Pilot study of circulating prolactin levels and endothelial function in men with hypertension

Abstract

BackgroundHyperprolactinemia has been recently associated with hypertension and endothelial dysfunction in humans, confirming animal studies performed in the 1970s that showed high prolactin levels to exert positive chronotropic and vasoconstrictive effects. Whether prolactin affects endothelial function, in the absence of hyperprolactinemia, remains unknown. Considering that secretion of prolactin presents circadian rhythmicity, we tested the hypothesis that in patients with hypertension, who present diurnal variation in their endothelial function as well, prolactin levels correlate with endothelial function and/or blood pressure.MethodsEndothelial function, assessed by flow-mediated dilatation (FMD) and serum prolactin were examined successively at 12PM, 9PM, and 7AM in 27 nonhyperprolactinemic men with newly diagnosed, untreated essential hypertension.ResultsBoth FMD and prolactin presented 24-h variation (P <0.01). FMD reached its lowest values at 7AM (2.1 ±1.8%, mean± s.d.); concurrently prolactin levels peaked (7.18ng/ml, median). Across the three time points, prolactin changes inversely interacted with FMD changes (P = 0.002). Systolic and diastolic blood pressure also varied significantly but no interaction with prolactin changes was evident.ConclusionsDiurnal fluctuations of prolactin levels are associated with decreased endothelial function that occurs early in the morning in men with hypertension, although this study did not assess causality. Additional studies are required to determine whether these responses differ from normotensive individuals. © 2011 American Journal of Hypertension, Ltd.