Source: Lancet  |  Posted 9 years ago

Females with acromegaly have lower levels of serum insulin growth factor-1 (IGF-I) for equivalent mean serum growth hormone levels. This sex-dependent difference is independent of disease activity and concomitant medication.

Investigators from the Christie Hospital, Manchester, England, also report that the age of patients with acromegaly significantly influences IGF-I concentration for a given serum growth hormone level.

These data have "important implications" for the use of serum IGF-I and growth hormone as markers of disease activity in acromegaly, the researchers say. As IGF-I was increasingly used as a marker of disease activity in acromegaly, its relationship with serum growth hormone was of great interest.

Healthy females secreted three times more growth hormone than males but had similar serum IGF-I levels. In those with growth hormone deficiency, women needed 30-50 percent more exogenous growth hormone to maintain the same serum IGF-I as men.

The researchers had previously reported that, for a given level of growth hormone, women had significantly lower circulating IGF-I. This finding emerged from investigations of a selected cohort of patients with active acromegaly. These patients were studied while they were off medical therapy using a single fasting serum growth hormone and IGF-I measurement.

The researchers now assessed the influence of age and sex on the relationship between serum growth hormone and IGF-I in an unselected cohort of patients with acromegaly independent of disease control and medical treatment.

The researchers studied 60 unselected patients (m=34, f=26) aged 24-81 years with acromegaly. Of these, 45 had received pituitary radiotherapy. Patients had varying degrees of disease control and received medication where appropriate.

Mean serum growth hormone was calculated from an eight-point day profile (n=45) and values obtained during a 75-gram oral glucose tolerance test (n=15).

The median calculated growth hormone value was 4.7 mU/l (range 1-104 mU/l). There was a significant linear association between serum IGF-I and log10 mean serum growth hormone for the cohort.

After statistical adjustments, there was a significant difference in the relationship between mean serum growth hormone and IGF-I in both sexes. Women had average serum IGF-I levels 11.44 nmol/l lower than men with the same mean serum growth hormone.

Age significantly influenced the relationship and, for a given serum growth hormone, IGF-I was estimated to fall by 0.37 nmol/l annually.