[What is the value of determining immunoreactive GHRH in acromegaly?]

Acromegaly is usually due to autonomous, excessive secretion of growth hormone from a pituitary adenoma. One would expect growth hormone-releasing factor (GHRH) in these patients to be suppressed. In the available literature referring to acromegaly, immunoreactive GHRH levels were determined in 259 acromegalic patients. When growth hormone was measured simultaneously, no correlation was found between serum growth hormone and plasma GHRH concentrations, irrespective of whether the acromegalic patients were treated or not. A possible explanation for this finding might be the lack of a feedback regulation between plasma growth hormone and GHRH. Also, since growth hormone is secreted in a pulsatile fashion the interpretation of single growth hormone values can be difficult. IGF I, which correlates well with mean growth hormone production, may therefore represent a more valuable criterion for the assessment of activity and GHRH plasma levels in acromegalics. However, no study has yet been performed to elucidate the relationship between GHRH and IGF I in acromegaly. To examine this relationship we measured the concentration of plasma GHRH and IGF I in 18 treated patients with acromegaly (age range 32-64 years median 50.5 years; median follow-up 6.5 years, range 3 months to 33 years). All immunoreactive GHRH levels were within the limits described as normal in the literature (mean +/- SD 22.89 +/- 2.72 pg/ml, range 19-28 pg/ml). The IGFI level was 396.78 +/- 224.26 ng/ml (mean +/- SD, range 71-876 ng/ml; reference ranges, age group 25-39 years: 114-492 ng/ml; 40-54 years: 90-360 ng/ml; > 55 years: 71-290 ng/ml). We found no correlation between IGF I and GHRH concentrations (r = 0.17). We therefore conclude that measuring plasma GHRH is not useful in the evaluation of the activity or therapy of acromegaly but may be helpful in its differential diagnosis since a massive elevation of GHRH is typically associated with the ectopic GHRH syndrome, a rare cause of acromegaly.