This Article Full Text (PDF) Submit a related Letter to the Editor Alert me when this article is cited Alert me when eLetters are posted 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 Reprints, Permissions and Rights Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by SNEID, D. S. Articles by DAUGHADAY, W. H. Search for Related Content PubMed PubMed Citation Articles by SNEID, D. S. Articles by DAUGHADAY, W. H.

Radioreceptor-Inactive Growth Hormone Associated with Stimulated Secretion in Normal Subjects¹

Metabolism Divisions, Departments of Internal Medicine and Pediatrics, Washington University School of Medicine St. Louis, Missouri 63110

We have previously reported systematic discrepancies between radioreceptor (RRA) and radioimmunoassay (RIA) measurements of growth hormone (hGH) in acromegalic patients. Due to limitations in RRA sensitivity, such comparisons could not be made in normal subjects. RRA methodology has now been adapted to allow detection of hGH at normal circulating levels. Since variations in Na+, K+, Ca++, and Mg++, incubation at 37 C and 4 C, and delayed tracer addition failed to improve assay sensitivity, specimen size was increased at 37 C and 4 C, and delayed tracer addition failed to improve assay sensitivity, specimen size was increased to 300 µl and incubation volume to 1.5 ml, while holding the quantity of added receptor constant. Best assay sensitivity, in room temperature incubations in 25 mM Tris for 16 h at pH 7.6 and 10 mM Ca++, was 0.66 ± 0.30 ng hGH per ml serum. Under these conditions, 200 µg hepatic receptor protein bound 15.8 ± 0.83% of added ¹²⁵I-hGH, and 8.72 ± 0.85% of bound tracer was displaced by 0.25 ng added unlabeled hGH. Nonspecific depression of binding by serum did not impair assay sensitivity with most receptor preparations. The basal hGH measured by RIA (antiserum 68–416) in a group of normal short children was 1.97 ng/ml, similar to the RRA result, 1.89 ng/ml (P = NS). Comparative measurements were also made in selected samples of sufficient volume during the 1 h following administration of hGH secretagogues (insulin, arginine, L-dopa). In these samples, the RIA value was 9.34 ± 0.68 and the RRA value 6.29 ± 0.62 ng/ml (P < 0.01); the RIA/RRA was 1.77 ± 0.18. Thus, no significant measurement discrepancy was found inbasal samples from normal subjects, in contrast to previous findings in acromegalics. The appearance of such a discrepancy within 90 min after stimulation of hGH might be due to RIA/RRA discordance insecreted molecular subspecies, or might arise from peripheral hGH metabolism.

Supported in part by grants from the U.S. Public Health Service (AM-05027, AM-05105)

¹ Trainee in Metabolism.

² Research Career Development Awardee, USPHS, 5 KO4 AM-70521

Received February 11, 1975.

This article has been cited by other articles:

				S. LaFranchi, C. E. Hanna, and B. Jelen Growth Hormone Assessment by Radioreceptor and Radioimmunoassay: Radioreceptor Assay and Radioimmunoassay Comparisons Arch Pediatr Adolesc Med, January 1, 1984; 138(1): 23 - 27. [Abstract] [PDF]