Peripheral metabolism of [35S]parathyroid hormone in vivo: influence of alterations in calcium availability and parathyroid status

1989 ◽  
Vol 122 (1) ◽  
pp. 237-245 ◽  
Author(s):  
F. R. Bringhurst ◽  
A. M. Stern ◽  
M. Yotts ◽  
N. Mizrahi ◽  
G. V. Segre ◽  
...  
Keyword(s):  
Parathyroid Hormone ◽  
Plasma Concentrations ◽  
Biologically Active ◽  
High Calcium Intake ◽  
Amino Terminal ◽  
High Calcium ◽  
Calcium Availability ◽  
Peripheral Metabolism

ABSTRACT Parathyroid hormone (PTH) is rapidly metabolized, mainly by liver and kidney, to smaller fragments that are believed to be biologically inactive. The significance of this peripheral metabolism in the overall actions of PTH is unclear. Generation of circulating biologically active amino-terminal PTH fragments during metabolism in vivo has been suggested by certain observations in vitro, and what are believed to be amino-terminal fragments may be detectable in blood under pathological circumstances in vivo (such as renal failure and coexistent hyperparathyroidism) when highly sensitive assays are employed. We recently reported, however, that administration to normal rats of [35S]bovine PTH ([35S]bPTH) directly labelled at amino-terminal methionines, followed by high-resolution chromatographic analysis of extracted [35S]peptides, does not result in appearance of radioactive amino-terminal fragments in blood, even when the tracer is continuously infused to near-physiological plasma concentrations. We have now employed these techniques to address a second question regarding hormonal metabolism: is hormonal metabolism modified during metabolic perturbations such as changing calcium availability or altered levels of calciotrophic hormones? Metabolism of [35S-Met]bPTH (900 Ci/mmol), either alone or together with [3H-Pro]bPTH, however, did riot lead to alterations in the rate of hormonal clearance nor to detectable circulating amino-terminal fragments, either in calcium-deprived or thyroparathyroidectomized rats or when animals were first rendered intoxicated with vitamin D or maintained on a high calcium intake. Likewise, tissue localization and specific cleavage patterns of intact hormone in liver or kidney were all unaltered by these various manoeuvres. We conclude that regulation of peripheral metabolism of PTH does not exert important physiological control over the concentration of circulating biologically active PTH and that active amino-terminal fragments of the hormone are not released into blood even under circumstances of calcium deprivation or hypocalcaemia. Journal of Endocrinology (1989) 122, 237–245

Peripheral metabolism of PTH: fate of biologically active amino terminus in vivo

1988 ◽  
Vol 255 (6) ◽  
pp. E886-E893 ◽  
Author(s):  
F. R. Bringhurst ◽  
A. M. Stern ◽  
M. Yotts ◽  
N. Mizrahi ◽  
G. V. Segre ◽  
...  
Keyword(s):  
Specific Activity ◽  
Limited Proteolysis ◽  
High Specific Activity ◽  
Biologically Active ◽  
Amino Terminal ◽  
Liver And Kidney ◽  
Low Levels ◽  
Peripheral Metabolism

Clearance of intact parathyroid hormone (PTH) from blood is associated with rapid uptake by liver and kidney, limited proteolysis by tissue endopeptidases and, within minutes, appearance of circulating carboxyl-(COOH)-terminal PTH fragments. The fate of the corresponding amino(NH2)-terminal portion of the hormone during this peripheral metabolism is still unknown, however. To determine this, we have employed [35S]bovine PTH (bPTH) labeled to high specific activity at NH2-terminal methionines, which permits direct monitoring of the fate of the PTH NH2-terminus during metabolism in vivo. The [35S]PTH was administered by bolus or continuous intravenous infusion to anesthetized normal rats, to rats subjected to acute ablation of the liver, the kidneys, or both, and to rats receiving co-infusions of excess synthetic bPTH(1-34) NH2-terminal fragments. Analysis by high-resolution chromatographic techniques sensitive to 10(-13) M [35S]PTH peptides in plasma yields no evidence that peripheral metabolism of PTH generates circulating NH2-terminal fragments, even when special measures are taken to block clearance of such putative fragments from blood. We find that the NH2-terminus of PTH is rapidly degraded in situ by the liver but that both liver and especially kidney nevertheless contain low levels of NH2-terminal PTH fragments that, although not released into the blood, are large enough to be potentially active. Thus, the peripheral metabolism of PTH in normal animals does not normally lead to the formation of circulating amino terminal fragments of the hormone that might act independently of intact PTH on peripheral target tissues.

Effects of parathyroid hormone and the synthetic 1–34 amino-terminal fragment in rats and dogs

1983 ◽  
Vol 97 (1) ◽  
pp. 21-30
Author(s):  
R. W. Stevenson ◽  
J. A. Parsons
Keyword(s):  
Parathyroid Hormone ◽  
Infusion Rate ◽  
Calcium Absorption ◽  
Biological Activities ◽  
Direct Action ◽  
Plasma Calcium ◽  
Biologically Active ◽  
Amino Terminal ◽  
Active Fragments

Since the structural requirements for all known biological activities of parathyroid hormone (PTH(1–84)) are virtually satisfied by the amino-terminal 34 amino acid fragment, PTH(1–34), we investigated whether this fragment could elaborate the overall actions of the intact hormone in the whole animal by comparing the effects of equimolar infusions of each peptide to dogs and rats. Infusion of bovine PTH(1–84) (bPTH(1–84)) at 17 pmol/kg per h for 20 h to three dogs or at 100 and 200 pmol/kg per h to groups of six rats for 5 days produced greater hypercalcaemia (3·02±0·03, 2·52±0·07 and 3·24±0·11 mmol/l respectively) than equimolar infusions of human PTH(1–34) (hPTH(1–34)) (2·61±0·03, 2·46 ± 0·05 and 2·71 ±0·09 mmol/l respectively). A significant calcium rise was not observed in dogs until after 4 h of PTH infusion. No rise in plasma calcium was apparent in rats, however, until the third day of PTH infusion. Only in parathyroidectomized rats was there a rise in plasma calcium within 24 h of starting an infusion of PTH. The hypercalciuria and plasma phosphate responses in dogs during equimolar infusions of hPTH(1–34) and bPTH(1–84) were not significantly different. However, by day 5 of infusion in rats greater hypercalciuria was produced by bPTH(1–84). Although infusion of hPTH(1–34) and bPTH(1–84) caused rises in urinary cyclic AMP excretion (measured only in the dog) of immediate onset and equal magnitude, bPTH(1–84) tended to produce greater phosphaturia than hPTH(1–34) in both species. If the assumption is correct that the half-lives of hPTH(1–34) and bPTH(1–84) in the circulation are similar and provided that hPTH does not inherently have less biological activity than bPTH, then during equimolar infusions of these peptides into dogs and rats, the greater responses observed with bPTH(1–84) suggest that intact PTH may have a direct action of its own in vivo before being metabolized into smaller biologically active fragments. In additional experiments using parathyroidectomized rats, the infusion rate of bPTH(1–84) required to restore normocalcaemia was 26 pmol/kg per h. Although near-normal calcaemia and intestinal calcium absorption could still be maintained when the infusion rate was increased to 39 pmol/kg per h, hypercalciuria and phosphaturia became apparent.

Effect of high calcium intake on pressor responsivity in hypertensive rats

1987 ◽  
Vol 252 (6) ◽  
pp. H1112-H1119
Author(s):  
N. Stern ◽  
M. Golub ◽  
M. Nyby ◽  
M. Berger ◽  
P. Eggena ◽  
...  
Keyword(s):  
Calcium Intake ◽  
Vascular Reactivity ◽  
Pressor Response ◽  
Hypotensive Effect ◽  
Ang Ii ◽  
Hypertensive Rats ◽  
High Calcium Intake ◽  
High Calcium

Some proposed mechanisms for the hypotensive effect of high calcium intake involve reduction in vascular responsivity. To assess the effect of dietary calcium on vascular responsivity, spontaneously hypertensive rats (SHR) were placed on normal (N-Ca; 0.4%) or high (H-Ca; 2.8%) casein-based synthetic diet for 4 wk. Intraarterial pressure, pressor response to graded intravenous infusion of norepinephrine (NE) and angiotensin II (ANG II), and in vitro vascular reactivity of tail artery segments to NE and transmural nerve stimulation (TNS) were studied. Urinary electrolyte excretion, plasma renin activity (PRA), aldosterone, NE, and epinephrine (EPI) were also determined. H-Ca SHR had a lower intraarterial systolic and diastolic pressure. However, H-Ca SHR had greater in vivo pressor response to both ANG II and NE. Maximal contractile force developed by tail artery segments in vitro in response to NE and TNS was slightly, but not significantly, higher in H-Ca SHR. In vitro dose-response curves to NE and TNS were not significantly different. Although H-Ca SHR had increased urinary excretion of sodium throughout the study period, PRA and aldosterone levels were similar in both groups. Plasma NE and EPI levels in the two groups were also not different. Despite lowered intra-arterial blood pressure, H-Ca SHR exhibited enhanced pressor response to ANG II and NE in vivo and a similar in vitro vascular reactivity to NE and TNS when compared with N-Ca SHR. Our results do not support a role for alterations in vascular reactivity to NE or ANG II in the hypotensive effect of high calcium intake in SHR.(ABSTRACT TRUNCATED AT 250 WORDS)

FURTHER STUDIES ON HYPOTHALAMIC-PITUITARY-TESTICULAR FUNCTION IN OLD RATS

1979 ◽  
Vol 92 (2) ◽  
pp. 358-369 ◽  
Author(s):  
Karl M. Pirke ◽  
Beate Krings ◽  
Hermann-J. Vogt
Keyword(s):  
Old Age ◽  
Plasma Concentrations ◽  
Biologically Active ◽  
Repeated Injection ◽  
Lh Receptor ◽  
Male Wistar Rats ◽  
Old Rats ◽  
Lh Rh

ABSTRACT The dysfunction of the hypothalamic-pituitary-gonadal axis in old age was studied in 24-month old male Wistar rats which were compared with 3-month old animals. The hypothalamic LH-RH content and the pituitary LH were significantly lower in the old than in the young adult animals. The plasma concentrations of LH and testosterone were significantly higher in the young rats. The primary cause of these age-dependent changes probably is a hypothalamic dysfunction. When isolated Leydig cells of young and old rats were incubated in vitro, the testosterone secretion per cell was significantly smaller in old than in young cells with as well as without HCG stimulation. In vivo stimulation of rats by iv injection of biologically active iodinated hCG revealed that the intratesticular uptake of the gonadotrophin was not different in young and old rats. The testosterone response, however, was significantly reduced in old age. An in vitro "desensitisation" experiment in which the LH receptor capacity was artificially reduced demonstrated that the 40 % reduction of receptor capacity in old testes as described earlier will not impair the testicular uptake of gonadotrophin from blood. Repeated injection of hCG results in equally elevated testosterone concentrations in young and old rats.

Regulation of parathyroid hormone release in primary and secondary hyperparathyroidism studies in vivo and in vitro

1982 ◽  
Vol 101 (3) ◽  
pp. 408-413 ◽  
Author(s):  
C. Rudberg ◽  
G. Åkerström ◽  
S. Ljunghall ◽  
L. Grimelius ◽  
H. Johansson ◽  
...  
Keyword(s):  
Parathyroid Hormone ◽  
Serum Calcium ◽  
Absolute Number ◽  
High Calcium ◽  
Basal Release ◽  
Calcium Infusion ◽  
The Individual ◽  
Serum Pth

Abstract. The effects of calcium on parathyroid hormone (PTH) release were studied in vivo and in vitro in primary hyperparathyroidism (HPT) and in vitro in secondary HPT. In vivo the serum PTH was clearly reduced by intravenous calcium infusion in all the examined patients with primary HPT caused by adenoma. In vitro the release of PTH from dispersed parathyroid cells was likewise suppressed by raising the calcium concentrations in the incubation media, though in all cases a basal release of PTH still persisted even at high calcium concentrations. The degree of suppressibility in vitro varied, but in both primary HPT with adenoma and in secondary HPT it was inversely related to the patients' serum calcium values. These results suggest that the secretion of PTH in patients with primary and secondary HPT is not autonomous either in vivo or in vitro. Furthermore, the non-suppressible basal release of PTH indicates that a major cause for the increased secretion of PTH is the increased number of parenchymal cells. However, the degree of suppressibility of the individual cells rather than the absolute number of cells, seems to be of great importance for the individual serum calcium values in HPT.

Comparison of Specific Antibody, D-Phe-Pro-Arg-CH2Cl and Aprotinin for Prevention of In Vitro Effects of Recombinant Tissue-Type Plasminogen Activator on Haemostasis Parameters

1987 ◽  
Vol 58 (03) ◽  
pp. 921-926 ◽  
Author(s):  
E Seifried ◽  
P Tanswell
Keyword(s):  
Specific Antibody ◽  
Plasma Concentrations ◽  
Fibrinolytic Therapy ◽  
Tissue Type ◽  
Control Value ◽  
Type Plasminogen Activator ◽  
In Vitro Effects ◽  
Fibrinolytic Parameters

SummaryIn vitro, concentration-dependent effects of rt-PA on a range of coagulation and fibrinolytic assays in thawed plasma samples were investigated. In absence of a fibrinolytic inhibitor, 2 μg rt-PA/ml blood (3.4 μg/ml plasma) caused prolongation of clotting time assays and decreases of plasminogen (to 44% of the control value), fibrinogen (to 27%), α2-antiplasmin (to 5%), FV (to 67%), FVIII (to 41%) and FXIII (to 16%).Of three inhibitors tested, a specific polyclonal anti-rt-PA antibody prevented interferences in all fibrinolytic and most clotting assays. D-Phe-Pro-Arg-CH2Cl (PPACK) enabled correct assays of fibrinogen and fibrinolytic parameters but interfered with coagulometric assays dependent on endogenous thrombin generation. Aprotinin was suitable only for a restricted range of both assay types.Most in vitro effects were observed only with rt-PA plasma concentrations in excess of therapeutic values. Nevertheless it is concluded that for clinical application, collection of blood samples on either specific antibody or PPACK is essential for a correct assessment of in vivo effects of rt-PA on the haemostatic system in patients undergoing fibrinolytic therapy.

Metabolomics of Healthy Berry Fruits

2019 ◽  
Vol 25 (37) ◽  
pp. 4888-4902 ◽  
Author(s):  
Gilda D'Urso ◽  
Sonia Piacente ◽  
Cosimo Pizza ◽  
Paola Montoro
Keyword(s):  
Biological Activities ◽  
Biologically Active ◽  
In Vivo Studies ◽  
Bioactive Metabolites ◽  
Active Metabolites ◽  
Positive Effects ◽  
Cell Functions ◽  
Berry Fruits

The consumption of berry-type fruits has become very popular in recent years because of their positive effects on human health. Berries are in fact widely known for their health-promoting benefits, including prevention of chronic disease, cardiovascular disease and cancer. Berries are a rich source of bioactive metabolites, such as vitamins, minerals, and phenolic compounds, mainly anthocyanins. Numerous in vitro and in vivo studies recognized the health effects of berries and their function as bioactive modulators of various cell functions associated with oxidative stress. Plants have one of the largest metabolome databases, with over 1200 papers on plant metabolomics published only in the last decade. Mass spectrometry (MS) and NMR (Nuclear Magnetic Resonance) are the most important analytical technologies on which the emerging ''omics'' approaches are based. They may provide detection and quantization of thousands of biologically active metabolites from a tissue, working in a ''global'' or ''targeted'' manner, down to ultra-trace levels. In the present review, we highlighted the use of MS and NMR-based strategies and Multivariate Data Analysis for the valorization of berries known for their biological activities, important as food and often used in the preparation of nutraceutical formulations.

Design, Synthesis, and Pharmacokinetic Evaluation of O-Carbamoyl Tizoxanide Prodrugs

2020 ◽  
Vol 16 ◽  
Author(s):  
Xi He ◽  
Wenjun Hu ◽  
Fanhua Meng ◽  
Xingzhou Li
Keyword(s):  
Plasma Concentration ◽  
Broad Spectrum ◽  
Plasma Concentrations ◽  
Antiviral Drug ◽  
Systemic Exposure ◽  
Pharmacokinetic Profile ◽  
Hydroxyl Group ◽  
First Pass

Background: The broad-spectrum antiparasitic drug nitazoxanide (N) has been repositioned as a broad-spectrum antiviral drug. Nitazoxanide’s in vivo antiviral activities are mainly attributed to its metabolitetizoxanide, the deacetylation product of nitazoxanide. In reference to the pharmacokinetic profile of nitazoxanide, we proposed the hypotheses that the low plasma concentrations and the low system exposure of tizoxanide after dosing with nitazoxanide result from significant first pass effects in the liver. It was thought that this may be due to the unstable acyloxy bond of nitazoxanide. Objective: Tizoxanide prodrugs, with the more stable formamyl substituent attached to the hydroxyl group rather than the acetyl group of nitazoxanide, were designed with the thought that they might be more stable in plasma. It was anticipated that these prodrugs might be less affected by the first pass effect, which would improve plasma concentrations and system exposure of tizoxanide. Method: These O-carbamoyl tizoxanide prodrugs were synthesized and evaluated in a mouse model for pharmacokinetic (PK) properties and in an in vitro model for plasma stabilities. Results: The results indicated that the plasma concentration and the systemic exposure of tizoxanide (T) after oral administration of O-carbamoyl tizoxanide prodrugs were much greater than that produced by equimolar dosage of nitazoxanide. It was also found that the plasma concentration and the systemic exposure of tizoxanide glucuronide (TG) were much lower than that produced by nitazoxanide. Conclusion: Further analysis showed that the suitable plasma stability of O-carbamoyl tizoxanide prodrugs is the key factor in maximizing the plasma concentration and the systemic exposure of the active ingredient tizoxanide.

Phytochemical, Analytical and Medicinal Studies of Holoptelea integrifolia Roxb. Planch - A Review

2019 ◽  
Vol 5 (4) ◽  
pp. 270-277 ◽  
Author(s):  
Vijay Kumar ◽  
Simranjeet Singh ◽  
Ragini Bhadouria ◽  
Ravindra Singh ◽  
Om Prakash
Keyword(s):  
Liquid Chromatography ◽  
Thin Layer ◽  
Thin Layer Chromatography ◽  
High Performance ◽  
Biologically Active ◽  
Toxicological Studies ◽  
Wide Range ◽  
Layer Chromatography

Holoptelea integrifolia Roxb. Planch (HI) has been used to treat various ailments including obesity, osteoarthritis, arthritis, inflammation, anemia, diabetes etc. To review the major phytochemicals and medicinal properties of HI, exhaustive bibliographic research was designed by means of various scientific search engines and databases. Only 12 phytochemicals have been reported including biologically active compounds like betulin, betulinic acid, epifriedlin, octacosanol, Friedlin, Holoptelin-A and Holoptelin-B. Analytical methods including the Thin Layer Chromatography (TLC), High-Performance Thin Layer Chromatography (HPTLC), High-Performance Liquid Chromatography (HPLC) and Liquid Chromatography With Mass Spectral (LC-MS) analysis have been used to analyze the HI. From medicinal potency point of view, these phytochemicals have a wide range of pharmacological activities such as antioxidant, antibacterial, anti-inflammatory, and anti-tumor. In the current review, it has been noticed that the mechanism of action of HI with biomolecules has not been fully explored. Pharmacology and toxicological studies are very few. This seems a huge literature gap to be fulfilled through the detailed in-vivo and in-vitro studies.

Sign in / Sign up

Export Citation Format

Share Document