Adrenergic mechanisms and remodeling of subcutaneous small resistance arteries in humans

Abstract

Background: Vascular structural alterations in small resistance arteries of patients with essential hypertension (EH) are mostly characterized by inward eutrophic remodeling. In fact, no difference in the smooth muscle cell volume (CV) between normotensive subjects (NT) and essential hypertensive patients was observed. However, experimental models of hypertension with chronic infusion of agonists of adrenergic receptors were characterized by the presence of smooth muscle cell hypertrophy or hyperplasia. Recently, we have observed the presence of vascular smooth muscle cell hypertrophy in patients with renovascular hypertension.

Objective: The aim of the study to investigate the structural characteristics of subcutaneous small resistance arteries of NT, of EH, and of patients with phaeochromocytoma (Phaeo).

Patients and methods: Thirty Phaeo, 30 NT and 30 EH were included in the study. A biopsy of subcutaneous fat was taken from all subjects. Small resistance arteries (relaxed diameter 160-280 microm) were dissected and mounted on a micromyograph and the media : lumen ratio was calculated. In nine Phaeo, nine NT and 13 EH the cell volume was measured by an unbiased stereological principle, the 'disector' method. RESULTS No difference in smooth muscle cell volume was observed between groups. However, inward remodeling in Phaeo was less marked than in EH, although the increase in media : lumen ratio was similar compared with NT. However, the lack of changes in media cross-sectional area, compared with NT, suggest that there has been little hypertrophy, the changes observed thus being eutrophic.

Conclusions: Our data show, based on a reasonably large sample, that a pronounced activation of the adrenergic system is not associated with vascular smooth muscle cell hypertrophy or hyperplasia in humans. It is therefore possible that adrenergic mechanisms may have a relevant role in the development of eutrophic remodeling in small vessels.