Expression and specific immunolocalization of the human parathyroid hormone/parathyroid hormone-related protein receptor in the uteroplacental unit

Parathyroid Hormone-Related Protein-induced Relaxation of Rat Uterine Arteries: Influence of the Endothelium During Gestation

OBJECTIVE

Parathyroid hormone-related protein (PTHrP) has been reported to relax different vessels. We investigated the influence of both endothelium and gestation on the relaxation of uterine arteries (UA), which supply blood to myometrium and placenta.

METHODS

Small uterine and mesenteric arteries (MA) with (E+) and without endothelium (E-) from day 20 pregnant (P) and nonpregnant (NP) rats were mounted in a myograph, precontracted with phenylephrine (PE) in a physiologic salt solution. Relaxations to PTHrP, acetylcholine, and forskolin were performed and expressed as a percentage of the PE-induced contraction. Blockade of nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) was also studied with Nomega-nitro-L-arginine methyl ester (L-NAME) and with charybdotoxin + apamin, respectively.

RESULTS

Gestation significantly increases maximal vasodilating effect of acetylcholine in UA (68% vs 52%, P < .05) and sensitivity to acetylcholine in small mesenteric vessels (P < .05). PTHrP relaxes uterine (maximal relaxation P: 32%, NP: 46%), as well as small MA (P: 68%, NP: 89%), but the maximal relaxation is significantly greater in NP than in P rats (P: 32%, NP: 46%, P < .01) in both vascular beds. In addition, in the UA of P rats, PTHrP only produces relaxation if functional endothelium is present; nevertheless in the absence of endothelium, forskolin still elicits relaxation (65%, P < .01). L-NAME significantly impairs relaxation of E+ UA (P < .05), and so does the association of charybdotoxin + apamin (P < .05). Thus, NO and EDHF contribute largely to this vasorelaxant effect.

CONCLUSION

PTHrP induces a relaxation on UA that is strongly endothelium-dependent during gestation, in contrast to what happens simultaneously in MA.

Bone development and mineral homeostasis in the fetus and neonate: roles of the calciotropic and phosphotropic hormones

Mineral and bone metabolism are regulated differently in utero compared with the adult. The fetal kidneys, intestines, and skeleton are not dominant sources of mineral supply for the fetus. Instead, the placenta meets the fetal need for mineral by actively transporting calcium, phosphorus, and magnesium from the maternal circulation. These minerals are maintained in the fetal circulation at higher concentrations than in the mother and normal adult, and such high levels appear necessary for the developing skeleton to accrete a normal amount of mineral by term. Parathyroid hormone (PTH) and calcitriol circulate at low concentrations in the fetal circulation. Fetal bone development and the regulation of serum minerals are critically dependent on PTH and PTH-related protein, but not vitamin D/calcitriol, fibroblast growth factor-23, calcitonin, or the sex steroids. After birth, the serum calcium falls and phosphorus rises before gradually reaching adult values over the subsequent 24-48 h. The intestines are the main source of mineral for the neonate, while the kidneys reabsorb mineral, and bone turnover contributes mineral to the circulation. This switch in the regulation of mineral homeostasis is triggered by loss of the placenta and a postnatal fall in serum calcium, and is followed in sequence by a rise in PTH and then an increase in calcitriol. Intestinal calcium absorption is initially a passive process facilitated by lactose, but later becomes active and calcitriol-dependent. However, calcitriol's role can be bypassed by increasing the calcium content of the diet, or by parenteral administration of calcium.

Parathyroid Hormone's Acute Effect on Vasodilatory Function

Parathyroid hormone (PTH) seems to affect the risk of cardiovascular disease. The aim of the present study was to investigate PTH's acute effect on endothelial vasodilatory function in forearm resistance vessels. Ten healthy subjects underwent forearm venous occlusion plethysmography. We measured forearm blood flow at baseline and at a stable, locally increased PTH level after intra-arterial infusion of metacholine and nitroprusside. The contralateral arm served as a control. Ionized calcium (Ca++) and PTH values were normal in all subjects at baseline (1.26 ± 0.02 mM/L, 3.6 ± 1.2 pM/L). After 30 minutes of PTH infusion, the PTH level increased in the active arm (13.8 ± 4.0 pM/L P < 0.01), while the Ca++ level was unchanged (1.25 ± 0.04; mM/L). Both the PTH and the Ca++ level in the contralateral arm remained unchanged, which indicates no systemic influence. The endothelial-dependent vasodilation was inversely correlated to the Ca++ level at baseline (r = -0.75, P < 0.05) and after PTH infusion (r = -0.68, P < 0.05). The vasodilatory function was not affected during PTH-infusion.

Expression and biological activity of parathyroid hormone-related peptide in pregnant rat uterine artery: any role for 8-iso-prostaglandin F2alpha?

PTHrP is produced in vessels and acts as a local modulator of tone. We recently reported that PTHrP(1-34) is able to induce vasorelaxation in rat uterine arteries, but in pregnancy, this response is blunted and becomes strictly endothelium dependent. The present study aimed to get insights into the mechanisms involved in these changes because the adaptation of uterine blood flow is essential for fetal development. On d 20 of gestation, RT-PCR analysis of uterine arteries showed that PTH/PTHrP receptor (PTH1R) mRNA expression was decreased, whereas that of PTHrP mRNA was increased. This was associated with a redistribution of the PTHrP/PTH1R system, with both PTH1R protein and PTHrP peptide becoming concentrated in the intimal layer of arteries from pregnant rats. On the other hand, the blunted vasorelaxation induced by PTHrP(1-34) in uterine arteries from pregnant rats was specifically restored by indomethacin and a specific cyclooxygenase-2 inhibitor, NS 398. This was associated with an increase in cyclooxygenase-2 expression and in 8-iso-prostaglandin F(2alpha) release when uterine arteries from pregnant rats were exposed to high levels of PTHrP(1-34). Most interestingly, 8-iso-prostaglandin F(2alpha) itself was able to increase PTHrP expression and reduce PTH1R expression in cultured rat aortic smooth muscle cells. These results suggest a local regulation of uterine artery functions by PTHrP during pregnancy resulting from PTH1R redistribution. Moreover, they shed light on a potential role of 8-iso-prostaglandin F(2alpha).

The role and regulation of the nuclear factor kappa B signalling pathway in human labour

Within the discipline of reproductive biology, our understanding of one of the most fundamental biological processes is lacking--the cellular and molecular mechanisms that govern birth. This lack of understanding limits our ability to reduce the incidence of labour complications. The incidence of labour complications including: preterm labour; cervical incompetence; and post-date pregnancies has not diminished in decades. The key to improving the management of human labour and delivery is an understanding of how the multiple processes that are requisite for a successful labour and delivery are coordinated to achieve a timely birth. Processes of human labour include the formation of: contraction associated proteins; inflammatory mediators (e.g. cytokines); uterotonic phospholipid metabolites (e.g. prostaglandins); and the induction of extracellular matrix (ECM) remodelling. Increasingly, it is becoming evident that labour onset and birth are the result of cross-talk between multiple components of an integrated network. This hypothesis is supported by recent data implicating various upstream regulatory pathways in the control of key labour-associated processes, including the activity of enzymes involved in the formation of prostaglandins and extracellular matrix remodelling, and mediators of inflammation. Clearly, the biochemical pathways involved in the formation of these mediators represent potential sites for intervention that may translate to therapeutic interventions to delay or prevent preterm labour and delivery. Available data strongly implicate the nuclear factor-kappaB (NF-kappaB) family as candidate upstream regulators of multiple labour-associated processes. Not only do these data warrant further detailed analysis of the involvement of these pathways in the process of human labour but also promise new insights into the key mechanisms that trigger birth and the identification of new therapeutic interventions that will improve the management of labour.

Effect of nuclear factor-kappa B inhibitors and peroxisome proliferator-activated receptor-gamma ligands on PTHrP release from human fetal membranes

Parathyroid hormone-related protein (PTHrP) has been implicated in many processes during normal and pathological pregnancies. In the human fetal membranes, PTHrP exhibits cytokine-like actions. We have recently shown that inhibitors of the nuclear factor-kappa B (NF-kappaB) and activators of the peroxisome proliferator-activated receptor (PPAR)-gamma signalling pathways down-regulate cytokine release from human gestational tissues. Therefore, the aim of this study was to determine whether NF-kappaB and PPAR-gamma also regulate PTHrP release from human fetal membranes. Human amnion and choriodecidua explants were incubated in the absence (control) or presence of two known NF-kappaB inhibitors (1, 5 and 10 mM sulphasalazine (SASP) or 5, 10 and 15 mM N-acetyl-cysteine (NAC)), and two PPAR-gamma ligands (15 and 30 microM 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)) or 15 and 30 microM troglitazone), under basal conditions. After 18 h incubation, the tissues were collected and NF-kappaB p65 DNA binding activity in nuclear extracts was assessed by ELISA, and the incubation medium was collected and the release of PTHrP was quantified by RIA. Treatment of amnion and choriodecidual tissues with SASP concentrations greater than 5 mM, 15 mM NAC, 30 microM 15d-PGJ(2) and 30 microM troglitazone significantly reduced the release of PTHrP (p < 0.05). This study demonstrates that PTHrP release from human fetal membranes is regulated by inhibitors of NF-kappaB, and ligands of PPAR-gamma.

Parathyroid hormone-related protein and its receptors: nuclear functions and roles in the renal and cardiovascular systems, the placental trophoblasts and the pancreatic islets

The cloning of the so-called 'parathyroid hormone-related protein' (PTHrP) in 1987 was the result of a long quest for the factor which, by mimicking the actions of PTH in bone and kidney, is responsible for the hypercalcemic paraneoplastic syndrome, humoral calcemia of malignancy. PTHrP is distinct from PTH in a number of ways. First, PTHrP is the product of a separate gene. Second, with the exception of a short N-terminal region, the structure of PTHrP is not closely related to that of PTH. Third, in contrast to PTH, PTHrP is a paracrine factor expressed throughout the body. Finally, most of the functions of PTHrP have nothing in common with those of PTH. PTHrP is a poly-hormone which comprises a family of distinct peptide hormones arising from post-translational endoproteolytic cleavage of the initial PTHrP translation products. Mature N-terminal, mid-region and C-terminal secretory forms of PTHrP are thus generated, each of them having their own physiologic functions and probably their own receptors. The type 1 PTHrP receptor, binding both PTH(1-34) and PTHrP(1-36), is the only cloned receptor so far. PTHrP is a PTH-like calciotropic hormone, a myorelaxant, a growth factor and a developmental regulatory molecule. The present review reports recent aspects of PTHrP pharmacology and physiology, including: (a) the identification of new peptides and receptors of the PTH/PTHrP system; (b) the recently discovered nuclear functions of PTHrP and the role of PTHrP as an intracrine regulator of cell growth and cell death; (c) the physiological and developmental actions of PTHrP in the cardiovascular and the renal glomerulo-vascular systems; (d) the role of PTHrP as a regulator of pancreatic beta cell growth and functions, and, (e) the interactions of PTHrP and calcium-sensing receptors for the control of the growth of placental trophoblasts. These new advances have contributed to a better understanding of the pathophysiological role of PTHrP, and will help to identify its therapeutic potential in a number of diseases.

Parathyroid hormone-related protein regulates the growth of orthotopic human lung tumors in athymic mice

BACKGROUND

Parathyroid hormone-related protein (PTHrP) has growth regulatory effects for many malignant cells and may influence the progression of carcinomas of the breast, prostate, and lung. In the current study, the authors investigated the in vivo and in vitro effects of PTHrP neutralizing antibody and PTHrP treatment on the growth of BEN cells, a human lung squamous cell carcinoma line that expresses PTHrP and its receptor.

METHODS

Orthotopic lung tumors were produced in 20 athymic mice with BEN-GFP cells (a clonal line that stably expresses green fluorescent protein [GFP]) by instilling suspensions of 3 x 10(6) cells per mouse into the lungs of anesthetized animals. The mice were divided into 2 groups receiving either subcutaneous mouse antihuman PTHrP antibodies or irrelevant mouse immunoglobulin (Ig) G (150 microg) twice weekly.

RESULTS

After 30 days, 6 of 10 mice receiving anti-PTHrP antibodies had lung tumors visible on macroscopic inspection, but only 1 of the 10 mice treated with irrelevant IgG had a lung tumor that was of that size (P < 0.01). GFP fluorescence was significantly greater in lung homogenates of the PTHrP antibody-treated mice than in the mice treated with IgG (6006 +/- 411 vs. 2907 +/- 282 relative fluorescent units, respectively; P < 0.001). Although neutralizing antibodies stimulated BEN cell lung tumor growth, exogenous PTHrP 1-34 treatment (0.01-1 nM) inhibited the growth of cultured BEN cells by approximately 40%.

CONCLUSIONS

Although PTHrP expression has been reported to be associated with more aggressive malignancies, the data from the current study suggest that PTHrP 1-34 was a paracrine growth inhibitor in BEN human lung carcinoma cells. The growth-related effects of PTHrP are complex, and can be both stimulatory and inhibitory.

Effect of parathyroid hormone-related peptide on human and rat myometrial contractility in vitro

OBJECTIVES

The aims of this study were primarily to investigate the effects of parathyroid hormone-related peptide (human fragment 1-34) on human nonpregnant and pregnant (nonlabor and labor) myometrial contractility in vitro and secondarily to compare these effects with those of parathyroid hormone-related peptide on rat myometrial contractility.

STUDY DESIGN

Isometric tension recording was performed under physiologic conditions in isolated myometrial strips obtained at hysterectomy and cesarean delivery and from Sprague-Dawley rats. The effect of cumulative additions of parathyroid hormone-related peptide (1, 10, and 100 nmol/L) on myometrial contractility was measured and the significance of results was assessed by 2-way analysis of variance.

RESULTS

Parathyroid hormone-related peptide exerted a statistically significant net relaxant effect on myometrial contractility in human nonpregnant myometrium (34.71%; P<.01), in human pregnant myometrium obtained before (18.27%; P <.05) but not after (10.32%; P>.05) the onset of labor, and in rat tissue (31.60%; P<.01).

CONCLUSIONS

Parathyroid hormone-related peptide exerts a relaxant effect on human and rat myometrial tissue. In human myometrium, sensitivity to parathyroid hormone-related peptide is reduced in pregnancy and abolished by the onset of labor.