Radiorespirometric patterns of ¹⁴C-substrates in rats II. Differences in nature and administration route of the injection fluid

Abstract

Effects on ¹⁴CO₂ expiratory patterns of nature and administration route of the injection fluid were studied.
1) In case of rapid i.v. injection, no difference in the pattern was found by difference in glucose concentrations and volumes of the aqueous injection fluid.
2) By the same route as mentioned above, lower P₁ height and more longdrawn plateau by the ¹⁴C-glucose-blood mixture than the aqueous injection fluid were recorded for radiorespirometric patterns.
Results indicated that ¹⁴C-glucose molecules in the aqueous fluid infused into the blood vessel could be supplied into organs or tissues before mixing of the aqueous ¹⁴C-glucose solution with the blood fluid in the blood vessel system. And it is suggested that much more amount of ¹⁴C-glucose might be taken up in organs and tissues when the label was resoluble in aqueous solution than in blood.
3) In case of intraduodenal infusion, a tracer of glucose in a small volume such as 0.05 ml of the aqueous solution gave a similar radiorespirometric pattern to that by the aqueous ix. injection fluid. This is an indication that there was fast absorption of glucose by the intestinal mucosa, which might be not rate determining step.
A relatively large volume and very high concentration of glucose in the infusion fluid caused big suppression of the radiorespirometric pattern. This might be suggestive that the above factors might give physical suppression to the peristalsis of the intestine.