Effects of synthetic xenopsin on endocrine pancreas and gastric antrum in anesthetized dogs were studied. Synthetic xenopsin was administered into the superior pancreaticoduodenal artery and plasma insulin, glucagon and gastrin in the superior pancreaticoduodenal vein and gastrin in the right gastroepiploic vein were measured radioimmunologically. Administration of 10 microgram of xenopsin per kg of body weight brought about a hyperglycemic response and rapid and sharp elevations of the hormones in the pancreatic vein. Plasma gastrin level in the gastric vein also showed an immediate and sharp increase following xenopsin administration. Xenopsin appeared more potent inducer of the glucagon. It is concluded that xenopsin acts directly on endocrine pancreas and gastric antrum to secrete their hormones.
C-peptide immunoreactivity (CPR) levels were measured in dog superior pancreaticoduodenal vein using synthetic dog C-peptide and its antiserum. The basal CPR level was approximately twice as high as the basal immunoreactive insulin (IRI) level on a molar basis. Glucose (10 mg/kg/min) or arginine (250 mg/kg/min) infusion for 5 min into the superior pancreaticoduodenal artery caused a prompt, parallel increase in IRI and CPR. IRI and CPR were closely equimolar at peak secretions. One bolus administration of synthetic neurotensin (10 microgram/kg) into the same artery produced a mild hyperglycemic response and biphasic IRI and CPR responses at 30 min in the vein. The IRI and CPR increases were closely equimolar during the first phase of secretion, but during the second peak a larger increase was found in CPR than IRI. Upon infusion of synthetic substance P (50 ng/kg/min) for 30 min, IRI and CPR concentrations showed a parallel and closely equimolar fall. These results indicate that insulin and C-peptide were released from beta cells in equimolar concentrations.
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