472 ESTROGEN AT LOW DOSES RAPIDLY AUGMENTS GROWTH HORMONE (GH) RELEASE INDEPENDENTLY OF SOMATOMEDIN-C (SM-C)

Abstract

We tested whether low doses of ethinyl estradiol (EE) would stimulate GH independently of SM-C inhibition, after we found EE 50 mcg/m2/d × 2d to augment peak GH responses to L-dopa testing (LDT) while lowering SM (Rich et al, Pediatr.Res. 13:329A, 1979). We first examined the effect of one bedtime dose EE(29±2(SEM) mcg/m2) upon GH reserve in 8 prepubertal short-normal children. L-dopa(0.3 gm/m2) stimulated GH to ≥7 ng/ml inconsistently (6/8) before EE. EE resulted in a significant increase in peak GH response (29±5 ng/ml)(p<.05) to LDT. EE (10-30mcg/m2) was then given for 2 days prior to repeat LDT in 15 prepubertal children with the following results. GH responses to LDT were <7 ng/ml in 3/15 prior to EE but were consistently ≥7 ng/ml after EE. Augmentation of the GH response by EE at 27±1 mcg/m2/d was of similar magnitude to that noted with 50 mcg/m2/d EE, but this low-dose EE did not act via lowering SM-C levels (.54±.09 vs .47±.07, n=8). We conclude that a single bedtime dose of EE as low as 29±2 mcg/m2 augments the peak GH response to LDT and enhances the discrimination of L-dopa testing for GH reserve. Our results suggest low-dose estrogen rapidly and directly augments GH release, consistent with its enhancing effect on growth.