PLASMA GROWTH HORMONE SUPPRESSIVE EFFECT OF BROMOCRIPTINE IN ACROMEGALY. EVALUATION BY PLASMA GH DAY PROFILES AND PLASMA GH CONCENTRATIONS DURING ORAL GLUCOSE TOLERANCE TESTS

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Abstract
In most studies reporting favorable results of chronic bromocriptine treatment in acromegaly, plasma GH [growth hormone] levels are measured at fixed intervals during the day. Negative results are reported in 1 major study measuring plasma GH levels during oral glucose tolerance tests. This study does not mention the time interval between the last dose of bromocriptine and the performance of an OGTT [oral glucose tolerance test], but due to the short duration of action of bromocriptine this may be critical. The plasma GH suppressive effect of bromocriptine in acromegaly is studied using plasma GH day-profiles as well as OGTT during continued bromocriptine administration and OGTT at 2 different time intervals after the last dose of bromocriptine. Twelve patients with clinically active acromegaly were treated with 10-20 mg bromocriptine for 6-9 mo. After 6-9 mo. during continued bromocriptine administration the plasma GH suppressive effect of bromocriptine was evaluated by the mean of 4 plasma GH determinations during the day and by the mean of 7 plasma determinations during oral OGTT performed 1 h, 10 h and 34 h after the last dose. The percentage decrease of the mean plasma GH level during the day induced by chronic bromocriptine treatment showed a good correlation (r = 0.86, P < 0.001) with the percentage decrease of the mean plasma GH level during OGTT, if the post-treatment test was carried out 1 h after the last dose of bromocriptine. When OGTT was performed 10 h after the last dose no significant correlation (r = 0.17) was found and after 34 h a rebound of the mean plasma GH level occurred in 8 patients. Measurement of the mean plasma GH level during the day or during OGTT are equally effective indicators of the suppressive effect of bromocriptine treatment on GH secretion in acromegaly if the OGTT is performed 1 h after the last dose of bromocriptine.