Effects of two oral contraceptives on plasma levels of insulin-like growth factor I (IGF-I) and growth hormone (hGH).

In 18 healthy women the effect of two oral contraceptives (OCs) on insulin-like growth factor (IGF-I) and its binding protein-3 (IGFBP-3) and growth hormone (hGH) plasma level were studied before and after intake of either of two OC formulations over 21 days one containing 2 mg dienogest and 0.03 mg ethinyl estradiol (group A) and the other 0.125 mg levonorgestrel and 0.03 mg ethinyl estradiol (group B). There was a reduction of the mean IGF-I concentration of 30% (p = 0.008) in the women receiving dienogest-containing pills and 12% (p = 0.006) in women taking the levonorgestrel-containing preparation. This difference between drug groups was statistically significant (p = 0.002). A correlation between the control values and the basal-treatment difference (r = 0.945; p = 0.000) was observed only in women of group A. Between basal and treatment cycles the mean plasma levels of hGH remained unchanged in both groups tested but the 23.5 hours integrated mean hGH plasma concentrations (AUC0-23.5 hours) were significantly elevated by 36% (p = 0.016) in comparison to basal values before treatment only in women receiving the levonorgestrel-containing pills. Also in the women who received the dienogest-containing preparation the changes of integrated mean plasma were inversely associated with the control values (r = -0.723; p = 0.025). Neither in group A nor in group B was the mean plasma level of IGFB-3 changed. In conclusion: the results of the present analysis indicate that hormonal contraceptives can modulate the GH and IGF-I-axis in the reproductive age. Probably the androgenic progestogen levonorgestrel (0.125 mg/day) opposes the estrogen-induced action. In the women who took the dienogest-containing formulations (anti-androgenic progestogen--group A) the extent of individual changes (hGH and IGF-I) depends on the basal level prior to pill intake. Further studies especially of long-term intake of OCs are necessary to confirm these results and to assess the practical relevance for possible effects on connective tissue and bone. (authors)