Effects of continuous versus intermittent exercise, obesity, and gender on growth hormone secretion.

CONTEXT: Obesity attenuates spontaneous GH secretion and the GH response to exercise. Obese individuals often have low fitness levels, limiting their ability to complete a typical 30-min bout of continuous exercise. An alternative regimen in obese subjects may be shorter bouts of exercise interspersed throughout the day. OBJECTIVE: The objective of the study was to examine whether intermittent and continuous exercise interventions evoke similar patterns of 24-h GH secretion and whether responses are attenuated in obese subjects or affected by gender. DESIGN: This was a repeated-measures design in which each subject served as their own control. SETTING: This study was conducted at the University of Virginia General Clinical Research Center. SUBJECTS: Subjects were healthy nonobese (n = 15) and obese (n = 14) young adults. INTERVENTIONS: Subjects were studied over 24 h at the General Clinical Research Center on three occasions: control, one 30-min bout of exercise, and three 10-min bouts of exercise. MAIN OUTCOME MEASURES: Twenty-four hour GH secretion was measured. RESULTS: Compared with unstimulated 24-h GH secretion, both intermittent and continuous exercise, at constant exercise intensity, resulted in severalfold elevation of 24-h integrated serum GH concentrations in young adults. Basal and pulsatile modes of GH secretion were attenuated both at rest and during exercise in obese subjects. CONCLUSIONS: The present data suggest that continuous and intermittent exercise training should be comparably effective in increasing 24-h GH secretion.

Administration of recombinant human GHRH-1,44-amide for 3 months reduces abdominal visceral fat mass and increases physical performance measures in postmenopausal women.

OBJECTIVE: A recent study indicated that twice-daily s.c. administration of a high dose of recombinant human GHRH-1,44-amide (GHRH) for 90 days can alter body composition in healthy older men. No data establish whether this is also true in postmenopausal women. The present study tests the hypothesis that the same GHRH regimen applied in women will: (i) elevate both IGF-I and GH concentrations; and (ii) reduce abdominal visceral fat mass, augment total body water and enhance functional performance. DESIGN: Ten postmenopausal volunteers underwent baseline study and then received 1 mg GHRH twice daily s.c. for 3 months. METHODS: Statistical comparisons were made with pre-intervention baseline data. RESULTS: GHRH administration stimulated: (i) a mean 98 +/- 14% elevation of overnight GH concentrations after administration of the peptide for 1 and 3 months (P < 0.005); (ii) a sustained 71 +/- 3.5% rise in IGF-I concentrations over the interval from 2 weeks to 3 months (P < 0.0012); (iii) a 16 +/- 7% reduction in abdominal visceral fat mass (P = 0.029) and a 14 +/- 5% increase in tri-tiated water space (P < 0.025); (iv) an abbreviation of the times required to walk 30 m (P = 0.015) and ascend two flights of stairs (P = 0.003). Most (70%) subjects experienced local skin reactivity. There were no systemic adverse events. CONCLUSIONS: A 3-month regimen of GHRH supplementation in postmenopausal women can stimulate GH and IGF-I production, reduce abdominal visceral fat and improve selected measures of physical performance, while inducing significant local skin reactivity.

Sustained growth hormone (GH) and insulin-like growth factor I responses to prolonged high-dose twice-daily GH-releasing hormone stimulation in middle-aged and older men.

Postulated mechanisms underlying the relative hyposomato-tropism of aging include reduced hypothalamic drive by GHRH. To test this notion, we administered 1 mg (n = 11) vs. 4 mg (n = 11) recombinant human GHRH-1,44-amide s.c. twice daily for 3 months in a double-blind, parallel-cohort design to 22 healthy men (ages, 53-68 yr). After 3 months, GHRH elevated: overnight GH concentrations from 0.71 +/- 0.19 to 1.74 +/- 0.39 microg/liter (P < 0.001; 1 mg) and from 0.80 +/- 0.15 to 5.12 +/- 0.40 microg/liter (P < 0.001; 4 mg) and IGF-I concentrations from 117 +/- 14 to 234 +/- 20 microg/liter (P = 0.007; 1 mg) and from 147 +/- 13 to 286 +/- 22 microg/liter (P < 0.001; 4 mg). Only the higher GHRH dose also increased total body water (tritium space; P = 0.024) and fat-free mass (dual-energy x-ray absorptiometry; P = 0.021), and reduced total abdominal adiposity (computed axial tomography scan; P = 0.042). Both supplementation schedules shortened the time required to walk 30 m and ascend four flights of stairs (P < 0.025 each). Lower extremity strength, aerobic capacity, and bone mineral density did not change. Local injection site reactions were common. We conclude that sc administration of a large dose of GHRH (4 mg) twice daily for 3 months elevates GH and IGF-I concentrations, increases total body water and fat-free mass, reduces total abdominal adiposity, and enhances certain performance measures in healthy aging men but causes local skin reactions.

The effects of time following acute growth hormone administration on metabolic and power output measures during acute exercise.

We examined the effects of GH infusion on metabolism and performance measures during acute exercise. Nine males [(X+/-SEM): age 23.7+/-1.9 yr, height 182.6+/-1.6 cm, weight 77.3+/- 2.6 kg, percent fat 17.7+/-1.9%, peak oxygen consumption 37.9 +/- 2.9 ml/kg.min] completed six 30-min randomly assigned bicycle ergometer exercise trials at a power output midway between the lactate threshold and peak oxygen consumption. In five of the six trials, the subjects received a recombinant humanGHinfusion (10 microg/kg, 6-min square wave pulse) at 0800 h, followed by a 30-min exercise trial initiated at one of the following times: 0845, 0930, 1015, 1100, or 1145 h. During one of the six trials, the subject received a saline infusion followed by a 30-min exercise trial initiated at 0845 h. Mixed-effect, repeated-measures ANOVA analyses corrected for multiple comparisons revealed that there were no significant condition effects for total work, caloric expenditure, heart rate response, the blood lactate response, or ratings of perceived exertion response. However, acute GH administration resulted in a lower exercise oxygen consumption without a drop-off in power output. We conclude that the time of exercise initiation after GH infusion does not affect total work, caloric expenditure, heart rate response, blood lactate response, or ratings of perceived exertion but reduces oxygen consumption in response to 30 min of constant load exercise at an intensity above the lactate threshold. The last outcome may suggest that GH administration can improve exercise economy.