Pharmacokinetics and effects of intravenous infusion of somatostatin in normal subjects--a two-compartment open model.

A direct radioimmunoassay of plasma somatostatin-like immunoreactivity (SRIF-LI) was developed and validated. The sensitivity was 16.0 pg/ml, and the specificity was good. The recovery of plasma SRIF-LI was 98.8 +/- 6.3%. The Scatchard plot of the antiserum binding data revealed a straight line, with a binding affinity of 3.52 X 10(-12) M and a binding capacity 4.06 X 10(-10) M. Synthetic SRIF (Stilamin), 250 micrograms, was infused intravenously over a 30-min period in 9 healthy volunteers. Plasma glucose, insulin (IRI), glucagon (IRG) and SRIF-LI were measured. A two-compartment open model was adopted to analyze the pharmacokinetic data of SRIF-LI. The results showed that plasma SRIF-LI rose from 192.2 +/- 16.2 pg/ml to a plateau of 2,129.8 +/- 288.2 pg/ml within 5-10 min after starting the infusion. The half disappearance time from plasma (Ta1/2) was 1.36 +/- 0.18 min, the half disappearance time from the 'remote' compartment (Tb1/2) was 49.6 +/- 10.9 min and the net half disappearance time from the two compartments together (Tn1/2) was 9.19 +/- 1.49 min. The metabolic clearance rate was 50.3 +/- 7.0 ml/kg/min. The plasma IRI, IRG and the IRI/IRG molar ratio were all suppressed during the infusion period. The recovery time of plasma IRG was mildly delayed in comparison to that of IRI. This indicates that there are dissociations between IRI and IRG in the extent and the duration of suppression caused by somatostatin infusion.