Provocative Tests of Growth-Hormone Release

Seven tests of growth-hormone release were evaluated in 31 hospitalized nonobese persons without evidence of endocrine disease. Plasma growth-hormone levels were measured before and after administration of insulin, 0.1 unit/kg body weight intravenously; glucagon, 1 mg intramuscularly; levodopa, 500 mg by mouth; metyrapone, 750 mg by mouth; α 1-24-ACTH (cosyntropin), 0.25 mg intravenously; and 1 to 2 hours after the onset of nocturnal sleep, and after 15 minutes of vigorous stair climbing. Insulin uniformly stimulated growth-hormone release in all 19 persons tested, whereas 21 of 24 (87%) responded to levodopa and 17 of 21 (81%) to glucagon. ACTH stimulated growth-hormone release in only 7 of 12 persons, whereas metyrapone had no effect. A growth-hormone response to sleep was found in only 2 of 11, whereas exercise stimulated growth-hormone release in 4 of 10. Although the highest growth-hormone levels were associated with insulin hypoglycemia, these were not significantly different from levels after administration of levodopa or glucagon (P > 0.05). These data suggest that levodopa is a reasonably effective alternative to insulin hypoglycemia as a test of growth-hormone release. Its advantages are that it is given orally, and there are minor side effects. The efficacy of glucagon approaches that of levodopa.