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 gluc ose homeostasis in acromegaly is limited by a certain duration of ther apy. To elucidate this problem, oral glucose tolerance tests were perf ormed 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 therap y. During drug withdrawal the mean fasting glucose level and the mean glucose concentration at 120 min after oral glucose load increased fro m 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in 9 patients, and impaired glucose tolerance was amelio rated (but not to normal range) in 2 when bromocriptine was withdrawn. The proportion of alterations in glucose tolerance during drug withdr awal corresponded to that before the beginning of long-term bromocript ine treatment. Impaired glucose tolerance, observed in 2 patients unde r bromocriptine treatment, seemed to be compensated because a distinct elevation of glycosylated hemoglobin A1c was not observed. Bromocript ine led to a significant decrease in basal as well as glucose-stimulat ed insulin levels, and growth hormone secretion during oral glucose lo ad was reduced in all 12 patients. Similarly to the increased growth h ormone secretion after drug withdrawal in 11 patients, a rise in gluco se-stimulated insulin secretion was found in all patients; hereby, the mean insulin levels at 0 and 120 min during oral glucose load rose si gnificantly from 7.5 +/- 2.6 to 12.1 +/- 5.1 mU/l (P<0.01) and from 71 .3+/-52.1 to 101.4+/-50.7 mU/l (P<0.02), respectively. A direct relati onship between disturbance in glucose homeostasis and degree of hypers omatotropism was not observed. Our data confirm that the beneficial ef fect of bromocriptine therapy on glucose homeostasis in selected patie nts with acromegaly is still present after dopaminergic treatment over a mean period of 12 years. Compared with the published rates on impro ved glucose homeostasis under octreotide, the effect of bromocriptine seems to be more favorable.