Continuous subcutaneous infusion of low dose growth hormone decreases serum sex-hormone binding globulin and testosterone concentrations in moderately obese middle-aged men.

Abstract

Sex-hormone binding globulin (SHBG) is a liver derived protein whose concentration has been shown to be affected by a number of factors. The aim of the present study was to investigate the possible effect of increased basal GH concentrations on serum concentrations of SHBG, testosterone and thyroid hormones. Recombinant human growth hormone (rhGH) was given as a continuous subcutaneous infusion in a low dose (0.02 U/kg/day) over a period of 14 days in an open study. Eight middle-aged (42-59 years) overweight (body mass index 26.1-33.8 kg/m2) but otherwise healthy men were studied. Blood samples were obtained after an over-night fast before and after 2, 7 and 14 days of treatment. Serum was separated and stored at -20 degrees C until assay. Serum GH concentrations increased to a steady level of 2-4 mU/l. Serum SHBG concentration decreased between 2 and 7 days of treatment and serum testosterone concentration changed in parallel. There was no change in the ratio between serum SHBG and serum testosterone. Serum T4 and free T4 concentrations decreased, and that of T3 increased as a result of continuous GH infusion. Simple correlations between changes in SHBG concentrations and other hormonal changes showed positive significant correlations between changes of SHBG and of testosterone. Low dose continuously infused GH resulted in a parallel decrease in serum SHBG and testosterone concentrations. Thyroid hormone concentrations were affected in a similar way to that previously demonstrated following daily injections of GH.