Cobalt as a gastric juice volume marker: Comparison of two methods of estimation

We investigated the use of cobalt-EDTA, a novel, non-absorbable liquid phase marker, in the estimation of secretory volumes during topical misoprostol (synthetic PGE, analog) administration in the canine chambered gastric segment. We compared atomic absorption spectrophotometry (AAS) and instrumental neutron activation analysis (INAA) in the estimation of [Co]. Mucosal bathing solutions containing cobalt-EDTA were instilled into and recovered from the chamber by gravity every 15-min period as follows: (i) basal-60 min; (ii) misoprostol periods-150 min (plus 0.1-, 1-, 10-, 100-, and 1000-μg doses of misoprostol for two periods per dose). The recovered solutions were analyzed for [Co] by AAS and INAA. Total cobalt recovery by AAS after chamber washout was 102.97 ± 0.98%. Mean ± SE volumes (12.14 ± 0.33 and 13.24 ± 0.60 ml/15 min) obtained respectively from AAS and INAA were significantly higher (P < 0.001) than the recovered mean volumes (10.51 ± 0.17 ml/15 min). The percentage error in volume collection increased (range: 9.3-52.7%) with the volume of secretion. Values of [Co] obtained by the two techniques were comparable and not significantly different from each other (P < 0.05). INAA-estimated mean ± SE [Co] showed consistently higher coefficients of variation. Spectra obtained for all samples during INAA measurements showed significant Compton background activity from ²⁴Na and ³⁸Cl. Cobalt-EDTA did not grossly or histologically damage the gastric mucosa. We conclude that cobalt is not adsorbed, absorbed, or metabolized, and is a suitable and reliable volume marker in this model. AAS and INAA offer comparable and valid measurements of [Co] and are specific, rapid, and simple to perform. In a sample matrix with high NaCl content, AAS may be preferable because of its higher sensitivity, less variability, and absence of interference from Na and Cl.