Hypertension Grand Rounds Primary Hyperparathyroidism With Concurrent Primary Aldosteronism

Primary aldosteronism (PA) is a common cause of secondary hypertension, because it involves 11.2% of referred hypertensive patients.1 Primary hyperparathyroidism (PPTH) is much less common, with a prevalence that, albeit imprecisely known, is probably 0.01% in unselected hypertensives. However, arterial hypertension develops in the majority (56% to 80%) of the PPTH patients,2 which can explain why they are held to be at increased risk for cardiovascular complications and death.3 The association of PPTH with arterial hypertension and increased cardiovascular risk would appear to be paradoxical, inasmuch as the parathyroid hormone (PTH) has been described to induce vasodilation through endothelium-independent mechanisms.4 Therefore, it would be expected to lower rather than to raise blood pressure.5 The mechanisms by which excess PTH increases blood pressure remained obscure until Mazzocchi et al6 reported that PTH stimulates in vitro the secretion of aldosterone from human adrenocortical cells in a concentrationdependent manner. These findings suggested that PTH acts as an aldosterone secretagogue that might be involved in causing human PA. However, whether this mechanism, although appealing, could be involved in causing human PA and might explain the development of arterial hypertension in patients with PPTH remained unsupported by any clinical data. We herein report on a patient who presented with resistant arterial hypertension and was found to have PA. Unilateral adrenalectomy resulted in cure of the PA and control of blood pressure despite a tapering of antihypertensive treatment, but the patient developed hyperparathyroidism caused by a PTHsecreting adenoma that was surgically removed. Gene expression and immunohistochemistry studies unveiled the expression of type 1 PTH receptor in the aldosterone-producing adrenocortical nodules and of the mineralocorticoid receptor (MR) in the nuclei of parathyroid adenoma cells. This latter finding was confirmed in a series of normal human parathyroid glands. Thus, this unique case and the related findings support the notion that undetected hyperfunctioning of the parathyroid gland can contribute to maintaining hyperaldosteronism in PA. It also suggests the existence of a bidirectional link between the adrenocortical zona glomerulosa and the parathyroid gland, which can be relevant for the regulation of calcium metabolism and blood pressure.