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Journal of Clinical Endocrinology & Metabolism, Vol 70, 1219-1224, Copyright © 1990 by Endocrine Society

ARTICLES

Regulation of pituitary glycoprotein alpha-subunit secretion after administration of a luteinizing hormone-releasing hormone antagonist in normal men

J Lindner, JE Rivier, WW Vale and SN Pavlou
Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.

Pituitary glycoprotein hormones are composed of two different subunits, the alpha- and beta-subunits. The alpha-subunit is common to all FSH, LH, and TSH, while the beta-subunit is specific for each of these hormones. We studied the effects of a potent LHRH antagonist on alpha- subunit and LH secretion in normal men. The LHRH antagonist Nal-Glu, ([Ac-D2Nal1,D4ClPhe2,D3Pal3,Arg5,DGlu6(AA) ,Ala10]LHRH), was given (10 mg daily) as one injection of 5 mg every 12 h. Blood samples were drawn every 24 h, and on days 1 and 7 a day curve was established by drawing hourly blood samples for 26 h. Mean serum alpha-subunit levels decreased progressively (P less than 0.001) from 2.9 +/- 0.49 micrograms/L at baseline to a nadir of 1.4 +/- 0.27 micrograms/L on day 8. In contrast, mean immunoreactive LH (IR-LH) levels decreased rapidly from 3.2 +/- 0.6 U/L at baseline to 0.9 +/- 0.08 U/L on day 2 and remained suppressed (P less than 0.001) throughout the treatment period. On day 1 after the administration of Nal-Glu mean alpha-subunit levels decreased, although not significantly (P = 0.054), from 3.0 +/- 0.6 micrograms/L at baseline to a nadir of 2.0 +/- 0.3 micrograms/L at 17 h. alpha-Subunit remained at this level for the remainder of day 1. On day 7, however, the baseline serum alpha-subunit level was 1.5 +/- 0.3 micrograms/L, significantly suppressed (P less than 0.01) compared to the level on day 1, and no further decrease was seen after administration of Nal-Glu. IR-LH on day 1 before the first injection of 5 mg Nal-Glu was 3.5 +/- 0.8 U/L. Then, IR-LH levels decreased significantly (P less than 0.001) to a nadir of 0.9 +/- 0.1 U/L and remained at this level throughout day 1. IR-LH levels on day 7 were at or below 1.0 U/L throughout the sampling period. These results indicate that alpha-subunit secretion can be partially suppressed after chronic administration of a LHRH antagonist. Furthermore, LH serum levels dissociate from those of pituitary glycoprotein alpha-subunit after administration of LHRH antagonist analogs.


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B. Couzinet, J. Pantel, P. Chanson, J. Young, S. Brailly, I. T. Huhtaniemi, J.-M. Bidart, and G. Schaison
Measurement of Plasma Free Luteinizing Hormone {beta}-Subunit in Women
J. Clin. Endocrinol. Metab., June 1, 2000; 85(6): 2293 - 2298.
[Abstract] [Full Text]


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