Secretory patterns of glucoregulatory hormones in prehepatic circulation of dogs.

The temporal organization of patterns of secretion of insulin, glucagon, and somatostatin was studied in basal conditions in normal or pancreatectomized dogs fitted with an indwelling hepatic portal catheter. Portal and peripheral blood samples were collected at a 7.5- or 15-min frequency, which covered the medium range of the ultradian period. The raw data were studied using spectral analyses employing fast Fourier transformation (FFT) techniques. The results indicate that in normal dogs: 1) endogenous physiological periodicities, statistically significant at a level of alpha = 0.05 (i.e., 95% confidence interval), were found to exist for the three pancreatic hormones in portal blood between 0.54 and 1.78 h/cycle and in peripheral blood between 0.59 and 1.84 h/cycle; 2) the portal levels of the hormones are significantly higher than peripheral ones; and, 3) whereas pancreatic hormones oscillated, glucose was found to maintain a steady level. In pancreatectomized dogs, no regular rhythm was detected. Thus, whereas endogenous periodicities exist for the secretion of pancreatic hormones in the normal dog, in the pancreatectomized dog the extrapancreatic glucagon and somatostatin are secreted in nonperiodic, randomly occurring pulses.