Bromocriptine treatment over 12 years in acromegaly: effect on glucose tolerance and insulin secretion.

It is not known whether the beneficial effect of bromocriptine on glucose homeostasis in acromegaly is limited by a certain duration of therapy. To elucidate this problem, oral glucose tolerance tests were performed in 12 acromegaly patients before bromocriptine medication, under therapy (15.0 +/- 6.8 mg/day for 12 +/- 3 years), and during a 2-week drug withdrawal after long-term treatment. Initially altered glucose tolerance was normalized in 4 of 5 patients under bromocriptine therapy. During drug withdrawal the mean fasting glucose level and the mean glucose concentration at 120 min after oral glucose load increased from 5.05 +/- 0.61 to 5.77 +/- 0.78 mmol/l and from 5.61 +/- 2.05 to 7.55 +/- 3.05 mmol/l, respectively. A deterioration in glucose homeostasis was observed in 9 patients, and impaired glucose tolerance was ameliorated (but not to normal range) in 2 when bromocriptine was withdrawn. The proportion of alterations in glucose tolerance during drug withdrawal corresponded to that before the beginning of long-term bromocriptine treatment. Impaired glucose tolerance, observed in 2 patients under bromocriptine treatment, seemed to be compensated because a distinct elevation of glycosylated hemoglobin A1c was not observed. Bromocriptine led to a significant decrease in basal as well as glucose-stimulated insulin levels, and growth hormone secretion during oral glucose load was reduced in all 12 patients.(ABSTRACT TRUNCATED AT 250 WORDS)