Changes in circulating levels of LH, FSH, LHbeta- and alpha-subunit after gonadotropin-releasing hormone, and of TSH, LHbeta- and alpha-subunit after thyrotropin-releasing hormone

The effect of the gonadotropin-releasing hormone (LRH) and thyrotropin-releasing hormone (TRH) on the blood levels of LH, FSH and TSH, and LHbeta- and alpha-subunit have been studied in 4 normal subjects during the first 20 min after administration of these releasing hormones. Increases in serum immunoreactive LH, LHbeta and alpha-subunit were seen in all subjects after LRH (100 mug iv) but in all subjects the rise in LH was preceded by a rise in alpha-subunit. All subjects showed an increase in TSH and 3 of the 4 subjects a rise in alpha-subunit after TRH (200 mug) but the alpha-subunit responses were smaller and less consistent than after LRH. Levels of LHbeta remained unchanged after TRH. The results demonstrate that the immunoreactive alpha-subunit of the pituitary glycoprotein hormones can be released independently of the intact hormones and that release occurs in response to the same releasing hormones, LRH and TRH, that release the intact hormones.