Bromocriptine and glucose tolerance in acromegalics

Acromegaly is very often accompanied by impaired glucose tolerance or a manifest diabetes mellitus, with increased immunoreactive insulin (IRI) levels whose response during oral glucose tolerance tests (OGTT) is quite often exaggerated. When the dopaminergic drug bromocriptine is administered to acromegalics, their elevated growth hormone (GH) levels very often decrease, their impaired glucose tolerance (as manifested in OGTT) improves and their exaggerated IRI response becomes more normal. Eighteen patients were treated with bromocriptine. They were followed-up repeatedly during their treatment of varying duration for up to 6 years. These results indicate that raised GH levels are not the only factor that impairs glucose tolerance in acromegalics. During bromocriptine administration, impaired glucose tolerance improved and abnormal IRI levels (OGTT) became more normal even without any decrease in the high GH levels. In non-diabetic acromegalics, when bromocriptine was administered, there was not only an average decrease in the elevated GH values during OGTT, but a normalization of increased IRI values as well, without any major change in the corresponding blood glucose levels. During insulin tolerance tests (ITT), after i.v. insulin, the IRI levels after 30 and 60 min were markedly higher in acromegalics on bromocriptine than in the same patients before its administration, without any significant change in the corresponding blood glucose values. In 2 diabetic acromegalics, bromocriptine administration re-established their lost ability to increase IRI levels during OGTT. This was accompanied by a marked improvement in their glucose tolerance. It is probable that bromocriptine decreases glucagon levels in acromegalics, or at least in some of them. It is suggested that bromocriptine could protect the beta-cells of acromegalics from "exhaustion'.