IGF receptors in myocardial capillary endothelium: potential regulation of IGF-I transport to cardiac muscle.
Beating rat hearts were perfused with 125I-IGF-II alone or 125I-IGF-II and unlabeled IGF-II or insulin, then prepared for radioautography. Maximal 125I-IGF-II grain counts over capillaries were decreased in a dose-dependent manner by unlabeled IGF-II but were unaffected by coperfusion with insulin. To determine a potential role for capillary receptors in the transfer of circulating IGF to cardiac muscle, the effects of sequential loss of capillary IGF binding sites was determined. For IGF-I, loss of capillary binding sites by trypsin perfusion was accompanied by proportional decreases in the subsequent appearance of IGF-I in cardiac muscle. In contrast, similar decrements of capillary IGF-II binding did not affect muscle levels of IGF-II. We conclude that capillary endothelium of the intact heart possesses distinct IGF-I and IGF-II binding sites, with the capillary IGF-I binding sites being of potential importance in the transfer of vascular IGF-I to subendothelial cardiac muscle.
Bar
R S
RS
Veterans Administration Hospital, Department of Internal Medicine, University of Iowa, Iowa City 52242.
Boes
M
M
Sandra
A
A
D000818:Animals; D002196:Capillaries / Q000378:metabolism; D002478:Cells, Cultured; D003331:Coronary Vessels / Q000378:metabolism; D004730:Endothelium, Vascular / Q000378:metabolism*; D066298:In Vitro Techniques; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D007700:Kinetics; D009206:Myocardium / Q000378:metabolism*; D051381:Rats; D011972:Receptor, Insulin / Q000378:metabolism*; D017451:Receptors, Somatomedin; D013002:Somatomedins / Q000378:metabolism*
D017451:Receptors, Somatomedin; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D011972:Receptor, Insulin