Serum calcitonin levels in anesthetized rats

Simple liquid chromatography-electrospray ionization mass spectrometry method for the routine determination of salmon calcitonin in serum

A simple liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) method was developed for the quantification of salmon calcitonin (sCT) in serum. Serum samples from rats and dogs were deproteinized and freeze-dried. The residue was then reconstituted with 57% acetonitrile in water containing 0.1% trifluoroacetic acid and 0.005% benzalkonium chloride. A 20-microl aliquot of the reconstituted solution was injected onto a polymer based RP-C18 column, The outlet was connected to an ion-trap mass spectrometer equipped with an ESI source, and spectra were recorded in a positive-ion, selected-ion monitoring mode. The limit of quantification of the method was 10 ng/ml. Biexponential curves were observed for the temporal serum concentration of sCT following intravenous administration of sCT to rats (100 microg/kg) and dogs (250 microg/kg), resulting in reasonable pharmacokinetic parameters. The present method appears applicable to routine analysis of serum sCT in pharmacokinetic studies with good selectivity, accuracy and precision.

Influence of Ca2+ concentration on the clearance and circulating levels of intact and carboxy-terminal iPTH in pentobarbital-anesthetized dogs

The role of hormone secretion and hormone clearance in the differential control of circulating levels of intact (I-) and carboxy-terminal (C-) immunoreactive parathyroid hormone (iPTH) was evaluated in 18 pentobarbital-anesthetized dogs. Catheters were installed in the aorta, left renal, and hepatic veins for sampling. Hepatic and renal blood flows were calculated from sulfobromophtalein (BSP) and p-aminohippuric acid (PAH) extraction and clearance. I- and C-iPTH were measured during a 1 h of infusion of CaCl2 or Na2EDTA. High-performance liquid chromatography (HPLC) profiles of I- and C-iPTH in and out of the liver and kidney were also obtained. Data on two dogs (one CaCl2 and one Na2EDTA infusion) were pooled for the analysis of one parathyroid function using a four-parameter mathematical model. Results obtained in the basal state and during analysis of the parathyroid function were also compared with those of 24 awakened dogs. Results are means +/- SD. Anesthetized dogs had lower levels of Ca2+ (1.29 +/- 0.03 vs. 1.34 +/- 0.04 mmol/l; p < 0.001) and higher levels of I- (11.5 +/- 5.7 vs. 3.0 +/- 1.9 pmol/l, p < 0.001) and C-iPTH (52 +/- 20.9 vs. 22.8 +/- 10.5 pmol/l; p < 0.001) than awakened dogs. Their stimulated (S) and nonsuppressible (NS) I-iPTH levels were increased 2- and 4-fold, respectively, while similar C-iPTH levels rose only 1.35- and 1.75-fold; this caused their S (4.4 +/- 0.7 vs. 6.8 +/- 1.9; p < 0.001) and NS (24.6 +/- 11.8 vs. 49.8 +/- 27.5; p < 0.05) C-iPTH/I-iPTH ratios to decrease. This was not explained by different renal clearance rates of I- and C-iPTH since both were similar at approximately 10 ml/kg/minute and unaffected by Ca2+ concentration. Clearance of all I- and C-iPTH HPLC molecular forms by the kidney appeared equal. A 50% decrease in the hepatic clearance of I-iPTH to approximately 12 ml/kg/minute in pentobarbital-anesthetized dogs, related to a lower hepatic blood flow, explained the higher levels of S and NS I-iPTH in these animals. I-iPTH hepatic clearance was unaffected by Ca2+ concentration. C-iPTH hepatic clearance was much lower at approximately 5 ml/kg/minute, abolished by hypercalcemia, and reduced by the influence of anesthesia on hepatic blood flow. This also explained the higher S C-iPTH levels in anesthetized animals. I-PTH(1-84) detected by the C-iPTH assay explained only 37.6% of the hepatic C-iPTH clearance in hypocalcemia and 73.3% in hypercalcemia. Overall, our results indicate that total C-iPTH clearance is about 40.2% that of I-iPTH in hypocalcemia and 41.3% in hypercalcemia. This would only explain a 2.4- to 2.5-fold difference in circulating levels of I- and C-iPTH if secretion rates were equal; the larger difference observed in S and NS C-iPTH/I-iPTH ratio values is thus mainly explained by different production rates.

A noncompetitive enzyme immunoassay (hetero-two-site enzyme immunoassay) for salmon calcitonin: determination of the bioavailability of subcutaneous salmon calcitonin and its correlation with the hypocalcemic activity in rats

A noncompetitive enzyme immunoassay method (hetero-two-site enzyme immunoassay) for salmon calcitonin (SCT) and its usability for the pharmacokinetic study are described. The method in brief proceeds as follows: centrifugal filtration through a polysaccharide membrane to remove plasma proteins, biotinylation, trapping onto an anti-SCT IgG-coated polystyrene ball, acid elution, coupling with affinity-purified anti-SCT Fab'-peroxidase conjugate, final trapping onto streptavidin-coated polystyrene balls, and measurement of peroxidase activity bound to the balls by fluorometry. The practical detection limit of SCT was 0.1 pg (30 amol)/assay and 2 pg/ml as the assay sample's concentration, which was at least fivefold lower than those previously reported by competitive radioimmunoassays. The application of this method has enabled us to 1) directly estimate the bioavailability of SCT dosed subcutaneously at the therapeutic levels (1.2 and 4.7 micrograms/kg) for its antiosteoporotic effect as compared to an intravenous dose (1.2 micrograms/kg) and 2) search for the relationship between blood level and the hypocalcemic activity of SCT. The pharmacokinetic parameters of subcutaneous SCT (1.2 and 4.7 micrograms/kg) thus estimated were as follows: the area under the blood concentration-time curve (AUC) = 89 and 550 pg.hr/ml, and mean residence time (MRT) = 44 and 65 minutes, respectively, when the AUC for an intravenous SCT (1.2 micrograms/kg) = 160 pg.hr/ml and the MRT = 10 minutes.