Dopaminergic treatment of acromegaly: different effects on hormone secretion and tumor size

We studied the effects of long term treatment with bromocriptine (Br) or lisuride (L) on GH secretion and tumor size in 19 acromegalic patients with large pituitary adenomas. In 22 additional patients with smaller adenomas, only plasma GH levels were monitored during treatment. All patients underwent an acute test with 2.5 mg Br or 0.3 mg L and, on the basis of GH changes, were classified as responders, i.e. reduction in circulating GH concentrations by at least 50% below baseline, or as nonresponders. The chronic treatment was 5-20 mg/day Br in 26 patients or 0.3-2.0 mg/day L in 15 patients. Treatment was given for 4-26 months (mean +/- SE, 13.3 +/- 2.8 months). Plasma GH levels (baseline, 46.3 +/- 8.3 ng/ml) were significantly lower in the group as a whole (22.7 +/- 3.6 ng/ml; P less than 0.01) after the first month of treatment with dopamine agonist agents. GH levels decreased significantly in those acromegalic patients who responded to the acute test (P less than 0.001), but were unchanged in the nonresponders. In addition, there was a significant correlation between the maximal percent GH decrease in the acute test and the response during chronic treatment (r = 0.73; P less than 0.01). Computed tomography failed to show any tumor size changes in any of the GH nonresponders who had a macroadenoma . However, in two patients in the acute responder group with macroadenomas, chronic dopamine agonist therapy resulted in reduction of the extrasellar portion of the tumor (-30% and -40% of tumor area, respectively). These data show that although dopaminergic drugs lower GH levels and reverse signs and symptoms of active disease in those acromegalic patients who are responsive to an acute challenge, tumor size reduction occurred in a minority of such patients.