PORTAL-VEIN INSULIN FLUX AND ARTERIAL GLUCOSE FLUCTUATIONS IN RESPONSE TO AN ORAL MEAL TEST IN ISLET CELL-TRANSPLANTED DOGS

Insulin flux was determined in the portal vein and simultaneously arte rial blood glucose was measured before and during an oral glucose meal in conscious normal and pancreatic islet cell-autotransplanted dogs t o test their insulinogenic reserve. These dogs had previously been chr onically instrumented with blood flow probes on the portal vein and ca rotid artery, and brood sampling catheters in the portal vein, hepatic vein, carotid artery, and right external jugular vein. Such a model p ermits quantitative portal-peripheral comparisons and assessment of he patic extraction. Sixteen dogs, 10 normal (N) and six long-term (2 mon ths to 2 yrs) islet cell-transplanted dogs (IT) were fed an oral gluco se meal as a test (OMT). Baseline portal vein insulin fluxes (PVF) wer e similar in both groups (25.6 +/- 0.04 pmol/min in N and 24.7 +/- 19. 4 pmol/min in IT). Immediately after OMT, PVF rose to 248.2 +/- 40.9 p mol/min in N, but only to 55.9 +/- 17.9 pmol/min in IT. After 30 min P VF peaked for the second time in N at 156 +/- 35.9 pmol/min, declining slowly to baseline after 3 h. In IT, a similar peak at 30 min was see n (143.7 +/- 22.1 pmol/min), declining to a value not different from b aseline after 3 h. However, cumulative insulin PV fluxes in the two gr oups over 3 h were not different. Differences were also seen in postpr andial glucose fluctuations, which reached a maximum excursion of 11.8 +/- 0.45 mM in IT, while never rising above 7.8 +/- 0.33 mM in N. Aft er 3 h both groups had similar glucose values. The principal defect di scerned in IT was the lack of adequate first-phase insulin secretory r esponse to OMT. Consequently, whereas islet cell-transplanted dogs wer e able to maintain fasting blood glucose within a normal range, the po stprandial glucose responses showed greater fluctuations than normal.