Endocrinology, Vol 107, 1572-1576, Copyright © 1980 by Endocrine Society
Free somatostatin in the circulation: amounts and molecular sizes of somatostatin-like immunoreactivity in portal, aortic, and vena caval plasma of fasting and meal-stimulated dogs
V Schusdziarra, E Zyznar, D Rouiller, V Harris and RH Unger
Somatostatin-like immunoreactivity (SLI) of plasma from the portal vein,
aorta, and inferior vena cava and of lymph from the thoracic duct of both
fasted and meal-stimulated dogs was measured and characterized with respect
to molecular size. Significant portal vein-arterial and arteriovenous SLI
gradients were present in fasting dogs, and they increased sharply after
the intragastric infusion of liver extract and HCl. Chromatography of
fasting plasma at pH 7.4 revealed all measurable SLI to be confined to the
void volume fractions of a Bio-Gel P-6 column, although, after a 7-fold
concentration of fractions coeluting with somatostatin, approximately
1600-daltion SLI was detected in the portal venous plasma. The rise in SLI
after a meal was due primarily to an increase of approximately 1600-dalton
SLI; approximately 1600-dalton SLI was detectable in unconcentrated portal
venous and aortic plasma and in the peripheral venous plasma concentrated
7-fold. SLI levels in lymph were similar to those of basal venous plasma
and did not increase with a meal. This first demonstration at a
physiological pH of a approximately 1600-dalton SLI in the arterial
circulation suggests that a free, readily available form of endogenous
somatostatin is present in the canine circulation and could be playing a
hormonal role.
