Studies on the subunits of the human glycoprotein hormones in relation to reproduction

Immunoreactivity for the alpha-subunit of the pituitary glycoprotein hormones in pulmonary neuroendocrine cells of developing human lung and various perinatal diseases

Infant lung tissue, obtained at autopsy, was studied by immunohistochemistry for the presence of pituitary glycoprotein hormones (PGHs) in the lung. The infants, born at term or preterm, died of various causes. The results provide the first immunological evidence of the presence of the common a-subunit of the pituitary glycoprotein hormones (alphaPGH) in the lung. The immunoreactivity is located in the pulmonary neuroendocrine cells and neuroepithelial bodies. In addition, the cells labelled by alphaPGH antisera (alphaPGH cells) form a subpopulation of the neuroendocrine cells detected by anti-calcitonin immunohistochemistry (CT cells). Moreover, the number of alphaPGH cells appears to increase after neonatal pneumonia or when the number of CT cells is elevated following the development of disease. Also, the weak staining of one of the monoclonal antibodies against the specific b-subunit of thyrotropin (TSH) might, in combination with the increased detectability of a-subunits, indicate that TSH can be endogenously produced in the lung.

Dopaminergic inhibition of glycoprotein hormone alpha-subunit in normal subjects

The pituitary glycoprotein hormones thyrotropin (TSH), luteinizing hormone (LH), and follicle-stimulating hormone (FSH) consist of two noncovalently linked subunits, alpha and beta. In addition to producing intact hormone, the pituitary releases free alpha-subunit, which is stimulated by gonadotropin-releasing hormone (GnRH) and thyrotropin-releasing hormone (TRH). However, little is known about the dopaminergic regulation of free alpha-subunit in vivo. The effect of dopamine (DA), metoclopramide (MTC), and the specific DA D-1 receptor agonist, fenoldopam, on circulating alpha-subunit levels was studied in normal men and women. Normal women received 4-hour infusions of either glucose (n = 6) or DA at rates of 0.04 (n = 6), 0.4 (n = 6), and 4.0 micrograms/kg.min (n = 6). After 3 hours, 10 mg MTC was administered intravenously (IV). The high dose of DA significantly lowered alpha-subunit levels (P less than .05). No response to MTC was observed in any of the groups. Six women received glucose or DA infusion (4.0 micrograms/kg.min) for 18 hours. DA significantly reduced basal alpha-subunit levels compared with control infusion (P less than .05). MTC administration after 17 hours induced a significant increase in alpha-subunit levels on the day of DA infusion compared with control (P less than .05). In a third study, nine normal males received fenoldopam (0.5 microgram/kg.min) or placebo infusions for 4 hours. Fenoldopam did not affect basal alpha-subunit levels, but the alpha-subunit response to a GnRH/TRH bolus was significantly increased during fenoldopam compared with control (P less than .05). The results suggest that alpha-subunit release may be modulated by the dopaminergic system in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)