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Influence of Body Mass Index and Gender on Growth Hormone (GH) Responses to GH-Releasing Hormone Plus Arginine and Insulin Tolerance Tests

Divisions of Endocrinology (X.-D.Q., I.T.G.G., M.Y.A.S., P.C., P.D.C., R.S.S., C.W.) and Neurosurgery (D.F.K.), Departments of Medicine and Surgery, Harbor-University of California Los Angeles (UCLA) Medical Center and Los Angeles Biomedical Research Institute, Torrance, California 90509; and David Geffen School of Medicine at UCLA (X.-D.Q., I.T.G.G., M.Y.A.S., P.C., P.D.C., R.S.S., D.F.K., C.W.), Los Angeles, California 90024

Address all correspondence and requests for reprints to: Christina Wang, M.D., General Clinical Research Center, Harbor-University of California Los Angeles (UCLA) Medical Center, 1000 West Carson Street, Torrance, California 90509. E-mail: wang{at}labiomed.org.

The aim of this study is to assess whether gender and body mass index (BMI) should be considered in developing thresholds to define GH deficiency, using GH responses to GHRH + arginine (ARG) stimulation and insulin tolerance test (ITT). Thirty-nine healthy subjects (19 males, 20 females; ages 21–50 yr) underwent GHRH + ARG, and another 27 subjects (19 males, 8 females; ages 20–49 yr) underwent ITT. Peak GH response was significantly higher (P = 0.005) after GHRH + ARG than with ITT, and this difference could not be explained by age, gender, or BMI. Peak GH response was negatively correlated with BMI in both tests (GHRH + ARG, r = –0.76; and ITT, r = –0.65). Peak GH response to GHRH + ARG was higher in females than males (P = 0.004; ratio = 2.4), but it was attenuated after eliminating the influence of BMI (P = 0.13; ratio = 1.6). No significant gender differences were found in peak GH responses to ITT, which could be due to the smaller number of female subjects studied. GH response to GHRH + ARG and ITT stimulation is sensitive to BMI differences and less so to gender differences. A higher BMI is associated with a depressed GH response to both stimulation tests. BMI should therefore be considered as a factor when defining the diagnostic cut-off points in the assessment of GH deficiency, whereas whether gender should be likewise used is inconclusive from this study.

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