How (not) to diagnose growth hormone deficiency in adults: stimulated serum concentrations of growth hormone in healthy subjects and in patients with pituitary macroadenomas

Unchanged testosterone production rates in growth hormone-treated healthy men

The effect of biosynthetic human GH on the production rates of testosterone was determined in healthy men (n = 7) using the stable isotope dilution technique and mass spectrometry. 1Alpha,2alpha-d-testosterone (20 microg/h) was infused for 10 h (0800-1800 h). Blood samples obtained at 20-min intervals from 1400-1800 h were pooled during two 2-h periods. Subsequently, each volunteer received a daily dose of biosynthetic human GH (4 IU/day sc) for 7 days. This resulted in a rise in plasma concentrations of somatomedin-C from, basal, 0.67+/-0.13 U/mL to 1.20+/-0.2 U/mL on day 7 (P < 0.0001). Testosterone production rates (basal: 209.9+/-31.0 microg/h) were unchanged by treatment with GH (day 7: 192.2+/-30.1 microg/h). In healthy men, short-term treatment with sc GH does not influence endogenous testosterone production rates.

Role, sensitivity and validity of GH stimulation tests in the diagnosis of growth hormone deficiency in adults

This study was conducted to evaluate whether stimulated concentrations of growth hormone (GH) are of practical use in establishing the diagnosis of acquired GH deficiency. The secretion of GH as stimulated by GH releasing hormone (GHRH; 100 microg i.v.) was studied in 33 patients with non-functioning pituitary macroadenomas prior to and after trans-sphenoidal adenomectomy, as well as in 25 non-selected subjects who had been referred for evaluation of various suspected non-pituitary diseases. Patients with pituitary macroadenomas, who needed substitution therapy for at least one additional pituitary hormone, presented with lower (P<0.05) GHRH-stimulated GH secretion (3.2 +/- 4.3 ng/ml) than the remaining patients with pituitary tumours (7.2 +/- 6.6 mg/ml). Both groups showed a marked overlap with the control group (7.1 +/- 5.5 ng/ml). Although GH stimulation tests are superior to other biochemical criteria of GH deficiency, they are still an inadequate method to reliably diagnose GH deficiency in an individual patient. In clinical practice GH replacement therapy should, therefore, only be considered if, in addition to impaired GH secretion, the patients present with additional defects in anterior pituitary function and clinical symptoms are compatible with a lack of GH.