Effects of growth hormone administration on luteinizing hormone secretion in healthy older men and women

摘要

The known interactions between the somatotropic and hypothalamic‐pituitary‐gonadal (HPG) axes have not been well delineated in older individuals. Aging‐associated decline in insulin like growth factor‐1 (IGF‐1) levels has been proposed to play a role in reproductive senescence in animals. However, the effects of GH on LH secretion are unknown in older individuals. Our objective was to determine whether GH modulates LH secretion or levels of sex steroids (SS) in healthy older (ages 65–88 years) men (n = 24) and women (n = 24) with low‐normal plasma IGF‐1 levels. In a double‐masked, placebo‐controlled (n = 24), randomized study, we evaluated the effects of GH (n = 24, 20 μg/kg sc 3×/week) for 26 weeks on nocturnal LH secretory dynamics [(8 pm to 8 am, Q20) min sampling and analyzed by multiparameter deconvolution algorithm]. Indices of LH secretion [frequency, mass per burst, pulsatile production rate, and approximate entropy (ApEn)] and fasting serum IGF‐1, SHBG, and SS ( style="fixed-case">TT, style="fixed-case"> fT, or E2) were measured. At baseline, all indices of style="fixed-case">LH secretion (frequency, mass per burst, pulsatile production rate) were inversely (P < 0.05) related to style="fixed-case">IGF‐1, but not to mean nocturnal serum style="fixed-case">GH concentrations. style="fixed-case">GH administration for 26 weeks increased serum style="fixed-case">IGF‐1, but exerted no significant effects on style="fixed-case">LH secretory dynamics, or concentrations of style="fixed-case">SSs ( style="fixed-case">TT, style="fixed-case"> fT, or E2) or style="fixed-case">SHBG in older women or men. These data suggest that style="fixed-case">GH‐mediated increases in style="fixed-case">IGF‐1 do not modulate the style="fixed-case">HPG axis in older individuals.