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Biomedical subjects

P A Farrell

Publications and source records attributed to P A Farrell.

At least 37 records · Page 2Linked to original sources
PubMed1998

Effect of resistance exercise training on cortical and cancellous bone in mature male rats.

The effect of resistance training on tibial cancellous and cortical bone was evaluated in rats by using static histomorphometry and Northern analysis. Five-month-old male Sprague-Dawley rats were randomly assigned to exercise (Ex; n = 8) or control (Con; n = 4) groups. Animals were operantly conditioned to press two levers, facilitating full extension and flexion of the hindlimbs ("squats"), while wearing an unweighted vest. After an 8-wk familiarization period, Ex animals performed 3 sessions/wk for 17-19 sessions with progressively increased amounts of weight applied to the vest. Con rats completed the same exercise protocol without applied resistance. No difference in cross-sectional, medullary, or cortical bone area was observed between Ex and Con rats in the tibial diaphysis. In contrast, the cancellous bone area in the proximal tibial metaphysis was significantly larger in trained rats. Trabecular number, trabecular thickness, and the percentage of cancellous bone covered by osteoid were significantly greater in the Ex animals compared with Con animals. In addition, steady-state mRNA levels for osteocalcin for the Ex group were 456% those expressed in the Con group. The data demonstrate that resistance training increases cancellous bone area in sexually mature male rats and suggest that it does so, in part, by stimulating bone formation.

Animals↗
PubMed1998

Effects of intensity of acute-resistance exercise on rates of protein synthesis in moderately diabetic rats.

These studies determined whether increases in rates of protein synthesis observed in skeletal muscle after moderate or severe acute-resistance exercise were blunted by insulinopenia. Rats (n = 6-9 per group) were made insulin deficient by partial pancreatectomy or remained nondiabetic. Groups either remained sedentary or performed acute-resistance exercise 16 h before rates of protein synthesis were measured in vivo. Exercise required 50 repetitions of standing on the hindlimbs with either 0.6 g backpack wt/g body wt (moderate exercise) or 1.0 g backpack wt/g body wt (severe exercise). Insulin-deficient rats had a mean blood glucose concentration >15 mM and reduced insulin concentrations in the plasma. Rates of protein synthesis in gastrocnemius muscle were not different in all sedentary groups. The moderate-exercised nondiabetic group (192 +/- 12 nmol phenylalanine incorporated. g muscle-1. h-1) and moderate-exercised diabetic group (215 +/- 18) had significantly (P < 0.05, ANOVA) higher rates of protein synthesis than did respective sedentary groups. In contrast, diabetic rats that performed severe-resistance exercise had rates of protein synthesis (176 +/- 12) that were not different (P > 0.05) from diabetic sedentary rats (170 +/- 9), whereas nondiabetic rats that performed severe exercise had higher (212 +/- 24) rates compared with nondiabetic sedentary rats (178 +/- 10) P < 0.05. The present data in combination with previous studies [J. D. Fluckey, T. C. Vary, L. S. Jefferson, and P. A. Farrell. Am. J. Physiol. 270 (Endocrinol. Metab. 33): E313-E319, 1996] show that the amount of insulin required for an in vivo permissive effect of insulin on rates of protein synthesis can be quite low after moderate-intensity resistance exercise. However, severe exercise in combination with low insulin concentrations can ablate an anabolic response.

Animals↗
PubMed1998

Sodium chloride-citrate beverages attenuate hypovolemia in men resting 12 h at 2800 m altitude.

BACKGROUND: The mechanism for reduction and restoration of total body water and plasma volume (PV) during initial exposure to acute altitude (ALT) is not clear but may involve involuntary dehydration; i.e., delayed voluntary fluid intake. METHOD: Ten men (24 +/- SD 3 yr, 180.8 +/- 8.1 cm height, 78.8 +/- 12.8 kg weight, 1.99 +/- 0.19 m2 surface area, and 12.2 +/- 4.0% body fat) were in a semi-reclining position for 12 h in a chamber at 2800 m (539 mmHg) ALT or at 321 m (732 mmHg; ground). They ate a controlled breakfast (450 kcal + 3 ml x kg(-1) H2O) on the ground, and lunch and dinner at ALT (or on the ground) for a total daily intake of 2850 kcal (14% PRO, 67% CHO, 16% fat, 2.6g NaCl). At hour 10 they consumed fluid-electrolyte beverages or water (12 ml x kg(-1), 948 ml x d(-1)) in 4 sessions at weekly intervals. Beverage compositions were: a) 185 mEq x L(-1) Na+, 283 mOsm x kg(-1); b) 21.6 mEq x L(-1) Na+, 365 mOsm x kg(-1); c) water at ALT; and d) water on the ground. RESULTS: After 10 h at ALT % deltaPV (Hb-Hct) decreased (p < 0.05) by: a) 9.0 +/- SE 1.5%; b) 6.2 +/- 1.7%; c) 7.4 +/- 2.2%; and d) by 9.0 +/- 2.4%, respectively. After drinking from 1000-1030 h, PV at 1200 h changed by: a) +8.3 +/- SE 2.0% (p < 0.05); b) +2.8 +/- 2.7% (NS); c) -0.9 +/- 1.5% (NS); and d) by +0.8 +/- 3.5% (NS), respectively. The similar ground-induced hypovolemia suggests a response to confinement rather than an ALT effect and involuntary dehydration does not appear to be implicated. CONCLUSION: The significant increase in PV after consuming the (a) NaCl-NaCitrate beverage indicates that drink ionic composition appears to be more important than its osmolality for restoring PV in these conditions. Practical considerations: Because this hypovolemia was probably due to the confinement rather that reduced ambient pressure, appropriate countermeasures could be consumption of isotonic beverages, elastic stockings, leg exercise, and leg elevation.

Adult↗
PubMed1997

Age, fitness, and regional blood flow during exercise in the heat.

During dynamic exercise in warm environments, the requisite increase in skin blood flow (SkBF) is supported by an increase in cardiac output (Qc) and decreases in splanchnic (SBF) and renal blood flows (RBF). To examine interactions between age and fitness in determining this integrated response, 24 men, i.e., 6 younger fit (YF), 6 younger sedentary (YS), 6 older fit (OF), and 6 older sedentary (OS) rested for 50 min, then exercised at 35 and 60% maximal O2 consumption (VO2max) at 36 degrees C ambient temperature. YF had a significantly higher Qc and SkBF than any other group during exercise, but fitness level had no significant effect on any measured variable in the older men. At 60% VO2max, younger subjects had significantly greater decreases in SBF and RBF than the older men, regardless of fitness level. Total flow redirected from these two vascular beds (deltaSBF + deltaRBF) followed YF >> YS > OF > OS. A rigorous 4-wk endurance training program increased exercise SkBF in OS, but deltaSBF and deltaRBF were unchanged. Under these conditions, older men distribute Qc differently to regional circulations, i.e., smaller increases in SkBF and smaller decreases in SBF and RBF. In younger subjects, the higher SkBF associated with a higher fitness level is a function of both a higher Qc and a greater redistribution of flow from splanchnic and renal circulations, but the attenuated splanchnic and renal vasoconstriction in older men does not appear to change with enhanced aerobic fitness.

Adult↗
PubMed1996

Insulin stimulation of protein synthesis in rat skeletal muscle following resistance exercise is maintained with advancing age.

This study examined whether or not insulin elevates rates of protein synthesis in muscle following four days of resistance exercise in young (4-mo), middle-aged (12-mo), and old (32-mo) rats. Thirty-six male Fischer 344/BN F1 rats (n = 12 in each group) performed an operantly conditioned activity which required full extension of the hindlimbs with weights over the scapula (ACUTE; n = 6 for each age group) or with no additional weight (nonexercised; NONEX; n = 6 for each age group). Acutely exercised animals engaged in four distinct exercise sessions with each session separated by 48 h. Rates of protein synthesis were assessed in soleus, gastrocnemius (GAST), and extensor digitorum longus (EDL) muscles 16 h after the last exercise bout using a bilateral hindlimb perfusion to measure the incorporation of tritiated phenylalanine (F) into muscle protein. One limb of the bilateral hindlimb preparation received a medium that contained rat insulin at a physiological concentration (6.25 ng.ml-1), while the other limb did not. Rates of protein synthesis in soleus with insulin supplementation were significantly higher within all age groups following resistance exercise vs ACUTE without insulin and NONEX with or without insulin (p < .05). Rates of protein synthesis in soleus were not different within age groups for NONEX with or without insulin (p < .05), but rates of protein synthesis for young NONEX were significantly higher (p < .05) than middle-aged or old NONEX (204 +/- 9 vs 149 +/- 6 or 141 +/- 9 nmol F incorporated.g-1.h-1, respectively; means +/- SE). Rates of protein synthesis in GAST with insulin were also significantly higher within all age groups following resistance exercise than ACUTE without insulin or NONEX with or without insulin (p < .05). Unlike soleus, rates of protein synthesis in GAST were significantly higher for old NONEX vs young NONEX (68 +/- 6 vs 45 +/- 5 nmol F incorporated.g-1.h-1, respectively; P < .05), but not middle-aged NONEX (51 +/- 3 nmol F incorporated.g-1.h-1). Translational efficiency (rates of protein synthesis.unit of RNA-1.h-1) for GAST supplemented with insulin was significantly greater in ACUTE with insulin than ACUTE without insulin or NONEX with or without insulin (p < .05). There were no effect of age, insulin, or exercise on rates of protein synthesis in EDL (p > .05). These data suggest that following resistance exercise, insulin increased rates of protein synthesis in both soleus and GAST regardless of age, and it appeared that this insulin-mediated elevation may have occurred at the level of translation.

Aging↗
PubMed1996

Augmented insulin action on rates of protein synthesis after resistance exercise in rats.

This study investigated whether insulin has a modulatory effect on protein synthesis rates in skeletal muscle after four sessions of resistance exercise. Male rats engaged in resistance exercise (Acute) that required full extension of the hindlimbs with weights over the scapula or performed the standing movement with no additional weight (Nonex). Two separate studies were conducted. Rates of protein synthesis for study 1 (Acute, n = 6; Nonex, n = 6) were assessed 16 h postexercise by incorporation of [3H]phenylalanine ([3H]F) into muscle protein by use of an in vivo flooding dose protocol. Rates of protein synthesis in soleus of Acute (100 +/- 9 nmol F.g-1.h-1) were significantly higher than in Nonex (72 +/- 9 nmol F.g-1.h-1, P < 0.05). Rates of protein synthesis were significantly higher in gastrocnemius of Acute vs. Nonex (48 +/- 7 vs. 25 +/- 2 nmol F.g-1.h-1) but not in extensor digitorum longus (EDL). Assessment of protein synthesis rates for study 2 was conducted 16 h after resistance exercise with use of [3H]F incorporation into muscle protein during in situ bilateral hindlimb perfusion, with each leg perfused simultaneously but separately. Perfusion medium for one leg, but not the other, contained insulin (6.25 ng/ml). Soleus and gastrocnemius of Acute had higher protein synthesis rates than Nonex only in the leg that received insulin. For gastrocnemius, rates of protein synthesis in Acute without insulin were significantly lower than in Nonex with or without insulin. Insulin had no effect on protein synthesis rates for any muscle in Nonex rats. Neither exercise nor insulin affected protein synthesis rates in EDL. We conclude that insulin is a necessary component in elevated protein synthesis rates after resistance exercise in muscles composed of primarily slow-or fast-twitch fibers, and that a physiological perturbation (resistance exercise in this study) is required to observe such modulation, because rates of protein synthesis in Nonex muscles were not influenced by insulin.

Animals↗
PubMed1995

Exercise training-induced changes in anterior pituitary gonadotrope of the female rat.

Chronic exercise training may alter the hypothalamic-pituitary-ovarian axis by affecting gonadotropin secretion and structural indexes of the anterior pituitary gonadotropes. Young female Harlan Sprague-Dawley rats were randomly assigned to either a 12-wk intensive treadmill-running program (n = 16) or to a sedentary untrained group [untrained-proestrus (UTP), n = 16]. After training for 3 mo, animals were killed on proestrous morning, and individual pituitary glands were enzymatically dispersed into single-cell suspensions. Trained rats maintained either predominantly regular estrous cycles [trained-proestrus (TP), n = 11] or exhibited anestrous vaginal cytology [trained-anestrus (TA), n = 5]. At death, plasma estradiol concentrations for TP (57.4 +/- 6 pg/ml, mean +/- SE) and UTP (54.6 +/- 5 pg/ml) were similar. However, TA had plasma estradiol levels (2.7 +/- 0.2 pg/ml; P < 0.05) reflecting their anestrous status. Basal luteinizing hormone (LH) secretion (20-h static incubation) was significantly reduced in gonadotropes from TA (7.8 +/- 1.1 ng/pooled wells) compared with TP (13.6 +/- 1.6 ng/pooled wells) and UTP (12.6 +/- 1.0 ng/pooled wells). Immunofluorescence LH staining and cytoplasmic granularity were significantly lower within the TA gonadotrope population compared with those of TP and UTP rats. Evidence of impaired basal LH secretion, reduced gonadotrope LH-specific fluorescein content, and reduced gonadotrope cytoplasmic granularity in TA rats suggests that, concomitant with proposed changes in the central neural drive, there are important exercise training-induced alterations of the anterior pituitary gonadotrope that influence rats' estrous cycles and affect their reproductive status.

Animals↗
PubMed1995

Pancreatic islet insulin secretion is increased after resistance exercise in rats.

The purpose of this study was to determine whether 4 days of resistance exercise facilitated insulin secretory adaptations at the level of the pancreatic islets. Eighteen male 400-g Sprague-Dawley rats were randomly assigned to two groups. All animals were operantly conditioned to engage in a resistance exercise protocol that required full extension of the hindlimbs. Resistance was applied to the animals via a leather-and-Velcro vest to which weighted pouches were attached. The acute (Acute, n = 9) group engaged in four exercise sessions (50 reps each) with increased resistance for each session (70-->120-->120-->190 g). Sessions were separated by 48 h of rest. The nonexercised (Nonex, n = 9) group engaged in the same protocol without resistance. Islets were dispersed 16 h postexercise, incubated for 48 h, and perifused (17-20 islets/rat) with a medium containing 10 mM L-arginine or 16 mM glucose as the insulin secretagogue. Basal insulin secretion from the islets before the introduction of L-arginine or 16 mM glucose was the same for the Acute and Nonex groups (P > 0.05). The total insulin response to 10 mM arginine was significantly higher for the Acute than for the Nonex group (1.16 +/- 0.30 and 0.31 +/- 0.10 ng insulin.islet-1.25 min-1, respectively, P < 0.05). There were no differences between groups for the overall insulin response to glucose (P > 0.05). However, the late-phase insulin response to glucose was higher for the Acute group (P < 0.05). These data suggest that insulin secretory adaptations occur at the level of the pancreatic islets after 4 days of resistance exercise.

Animals↗
PubMed1995

Altered pulsatile insulin secretion associated with endurance training.

Endurance exercise training reduces glucose-stimulated insulin secretion while elevating insulin action on target tissues. Under some conditions, hormone action is enhanced by pulsatile delivery to tissues. We tested the hypothesis that different insulin secretory pulse profiles would be observed in endurance-trained vs. sedentary men. Seven endurance-trained [T; maximal O2 consumption 62.5 +/- 4.3 (SD) ml.kg-1.min-1)] and seven untrained (UT; maximal O2 consumption 40.3 +/- 3.3 ml.kg-1.min-1) age- and weight-matched men were studied. All subjects had normal oral glucose-tolerance tests; however, the insulin responses for the T subjects were significantly lower than for the UT subjects (P < 0.05). After 2 days of no exercise and an overnight fast, arterialized venous blood was sampled at 1-min intervals for 120 min and assayed for insulin. Characteristics of the insulin pulse profile were quantified with deconvolution analysis. The mass of insulin secreted per burst was significantly lower for the T than for the UT subjects (50.1 +/- 14 vs. 107.4 +/- 35 pM; P < 0.05), as was the peak height per burst (14.3 +/- 5 vs. 37.5 +/- 3.2 pM), rate of insulin production (429.6 +/- 161 vs. 1,002.4 +/- 393 pmol/90 min), and mean plasma insulin concentration (32.2 +/- 17 vs. 53.7 +/- 35 pM). The interpulse interval between bursts and the half-duration of insulin secretory bursts were not significantly different between the groups. Nonpulsatile basal insulin secretion was similar for the T and UT subjects (3.58 +/- 1.6 vs. 5.55 +/- 2.3 pM/min). These data show that regular endurance exercise in young men is associated with an insulin pulse profile in the resting fasted state characterized by less insulin secreted per burst but a similar number of bursts over a 90-min period. As a working hypothesis, we suggest that training-induced elevations in target-tissue sensitivity to insulin reduce the requirement for pulsatile insulin secretion.

Adult↗
PubMed1994

Influence of opioids in hypothalamic nuclei on cold thermogenesis of lean and obese LA/N-cp rats.

An overactive endogenous opioid peptide system (EOP) in the hypothalamus of the obese rats could contribute to a subnormal metabolic response to cold stress. Specific mu, delta, kappa opioid receptor antagonists and naloxone were infused into cannulaes aimed at the paraventricular nucleus (PVN) of awake freely moving obese (LA/N-cp corpulent) and lean littermate rats. Metabolic responses were measured by indirect calorimetry during thermoneutrality (30 degrees C) and at 10 degrees C for 60 minutes each. When expressed relative to metabolic body size (kg(-.75)) obese rats had lower values (obese = 21.1 +/- 1.9 vs. lean = 27.9 +/- 2.7 ml x kg(-.75) x min, mean +/- s.d., p < 0.05) at 10 degrees C during saline infusion. EOP antagonist infusions at 30 degrees C had no effect on metabolic rate for either lean or obese animals. Mu (23.5 +/- 3.4 ml x kg x (-75) x min) and delta (23.0 +/- 2.0) antagonism and naloxone (25.0 +/- 2.3) significantly increased the metabolic response to cold in obese but not lean rats. These data suggest that certain subtypes of EOP receptors in or near PVN are overactive in obese rats. This overactive state may inappropriately inhibit the thermogenic response to cold stress in obesity.

Animals↗
PubMed1994

Human and rodent muscle Na(+)-K(+)-ATPase in diabetes related to insulin, starvation, and training.

As determined by vanadate-facilitated [3H]ouabain binding to intact samples, semistarvation and untreated streptozotocin- or partial pancreatectomy-induced diabetes reduced rat soleus muscle Na(+)-K(+)-adenosinetriphosphatase (Na(+)-K(+)-ATPase) concentration by 12-21% (P < 0.05). Conversely, insulin treatment of rats with streptozotocin-induced diabetes induced an increase of 18-26% above control (P < 0.05). Treadmill training diminished the reduction in muscle [3H]ouabain binding site concentration induced by untreated diabetes to only 2-5%. No significant variation was observed in rat cerebral cortex Na(+)-K(+)-ATPase concentration as a result of diabetes, semistarvation, or insulin treatment. In human subjects, Na(+)-K(+)-ATPase concentration in vastus lateralis muscle biopsies was 17 and 22% greater (P < 0.05), respectively, in patients with treated non-insulin-dependent diabetes mellitus (n = 24) and insulin-dependent diabetes mellitus (n = 7) than in control subjects (n = 8). A positive linear correlation between muscle Na(+)-K(+)-ATPase and plasma insulin concentrations was observed (r = 0.50, P = 0.006; n = 29). Thus, insulin seems a regulator of muscle Na(+)-K(+)-ATPase concentration, reduction of muscle Na(+)-K(+)-ATPase concentration with untreated diabetes bears similarities with undernourishment, and physical conditioning may ameliorate the muscle Na(+)-K(+)-ATPase concentration decrease induced by diabetes.

Adult↗
PubMed1994

Effect of exercise training on the onset of type I diabetes in the BB/Wor rat.

The effects of regular exercise training on the onset and/or severity of hyperglycemia were studied in female diabetes-prone Biobreeding/Worcester (DP BB/Wor) rats. At 38-39 d of age, animals were weight-matched and randomly assigned to exercise-trained (T) and untrained (Unt) groups. The T rats exercised on a rodent treadmill at a moderate workload, 5 successive days with the 6th day being one of rest. Training lasted 5-11 wk until rats became moribund. Red gastrocnemius muscle citrate synthase activity was significantly higher in T (54.2 +/- 4.7 mumol.g-1.min-1) compared with Unt (42.9 +/- 5.1). No significant difference was found between the T and Unt groups in the following: age at onset of hyperglycemia (T = 82.9 +/- 8.7 d; Unt = 82.0 +/- 13.5 d, mean +/- SD), ultimate level of hyperglycemia, age of death (T = 89.9 +/- 9.2 d; Unt = 89.4 +/- 13.9 d), number of days between onset of hyperglycemia and death, or body weights at the onset of hyperglycemia. No significant difference was found between groups in pancreatic insulin concentration (microgram.g-1 of protein), T = 0.22 +/- 0.04; Unt = 0.20 +/- 0.34. These data suggest that a program of regular exercise training may not delay the onset and/or reduce the severity of hyperglycemia in the DP BB/Wor rat. Regular exercise training had no beneficial or detrimental effect on pancreatic beta-cell destruction.

Age of Onset↗
PubMed1993

Effects of preexercise candy bar ingestion on glycemic response, substrate utilization, and performance.

This study examined the effects of preexercise candy bar ingestion on glycemic response, substrate utilization, and performance in 8 trained male cyclists. The cyclists randomly ingested one large milk chocolate bar (1CB), two large milk chocolate bars (2CB), or a placebo (P) 30 min prior to a 90-min cycle ride at 70% VO2max followed by a 33-W increase every 2 min until exhaustion (approximately 10 min). Glucose decreased after 15 min of exercise but returned to preexercise values by 30 min of exercise. Glucose concentration for 2CB was significantly higher than for P and 1CB at exhaustion. Insulin concentration increased in response to 1CB and 2CB and returned to preexercise values within 15 min of exercise. No significant differences were noted for free fatty acid (FFA) concentrations, lactate concentrations, respiratory exchange ratio, total carbohydrate oxidation, or estimated fat and carbohydrate oxidation rates. Time to exhaustion was similar among the groups. The results suggest that the transient lowering of blood glucose observed with preexercise milk chocolate bar ingestion 30 min prior to exercise may not cause major metabolic perturbations that impair athletic performance in trained athletes performing moderately intense cycle exercise.

Adult↗
PubMed1993

Hepatic glucose production and insulin sensitivity and responsiveness in iron-deficient anemic rats.

We performed euglycemic hyperinsulinemic glucose clamps at insulin infusion rates of 1.9, 4.0, 9.3, and 19.3 mU.kg-1 x min-1 in rats with varying severities of iron deficiency anemia (IDA; mean hemoglobin concentrations of 59, 79, 107, and 137 g/l) to assess the effect of IDA on insulin sensitivity and responsiveness. Glucose appearance and disappearance (Rd) rates were determined using a primed continuous infusion of [3-3H]glucose. Basal plasma glucose and insulin concentrations were similar between the IDA and control rats. Basal hepatic glucose production was significantly (P = 0.0001) elevated in the two most anemic groups (13.6 +/- 2.4 and 12.6 +/- 3.1 vs. 10.6 +/- 2.2 and 10.2 +/- 2.0 mg.kg-1 x min-1). A significant upward shift in the insulin dose-response curves for Rd indicated an increase in peripheral insulin responsiveness in the two most anemic groups while a slight leftward shift was suggestive of an increase in insulin sensitivity in all three anemic groups. Hepatic insulin sensitivity and responsiveness were unaffected by IDA. We conclude that increased glucose utilization rates in IDA rats are due primarily to an increase in peripheral insulin responsiveness.

Anemia, Hypochromic↗
PubMed1993

Plasma lactate accumulation and distance running performance. 1979.

Laboratory and field assessments were made on eighteen male distance runners. Performance data were obtained for distances of 3.2, 9.7, 15, 19.3 km (n = 18) and the marathon (n = 13). Muscle fiber composition expressed as percent of slow twitch fibers (%ST), maximal oxygen consumption (VO2max), running economy (VO2 for a treadmill velocity of 268 m/min), and the VO2 and treadmill velocity corresponding to the onset of plasma lactate accumulation (OPLA) were determined for each subject. %ST (R > or equal to .47), VO2max (r > or equal to .83), running economy (r > or equal to .49), VO2 in ml/kg min corresponding to the OPLA (r > or equal to .91) and the treadmill velocity corresponding to OPLA (r > or equal to .91) were significantly (p < .05) related to performance at all distances. Multiple regression analysis showed that the treadmill velocity corresponding to the OPLA was most closely related to performance and the addition of other factors did not significantly raise the multiple R values suggesting that these other variables may interact with the purpose of keeping plasma lactates low during distance races. The slowest and fastest marathoners ran their marathons 7 and 3 m/min faster than their treadmill velocities corresponding to their OPLA which indicates that this relationship is independent of the competitive level of the runner. Runners appear to set a race pace which allows the utilization of the largest possible VO2 which just avoids the exponential rise in plasma lactate.

Anaerobic Threshold↗
PubMed1992

Münchausen's syndrome by proxy. A little-known type of abuse.

Clinical decisions are guided by a patient's medical history and symptoms, but when the history is factitious or the symptoms are produced, such decisions may have catastrophic results. In Münchausen's syndrome by proxy, patients are at the mercy of "illness manufacturers." Drs Leonard and Farrell discuss characteristic features and offer a profile of perpetrators that may help physicians distinguish medical fact from medical fiction.

Aged↗
PubMed1992

Effect of training on insulin secretion from single pancreatic beta cells.

The objective of this study was to determine whether insulin secretion from single pancreatic beta cells is reduced by endurance training. Male Sprague Dawley rats either trained (T, N = 9) for 11 wk on a rodent treadmill, remained sedentary, and were fed ad libitum (S, N = 8) or remained sedentary and were food restricted (pair fed, PF, N = 8) so that final body weights were similar to T. After training, T had significantly higher red gastrocnemius muscle citrate synthase activity compared with S and PF. In vivo insulin secretion was lower in T (4.6 +/- 1.4 ng.ml-1, mean +/- SEM of 70' + 90' concentrations during a hyperglycemic glucose clamp) when compared with S, 8.1 +/- 1.6 and PF, 9.7 +/- 1.7 ng.ml-1. In vitro insulin secretion from single beta cells was measured using the cell blot assay (Kendall and Hymer, Endocrinology, 121:2260-2262, 1987) and T, had lower secretion 2.6 +/- 1.4 pg.cell-1 when compared (P less than 0.05) with S, 6.7 +/- 0.6, but not lower than PF, 4.1 +/- 1.7 pg.cell-1. These data suggest that some of the training-induced reduction in insulin secretory response to glucose may be attributable to changes within the beta cell itself.

Adaptation, Physiological↗