O-020. The approximate entropy (ApEn) of GH secretion in young males with hypogonadotropic hypogonadism (HH): A longitudinal study during testosterone replacement

Approximate entropy (ApEn) is a modern method that measures the likelihood that runs of patterns remain close in incremental comparisons. Smaller ApEn values indicate more regular patterns. We applied this method to analyze the patterns of spontaneous GH secretion, occurring during pubertal development, in 6 young males with HH (age 16.6±0.4yrs, BMI 22.3±1 kg/m², mean serum testosterone 0.35±0.04 ng/ml) undergoing three incremental doses of testosterone enantate (Testoenant, Geymonat, Italy): 25, 50 and 100 mg i.m. injections; each dose was administered three times (1 injection every 2 weeks). Nocturnal GH secretion (from 2200 to 600, blood samples taken every 20 minutes) was studied 4 times (at baseline, T1, and one week after the second administration of each dose of testosterone, T2: 25 mg, T3: 50 mg and T4: 100 mg). The ApEn scores of GH nocturnal profiles (1,20%) were significantly higher already after 25 mg testosterone (mean serum testosterone 1.1±0.2 ng/ml) as compared to baseline (0.71±0.02 vs 0.51±0.07). Moreover, ApEn scores of GH secretion did not further significantly increase vs 25 mg with the higher doses of testosterone used, 50 mg (0.67±0.07) and 100 mg (0.78±0.06). The ApEn scores were overall significantly correlated with both total testosterone (r = 0.496, p = 0.014) and free testosterone (r = 0.455, p = 0.026). In conclusion, our data suggest that the increase in testosterone during male puberty sustains an increase in disorderliness of GH secretion and that this phenomenon is very sensitive to even small increases in serum testosterone.