A Sensitive Radioimmunoassay for Immunoreactive Somatostatin in Extracted Plasma: Measurement and Characterization of Portal and Peripheral Plasma in the Rat*

Clearance of Immunoreactive Somatostatin by Perfused Rat Liver

“…Concentrations of immunoreactive somatostatin (IRS)' in serum or plasma from man (1) and animals (2)(3)(4)(5)(6)(7) are higher in the hepatic portal vein or its major tributaries than in simultaneous samples drawn from the hepatic or peripheral systemic veins. Although the absolute concentrations ofIRS are lower ifthe sample is extracted before the assay (-20-600 pg/ml) (1,2,4) than not (-300-2,000 pg/ml) (3,5), the values suggest that hepatic extraction of IRS might accouint for the negative transhepatic gradients that have also been shown previously for insulin (8) and glucagon (9,10).…”

“…Although the absolute concentrations ofIRS are lower ifthe sample is extracted before the assay (-20-600 pg/ml) (1,2,4) than not (-300-2,000 pg/ml) (3,5), the values suggest that hepatic extraction of IRS might accouint for the negative transhepatic gradients that have also been shown previously for insulin (8) and glucagon (9,10). However, definitive proof of IRS uptake requires measurements of total hepatic blood flow and transit time with careful attention to the manner and site of sainpling within the vessels (8,9).…”

“…A significant proportion of the total IRS can however exist in the unbound state after a meal (15). However, there is little evidence that IRS binds to high molecular weight protein in rat plasma (4). Also, rat portal venous plasma IRS appears to be heterogeneous, existing in approximately equal amounts of a 1,600 mol wt form which is similar to synthetic somatostatin and a bigger molecular weight form (4).…”

“…The purpose of this study, therefore, was to determine whether synthetic cyclic somatostatin would be cleared in vitro by the isolated rat liver, perfused in situ with a plasma-free medium that would limit degradation of IRS caused by plasma itself (4,16). Clearance of IRS from the perfusate was found and further experiments were performed to characterize the effects of IRS concentration, temperature, pH, and pharmacologic amounts of insulin and glucagon on the clearance process.…”

Modulation by somatostatin of nerve‐mediated activation of glycogenolysis in the perfused rat liver

“…Many effects of the hormone were described using pharmacological doses in a range of 10 -7 mol.l -~ [20][21][22]. In the portal vein plasma levels of maximal 500 pg/ml were reported [23]. This corresponds to about 2 x 10 -1° mol.1-1 taking into account that somatostatin-14 and somatostatin-28 are the two principal biologically active forms of the hormone.…”