significantly smaller diameter. The stress-strain curve for coronary arteries was shifted significantly to the left-hand side for the SHR group indicating more stress per unit strain, whereas the opposite was found for mesenteric resistance arteries. When Einc was determined under isobaric conditions, we found no difference between SHR and WKY rat coronary arteries, whereas this parameter was decreased significantly for SHR mesenteric resistance arteries. When Einc was estimated at the respective operating pressures, it was 1.7- to 2.8-fold greater for SHR than it was for WKY rat mesenteric resistance and coronary arteries. Moreover, the total collagen area: lumen area ratio was significantly greater for the SHR than it was for the WKY rat coronary artery wall, but this ratio was similar for mesenteric preparations from the two strains.

These results show that, at a given stress or operating pressure level, the material of SHR coronary artery wall is characterized by an increase in Einc, whereas there is no increase in Einc for in mesenteric resistance arteries. This functional alteration is accompanied by an increase in the relative proportion of collagen, a component with a high elastic modulus, in the wall. In contrast, we found no change in elastic modulus and in the relative proportion of collagen for the SHR mesenteric resistance arteries. Furthermore, the present results support the hypothesis that alterations in distensibility differ among the components of the SHR vasculature.