Parathyroid hormone-related peptide (PTHrP)

PTHrP, which causes humoral malignant hypercalcaemia in man and animals, acts on bone and kidney in a way similar to that of parathyroid hormone. PTHrP released by fetal parathyroid glands stimulates placental calcium transport in pregnant ewes and maintains the calcium gradient from the dam to its foetus. PTHrP, which is also present in the mammary gland, colostrum and milk, might play an important physiological role in regulating calcium secretion through milk and calcium metabolism in newborn animals.     

Dexamethasone treatment improves sarcoplasmic reticulum function and contractile performance in aged myocardium

Corticosteroids are thought to be involved in the maintenance of normal myocardial function by mechanisms incompletely understood. This study investigated the potential therapeutic benefit of the synthetic glucocorticoid, dexamethasone, in reversing age-associated deterioration in cardiac contractile performance and Ca2+ sequestration function of the sarcoplasmic reticulum. Dexamethasone was administered to senescent (26-28-month old), male Fischer 344 rats at a rate of 4 microg/h for 5 days via subcutaneously implanted osmotic mini pumps. Control rats received vehicle solution in similar manner. Contractile performance was assessed in Langendorff-perfused, electrically paced hearts from control and dexamethasone-treated rats. The results obtained showed that dexamethasone-treatment of aged rats resulted in significant improvement in myocardial contractile performance as evidenced by (i) increase (approximately 30-60%) in developed peak tension at a wide range of beating frequencies (2-6 Hz), (ii) unaltered time to peak tension, and (iii) decrease (approximately 8-15%) in time to half-relaxation. Also, SR isolated from dexamethasone-treated rats displayed approximately 2-fold higher rates of ATP-energized Ca2+ uptake compared to SR from control rats. The deficits in contractile performance of the senescent heart (prolonged contraction duration and diminished contractile force) are reversible through a glucocorticoid-mediated improvement in SR Ca2+ pump function.     

Influence of insulin and free fatty acids on contractile function in patients with chronically stunned and hibernating myocardium

It is unknown whether short-term modulation of substrate supply affects cardiac performance in heart failure patients with chronic ischemic myocardium. The aim of this study was to determine whether modulation of myocardial substrate metabolism with insulin and free fatty acids (FFAs) affects contractile function of chronically stunned (CST) and hibernating (HIB) myocardium at rest and after maximal exercise. We studied eight nondiabetic patients with ejection fraction (EF) 30 +/- 4% (SE) and CST/HIB in 49 +/- 6% of the left ventricle: 36 +/- 6% CST and 13 +/- 2% HIB as determined by 99m Technetium-Sestamibi single photon emission computed tomography (SPECT) and [18F]fluorodeoxyglucose (FDG) positron emission tomography (PET). Each patient was subjected to a 3-h infusion of 1) saline, 2) insulin-glucose (i.e., euglycemic insulin clamp; high insulin, suppressed FFA), and 3) somatostatin-heparin (suppressed insulin, high FFA). Echocardiographic endpoints were global EF and regional contractile function [maximum velocity (Vmax) and strain rate (epsilon max)] as determined by tissue Doppler imaging at steady state and after maximal exercise. EF was similar at baseline and steady state and increased after exercise to 36 +/- 5% (P < 0.05). Baseline regional Vmax and epsilon max were highest in control, intermediate in CST and HIB, and lowest in infarct regions (P < 0.05). Steady-state EF, Vmax, and epsilon max were not affected by metabolic modulation in any region. After maximal exercise, contractile function increased in control, CST, and HIB (P < 0.05), but not in infarct, regions. Exercise-induced contractile increments were unaffected by metabolic modulation. Metabolic modulation does not influence contractile function in CST and HIB regions. Chronic ischemic myocardium has preserved ability to adapt to extreme, short-term changes in substrate supply at rest and after maximal exercise.     

Parathyroid hormone and parathyroid hormone-related peptide, and their receptors

Parathyroid hormone (PTH) has a central role in the regulation of serum calcium and phosphate, while parathyroid hormone-related peptide (PTHrP) has important developmental roles. Both peptides signal through the same receptor, the PTH/PTHrP receptor (a class B G-protein-coupled receptor). The different biological effects of these ligands result from their modes of regulation and secretion, endocrine vs. paracrine/autocrine. The importance of PTH and PTHrP is evident by the variety of clinical syndromes caused by deficiency or excess production of either peptide, and the demonstration that intermittent injection of PTH increases bone mass, and thus provides a means to treat osteoporosis. This, in turn, has triggered increased interest in understanding the mechanisms of PTH/PTHrP receptor action and the search for smaller peptide or non-peptide agonists that have efficacy at this receptor when administered non-parenterally.     

Parathyroid hormone-related peptide as an endogenous inducer of parietal endoderm differentiation

Parathyroid hormone related peptide (PTHrP), first identified in tumors from patients with the syndrome of "Humoral Hypercalcemia of Malignancy," can replace parathyroid hormone (PTH) in activating the PTH-receptor in responsive cells. Although PTHrP expression is widespread in various adult and fetal tissues, its normal biological function is as yet unknown. We have examined the possible role of PTHrP and the PTH/PTHrP-receptor in early mouse embryo development. Using F9 embryonal carcinoma (EC) cells and ES-5 embryonic stem (ES) cells as in vitro models, we demonstrate that during the differentiation of these cells towards primitive and parietal endoderm-like phenotypes, PTH/PTHrP-receptor mRNA is induced. This phenomenon is correlated with the appearance of functional adenylate cyclase coupled PTH/PTHrP- receptors. These receptors are the mouse homologues of the recently cloned rat bone and opossum kidney PTH/PTHrP-receptors. Addition of exogenous PTH or PTHrP to RA-treated EC or ES cells is an efficient replacement for dBcAMP in inducing full parietal endoderm differentiation. Endogenous PTHrP is detectable at very low levels in undifferentiated EC and ES cells, and is upregulated in their primitive and parietal endoderm-like derivatives as assessed by immunofluorescence. Using confocal laser scanning microscopy on preimplantation mouse embryos, PTHrP is detected from the late morula stage onwards in developing trophectoderm cells, but not in inner cell mass cells. In blastocyst stages PTHrP is in addition found in the first endoderm derivatives of the inner cell mass. Together these results indicate that the PTH/PTHrP-receptor signalling system serves as a para- or autocrine mechanism for parietal endoderm differentiation in the early mouse embryo, thus constituting the earliest hormone receptor system involved in embryogenesis defined to date.     

Parathyroid hormone-related peptide (hPTHrP) and parathyroid hormone-related peptide receptor type 1 (PTHR1) expression in human thymus.

Parathyroid hormone-related peptide (hPTHrP) is expressed in human tissues and regulates cellular proliferation, differentiation, and apoptosis by an autocrine/paracrine loop. In rodent thymus, both parathormone and parathyroid hormone-related peptide (PTHrP) are expressed by thymic epithelial cells (TECs). The present study demonstrated by RT-PCR and immunohistochemistry that hPTHrP and parathyroid hormone-related peptide receptor type 1 (PTHR1) were expressed in human thymus at both RNA and protein levels. hPTHrP was expressed mainly in the thymic medulla by epithelial (cytokeratin-positive), mature dendritic (CD40+/86+) and plasmacytoid interleukin (IL)-3Ralpha1 cells. This protein was also present in some cells forming Hassall's bodies and a few subcapsular and cortical TECs. PTHR1 was expressed by scattered subcapsular and cortical TECs and by rare TECs in the medulla. Thymocytes did not express either hPTHrP or PTHR1. Primary cultures of human TECs revealed the presence of both hPTHrP and PTHR1 mRNAs, confirming the capacity of TECs to synthesize both peptides. Moreover, synthetic (1-39) hPTHrP peptide administered on cultured TECs induced the expression of IL-6 mRNA, suggesting that hPTHrP can regulate thymic functions by inducing in TECs the expression of IL-6, which is involved in the development and maturation of thymocytes.     

Parathyroid hormone-related protein induction in focal stroke: a neuroprotective vascular peptide

Parathyroid hormone-related protein (PTHrP) is a multifunctional peptide that enhances blood flow in non-central nervous system (CNS) vascular beds by causing vasodilation. PTHrP expression is induced in non-CNS organs in response to ischemia. Experiments were therefore undertaken to determine whether PTHrP can be induced in brain in response to ischemic injury and whether PTHrP can act locally as a vasodilator in the cerebral vasculature, an effect that could be neuroprotective in the setting of stroke. PTHrP expression was examined by Northern analysis and immunohistochemical staining in male Sprague-Dawley rats subjected to permanent middle cerebral artery occlusion (MCAO). Vasodilatory effects of superfused PTHrP(1-34) on pial arterioles were determined by intravital fluorescence microscopy. Effects of PTHrP(1-34) peptide administration on MCAO infarction size reduction were assessed. PTHrP expression was induced in the ischemic hemisphere as early as 4 h after MCAO and remained elevated for up to 24 h. Increased immunoreactive PTHrP at sites of ischemic tissue injury was located in the cerebral microvessels. Superfusion with PTHrP(1-34) peptide for up to 25 min increased pial arteriolar diameter by 30% in normal animals. In animals with permanent MCAO, PTHrP(1-34) peptide treatment significantly decreased cortical infarct size (-47%). In summary, PTHrP expression increases at sites of ischemic brain injury in the cerebrovasculature. This local increase in PTHrP could be an adaptive response that enhances blood flow to the ischemic brain, thus limiting cell injury.     

Smooth muscle cell transplantation improves bladder contractile function in streptozocin-induced diabetic rats

Background aimsDamage to smooth muscle has been the primary cause of dysfunction in diabetic bladders. Major changes in the filling phase of the bladder result in the loss of compliance and incomplete emptying in patients.MethodsCell-based therapies in the lower urinary tract have shown promising results. We argue that because diabetic bladder dysfunction is primarily a problem arising out of altered smooth muscle cells (SMCs), it would be an interesting approach to introduce healthy SMCs into the bladder wall.ResultsFurthering this hypothesis, in this experiment, we were successful in introducing syngeneic, healthy SMCs into diabetic bladders. We attempted a method wherein bladder function can be improved in streptozocin-induced diabetes mellitus. Ex vivo–cultured healthy SMCs were introduced into the diabetic bladders of syngeneic Sprague-Dawley rats during the hypercontractile phase after induction of diabetes. Cystometry, metabolic cage evaluation, organ bath studies and histological analyses were performed on the healthy control, the diabetic and the diabetic group transplanted with SMCs.ConclusionsDuring the 2-week follow-up period after transplantation, we noticed an increase in contractile response of the bladder correlating to a decrease in residual urine. Cell survival studies revealed a cell survival rate close to 1.5%.     

Glibenclamide improves postischemic recovery of myocardial contractile function in trained and sedentary rats.

In this study, we sought to determine whether there was any evidence for the idea that cardiac ATP-sensitive K+ (K(ATP)) channels play a role in the training-induced increase in the resistance of the heart to ischemia-reperfusion (I/R) injury. To do so, the effects of training and an K(ATP) channel blocker, glibenclamide (Glib), on the recovery of left ventricular (LV) contractile function after 45 min of ischemia and 45 min of reperfusion were examined. Female Sprague-Dawley rats were sedentary (Sed; n = 18) or were trained (Tr; n = 17) for >20 wk by treadmill running, and the hearts from these animals used in a Langendorff-perfused isovolumic LV preparation to assess contractile function. A significant increase in the amount of 72-kDa class of heat shock protein was observed in hearts isolated from Tr rats. The I/R protocol elicited significant and substantial decrements in LV developed pressure (LVDP), minimum pressure (MP), rate of pressure development, and rate of pressure decline and elevations in myocardial Ca(2+) content in both Sed and Tr hearts. In addition, I/R elicited a significant increase in LV diastolic stiffness in Sed, but not Tr, hearts. When administered in the perfusate, Glib (1 microM) elicited a normalization of all indexes of LV contractile function and reductions in myocardial Ca(2+) content in both Sed and Tr hearts. Training increased the functional sensitivity of the heart to Glib because LVDP and MP values normalized more quickly with Glib treatment in the Tr than the Sed group. The increased sensitivity of Tr hearts to Glib is a novel finding that may implicate a role for cardiac K(ATP) channels in the training-induced protection of the heart from I/R injury.     

Parathyroid hormone-related peptide mediates hypercalcemia in an islet cell tumor of the pancreas.

Hypercalcemia occurring in a patient with an islet cell carcinoma of the pancreas suggests the diagnosis of Multiple Endocrine Neoplasia Type I and associated hyperparathyroidism. We describe a patient with an islet cell carcinoma and hypercalcemia in whom low concentrations of PTH, the absence of skeletal metastases, hypophosphatemia, and elevated nephrogenous cAMP alternatively suggested the syndrome of humoral hypercalcemia of malignancy. The peptide PTHrP was measured in the patient's serum during the course of therapy by an immunoradiometric assay directed toward the midportion of the molecule. Hypercalcemia was treated with an investigational aminobisphosphonate. The concentration of PTHrP[56-86] increased over time and fell after the patient received chemotherapy directed toward the islet cell tumor.     

Parathyroid hormone-related peptide is a naturally occurring,protein kinase A-dependent angiogenesis inhibitor

Angiogenesis is a highly regulated process that results from the sequential actions of naturally occurring stimulators and inhibitors. Here, we show that parathyroid hormone-related peptide, a peptide hormone derived from normal and tumor cells that regulates bone metabolism and vascular tone, is a naturally occurring angiogenesis inhibitor. Parathyroid hormone-related peptide or a ten-amino-acid peptide from its N terminus inhibits endothelial cell migration in vitro and angiogenesis in vivo by activating endothelial cell protein kinase A. Activation of protein kinase A inhibits cell migration and angiogenesis by inhibiting the small GTPase Rac. In contrast, inhibition of protein kinase A reverses the anti-migratory and anti-angiogenic properties of parathyroid hormone-related peptide. These studies show that parathyroid hormone-related peptide is a naturally occurring angiogenesis inhibitor that functions by activation of protein kinase A.     

Parathyroid hormone-related protein reduces alveolar epithelial cell proliferation during lung injury in rats

Parathyroid hormone-related protein (PTHrP) is a growth inhibitor for alveolar type II cells and could be a regulatory factor for alveolar epithelial cell proliferation after lung injury. We investigated lung PTHrP expression in rats exposed to 85% oxygen. Lung levels of PTHrP were significantly decreased between 4 and 8 days of hyperoxia, concurrent with increased expression of proliferating cell nuclear antigen and increased incorporation of 5-bromo-2'-deoxyuridine (BrdU) into DNA in lung corner cells. PTHrP receptor was present in both normal and hyperoxic lung. To test whether the fall in PTHrP was related to cell proliferation, we instilled PTHrP into lungs on the fourth day of hyperoxia. Eight hours later, BrdU labeling in alveolar corner cells was 3.2 +/- 0.4 cells/high-power field in hyperoxic PBS-instilled rats compared with 0.5 +/- 0.3 cells/high-power field in PTHrP-instilled rats (P < 0. 01). Thus PTHrP expression changes in response to lung injury due to 85% oxygen and may regulate cell proliferation.     

Role of calmodulin in the contractile function of the myocardium

The effect of phenothiazines-trifluoroperazine frenolone, majeptile and aminazine on contractility of papillar muscle of Wistar male rats associated with short-term Ca-concentration increase up to 4 mM has been studied. There has been found the parameter-relaxation index-the change of which under the effect of phenothiazines (10(-5) M in all the cases) made use of significantly correlates with the constants, which reflect the similarity of given agents with calmodulin.     

L-propionylcarnitine and myocardial performance in stunned porcine myocardium

Recently, we showed that L-propionylcarnitine did not affect recovery of regional contractile function of porcine myocardium subjected to 1 h of low-flow ischemia followed by 2 hr of reperfusion. In that study, ischemia may have been too severe and/or the duration of reperfusion too short to detect a beneficial effect of the compound. Therefore, in the present study we investigated the effects of saline (control group; n = 14) or pretreatment with L-propionylcarnitine (3 days of 50 mg/kg p.o. b.i.d. + 50 mg/kg i.v. prior to the experiment; n = 13) on recovery of regional contractile function of the myocardium in open-chest anesthetized pigs, subjected to two cycles of 10 min of left anterior descending coronary artery (LADCA) occlusion, each followed by 30 min of reperfusion. In the control animals, at the end of the second reperfusion period, systemic vascular resistance had increased by 18%, which, however, was not observed in the L-propionylcarnitine-treated pigs. In the control group, during the first occlusion, systolic segment length shortening (SSLS) of the LADCA-perfused area decreased from 18.5 ± 5.5% to - 3.7 = 3.2%. After 30 min of reperfusion, SSLS of the LADCA-perfused area had only partially recovered to 6.2 ±5.9%. During the second occlusion-reperfusion cycle similar values for SSLS were observed. In the treated animals., SSLS of the LADCA-perfused area was slightly improved after the second occlusion-reperfusion cycle (p = 0.056). This effect did not result in an overall improvement in cardiac pump function. We conclude that in a model of myocardial stunning, L-propionylcarnitine prevents systemic vasoconstriction in response to ischemia and reperfusion and, possibly as a result of this effect, slightly ameliorates post-ischemic hypofunction. (Mol Cell Biochem116: 147–153, 1992)     

Increased cross-bridge cycling rate in stunned myocardium

It is well known that the implantation of bone marrow mononuclear cells (BM-MNCs) into ischemic hearts can induce angiogenesis and improve cardiac function after myocardial infarction, but the precise mechanisms of these actions are unclear. We hypothesize that the cytokines produced by BM-MNCs play a key role in this cell-based therapy. BM-MNCs from rats were cultured under normoxic or hypoxic (1% O2) conditions for 24 h, and then supernatants were collected for study. ELISA and Western blotting analysis showed that various cytokines, including VEGF, IL-1 beta, PDGF, and IGF-1, were produced from BM-MNCs, some of which were enhanced significantly under hypoxia stimulation. When compared with a control blank medium, the supernatants of BM-MNCs cultured under normoxic or hypoxic conditions inhibited apoptosis significantly and preserved the contractile capacity of isolated adult rat cardiomyocytes in vitro (P < 0.05). Using a rat model of acute myocardial infarction, we injected the supernatants of BM-MNCs or control medium intramyocardially on day 0 and then intraperitoneally on days 2, 4, and 6 after infarction. When compared with the control medium, the supernatants of BM-MNCs cultured under both normoxic or hypoxic conditions increased the microvessel density and decreased the fibrotic area in the infarcted myocardium significantly, contributing to remarkable improvement in cardiac function. Various cytokines were produced by BM-MNCs, and these cytokines contributed to functional improvement of the infarcted heart by directly preserving the contractile capacity of the myocardium, inhibiting apoptosis of cardiomyocytes, and inducing therapeutic angiogenesis of the infarcted heart.     

Exercise training improves systolic function in hypertensive myocardium

The general purpose of this study was to test the effect of exercise training on the left ventricular (LV) pressure-volume relationship (LV/PV) and apoptotic signaling markers in normotensive and hypertensive hearts. Four-month-old female normotensive Wistar-Kyoto rats (WKY; n = 37) and spontaneously hypertensive rats (SHR; n = 38) were assigned to a sedentary (WKY-SED, n = 21; SHR-SED, n = 19) or treadmill-trained (WKY-TRD, n = 16; SHR-TRD, n = 19) group (～60% Vo(2 peak), 60 min/day, 5 days/wk, 12 wk). Ex vivo LV/PV were established in isovolumic Langendorff-perfused hearts, and LV levels of Akt, phosphorylated Akt (Akt(Pi)), Bad, phosphorylated Bad (Bad(Pi)) c-IAP, x-IAP, calcineurin, and caspases 3, 8, and 9 were measured. Heart-to-body weight ratio was increased in SHR vs. WKY (P < 0.05), concomitant with increased calcineurin mRNA (P < 0.05). There was a rightward shift in the LV/PV (P < 0.05) and a reduction in systolic elastance (E(s)) in SHR vs. WKY. Exercise training corrected E(s) in SHR (P < 0.05) but had no effect on the LV/PV in WKY. Caspase 3 was increased in SHR-SED relative to WKY-SED, while Bad(Pi,) c-IAP, and x-IAP were significantly lower in SHR relative to WKY (P < 0.05). Exercise training increased Bad(Pi) in both WKY and SHR but did not alter caspase 9 activity in either group. While caspase 3 activity was increased with training in WKY (P < 0.05), it was unchanged with training in SHR. We conclude that moderate levels of regular aerobic exercise attenuate systolic dysfunction early in the compensatory phase of hypertrophy, and that a differential phenotypical response to moderate-intensity exercise exists between WKY and SHR.     

Transmural distribution of FDG uptake in stunned myocardium

Fasting [(18)F]fluoro-2-deoxyglucose (FDG) uptake is increased in viable, chronically dysfunctional myocardium, but the relationship to acute episodes of ischemia remains undefined. To investigate FDG uptake in acute stunning, chronically instrumented pigs (n = 9) and sham controls (n = 8) were studied while in a fasted, closed-chest, anesthetized state. One-hour partial occlusion reduced subendocardial flow from 1.24 +/- 0.14 to 0.35 +/- 0.06 ml. min(-1). g(-1) and wall thickening from 16.8 +/- 2.1 to 3.7 +/- 0.7%. Regional function remained depressed during reperfusion (8.3 +/- 1. 4%) despite the return of flow to resting levels. Triphenyl tetrazolium chloride staining showed no irreversible injury. FDG uptake in stunned myocardium was variably increased and averaged 1. 5-fold higher than that of normal regions, with no consistent transmural variation. Subgroup analysis showed that variability in FDG uptake was related to alterations in insulin levels that varied directly with ischemic risk region.