Parathyroid hypertensive factor.

A new circulating hypertensive factor, parathyroid hypertensive factor (PHF), has been demonstrated in the plasma of spontaneously hypertensive rats (SHR) but not in that of normotensive rats. PHF produced a delayed increase in blood pressure with a peak response after 45 min (bolus injection) or 60-90 min (continuous infusion). This increase in blood pressure was coupled with an in vitro increase in calcium uptake in the rat tail artery which had a similar time-course. The evidence that calcium is involved in the mechanism of action is supported by the inhibitory effect of calcium antagonists on the vascular action of PHF. Furthermore, PHF increased the intracellular free calcium concentration in cultured smooth muscle cells from the rat tail artery. Parathyroidectomy and parathyroid transplant experiments indicated that PHF originated in the parathyroid gland. Cultured parathyroid glands from SHR but not from normotensive rats produced a factor in the medium with the same biological property and retention time on high performance liquid chromatography as plasma PHF. A novel cell type was described in the parathyroid gland of SHR, but not normotensive rats, and the percentage of these cells was correlated significantly with the plasma PHF level and the blood pressure level. In some hyperparathyroid patients, plasma PHF and hypertension were both present, and both disappeared after surgical removal of the parathyroid gland. In both animal models and human studies, PHF seems to be associated with low or normal levels of plasma renin and the salt-sensitive type of hypertension.