Correlations between parameters of parathyroid activity and blood pressure during the onset of DOCA + saline hypertension in the rat

Influence of transplantation of parathyroid glands on blood pressure development in stroke prone spontaneously hypertensive rats and in normotensive Wistar Kyoto rats

The influence of the parathyroid glands (PTG) on the development of high blood pressure (BP) in stroke prone spontaneously hypertensive (SHR/SP) and Wistar Kyoto (WKY) rats has been studied. After ablation of their own PTG's SHR/SP received PTG's from WKY rats and vice versa. After transplantation (TRPL) a normal calcium and parathyroid hormone (PTH) status was preserved during the whole observation period. One group of animals received a high salt diet (8% NaCl) for 4 weeks after transplantation, the other group received a normal rat chow for 3 months. In SHR/SP, which had PTG-transplants from WKY rats, the development of BP was clearly attenuated compared to sham operated rats in both experimental groups. WKY rats with PTG's from SHR/SP became hypertensive after two weeks during salt loading and after six weeks under normal diet. Sham operated WKY rats remained normotensive. The results demonstrate that the parathyroid gland is involved in the pathogenesis of hypertension, but the only known secretory product of PTG's parathyroid hormone, seems not to be responsible for these effects.

Acute effect of parathyroid hormone-(1-34) fragment on blood pressure in rats fed a low calcium diet

1. Acute effects of human PTH-(1-34) fragment on blood pressure were examined in rats fed a low or normal calcium diet. 2. Plasma biochemistry showed that a low calcium diet evoked hyperparathyroidism as well as hypocalcemia in rats. 3. Subcutaneous administration of human PTH-(1-34) caused a significant decrease in tail-cuff systolic blood pressure in rats fed a normal calcium diet, but not in rats fed a low calcium diet. 4. Intravenous administration of human PTH-(1-34) reduced the arterial blood pressure in rats, dose-dependently. The reduction of blood pressure was more pronounced in rats fed a normal calcium diet than that in the rats fed a low calcium diet. 5. It is suggested that the hypotensive action of human PTH-(1-34) was more pronounced in the rats fed a normal diet than in the rats fed a low calcium diet, and that PTH has different cardiovascular consequences under chronic hyperparathyroidism and/or hypocalcemia.

Parathyroid hormone in sodium-dependent hypertension

Plasma parathyroid hormone (pPTH) levels have been assessed in three separate radioimmunoassay systems in samples from Wistar-Kyoto rats. The animals were subjected to one of three dietary regimens throughout the study period: Group 1 animals consumed normal rat chow and drank tap water; Group 2 animals consumed normal rat chow and tap water was replaced with 0.5% saline solution; Group 3 animals consumed normal rat chow to which 2.5% CaCO3 (by weight) had been added and also drank 0.5% saline solution. Animals had consumed these diets for approximately 7 months prior to sacrifice for blood collection. Blood pressure was measured by tail cuff plethysmography in these animals and, as previously reported, saline consuming animals showed a moderate hypertension (Gp 2) only when diets did not contain added calcium (Gp 3). In the week prior to sacrifice, mean blood pressures were: Gp 1: 128.0 +/- 3.46 mmHg; Gp 2: 140.2 +/- 3.15 mmHg; and Gp 3: 133.5 +/- 2.90 mmHg. Three assay systems were used to measure pPTH levels from trunk blood samples obtained by guillotine decapitation. One assay used an antiserum directed toward the vasoactive N terminal fragment 1-34 and produced pPTH measurements of 0.74 +/- 0.05 ng/ml in Gp 1 animals, 1.04 +/- 0.07 ng/ml in Gp 2 animals and 1.12 +/- 0.08 ng/ml in Gp 3 animals. This pattern was consistent with that obtained by another antiserum which had been raised against the intact 1-84 PTH molecule and produced values of 0.25 +/- 0.03 ng/ml in Gp 1 animals, 0.55 +/- 0.07 ng/ml in Gp 2 animals and 0.74 +/- 0.04 ng/ml in Gp 3 animals. Antiserum raised against the C-terminal did not show any difference in pPTH across groups. We conclude that saline consumption may increase some portions of circulating PTH. Such elevation of pPTH may not be a pathophysiological component in the sodium dependent elevation of blood pressure since animals concurrently consuming both saline and calcium supplemented diets retained elevated pPTH levels even though blood pressures did not differ from controls. Rather, elevation of circulating PTH levels may be a response to prolonged increases in sodium consumption.

Update on secondary forms of hyperparathyroidism

Recent information has shed a new light on the control of parathyroid hormone (PTH) secretion by calcium and 1,25-(OH)2D. These new data have permitted a better understanding of the pathogenesis and management of secondary hyperparathyroidism in end-stage renal disease. Emerging evidence has suggested a role for secondary hyperparathyroidism in the development of certain forms of hypertension and osteoporosis. Recent insights have been obtained regarding the occurrence of secondary hyperparathyroidism in obese and black subjects, in patients with multiple endocrine neoplasia type I, and in manic-depressive patients receiving lithium therapy. This review examines some of these recent gains in knowledge concerning secondary hyperparathyroidism, as well as their clinical implications.