Estrogen (E) reduces bioassayable GH-dependent serum somatomedin (SM) activity in acromegalics without affecting plasma growth hormone (GH) levels and inhibits the rise of SM activity normally produced by GH administration in GH-deficient subjects. We have now investigated the effect of E administration on serum SM activity and on plasma GH and prolactin (PRL) in 6 adult male subjects without pituitary pathology. Chronic E administration (ethinyl estradiol 0.5 mg/day for 7 to 70 days) reduced serum SM activity by 40 to 62% in each of 4 subjects (P less than 0.02 to less than 0.001). In 3 of the subjects, basal GH levels increased by 75 to 300% (P less than 0.05 to less than 0.001) and basal PRL levels increased by 90 to 200% (P less than 0.01 to less than 0.001). While iv administration of normal saline did not significantly affect either SM or GH, iv administration of E (bolus injection of 25 mg conjugated estrogens, USP) to 5 subjects resulted in: a) a 46 to 80% decrease in serum SM activity in all subjects, proceeding with an apparent half-life of 2 hours, becoming significant (P less than 0.05) at 2 hours (1 subject) to 3 hours (4 subjects), maximal at 6 hours, and persisting for 12 to 24 hours; b) GH elevation to 3 to 16 times baseline level (P less than 0.01) at 2 to 3 hours in 4 subjects; and c) no significant change of PRL levels in any subject. The mean GH response to iv E was maximal at a time (2 hours) when the mean SM activity had decreased only 20% and subsided well before the nadir of SM activity. The one patient without GH response to chronic or acute E administration may have been affected by absorption of triamcinolone being applied topically during the study. These results demonstrate that in males with normal pituitary function, E reduces serum SM activity, enhances basal GH and PRL secretion, and, upon iv injection, stimulates acute GH release. Although opposite chronic E effects upon GH and SM activity support a putative negative SM-GH feed-back mechanism, iv E administration apparently provokes acute GH release by a different mechanism. The half-life of serum SM activity in the human is probably much shorter than previously estimated.
PIP: Acute and chronic estrogen effects upon serum somatomedin (SM) activity, growth hormone (GH), and prolactin were studied in adult male subjects. Administration of .5 mg ethinyl estradiol/day for 7-70 days reduced serum SM activity by 40-62% in each of 4 subjects (p less than .02 to less than .001). In 3 subjects, basal GH levels increased 75-300% (P less than .05 to less than .001) and basal prolactin levels increased by 90-200% (p less than .01 to less than .001). Intravenous (iv) administration of saline did not markedly affect SM or GH while the iv administration of 25 mg conjegated estrogens to 5 subjects resulted in: 1) a 46-80% decrease in serum SM activity in all subjects proceeding with an apparent 1/2-life of 2 hours, becoming significant (p .05) at 2-3 hours and persisting for 12-24 hours, 2) GH elevation to 3-16 times baseline level (p .01) at 2-3 hours and 3) no marked change in prolactin levels. These results indicate that in males with normal pituitary function, estradiol reduces serum SM activity, enhances basal GH and prolactin secretion and, upon iv injection, stimulates acute GH release. It is suggested that the 1/2-life of serum SM activity in the human is probably much shorter than previously estimated.