EXERCISE-INDUCED CHANGES IN CIRCULATING GROWTH-FACTORS WITH CYCLIC VARIATION IN PLASMA ESTRADIOL IN WOMEN

The effect of 10 min of high-intensity cycling exercise on circulating growth hormone (GH), insulin-like growth factors I and II (IGF-I and -II), and insulin-like growth factor binding protein 3 (IGF BPS)was st udied in nine eumenorrheic women (age 19-48 yr) at two different phase s of the menstrual cycle. Tests were performed on separate mornings co rresponding to the follicular phase and to the periovalatory phase of the menstrual cycle, during which plasma levels of endogenous estradio l (E-2) were relatively low (272 +/- 59 pmol/l) and high (1,112 +/- 40 7 pmol/l), respectively. GH increased significantly in response to exe rcise under both E-2 conditions. Plasma GH before exercise (2.73 +/- 2 .48 vs. 1.71 +/- 2.09 mu g/l) and total GH over 10 min of exercise and 1-h recovery (324 +/- 199 vs. 197 +/- 163 ng) were both significantly greater for periovulatory phase than for follicular phase studies. IG F-I, but not IGF-II, increased acutely after exercise. IGF BP-3, assay ed by radioimmunoassay, was not significantly different at preexercise ,end exercise, or at 30-min recovery time points and was not different between the two study days. When assayed by Western blot, however, th ere was a significant increase in IGF BP-3 30 min after exercise for t he periovulatory study. These findings indicate that the modulation of GH secretion associated with menstrual cycle variations in circulatin g E-2 affects GH measured after exercise, at least in part, by an incr ease in baseline levels. The acute increase in IGF-I induced by exerci se appears to be independent of the GH response and is not affected by menstrual cycle timing.