THE EFFECT OF SURGICAL-TREATMENT ON SECONDARY HYPERALDOSTERONISM AND RELATIVE HYPERINSULINEMIA IN PRIMARY HYPERPARATHYROIDISM

Objective: To evaluate the renin-aldosterone system and insulin secret ion in hyperparathyroidism and their effects on blood pressure regulat ion. Design: Studies were carried out on patients with primary hyperpa rathyroidism (PHPT) prior to and following removal of the parathyroid tumor. Methods: Sixteen normotensive and euglycemic patients with PHPT were studied. The following parameters were measured: basal and stimu lated plasma renin activity (PRA) and aldosterone (ALD) secretion; par athormone (PTH) and serum electrolytes. Insulin and glucose levels wer e measured during an oral glucose tolerance test. Results: Systolic bu t not diastolic blood pressure showed a decrease following surgery, fr om 123.3 +/- 13.0/80 +/- 8.6 to 116.7 +/- 13.5/77.3 +/- 8.8 mmHg. The decrease in the systolic pressure was not clinically significant. Afte r surgery, both the basal and stimulated PRA and ALD values decreased, and the preoperative pathological Values returned to normal: PRA basa l: 1.79 --> 0.70 ng/ml/h, P = 0.0049; PRA stimulated: 7.76 --> 1.90 ng /ml/h, P = 0.0031; ALD basal: 111.5 --> 73.0 pg/ml, P = 0.0258; ALD st imulated: 392.5 --> 236.0 pg/ml, P = 0.0157. The postoperative decreas e in the PRA correlated with the changes in PTH levels (r = 0.5442, P < 0.05, n = 16) but did not correlate with the changes in serum calciu m concentrations, Both the fasting and stimulated insulin levels decre ased after surgery but remained within the normal range: insulin fasti ng 10.2 --> 5.0 mIU/l, P = 0.0218; insulin area under the curve: 5555 --> 3296 mIU/lmin, P = 0.0218. There was no correlation between the c hanges in insulin levels and PTH or ion levels. Sodium, potassium and blood glucose levels remained unaffected by parathyroid surgery. Concl usions: In a population of normotensive hyperparathyroid patients an i ncreased activity of the renin-aldosterone system related to PTH was f ound and surgery resulted in a small and insignificant decrease in blo od pressure. This change was accompanied by a significant decrease in the activity of the renin-aldosterone system indicating the role of th e renin-aldosterone system in the regulation of blood pressure in PHPT . Both fasting and stimulated insulin values decreased following remov al of the parathyroid tumor, but with no individual correlation with P TH and calcium levels.