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  • Author: J Kanaley x
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J A Kanaley, I Giannopoulou, S Collier, R Ploutz-Snyder and R Carhart Jr

Objective: This study examined the effect of hormone-replacement therapy (HRT) use on the incremental GH response to aerobic exercise in postmenopausal women and established whether racial differences in the GH response were seen at rest and in response to exercise.

Methods: 13 white (n = 6, HRT; n = 7, no HRT) and seven black women (no HRT) were studied on two occasions, a control day and an exercise day (30 min at 70% VO2max on a cycle ergometer). Blood was sampled every 10 min for a 4-h period and analyzed for GH using an ultrasensitive chemiluminescent assay.

Results: The mean 4-h GH concentration was higher on both study days in the HRT women than the non-HRT users. The integrated GH concentrations were greater in the HRT women both at rest and in response to exercise (rest, 352 ± 53 min μg l−1; exercise, 711 ± 57 min μg l−1; P < 0.01) than in the non-HRT women (rest, 157 ± 87 min μg l−1; exercise, 248 ± 94 min μg l−1). The incremental GH response was greater in the HRT users than in the non-HRT women (358 ± 130 versus 90.8 ± 94 min μg l−1, respectively; P < 0.05). GH-production rate during the 4-h period was greater in the HRT women than in the non-HRT women (P < 0.01), due to an increase in the GH mass secreted/pulse (P < 0.05), with no change in GH pulse number or GH half-life. No racial differences in the mean 4-h GH concentrations or integrated GH concentrations were found at rest or in response to exercise.

Conclusion: HRT use resulted in a greater incremental exercise response compared with non-HRT users, due to changes in the secretory pulse characteristics in the HRT users. This study also demonstrated that no racial differences exist at rest and in response to exercise in the morning hours.

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R Dall, J Kanaley, TK Hansen, N Moller, JS Christiansen, H Hosoda, K Kangawa and JO Jorgensen

OBJECTIVE: To characterise plasma levels of the recently identified endogenous ligand for the GH secretagogue receptor (ghrelin) during submaximal aerobic exercise in healthy adults and in GH-deficient adults. DESIGN: Eight healthy males (mean+/-s.e. age, 40.8+/-2.9 years) and eight hypopituitary males with verified GH deficiency (mean+/-s.e. age, 40.8+/-4.7 years) underwent a baseline test of their peak aerobic capacity (VO(2) peak) and lactate threshold (LT) on a cycle ergometer, as well as an evaluation of body composition. The patients were then studied on two occasions in random order when they exercised for 45 min at their LT. On one occasion, GH replacement had been discontinued from the evening before, whereas on the other occasion they received their evening GH in addition to an intravenous infusion of GH (0.4 IU) during exercise the following day. The healthy subjects exercised at their LT on one occasion without GH. RESULTS: The patients were significantly more obese and had lower VO(2) max (corrected for body weight) and LT as compared with the control subjects. Exercise induced a peak in serum GH concentrations after 45 min in the control group (11.43+/-3.61 microg/l). Infusion of GH in the patients resulted in a peak level after 45 min, whereas no increase was detected when exercising without GH (9.77+/-2.40 (GH) vs 0.11+/-0.07 microg/l (no GH)). Plasma ghrelin levels did not change significantly with time in either study, and no correlations were detected between ghrelin levels and parameters such as GH and IGF-I levels, age or body composition. Plasma ghrelin levels were significantly lower during the study period with GH as compared with the study with no GH. CONCLUSIONS: Submaximal aerobic exercise of an intensity sufficient to stimulate GH release was not associated with significant alterations in plasma ghrelin concentrations, which indicated that systemic ghrelin is not involved in the exercise-induced stimulation of GH secretion. The observation that ghrelin levels were lower during GH replacement suggests that GH may feedback-inhibit systemic ghrelin release.

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Timothy D Heden, Ying Liu, Lauren Sims, Monica L Kearney, Adam T Whaley-Connell, Anand Chockalingam, Kevin C Dellsperger, Timothy J Fairchild and Jill A Kanaley

Objective

The purpose of this study was to compare postprandial satiety regulating hormone responses (pancreatic polypeptide (PP) and peptide tyrosine tyrosine (PYY)) and visual analog scale- (VAS) assessed perceived appetite and satiety between liquid high-protein (HP) and high-carbohydrate (HC) meals in obese women during acute (24-h) caloric restriction.

Design

Eleven obese premenopausal women completed two conditions in random order in which they consumed 1500 calories as six 250-calorie HP meals or six 250-calorie HC meals over a 12-h period. Blood samples were taken at baseline and every 20 min thereafter and analyzed for PP and PYY concentrations. At these same points, perceived hunger and fullness were assessed with a VAS. The incremental area under the curve (iAUC) was used to compare postprandial responses.

Results

The 12-h PP and PYY iAUC were greater (P≤0.05) during the HP condition (PP: 4727±1306 pg/ml×12 h, PYY: 1373±357 pg/ml×12 h) compared with the HC condition (PP: 2300±528 pg/ml×12 h, PYY: 754±246 pg/ml×12 h). Perceived hunger and fullness were not different between conditions (P>0.05). The greatest changes in PYY and perceived fullness occurred after the morning meals during both conditions.

Conclusions

These data suggest that in obese women during acute caloric restriction before weight loss, i) liquid HP meals, compared with HC meals, result in greater postprandial PP and PYY concentrations, an effect not associated with differential appetite or satiety responses, and ii) meal-induced changes in PYY and satiety are greatest during the morning period, regardless of dietary macronutrient composition.