Abstract
The adrenal gland of the mouse takes up intravenously administered 125I-labeled human low density lipoprotein (LDL) by a high affinity, receptor-mediated mechanism. Uptake is enhanced by treatment of mice with a combination of 4-aminopyrazolopyrimidine, which eliminates endogenous mouse lipoproteins from the plasma, and adrenocorticotropin, which increases the number of adrenal LDL receptors. In the current studies, we show that adrenal uptake of 125I-LDL is blocked when the mice have received a prior intravenous injection of a rabbit antibody directed against the LDL receptor purified from bovine adrenal cortex. The antibody-mediated inhibition of 125I-LDL uptake persisted for 6 h and was reversed by 19 h. Adrenal uptake of 125I-labeled high density lipoprotein was not affected by the antibody, supporting the previous suggestion that high density lipoprotein uptake by the adrenal gland is mediated by a receptor that differs from the LDL receptor. The current studies illustrate the usefulness of antibodies in probing the process of receptor-mediated endocytosis in intact animals.
Highlights
The adrenal gland of themouse takes up intravenously administered251-labeled human low density lipoprotein (LDL) by a high affinity, receptor-mediated mechanism
We show that adrenal uptake of '25I-LDL is blocked when the mice have received a prior intravenous injection of a rabbit antibody directed against the LDL receptor purified from bovine adrenal cortex
Adrenal uptake of251-labeled high density lipoprotein was not affected by the antibody, supporting the previous suggestion that high density lipoprotein uptake by the adrenal gland is mediated by a receptor that differs from the LDL receptor
Summary
CaCl2, and 50 mM NaCl, pH 8) by aspiration through a 25-gauge needle followed by sonication gg of membrane protein were fmorix2e0ds.wAiltihqu4o4tsgd (16 of gl) containing buffer B Adrenal Uptake of '25I-Lipoproteins-Two to 10 h after the final dose of 4-APP and ACTH, mice were injected intravenously with the indicated amounts of preimmune or antireceptor IgG. The animals were injected intravenously with 12511 LDL or 125I-HDL. After 30 min the animals were given an intravenous injection of 1251-LDL. Thirty min thereafter the animals were killed, the organs were perfused via the inferior vena cava, and the adrenal glands were removed for determination of radioactivity.
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