V. D. Castracane

Rigorous Running Increases Growth Hormone and Insulin-Like Growth Factor-I Without Altering Ghrelin

It has been suggested that ghrelin may play a role in growth hormone (GH) responses to exercise. The present study was designed to determine whether ghrelin, GH, insulin-like growth factor-I (IGF-I), and IGF-binding protein-3 (IGFBP-3) were altered by a progressively intense running protocol. Six well-trained male volunteers completed a progressively intense intermittent exercise trial on a treadmill that included four exercise intensities: 60%, 75%, 90%, and 100% of Vo2max. Blood samples were collected before exercise, after each exercise intensity, and at 15 and 30 mins following the exercise protocol. Subjects also completed a separate control trial at the same time of day that excluded exercise. GH changed significantly over time, and GH area under the curve (AUC) was significantly higher in the exercise trial than the control trial. Area under the curve IGF-I levels for the exercise trial were significantly higher than the control trial. There was no difference in the ghrelin and IGFBP-3 responses to the exercise and control trials. Pearson correlation coefficients revealed significant relationships between ghrelin and both IGF-I and IGFBP-3; however, no relationship between ghrelin and GH was found. In conclusion, intense running produces increases in total IGF-I concentrations, which differs from findings in previous studies using less rigorous running protocols and less frequent blood sampling regimens. Moreover, running exercise that produces substantial increases in GH does not affect peripheral ghrelin levels; however, significant relationships between ghrelin and both IGF-I and IGFBP-3 exist during intense intermittent running and recovery, which warrants further investigation.

Growth hormone, Igf-i, and testosterone responses to resistive exercise

It has been suggested that growth hormone (GH), testosterone (T), and insulin-like growth factor I (IGF-I) play large roles in muscle tissue growth; however, in only two investigations IGF-I responses to resistive exercise have been examined. Eight young males who had not weight trained for a minimum of 5 months participated in the study. Three sets of bench press (BP), lat-pull (LP), leg extension (LE), and leg curl (LC) exercises were performed at a 10-RM load for 10 repetitions or until failure. Blood samples were collected from an IV catheter before exercise (-30 min and -10 min), after each individual exercise (BP, LP, LE, LC), and after the exercise session (+5, +15, +25, +35, +95 min; +5:35, +22:30, and +23:30 h). GH, IGF-I, and T determinations were corrected for plasma volume change. GH significantly increased (P < 0.05), but IGF-I did not change. Correction for plasma volume accounted for significant increases in T, but did not account for GH and IGF-I results. These data suggest that moderate resistive exercise may increase GH concentrations, whereas elevated T levels can be accounted for by exercise-induced alteration of plasma volume.

Ghrelin and Other Glucoregulatory Hormone Responses to Eccentric and Concentric Muscle Contractions

Objective: Heavy resistance exercise increases growth hormone (GH) and blood glucose levels. Ghrelin is an endogenous ligand for the GH secretagory receptor that stimulates growth hormone release. Circulating ghrelin levels are suppressed by insulin and glucose. The study was conducted to determine effects of concentric (CON) and eccentric (ECC) muscle actions at the same absolute workload on circulating ghrelin and glucose as well as related glucoregulatory peptides.Methods: Ten-RM loads for bench press, leg extension, military press, and leg curl were obtained from nine males, mean age 25.±1.2 yr and body fat 17.2±1.6%. Subjects then completed two experimental trials of either CON or ECC contractions at the same absolute workload. Subjects performed four sets of 12 repetitions for each exercise at 80% of a 10-RM with 90 s rest periods. A pulley system or steel levers were positioned on each machine to raise or lower the weight so only CON or ECC contractions were performed. Pre-, post-, and 15-min post-exercise blood samples were collected.Results: Ghrelin did not increase in response to either muscle action and actually declined during the CON trial. Glucose and insulin increased regardless of the form of muscle action, but amylin and C-peptide did not change.Conclusions: Data indicate that ghrelin does not contribute to moderate resistance exercise-induced increases in growth hormone, whether from CON or ECC muscle actions. Results suggest that with a moderate loading protocol both CON and ECC muscle actions performed at the same absolute workload elevate glucose and insulin concentrations, but are not related to post-CON exercise ghrelin suppression.

Leptin and steroid hormone responses to exercise in adolescent female runners over a 7-week season

Abstract. The purpose of the study was to investigate the responses of leptin and steroid hormones to maximal exercise in adolescent female runners over a competitive season. Seven adolescent female distance runners completed three testing trials during weeks 1, 4 and 7 of their high-school track season. Blood samples were collected before and after a discontinuous graded exercise test to exhaustion (GXT) for each trial. Tests were administered during the subjects normal training time (3:30xa0p.m.–5:00xa0p.m.). Compared to week 1, peak O2 uptake rose significantly during the season and was 10% and 7% higher at weeks 4 and 7, respectively. Levels of dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulfate (DHEAS), cortisol, testosterone, and leptin increased significantly in response to the graded exercise tests. Testosterone levels were also changed over the course of the study. Resting testosterone levels and testosterone responses to exercise in weeks 4 and 7 were both higher than in week 1. Resting concentrations and acute increases of the other hormones were not changed over the season. It appears, therefore, that DHEA, DHEAS, cortisol, testosterone and leptin concentrations increase in response to running in adolescent female runners. Data also suggest that training and/or maturation increases resting testosterone concentrations and testosterone responses to running in adolescent female runners during a training season.

Effects of aerobic exercise on serum leptin levels in obese women

Abstract It has been demonstrated that leptin concentrations in obese patients may be altered by weight loss. We examined the effects of a 9-week aerobic exercise program on serum leptin concentrations in overweight women (20–50% above ideal body mass) under conditions of weight stability. Sixteen overweight women, mean (SE) age 42.75 (1.64) years, comprised the exercise group which adhered to a supervised aerobic exercise program. A graded exercise treadmill test was conducted before and after the exercise program to determine maximal oxygen uptake (V˙O2max) using open-circuit spirometry. The women demonstrated improved aerobic fitness (V˙O2max increased 12.29%), however, body fat and the body mass index did not change significantly [42.27 (1.35)–41.87 (1.33)%]. Fourteen women, age 40.57 (2.80) years, did not exercise over the same time period and served as a control group. Serum leptin levels were not significantly altered for either the exercise [28.00 (2.13)–31.04 (2.71)u2009ngu2009·u2009ml−1] or the control group [33.24 (3.78)–34.69 (3.14) ngu2009·u2009mg−1]. The data indicate that 9 weeks of aerobic exercise improves aerobic fitness, but does not affect leptin concentrations in overweight women.

Follicular and luteal phase hormonal responses to low-volume resistive exercise.

The purpose of the study was to 1) determine the effects of a low-volume resistive exercise protocol on serum concentrations of estradiol (E2), progesterone (P4), growth hormone (GH), testosterone (T), and androstenedione (AN) and 2) ascertain whether the endocrine responses are affected by the phase of the menstrual cycle. Eleven untrained, healthy women were assigned to either an early follicular or luteal testing group. The subjects completed three sets of bench press, lat-pull, leg extension, and leg curl exercises at a 10 repetition maximum load on fixed machines with 2-min of rest between sets. Blood samples were collected through an indwelling cannula before, during, and after the exercise. Area-under-the-response-curve (AUC) data demonstrated that E2 concentrations were significantly elevated in both follicular and luteal phases with a greater response in the luteal phase. Moreover, data suggest there is a luteal phase-induced increase in GH and AN in response to the low-volume resistive exercise; however, P4 and T concentrations in untrained women are not increased by low-volume resistive exercise with 2-min rest periods, nor does the altered hormonal milieu produced by the phase of the menstrual cycle affect these hormonal responses.

Genetic Variation in Plasma Androgens and Ovarian Aromatase Activity During Mouse Pregnancy

Abstract Genetic variation in fetal survival, maternal plasma androgen levels, and ovarian aromatase activity was examined mid (Day 9) and late gestation (Day 16) in strains of mice that differ in reproductive performance (A/J, C57BL/6J, C8/Jls, C17/Jls, and S15/Jls). At both gestational stages, females selected for large litter size (S15/Jls) carried more fetuses than any of the other strains examined. Particularly at midpregnancy, S15/Jls females also maintained higher plasma levels of androstenedione and testosterone relative to both control strains, C8/Jls and C17/Jls. Consistent with previously reported changes in peripheral estrogen levels during mouse pregnancy, aromatase activity was higher on Day 16 than on Day 9. This study demonstrates genetic variation in fetal survival that is correlated with increased maternal androgen levels. A stage-specific gestational increase in aromatase activity occurs in several strains of mice and is associated with elevated plasma estrogen during the second half of pregnancy.

Responses of growth hormone aggregates to different intermittent exercise intensities

The purpose of this study was to determine the impact of high-intensity intermittent exercise on the presence of circulating growth hormone (GH) aggregates measured using two different assay techniques. Six male subjects with endurance training background participated in this study under both exercise and no-exercise control conditions. After resting blood sampling, subjects completed an intermittent treadmill exercise protocol at four speeds predicted to elicit a specific V̇O2:60% V̇O2max for 10xa0min, 75% for 10xa0min, 90% for 5xa0min, and 100% for 2xa0min. After each exercise intensity was completed treadmill speed was reduced to a walk (3.5–4xa0min) for blood sampling. Sampling continued every 15xa0min for 1xa0h into recovery. All samples were then measured for GH concentrations using Nichols immunoradiometric assay (IRMA) and Diagnostic Systems Laboratorys immunofunctional assay (IFA). A second set of samples was chemically reduced using reduced glutathione (GSH; 10xa0mM for 18xa0h at room temperature) to break disulfide bonds between possible oligomeric GH complexes, and subsequently assayed using the same GH assays. With the IRMA, GH was significantly elevated (P<0.05) after the 75% workload and remained elevated through 30xa0min post-exercise. After adding GSH to the sample, the IRMA indicated significant increases in GH as early as the 60% exercise intensity and remained elevated through 45xa0min into recovery. At 75%, the GSH assay run was significantly higher than the non-GSH assay run. With the IFA, GH was significantly elevated at 60% in the non-GSH condition, whereas the GSH assay run indicated significant elevations at 75%. Both GSH and non-GSH conditions remained elevated through 30xa0min into recovery. These data indicate that the addition of GSH to serum samples prior to assay via an IRMA may break existing disulfide bonds between aggregated GH molecules, thus altering the apparent assay signal to reveal greater total GH in the sample.