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PubMed2002

Method of lactate elevation does not affect the determination of the lactate minimum.

PURPOSE: The aim of the study was to examine the effects of different lactate elevation protocols on the determination of the lactate minimum (Lac(min)) point. METHODS: Eight highly trained racing cyclists each completed four continuous ramp lactate minimum tests using the following blood lactate elevation protocols: 1) continuous ramp maximal aerobic power (RMP(max)) assessment, 2) 30-s maximal sprint, 3) 40-s maximal sprint, and 4) two 20-s maximal sprints separated by a 1-min recovery. Each blood lactate elevation protocol was followed by a 5-min active recovery leading into a continuous ramp test commencing at a power of 60% of RMP(max), using a 6 W x min ramp rate, lasting 15 min. RESULTS: Peak [La](b) values were significantly higher (P > 0.05) after the RMP(max) compared with all other protocols and higher in the 40-s versus 30-s sprint. However, by the start of Lac(min) ramp, [La](b) after the RMP(max) was no longer higher than the 40-s sprint, but Lac(min) [La](b) was similar for all protocols. This resulted in no differences in the total decline of [La](b) measured as a percentage from the highest to the lowest value. At Lac(min) point, there were no significant differences in power (P > 0.05), but heart rate was higher in the RMP versus 2 x 20 s and VO(2) was significantly higher after the 40 s compared with the 2 x 20 s protocol. CONCLUSION: This study demonstrated that the determination of lactate minimum power in cycling is not dependent upon the lactate elevation protocol.

Adult↗
PubMed1984

In-vitro wall shear measurements at aortic valve prostheses.

Wall shear distributions during the cardiac cycle at the valve rings of Starr-Edwards, Björk-Shiley and Lillehei-Kaster aortic valves are measured and compared with thresholds reported for shear-induced trauma of blood components. Further, for the disk valves, the influence of pulse rate on wall shear stresses is evaluated. Hot film anemometry with flush-mounted wall shear probes is used as measurement technique in a pulsatile flow mock circuit. The experimental systolic data support the better hemodynamic characteristics of the disk valves over the ball valve also with respect to the threshold shear stresses of flow induced blood trauma. These results are confirmed by postoperative clinical studies, where lower LDH-values are found with the disk than with the ball valves. During diastole, however, high shear stresses are measured and calculated at the valve ring of the Björk-Shiley prosthesis, which can be referred to the non-overlapping closing mechanism. This result is discussed with respect to the often observed thrombus formation at the disk downstream of the smaller orifice of the Björk-Shiley valve.

Aortic Valve↗
PubMed1993

Brainstem bilirubin toxicity in the newborn primate may be promoted and reversed by modulating PCO2.

The auditory brainstem response (ABR) was monitored during infusion of bilirubin in six ventilated newborn rhesus monkeys (138-145 d gestation) while acute changes in pH were produced by varying inspired CO2. Prolonged respiratory acidosis without bilirubin infusion produced minimal changes in the ABR (one animal). CO2 exposure, usually initiated when the bilirubin level reached approximately 20 mg/dL, decreased arterial pH to values ranging from 6.85 to 7.10. ABR changes, including prolongation of the wave II-IV peak to peak intervals and decreased wave amplitudes, first developed 2-4 h after initial exposure to CO2. Total and unbound bilirubin levels at this time ranged from 376 to 564 mumol/L (22-33 mg/dL) and 38 to 65 nmol/L (2.5-3.8 micrograms/dL), respectively. Correction of respiratory acidosis produced partial to complete reversal of ABR changes within 3 to 20 min. Reexposure to CO2 immediately reproduced the ABR abnormality. Production and reversal of the abnormal ABR was obtained through two to three cycles in three animals. Thus, when the brainstem bilirubin level was near the threshold for toxicity, the effect of changes in PCO2 on the ABR were immediate, suggesting that auditory pathway toxicity is initially mediated by a reversible pH-dependent bilirubin-membrane complex. In contrast to humans, in monkeys auditory toxicity appeared to be a late manifestation of bilirubin toxicity, inasmuch as all monkeys were obtunded and apneic 30-70 min before ABR abnormalities appeared. Notwithstanding these limitations, the results support the hypothesis that bilirubin toxicity can be both promoted and reversed by modulating brain pH.

Acidosis, Respiratory↗
PubMed1985

Response to muscular exercise following repeated simulated weightlessness.

The effect of repeated weightlessness exposures on maximal aerobic capacity was determined when seven healthy men (36-48 yr) underwent two 10-d bedrest (BR) periods in the -6 degrees headdown position, which were separated by a 14-d recovery period. No prescribed exercise was performed by the subjects during the course of the experiment. A graded supine cycle ergometer test consisting of 4 min of unloaded pedaling at 60 rpm followed by increased work rate of 15 W X min-1 until volitional fatigue (max) was performed before (pre) and after (post) the first and second BR periods, i.e., BR1 and BR2, and again 14 d after BR2 (REC). During exercise, submaximal and maximal oxygen uptake (VO2), ventilation (VE), heart rate (HR), systolic (SBP) and diastolic (DBP) blood pressures were measured and the gas exchange anaerobic threshold (AT) was determined. Plasma volume (Vp, T-1824) and body composition were measured pre- and post-BR1 and BR2 and following REC. Compared to the respective pre-BR control values, VO2max decreased (p less than 0.05) by 8.7% after BR1 and 5.2% after BR2 but returned to pre-BR values following 14 d REC. Submaximal and maximal HR increased (p less than 0.05) post-BR1 and BR2 but returned to pre-BR levels after REC. The AT and Vp decreased (p less than 0.05) post-BR1 and BR2 but returned to pre-BR levels after REC. Body weight increased (p less than 0.05) gradually during the experiment and did not return to control values.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1999

Stability of the blood lactate-heart rate relationship in competitive athletes.

INTRODUCTION: The identification of the HR (or RPE) associated with blood lactate concentrations of 2.5 mmol x L(-1)(aerobic threshold) (AerT) and 4.0 mmol x L(-1)(anaerobic threshold) (AnT) is a common method for defining training intensities. It is often assumed that the HR at AerT and AnT changes with changes in fitness, much as the power output (Watts: W) associated with AerT and AnT is known to change. METHODS: We studied speed skaters (N = 13, 7 male, 6 female) during spring (deconditioned) and fall (conditioned) evaluations, using cycle ergometry (stage duration = 5 min) to determine W, HR, and RPE at AerT, AnT, and at maximal exercise (3000 (female) and 5000 (male) m cycle time trials). RESULTS: In the spring vs. fall evaluations, the power output at AerT was 127+/-12 vs 162+/-9 W (P<0.05), at AnT was 216+/-14 vs. 230+/-13 W (P<0.05), and at maximal exercise was 341+/-15 vs. 364+/-19 W (P<0.05); HR at AerT was 129+/-6 vs. 130+/-7 bpm (P>0.05), at AnT was 162+/-7 vs. 164+/-7 bpm (P>0.05), and at maximal exercise was 196+/-6 vs. 198+/-5 bpm (P>0.05); RPE at AerT was 2.7+/-0.9 vs. 2.6+/-0.8 (P>0.05), at AnT was 5.3+/-1.0 vs. 5.3+/-0.9 (P>0.05). CONCLUSIONS: These data suggest that although power output at AerT, AnT, and maximal exercise changes significantly with conditioning, there is no systematic change in the associated values for HR and/or RPE used as practical markers of training intensity. Accordingly, a single well-conducted evaluation may allow evaluation of appropriate training markers that may be longitudinally stable.

Anaerobic Threshold↗
PubMed1989

Neural response to very low-frequency sound in the avian cochlear nucleus.

Recordings were made in the chick cochlear nucleus from neurons that are sensitive to very low frequency sound. The tuning, discharge rate response and phase-locking properties of these units are described in detail. The principal conclusions are: 1. Low frequency (LF) units respond to sound frequencies between 10-800 Hz. Best thresholds average 60 dB SPL, and are occasionally as low as 40 dB SPL. While behavioral thresholds in this frequency range are not available for the domestic chick, these values are in good agreement with the pigeon behavioral audiogram (Kreithen and Quine 1979). 2. About 60% of the unit population displays tuning curves resembling low-pass filter functions with corner frequencies between 50-250 Hz. The remaining units have broad band-pass tuning curves. Best frequencies range from 50-300 Hz. 3. Spontaneous discharge rate was analyzed quantitatively for LF units recorded from nucleus angularis. The distribution of spontaneous rates for LF units is similar to that seen from higher CF units (300-5000 Hz) found in the same nucleus. However, the spontaneous firing of LF units is considerably more regular than that of their higher CF counterparts. 4. Low frequency units with low spontaneous rates (SR's less than 40 spikes/s) show large driven rate increases and usually saturate by discharging once or twice per stimulus cycle. Higher SR units often show no driven rate increases. 5. All LF units show strong phase-locking at all excitatory stimulus frequencies. Vector strengths as high as 0.98 have been observed at moderate sound levels. 6. The preferred phase of discharge (relative to the sound stimulus) increases with stimulus frequency in a nearly linear manner. This is consistent with the LF units being stimulated by a traveling wave. The slope of these phase-frequency relationships provides an estimate of traveling wave delay. These delays average 7.2 ms, longer than those seen for higher CF auditory brainstem units. These observations suggest that the peripheral site of low frequency sensitivity is the very distal region of the basilar papilla, an area whose morphology differs significantly from the rest of the chick basilar papilla. 7. LF units are described whose response to sound is inhibitory at frequencies above 50 Hz.

Acoustic Stimulation↗
PubMed1984

Safety factor for precordial pacing: minimum current thresholds for pacing and for ventricular fibrillation by vulnerable-period stimulation.

Temporary cardiac pacing by means of rapidly applied, precordial electrodes can be of great value in selected patients suffering cardiac arrest or profound bradycardia, post-defibrillation atrioventricular block, or digitalis intoxication. This study provides data pertaining to the safety of precordial pacing measured as the ratio of the minimum current required to induce ventricular fibrillation (VF) to the minimum current required to pace the ventricular myocardium. Single rectangular pulse stimuli having durations of 1-50 ms were evaluated. In 6 anesthetized dogs, a cutaneous electrode was centered over the shaved apex beat area of the left chest and paired with a larger electrode sutured to the right chest wall. Using a specially fabricated, synchronized, high-energy pulse generator, the "most vulnerable" time in the cardiac cycle at which the least current was required to induce VF with a single shock was identified. This current was compared to the much lower current required to pace the heart in the diastolic interval. While the current required to produce either fibrillation or pacing decreased as pulse duration increased, the safety factor (i.e., the ratio of fibrillation current to pacing current) remained nearly constant, averaging 12.6 for all pulse durations examined. That is, on the average, a stimulus of any given duration between 1 and 50 ms required at least 12 times the current required for pacing to produce ventricular fibrillation. We conclude that in normal canine hearts, the risk of inducing VF during precordial pacing is small.

Animals↗
PubMed2004

Effect of systemic hypoxia and reoxygenation on electrical stability of the rat myocardium: chronophysiological study.

The aim of the study was to determine the dependence of changes in the electrical stability of the heart on the light-dark cycle (LD cycle) in disorders of pulmonary ventilation. The ventricular arrhythmia threshold (VAT) was measured in female Wistar rats (adaptation to the light regime 12:12 h, ketamine/xylazine anesthesia 100 mg/15 mg/kg, i.m., open chest experiments). The conditions of the normal artificial ventilation and reoxygenation were V(T) = 1 ml/100 g, respiratory rate 40 breaths/min, hypoventilation V(T) = 0.5 ml/100 g, respiratory rate 20 breaths/min. The animals (n=11 light group; n=19 dark group) were subjected to 20 min hypoventilation followed by 20 min reoxygenation. The control prehypoventilatory VAT differences were not found between the light (1.90+/-0.84 mA) and dark (1.88+/-0.87 mA) part of the day. Artificial hypoventilation changed the VAT values in light and dark part of the day differently. While during the light period, the average VAT values in most animals (90.9 %) were significantly decreased (1.29+/-0.59 vs. 1.90+/-0.84 mA control, p<0.05), during the dark part these values showed either significant increase (63.2 %) (2.23+/-0.77 vs. 1.48+/-0.39 mA, p<0.005) or a slight non-significant decrease (36.8 %) (2.18+/-0.89 vs. 2.54+/-0.99 mA). Reoxygenation returned the VAT values to the level before hypoventilation by an increase of the VAT (81.8 %) in the light part of day and by decrease of the VAT (68.4 %) in the dark part of the day. It is concluded that 1) in hypoventilation/reoxygenation model, the significant higher average VAT values are in the dark part of the day vs. the light one, 2) rat hearts are more resistant to systemic hypoxia and reoxygenation in the dark part of day, and 3) proarrhythmogenic effect of the systemic hypoxia is only seen in the light part of the day.

Animals↗
PubMed1996

Estrous cycle phase variations in visceromotor and cardiovascular responses to colonic distension in the anesthetized rat.

Visceromotor and cardiovascular responses to colonic distension were measured in female rats, anesthetized with halothane in oxygen, in the proestrus, estrus, metestrus and diestrus phases of the estrous cycle. Ten rats were studied in each group and responses were measured at 5-min intervals for 60 min. A mixed model analysis of variance showed that there was no real change in either the visceral or cardiovascular response with time. There was a highly significant difference in visceromotor responses between the phases of the estrous cycle (P < 0.001). During the phase of proestrus the balloon pressure at which a response was triggered was much lower, with a mean value (95% confidence interval) of 18.7 (16.1, 21.8) mmHg, than the other phases with mean values (95% confidence interval) of 31.9 (27.4, 37.2) mmHg for estrus, 28.1 (24.2, 32.8) mmHg for metestrus, and 31.1 (26.7, 36.3) mmHg for diestrus. The mean arterial blood pressure increased in all groups (range 3.2, 5.4%) as a response to the stimulus, but there was no associated heart rate variability and no significant differences in cardiovascular changes between the groups (P = 0.6). The visceromotor responses measured during the phase of proestrus occurred at a significantly lower threshold than in the other phases of estrous.

Anesthesia↗
PubMed1998

Mannose ligand receptor assay as a test to predict fertilization in vitro: a prospective study.

OBJECTIVE: To assess whether mannose receptor assays can predict fertilization outcome in vitro. DESIGN: A prospective, double-blind study of the mannose receptor properties of spermatozoa. SETTING: Assisted human reproduction program at a university hospital. PATIENT(S): Partners of 140 consecutive women undergoing their first in vitro fertilization cycle. INTERVENTION(S): Motile sperm populations were tested for surface receptors for mannose by measuring their ability to bind fluorescein-labeled mannosylated albumin and to undergo a free mannose-induced acrosome reaction as judged by Pisum, sativum agglutinin binding. MAIN OUTCOME MEASURE(S): Mannose receptor assay results were correlated with fertilization outcomes using several statistical tests, including the chi2 test, chi2 for proportions, t-tests, analysis of variance with Student-Newman-Keuls tests and correlational and receiver operating characteristic (ROC) curve analysis. RESULT(S): The fractional increment increase on incubation in the percent of sperm binding mannose ligand over an intact acrosome correlated with fertilization rates in vitro. Threshold values of mannose ligand binding and of mannose-induced acrosome reactions predictive of fertilization rates were identified by ROC curve analysis. Men were thus classified into one of four groups with differing fertilization rates in vitro. CONCLUSION(S): The increment increase in sperm surface mannose ligand binding by acrosome-intact sperm correctly predicts high and low fertilization rates in vitro and identifies cases where conventional insemination can result in failed fertilization.

Adult↗
PubMedDate not supplied

MZ twinning: chance or determinism? An essay in nonlinear dynamics (chaos).

Classically, researchers considered monozygotic twinning (MZT) a random phenomenon. This paper tests the hypothesis with the aid of nonlinear dynamics techniques. The latter can tell true randomness from chance-like variation. Chaos, the endpoint of the threshold state of a nonlinear deterministic system, can mimic constrained randomness. From a practical standpoint, recognizing chaos in a time series data set means that the paradigmatic multifactorial model of causation is essentially ruled out. Specifically, time series of MZ, DZ, and single maternities were analysed. First, spectral analysis was used to uncover periodicities embedded in the series. Second, a singular value decomposition was undertaken to reduce noise from the series. Third, phase space attractors were drawn up that describe the 'asymptotic' trajectory of the system at any time. Results suggested that DZ, MZ, and single maternities shared a similar 32-year periodicity. Owing to two interwoven similar periodicities, the single-maternity cycle kinetics proved to be faster than that of DZ's. The MZ series was the only one to display secondary interacting harmonics, thus eliciting a rather unusual trajectory in the bidimensional phase space. The MZ time points were not spread in a haphazard fashion; on the contrary, a fine structure was present that did not reduce to a limit cycle such as the one characterizing the DZ- or the single-maternity trajectory. It was concluded that a complex nonlinear dynamic underlies MZ twinning. Therefore, calling for extrinsic causes to account for what appears to be random variation overtime would be pointless. MZ twinning should rather be traced to a limited number of intrinsic and deterministic interacting system components. The most likely candidates are presented and discussed.

Bias↗
PubMed1984

Computer analysis of cross sectional echocardiogram for quantitative evaluation of left ventricular asynergy in myocardial infarction.

Left ventricular asynergy in myocardial infarction was assessed quantitatively by computer analysis of the cross sectional echocardiogram. Short axis cross sectional images of the left ventricle at the levels of the mitral valve, papillary muscle, and apex were recorded by a phased array sector scanner in 30 patients with healed myocardial infarction and 15 normal controls. Endocardial and epicardial short axis images of the left ventricle were transferred from video tape to a minicomputer through the interface circuits, then digitised and processed automatically by a minicomputer. Automatic edge detection of the endocardial and epicardial wall was performed by applying sequential steps including smoothing, second derivative technique, dynamic thresholding, and approximation of boundaries by a spline curve. To quantify regional wall motion, the short axis cross sectional left ventricular wall of each level was divided into eight octants with eight axes at 45 degrees angles from the initial standard axis which was constructed from the geometric centre of the end diastolic left ventricular cavity to the posterior end of the right side of the interventricular septum. Segmental hemiaxis, segmental area, segmental wall thickness, and those changes during cardiac cycle were measured and calculated in each segment automatically by a computer. Regional contractility of the left ventricle was evaluated by percentage systolic changes of the segmental hemiaxis, area, and wall thickness. These values were significantly reduced in the infarcted left ventricular wall as defined by left ventriculography and electrocardiography. Moreover, percentage hemiaxis changes obtained by quantitative left ventriculography described by Herman and colleagues correlated well with those using our analytical method of cross sectional echocardiography in the corresponding segments. The geometric centre of the left ventricular cavity determined by the computer moved slightly towards the anterior wall during systole in normal subjects, possibly reflecting the anterior swinging motion of the heart. The geometric centre of the left ventricular cavity in myocardial infarction moved towards the infarcted wall, showing that the floating reference system was inferior to the fixed reference system for the quantification of abnormal wall motion in myocardial infarction. In conclusion, a computer analysis of the short axis cross sectional echocardiogram of the left ventricle using the fixed reference system has shown its ability to evaluate left ventricular contraction abnormalities, especially systolic wall thickening, which is relatively free of arbitrary interpretation of the wall motion caused by the anterior swinging motion of the heart.

Adult↗
PubMed1989

Perturbation in liver mitochondrial Ca2+ homeostasis in experimental iron overload: a possible factor in cell injury.

The functional state of isolated mitochondria and specifically the integrity of the inner membrane, were investigated in the liver of rats made siderotic by dietary supplementation with carbonyl iron. The concentration of iron in the hepatic tissue increased progressively up to nearly 40 days and reached a steady-state level. When the iron content reached a threshold value (higher than 90 nmol/mg protein) the occurrence of in vivo lipid peroxidation in the mitochondrial membrane was detected. This process did not result in gross alterations in the mitochondrial membrane, as indicated by electron microscopy, phosphorylative capability and membrane potential measurements. On the contrary, the induction of lipoperoxidative reaction appeared to be associated with the activation of Ca2+ release from mitochondria. This was shown to occur as a consequence of rather subtle modifications in the inner membrane structure via a specific efflux route, which appeared to be linked to the oxidation level of mitochondrial pyridine nucleotides. The induction of this Ca2+ release from iron-treated mitochondria resulted in enhancement of Ca2+ cycling, a process which dissipates energy to reaccumulate into mitochondria the released Ca2+. The perturbation in mitochondrial Ca2+ homeostasis reported here may be a factor in the onset of cell damage in this experimental model of hepatic iron overload.

Animals↗
PubMed2005

Model of microtine cycles caused by lethal toxins in non-preferred food plants.

A recent model of microtine cycles has hypothesized that plant chemical defences can drive the precipitous decline phase, through periodic lethal toxin production (PLTP) by non-preferred plant foods. Here we enumerate possible mechanisms using a previously published model of optimal foraging by one consumer (microtine rodent) of two types of food plant (1 preferred and 1 non-preferred). Rate constants for each of the model parameters were sought from the extensive literature on vole cycles. For a range of likely values of input parameters, we evaluated model fit by applying five empirically derived criteria for cyclic behaviour. These were: cycles with a period length of 2-5 yr, peak densities of 100-350 voles per ha and trough densities of 0-25 ha(-1), ratio of peak to trough densities of 10-100, and the occurrence of a catastrophic collapse in the vole population followed by a prolonged low phase. In contrast to previous models of food-induced microtine cycles, the optimal foraging model successfully reproduced the first four criteria and the prolonged low phase. The criterion of population collapse was met if the non-preferred food began producing lethal toxins at a threshold grazing intensity, as predicted by PLTP. Fewer criteria could be met in variations on the model, in which the non-preferred food was equally as nutritious as the preferred food or was continuously toxic.

Animals↗
PubMed1995

Quantifying parameters in the transmission of Babesia microti by the tick Ixodes trianguliceps amongst voles (Clethrionomys glareolus).

The estimation of two parameters in the transmission of Babesia microti by the tick Ixodes trianguliceps amongst small mammals, (1) the duration of infectivity in natural hosts and (2) the probability of transmission from an infected to a susceptible vole, is described. When B. microti was maintained by direct tick transmission, the probability of a complete cycle of transmission via the larval-nymphal and nymphal-adult transstadial routes was 1.0 and 0.71 respectively, but only if the larvae or nymphs had engorged, as distinct from feeding slowly, while the source parasitaemia exceeded 2 or 0.2% respectively, but had not yet passed the peak level. The duration of this condition for infectivity in voles infected by nymphal bites was only 1-4 days, whilst infections delivered by adult ticks barely reached the threshold level necessary for successful transmission. When syringe passage was introduced into the parasite maintenance schedule (a) the probability of transmission declined markedly and (b) the time-course of the parasitaemia was altered. If these parameter values are put into a simple model, together with field data on tick and host survival rates, it becomes apparent that additional factors, such as the highly aggregated distribution of ticks on their hosts, must account for the maintenance of B. microti at the levels seen in wild small mammal populations.

Animals↗
PubMed1998

Intracardiac QRS electrogram width--an arrhythmia detection feature for implantable cardioverter defibrillators: exercise induced variation as a base for device programming.

Delivery of inappropriate therapy of implantable cardioverter defibrillators (ICD) due to inaccurate arrhythmia detection represents a major clinical problem. Different arrhythmia detection criteria such as the "stability" of the cycle length or the suddenness of "onset" of tachycardia have been implemented in ICD software to prevent inappropriate therapy. The new Medtronic model 7223Cx ICD offers an additional detection parameter (QRS width), which reflects changes in the duration of ventricular depolarization as a tool to distinguish supraventricular from ventricular tachycardias. Although this criterion can be programmed based on ECG parameters derived from resting ECGs, this may not be sufficient since QRS width is subject to considerable changes due to transient myocardial ischemia, changes in autonomic tone, or frequency dependent effects of antiarrhythmic drugs. The present study aimed to determine frequency dependent changes in QRS width in individual patients at rest and during symptom-limited exercise testing in 16 patients with documented ventricular tachycardia (N = 13) or ventricular fibrillation (N = 3). The optimal EGM slew threshold and the individual variation of QRS width were determined. Measurements obtained at the end of the implantation procedure were compared to those performed at hospital discharge. The majority of patients showed a wider variation in QRS duration as measured from 30 consecutive cycles during exercise as compared to rest. For example, the QRS range (i.e., the difference between the maximal and the minimal QRS width measured) averaged 7 +/- 3 ms at rest and increased to 11 +/- 3 ms during exercise (P = 0.004) with an increase of > or = 4 ms observed in 11 (69%) of 16 patients. In 13 (81%) of 16 patients a reprogramming of at least one QRS width parameter from its value at the time of implantation was necessary. Thus, the QRS width measured from the intracardiac EGM shows significant intraindividual variations in different physiological conditions. For optimal programming of the QRS width parameter, measurements obtained during exercise are important.

Defibrillators, Implantable↗
PubMed1993

Evaluation of ovarian and adrenal sources of androgens in women with polycystic ovary syndrome. Dexamethasone and GnRH-agonist administration.

Ovarian and adrenal production of androgens was evaluated in 18 patients with polycystic ovary syndrome (PCOS) by administering a combination of short-term dexamethasone (DEX) and long-term gonadotropin-releasing hormone agonist (GnRH-A). At day 6 of the cycle, blood samples were collected at 7 A.M. (basal) and 11 P.M. At midnight, 2 mg DEX was given orally, and blood samples were collected at 7 A.M. the following day (DEX1). Blood samples were obtained for 6 weeks at the same time after administration of a potent GnRH-A (400 micrograms/day given subcutaneously). Eight normal subjects served as controls. The amounts of androgens and 17-hydroxyprogesterone (17-OHP) suppressed by using DEX (adrenal-source suppression) and GnRH-A (ovarian-source suppression) were greater in PCOS patients than in controls. We differentiated PCOS patients as having a normal or an exaggerated response to DEX or GnRH-A administration; threshold values were considered average +2SD of the suppressed androgen amounts of controls. Three patients had an exaggerated response to GnRH-A treatment for androstenedione, testosterone and 17-OHP, while DEX inhibition was similar to controls. The remaining 15 patients had an exaggerated response to DEX for all three androgens; seven also had an exaggerated response to GnRH-A. Thus, the combination of GnRH-A and DEX permitted us to selectively study and identify adrenal and ovarian sources of hyperandrogenemia.

Adrenal Glands↗
PubMed1991

Discharge characteristics of medial rectus and abducens motoneurons in the goldfish.

1. The discharge of antidromically identified medial rectus and abducens motoneurons was recorded in restrained unanesthesized goldfish during spontaneous eye movements and in response to vestibular and optokinetic stimulation. 2. All medial rectus and abducens motoneurons exhibited a similar discharge pattern. A burst of spikes accompanied spontaneous saccades and fast phases during vestibular and optokinetic nystagmus in the ON-direction. Firing rate decreased for the same eye movements in the OFF-direction. All units showed a steady firing rate proportional to eye position beyond their recruitment threshold. 3. Motoneuronal position (ks) and velocity (rs) sensitivity for spontaneous eye movements were calculated from the slope of the rate-position and rate-velocity linear regression lines, respectively. The averaged ks and rs values of medial rectus motoneurons were higher than those of abducens motoneurons. The differences in motoneuronal sensitivity coupled with structural variations in the lateral versus the medial rectus muscle suggest that symmetric nasal and temporal eye movements are preserved by different motor unit composition. Although the abducens nucleus consists of distinct rostral and caudal subgroups, mean ks and rs values were not significantly different between the two populations. 4. Every abducens and medial rectus motoneuron fired an intense burst of spikes during its corresponding temporal or nasal activation phase of the "eye blink." This eye movement consisted of a sequential, rather than a synergic, contraction of both vertical and horizontal extraocular muscles. The eye blink could act neither as a protective reflex nor as a goal-directed eye movement because it could not be evoked in response to sensory stimuli. We propose a role for the blink in recentering eye position. 5. Motoneuronal firing rate after ON-directed saccades decreased exponentially before reaching the sustained discharge proportional to the new eye position. Time constants of the exponential decay ranged from 50 to 300 ms. Longer time constants after the saccade were associated with backward drifts of eye position and shorter time constants with onward drifts. These postsaccadic slide signals are suggested to encode the transition of eye position to the new steady level. 6. Motoneurons modulated sinusoidally in response to sinusoidal head rotation in the dark, but for a part of the cycle they went into cutoff, dependent on their eye position recruitment threshold. Eye position (kv) and velocity (rv) sensitivity during vestibular stimulation were measured at frequencies between 1/16 and 2 Hz. Motoneuronal time constants (tau v = rv/kv) decreased on the average by 25% with the frequency of vestibular stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗