Objective - We sought to characterize pulsatile growth hormone (GH) release in normal women during the menstrual cycle and to document possible relationships between such characteristics and concentrations of 17 β-oestradiol and progesterone. Subjects - Fifteen women with ostensibly normal menstrual function were studied during the early follicular phase, 15 during the late folicular phase and 15 during the mid-luteal phase of the menstrual cycle. Design - The phase of the menstrual cycle having been documented, blood samples were obtained from each woman every 10 minutes for 24 hours. Measurements - Serum GH was measured in each sample by immunoradiometric assay. Pulsatile GH release was appraised utilizing the objective, statistically-based pulse detection algorithm Cluster. Results - The mean (± SEM) integrated serum GH concentration (mU/l min) in late follicular phase women (5335 ± 848) was higher than that observed in early follicular phase women (3156 ± 322; P = 0.032). The integrated GH concentration calculated for mid-luteal phase women (3853 ± 788) was intermediate between but not statistically different from that observed in early follicular (P = 0.48) and late follicular (P = 0.14) phase women. No differences in GH pulse frequency (pulses/24 hours) were found among early follicular (8.27 ± 0.55), late follicular (7.93 ± 0.91) or mid-luteal (8.47 ± 0.66) phase women. Mean maximal GH pulse amplitude (mU/l) was higher in late follicular phase (8.93 ± 1.00) than early follicular phase (5.74 ± 0.67; P = 0.008) and mid-luteal phase (5.76 ± 0.74; P = 0.008) women. Similarly, incremental GH pulse amplitude (mU/l) was higher in late follicular phase (7.33 ± 0.83) than early follicular phase (4.68 ± 0.58; P = 0.005) and mid-luteal phase (4.36 ± 0.39; P = 0.002) women. No differences in mean pulse widths or in the interpeak valley mean GH concentrations were found among the groups. Multiple regression of each pulse parameter against serum concentrations of testosterone, 17β-oestradiol and progesterone revealed a significant (P = 0.045) positive correlation between maximum GH pulse amplitude and oestradiol and a significant (P = 0.04) negative correlation between maximal GH pulse amplitude and progesterone (r = 0.41). Conclusion - These results suggest that late follicular phase concentrations of oestradiol may enhance circulating GH via an amplitude-modulated rather than a frequency-modulated effect on the endogenous GH pulse. Progesterone may blunt this oestrogen-associated effect, thus resulting in the observed mid-luteal phase concentrations of GH. Whether these gonadal hormones act primarily at the hypothalamus and/or anterior pituitary gland remains to be clarified, but the present observations indicate that pulsatile GH release throughout the normal menstrual cycle is significantly amplitude regulated.
|Original language||English (US)|
|Number of pages||6|
|State||Published - 1992|
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