Effects of parathyroidectomy and calcium supplementation on the pressor response to angiotensin II in conscious rats.

Objective: We evaluated the effect of parathyroidectomy (PTx) and of calcium supplementation on the pressor response to angiotensin II (Ang II) in conscious rats.

Study design: PTx and sham surgery were performed on 10-week-old male Wistar rats. The mean arterial pressure (MAP), heart rate, and the effective pressor dose of Ang II (EPD) which defined as the dose of Ang II required to elicit a rise of 20 mmHg in MAP, were evaluated in PTx and sham operated rats. Intracellular free calcium in platelets was assessed with the fluorescent dye, fura-2 acetoxymethyl ester. In addition, after administering a dose of supplemental calcium chloride, a 10, 20, or 40 mg/rat, we determined the changes in the MAP, EPD, and serum calcium level.

Results: The EPD in the PTx rats was significantly lower than the sham operated rats. The serum concentration of calcium in PTx was also significantly lower than the sham operated rats. A statistically significant negative relationship was observed between the EPD and intracellular free calcium in PTx rats. Following administration of 20 mg of calcium chloride (7.4 mg of elemental calcium) to the PTx rats, the EPD returned to the level seen in sham operated rats.

Conclusion: Results suggest that a depletion of parathyroid hormone is associated with the pressor response to Ang II, and is involved in the regulation of intracellular free calcium.