Effect of prostaglandin E2, DL-cloprostenol,and prostaglandin E2 in combination with D-cloprostenol on uterine motility during diestrus in experimental cows

Prostaglandin F(2alpha) is used in dairy herd management because of its luteolytic properties and for its direct effect on the myometrium in cows diagnosed with endometritis. Prostaglandin E(2) has a contractile effect on the bovine uterus. In human medicine, prostaglandin E(2) is routinely used to maintain labor and to ripen the cervix. We hypothesized, that a combination of prostaglandin F(2alpha) and prostaglandin E(2) would provoke a long-lasting increase in intrauterine pressure (IUP) and uterine motility as compared to either prostaglandin group. Intrauterine pressure was recorded during the diestrus of eight lactating dairy cows using a transcervically placed intraluminal pressure microtransducer. After recording of physiologic uterine motility for 30min, prostaglandins (DL-cloprostenol, PGE(2), PGE(2) in combination with D-cloprostenol) or placebo were administered, followed by a 2h recording period. Significant differences were found for the area under the curve, the mean amplitude and the intrauterine pressure, whereas the number of pressure waves did not differ significantly among treatments. Peak values for area under the curve and mean amplitude were found during the first 15min for the combination of PGE(2) and D-cloprostenol. During the last 15min of the recording session, area under the curve and mean amplitude were increased only for the combination of PGE(2) and D-cloprostenol as compared to placebo. Although PGF(2alpha) and PGE(2) provoke an increase in intrauterine pressure, only their combination guarantees a significant effect over a 2h recording period.     

Effect of different doses of prostaglandin E2 on intrauterine pressure and uterine motility during diestrus in experimental cows

Studies in human medicine proved the important role of prostaglandin E2, which stimulates uterine contractions in vivo and in vitro and has been extensively used to ripen the cervix around labor. We wanted to demonstrate that increasing the dosage of prostaglandin E2 (1.25 mg, 2.5 mg, 5 mg and 10 mg) provokes an increase in intrauterine pressure and uterine motility in cattle. Five healthy, lactating dairy cows were used as experimental animals for this study. Intrauterine pressure was recorded during the diestrus phase (1 recording per cow and diestrus phase) by means of a transcervically placed intraluminal pressure microtransducer. Physiologic uterine motility was recorded for 30 min, then placebo or one of the prostaglandin E2- dosages was administered through an indwelling catheter in the jugular vein, followed by a 2-h recording period (eight 15-min periods). Area under the curve (AUC), mean amplitude, frequency of pressure waves and intrauterine pressure were analyzed. Furthermore, we recorded protocols for monitoring heart and respiratory rates and side effects at 9 given examination times. Significant differences were found for the AUC, the mean amplitude and the intrauterine pressure (P < or = 0.05), whereas the number of pressure waves per 15 min did not differ significantly among treatments. Peak values for AUC, mean amplitude and intrauterine pressure were found during the first 15 min after administration of 10 mg of prostaglandin E2. Dose-effect curves showed that the 2.5 mg dosage provided the optimal ratio between myometrial stimulation and undesirable side-effects.     

Ambulatory 24-h colonic manometry in healthy humans

Our aim was to investigate motor activity of the healthy, relatively unprepared colon in the ambulatory state. Twenty-five age- and gender-matched adults had a six-sensor solid-state probe inserted into the proximal transverse colon without sedation. Subjects ambulated freely and ate standard meals. In 528 h of recording, we found a lower (P < 0.05) area under the curve during the night. Waking induced a threefold increase in motility, whereas meals induced a twofold increase. Women showed less activity (P < 0.05) in the transverse/descending colon than men. The transverse/descending colon showed more (P < 0.05) activity than the rectosigmoid colon. Seven patterns were recognized; predominantly, they were simultaneous, propagated, or periodic bursts of 3-cycles/min (cpm) waves. A specialized propagating pressure wave with a high amplitude (>105 mmHg) and a prolonged duration (>14 s) occurred in all subjects (mean 10/day), mostly after waking, after meals, or with defecation. A 3-cpm motor activity was seen in the rectosigmoid region predominantly at night. The colon exhibits a wide spectrum of pressure activity around the clock, with gender and regional differences and circadian rhythm. This comprehensive study provides qualitative and quantitative normative data for colonic manometry.     

Continuous fetal heart rate monitoring during late gestation in cattle by means of Doppler ultrasonography: reference values obtained by computer-assisted analysis

Continuous fetal heart rate (FHR) monitoring using transabdominal Doppler ultrasonography can be assumed to provide information about the viability of the bovine fetus during late gestation, as has been found in humans. To be able to recognize unfavourable fetal conditions, first the normal ranges of FHR parameters in cattle should be established. Therefore, in this study we aimed to determine the normal ranges of computerized FHR parameters, like basal fetal heart rate (BHR), number of accelerations and decelerations per hour and short and long term variation (STV and LTV) during the last 3 weeks before calving (n = 21 cows). Each cow had one recording in each of three episodes of 7 days before parturition. As recording time in the cow is limited, we also studied whether these FHR parameters differ between recordings of 30 and 60 min duration (n = 31 pairs of recordings). The outcomes of FHR recordings with a duration of 30 or 60 min did not differ significantly, except for a higher percentage of signal loss in the 60 min recordings. Therefore, determination of normal ranges was performed in 30 min recordings. BHR decreased from 3 to 2 weeks (114 to 109 bpm; P < 0.0001) before parturition and then remained constant until 2 days before calving. The mean number of accelerations per hour ranged between 4.4 and 5.0 h(-1) and did not change significantly with time. Compared to 3 weeks before parturition, STV was significantly higher at 2 weeks (P < 0.05), but not at 1 week before parturition (8.1, 10.0, and 9.2 ms, respectively). Changes in LTV showed a time course comparable to that of STV, but significance was not reached (51.4, 58.6, and 58.4 ms for respectively 3, 2 and 1 weeks before parturition). No decelerations were found during the period understudy. In conclusion, this study has provided normal ranges of bovine computerized FHR parameters during the last 3 weeks of gestation, allowing a comparison with data from cows with compromised gestations in future.     

Influence of acute alcohol ingestion on sympathetic neural responses to orthostatic stress in humans

Acute alcohol consumption is reported to decrease mean arterial pressure (MAP) during orthostatic challenge, a response that may contribute to alcohol-mediated syncope. Muscle sympathetic nerve activity (MSNA) increases during orthostatic stress to help maintain MAP, yet the effects of alcohol on MSNA responses during orthostatic stress have not been determined. We hypothesized that alcohol ingestion would blunt arterial blood pressure and MSNA responses to lower body negative pressure (LBNP). MAP, MSNA, and heart rate (HR) were recorded during progressive LBNP (-5, -10, -15, -20, -30, and -40 mmHg; 3 min/stage) in 30 subjects (age 24 ± 1 yr). After an initial progressive LBNP (pretreatment), subjects consumed either alcohol (0.8 g ethanol/kg body mass; n = 15) or placebo (n = 15), and progressive LBNP was repeated (posttreatment). Alcohol increased resting HR (59 ± 2 to 65 ± 2 beats/min, P < 0.05), MSNA (13 ± 3 to 19 ± 4 bursts/min, P < 0.05), and MSNA burst latency (1,313 ± 16 to 1,350 ± 17 ms, P < 0.05) compared with placebo (group × treatment interactions, P < 0.05). During progressive LBNP, a pronounced decrease in MAP was observed after alcohol but not placebo (group × time × treatment, P < 0.05). In contrast, MSNA and HR increased during all LBNP protocols, but there were no differences between trials or groups. However, alcohol altered MSNA burst latency response to progressive LBNP. In conclusion, the lack of MSNA adjustment to a larger drop in arterial blood pressure during progressive LBNP, coupled with altered sympathetic burst latency responses, suggests that alcohol blunts MSNA responses to orthostatic stress.     

Serum luteinizing hormone, 13,14-dihydro-15-keto-prostaglandin F2alpha and cortisol profiles during postpartum anestrus in Brahman and Angus cows

Pluriparous suckled Brahman and Angus cows were utilized to evaluate the effect of breed, day after calving and endogenous opioid peptides (EOP) on hormonal profiles during postpartum anestrus. On Days 17 and 34 after calving, blood samples with and without heparin were collected at 15- and 30-min intervals, respectively, for a 7-h period via jugular cannula. Two hours after the start of blood sampling, cows of each breed were administered either 1 mg/kg iv naloxone or saline. Three hours later, all animals received 10 ng/kg iv GnRH. On Day 34 after calving cows received 0.2 IU/kg iv ACTH. Mean LH, basal LH and area under the LH curve increased (P < 0.01) from Day 17 to Day 34 after calving. Height of LH pulses increased (P < 0.05) by Day 34 after calving. Brahman cows had higher (P < 0.05) mean LH, basal LH, LH pulse frequency and area under the LH curve than Angus cows. Naloxone increased postchallenge area under the LH curve in treated cows above that of control cows (P < 0.06). Naloxone also increased the postchallenge area under the LH curve above that of the prechallenge level (P < 0.01). No breed differences in the response to the naloxone challenge were observed. The LH response to naloxone challenge occurred earlier on Day 34 than on Day 17 after calving but the amount of LH released was similar between days. The GnRH-induced LH release was greater in Brahman than in Angus cows (P < 0.04). Mean cortisol concentrations and area under the cortisol curve decreased (P < 0.05) between Day 17 and Day 34 after calving. Mean cortisol concentrations and area under the cortisol curve were lower (P < 0.01) in Brahman than in Angus cows. Cortisol secretion after ACTH treatment was similar between Brahman and Angus cows. The cortisol response after ACTH challenge was positively correlated (r=0.68; P < 0.001) to the prechallenge area under the cortisol curve. Under optimal environmental conditions Brahman cows have a greater LH release and their anterior hypophysis is more sensitive to GnRH challenge than the Angus cows.     

The effect of a single oxytocin or carbetocin treatment on uterine contractility in early postpartum dairy cows

The uterotonic characteristics and effectiveness of a single treatment with either oxytocin or carbetocin were quantified in early postpartum dairy cows after normal, uncomplicated calvings. Both the short-term (within 4 h), and the long-term effects (between 12 and 36 h) of the two treatments were compared. Between 14 and 16 h after parturition, 27 multiparous Holstein-Friesian dairy cows, without fetal membrane retention, were selected and divided into three groups. The first group (n = 9) was administered 50 IU oxytocin intramuscularly, the second group (n = 10) received 0.35 mg carbetocin, while animals of the third group (n = 8), serving as a control, were administered 5 mL saline solution. A transcervically introduced open tip catheter system was used for the non-invasive acquisition of the intrauterine pressure (IUP) recording. After digitalization, the signals were analyzed, using a specially adapted graphical software program. A significant short-term effect was found both in the oxytocin and carbetocin treated groups from the analysis of the contraction frequencies (FREQ) and of the total area under the curve (TAUC). After significant peaking during the first post-treatment hour, the values of the parameters for these two groups remained higher during the second hour, returning to the initial levels again during the third hour and reaching the level of the control group by the 12th hour. Mean amplitude (AMP), duration (DUR) and area under the curve (AUC) of pressure cycles were not significantly affected by any of the treatments. Although mean FREQ and TAUC significantly declined from the initial values to 12, 24 and 36 h in all groups, mean AMP and AUC in the oxytocin and carbetocin treated groups, and mean DUR only in the carbetocin treated group to 12 and 36 h, the long-term analysis revealed no significant treatment differences for any IUP parameters. Because treatment with either oxytocin, or carbetocin elicited similar uterotonic effects in healthy, early postpartum cows, it cannot be expected, that using carbetocin in preference to oxytocin, will result in a more beneficial clinical effect on uterine involution during this period.     

Maturational changes in opioidergic control of luteinizing hormone and follicle-stimulating hormone in ram lambs

Stimulation by naloxone, an opioid antagonist, of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion was examined in spring-born crossbred ram lambs raised under natural photoperiod. Vehicle (n = 6) or 1 mg naloxone/kg vehicle (n = 6) was injected (i.m.) 3 times at 2-h intervals at 5, 10 and 15 weeks of age and 4 times at 2-h intervals at 20, 25, 30 and 35 weeks of age. Blood samples were taken every 12 min for 6 h at 5, 10 and 15 weeks of age and for 8 h at 20, 25, 30 and 35 weeks of age. Naloxone had no effect on age at sexual maturity (controls 239 +/- 23 days; naloxone 232 +/- 33 days). The only significant (P less than 0.05) effect of naloxone on FSH was a greater pulse amplitude in 10-week-old treated lambs than in control lambs. Naloxone treatment resulted in greater LH pulse amplitude at 5 and 10 weeks of age (P less than 0.05), lower basal serum concentration of LH at 10 weeks of age (P less than 0.05), greater LH pulse frequency at 25 weeks of age (P less than 0.05), and greater mean serum concentrations of LH, basal LH and LH pulse amplitude at 35 weeks of age (P less than 0.01) than in the controls. In both groups of lambs, mean and basal FSH, and LH and FSH pulse amplitude were highest at 5 weeks of age and fell with age. LH pulse amplitude was lowest at 35 weeks of age (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Observations on variability in LH release and fertility during oestrus in the domestic cat (Felis catus)

Hormonal changes, behaviour, ovulation and fertility were examined in response to coitus at two different times during oestrus in the female domestic cat housed in conditions of natural light (N = 13). On Day 2 or Day 4/5 of oestrus females were allowed 1 copulation in 15 min (single matings) or 2-3 copulations in 30 min (multiple matings). Plasma LH, oestradiol-17 beta and progesterone concentrations during the 24-h period after coitus were measured by radioimmunoassay; ovulation was assumed to have occurred if progesterone values were elevated 7-30 days after coitus. With the exception of 2 out of 3 animals receiving single matings on Day 2 of oestrus, all animals showed subsequent elevated progesterone values. Females receiving multiple matings had significantly greater releases of LH as measured by the area under the curve than those receiving single matings. There was significantly greater variability in the LH response of queens on Day 2 of oestrus compared to those on Day 4/5 for peak values and area under the curve; the only failure in release of LH was in queens on Day 2. Oestradiol levels did not differ significantly between Day 2 and Day 4/5 of oestrus. Progesterone values remained less than 1 ng/ml for 24 h after coitus. Both LH peak values and area under the curve were significantly greater for animals that became pregnant. There were also significant differences in coital behaviour between queens on Day 2 and those on Day 4/5 of oestrus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of prior exercise on glucose metabolism in trained men

Several studies have demonstrated that oral glucose tolerance is impaired in the immediate postexercise period. A double-tracer technique was used to examine glucose kinetics during a 2-h oral glucose (75 g) tolerance test (OGTT) 30 min after exercise (Ex, 55 min at 71 +/- 2% of peak O(2) uptake) and 24 h after exercise (Rest) in endurance-trained men. The area under the plasma glucose curve was 71% greater in Ex than in Rest (P = 0.01). The higher glucose response occurred even though whole body rate of glucose disappearance was 24% higher after exercise (P = 0.04, main effect). Whole body rate of glucose appearance was 25% higher after exercise (P = 0.03, main effect). There were no differences in total (2 h) endogenous glucose appearance (R(a)E) or the magnitude of suppression of R(a)E, although R(a)E was higher from 15 to 30 min during the OGTT in Ex. However, the cumulative appearance of oral glucose was 30% higher in Ex (P = 0.03, main effect). There were no differences in glucose clearance rate or plasma insulin responses between the two conditions. These results suggest that adaptations in splanchnic tissues by prior exercise facilitate greater glucose output from the splanchnic region after glucose ingestion, resulting in a greater glycemic response and, consequently, a greater rate of whole body glucose uptake.     

Effects of dehydration on cerebrovascular control during standing after heavy resistance exercise

We tested the hypothesis that dehydration exacerbates reductions of middle cerebral artery blood velocity (MCAv) and alters cerebrovascular control during standing after heavy resistance exercise. Ten males participated in two trials under 1) euhydration (EUH) and 2) dehydration (DEH; fluid restriction + 40 mg furosemide). We recorded finger photoplethysmographic arterial pressure and MCAv (transcranial Doppler) during 10 min of standing immediately after high-intensity leg press exercise. Symptoms (e.g., lightheadedness) were ranked by subjects during standing (1-5 scale). Low-frequency (LF) oscillations of mean arterial pressure (MAP) and mean MCAv were calculated as indicators of cerebrovascular control. DEH reduced plasma volume by 11% (P = 0.002; calculated from hemoglobin and hematocrit). During the first 30 s of standing after exercise, subjects reported greater symptoms during DEH vs. EUH (P = 0.05), but these were mild and resolved at 60 s. While MAP decreased similarly between conditions immediately after standing, MCAv decreased more with DEH than EUH (P = 0.02). With prolonged standing under DEH, mean MCAv remained below baseline (P ≤ 0.01), and below EUH values (P ≤ 0.05). LF oscillations of MAP were higher for DEH at baseline and during the entire 10 min of stand after exercise (P ≤ 0.057), while LF oscillations in mean MCAv were distinguishable only at baseline and 5 min following stand (P = 0.05). Our results suggest that mean MCAv falls below a "symptomatic threshold" in the acute phase of standing after exercise during DEH, although symptoms were mild and transient. During the prolonged phase of standing, increases in LF MAP and mean MCAv oscillations with DEH may help to maintain cerebral perfusion despite absolute MCAv remaining below the symptomatic threshold.     

Secretion patterns of luteinizing hormone in growing mithuns (Bos frontalis)

To characterize the luteinizing hormone (LH) secretion patterns in growing mithun (Bos frontalis), a semi-wild ruminant, six female mithuns (1 year old; BW: 145.5 kg) were maintained in a semi-intensive system. Plasma progesterone (P(4)) level was measured in twice-a-week samples collected for six weeks to assess ovarian status. This was followed by a frequent sampling period. Blood samples collected at 15 min intervals for 9 h were assayed for plasma LH. Luteinizing hormone patterns consisted of pulses of varying amplitudes. Luteinizing hormone pulses occurred at an average rate of 0.54/h ( approximately 5 pulses/9 h). The rate did not differ among mithuns. The mean plasma LH levels was correlated with body weight (r=0.82; p<0.05) and pulse amplitude (r=0.87; p<0.01). Neither the LH amplitude nor the frequency was affected by time (p>0.05). The mean plasma P(4) concentration was 0.37 ng/ml. In conclusion, we demonstrated a pulsatile nature of LH secretion in growing mithuns. In addition, the mean plasma LH level and LH amplitude were positively correlated with body weight. It appears that in contrast to cattle, five LH pulses per nine hours recorded in mithuns were not an indication of approaching puberty.     

Effects of season of birth on the prepubertal pattern of gonadotropin secretion and age at puberty in beef heifers

There is an early transient rise in gonadotropin secretion in spring-born prepubertal heifers and there is an indication that this pattern is different in autumn-born heifers. The effect of season of birth on age and weight at puberty is equivocal. This study was designed to compare the temporal patterns of LH and FSH secretion between spring- and autumn-born heifers and to determine the effects of season of birth on age and weight at puberty. Blood samples from 2 groups of heifer calves born in spring (last week of March, n = 5) or autumn (last week of October, n = 5) were collected every other week from birth to puberty and every 15 min for 10 h at 6, 12, 18, 24 and 32 wk of age. Timing of puberty was determined by measuring progesterone in plasma samples collected every 2 to 3 d starting at 42 wk of age. Age and weight at onset of puberty did not differ between the 2 groups of heifers (P > 0.05); however, the autumn-born heifers tended to mature in a wider range of ages and weights. Based on the 10-h sampling periods, mean serum concentrations of LH and LH pulse frequency and amplitude were higher in spring-born heifers at 18 wk of age than in autumn-born heifers (P < 0.05). In spring-born heifers, LH pulse frequency increased over time to 32 wk of age, and LH pulse amplitude was higher at 12 and 18 wk than at 32 wk of age (P < 0.05). Autumn-born heifers had higher LH pulse frequency at 6 wk and showed a decrease in mean concentrations of LH at 12 and 18 wk of age (P < 0.05). The FSH pulse frequency of spring-born heifers was higher at 12 wk of age than in autumn-born heifers (P < 0.05), FSH pulse amplitude in autumn-born heifers decreased from 6 to 32 wk of age. It was concluded that although the mean age and weight at puberty did not differ between spring- and autumn-born heifers, the range in age and weight at puberty was wider in the autumn-born heifers. The patterns of LH secretion differed between spring- and autumn-born prepubertal heifers, with spring-born calves exhibiting an early rise in LH secretion, while mean serum concentrations of LH decreased during this period in autumn-born heifers.     

Increase in progesterone and luteal blood flow without a luteolytic response after prostaglandin F2α treatment in early luteal-phase heifers

Acute changes in circulating progesterone concentration and luteal blood flow in heifers after a conventional dose of prostaglandin F(2α) (PGF; 25mg dinoprost, i.m.) were compared between the early luteal phase (Day 3) and midluteal phase (Day 10; Day 0=ovulation), using four groups (Day-3 control, Day-3 PGF, Day-10 control, and Day-10 PGF; n=6 heifers/group). Blood samples were collected at 0, 2, 5, 10, 15, 30, 60, and 120 min (0 min=treatment). Percentage of luteal area with color-Doppler blood-flow signals was estimated at 0, 10, and 30 min. In the Day-3 and Day-10 PGF groups, progesterone increased to a peak at 15 min. In the Day-3 PGF group, progesterone decreased to the pretreatment concentration by 60 min but did not decrease to below the pretreatment concentration during the 2-h experimental period. In the Day-10 PGF group, progesterone decreased to below pretreatment concentration by 30 min, indicating a luteolytic response. In the Day-3 and Day-10 PGF groups, luteal blood flow increased within 10 min and remained elevated until the last examination at 30 min. The absence of a decrease in progesterone to below pretreatment concentrations in the Day-3 PGF group indicated that luteolysis does not necessarily follow a transient increase in progesterone and a concomitant increase in luteal blood flow. The immediate transient increase in progesterone and an increase in luteal blood flow without a subsequent decrease in progesterone to below pretreatment concentrations after PGF treatment in early luteal-phase heifers are novel findings.     

The acute effect of 30 min of moderate exercise on high density lipoprotein cholesterol in untrained middle-aged men

Fifteen middle-aged, untrained (defined as no regular exercise) men (mean age 49.9 years, range 42-67) cycled on a cycle ergometer at 50 rpm for 30 min at an intensity producing 60% predicted maximum heart rate [(fc,max), where fc,max = 220 - age]. Total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C) and triglyceride (Tg) concentrations were measured from fasting fingertip capillary blood samples collected at rest, after 15 and 30 min of exercise, and at 15 min post-exercise. The mean HDL-C level increased significantly from the resting level of 0.85 mmol.l-1 to 0.97 mmol.l-1 (P < 0.05) after 15 min of exercise, increased further to 1.08 mmol.l-1 (P < 0.01) after 30 min of exercise and remained elevated at 1.07 mmol.l-1 (P < 0.01) at 15 min post-exercise. These increases represented changes above the mean resting level of 14.1%, 27.1% and 25.9% respectively. The HDL-C/LDL-C ratio increased significantly from a resting ratio of 0.20 to 0.26 after 30 min of exercise (P < 0.01) and to 0.24 at 15 min post-exercise (P < 0.05). The mean Tg level increased significantly from a resting level of 0.88 mmol.l-1 to 1.05 mmol.l-1 after 15 min, and to 1.06 mmol.l-1 after 30 min of exercise (P < 0.05 at each time). The TC/HDL-C ratio decreased significantly (P = 0.05) after 30 min of exercise and at 15 min post-exercise by 18.8% and 14%, respectively. No significant changes were observed in the levels of TC or LDL-C over time.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of etomidate on descending activation of motoneurons in neonatal rat spinal cord in vitro

Descending activation pathways in spinal cord are essential for inducing and modulating autokinesis, but whether the effects of general anesthetic agents on the descending pathways are involved in initiation of skeletal muscle relaxation or not, as well as the underlying mechanisms on excitatory amino acid receptors still remain unclear. In order to explore the mechanisms underlying etomidate's effects on descending activation of spinal cord motoneurons (MNs), the conventional intracellular recording techniques in MNs of spinal cord slices isolated from neonatal rats (7-14 days old) were performed to observe and analyze the actions of etomidate on excitatory postsynaptic potential (EPSP) elicited by electrical stimulation of the ipsilateral ventrolateral funiculus (VLF), which was named VLF-EPSP. Etomidate at 0.3, 3.0 (correspond to clinical concentration) and 30.0 μmol/L were in turn perfused to MN with steadily recorded VLF-EPSPs. At low concentration (0.3 μmol/L), etomidate increased duration, area under curve and/or half-width of VLF-EPSP and N-methyl-D-aspartate (NMDA) receptor-mediated VLF-EPSP component (all P < 0.05), as well as amplitude, area under curve and half-width of non-NMDA receptor-mediated VLF-EPSP component (all P < 0.05), or decreased amplitude and area under curve of VLF-EPSP, its NMDA receptor component, and non-NMDA receptor component (all P < 0.05). However, at 3.0 and 30.0 μmol/L, it was only observed that etomidate exerted inhibitory effects on amplitude and/or duration and/or area under curve of VLF-EPSP (P < 0.05 or P < 0.01) with concentration- and time-dependent properties. Moreover, NMDA receptor-mediated VLF-EPSP component was more sensitive to etomidate at ≥ 3.0 μmol/L than non-NMDA receptor-mediated VLF-EPSP component did. As a conclusion, etomidate, at different concentrations, exerts differential effects on VLF-EPSP and glutamate receptors mediating the synaptic transmission of descending activation of MNs in neonatal rat spinal cord in vitro.     

Growth hormone responses to repeated maximal cycle ergometer exercise at different pedaling rates.

The present study examined the growth hormone (GH) response to repeated bouts of maximal sprint cycling and the effect of cycling at different pedaling rates on postexercise serum GH concentrations. Ten male subjects completed two 30-s sprints, separated by 1 h of passive recovery on two occasions, against an applied resistance equal to 7.5% (fast trial) and 10% (slow trial) of their body mass, respectively. Blood samples were obtained at rest, between the two sprints, and for 1 h after the second sprint. Peak and mean pedal revolutions were greater in the fast than the slow trial, but there were no differences in peak or mean power output. Blood lactate and blood pH responses did not differ between trials or sprints. The first sprint in each trial elicited a serum GH response (fast: 40.8 +/- 8.2 mU/l, slow: 20.8 +/- 6.1 mU/l), and serum GH was still elevated 60 min after the first sprint. The second sprint in each trial did not elicit a serum GH response (sprint 1 vs. sprint 2, P < 0.05). There was a trend for serum GH concentrations to be greater in the fast trial (mean GH area under the curve after sprint 1 vs. after sprint 2: 1,697 +/- 367 vs. 933 +/- 306 min x mU(-1) x l(-1); P = 0.05). Repeated sprint cycling results in an attenuation of the GH response.     

Human growth hormone responses to repeated bouts of sprint exercise with different recovery periods between bouts.

This study examined the growth hormone (GH) response to repeated bouts of sprint cycling. Eight healthy men completed three trials consisting of two 30-s sprints on a cycle ergometer separated by either 60 min (Trial A) or 240 min (Trial B) of recovery and a single 30-s sprint carried out the day after Trial B (Trial C). Trials A and B were separated by at least 7 days. Blood samples were obtained at rest and during recovery from each sprint. In Trial A, GH was elevated immediately before sprint 2, and there was no further increase in GH following the second sprint [area under the curve: 460 (SD 348) vs. 226 min.mug(-1).l(-1) (SD 182), P = 0.05]. Free insulin-like growth factor I tended to be lower immediately before sprint 2 than sprint 1 (P = 0.06). Serum free fatty acids were not different immediately before each of the sprints. In Trial B, there was a trend for a smaller GH response to the second sprint [GH area under the curve: 512 (SD 396) vs. 242 min.mug(-1).l(-1) (SD 190), P = 0.09]. Free insulin-like growth factor I tended to be lower (P = 0.06), and serum free fatty acids were higher (P = 0.01) immediately before sprint 2 than sprint 1. There was no difference in the GH response to sprinting on consecutive days (Trials B and C). In conclusion, repeated bouts of sprint cycling on the same day result in an attenuation or even ablation of the exercise-induced increase in GH, depending on the recovery interval between sprints.     

Hypoxia potentiates exercise-induced sympathetic neural activation in humans.

Our purpose was to test the hypothesis that hypoxia potentiates exercise-induced sympathetic neural activation in humans. In 15 young (20-30 yr) healthy subjects, lower leg muscle sympathetic nerve activity (MSNA, peroneal nerve; microneurography), venous plasma norepinephrine (PNE) concentrations, heart rate, and arterial blood pressure were measured at rest and in response to rhythmic handgrip exercise performed during normoxia or isocapnic hypoxia (inspired O2 concn of 10%). Study I (n = 7): Brief (3-4 min) hypoxia at rest did not alter MSNA, PNE, or arterial pressure but did induce tachycardia [17 +/- 3 (SE) beats/min; P less than 0.05]. During exercise at 50% of maximum, the increases in MSNA (346 +/- 81 vs. 207 +/- 14% of control), PNE (175 +/- 25 vs. 120 +/- 11% of control), and heart rate (36 +/- 2 vs. 20 +/- 2 beats/min) were greater during hypoxia than during normoxia (P less than 0.05), whereas the arterial pressure response was not different (26 +/- 4 vs. 25 +/- 4 mmHg). The increase in MSNA during hypoxic exercise also was greater than the simple sum of the separate responses to hypoxia and normoxic exercise (P less than 0.05). Study II (n = 8): In contrast to study I, during 2 min of exercise (30% max) performed under conditions of circulatory arrest and 2 min of postexercise circulatory arrest (local ischemia), the MSNA and PNE responses were similar during systemic hypoxia and normoxia. Arm ischemia without exercise had no influence on any variable during hypoxia or normoxia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of central venous pressure change on plasma vasopressin in humans

After overnight food and fluid restriction, nine healthy males were examined before, during, and after lower body positive pressure (LBPP) of 11 +/- 1 mmHg (mean +/- SE) for 30 min and before, during, and after graded lower body negative pressure (LBNP) of -10 +/- 1, -20 +/- 2, and -30 +/- 2 mmHg for 20 min each. LBPP and LBNP were performed with the subject in the supine position in a plastic box encasing the subject from the xiphoid process and down, thus including the splanchnic area. Central venous pressure (CVP) during supine rest was 7.5 +/- 0.5 mmHg, increasing to 13.4 +/- 0.8 mmHg (P less than 0.001) during LBPP and decreasing significantly at each step of LBNP to 2.0 +/- 0.5 mmHg (P less than 0.001) at 15 min of -30 +/- 2 mmHg LBNP. Plasma arginine vasopressin (AVP) did not change significantly in face of this large variation in CVP of 11.4 mmHg. Mean arterial pressure increased significantly during LBPP from 100 +/- 2 to 117 +/- 3 Torr (P less than 0.001) and only at one point during LBNP of -30 +/- 2 mmHg from 102 +/- 1 to 115 +/- 5 mmHg (P less than 0.05). Heart rate did not change during LBPP but increased slightly from 51 +/- 3 to 55 +/- 3 beats/min (P less than 0.05) only at 7 min of LBNP of -30 +/- 2 mmHg. Plasma osmolality, sodium, and potassium did not change during the experiment. Hemoglobin concentration increased during LBPP and LBNP, whereas hematocrit only increased during LBNP.(ABSTRACT TRUNCATED AT 250 WORDS)