The acute effect of a single application of cabergoline on endogenous GH levels in patients with acromegaly on pegvisomant treatment.

OBJECTIVE: Treatment with pegvisomant, an antagonist of growth hormone (GH) receptors, increases GH levels in a dose dependent manner. Cabergoline can suppress GH secretion in approximately 40% of acromegalic patients. However, the acute effects of cabergoline have not been studied in patients treated with pegvisomant. We performed this cross-sectional study to evaluate endogenous GH after an additional single cabergoline administration.

DESIGN: 9 acromegalic patients on pegvisomant therapy were included. A 6h GH profile after pegvisomant alone (P) and a 9h profile in combination with oral cabergoline 0.5mg (PC) were performed. After 3 or 6h, all patients received a standardized light mixed meal. Endogenous serum GH and pegvisomant levels were measured by special in-house assays. The GH assay showed no interference with pegvisomant.

RESULTS: Endogenous GH levels at baseline did not differ significantly between the profiles (P: 16.5 μg/l (range 3.2-36.6 μg/l), PC: 8.0 μg/l (1.6-48 μg/l), p>0.05). In both profiles, GH fluctuated before meal. GH decreased more pronounced in PC but this decrease was not statistically significant. After meal, a significant decline in endogenous GH levels from 16.4 μg/l (0.4-27.1 μg/l, 100%) to 8.1 μg/l (0.2-24.7 μg/l, 66%) appeared in P at 300 min (p<0.01). Also in PC a decline from 7.8 μg/l (1.1-29.6 μg/l, 100%) to 5.2 μg/l (0.4-23.9 μg/l, 75%) at 300 min was observed but it was not significant.

CONCLUSION: Endogenous GH is not significantly decreased after a single oral cabergoline application during pegvisomant treatment in acromegaly.