Growth hormone secretory dynamics over the menstrual cycle

Whether GH secretion in women varies over the menstrual cycle is uncertain. Previous investigations have led to conflicting conclusions; some studies suggested that there is an estrogen mediated rise in GH during the periovul atory (PO) and luteal (L) phases whereas others indicated no change in CH a xis over the cycle. Differences in conclusions could relate to heterogeneit y of the study populations, GH sampling paradigms or sensitivity of the GH assays used. In order to investigate whether GH secretion varied over the c ycle, 24-h GH profiles using every 10-min sampling were obtained in 6 ovula tory women during the early follicular (EF), PO and L phases of the cycle. The TSH response to TRH, GH response to GRH and fasting plasma IGF-I were m easured on each occasion. There was a trend toward higher integrated GH con centration (IGHC) during the PO phase, although this difference was not sta tistically significant (3284+/-721 vs 4542+/-872 vs 4071+/-699 mug/min/L; E F vs PO vs L; p=0.09). Similarly, deconvolution estimated GH secretion did not vary over the cycle (p=0.56). There were no differences in GH pulse amp litude or frequency. There were no correlations between IGHC and sex steroi ds. Serum IGF-I was constant over the cycle (272+/-38 vs 277+/-31 vs 265+/- 38 mug/L; p=0.89). The TSH response to TRH and GH response to GRH did not v ary over the cycle. We concluded that the effect of changes in the ovarian steroid milieu on the GH axis during spontaneous menstrual cycles is minima l.