RELATIONSHIP BETWEEN AGE, PERCENTAGE BODY-FAT, FITNESS, AND 24-HOUR GROWTH-HORMONE RELEASE IN HEALTHY-YOUNG ADULTS - EFFECTS OF GENDER

We investigated whether gender affects the physiological relationships between the release of GH and age, body composition, and levels of ph ysical fitness in humans. We studied 32 eumenorrheic females (age = 31 +/- 5 yr) and 12 males (age = 27 +/- 5 yr). Significant gender differ ences were found for peak oxygen consumption [VO2 peak = 40.5 +/- 6.9 (females) vs. 50.1 +/- 11.6 (males) ml/kg.min(-1), P < 0.05] and body composition [hydrostatic weighing, percentage body fat = 28.7 +/- 5.4 (females) vs. 18.1 +/- 9.8 (males), P < 0.05] but not for body mass in dex [BMI = 23.7 +/- 3.1 (females) vs. 24.0 +/- 3.3 (males)]. Blood sam ples were drawn every 10 min for 24 h from 0800 h to determine integra ted serum GH concentration [2350 +/- 1260 (females) us. 3110 +/- 1760 (males) mu g/L x min]; females were studied during the early follicula r phase (days 4-5) of the menstrual cycle. In females, a significant r elationship existed between 24-h integrated serum GH concentration and age (r = -0.35, P = 0.05) but not BMI (r = -0.19, P = 0.29); the rela tionships between 24-h integrated serum GH concentration and VO2 peak (r = 0.31, P = 0.08) and percentage body fat (r = 0.29, P = 0.11) appr oached significance. In males, significant relationships existed betwe en 24-h integrated serum GH concentration and age (r = -0.79, P = 0.00 2), percentage body fat (r = -0.75, P = 0.005), and VO2 peak (r = 0.58 , P = 0.05) but not between 24-h integrated serum GH concentration and BMI (r = -0.53, P = 0.08). Standardized regression coefficients revea led that for each so change in age, BMI, percentage body fat, or VO2 p eak the associated change in 24-h integrated serum GH concentration wa s 1.9-2.6 times greater in males than in females. We conclude that age , percentage body fat (but not BMI), and fitness are related to 24-h G H release in young adults and that these relationships are considerabl y stronger in males than females.