Because administration for 1 week of the
GnRH antagonist
Nal-Glu GnRH had been shown to decrease FSH secretion from supranormal to normal in men with gonadotroph
adenomas, we investigated the effect of prolonged administration of
Nal-Glu on the size of gonadotroph
adenomas. To quantitate the effect of
Nal-Glu GnRH on gonadotroph
adenoma size, we first developed a technique for calculating
adenoma volume. The technique involved collecting magnetic resonance (MR) imaging data from each
adenoma at 1-mm slice intervals in the coronal, axial, and sagittal views and using the Softvu computer program to calculate
adenoma volume from the MR data. The precision of this technique, as judged by the coefficients of variation of the calculations of the same view of the same study three times, was 1.7%, 1.0%, and 1.0% for each of three studies. When
Nal-Glu GnRH (5 mg, sc, every 12 h) was self-administered for 3-12 months to five men with gonadotroph
adenomas and supra-normal serum FSH concentrations, the serum FSH concentrations decreased to normal or below normal for the entire treatment period.
Adenoma size, however, did not change during treatment in any of the five men. We conclude that calculating
pituitary adenoma volume from MR data using the Softvu computer program is a highly reproducible technique, but that
Nal-Glu GnRH is not an effective treatment for reducing gonadotroph
adenoma size. The failure of
Nal-Glu to reduce
adenoma size despite its success in reducing FSH secretion suggests that FSH secretion from gonadotroph
adenomas is dependent on endogenous
GnRH, but growth of gonadotroph
adenomas is not.