Active metabolite of vitamin D acutely reduces endothelium-dependent contractions in the isolated SHR aorta

Abstract

Recent studies proved that vitamin D has cardiovascular effects besides regulating calcium homeostasis.

Objectives: To study the effect of calcitriol (1,25-dihydroxyvitamin D3) on endothelium-dependent responses of the aorta of spontaneously hypertensive rats (SHR).

Methods: Rings of aortae were suspended in organ chambers for isometric force measurement. Agonist-induced endothelium-dependent and independent responses as well as prostacyclin release were measured in the absence or presence of calcitriol. Cytosolic calcium concentration was monitored by confocal microscopy after incubation with fluorescent dyes, Fluo-4 and Fura-red.

Results: Acetylcholine-induced relaxation was not affected by administration of calcitriol while the acetylcholine- and ATP-induced endothelium-dependent contractions were reduced compared to those obtained in the absence of the drug. This effect was not present if the calcium ionophore A23187 was used as agonist. Acetylcholine- but not A23187 -induced release of prostacylin was reduced by acute administration of calcitriol. Exposure to calcitriol reduced the increase in cytosolic free calcium concentration caused by acetylcholine in the endothelial cells.

Conclusions: This study shows that calcitriol can modulate vascular tone by reducing the release of endothelium-derived contracting factor(s). (Partly supported by the CeDAR Foundation)