This Article Abstract Full Text (PDF) Purchase Article View Shopping Cart Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Copyright Permission Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Frystyk, J. Articles by Baxter, R. C. Search for Related Content PubMed PubMed Citation Articles by Frystyk, J. Articles by Baxter, R. C.

Competitive Binding Assay for Determination of Rat Insulin-Like Growth Factor Binding Protein-3

Kolling Institute of Medical Research, University of Sydney, Royal North Shore Hospital, Sydney, NSW 2065, Australia

Address all correspondence and requests for reprints to: Dr. Jan Frystyk, Kolling Institute of Medical Research, Royal North Shore Hospital, St. Leonards, New South Wales 2065, Australia.

	Abstract

Top Abstract

 
We describe a novel competitive assay for rat insulin-like growth factor (IGF)-binding protein-3 (rIGFBP-3) based on the ability of IGFBP-3 to form a ternary complex with the acid labile subunit (ALS) in the presence of IGF. Human (h)ALS was bound to test tubes pre-coated with anti-human ALS antibody. The assay depends on competition between a covalent complex of ¹²⁵I-hIGF-I and hIGFBP-3, added as tracer, and hIGFBP-3 or rIGFBP-3 in standards and test samples, for binding to the immobilized hALS. Purified natural hIGFBP-3 served as standard. Human IGFBP-3 and rIGFBP-3 were able to compete for tracer binding in the presence, but not in the absence, of IGF-I. Before assay, rat serum samples were acidified to denature endogenous ALS. Standards ranged from 0.10 (lower detection limit) to 20 ng/tube. Rat serum, semipurified rIGFBP-3, human serum and purified hIGFBP-3 diluted in parallel. The level of rIGFBP-3 was 1.63 ± 0.28 mg/l (mean ± SEM) in young rats and increased to 3.41 ± 0.26 mg/l (p < 0.05) in old rats (n = 5–6). Fasting for 3 days reduced rIGFBP-3 from 2.41 ± 0.27 to 1.33 ± 0.14 mg/l (p < 0.05). Levels of rIGFBP-3 were reduced in hypophysectomized (0.16 ± 0.04 mg/l; p < 0.05) and diabetic rats (1.04 ± 0.30 mg/l; p < 0.05), and normal in insulin-treated diabetic rats (2.49 ± 0.04 mg/l; ns), when compared to controls (2.79 ± 0.22 mg/l). Changes in levels of IGFBP-3 paralleled those of immunoreactive rALS. We conclude that this assay provides a novel method of quantitating functional IGFBP-3 in rat serum.

Received October 6, 1997.

This article has been cited by other articles:

				S.-E. Kong, R. C. Baxter, and P. J. D. Delhanty Age-Dependent Regulation of the Acid-Labile Subunit in Response to Fasting-Refeeding in Rats Endocrinology, December 1, 2002; 143(12): 4505 - 4512. [Abstract] [Full Text] [PDF]

				P. J. D. Delhanty, C. D. Scott, S. Babu, and R. C. Baxter Acid-labile subunit regulation during the early stages of liver regeneration: implications for glucoregulation Am J Physiol Endocrinol Metab, February 1, 2001; 280(2): E287 - E295. [Abstract] [Full Text] [PDF]

				J. Frystyk, P. J. D. Delhanty, C. Skjarbak, and R. C. Baxter Changes in the circulating IGF system during short-term fasting and refeeding in rats Am J Physiol Endocrinol Metab, August 1, 1999; 277(2): E245 - E252. [Abstract] [Full Text] [PDF]

				J. Frystyk, H. Gronbak, C. Skjarbak, A. Flyvbjerg, H. Orskov, and R. C. Baxter Developmental Changes in Serum Levels of Free and Total Insulin-Like Growth Factor I (IGF-I), IGF-Binding Protein-1 and -3, and the Acid-Labile Subunit in Rats Endocrinology, October 1, 1998; 139(10): 4286 - 4292. [Abstract] [Full Text] [PDF]

This Article Abstract Full Text (PDF) Purchase Article View Shopping Cart Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Copyright Permission Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Frystyk, J. Articles by Baxter, R. C. Search for Related Content PubMed PubMed Citation Articles by Frystyk, J. Articles by Baxter, R. C.