Patients with active acromegaly often develop diabetes mellitus (DM) or impaired glucose
tolerance (IGT). Treatment with somatostatin analogues (SA) does not only inhibit
GH secretion but may also impair insulin secretion. In order to evaluate the influence
of SA on glucose metabolism we investigated insulin resistance (IR) and β-cell function
(HOMA-β), using the recommended combination of HOMA-R and HOMA-β model.
We measured fasting insulin, blood glucose (FBG) and IGF-I and repeated insulin and
blood glucose measurement after 120min. of an oral glucose tolerance test with 75g
of glucose. We studied 51 patients (27f/24m, age 54y (20–75)). 18 pat. were on SA-treatment,
33 pat. had no medical treatment. 74.5% of the pat. reached GH levels <2.5ng/ml, 74.5%
had normal IGF-I levels. According to WHO-criteria, there were 5 pat. with DM, 9 pat.
with IGT and 37 pat. with normal glucose tolerance.
We found no significant influence of disease activity on HOMA-R and HOMA-β. In the
33/51 subjects without any drug treatment median HOMA-β was 170.4% (36.0–624.0%).
In contrast, in the 18 pat. on SA treatment median HOMA-β was significantly lower
(84.2% (36.5–346.2%), p=0.001). Despite this, there was no difference in HOMA-R between
both groups (2.4 (0.7–8.4) versus 2.3 (0.7–6.1), respectively). Pat. with active acromegaly
did not differ in FBG from inactive ones. However we found a significant difference
between pat. on SA (median FBG 5.75mmol/L (4.61–9.78)) and those without medication
(4.83mmol/L (3.83–5.89), p<0.001) despite similar insulin values. The incidence of
DM in pat. on SA is significantly increased compared to pat. without SA treatment
(p<0.05).
In conclusion we found that SA decrease β-cell-function significantly without affecting
insulin resistance. Therefore we think that insulin secretagogues are probably more
effective in the treatment of DM in acromegalic patients on SA therapy than insulin
sensitizers.
