The effect of long-distance running on plasma immunoreactive glucagon levels

Twelve highly conditioned long-distance runners were studied to determine the effects of marathon (42 km) and 10,000 m running on plasma immunoreactive glucagon (IRG), serum immunoreactive insulin (IRI), and serum glucose (G) levels. Blood samples were drawn just prior to and immediately upon completion of the run. Marathon running resulted in no significant change in G, IRI, or IRG levels. After running 10,000 m, plasma IRG levels did not change significantly, while IRI and G increased significantly. In evaluating the pooled data from both runs, a significant inverse correlation was observed between delta G and delta IRG. This relationship between delta G and delta IRG suggests that glucagon plays a role in maintaining normal blood glucose levels during strenuous exercise.     

D-lactate concentrations in blood, urine and sweat before and after exercise.

The purpose of this study was to investigate changes in the concentrations of D-lactate, L-lactate, pyruvate and methylglyoxal (MG) in body fluids after exercise. Eight untrained male students and five male students who were boat club members engaged in the exercise. Each subject performed runs of short and long duration. Compared to pre-exercise values plasma concentrations of D-lactate, L-lactate and pyruvate increased after running; in trained men by 3.6, 5.0, 3.4 times after short runs and by 1.5, 4.6, 2.0 times after long runs, and in untrained men by 3.0, 12.0, 1.6 times after short runs and 2.5, 5.6, 1.6 times after long runs, respectively. In all cases, the increase of L-lactate was always higher than that of D-lactate after running. The MG contents in red blood cells decreased markedly after running, especially in the untrained students. After short runs the MG concentration had decreased to 13% in the untrained men and 30% in the trained men, and after long runs the concentration had decreased to 41% in the untrained and 60% in the trained men. The MG in plasma and red blood cells appeared to have been utilized during relatively anaerobic exercise, especially by the untrained subjects. The D-lactate and related substances were also determined in urine, but the concentration of these substances showed no relationship to exercise. The D-lactate concentration in sweat samples tripled after short periods of running but the relative concentration to sodium ion concentration was not altered.(ABSTRACT TRUNCATED AT 250 WORDS)     

Energetics of high-speed running: integrating classical theory and contemporary observations

We hypothesized that the anaerobic power and aerobic power outputs during all-out runs of any common duration between 10 and 150 s would be proportional to the maximum anaerobic (E(an-max)) and aerobic powers (E(aer-max)) available to the individual runner. Seventeen runners who differed in E(an-max) and E(aer-max) (5 sprinters, 5 middle-distance runners, and 7 long distance runners) were tested during treadmill running on a 4.6 degrees incline. E(an-max) was estimated from the fastest treadmill speed subjects could attain for eight steps. E(aer-max) was determined from a progressive, discontinuous, treadmill test to failure. Oxygen deficits and rates of uptake were measured to assess the respective anaerobic and aerobic power outputs during 11-16 all-out treadmill runs that elicited failure between 10 and 220 s. We found that, during all-out runs of any common duration, the relative anaerobic and aerobic powers utilized were largely the same for sprint, middle-distance, and long-distance subjects. The similar fractional utilization of the E(an-max) and E(aer-max) available during high-speed running 1) provides empirical values that modify and advance classic theory, 2) allows rates of anaerobic and aerobic energy release to be quantified from individual maxima and run durations, and 3) explains why the high-speed running performances of different event specialists can be accurately predicted (R(2) = 0.97; n = 254) from two direct measurements and the same exponential time constant.     

The effect of short-term (10- and 15-min) running at self-selected intensity on mood alteration

The primary purpose of this study was to contrast the effects of two short-duration exercises on mood changes. A secondary goal was to examine the relationship between pre-exercise and post-exercise mood states. The subjects were 15 healthy male graduate students. They were involved in a within-subject design in which each individual completed two trials of running on a treadmill, one trial for 10 minutes and the other for 15 minutes. The Mood Checklist Short-form 1 (MCL-S1) used in the present study represents the participants' mood states before, during, and after exercise. This questionnaire has three sub-scales measuring (a) pleasantness, (b) relaxation, and (c) anxiety. Participants ran on a treadmill for the assigned time at a self-selected intensity after being told to run at a rate that felt good and was not painful. ANOVA results showed that both of the short bouts of exercise affected the subjects' mood, because the main effect of time spent exercising was observed in all sub-scales of the MCL-S1 and there were no significant differences in trial-by-time interaction. In addition to these results, there was a significant correlation between the two trial lengths in the amount of pleasantness and the amount of anxiety felt at post-exercise. There were moderate differences in the effect size (ES) for pre- and post-exercise pleasantness and anxiety levels. These results revealed similar patterns of change. It seems reasonable to conclude, based on this study, that exercise between 10 and 15 minutes results in similar psychological benefits for the person exercising.     

Effect of carbohydrate ingestion on metabolism during running and cycling.

The effects of carbohydrate or water ingestion on metabolism were investigated in seven male subjects during two running and two cycling trials lasting 60 min at individual lactate threshold using indirect calorimetry, U-14C-labeled tracer-derived measures of the rates of oxidation of plasma glucose, and direct determination of mixed muscle glycogen content from the vastus lateralis before and after exercise. Subjects ingested 8 ml/kg body mass of either a 6.4% carbohydrate-electrolyte solution (CHO) or water 10 min before exercise and an additional 2 ml/kg body mass of the same fluid after 20 and 40 min of exercise. Plasma glucose oxidation was greater with CHO than with water during both running (65 +/- 20 vs. 42 +/- 16 g/h; P < 0.01) and cycling (57 +/- 16 vs. 35 +/- 12 g/h; P < 0.01). Accordingly, the contribution from plasma glucose oxidation to total carbohydrate oxidation was greater during both running (33 +/- 4 vs. 23 +/- 3%; P < 0.01) and cycling (36 +/- 5 vs. 22 +/- 3%; P < 0.01) with CHO ingestion. However, muscle glycogen utilization was not reduced by the ingestion of CHO compared with water during either running (112 +/- 32 vs. 141 +/- 34 mmol/kg dry mass) or cycling (227 +/- 36 vs. 216 +/- 39 mmol/kg dry mass). We conclude that, compared with water, 1) the ingestion of carbohydrate during running and cycling enhanced the contribution of plasma glucose oxidation to total carbohydrate oxidation but 2) did not attenuate mixed muscle glycogen utilization during 1 h of continuous submaximal exercise at individual lactate threshold.     

Moderate physical exercise induces the oxidation of human blood protein thiols

Exercise is known to induce the oxidation of blood low-molecular-weight (LMW) thiols such as reduced glutathione (GSH). We previously reported that full-marathon running induced a decrease in human plasma levels of protein-bound sulfhydryl groups (p-SHs). Moderate exercise, a 30-min running at the intensity of the individual ventilatory threshold, performed by untrained healthy females caused a significant decrease in erythrocyte levels of p-SHs (mostly hemoglobin cysteine residues) and LMW thiols, but their levels returned to each baseline by 2 h. No significant change in plasma LMW thiols was observed. However, plasma levels of p-SHs significantly decreased after running and remained unchanged after 24 h. These results suggest that moderate exercise causes the oxidation of blood thiols, especially protein-bound thiols.     

Physiological parameters related to running performance in college trackmen.

Submaximal and maximal oxygen consumption (VO2) and heart rate (HR) were correlated with running performance in events ranging from 100 yards to 2 miles, using as subjects 20 members of a college track team. In the first of two studies (n=11) a multi-stage walking test was used to determine VO2 and HR. Max VO2 expressed in ml/kg/min, was significantly related to 1 mile run performance but not to any of the other runs. Submaximal HR was significantly related to performance in both the 1 mile and 2 mile runs. Correlations between these physiological parameters and performance in the 220, 440, and 880 yard runs were nonsignificant. Multiple R's using max VO2 (ml/kg/min) and submaximal H were .758 and 9671, respectively, for the 1 and 2 mile runs. In study two (n=9) a running test for VO2 and HR was used, which resulted in a mean max VO2 about 7 ml higher than than elicited in the walking test, implying that for trained runners a running test was a more valid test of aerobic power. Marked relationships were found between body weight and performance, positive for the 100 yard dash and negative for the 2 mile run. Submaximal HR was again significantly related to performance in the 1 and 2 mile runs. Max VO2 was positively related to 2 mile performance and negatively related to 100 yard dash performance. Multiple R's using max VO2 and submaximal HR were .799 and .925 for the 1 and 2 mile runs, respectively. Using submaximal HR and weight the multiple R's were .777 and .945, showing that these two can account for a large amount of the variance in distance running performance. In neither study was submaximal VO2 significantly related to running performance.     

Energetic equivalent of the production of plasma lactate during running of supramaximal intensity

The energy equivalent of plasma lactate production (ELAp) represents the amount of energy that can be derived from the anaerobic glycolysis per kg body weight when the peak plasma lactate concentration (LAp) after exercise increases by 1 mM. ELAp has been calculated from the relationship between the oxygen deficit (Do2) and LAp in 32 subjects. LAp and oxygen uptake measurements were made during constant speed supramaximal running until exhaustion or during the course of constant-speed supramaximal runs of different duration interrupted by 8- to 10- min resting periods. The relationship between Do2 and LAp is described by a linear equation where the slope is equal to ELAp. This equation is: Do2 = 12.3 + 2.4 LAp (r = 0.958; P less than 0.001), where Do2 is expressed in ml O2/kg and LAp in mmol/litre (mM). These findings validate LAp measurements as an index of the anaerobic metabolism during supramaximal running.     

13C gas chromatography-combustion isotope ratio mass spectrometry analysis of N-pivaloyl amino acid esters of tissue and plasma samples

We present the analysis of the stable carbon isotope compositions of 14 individual N-pivaloyl-isopropyl (NPP) amino acid esters by gas chromatography-combustion isotope ratio mass spectrometry (GC-C-IRMS). The mean reproducibility of derivatization procedure and GC-C-IRMS analysis was 0.45 per thousand (range, 0.12-0.68), whereas the mean analytical error was 0.26 per thousand delta(13)C (range, 0.13-0.42). Furthermore, the delta(13)C values of N-pivaloyl-isopropyl and N-acetyl-n-propyl (NAP) amino acid esters were compared. Due to a reproducible isotopic fractionation introduced by the derivatization process an empirical correction factor for each individual amino acid was derived separately for both derivatives (NPP, -1.13 to -2.52 (lysine, +2.09) per thousand delta(13)C; NAP, -2.36 to -3.97 (lysine, +1.91) per thousand delta(13)C), and the original delta(13)C value of the underivatized amino acid was calculated. Further, we performed an animal study where rats (n = 5) ingested a mixed meal containing uniformly (13)C-labeled casein (indispensable amino acids 1.3 to 1.7 at.%). One hour after the meal delta(13)C values of protein-bound amino acids from small intestinal mucosa and liver and of free amino acids from mucosa and plasma were determined. Significant (13)C enrichments of indispensable amino acids of the free pools of mucosa and plasma (range, 0.0518 to 0.1700 at.% excess) and in mucosa and liver proteins (range, 0.0021 and 0.0161 at.% excess) were observed. The feasibility of various derivatives for the measurement of carbon isotopic composition is discussed.     

The effect of muscle fatigue on in vivo tibial strains

Stress fracture is a common musculoskeletal problem affecting athletes and soldiers. Repetitive high bone strains and strain rates are considered to be its etiology. The strain level necessary to cause fatigue failure of bone ex vivo is higher than the strains recorded in humans during vigorous physical activity. We hypothesized that during fatiguing exercises, bone strains may increase and reach levels exceeding those measured in the non-fatigued state. To test this hypothesis, we measured in vivo tibial strains, the maximum gastrocnemius isokinetic torque and ground reaction forces in four subjects before and after two fatiguing levels of exercise: a 2km run and a 30km desert march. Strains were measured using strain-gauged staples inserted percutaneously in the medial aspect of their mid-tibial diaphysis. There was a decrease in the peak gastrocnemius isokinetic torque of all four subjects' post-march as compared to pre-run (p=0.0001), indicating the presence of gastrocnemius muscle fatigue. Tension strains increased 26% post-run (p=0.002, 95 % confidence interval (CI) and 29% post-march (p=0.0002, 95% CI) as compared to the pre-run phase. Tension strain rates increased 13% post-run (p=0.001, 95% CI) and 11% post-march (p=0.009, 95% CI) and the compression strain rates increased 9% post-run (p=0.0004, 95% CI) and 17% post-march (p=0.0001, 95% CI). The fatigue state increases bone strains well above those recorded in rested individuals and may be a major factor in the stress fracture etiology.     

The effect of material characteristics of shoe soles on muscle activation and energy aspects during running

The purposes of this study were (a) to determine group and individual differences in oxygen consumption during heel-toe running and (b) to quantify the differences in EMG activity for selected muscle groups of the lower extremities when running in shoes with different mechanical heel characteristics. Twenty male runners performed heel-toe running using two shoe conditions, one with a mainly elastic and a visco-elastic heel. Oxygen consumption was quantified during steady state runs of 6 min duration, running slightly above the aerobic threshold providing four pairs of oxygen consumption results for comparison. Muscle activity was quantified using bipolar surface EMG measurements from the tibialis anterior, medial gastrocnemius, vastus medialis and the hamstrings muscle groups. EMG data were sampled for 5 s every minute for the 6 min providing 30 trials. EMG data were compared for the different conditions using an ANOVA (alpha=0.05). The findings of this study showed that changes in the heel material characteristics of running shoes were associated with (a) subject specific changes in oxygen consumption and (b) subject and muscle specific changes in the intensities of muscle activation before heel strike in the lower extremities. It is suggested that further study of these phenomena will help understand many aspects of human locomotion, including work, performance, fatigue and possible injuries.     

Relationship between plasma ammonia and blood lactate concentrations after maximal treadmill exercise in circumpubertal girls and boys

The purpose of the study was to define a relationship between plasma ammonia [NH3]pl and blood lactate concentrations [la-]b after exercise in children and to find out whether the [NH3]pl, determined during laboratory treadmill tests, may be useful as a predictor of the children's sprint running ability. A group of 20 girls and 14 boys trained in athletics or swimming and 8 untrained boys, aged 13.2 to 13.7 years, participated in the study. Their [NH3]pl and [la-]b were measured before and after incremental maximal treadmill exercise. In addition, the subjects' running performance was tested in 30-, 60- and 600- or 1000-m runs under field conditions. The [NH3]pl during the treadmill runs increased by 20.1 (SD 17.3), 24 (SD 16.7) and 10 (SD 4.3) mumol.l-1 in the girls, the trained boys and the untrained boys, respectively. The postexercise [NH3]pl correlated positively with [la-]b (r = 0.565 in the girls and 0.812 in the boys) and treadmill speed attained during the test (r = 0.489 in the girls and 0.490 in the boys). Significant correlations were also found between [NH3]pl obtained during the treadmill test and the times of 30- and 60-m runs (r = -0.676 and -0.648, respectively) in the boys but not in the girls. A comparison of the present data with those reported previously in adults showed that increases in [NH3]pl during maximal exercise in children would seem to be lower than in adult subjects both in absolute values and in relation to [la-]b.(ABSTRACT TRUNCATED AT 250 WORDS)     

Feedback effects of ovarian steroids on the hypothalamic-hypophyseal axis in the rabbit

The feedback effects of two ovarian steroids, estradiol-17 beta (E2) and 20 alpha-hydroxypregn-4-en-3-one (20 alpha OH), were examined in both intact (INT) and ovariectomized (OVEX) does. We measured steroid-induced alterations in endogenous gonadotropin-releasing hormone (GnRH) from sequential 10-min samples of hypothalamic perfusates, simultaneous changes in peripheral plasma luteinizing hormone (LH) and follicle-stimulating hormone (FSH), and the modification of pituitary responsiveness, i.e., increments in plasma LH (delta LH) and plasma FSH (delta FSH), after 50 ng, 250 ng, and 1 microgram of exogenous GnRH in individual does of 6 treatment groups. The groups were: INT does, OVEX does, OVEX does receiving either one (1 E2) or two (2 E2) E2-filled Silastic capsules, OVEX does receiving a 20 alpha OH-filled capsule (20 alpha OH), and OVEX does receiving both capsules of E2 and 20 alpha OH (1 E2 + 20 alpha OH). Ovariectomy enhanced the pulsatile release of hypothalamic GnRH and pituitary LH and FSH, and increased the LH response (delta LH) to exogenous GnRH (OVEX vs. INT, p less than 0.05). Replacement of E2 at the time of ovariectomy prevented the increased GnRH and gonadotropin secretion as well as the enhanced delta LH that were observed in untreated OVEX does. The release of hypothalamic GnRH in the 20 alpha OH group was lower (p less than 0.05) than that in the OVEX group and not different from that in the INT group. The release of pituitary LH and FSH and the delta LH in the 20 alpha OH group was not different from that in the OVEX group, but these parameters were greater (p less than 0.05) than those in the INT group. The hypothalamic GnRH pulse frequency in the 1 E2 + 20 alpha OH group was lower (p less than 0.05) than that in either the 1 E2 or the 20 alpha OH group, but the delta LH in the 1 E2 + 20 alpha OH group was not different from that in either the 1 E2 or the 20 alpha OH group. The highest dose (1 microgram) of exogenous GnRH stimulated a modest increase in FSH in the OVEX, 20 alpha OH, 1 E2 + 20 alpha OH, and 1 E2 groups; but a steroid effect on delta FSH among these 4 groups was not apparent.(ABSTRACT TRUNCATED AT 250 WORDS)     

Marathon fatigue: the role of plasma fatty acids, muscle glycogen and blood glucose

The role of carbohydrate depletion in marathon fatigue was examined in 6 marathon runs. Four of the runs were potentially 'fast-time' marathons and culminated in fatigue. The utilization of carbohydrate, lipid and protein, and plasma concentrations of free fatty acids (FFA), glucose and lactate were measured at intervals throughout the runs. The contribution from protein to energy output was low (1-2%). The utilization of lipid was dependent upon plasma concentrations of FFA, which rose throughout the run. The utilization of carbohydrate mirrored that of FFA and thus fell throughout the run. Fatigue was characterized by a drop in running speed, a drop in carbohydrate utilization, an unchanging FFA utilization and a fall in blood glucose. The fall in blood glucose was not seen in the non-fatigued runners. These results are consistent with carbohydrate depletion being the cause of fatigue. The implications of these data are that lipid is the preferred fuel, but is rate-limiting, and that carbohydrate depletion, even though it causes fatigue, ensures an optimal-time marathon.     

Reduced volume but increased training intensity elevates muscle Na+-K+ pump alpha1-subunit and NHE1 expression as well as short-term work capacity in humans

The present study examined muscle adaptations and alterations in work capacity in endurance-trained runners after a change from endurance to sprint training. Fifteen runners were assigned to either a sprint training (ST, n = 8) or a control (CON, n = 7) group. ST replaced their normal training by 30-s sprint runs three to four times a week, whereas CON continued the endurance training (approximately 45 km/wk). After the 4-wk sprint period, the expression of the muscle Na+-K+ pump alpha1-subunit and Na+/H+-exchanger isoform 1 was 29 and 30% higher (P < 0.05), respectively. Furthermore, plasma K+ concentration was reduced (P < 0.05) during repeated intense running. In ST, performance in a 30-s sprint test, Yo-Yo intermittent recovery test, and two supramaximal exhaustive runs was improved (P < 0.05) by 7, 19, 27, and 19%, respectively, after the sprint training period, whereas pulmonary maximum oxygen uptake and 10-k time were unchanged. No changes in CON were observed. The present data suggest a role of the Na+-K+ pump in the control of K+ homeostasis and in the development of fatigue during repeated high-intensity exercise. Furthermore, performance during intense exercise can be improved and endurance performance maintained even with a reduction in training volume if the intensity of training is very high.     

Assessment of anaerobic capacity in runners

A new method for assessment of anaerobic capacity is presented. It consists of two treadmill runs at 22 km X h-1 and 7.5% slope, the first one being interrupted after 40 s (submax. test), the second continuing until volitional exhaustion (max. test). Measured variables are the increase in arterial lactate concentration over the pre-exercise value in the submax. test (delta L40), the maximal arterial lactate level in the max. test (Lmax), and time to exhaustion (tmax). Fifty-five male runners of high competitive level were examined with this procedure, including 400-m runners of differing performance capacity (400 m A and B/C), middle-distance (MD), long-distance (LD), and marathon runners (M). Eleven physical education students served as controls (C). tmax was 88.3 +/- 11.0, 85.2 +/- 11.4, 83.1 +/- 12.7, 63.1 +/- 11.4, 43.7 +/- 7.5, and 50.7 +/- 5.0 s for 400 m A, 400 m B/C, MD, LD, M, and C. The corresponding values for Lmax were 17.47 +/- 1.68, 17.52 +/- 2.03, 16.27 +/- 2.18, 13.44 +/- 2.13, 10.13 +/- 2.68, and 15.54 +/- 1.43 mmol X 1(-1) and for delta L40 5.93 +/- 1.10, 7.13 +/- 1.55, 6.39 +/- 0.89, 6.68 +/- 1.18, 8.19 +/- 1.37, and 10.76 +/- 1.62 mmol X 1(-1). The differences in delta L40, most likely reflecting differences in high energy phosphate utilization, suggest that excellent performance in any running event is associated with increased alactacid anaerobic capacity.(ABSTRACT TRUNCATED AT 250 WORDS)     

A comparison of the oxygen drift in downhill vs. level running.

This investigation explored the recent theory that muscle damage causes the drift in oxygen consumption (VO2) during low-intensity downhill running. Seven subjects participated in a maximal VO2 (VO2max) test and three submaximal bouts [one level (Level) and two downhill runs (Down 1, Down 2) at 40% peak VO2]. Two downhill runs (30 min at -10% grade) were performed to vary the extent of muscle damage. Creatine kinase (CK) increased more after Down 1 (61%) than after Down 2 (11%), as did soreness ratings, indicating reduced muscle damage during Down 2. Significantly greater increases in VO2 over time were noted for Down 1 (15.6%) and Down 2 (14.7%) than for Level (1.2%). Heart rate increased 8 beats/min for Level but 29 and 25 beats/min for Down 1 and Down 2, respectively. Expired ventilation increased more for Down 1 (20.5%) and Down 2 (24%) than for Level (3.5%). Rectal temperature increased approximately 0.8 degree C for all bouts. Because the magnitude of the drift was similar in the two downhill bouts, the findings suggest that muscle damage does not cause the drift in VO2 during low-intensity downhill running.     

Training-overtraining: influence of a defined increase in training volume vs training intensity on performance, catecholamines and some metabolic parameters in experienced middle- and long-distance runners.

The influence of an increase in training volume (ITV; February 1989) vs intensity (ITI; February 1990) on performance, catecholamines, energy metabolism and serum lipids was examined in two studies on eight, and nine experienced middle- or long-distance runners; seven participated in both studies. During ITV, mean training volume was doubled from 85.9 km.week-1 (pretrial phase) to 174.6 km within 3 weeks. Some 96%-98% of the training was performed at 67 (SD 8)% of maximal performance. During ITI, speed-endurance, high-speed and interval runs increased within 3 weeks from 9 km.week-1 (pretrial phase) to 22.7 km.week-1 and the total training distance from 61.6 to 84.7 km.week-1. The ITV resulted in stagnation of running velocity at 4 mmol lactate concentration and a decrease in total running distance in the increment test. Heart rate, energy metabolic parameters, nocturnal urinary catecholamine excretion, low density, very low density lipoprotein-cholesterol and triglyceride concentrations decreased significantly; the exercise-related catecholamine plasma concentrations increased at an identical exercise intensity. The ITI produced an improvement in running velocity at 4 mmol lactate concentration and in total running distance in the increment test; heart rate, energy metabolic parameters, nocturnal catecholamine excretion, and serum lipids remained nearly constant, and the exercise-related plasma catecholamine concentrations decreased at an identical exercise intensity. The ITV-related changes in metabolism and catecholamines may have indicated an exhaustion syndrome in the majority of the athletes examined but this hypothesis has to be proven by future experimental studies.     

Plasma renin activity, aldosterone and catecholamine levels when swimming and running

The purpose of this study was to determine the response of plasma renin activity (PRA), plasma aldosterone concentration (PAC) and catecholamines to two graded exercises differing by posture. Seven male subjects (19-25 years) performed successively a running rest on a treadmill and a swimming test in a 50-m swimming pool. Each exercise was increased in severity in 5-min steps with intervals of 1 min. Oxygen consumption, heart rate and blood lactate, measured every 5 min, showed a similar progression in energy expenditure until exhaustion, but there was a shorter time to exhaustion in the last step of the running test. PRA, PAC and catecholamines were increased after both types of exercise. The PRA increase was higher after the running test (20.9 ng AngI X ml-1 X h-1) than after swimming (8.66 ng AngI X ml-1 X h-1). The PAC increase was slightly greater after running (123 pg X ml-1) than swimming (102 pg X ml-1), buth the difference was not significant. Plasma catecholamine was higher after the swimming test. These results suggest that the volume shift induced by the supine position and water pressure during swimming decreased the PRA response. The association after swimming compared to running of a decreased PRA and an enhanced catecholamine response rule out a strict dependence of renin release under the effect of plasma catecholamines and is evidence of the major role of neural pathways for renin secretion during physical exercise.     

The shadow response of the cockroach periplaneta americana

We show that the “escape response” (running) of the cockroach Periplaneta americana is interrupted when the insect runs through a shadow. Shadows were cast by holding an opaque plastic sheet so that the cockroach ran beneath it. In control experiments, a similarly positioned clear plastic sheet was ineffective. Removal of the shadow stimulus allowed running to continue. The likelihood that cockroaches would resume running after removal of the shadow stimulus decreased with the time they were allowed to remain in shadow.