Hypersecretion of growth hormone and prolactin in McCune-Albright syndrome

Acromegaly and hyperprolactinemia have been reported in association with the McCune-Albright syndrome, but the pathophysiology of the GH and PRL hypersecretion that occurs in patients with this disorder has not been defined. We studied GH and PRL secretory dynamics in three patients with McCune-Albright syndrome and hypersecretion of these hormones. Each patient had excessive linear growth, glucose-non-suppressible plasma GH concentration, and GH responsiveness to TRH and GHRH. In response to exogenous GHRH, plasma GH concentrations rose approximately 2-fold in all three patients. Plasma GHRH levels were 20-40 ng/L (normal, less than 30). Study of the spontaneous GH secretory pattern in two patients indicated nocturnal augmentation of GH release. Bromocriptine therapy failed to reduce plasma GH in all patients; in one patient treatment with octreotide, a long-acting somatostatin analog, partially suppressed plasma GH and insulin-like growth factor I levels. These results suggest that hypersecretion of GH in the McCune-Albright syndrome is not due to ectopic GHRH production or autonomous somatotroph function. The results are similar to those described in classic acromegaly due to GH-secreting pituitary tumors. However, the lack of radiographic pituitary enlargement, the variable pituitary pathology reported in similar patients, and frequent concordance of GH and PRL excess suggest that the pathogenesis of this disorder may differ fundamentally from other forms of acromegaly or gigantism. The pathophysiology may reflect abnormal hypothalamic regulation and/or an embryological defect in pituitary cellular differentiation and function.