Parathyroid hormone - Wikipedia
Parathyroid hormone (PTH), also called parathormone or parathyrin, is a hormone secreted by . Via the kidney, PTH enhances the absorption of calcium in the intestine by increasing the production of activated vitamin A mild decrease in serum magnesium levels stimulates the resorptive activity PTH has on the kidneys. Curr Opin Nephrol Hypertens. Jul;11(4) Magnesium and the parathyroid. Vetter T(1), Lohse MJ. Author information: (1)Institute for Pharmacology. Relationship between the Serum Parathyroid Hormone and Magnesium Levels in Continuous Ambulatory Peritoneal Dialysis (CAPD) Patients using.
Methods The work was performed in vitro by incubating intact rat parathyroid glands in different calcium Ca and Mg concentrations.
Results Increasing Mg concentrations from 0. With Mg 5 mM, the secretory response was practically abolished. Mg was able to reduce PTH only if parathyroid glands were exposed to moderately low Ca concentrations; with normal—high Ca concentrations, the effect of Mg on PTH inhibition was minor or absent. After 6-h incubation at a Ca concentration of 1.
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Parathyroid cells have cell-surface calcium-sensing receptors CaRswhich enable them to respond to changes in extracellular Ca [ 12 ]; thus, even small changes in extracellular Ca induce rapid changes in PTH secretion. Calcitriol and FGF23 also decrease parathyroid function through their specific parathyroid cell receptors: In vivo and in vitro studies have also shown a direct effect of phosphate on PTH synthesis and secretion, although a specific cell sensor for phosphate has not been identified, yet.
Although Ca is the main CaR agonist, other divalent and trivalent cations are also able to activate the CaR [ 2 ]. For example, an increase in extracellular magnesium Mg inhibits PTH secretion and reduces agonist-stimulated cAMP accumulation from parathyroid cells [ 10 — 13 ].
Magnesium and the parathyroid.
In dialysis patients, high serum Mg concentrations have been associated with low serum PTH levels. This inverse relationship between extracellular levels of Mg and PTH led to the notion of an inhibitory effect of Mg on PTH secretion in these patients [ 214 — 17 ]. However, the PTH secretory response to changes in extracellular Mg concentration has not been formally evaluated in patients.
The interest on Mg has grown since clinical studies have shown the efficacy of Mg-containing phosphate binders [ 18 ], and some concern has arisen related to the potential effect of a moderate increase in serum Mg on PTH secretion. In patients with normal serum Ca concentration and controlled PTH levels, it is not clear whether an increase in Mg may elicit an over suppression of PTH. For the statistical analysis, computations were performed with SPSS Demographic characteristics and laborarory parameters of the 56 patients included in the study Table 1 lists demographic and biochemical parameters of the 56 patients included in the study.
Among the 56 patients involved in this study, 34 were male and 22 were female. The mean age was The causes of the end stage renal disease were diabetes mellitus in 8 patients The remaining 38 patients The mean serum magnesium level was 1. Among the total 56 patients, 15 patients Relationship between serum iPTH levels and serum magnesium, total and ionized serum calcium, alkaline phosphatase bony isoenzyme, inorganic phosphate levels among all 56 CAPD patients Among all 56 patients, serum iPTH level was not correlated with serum magnesium level Figure 1.
But there was no correlation between serum iPTH level and serum inorganic phosphate level Figure Calcium exerts a negative feedback control on serum PTH level. A decrease in extracellular calcium leads not only to an increase in PTH secretion but also to increases in the mRNA expression of PTH and proliferation of parathyroid cell and release of PTH is suppressed during acute hypercalcemia 8 — Phosphate exerts indirect stimulatory effects on PTH secretion by decreasing renal production of calcitriol and by lowering plasma ionized calcium.
It also plays a direct stimulatory role at the level of parathyroid gland 910 Calcitriol diminishes transcription of PTH mRNA by binding to Vitamin D receptor and stimulates intestinal absorption of calcium and the skeletal mobilization of calcium, thereby increasing plasma calcium and inhibiting PTH secretion 9 — Recently, in addition to these factors, magnesium is suggested to play an important role in regulating PTH level.
An intravenous magnesium sulfate infusion significantly suppressed iPTH secretion in patients with primary hyperparathyroidism In addition, an intravenous magnesium sulfate infusion depressed iPTH levels in healthy men 20 The use of magnesium carbonate as a phosphate binder depressed serum PTH level Normalization of serum magnesium by using low dialysate magnesium in hypermagnesemic hemodialysis patients was followed by a rise in circulating PTH levels 18 Magnesium is the fourth most abundant cation in the body.
Renal excretion is the major route of magnesium elimination from the body in health. As renal failure progresses, the fraction of filtered magnesium increases, but total filtration amount decreases.
So, at last, absorption from the gastrointestinal tract exceeds excretion from the kidney In this context, hypermagnesemia is common in patients with advanced renal failure 15 — Dialysate magnesium plays a critical role in determining serum magnesium level in peritoneal dialysis patients 15 — In the present study, the mean peritoneal dialysate calcium level was 3.
These results suggest that dialysate magnesium plays a critical role in determining serum magnesium level in peritoneal dialysis patients 15 — It is well known that serum iPTH level is correlated wtih bone forming rate, so serum iPTH level is regarded as a useful marker for detecting renal osteodystrophy 3 — 7. Recently, it is reported that the incidence of low-turnover osteodystrophy, including adynamic bone disease, has increased 5 — 7. Typically, these patients have relatively low levels of IPTH 3 — 7.
In the present study, serum iPTH level was not correlated with serum magnesium level among all 56 patients. However, it was inversely correlated with serum total calcium and ionized calcium levels. Serum iPTH level was positively correlated with alkaline phosphatase bony isoenzyme level and serum inorganic phosphate level. Serum iPTH level was positively correlated with alkaline phosphatase bony isoenzyme level.
But there was no correlation between serum iPTH level and serum inorganic phosphate level.