M. Westwood et al., Modification of plasma insulin-like growth factors and binding proteins during oral contraceptive use and the normal menstrual cycle, AM J OBST G, 180(3), 1999, pp. 530-536
OBJECTIVE: Sex steroid regulation of the insulin-like growth factor axis is
a subject of contention. We examined the effect of combined oral contracep
tives and investigated the cyclic variations in the insulin-like growth fac
tor axis.
STUDY DESIGN: Fasting blood samples were taken from 9 women receiving oral
contraceptives, 10 women receiving no medication, and 10 male subjects.
RESULTS: In women receiving oral contraceptives, insulin-like growth factor
binding protein 1 remained highly phosphorylated and levels were acutely i
ncreased by sex steroid treatment (305 +/- 110 mu g/L on day 14 of the cycl
e [medication phase] vs 118 +/- 70 mu g/L during the medication-free period
, P <.03). In women receiving no medication, insulin-like growth factor bin
ding protein 1 levels were significantly lower (69 +/- 50 mu g/L. on day 14
of the menstrual cycle, P <.001) and varied cyclically with a rise in the
late-secretory phase that coincided with the appearance of nonphosphorylate
d and less phosphorylated insulin-like growth factor binding protein 1 isof
orms. Compared with those in untreated women and in men, insulin-like growt
h factor I levels were decreased in women receiving oral contraceptives (40
5 +/- 104 ng/mL in untreated women and 330 +/- 28 ng/mL in men vs 287 +/- 7
3 ng/mL in women receiving oral contraceptives, P<.004). Oral contraceptive
use had no effect on insulin-like growth factor II levels, and neither ins
ulin-like growth factor I nor insulin-like growth factor II showed cyclic v
ariation.
CONCLUSION: The bioavailability of insulin-like growth factor I is reduced
in users of oral contraceptives. This may contribute to the metabolic chang
es observed in such subjects.