Effect of alcoholic cirrhosis on ethane and pentane levels in breath

Lipid peroxidation can be monitored by measuring one or several highly volatile alkanes in exhaled air. The concentrations of ethane and pentane were determined in breath samples from patients with alcoholic and non-alcoholic cirrhosis as well as from healthy subjects. The greatest increase of exhaled pentane was found in 17 patients with alcoholic cirrhosis (2.85 +/- 2.37 pmol/ml) in comparison with 10 patients with non-alcoholic cirrhosis (0.71 +/- 0.33 pmol/ml) and 10 control subjects (0.59 +/- 0.41 pmol/ml). On the contrary, no significant difference was detected as far as exhaled ethane is concerned. These data suggest that: a) gas-chromatographic determination of exhaled pentane may play a significant role in detecting alcohol-induced liver disease; b) hepatic injury may be mediated by lipid peroxidation in these patients.     

In vivo lipid peroxidation in man as measured by the respiratory excretion of ethane, pentane, and other low-molecular-weight hydrocarbons

A method for the collection and measurement of low-molecular-weight volatile hydrocarbons exhaled in human breath as a result of lipid peroxidation in vivo is described. Subjects breathed in a closed-circuit rebreathe system and samples were taken over a 2-h period, extracted, and analyzed by gas-liquid chromatography isothermally on a 3-m column of n-octane/Porasil-C. Immediately, prior to rebreathing subjects were equilibrated with scrubbed air containing very low ambient levels of hydrocarbons to eliminate the effects of previous exposure to hydrocarbon-contaminated environments. Only under these conditions could hydrocarbon exhalation be measured. In the rebreathe system C3-C5 hydrocarbon concentrations increased linearly initially but reached a steady state after 1.5 h while ethane did not approach equilibrium even after 2 h. The steady-state equilibrium was demonstrated to be due to tissue uptake and metabolism of the hydrocarbon gases. Ethane metabolism was slow, allowing calculation of the endogenous production from the initial rate of change in concentration and an experimentally determined total body solubility coefficient. Similar calculations for pentane were not valid as metabolism was rapid; therefore production was estimated from the equilibrium value reached after 2 h. Ethane production in six healthy subjects was calculated to be 95.1 +/- 19.0 pmol/kg/h while equilibrium values for pentane were 120 +/- 50 pmol/liter. This method now allows the quantitation in man of lipid peroxidation in vivo.     

Ethane production rate in vivo is reduced with dietary restriction

Dietary restriction without malnutrition prolongs life and has a beneficial effect on age-related diseases and metabolic derangements. To test the effect of food restriction on ethane production rate, ethane exhalation was measured in rats with partial food restriction. Ethane production rate in room air in rats fed 60% of food consumed by ad libitum-fed animals for 2 wk was significantly reduced (3.50 +/- 0.25 vs. 5.21 +/- 0.34 pmol.min-1.100 g body wt-1, P less than 0.01). In 100% oxygen, ethane production in food-restricted rats was not different from that of ad libitum-fed rats (21.81 +/- 1.25 vs. 19.57 +/- 1.89 pmol.min-1.100 g-1). Fifteen hours of fasting compared with ad libitum feeding reduced ethane production modestly in room air (4.37 +/- 0.45 vs. 5.21 +/- 0.34 pmol.min-1.100 g-1) and more significantly in 100% oxygen (12.37 +/- 0.78 vs. 19.57 +/- 1.89 pmol.min-1.100 g-1). Thus, in 100% oxygen, 15 h of fasting, compared with ad libitum feeding, resulted in an approximately 40% decrease in ethane production rate. It is concluded that short-term food restriction significantly reduces ethane exhalation rate in rats when measured in room air.     

Methods for measuring ethane and pentane in expired air from rats and humans

Numerous studies in animals and humans provide evidence that ethane and pentane in expired air are useful markers of in vivo lipid peroxidation. The measurement of breath hydrocarbons, being noninvasive, is well suited for routine use in research and clinical settings. However, the lack of standardized methods for collecting, processing, and analyzing expired air has resulted in the use of a wide variety of different methods that have yielded highly disparate results among investigators. This review outlines the methods that we have developed and validated for measuring ethane and pentane in expired air from rats and humans. We describe the advantages of these methods, their performance, as well as potential errors that can be introduced during sample collection, concentration, and analysis. A main source of error involves contamination with ambient-air ethane and pentane, the concentrations of which are usually much greater and more variable than those in expired air. Thus, it appears that the effective removal of ambient-air hydrocarbons from the subject's lungs before collection is an important step in standardizing the collection procedure. Also discussed is whether ethane or pentane is a better marker of in vivo lipid peroxidation.     

A validated method for rapid analysis of ethane in breath and its application in kinetic studies in human volunteers

Oxidative stress may initiate lipid peroxidation that generates ethane. Ethane, at low concentrations, is eliminated by pulmonary exhalation. Previous methods have not allowed frequent sampling, thus ethane kinetics has not been studied in man. A validated method over the range 3.8-100,000 ppb with a limit of quantitation of 3.8 ppb (CV 9.3%) based on cryofocusing technique of a 60 ml breath sample allowed frequent sampling. Due to a rapid analytical procedure batches of more than 100 samples may be analyzed. In human volunteers (24-55 years) uptake was studied for up to 23 min (n=9), elimination was studied for 210 min (n=9). Ethane was inhaled (concentrations varied from 16 to 29 ppm (parts per million)) through a non-rebreathing system; sampling was performed with short intervals from the expiratory limb. Samples were also drawn from the inhalatory limb. Ninety-five percent of steady state (inspired) concentration was reached within 1.75 min. Five percent of the initially inhaled concentrations was found in exhaled air 1.5 min after termination of inhalation. A terminal mean half life of 31 min for ethane was also observed. The data indicate that frequent sampling will be necessary to capture relevant changes in breath ethane.     

A Validated Method for Rapid Analysis of Ethane in Breath and its Application in Kinetic Studies in Human Volunteers

Oxidative stress may initiate lipid peroxidation that generates ethane. Ethane, at low concentrations, is eliminated by pulmonary exhalation. Previous methods have not allowed frequent sampling, thus ethane kinetics has not been studied in man. A validated method over the range 3.8-100,000 ppb with a limit of quantitation of 3.8 ppb (CV 9.3%) based on cryofocusing technique of a 60 ml breath sample allowed frequent sampling. Due to a rapid analytical procedure batches of more than 100 samples may be analyzed. In human volunteers (24-55 years) uptake was studied for up to 23 min <formula>(<italic>n</italic>=9)</formula>, elimination was studied for 210 min <formula>(<italic>n</italic>=9).</formula> Ethane was inhaled (concentrations varied from 16 to 29 ppm (parts per million)) through a non-rebreathing system; sampling was performed with short intervals from the expiratory limb. Samples were also drawn from the inhalatory limb. Ninety-five percent of steady state (inspired) concentration was reached within 1.75 min. Five percent of the initially inhaled concentrations was found in exhaled air 1.5 min after termination of inhalation. A terminal mean half life of 31 min for ethane was also observed. The data indicate that frequent sampling will be necessary to capture relevant changes in breath ethane.     

Ethane production in copper-deficient rats

Evidence is accumulating which indicates that copper-deficient animals are prone to oxidative damage. To investigate this possibility further, we measured the production of breath ethane, a hydrocarbon by-product of lipid peroxidation, in copper-deficient rats. Male, weanling Sprague-Dawley rats were fed either a purified diet which was deficient in copper (CuD) or the same diet made sufficient with 5 ppm of copper (CuS). After 33 to 34 days the rats were placed individually in gastight metabolic cages through which ethane-free air or 100% O2 was passed. Expired ethane was absorbed onto cold, activated charcoal, liberated by heating, and measured by gas chromatography. Ethane production rates (pmoles/min/100 g +/- SD) were 3.3 +/- 0.8 (CuS-air), 4.3 +/- 1.4 (CuD-air), 8.3 +/- 2.5 (CuS-O2), and 12.2 +/- 4.3 (CuD-O2). Repeated measures analysis of variance indicated that both copper deficiency (P less than 0.01) and breathing 100% O2 (P less than 0.0001) enhanced ethane production, with no interaction between treatments. This finding complements previous evidence that increased lipid peroxidation occurs in copper-deficient rats.     

Simultaneous measurement of nitric oxide production by conducting and alveolar airways of humans.

Human airways produce nitric oxide (NO), and exhaled NO increases as expiratory flow rates fall. We show that mixing during exhalation between the NO produced by the lower, alveolar airways (VL(NO)) and the upper conducting airways (VU(NO)) explains this phenomenon and permits measurement of VL(NO), VU(NO), and the NO diffusing capacity of the conducting airways (DU(NO)). After breath holding for 10-15 s the partial pressure of alveolar NO (PA) becomes constant, and during a subsequent exhalation at a constant expiratory flow rate the alveoli will deliver a stable amount of NO to the conducting airways. The conducting airways secrete NO into the lumen (VU(NO)), which mixes with PA during exhalation, resulting in the observed expiratory concentration of NO (PE). At fast exhalations, PA makes a large contribution to PE, and, at slow exhalations, NO from the conducting airways predominates. Simple equations describing this mixing, combined with measurements of PE at several different expiratory flow rates, permit calculation of PA, VU(NO), and DU(NO). VL(NO) is the product of PA and the alveolar airway diffusion capacity for NO. In seven normal subjects, PA = 1.6 +/- 0.7 x 10(-6) (SD) Torr, VL(NO) = 0.19 +/- 0.07 microl/min, VU(NO) = 0.08 +/- 0.05 microl/min, and DU(NO) = 0.4 +/- 0.4 ml. min(-1). Torr(-1). These quantitative measurements of VL(NO) and VU(NO) are suitable for exploring alterations in NO production at these sites by diseases and physiological stresses.     

Ethane exhalation as an index of in vivo lipid peroxidation: Concentrating ethane from a breath collection chamber

A simple method is described for concentrating ethane from large volumes of air; the sensitivity limits for detecting exhaled ethane are increased by 100-fold or more. The method is intended for monitoring low-level ethane exhalation resulting from peroxidative damage to tissue lipids in vivo. Various adsorbents for concentrating ethane and ethylene were tested; in addition, the permeability characteristics of various types of tubing were studied in order to construct a suitable, inexpensive breath collection chamber for laboratory animals. Recommended adsorbents are activated charcoal and molecular sleve; activated alumina is a poor adsorbent. Polyvinyl and Teflon tubing are impermeable, whereas latex and silicone tubing are permeable to ethane. When ethane and ethylene are injected intraperitoneally into mice, the exhalation of these volatile hydrocarbons is readily monitored in the breath collection chamber. Whereas ethylene and the C₃–C₅ alkanes probably are metabolized by mice, ethane apparently is not; however, a portion of the ethane appears to be trapped by absorption within body tissues.     

Daily supplementation with iron increases lipid peroxidation in young women with low iron stores

The aim of this study was to determine whether women with low iron stores (plasma ferritin 相似文献   

Age and contraction type influence motor output variability in rapid discrete tasks.

The purpose of this study was to examine the ability to control knee-extension force during discrete isometric (IC), concentric (CC), and eccentric contractions (EC) in 24 young (mean age +/- SD = 25.3 +/- 2.8 yr) and 24 old (mean age +/- SD = 73.3 +/- 5.5 yr) healthy and active individuals. Subjects were to match a parabola with a time to peak force of 200 ms during IC, CC, and EC at six target levels of force [20, 35, 50, 65, 80, and 90% of the maximum voluntary contraction (MVC)]. ICs were performed at 90 degrees of knee flexion, whereas CCs and ECs ranged from 90 to 80 degrees of knee flexion (0 degrees is full extension) at a slow velocity (25 degrees /s). Results showed that subjects produced similar MVC forces for the three types of contractions. Young subjects produced greater MVC forces than old subjects, and within each age group, men produced greater force than women. The variability (standard deviation) of peak force and impulse in absolute values was greater for young compared with old subjects. When variability was normalized to the force produced [coefficient of variation (CV)], however, old subjects exhibited greater CV than young subjects for peak force and impulse. Both the standard deviation and CV of time to peak force and impulse duration were greater for the old adults. In general, ECs were more variable than ICs and CCs, and old adults exhibited greater CV compared with young adults during rapid, discrete ICs, CCs, and particularly ECs of the quadriceps.     

Effects of vitamin E, ascorbic acid and mannitol on alloxan-induced lipid peroxidation in rats

ω6- and ω3-unsaturated lipid hydroperoxides decompose to yield pentane and ethane, respectively. Alloxan toxicity was studied in rats in relation to pentane and ethane produced during lipid peroxidation induced by intraperitoneal injection of 20 mg of alloxan/100 g body wt. Fifteen minutes after injection, vitamin E-deficient rats exhaled 102- and 11.2-fold more pentane and ethane, respectively, than prior to injection. Injection of 75 mg ascorbic acid/100 g body wt 30 min prior to alloxan treatment prolonged the time over which peroxidation occurred and all vitamin E-deficient rats died before 4 h. Vitamin E-deficient rats injected with 100 mg of the radical scavenger mannitol/ 100 g body wt 30 min prior to alloxan treatment were completely protected against lipid peroxidation, and none of the rats died by 4 h. Rats fed 40 iu dl-α-tocopherol acetate/kg diet or injected with 100 mg dl-α-tocopherol/100 g body wt were either totally protected against alloxan and alloxan-ascorbic acid-induced peroxidation or were only slightly affected as shown by very low-level pentane and ethane production. Thiobarbituric acid reactants in plasma, liver and pancreas 4 h after alloxan treatment reflected the prooxidant nature of ascorbic acid and alloxan, the vitamin E status of the rats and the protective effect of mannitol. Plasma glucose levels 4 h after alloxan injection were lowest in vitamin E-injected rats and highest in vitamin E-deficient rats. Only in vitamin E-deficient rats were both lipid peroxidation and significantly elevated plasma glucose levels observed by 4 h post-alloxan treatment.     

Ethane production rates and minute ventilation

Ethane quantitated in the expired alveolar gas is a noninvasive measure of free radical activity. This method has been criticized for lack of control of minute ventilation (VE) in spontaneously breathing animals, although ethane, which is poorly soluble in tissues, should not be affected by changes in VE. We measured ethane elimination rates in six strain 13 guinea pigs (GP13) during spontaneous room air breathing and in six room air breathing, pentobarbital-anesthetized, tracheostomized, externally warmed, mechanically ventilated GP13s at various levels of VE. In the ventilated animals, weight0.75/VE (metabolic activity corrected for VE) was a linear function of arterial CO2 tension (PaCO2) drawn from arterial line (r = 0.72, P less than 0.005). However, weight0.75/VE did not correlate with ethane elimination rates (r = 0.12, not significant). The mean (+/- SD) ethane elimination rates in the spontaneously breathing animals was 3.15 +/- 0.96 pmol.min-1.100 g-1 and was not significantly different from the mean rate in the mechanically ventilated animals (3.11 +/- 1.37) over a range of VE's. These data demonstrate that ethane elimination rates are not affected by changes in VE and are unaffected by pentobarbital anesthesia.     

Seminal collection, seminal characteristics and pattern of ejaculation in llamas

Semen was collected from 10/10 llamas during 26/30 (87%) collection attempts using an artificial vagina mounted inside a surrogate female. For the 26 semen collections, the duration of copulation (mount to dismount) with the artificial vagina was 31.7 +/- 12.0 min (mean +/- SD). Seminal pH was 8.1 +/- 1.1, and seminal volume per collection was 3.0 +/- 1.9 ml. Sperm concentration per collection was 1.0 +/- 0.8 x 10(6) sperm/ml, total number of spermatozoa was 2.9 +/- 3.1 x 10(6), total sperm motility was 23.7 +/- 20.0%, and the percentage of morphologically normal spermatozoa was 39.7 +/- 18.5%. Morphologically abnormal spermatozoa were categorized according to abnormal heads (20.1 +/- 19.9%), tail-less heads (8.7 +/- 8.9%), abnormal acrosomes (12.9 +/- 12.4%), abnormal midpieces (1.0 +/- 3.7%), cytoplasmic droplets (11.1 +/- 12.4%), and abnormal tails (6.6 +/- 12.0%). There were 0.3 +/- 0.3 million motile, morphologically normal spermatozoa per collection: less than 1000 during the first 5 min of copulation, 0.01 +/- 0.01 x 10(6) between 5 and 10 min of copulation, 0.04 +/- 0.08 x 10(6) between 10 and 15 min of copulation, 0.09 +/- 0.21 x 10(6) between 15 and 20 min of copulation, and 0.15 +/- 0.28 x 10(6) between 20 min and the end of copulation.     

Tracheal vascular and smooth muscle responses to air temperature and humidity in dogs

Twenty-five dogs were anesthetized, paralyzed, and artificially ventilated. Their cranial tracheal arteries were perfused bilaterally with blood at constant flow, and the perfusion pressures (Patr) were measured. Tracheal smooth muscle function was assessed by recording changes in external diameter (delta Dtr). The perfused segment of the trachea was exposed to air at a constant unidirectional airflow of 25 l/min. Group 1 (n = 6) was exposed to cold dry air, ambient room air, and hot dry and hot humid air, each for 10 min with exposures starting from zero flow. The tracheal vascular responses to all four conditions were small vasodilations (delta Patr from -2 to -6%) followed by recovery or small vasoconstrictions. In group 2 (n = 19), exposures to cold dry and hot humid air were preceded and followed by body-temperature fully humidified air. Cold dry air caused a sustained vasodilation (delta Patr -9.0 +/- 1.1%), and hot humid air usually caused a biphasic response: a vasoconstriction (delta Patr 4.4 +/- 1.0%) followed by a vasodilation (delta Patr -5.7 +/- 1.9%). The warm humid air after cold dry air or hot humid air caused a further vasodilation, which lasted a short time after cold dry air (delta Patr -3.7 +/- 0.4%) but greater than 10 min after hot humid air (delta Patr -13.8 +/- 1.4%). In both groups, all exposures that cooled the trachea (cold dry air, ambient room air, and hot dry air) caused smooth muscle contraction, and hot humid air that warmed the trachea caused relaxation.     

High-performance liquid chromatography-based determination of total isothiocyanate levels in human plasma: application to studies with 2-phenethyl isothiocyanate

Dietary and pharmacologic isothiocyanates (ITCs) may play a role in reducing the risk of certain cancers. The quantification of ITCs in humans is important both for epidemiological and pharmacokinetic studies. We describe a modification of an HPLC-based assay of urinary ITCs for use with human plasma. The assay utilizes the cyclocondensation reaction of 1,2-benzenedithiol with ITCs present in human plasma, followed by a two-step hexane extraction and analysis by HPLC using UV detection at 365 nm. The method shows linearity and reproducibility with human plasma over a range of 49-3003 nM phenethyl isothiocyanate (PEITC) (r(2) = 0.996 +/- 0.003). A similar degree of linearity was seen with two other biologically occurring conjugates of PEITC: PEITC--N-acetylcysteine (PEITC--NAC) and PEITC--glutathione (PEITC--GSH). The recovery of PEITC assessed on multiple days was 96.6 +/- 1.5% and was 100% for PEITC--GSH and PEITC--NAC. The reproducibility of the assay on multiday samplings showed a mean %CV of 6.5 +/- 0.3% for PEITC, 6.4 +/- 4.3 for PEITC--NAC and 12.3 +/- 3.9 for PEITC--GSH. In clinical studies, mean plasma ITC level of 413 +/- 193 nM PEITC equivalents was determined for a non-dietary-controlled group of 23 subjects. Multiday analysis data from pharmacokinetic plasma sets of 3 subjects taking a single dose of PEITC at 40 mg showed a good CV (range: 16-21%). The applicability of the methodology to pharmacokinetic studies of PEITC in humans is demonstrated.     

Evidence for increased lipid peroxidation in multiple sclerosis

Pentane and ethane are degradation products of unsaturated fatty acids which are released during lipid peroxidation. In order to assess whether multiple sclerosis is associated with lipid peroxidation, we measured pentane and ethane excretion by 16 patients with multiple sclerosis and compared them to healthy control subjects. Patients with acute exacerbation of multiple sclerosis had significantly higher concentrations of pentane (10.5±4.2 nmol/l)(p<0.01) compared to either patients in remission (4.5±1.7 nmol/l) or control subjects (4.9±1.1 nmol/l). The concentrations of ethane were not significantly different among these groups. Of the patients with acute exacerbation who later achieved remission, the pentane excretion also returned to normal (5.6±0.9 nmol/l). One patient who failed to reachieve clinical remission continued to excrete large amounts of pentane. We conclude that oxygen free radical activity is enhanced during exacerbation multiple sclerosis.     

Chemiluminescent measurements of nitric oxide pulmonary diffusing capacity and alveolar production in humans.

Measurements of nitric oxide (NO) pulmonary diffusing capacity (DL(NO)) multiplied by alveolar NO partial pressure (PA(NO)) provide values for alveolar NO production (VA(NO)). We evaluated applying a rapidly responding chemiluminescent NO analyzer to measure DL(NO) during a single, constant exhalation (Dex(NO)) or by rebreathing (Drb(NO)). With the use of an initial inspiration of 5-10 parts/million of NO with a correction for the measured NO back pressure, Dex(NO) in nine healthy subjects equaled 125 +/- 29 (SD) ml x min(-1) x mmHg(-1) and Drb(NO) equaled 122 +/- 26 ml x min(-1) x mmHg(-1). These values were 4.7 +/- 0.6 and 4.6 +/- 0.6 times greater, respectively, than the subject's single-breath carbon monoxide diffusing capacity (Dsb(CO)). Coefficients of variation were similar to previously reported breath-holding, single-breath measurements of Dsb(CO). PA(NO) measured in seven of the subjects equaled 1.8 +/- 0.7 mmHg x 10(-6) and resulted in VA(NO) of 0.21 +/- 0.06 microl/min using Dex(NO) and 0.20 +/- 0.6 microl/min with Drb(NO). Dex(NO) remained constant at end-expiratory oxygen tensions varied from 42 to 682 Torr. Decreases in lung volume resulted in falls of Dex(NO) and Drb(NO) similar to the reported effect of volume changes on Dsb(CO). These data show that rapidly responding chemiluminescent NO analyzers provide reproducible measurements of DL(NO) using single exhalations or rebreathing suitable for measuring VA(NO).     

Impact of age on breathing and resistive pressure in people with and without sleep apnea.

We investigated the effect of age on breathing and total pulmonary resistance (RL) during sleep by studying elderly (>65 yr) and young (25-38 yr) people without sleep apnea (EN and YN, respectively) matched for body mass index (BMI). To determine the impact of sleep apnea on age-related changes in breathing, we studied elderly and young apneic patients (EA and YA, respectively) matched for apnea and BMI. In all groups (n = 11), breathing during periods of stable sleep was analyzed to evaluate the intrinsic variability of respiratory control mechanisms. In the absence of sleep apnea, the variability of the breathing was similar in the elderly and young [mean (+/- SD) coefficient of variation (CV) of tidal volume (VT); wake: EN 21.0 +/- 14.9%, YN 14.7 +/- 5.5%; sleep: EN 14.0 +/- 6.0%; YN 11.5 +/- 6.4%]. In patients with sleep apnea, breathing during stable sleep was more irregular, but there were no age-related differences (CV of VT; wake: EA 22.0 +/- 11.6%, YA 16.7 +/- 11.3%; sleep: EA 32.8 +/- 24.9%, YA 25.2 +/- 16.3%). In addition, EN tended to have a higher RL (n = 6, RL midinspiration, wake: EN 7.1 +/- 3.0; YN 9.1 +/- 6.4 cmH(2)O. l(-1). s, sleep: EN 17.5 +/- 11.7; YN 9.8 +/- 2.0 cmH(2)O. l(-1). s). We conclude that aging per se does not contribute to the intrinsic variability of respiratory control mechanisms, although there may be a lower probability of finding elderly people without respiratory instability.     

Endogenous ACTH concentration-dependent drive of pulsatile cortisol secretion in the human

According to current regulatory concepts, pulsatile ACTH concentrations (CON) stimulate time-lagged cortisol secretion rates (SEC) via an implicit CON-SEC dose-response relationship. The present analyses reconstruct nonlinear properties of this in vivo agonist-response interface noninvasively in order to investigate pulse-by-pulse coupling consistency and to obviate the need to infuse isotopes or exogenous effectors, which may disrupt pathway interactions. This approach required an ensemble strategy of 1) measuring ACTH and cortisol CON in plasma sampled every 10 min for 24 h in 32 healthy adults, and 2) estimating simultaneously a) variable-waveform ACTH and cortisol SEC bursts superimposed upon fixed basal SEC; b) biexponential kinetics of ACTH and cortisol disappearance; c) nonequilibrium exchange of cortisol among free and cortisol-binding globulin (CBG)- and albumin-bound moieties; d) two SEC-burst shapes demarcated by a statistically defined day/night boundary; e) feedforward efficacy, potency, and sensitivity; and f) stochastic variability in feedforward measures over time. Thereby, we estimate 1) ACTH SEC (microg.l(-1).day(-1)) of 0.27 +/- 0.04 basal and 0.87 +/- 0.07 pulsatile (means +/- SE); 2) cortisol SEC (micromol.l(-1).day(-1)) of 0.10 +/- 0.01 basal and 3.5 +/- 0.20 pulsatile; 3) free cortisol half-lives (min) of 1.8 +/- 0.20 (diffusion/advection) and 4.1 +/- 0.30 (elimination) and a half-life of total cortisol of 49 +/- 2.4 and of ACTH of 20 +/- 1.3; 4) ACTH potency (EC(50), ng/l) of 26 +/- 2.4, efficacy (nmol.l(-1).min(-1)) 10 +/- 1.8, and sensitivity (slope units) 0.65 +/- 0.09; 5) night/day augmentation of ACTH and cortisol SEC-burst mass by 2.1- and 1.7-fold (median); 6) abbreviation of the modal time to maximal ACTH and cortisol SEC rates by 4.4- and 4.3-fold, respectively, after a change point clock time of 0205 (median); 7) in vivo percentage distribution of cortisol as 6% free, 14% albumin bound, and 80% CBG bound with an absolute free cortisol CON (nmol/l) 11.5 +/- 0.54; and 8) significant (mean CV) stochastic variability in feedforward efficacy (140%), potency (38%), and sensitivity (56%) within the succession of paired ACTH/cortisol pulses of any given subject. In conclusion, the present composite formulation illustrates a platform for dissecting mechanisms of in vivo regulation of effector-response properties noninvasively in the corticotropic axis of the uninfused individual.