Estrogen deficiency may account for lower circulating GH and insulin-like growth factor I (IGF-I) concentrations in the menopause. Since the liver is the major source of circulating IGF-I and oral estrogens have nonphysiological effects on hepatic function, we have compared GH secretion over 24 h from 20 min sampling and serum IGF-I levels in premenopausal women (n = 7, follicular phase) and postmenopausal women before and after 2 months of cyclical replacement therapy with either oral ethinyl estradiol (EE, 20 micrograms daily; n = 7) or transdermal 17 beta-estradiol (E2, 100 micrograms patches applied twice weekly; n = 7). The extent of GH binding to its serum binding protein was also examined by measuring the percent specific binding of [125I] GH in serum. Mean 24-h serum GH and serum IGF-I were significantly lower (P less than 0.05) in postmenopausal than in premenopausal women. Oral and transdermal estrogen therapy resulted in a comparable degree of gonadotropin suppression. Oral EE treatment increased mean 24-h serum GH (2.0 +/- 0.4 to 7.0 +/- 0.6 mIU/L, P less than 0.0005) and mean pulse amplitude (5.3 +/- 1.2 to 11.2 +/- 2.5 mIU/L, P less than 0.01) but significantly reduced circulating IGF-I (0.70 +/- 0.09 to 0.47 +/- 0.04 U/mL, P less than 0.02) levels. Oral EE increased the percent specific binding of [125I]GH (22.0 +/- 1.6 to 32.0 +/- 1.9%, P less than 0.0005), however the derived mean 24-h free serum GH concentrations were significantly higher (P less than 0.0005) after treatment. By contrast, transdermal E2 administration, which restored circulating E2 concentrations to the midfollicular range, increased circulating IGF-I (0.86 +/- 0.15 to 1.10 +/- 0.14 U/mL, P less than 0.005) to levels that were not significantly different from those of premenopausal women (1.41 +/- 0.21 U/mL). This was not accompanied by changes in 24-h GH secretion or the percent specific binding of [125I]GH in serum. The route of administration is a major determinant of the effects of exogenous estrogens on the GH/IGF-I axis. Oral estrogen administration inhibits hepatic IGF-I synthesis and increases GH secretion through reduced feedback inhibition. Reduced GH secretion in the menopause is not explained by estrogen deficiency since GH secretion is not restored by the attainment of physiological E2 concentrations using the transdermal route. The contrasting route dependent IGF-I responses have important implications for the long-term benefit of hormone replacement therapy in the menopause.

Patients with active acromegaly secrete more GH than age-matched normal controls. GH secretion in acromegaly is characterized by marked blunting of pulsatile secretion and, in contrast to normal subjects, the failure of GH to fall to undetectable levels at any time during the 24-hour day. IGF-I measurement is a more practical alternative in the diagnosis of acromegaly and in the assessment of therapeutic outcome. Since abnormalities of GH regulation may persist despite normalization of IGF-I, a distinction between remission and cure should be made. Detailed post-treatment evaluation of GH secretion is necessary to define the nature of underlying GH regulation and to evaluate the risk of disease recurrence.

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