Parathyroid hormone and the vascular response to norepinephrine.

Norepinephrine blood pressure reactivity is reduced in uremia, an effect attributed to excess parathyroid hormone (PTH). Most, but not all, animal and human studies support the theory that high PTH levels diminish the pressor response to norepinephrine. In hemodialysis patients in whom norepinephrine infusion tests were performed to determine the effect of parathyroidectomy on vascular responsiveness, the vascular response to norepinephrine (100 ng/kg/min) improved significantly (11.3 +/- 1.3 mm Hg before and 17.5 +/- 2.4 mm Hg after parathyroidectomy; P less than .01). Excess parathyroid hormone appears to play an active role in reduced vascular responsiveness to norepinephrine, although the mechanisms of this effect are unknown.