Relationship between Somatomedin-C and Growtyh Hormone Levels in Acromegaly: Basal and Dynamic Evaluation*

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Abstract
The relationship between basal and stimulated plasma GH and somatomedin-C (SmC) levels in acromegalic patients was evaluated. The basal plasma SmC levels of 66 patients were significantly correlated (P < 0.01) with mean daily plasma GH levels, but not with the percent GH incease after GH-releasing hormone or TRH or the GH decrease after acute bromocriptine administration. Bromocriptine (7.5–15 mg/day) administration for 9.2 ± 0.9 (±SD) months in 20 patients significantly (P < 0.05) decreased GH levels. SmC decreased significantly [from 9.8 ± 1.9 to 5.1 ± 0.7 U/ml (mean ± SE)] only i n the 10 patients who had the more marked GH inhibition. The administration of a somatostatin analog, SMS 201–995 (100 μg twice daily), to 12 patients for 16 weeks significantly decreased plasma GH and SmC levels beginning on the second day of therapy; normal SmC levels were achieved in 5 of 12 patients. Pituitary adenomectomy resulted in normal GH and SmC levels n i 10 of 12 and 8 of 12 patients, respectively. Our data indicate an overall dependency of plasma SmC levels on plasma GH levels in acromegaly, although similar GH levels may have differing somatomedin-stimulating activities. A derangement in the feedback mechanisms controlling GH secretion is indicated by the failure of elevated SmC levels to influence the GH responsiveness to releasing hormones. In evaluating pharmacological or surgical treatments of acromegaly, a single plasma SmC value can reliably replace several plasma GH determinations. (J Clin Endocrinol Metab63: 1348, 1986)

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