GH responsiveness varies during the menstrual cycle.
Level 4 - case-series / case-control
Prospective single-arm within-subject repeated-measures physiological challenge
PubMed 16322382 · doi:10.1530/eje.1.02037
What was done
Nine women with regular menstrual cycles (mean age 38 ± 6 years) underwent an IGF-1 generation test (subcutaneous injection of 7 mg growth hormone) during the early-follicular (EF), periovulatory (PO), and midluteal (ML) phases of the menstrual cycle. Serum oestradiol, IGF-1, IGFBP-3, and acid-labile subunit (ALS) were measured at baseline and 24 hours post-injection.
What was found
Oestradiol levels were lower in the EF phase than in PO or ML phases (32.6 ± 7.8 vs 69.6 ± 16.2 vs 66.6 ± 23.6 pg/ml; P < 0.001). Baseline IGF-1 was lower in EF than PO or ML phases (291.8 ± 56.6 vs 335.0 ± 55.2 vs 346.6 ± 78.2 ng/ml; P = 0.008), but the 24-hour IGF-1 increment was significantly higher in EF than PO or ML phases (234.6 ± 59.2 vs 194.7 ± 37.8 vs 185.2 ± 37.3 ng/ml; P = 0.008). No numerical data were reported in the abstract for IGFBP-3 or ALS.
Why it matters
Endogenous estrogen fluctuations across the menstrual cycle significantly alter hepatic GH sensitivity, suggesting that women with GH deficiency on fixed-dose replacement may experience varying biological responses across cycle phases.
Limits
The sample size was very small (n = 9), with no control group. The study was conducted in healthy women rather than patients with GH deficiency, and abstract data omitted quantitative results for IGFBP-3 and ALS.
Cited by
- context Plasma estradiol levels can increase approximately tenfold from early in the follicular phase to its apex just before ovulation.