Modulates Parathyroid Hormone Research Articles

MiR-301a-5p modulates parathyroid hormone secretion in secondary hyperparathyroidism possibly by regulating calcium-sensing receptor

To explore the miRNAs that down- regulate calcium-sensing receptor (CaSR) in secondary hyperparathyroidism (SHPT) and their effects on parathyroid hormone (PTH) secretion. Whole transcriptome sequencing was performed for 6 normal parathyroid tissue samples and 11 SHPT parathyroid tissue samples. Based on bioinformatic prediction, we screened out 7 candidate miRNAs that regulate CaSR, among which the most likely miRNA for CaSR regulation was identified by double luciferase test. We detected the differential expression of miR-301a-5p and CaSR mRNA in SHPT and normal parathyroid tissue using qRT-PCR, and analyzed the correlation between their expressions and serum PTH levels of the patients. Western blotting was used to detect the expression of CaSR protein in primary SHPT parathyroid cells transfected with miR-301a-5p mimics or inhibitors, and the level of PTH in the supernatant of the cell culture was determined. Among the preliminarily selected 7 miRNAs that potentially regulate CaSR (miR-15a-5p, miR-15b-5p, miR- 16- 5p, miR- 221- 3p, miR- 222- 3p, miR- 301a- 5p and miR- 503- 5p), miR- 301a-5p was significantly upregulated in SHPT compared with normal parathyroid tissue (P < 0.05), and its expression appeared to be positively correlated with PTH level, but this correlation was not statistically significant (P > 0.05); The expression of CaSR mRNA was significantly downregulated in SHPT (P < 0.05), and its expression tended to inversely correlate with the patient's PTH level, but the correlation was not statistically significant (P > 0.05). In primary culture of SHPT parathyroid cells, miR-301a-5p overexpression caused a significant decrease of CaSR protein expression (P < 0.05), and conversely, inhibition of miR-301a-5p expression increased the expression of CaSR protein (P < 0.05). Although miR-301a-5p overexpression did not significantly affect PTH secretion of the cells (P > 0.05), inhibition of iR-301a-5p expression strongly increased the secretion of PTH (P < 0.05). MiR-301a-5p affects PTH secretion in SHPT possibly by regulating the expression of CaSR.

Inhibition of the calcium-sensing receptor by extracellular phosphate ions and by intracellular phosphorylation.

As both a sensor of extracellular calcium (Ca2+ o) concentration and a key controller of Ca2+ o homeostasis, one of the most interesting properties of the calcium-sensing receptor (CaR) is its sensitivity to, and modulation by, ions and small ligands other than Ca2+. There is emerging evidence that extracellular phosphate can act as a partial, non-competitive CaR antagonist to modulate parathyroid hormone (PTH) secretion, thus permitting the CaR to integrate mineral homeostasis more broadly. Interestingly, phosphorylation of certain intracellular CaR residues can also inhibit CaR responsiveness. Thus, negatively charged phosphate can decrease CaR activity both extracellularly (via association with arginine) and intracellularly (via covalent phosphorylation).

Insights into calcium-sensing receptor trafficking and biased signalling by studies of calcium homeostasis.

The calcium-sensing receptor (CASR) is a class C G-protein-coupled receptor (GPCR) that detects extracellular calcium concentrations, and modulates parathyroid hormone secretion and urinary calcium excretion to maintain calcium homeostasis. The CASR utilises multiple heterotrimeric G-proteins to mediate signalling effects including activation of intracellular calcium release; mitogen-activated protein kinase (MAPK) pathways; membrane ruffling; and inhibition of cAMP production. By studying germline mutations in the CASR and proteins within its signalling pathway that cause hyper- and hypocalcaemic disorders, novel mechanisms governing GPCR signalling and trafficking have been elucidated. This review focusses on two recently described pathways that provide novel insights into CASR signalling and trafficking mechanisms. The first, identified by studying a CASR gain-of-function mutation that causes autosomal dominant hypocalcaemia (ADH), demonstrated a structural motif located between the third transmembrane domain and the second extracellular loop of the CASR that mediates biased signalling by activating a novel β-arrestin-mediated G-protein-independent pathway. The second, in which the mechanism by which adaptor protein-2 σ-subunit (AP2σ) mutations cause familial hypocalciuric hypercalcaemia (FHH) was investigated, demonstrated that AP2σ mutations impair CASR internalisation and reduce multiple CASR-mediated signalling pathways. Furthermore, these studies showed that the CASR can signal from the cell surface using multiple G-protein pathways, whilst sustained signalling is mediated only by the Gq/11 pathway. Thus, studies of FHH- and ADH-associated mutations have revealed novel steps by which CASR mediates signalling and compartmental bias, and these pathways could provide new targets for therapies for patients with calcaemic disorders.

Vitamin D receptor agonist VS-105 directly modulates parathyroid hormone expression in human parathyroid cells and in 5/6 nephrectomized rats

Vitamin D receptor (VDR) agonists (VDRAs) are commonly used to treat secondary hyperparathyroidism (SHPT) associated with chronic kidney disease (CKD). Current VDRA therapy often causes hypercalcemia, which is a critical risk for vascular calcification. Previously we have shown that a novel VDRA, VS-105, effectively suppresses serum parathyroid hormone (PTH) without affecting serum calcium levels in 5/6 nephrectomized (NX) uremic rats. However, it is not known whether VS-105 directly regulates PTH gene expression. To study the direct effect of VS-105 on modulating PTH, we tested VS-105 and paricalcitol in the spheroid culture of parathyroid cells from human SHPT patients, and examined the time-dependent effect of the compounds on regulating serum PTH in 5/6 NX uremic rats (i.p. 3x/week for 14days). In human parathyroid cells, VS-105 (100nM) down-regulated PTH mRNA expression (to 3.6% of control) and reduced secreted PTH (to 43.9% of control); paricalcitol was less effective. VS-105 effectively up-regulated the expression of VDR (1.9-fold of control) and CaSR (1.8-fold of control) in spheroids; paricalcitol was also less effective. In 5/6 NX rats, one single dose of 0.05–0.2μg/kg of VS-105 or 0.02–0.04μg/kg of paricalcitol effectively reduced serum PTH by >40% on Day 2. Serum PTH remained suppressed during the dosing period, but tended to rebound in the paricalcitol groups. These data indicate that VS-105 exerts a rapid effect on suppressing serum PTH, directly down-regulates the PTH gene, and modulates PTH, VDR and CaSR gene expression more effectively than paricalcitol.

Disorders of the calcium-sensing receptor and partner proteins: insights into the molecular basis of calcium homeostasis.

The extracellular calcium (Ca2+o)-sensing receptor (CaSR) is a family C G protein-coupled receptor, which detects alterations in Ca2+o concentrations and modulates parathyroid hormone secretion and urinary calcium excretion. The central role of the CaSR in Ca2+o homeostasis has been highlighted by the identification of mutations affecting the CASR gene on chromosome 3q21.1. Loss-of-function CASR mutations cause familial hypocalciuric hypercalcaemia (FHH), whereas gain-of-function mutations lead to autosomal dominant hypocalcaemia (ADH). However, CASR mutations are only detected in ≤70% of FHH and ADH cases, referred to as FHH type 1 and ADH type 1, respectively, and studies in other FHH and ADH kindreds have revealed these disorders to be genetically heterogeneous. Thus, loss- and gain-of-function mutations of the GNA11 gene on chromosome 19p13.3, which encodes the G-protein α-11 (Gα11) subunit, lead to FHH type 2 and ADH type 2, respectively; whilst loss-of-function mutations of AP2S1 on chromosome 19q13.3, which encodes the adaptor-related protein complex 2 sigma (AP2σ) subunit, cause FHH type 3. These studies have demonstrated Gα11 to be a key mediator of downstream CaSR signal transduction, and also revealed a role for AP2σ, which is involved in clathrin-mediated endocytosis, in CaSR signalling and trafficking. Moreover, FHH type 3 has been demonstrated to represent a more severe FHH variant that may lead to symptomatic hypercalcaemia, low bone mineral density and cognitive dysfunction. In addition, calcimimetic and calcilytic drugs, which are positive and negative CaSR allosteric modulators, respectively, have been shown to be of potential benefit for these FHH and ADH disorders.

Magnesium modulates parathyroid hormone secretion and upregulates parathyroid receptor expression at moderately low calcium concentration

BackgroundThe interest on magnesium (Mg) has grown since clinical studies have shown the efficacy of Mg-containing phosphate binders. However, some concern has arisen for the potential effect of increased serum Mg on parathyroid hormone (PTH) secretion. Our objective was to evaluate the direct effect of Mg in the regulation of the parathyroid function; specifically, PTH secretion and the expression of parathyroid cell receptors: CaR, the vitamin D receptor (VDR) and FGFR1/Klotho.MethodsThe work was performed in vitro by incubating intact rat parathyroid glands in different calcium (Ca) and Mg concentrations.ResultsIncreasing Mg concentrations from 0.5 to 2 mM produced a left shift of PTH–Ca curves. 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 1.0 mM, the expression of parathyroid CaR, VDR, FGFR1 and Klotho (at mRNA and protein levels) was increased with a Mg concentration of 2.0 when compared with 0.5 mM.ConclusionsMg reduces PTH secretion mainly when a moderate low calcium concentration is present; Mg also modulates parathyroid glands function through upregulation of the key cellular receptors CaR, VDR and FGF23/Klotho system.

The calcium-sensing receptor mediates bone turnover induced by dietary calcium and parathyroid hormone in neonates

We have investigated, in neonates, whether the calcium-sensing receptor (CaR) mediates the effects of dietary calcium on bone turnover and/or modulates parathyroid hormone (PTH)–induced bone turnover. Wild-type (WT) pups and pups with targeted deletion of the Pth (Pth–/–) gene or of both Pth and CaR (Pth–/–CaR–/–) genes were nursed by dams on a normal or high-calcium diet. Pups nursed by dams on a normal diet received daily injections of vehicle or of PTH(1–34) (80 µg/kg) for 2 weeks starting from 1 week of age. In pups receiving vehicle and fed by dams on a normal diet, trabecular bone volume, osteoblast number, type 1 collagen–positive area, and mineral apposition rate, as well as the expression of bone-formation-related genes, all were reduced significantly in Pth–/– pups compared with WT pups and were decreased even more dramatically in Pth–/–CaR–/– pups. These parameters were increased in WT and Pth–/– pups but not in Pth–/–CaR–/– pups fed by dams on a high-calcium diet compared with pups fed by dams on a normal diet. These parameters also were increased in WT, Pth–/–, and Pth–/–CaR–/– pups following exogenous PTH treatment; however, the percentage increase was less in Pth–/–CaR–/– pups than in WT and Pth–/– pups. In vehicle-treated pups fed by dams on either the normal or high-calcium diet and in PTH-treated pups fed by dams on a normal diet, the number and surfaces of osteoclasts and the ratio of RANKL/OPG were reduced significantly in Pth–/– pups and less significantly in Pth–/–CaR–/– pups compared with WT pups. These parameters were further reduced significantly in WT and Pth–/– pups from dams fed a high-calcium diet but did not decrease significantly in similarly treated Pth–/–CaR–/– pups, and they increased significantly in PTH-treated pups compared with vehicle-treated, genotype-matched pups fed by dams on the normal diet. These results indicate that in neonates, the CaR mediates alterations in bone turnover in response to changes in dietary calcium and modulates PTH-stimulated bone turnover. © 2011 American Society for Bone and Mineral Research.

Vitamin D receptor ligand therapy in chronic kidney disease

Chronic kidney disease is a growing public health concern, and secondary hyperparathyroidism is one of the most serious associated comorbidities. In healthy individuals, precisely controlled feedback loops dynamically modulate parathyroid hormone (PTH) levels. As kidney function declines, phosphate retention, decreased 1a,25-dihydroxyvitamin D3, and a tendency to hypocalcemia leads to overstimulation of PTH production and parathyroid hyperplasia. Vitamin D receptor (VDR) ligands are essential tools for controlling parathyroid activity. This review highlights the current clinical and biochemical VDR ligand studies, focusing on the differences between selective and nonselective VDR ligands. It is apparent that VDR ligands have important roles in the management of secondary hyperparathyroidism. Selective VDR ligands, in particular, may offer additional benefits in the treatment of bone disease, and may potentially reduce adverse effects related to cardiovascular disease.

Role of the calcium-sensing receptor in parathyroid gland physiology.

The calcium-sensing receptor (CaSR) represents the molecular mechanism by which parathyroid cells detect changes in blood ionized calcium concentration and modulate parathyroid hormone (PTH) secretion to maintain serum calcium levels within a narrow physiological range. Much has been learned in recent years about the diversity of signal transduction through the CaSR and the various factors that affect receptor expression. Beyond its classic role as a determinant of calcium-regulated PTH secretion, signaling through the CaSR also influences both gene transcription and cell proliferation in parathyroid cells. The CaSR thus serves a broad physiological role by integrating several distinct aspects of parathyroid gland function. The current review summarizes recent developments that enhance our understanding of the CaSR and its fundamental importance in parathyroid gland physiology.

Calcium-sensing receptors

It is now known that variations in extracellular calcium concentration exert diverse physiologic effects in a variety of tissues that are mediated by a calcium-sensing receptor (CaSRs). In parathyroid tissue, the CaSR represents the molecular mechanism by which parathyroid cells detect changes in blood ionized calcium concentration, modulate parathyroid hormone (PTH) secretion accordingly, and thus maintain serum calcium levels within a narrow physiologic range. In the kidney, the CaSR regulates renal calcium excretion and influences the transepithelial movement of water and other electrolytes. More generally, activation of the CaSR represents an important signal transduction pathway in intestine, placenta, brain, and perhaps bone. Some of these actions involve cell cycle regulation, changes that may be relevant to understanding the pathogenesis of parathyroid gland hyperplasia in secondary hyperparathyroidism caused by chronic kidney disease. The CaSR represents an appealing target for therapeutic agents designed to modify parathyroid gland function in vivo, offering the prospect of novel therapies for selected disorders of bone and mineral metabolism. Other receptors capable of responding to extracellular calcium ions also have been identified, but the functional importance of these interactions remains to be determined.

Coupling of calcium receptors to inositol phosphate and cyclic AMP generation in mammalian cells and Xenopus laevis oocytes and immunodetection of receptor protein by region-specific antipeptide antisera.

Ca2+ and other divalent cations modulate parathyroid hormone secretion by interacting with cell-surface Ca2+-sensing receptors (CaRs). We assessed the ability of these receptors to couple to Ca2+ mobilization, inositol phosphate (InsP) accumulation, and cyclic AMP production in different expression systems. In Xenopus laevis oocytes injected with bovine parathyroid CaR cRNA, the addition of extracellular cations to 1.5 mM Ca2+, 5.5 mM Mg2+, or 10 microM Gd3+ significantly increased 45Ca efflux (p < 0.01). InsP accumulation also increased dramatically when adding these cations to human embryonic kidney (HEK) 293 cells stably transfected with wild-type bovine parathyroid CaR cDNA. Raising the extracellular [Ca2+] ([Ca2+]o) from 0.1 to > 1.4 mM in oocytes and to > 1.0 mM in HEK 293 cells stimulated significant increments in 45Ca efflux and InsP accumulation, respectively (p < 0.05). In contrast, Ca2+ and Mg2+ increased InsPs to a lesser extent in COS 7 cells transiently transfected with CaR cDNA. In HEK 293 cells stably expressing CaR cDNA, there were significant reductions in cAMP content when adding high Ca2+, Mg2+, Gd3+, or the CaR modulator NPS R-467. Three region-specific anti-CaR peptide antisera immunoblotted bands of approximately 140 and 155 kDa in membranes from CaR-transfected HEK 293 cells and bovine parathyroid tissue. Immunocytochemistry demonstrated strong cell-surface staining in CaR-transfected HEK 293 cells and parathyroid tissue, which was absent when antisera were preabsorbed with CaR peptides. These results indicate that the activation of the recombinant CaR by extracellular Ca2+ can couple negatively to adenylate cyclase but positively to phospholipase C (PLC), the latter at physiological [Ca2+]o.

Dexamethasone enhances the effects of parathyroid hormone on human periodontal ligament cells in vitro.

Periodontal ligament cells (PDL) are thought to play a major role in promoting periodontal regeneration. Recent studies, focused on characterizing PDL cells, have been directed at establishing their osteoblast-like properties and determining biological mediators and/or factors that induce osteoblastic cell populations in the PDL. The glucocorticoid, dexamethasone (Dex), has been shown to selectively stimulate osteoprogenitor cell proliferation and to induce osteoblastic cell differentiation in many cell systems. In the present study the ability of Dex to modulate parathyroid hormone (PTH)-stimulated cAMP synthesis in cultured human PDL cells was examined. PDL cells, obtained from premolar teeth extracted for orthodontic reasons, were cultured with Dex (0-1000 nM) for 7 days prior to PTH (1-34) stimulation. The exposure of PDL cells to Dex resulted in a dose-dependent increase in cAMP production in response to PTH stimulation. This response was seen in cells obtained from three different patients. The first significant Dex effect was seen on day 7 when compared to day 1 for 100 nM Dex. PTH (1-34) stimulation caused a dose-dependent increase in cAMP synthesis after Dex (1000 nM) treatment for 7 days. Conversely, stimulation of the cells with PTH (7-34) (0-1000 nM) did not increase cAMP production in PDL cells after Dex treatment. Forskolin- (1 microM) and isoproterenol- (1 microM) stimulated cAMP synthesis was not augmented by Dex treatment. Dex treatment did not alter calcitonin-(1 microM) stimulated cAMP production in PDL cells. Glucocorticoid enhancement of PTH-stimulated cAMP synthesis in these cells supports the presence of an osteoblast-like population in the PDL, in vitro.

Bidirectional modulation of parathyroid hormone-responsive adenylyl cyclase by protein kinase C.

The temporal pattern with which phorbol 12-myristate 13-acetate (PMA), an activator of protein kinase C (PKC), modulates parathyroid hormone (PTH)-responsive adenylyl cyclase (AC) was evaluated in a clonal osteoblast-like cell line (UMR-106). Brief (< or = 1 h) exposure of UMR-106 cells to PMA enhanced PTH stimulation of AC, whereas more prolonged PMA treatment decreased the PTH response, with maximum inhibition occurring at < or = 6 h. PMA treatment also resulted in initial activation followed by downregulation of PKC. Exposure of cells to 1,2-dioctanoyl-sn-glycerol, which activated but did not downregulate PKC, resulted in bidirectional modulation of PTH-responsive AC identical to that produced by PMA. Prolonged PMA exposure decreased PTH receptor number, as determined by radioligand binding studies, and reduced PTH receptor mRNA levels, assessed by Northern blot analysis. Forskolin activation of the catalytic subunit of AC was also decreased after prolonged PMA treatment. The results suggest that activation of PKC sequentially stimulates and then inhibits PTH responsiveness. Inhibition of the PTH response occurs by PKC actions exerted on the PTH receptor and the AC catalytic subunit.

Protein kinase C modulates parathyroid hormone- but not prostaglandin E2-mediated stimulation of cyclic AMP production via the inhibitory guanine nucleotide binding protein in UMR-106 osteosarcoma cells.

In UMR-106 osteosarcoma cells we found that PTH activated both the cAMP/protein kinase A and the Ca(2+)-dependent phosphoinositide/protein kinase C (PKC) pathways, but prostaglandin E2 (PGE2) activated only the cAMP pathway. Activation of PKC by the phorbol ester PMA had no effect on cAMP production but enhanced PTH-stimulated cAMP production by 50% or more; the effect on PGE2-induced cAMP was negligible. Inhibition of the alpha-subunit of the inhibitory guanine nucleotide binding protein (Gi) by pertussis toxin pretreatment also enhanced PTH-mediated cAMP production but had no effect on PGE2-induced cAMP production. These results suggest that although PTH-mediated adenylate cyclase activity is regulated via both the stimulatory (Gs) and inhibitory (Gi) guanine nucleotide binding proteins, only Gs regulates PGE2-mediated adenylate cyclase activity in UMR-106 cells. Costimulation with pertussis toxin and PMA did not increase PTH-stimulated cAMP production above that obtained with PMA alone. This implies a similar target of action for pertussis toxin and PMA, that is, the alpha-subunit of Gi. The alpha-subunit of Gi was found to be a substrate for in vitro PKC phosphorylation of membrane fractions from UMR-106 cells, seen as a +/- 40 kD band on SDS-PAGE. Stimulation of in situ 32P-labeled cells with either PMA or PTH also enhanced incorporation of 32P into the 40 kD band. Using the peptide antisera AS/7 and EC/2, we showed that pertussis toxin-labeled subunits of both Gi1 alpha/Gi2 alpha and Gi3 alpha could be immunoprecipitated, respectively, but immunoprecipitation of membrane proteins after in situ phosphorylation and stimulation with PMA precipitated only Gi2 alpha.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of beta-adrenergic blockade in an osteoblast-like cell line.

The beta-adrenergic blocking agent propranolol was shown in previous studies to increase orthotopic bone formation in rats. To understand the cellular mechanisms underlying this observation, propranolol was tested for its effects on osteoblastic cells, which possess adenylate cyclase-coupled beta-adrenergic receptors. The ability of propranolol to modulate parathyroid hormone (PTH) and isoproterenol effects on adenylate cyclase activity and on alkaline phosphatase expression was studied in the osteoblast-like rat osteosarcoma cell line ROS 17/2.8. At concentrations between 0.1 and 10 microM, DL-propranolol specifically inhibited adenylate cyclase stimulation by the beta-adrenergic agonist isoproterenol, but did not alter either basal or PTH-stimulated activity. At these concentrations, propranolol also blunted the inhibition of alkaline phosphatase activity by isoproterenol but not PTH. Propranolol alone had minimal effects on ROS alkaline phosphatase activity at low concentrations (0.1-1 microM), but became inhibitory at high concentrations (10-100 microM). Thus, the direct effects of physiologically relevant propranolol concentrations on osteoblastic cells can be attributed principally to beta-adrenergic blockade. These findings further suggest that propranolol may enhance bone formation by preserving osteoblastic activity in the face of inhibition by beta-adrenergic agonists.

Abnormal calcium distribution in human parathyroid adenomas as possible cause of primary hyperparathyroidism.

Current knowledge suggests that normal parathyroid glands and parathyroid adenomas have different sensitivities to environmental calcium. In search for morphological equivalents, 5 normal human and 10 porcine parathyroid glands, as well as 10 human parathyroid adenomas were investigated with regard to intracellular and extracellular calcium distribution. The glands were incubated for 2, 4, 6 and 20 h in tissue cultures using HAM's F10 medium with various calcium concentrations. For visualization of the calcium distribution in the tissue the method of pyroantimonate precipitation was applied. Specificity of the reaction was controlled by X-ray microanalysis. Shifts of the calcium pyroantimonate precipitates were quantitated by morphometry using an area-counting system. The results demonstrate that in normal parathyroid glands calcium precipitates are distributed randomly. Incubation of normal glands in medium with low calcium concentration (0.6 mM) provoked reduced amounts of intracellular and extracellular calcium complexes. When the incubations were performed in medium with high calcium content (2.6 mM), calcium accumulated inside parathyroid and stroma cells. In contrast to normal parathyroid glands, parathyroid adenomas fixed immediately after surgery showed an atypical calcium distribution with low amounts of intracellular and high amounts of extracellular calcium grains. The data suggest that in normal parathyroid glands the intracellular calcium concentration follows the extracellular environmental calcium concentration. Thus, calcium modulates parathyroid hormone (PTH) secretion via intracellular regulatory mechanisms. In parathyroid adenomas the calcium transport via the tumor cell membrane appears to be disturbed resulting in lowered intracellular calcium levels. This is remarkable since the environmental calcium concentration is elevated due to the hypercalcemia of primary hyperparathyroidism.(ABSTRACT TRUNCATED AT 250 WORDS)

Hydroxycholecalciferols modulate parathyroid hormone and calcitonin sensitive adenylyl cyclase in bone and kidney of rats: A possible physiological role for 24,25-dihydroxy vitamin D 3

In particulate fractions from rat bone cells, but not from kidney, 24,25-(OH) 2 D 3 inhibits in a dose dependent manner (1 nM and above) the parathyroid hormone (PTH)-activated adenylyl cyclase. In contrast, 24,25-(OH) 2D 3 enhances the calcitonin(CT) stimulated cyclase in bone, but attenuates the CT-induced cyclase response in kidney. In Supranormal concentrations 1,25-(OH) 2D 3 is also able to reduce the PTH-stimulated adenylyl cyclase in bone. In comparison, neither vitamin D 3 metabolite interferes with stimulation of adenylyl cyclase from pituitary cell membranes by thyroliberin (TRH) or vasoactive intestinal polypeptide (VIP). These findings may have important therapeutical consequences in preventing excessive PTH action and bone demineralization.