Growth hormone response to submaximal doses of ghrelin remains unchanged during the follicular phase of the cycle

Abstract

BackgroundPrevious data have shown that ghrelin-induced growth hormone (GH) secretion is augmented in women by exogenous but not by endogenous estrogens. The purpose of this study was to examine the response of GH to low-dose scheme of ghrelin administration in relation to physiological changes in estradiol levels during the normal menstrual cycle.MethodsTen normally cycling women were studied in two menstrual cycles. Two consecutive dosages of ghrelin (0.15 μg/kg and 0.30 μg/kg) were injected intravenously at 0 and 90 min in the early and late follicular phases of one cycle. Saline was injected in the preceding cycle. Blood samples were taken at −15, 0, 30, 60, 90, 120, 150 and 180 min. The GH response was assessed.ResultsSerum estradiol concentrations were significantly higher in the late than in the early follicular phase. After ghrelin, but not after saline administration, plasma ghrelin and serum GH levels increased significantly in both phases, peaking at 30 min and 120 min. The peak value at 120 min was significantly higher than at 30 min (P<0.001). There were no significant differences in ghrelin and GH levels between the two phases at all time points.ConclusionsThe present results show no difference in GH response to two consecutive submaximal doses of ghrelin between the early and the late follicular phase of the cycle. It is suggested that estradiol is not possibly involved in the physiological process that regulates ghrelin-induced GH secretion in women during the normal menstrual cycle.

Inhibitory Effect of Submaximal Doses of Ghrelin on Gonadotropin Secretion in Women

“…Also, thyroid and adrenal functions were normal based on specifi c blood tests. The women were investigated during 2 menstrual cycles as has been previously described [ 20 ] . In particular, all women participated in the same experimental procedure twice during a menstrual cycle, that is, in the early follicular phase (cycle day 2) and in the late follicular phase (follicle size by ultrasound 16-17 mm in diameter) (study cycle).…”

Submaximal doses of ghrelin do not inhibit gonadotrophin levels but stimulate prolactin secretion in postmenopausal women

“…These results are in agreement with previous data demonstrating that with the use of a similar protocol or a single high dose of ghrelin there was no significant difference in ghrelin-induced GH secretion between the late and the early follicular phase of the menstrual cycle. 14,20 However, previous studies in oestrogen-treated postmenopausal women have suggested an amplifying effect of oestradiol on the stimulating action of five graded physiological but not pharmacological dosages of ghrelin on the pulsatile secretion of GH. 19,29 In the present study, only basal secretion of GH was investigated.…”

“…Moreover, transdermal oestradiol potentiates ghrelin‐induced GH secretion in healthy postmenopausal women, suggesting that this steroid enhances hypothalamo‐pituitary sensitivity to ghrelin . However, further experiments in women have shown no difference in ghrelin‐induced GH response between the late and the early follicular phase of the menstrual cycle …”

“…19 However, further experiments in women have shown no difference in ghrelin-induced GH response between the late and the early follicular phase of the menstrual cycle. 20 This study was undertaken to investigate the hypothesis that in oestrogen-deprived postmenopausal women, exogenous ghrelin shows no inhibitory effect on gonadotrophin levels, while exogenous oestradiol potentiates ghrelin-induced PRL secretion.…”

Growth Hormone Releasing Peptide-2 Attenuation of Protein Kinase C-Induced Inflammation in Human Ovarian Granulosa Cells

“…In fact, blood ghrelin can be regularly detected in the women receiving in vitro fertilisation (IVF) procedure [ 20 ]; Ghrelin was previously shown to stimulate prolactin secretion in normal women [ 21 ]. The submaximal dose of ghrelin was not able to induce growth hormone secretion [ 22 ], but was able to suppress gonadotropin secretion in women [ 23 ]. Human ghrelin was also demonstrated to reduce the pituitary response to gonadotropin-releasing hormone (GnRH) in superovulated ewes [ 24 ].…”