Abstract
The binding of 125I-vasoactive intestinal peptide (125I-VIP) and 125I-insulin has been examined in highly enriched populations of rat hepatocytes and hepatic nonparenchymal cells. 125I-VIP bound to high-affinity sites (Ka = 1.7 X 10(9) M-1) in nonparenchymal cells. Specific binding in these cells was nearly fivefold greater than in hepatocytes (15.0 +/- 0.6% vs. 3.6 +/- 0.7% radioactivity bound per 4 X 10(5) cells). In contrast, 125I-insulin binding was similar in both cell populations (18.2 +/- 2.4% per 4 X 10(5) cells in hepatocytes vs. 17.1 +/- 1.0% in nonparenchymal cells). Glucagon and insulin had no effect on 125I-VIP binding in nonparenchymal cells. Secretin inhibited 125I-VIP binding but was only about 1% as potent as unlabeled VIP. VIP had no apparent effect on cAMP levels in either cell population, whereas glucagon increased cAMP levels in both cell types. Our findings suggest that VIP binds preferentially to hepatic nonparenchymal cells and that these cells are primarily responsible for the clearance of VIP from the portal circulation.
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