The purpose of this study was to validate serum creatinine (SCr) concentrations assayed in the Central Biochemistry Laboratory of the National Institutes of Health (NIH)-funded Chronic Kidney Disease in Children (CKiD) study utilizing an enzymatic assay (Siemens Advia 2400) against a method traceable to reference isotope dilution mass spectroscopy (IDMS) developed by the National Institute of Standards and Technology (NIST). High-performance liquid chromatography (HPLC) measured SCr after external validation utilizing IDMS-based standard reference materials. Sera from the first 201 subjects enrolled in CKiD were analyzed and compared for creatinine concentration by enzymatic and HPLC methods. Fifty "normal" pediatric sera were subsequently analyzed. Finally, a "pediatric" reference standard was prepared and examined for accuracy and precision. Enzymatic SCr concentrations (median 1.4 mg/dl) of CKiD subjects were well correlated with HPLC (r=0.984) but were slightly higher (+7%; p<0.001). Agreement was poorer at lower SCr (median 0.4 mg/dl) when using samples from normal children and the "pediatric" reference standard. However, the Roche enzymatic assay was comparable with HPLC in accuracy and precision. Referring physicians should be aware of the accuracy and reproducibility of their laboratory's SCr assay. Our enzymatic

Nerve fibers containing bombesin (BB)/gastrin-releasing polypeptide (GRP), pituitary adenylate cyclase-activating polypeptide (PACAP), vasoactive intestinal polypeptide (VIP), or galanin are known to innervate the mucosa of the upper small intestine. Both BB/GRP and PACAP have been shown to elicit secretin secretion in vivo. We studied whether the above-mentioned neuropeptides can act directly on secretin-producing cells, including the murine neuroendocrine cell line STC-1 and a secretin cell-enriched preparation isolated from rat upper small intestinal mucosa. Secretin release from both cell types was stimulated by various agents known to elicit secretin release and by the neuropeptides BB, GRP, and PACAP, suggesting a comparable response between the two cell preparations. The effects of neuropeptides were further studied in STC-1 cells. BB, GRP, and PACAP stimulated secretin release time and concentration dependently. VIP also stimulated secretin release concentration dependently. Stimulation by BB/GRP or PACAP was accompanied by elevation of inositol-1,4,5-trisphosphate (IP3) or cAMP, respectively. The stimulatory effect of PACAP on secretin release was synergistically enhanced by BB without any synergistic increase in IP3 or cAMP production, suggesting cross talk between different signal transduction pathways downstream of the production of these two second messengers. The L-type Ca2+ channel blocker diltiazem (10 μM) and the Ca2+ chelator EGTA (1 mM) significantly inhibited BB-stimulated secretin release by 64% and 59%, respectively, and inhibited PACAP-stimulated release by 75% and 55%, respectively. The protein kinase A-specific inhibitor Rp-cAMPS (100 μM) also inhibited both BB- and PACAP-stimulated secretin release by 30% and 62%, respectively. Galanin inhibited BB- and PACAP-stimulated secretin release and production of second messengers in a concentration-dependent and pertussis toxin-sensitive manner. These results suggested that the neuropeptides BB/GRP, PACAP, VIP, and galanin can modulate secretin release in secretin-producing cells and that STC-1 cells can serve as a useful model for studying the cellular mechanism of secretin secretion elicited by luminal secretagogues and neuropeptides.

Background: Iohexol is used for measurement of kidney glomerular filtration rate (GFR). Until recently, there have not been available proficiency standards to assist in calibrating a laboratory's results. In view of a shift in calibration at the University of Rochester Medical Center (URMC) laboratory, serving as Central Biochemistry Laboratory for the CKiD study, we performed a multicentered laboratory comparison. Methods: Two batches of 30 fortified sera and patient samples from serum or heparinized plasma were sent for duplicate analysis to URMC, University of Minnesota (UMN), Mayo Clinic, and University of Lund. Five proficiency testing materials from Equalis AB were also provided. Iohexol calibration was performed using dilutions of Omnipaque TM 300 and concentrations measured by HPLC or LC-MS/MS (Mayo). Results: The 2 batches sent to UMN and University of Lund agreed well. URMC calibration was 11%-13% lower, and Mayo was 4%-8% lower for fortified samples. URMC corrected calibration was 3%-8% higher for these samples. When measured values were adjusted for the results of the Equalis samples, all laboratories agreed within 1%-2% on all iohexol concentrations. Conclusions: For 12 URMC calibrator lots from November 2006 to March 2016, the factor quantifying the underestimation of measured to true iohexol concentration was 0.89. If each concentration was divided by 0.89, the calculated GFRs would be reduced by 10%-11%. GFR results for CKiD were adjusted for this shift in calibration. Regular examination of iohexol proficiency testing materials, free exchange of samples among laboratories, and standardized dilution of the stock iohexol for calibration would help to bring more universal agreement to this assay. Laboratories; 4 EQUALIS;