Great progress has been achieved in the study of pituitary tumors during the last two decades regarding early and adequate treatment; nevertheless, how to determine the effectiveness of treatment is still being discussed. In the particular case of acromegaly, the standard rule to assess efficacy of treatment is now the proportion of GH suppression following a glucose load; however, several investigators are exploring new tests that could be widely used as well as being less costly for assessing the somatotropic axis. It has been mentioned that overall GH output in acromegaly is often unrelated to either the duration of the disease or to the degree of symptoms. Some investigators have suggested that these parameters appear to correlate more closely with serum insulin-like growth factor–I (IGF-I). It is known that GH regulates the production of IGF-I in several tissues; in turn, IGF-I affects the pituitary secretion of GH. IGF-I is found in two major IGFBP complexes with molecular masses of 150 and 40 kD. Approximately 80% of the total IGF-I detected in sera is associated with the larger molecular complex and is completely saturated with IGFs. IGFBP-3 is the principal binding protein, sequestering about 75% of IGF-I and IGF-II in a large complex of 150 kDa. Both IGF-I and IGFBP-3 are GH-dependent, and therefore their measurement represents a stable index of long-term GH output. Because IGFBP-3 is GH-dependent and possesses a prolonged half-life but shows neither pulsatility nor circadian pattern, it could be an integrated marker of somatotroph function for the clinical evaluation of GH excess as well determining cure and recurrence in acromegaly. This study addresses the clinical usefulness of the measurements of both free and total IGF-I as well IGFBP-3 for the diagnosis of activity in acromegaly and the effectiveness of treatment in patients who have undergone transsphenoidal surgery.

The study included 13 patients aged 22–54 years with active acromegaly and who were treated by transsphenoidal pituitary surgery. The study was approved by the Ethics Committee of the Instituto Mexicano del Seguro Social, and all patients gave informed consent at the time of enrollment.. Baseline blood levels of GH, total IGF-I, free IGF-I, and IGFBP-3 were determined in all patients before a 75-g glucose load test was carried out prior to surgery and 3 months after transsphenoidal surgery. Glucose suppression was considered abnormal if GH failed to suppress to 2 ?g/L or less at any time points (30, 60, 90, or 120 min) after the administration of glucose load. The presence of somatotroph adenoma by immunocytochemistry analysis was confirmed in all cases. In addition, 6 of the 13 cases had positive cell immunochemistry for prolactin. The control group was comprised of 14 normal subjects who were age-, weight-, and sex-matched.

Blood samples were collected in a 10-mL vacuum tube between 7 and 8 h after an overnight fast and were centrifuged at 2,500 rpm for 10 min. Serum aliquots were separated, and all samples were maintained frozen at ?35°C until assayed in a single-assay run for each biochemical marker. GH was measured by a polyclonal double antibody RIA using a commercial kit (Diagnostic Products Co., Los Angeles, CA, USA). The sensitivity for this assay was 0.7 ng/mL, and the intra- and interassay coefficients of variation (CV) were 2.7 and 4.2%, respectively, as previously reported. Total IGF-I, free IGF-I, and IGFBP-3 were determined by two-site immunoradiometric assay (IRMA) using commercial kits (Diagnostic System Laboratories, Webster, TX, USA). Measurement of total IGF-I included an acid-ethanol extraction step to separate IGF-I from its binding protein. The sensitivity for this assay was 0.80 ng/mL, and the intra- and interassay CV were 2.6 and 4.4%, respectively. Free IGF-I had a sensitivity of 0.03 ng/mL, and the CV were 6.2 and 7.3%, respectively; as to IGFBP-3, the sensitivity was 0.5 ng/mL, and the CV were 1.9 and 3.9%.

All data are given as medians and ranges. The significance of any difference was analyzed using Wilcoxon-Whitney’s test. Spearman’s correlation analysis between different biochemical markers was performed.

Before patients were treated by transsphenoidal pituitary surgery, baseline levels of GH, of free and total IGF-I, as well as of IGFBP-3 were consistently elevated; all biochemical values significantly decreased after surgery. It was also observed that glucose load test before surgery was unable to decrease serum GH levels; likewise, free IGF-I and IGFBP-3 levels remained elevated. It shows the correlation analysis in controls, acromegaly, and in patients who exhibited either normal or abnormal suppression of GH levels with the glucose load test performed after pituitary surgery. In addition, IGFBP-3 demonstrated to be an accurate index because of its close correlation with GH suppression by glucose load test (0.91, p <0.001). In seven out of a total patients, the provocative glucose test resulted in a fall of GH to levels of less than 0.7 ng/mL three months after surgery; four of them had normal plasma IGFBP-3 and total IGF-I levels, and only three showed normal plasma IGF-I levels. Only IGFBP-3 after surgery was significantly higher in those patients who did not suppress their GH levels to <0.7 ng/mL compared to those who did. All patients exhibited a high correlation between IGFBP-3 levels and GH suppression induced by glucose. A negative correlation (r = ?0.67, p <0.01) between IGFBP-3 and free IGF-I was observed in all 13 patients at the time of enrollment before treatment; however, this correlation became positive (r = 0.54) 3 months after surgery. Postoperative total and free IGF-I levels were similar in those patients who suppressed their GH to levels of less than 0.7 ng/mL and those who did not. However, IGFBP-3 levels were consistently augmented in acromegalic patients before treatment, and uniformly decreased in treated patients who simultaneously exhibited GH levels below 0.7 ng/mL after glucose load. No correlation between total and free IGF-I was observed before treatment, but this correlation (r = 0.04) became significant (r = 0.60, p <0.05) after surgery.

Results of the present studies have shown that baseline serum levels of IGFBP-3 are consistently elevated in patients with active acromegaly and that they did not overlap with values observed in normal controls. Both IGF-I and IGFBP-3 are GH-dependent peptides that are elevated in patients with active acromegaly; both reflect the integrated secretion of GH. Our study showed that IGFBP-3 values correlate closely with the degree of GH suppression by glucose load test; conversely, baseline serum levels of total and free IGF-I did not show the same correlation with the amount of GH suppression obtained with the glucose load. From these results, it might be suggested that a single IGFBP-3 blood determination is a reliable biochemical marker in the initial study of patients with acromegaly. Additional studies are necessary to establish the precise cut-off limit for the IGFBP-3 value to obtain the diagnostic reference. After pituitary surgery, IGFBP-3 estimations showed values similar to those obtained by GH suppression by the glucose load test to establish acromegaly activity and effectiveness of surgical removal of the tumor. However, the criteria for GH suppression has changed considerably over the last decade; with the recent development of ultrasensitive GH assays, it has been shown that upon a glucose load, normal individuals suppress their GH levels to 0.029 ng/mL in males, and to 0.25 ng/mL in females. Because the glucose load test requires repeated blood samples for GH determinations as well as close vigilance of the patient, it may be advantageous to obtain a single basal determination of IGFBP-3 and IGF-I for diagnosis of acromegaly and to determine the effectiveness of transsphenoidal pituitary surgery.