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Evaluation of a Direct Method for Measuring Absorption from the Gut¹

Department of Animal Science, Iowa State University, Ames 50010

ABSTRACT

Portal-arterial (P-A) differences and portal blood flow were used to calculate absorption of ¹⁴C-glucose administered into the duodenum, from the small intestine of calves. Unabsorbed radioactivity was measured at the terminal ileum.

Portal blood flow for 14 glucose absorption experiments with four calves averaged 37.17 ± .80 ml/(min x kg body weight). No significant differences in flow between animals, between treatments, (glucose administration), or between times after feeding and (or) glucose administration were observed. There was close agreement (r = .99) between three different methods to calculate absorption from P-A differences and portal blood flow. The most convenient method involved computer fitting of a polynomial function to data points and subsequent integration to obtain portal and arterial curve areas. Total P-A difference in area was used in absorption calculations. Recovery of ¹⁴C dose (absorbed plus unabsorbed) averaged 104.1% (89.2 to 114.4) for seven experiments for which dye-dilution curves were acceptable and, therefore, supports the validity of this direct method. In two experiments in which dye-dilution curves were unsatisfactory, recoveries were 167.1 and 219.2%. Recalculation, with only the best curves of the experiments, produced recoveries of 103.5 and 106.8%. This suggests that accurate blood flow measurement is most critical for quantitating absorption.

¹ Journal Paper J-7202 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project 1324. Supported in part by funds provided by Grant HE-04969 and Grant AM-10706, Department of Health, Education and Welfare.

² Present address: Department of Animal Science, The Pennsylvania State University, University Park 16802.