Physiological Arousal, Attentiveness, Emotion, and Word Retrieval in Aphasia: Effects and Relationships

PURPOSE

This study aimed to (a) compare physiological arousal and attentiveness during a confrontational naming task between participants with aphasia and a control group across four conditions that varied according to emotionality of presented stimuli and (b) explore relationships among physiological arousal, attentiveness, perceived arousal, and naming performance. We hypothesized that participants with aphasia would show lower levels of arousal and attentiveness than control participants and that emotional conditions would lead to increased physiological arousal and attentiveness.

METHOD

Eight participants with aphasia and 15 control participants completed a confrontational naming task under positive, negative, and neutral conditions and rated their perceived arousal after each. Electrophysiological recordings were taken during the entire experiment to obtain measures of heart rate (HR), HR variability, and skin conductance (SC). Videos of confrontational naming trials were rated based on visual signs of participant attentiveness during each trial.

RESULTS

Statistically significant group differences were found for HR, SC, and attentiveness ratings, but no differences were found in these measures among conditions. Correlational analyses revealed statistically significant relationships between attentiveness and response time, HR, and naming accuracy. Significant correlations were also found for HR and naming accuracy as well as perceived arousal and naming accuracy.

CONCLUSIONS

Findings suggest that decreased physiological arousal or attentiveness may contribute to naming deficits for people with aphasia (PWA). Assisting PWA to fully attend to and engage in therapy tasks may be important for accurate assessment of language functions and for achieving optimal benefit in treatment.

Age-Related Changes in Speech and Voice: Spectral and Cepstral Measures

Purpose This study examined differences in selected acoustic measures of speech and voice according to age and sex and across families. Method Participants included 169 individuals, 79 men and 90 women, from 18 families, ranging in age from 17 to 87 years. Participants reported no history of articulation disorders, stroke or active neurologic disease, or severe-to-profound hearing loss. They read aloud two passages to facilitate examination of the following speech and voice acoustic parameters: fricative spectral moments (center of gravity, standard deviation, skewness, and kurtosis), the proportion of time spent speaking, mean speaking fundamental frequency, semitone standard deviation (STSD), and cepstral peak prominence smoothed. Results The results indicated a significant age effect for fricative spectral center of gravity, spectral skewness, and speaking STSD. There was a significant sex effect for spectral center of gravity, spectral kurtosis, and mean fundamental frequency. Familial relationship was significant for spectral skewness, STSD, and cepstral peak prominence smoothed. Conclusions These findings revealed that certain speech and voice features change with age and some change differently for men and women. Additionally, speakers from the same family units may demonstrate similar patterns for prosody, voicing, and articulatory behavior. The results also demonstrated normal differences in speech and voice variation across age, sex, and family unit. Understanding patterns and differences across these demographic variables in healthy speakers is important to distinguishing more confidently between normal and disordered speech and voice patterns clinically.

Speech Adaptation to Kinematic Recording Sensors: Perceptual and Acoustic Findings

PURPOSE

This study used perceptual and acoustic measures to examine the time course of speech adaptation after the attachment of electromagnetic sensor coils to the tongue, lips, and jaw.

METHOD

Twenty native English speakers read aloud stimulus sentences before the attachment of the sensors, immediately after attachment, and again 5, 10, 15, and 20 min later. They read aloud continuously between recordings to encourage adaptation. Sentence recordings were perceptually evaluated by 20 native English listeners, who rated 150 stimuli (which included 31 samples that were repeated to assess rater reliability) using a visual analog scale with the end points labeled as "precise" and "imprecise." Acoustic analysis began by segmenting and measuring the duration of the fricatives /s/ and /ʃ/ as well as the whole sentence. The spectral center of gravity and spectral standard deviation of the 2 fricatives were measured using Praat. These phonetic targets were selected because the standard placement of sensor coils on the lingual surface was anticipated to interfere with normal fricative production, causing them to become distorted.

RESULTS

Perceptual ratings revealed a decrease in speech precision after sensor attachment and evidence of adaptation over time; there was little perceptual change beyond the 10-min recording. The spectral center of gravity for /s/ decreased, and the spectral standard deviation for /ʃ/ increased after sensor attachment, but the acoustic measures showed no evidence of adaptation over time.

CONCLUSION

The findings suggest that 10 min may be sufficient time to allow speakers to adapt before experimental data collection with Northern Digital Instruments Wave electromagnetic sensors.

Nebulized isotonic saline improves voice production in Sjögren's syndrome

OBJECTIVE

This study examined the effects of a topical vocal fold hydration treatment on voice production over time.

STUDY DESIGN

Prospective, longitudinal, within-subjects A (baseline), B (treatment), A (withdrawal/reversal), B (treatment) experimental design.

METHODS

Eight individuals with primary Sjögren's syndrome (SS), an autoimmune disease causing laryngeal dryness, completed an 8-week A-B-A-B experiment. Participants performed twice-daily audio recordings of connected speech and sustained vowels and then rated vocal effort, mouth dryness, and throat dryness. Two-week treatment phases introduced twice-daily 9-mL doses of nebulized isotonic saline (0.9% Na(+)Cl(-)). Voice handicap and patient-based measures of SS disease severity were collected before and after each 2-week phase. Connected speech and sustained vowels were analyzed using the Cepstral Spectral Index of Dysphonia (CSID). Acoustic and patient-based ratings during each baseline and treatment phase were analyzed and compared.

RESULTS

Baseline CSID and patient-based ratings were in the mild-to-moderate range. CSID measures of voice severity improved by approximately 20% with nebulized saline treatment and worsened during treatment withdrawal. Posttreatment CSID values fell within the normal-to-mild range. Similar patterns were observed in patient-based ratings of vocal effort and dryness. CSID values and patient-based ratings correlated significantly (P < .05).

CONCLUSION

Nebulized isotonic saline improves voice production based on acoustic and patient-based ratings of voice severity. Future work should optimize topical vocal fold hydration treatment formulations, dose, and delivery methodologies for various patient populations. This study lays the groundwork for future topical vocal fold hydration treatment development to manage and possibly prevent dehydration-related voice disorders.

LEVEL OF EVIDENCE

2b.

Voice, Speech, and Laryngeal Features of Primary Sjögren’s Syndrome

Objective:

This study examined voice, speech, and laryngeal characteristics in primary Sjögren’s syndrome (pSS).

Methods:

Eleven patients (10 female, 1 male; mean [SD] age = 57 [14] years) from The University of Utah Division of Rheumatology provided connected speech and sustained vowel samples. Analyses included the Multi-Dimensional Voice Profile, the Analysis of Dysphonia in Speech and Voice, and dysphonia severity, speech clarity, and videolaryngostroboscopy ratings.

Results:

Shimmer, amplitude perturbation quotient, and average fundamental frequency differed significantly from normative values ( P < .01). Cepstral Spectral Index of Dysphonia values indicated mild-to-moderate dysphonia in connected speech (mean [SD] = 20.26 [8.36]) and sustained vowels (mean [SD] = 16.91 [11.08]). Ratings of dysphonia severity and speech clarity using 10-cm visual analog scales suggested mild-to-moderate dysphonia in connected speech (mean [SD] = 2.11 [1.72]) and sustained vowels (mean [SD] = 3.13 [2.20]) and mildly reduced speech clarity (mean [SD] = 1.46 [1.36]). Videolaryngostroboscopic ratings indicated mild-to-moderate dryness and mild reductions in overall laryngeal function. Voice Handicap Index scores indicated mild-to-moderate voice symptoms (mean [SD] = 43 [23]).

Conclusion:

Individuals with pSS may experience dysphonia and articulatory imprecision, typically in the mild-to-moderate range. These findings have implications for diagnostic and referral practices in pSS.

The Effect of Dialect on Speech Audiometry Testing

Purpose

In this study, the authors examined the validity of using materials from 2 nonregional yet mutually intelligible dialects to evaluate an individual's speech recognition threshold (SRT) and word recognition (WR) abilities and whether a speaker of 1 dialect could accurately administer and score materials in the other dialect.

Method

Previously created SRT and WR materials were presented to 32 Mandarin listeners with normal hearing: 16 speakers of Mainland Mandarin and 16 speakers of Taiwan Mandarin. Hearing abilities were examined using SRT and WR materials created for speakers from 2 different regional dialects. Presentation of the materials occurred during 2 test sessions, counterbalanced across material and listener dialect. Listener responses were evaluated by 2 judges; 1 spoke Mainland Mandarin, and the other spoke Taiwan Mandarin.

Results

For the SRT and WR results, differences in listener performance were statistically significant across material and listener dialect, with threshold differences of less than 2 dB HL when collapsed across session. The interscorer percentage of agreement was 99.5% for SRT and 99.1% for WR testing.

Conclusion

Testing with materials in a different regional dialect does have a measurable impact on SRT and WR performance. However, this difference, though reliable, is small enough to have a negligible impact on clinical findings.

Acoustic and spectral patterns in young children's stop consonant productions

The aim of this study was to examine the acoustic and spectral patterns of stop articulation in the speech of pre-pubescent children. A set of voiceless stop consonants, /ptk/, produced by a group of adults and typically developing children 3-5 years of age were examined in terms of multiple acoustic and spectral parameters. Findings indicated that, with the exception of spectral kurtosis, the acoustic and spectral characteristics of the stop productions varied significantly as a function of place of articulation and vowel context. Sex-specific differences in spectral slope, mean, and skewness were found for the 5-year-old and adult speakers. Such differences in adult speakers can be explained in part by variation in vocal tract size across the sex of the speaker; however, vocal tract dimorphism is typically not present in pre-pubescent children. Thus, the findings of this study provide some support that sex-specific differences in the speech patterns of young children may be associated with learned or behavioral factors, such as patterns of obstruent articulation that depend in part on a culturally determined male-female archetype.

Psychometrically equivalent mandarin bisyllabic speech discrimination materials spoken by male and female talkers

The purpose of this study was to develop, digitally record, evaluate, and psychometrically equate a set of Mandarin bisyllabic word lists for use in measurement of speech discrimination. Familiar bisyllabic words were digitally recorded by male and female talkers of Standard Mandarin. Percentage of correct word recognition was measured for each word at ten intensity levels ( -5 to 40 dB HL) in 5 dB increments using 20 normally hearing subjects. Using logistic regression, 200 words with the steepest logistic regression slopes were included in four psychometrically equivalent word lists of 50 words each, and eight half-lists of 25 words each. To increase auditory homogeneity of the lists, the intensity of words in each list was digitally adjusted so that the threshold of each list was equal to the midpoint between the mean thresholds of the male and female half-lists. Digital recordings of the psychometrically equivalent word recognition lists are available on compact disc.

Psychometrically equivalent trisyllabic words for speech reception threshold testing in Mandarin

The aim of this investigation was to develop, digitally record, evaluate, and equate Mandarin trisyllabic words, which could then be used to measure the SRT. A selection of 90 frequently utilized trisyllabic words were digitally recorded by male and female talkers of Standard Mandarin and presented to 20 normally hearing subjects at 13 intensity levels (-10 to 14dB HL) in 2dB increments. Using logistic regression, psychometric functions were then calculated for all words. Twenty-four trisyllabic words with steep psychometric function slopes were selected, and their intensities were digitally adjusted to match the mean subject PTA (3.0 dB HL). The mean slopes for the 24 selected male and female trisyllabic Mandarin Chinese words were 11.3%/dB and 12.1%/dB, respectively. Thus we developed a list of words which were homogeneous with respect to audibility and slope. Digital recordings of the psychometrically equivalent trisyllabic words are available on compact disc.

Development of speech reception threshold materials for speakers of Taiwan Mandarin

The aim of this research was to develop, digitally record, evaluate, and equate speech audiometry materials that can be used to measure the speech reception threshold (SRT) in quiet for native speakers of Taiwan Mandarin. Familiar trisyllabic words were digitally recorded by male and female talkers of Taiwan Mandarin and subsequently evaluated by 20 native listeners with normal hearing at 14 intensity levels (-10 to 16 dB HL) in 2 dB increments. Using logistic regression, psychometric functions were calculated for all words. Twenty-eight words with comparatively steep psychometric functions were selected and digitally adjusted to match the mean subject pure-tone average (5.0 dB HL). This resulted in a list of words that are relatively homogeneous in threshold audibility and psychometric function slope. The mean slopes for the 28 selected male and female trisyllabic Taiwan Mandarin words were 11.3%/dB and 11.7%/dB, respectively.

Articulatory changes in muscle tension dysphonia: evidence of vowel space expansion following manual circumlaryngeal therapy

In a preliminary study, we documented significant changes in formant transitions associated with successful manual circumlaryngeal treatment (MCT) of muscle tension dysphonia (MTD), suggesting improvement in speech articulation. The present study explores further the effects of MTD on vowel articulation by means of additional vowel acoustic measures. Pre- and post-treatment audio recordings of 111 women with MTD were analyzed acoustically using two measures: vowel space area (VSA) and vowel articulation index (VAI), constructed using the first (F1) and second (F2) formants of 4 point vowels/ a, i, ae, u/, extracted from eight words within a standard reading passage. Pairwise t-tests revealed significant increases in both VSA and VAI, confirming that successful treatment of MTD is associated with vowel space expansion. Although MTD is considered a voice disorder, its treatment with MCT appears to positively affect vocal tract dynamics. While the precise mechanism underlying vowel space expansion remains unknown, improvements may be related to lowering of the larynx, expanding oropharyngeal space, and improving articulatory movements.

LEARNING OUTCOMES

The reader will be able to: (1) describe possible articulatory changes associated with successful treatment of muscle tension dysphonia; (2) describe two acoustic methods to assess vowel centralization and decentralization, and; (3) understand the basis for viewing muscle tension dysphonia as a disorder not solely confined to the larynx.

Word Recognition Materials for Native Speakers of Taiwan Mandarin

Purpose

To select, digitally record, evaluate, and psychometrically equate word recognition materials that can be used to measure the speech perception abilities of native speakers of Taiwan Mandarin in quiet.

Method

Frequently used bisyllabic words produced by male and female talkers of Taiwan Mandarin were digitally recorded and subsequently evaluated using 20 native listeners with normal hearing at 10 intensity levels (−5 to 40 dB HL) in increments of 5 dB.

Results

Using logistic regression, 200 words with the steepest psychometric slopes were divided into 4 lists and 8 half-lists that were relatively equivalent in psychometric function slope. To increase auditory homogeneity of the lists, the intensity of words in each list was digitally adjusted so that the threshold of each list was equal to the midpoint between the mean thresholds of the male and female half-lists.

Conclusions

Digital recordings of the word recognition lists and the associated clinical instructions are available on CD upon request.

Acoustic characteristics of English lexical stress produced by native Mandarin speakers

Native speakers of Mandarin Chinese have difficulty producing native-like English stress contrasts. Acoustically, English lexical stress is multidimensional, involving manipulation of fundamental frequency (F0), duration, intensity and vowel quality. Errors in any or all of these correlates could interfere with perception of the stress contrast, but it is unknown which correlates are most problematic for Mandarin speakers. This study compares the use of these correlates in the production of lexical stress contrasts by 10 Mandarin and 10 native English speakers. Results showed that Mandarin speakers produced significantly less native-like stress patterns, although they did use all four acoustic correlates to distinguish stressed from unstressed syllables. Mandarin and English speakers' use of amplitude and duration were comparable for both stressed and unstressed syllables, but Mandarin speakers produced stressed syllables with a higher F0 than English speakers. There were also significant differences in formant patterns across groups, such that Mandarin speakers produced English-like vowel reduction in certain unstressed syllables, but not in others. Results suggest that Mandarin speakers' production of lexical stress contrasts in English is influenced partly by native-language experience with Mandarin lexical tones, and partly by similarities and differences between Mandarin and English vowel inventories.

First and second language tongue movements in Spanish and Korean bilingual speakers

A number of previous studies have relied on perceptual judgments or acoustic analysis to examine second language (L2) production. However, few researchers have studied L2 performance by directly tracking the physical movements of the articulators. The purpose of the present study was to investigate intraspeaker differences in native (Korean or Spanish) and L2 (English) production through kinematic indices of tongue activity. This involved measurement of the speed, duration, and distance of tongue movements or strokes during speech. Findings indicated that the speakers had significantly slower stroke speeds and longer movement durations for L2 when compared to their native language (L1), yet no significant differences in stroke distance. The bilingual speakers were found to pause more and speak proportionally less of the time in their L2. Interestingly, those speakers who exhibited greater relative kinematic changes from L1 to L2 were also rated as having a stronger perceived accent.

Articulatory changes following treatment of muscle tension dysphonia: preliminary acoustic evidence

PURPOSE

Primary muscle tension dysphonia (MTD), a voice disturbance that occurs in the absence of structural or neurological pathology, may respond to manual circumlaryngeal techniques, which ostensibly alter the posture of the larynx and/or the configuration of the vocal folds without directly targeting supralaryngeal articulatory structures. Although the phonatory benefits of these techniques have been documented previously, this investigation examined whether acoustic evidence exists for articulatory changes accompanying successful management.

METHOD

In this retrospective study of a clinical database, pre- and post-treatment speech samples from 111 women with MTD were analyzed for acoustic evidence of supraglottal vocal tract changes associated with voice improvement, which was confirmed by perceptual ratings of dysphonia severity. The slopes of the first and second formants in diphthongs, as well as global measures of speech timing were acquired. Twenty younger females with normal voices were recorded twice, across a similar time-span to the disordered speakers, to allow comparisons in performance.

RESULTS

Repeated measures analysis of variance was used to evaluate changes accompanying treatment. Significant time by group interactions for /I/ F2 slope, /eI/ F2 slope, sample duration, and speaking time ratio were observed. As compared to the controls, diphthong second formant transitions increased in slope, and timing measures showed increases in speech continuity for the speakers with MTD.

CONCLUSIONS

Collectively, these preliminary findings suggest that individuals with MTD experience changes in both articulatory and phonatory behavior following successful treatment that targets the larynx.

Psychometrically equivalent Russian speech audiometry materials by male and female talkers

Despite the large number of individuals who speak Russian, only a limited number of high-quality speech audiometry materials are available in a standard dialect of Russian. Thus, the purpose of this study was to develop and evaluate speech audiometry materials that can be used to measure word recognition and SRT testing in quiet for native speakers of Russian. Familiar monosyllabic and bisyllabic words were digitally recorded by male and female talkers of Russian and subsequently evaluated by native listeners. Using logistic regression, psychometric functions were then calculated for all words. Selected monosyllabic words were digitally adjusted to create word recognition lists which are relatively homogeneous with respect to audibility and psychometric slope. Speech reception threshold materials were developed by selecting twenty-five bisyllabic words with relatively steep psychometric function slopes (12.1%/dB and 9.9 %/dB) and digitally equating their intensity to match the mean PTA of the native listeners. Digital recordings of the resulting psychometrically equivalent speech audiometry materials are available on compact disc.

Acoustic and spectral characteristics of young children's fricative productions: a developmental perspective

Scientists have made great strides toward understanding the mechanisms of speech production and perception. However, the complex relationships between the acoustic structures of speech and the resulting psychological percepts have yet to be fully and adequately explained, especially in speech produced by younger children. Thus, this study examined the acoustic structure of voiceless fricatives (/f, theta, s, S/) produced by adults and typically developing children from 3 to 6 years of age in terms of multiple acoustic parameters (durations, normalized amplitude, spectral slope, and spectral moments). It was found that the acoustic parameters of spectral slope and variance (commonly excluded from previous studies of child speech) were important acoustic parameters in the differentiation and classification of the voiceless fricatives, with spectral variance being the only measure to separate all four places of articulation. It was further shown that the sibilant contrast between /s/ and /S/ was less distinguished in children than adults, characterized by a dramatic change in several spectral parameters at approximately five years of age. Discriminant analysis revealed evidence that classification models based on adult data were sensitive to these spectral differences in the five-year-old age group.

Sex-related acoustic changes in voiceless English fricatives

This investigation is a comprehensive acoustic study of 4 voiceless fricatives (/f theta s /) in English produced by adults and pre- and postpubescent children aged 6-14 years. Vowel duration, amplitude, and several different spectral measures (including spectral tilt and spectral moments) were examined. Of specific interest was the pattern of normal development of the acoustic properties of fricatives and the nature of sex-specific patterns of fricative articulation in prepubescent children. Little evidence of amplitude or duration differences was found between speakers that was related to sex of the speaker. However, significant sex-specific differences in fricative articulation were found in all groups of speakers-even in the youngest children (ages 6-7 years)-although there was an indication that some of the acoustic differences between females and males is reduced or absent in the youngest children. Results from discriminant analysis demonstrated that a discriminant function based on the adult male tokens was generally better at classifying fricatives produced by male speakers than female speakers, regardless of age. This showed that sex-related differences (presumably a function of sex-linked vocal tract variation) were present even in the youngest speaker group. However, the classification accuracy of the female model showed a steady improvement with the increased age of the female speakers and may provide support for the claim that sex-related developmental differences may just be emerging in the youngest age group.

Development and application of a compartmental model of 3-methylhistidine metabolism in humans and domestic animals

Measurement of urinary 3-methylhistidine (3MH) excretion is the primary in vivo method to measure skeletal muscle (myofibrillar) protein breakdown. This method requires quantitative collection of urine and is based on the assumption that no metabolism of 3MH occurs once it is released from actin and myosin. This is true in most species, but in sheep and swine a proportion is retained in muscle as a dipeptide, balenine. In neither of these species does urine 3MH yield any data on the metabolism of 3MH. We have conducted studies that propose that 3MH metabolism in humans, cattle, dogs, swine, and sheep can be defined from a single bolus infusion of a stable isotope 3-[methyl-2H3]-methylhistidine. Following the bolus dose of the stable isotope tracer, serial blood samples and/or urine was collected over three to five days. A minimum of three exponentials were required to describe the plasma decay curve adequately. The kinetic linear-time-invariant models of 3MH metabolism in the whole animal were constructed by using the SAAM/CONSAM modeling program. Three different configurations of a three-compartment model are described: (A) A simple three-compartment model for humans, cattle, and dogs, in which plasma kinetics (3-[methyl-2H3]-MH/3MH) are described by compartment 1 and with one urinary exit from compartment 1. (B) A plasma-urinary kinetic three-compartment model with two exits was used for sheep with a urinary exit out of compartment 1 and a balenine exit out of a tissue compartment 3. (C) A plasma three-compartment model was used in swine with an exit out of a tissue compartment 3. The kinetic parameters reflect the differences in known physiology of humans, cattle, and dogs as compared to sheep and swine that do not quantitatively excrete 3MH into the urine. Steady-state model calculations define masses and fluxes of 3MH between three compartments and, importantly, the de novo production of 3MH. The de novo production of 3MH for humans, cattle, dogs, sheep, and swine are 3.1, 6.0, 12.1, 10.3, and 7.2 mumol x kg-1 x d-1, respectively. The de novo production of 3MH as calculated by the compartmental model was not different when compared to 3MH production as calculated via traditional urinary collection. Additionally, data suggest that steady-state compartment masses and mass transfer rates may be related to fat free mass and muscle mass in humans and swine, respectively. In conclusion, models of 3MH metabolism have been developed in numerous species, and these models can be used for the assessment of muscle proteolysis and 3MH kinetics without the collection of urine. This methodology is less evasive and will be useful in testing further experimental designs that alter myofibrillar protein breakdown.

Conversion of beta-methylbutyric acid to beta-hydroxy-beta-methylbutyric acid by Galactomyces reessii

beta-Hydroxy-beta-methylbutyric acid (HMB) has been shown to increase strength and lean mass gains in humans undergoing resistance-exercise training. HMB is currently marketed as a calcium salt of HMB, and thus, environmentally sound and inexpensive methods of manufacture are being sought. This study investigates the microbial conversion of beta-methylbutyric acid (MBA) to HMB by cultures of Galactomyces reessii. Optimal concentrations of MBA were in the range of 5 to 20 g/liter for HMB production. Preliminary shake flask experiments indicated that HMB yields were sensitive to dissolved oxygen levels and that cell growth decreased significantly as MBA concentrations increased. Degradation of HMB was faster at acidic pH, and pH 7.0 was optimal for HMB production. Resting cells obtained from media without MBA could efficiently convert MBA to HMB. Thus, a two-step, fed-batch fermentation procedure in which biomass was first produced, followed by coaddition of MBA and glucose, while dissolved oxygen was maintained at 20% of saturation, was designed. A maximum HMB concentration of 38 g/liter was obtained after 136 h, and the molar conversion yield was more than 0.50 mol of HMB/mol of MBA during the fermentation.

Estimation of 3-methylhistidine production in pigs by compartmental analysis

Direct in vivo methodology is not available to accurately evaluate muscle turnover in pigs. Urinary 3-methylhistidine (3MH) excretion, which is used as an in vivo marker of muscle protein breakdown in humans and cattle, is not a valid indicator for pigs. The present study proposes that data from a single bolus dose of 3-[methyl-2H3]methylhistidine tracer can mathematically describe 3MH metabolism in pigs. Plasma concentration of the tracer is described by a linear time-invariant three-compartment model by using the SAAM/CONSAM computer modeling program. The model defines masses and fluxes of 3MH within the pigs and, in particular, the intracellular de novo production of 3MH, which should reflect muscle proteolysis. The de novo production of 3MH as calculated by the model was 621 mumol/d, corresponding to a fractional breakdown rate of 2.28%/d, which is similar to values reported by using indirect methodology. These data also suggest that certain model compartments may be indicators of body muscle mass (mass of compartment 3, r = .59, P = .006). The mathematical model developed does not depend on urine collections and can be used to assess changes in muscle proteolysis in vivo.

Comparison between 3-methylhistidine production and proteinase activity as measures of skeletal muscle breakdown in protein-deficient growing barrows

This experiment was conducted to determine the relationship between 3-methylhistidine (3MH) production and proteinase activity in skeletal muscles of growing barrows. Barrows at 13 wk of age were randomly assigned to either control diet available on an ad libitum basis (21% of ME consisted of protein; control group), control diet fed restricted (pair-fed with barrows in protein-free group; intake-restricted group), or protein-free diet available on an ad libitum basis (protein-free group) for 14 d. During the last 3 d, blood samples were collected for determination of 3MH production rate, which is a measure of myofibrillar protein breakdown. At slaughter, two muscles were taken: masseter (M) and longissimus (L) muscles. The muscle samples were analyzed for calpastatin, mu-calpain, m-calpain, multicatalytic proteinase (MCP), cathepsin B, cathepsins B+L, and cystatins activities. Both muscles were also analyzed for amounts of DNA, RNA, total protein, and myofibrillar and sarcoplasmic proteins. Growth rate (kilograms/day) was influenced by dietary treatments (P < .05). Fractional breakdown rate (FBR, percentage/day) of skeletal muscle, as calculated from 3MH production rate (micromoles.kilogram-1.day-1), was 27% higher for the protein-free group than for the control group. However, no differences in proteinase activities were observed, except for lower MCP activity in the M muscle of the protein-free group than in that of the other groups (P < .05). In the present study, no direct relation was observed between myofibrillar protein degradation rate and proteinase activities in skeletal muscle during a protein-free feeding strategy.

A compartmental model of 3-methylhistidine metabolism in humans

Urinary 3-methylhistidine (3MH) excretion has been proposed as a noninvasive in vivo marker of muscle protein breakdown, but such analysis requires quantitative collection of urine and yields few details about the metabolism of 3MH. In this study, we propose that data from a single bolus dose of tracer and serial blood samples over 72 h can be described by a kinetic model that defines 3MH metabolism in humans. Plasma concentration of the tracer was described by a linear time-invariant three-compartment model. The model defines masses and fluxes of 3MH within the subjects and, in particular, the intracellular de novo production of 3MH. The de novo production of 3MH as calculated by the model was not different from that calculated via the traditional collection of urinary 3MH (3.09 vs 2.57 mumol.kg-1.day-1, respectively; P > 0.30). These data indicate that 3MH production can be measured by a compartmental model that can be used to measure muscle proteolysis without quantitative urine collections.

Effects of excess dietary leucine and leucine catabolites on growth and immune responses in weanling pigs

Two experiments with weanling pigs were conducted to study the effects on growth and immune responses of excess dietary L-leucine (LEU) and dietary supplementation with the LEU catabolites, alpha-ketoisocaproic acid (KIC) and beta-hydroxymethyl butyrate (HMB). In Exp. 1, 80 pigs were randomly allocated according to initial BW and ancestry to five replications of four dietary treatments (four pigs/pen). The control diet contained wheat, oat groats, menhaden fish meal, and dried whey and provided 1.12% LEU. Treatment diets were the control plus 1.12% LEU, 1.12% KIC, or .4% HMB. The experiment lasted 6 wk. In Exp. 2, 36 pigs were randomly allocated to nine replications of four dietary treatments in a 2 x 2 factorial arrangement. Treatments consisted of two concentrations of dietary LEU and a daily i.m. injection of dexamethasone (DEX) or saline. Pigs were fed a control corn-soybean meal and dried whey diet (1.56% LEU) or the control diet plus 1.56% of crystalline LEU. Pigs were individually penned and the experiment lasted 4 wk. Growth performance, plasma free amino acids, plasma urea nitrogen, and humoral and cellular immune responses were measured. Results indicated that LEU concentrations in practical diets and supplementation with KIC and HMB (Exp. 1) did not detrimentally affect growth and immune response. The high LEU concentration and DEX injection used in Exp. 2, however, were detrimental to both growth and immune response.

Use of 18O-labelled leucine and phenylalanine to measure protein turnover in muscle cell cultures and possible futile cycling during aminoacylation

Amino acids labelled with 18(O) on both carboxy oxygen atoms have the potential for use as non-recyclable tracers to measure protein turnover. During protein synthesis one of the labelled oxygen atoms is removed, and thus release of the mono-labelled amino acid could be used to determine proteolysis. Primary cultures of embryonic-chick skeletal-muscle cells were used to test the use of 18(O2)-labelled Leu to measure proteolysis. For 9-day cultures, prelabelled on days 2-8 with medium containing one-half the Leu as [18O2]Leu and one-half as [2H3]Leu, release of [18(O)]Leu was less than 50% that of [2H]Leu over 24 h, suggesting a loss of the 18O label by a mechanism other than protein synthesis. Medium containing [18(O2)]Leu, [2H3]Leu, [18O2]Phe and [13C]Phe was then incubated with 9-day cultures to compare the rate of loss of the 18(O)-label from Leu and Phe with the rate of uptake of the non-carboxy-oxygen-labelled amino acids. Results for Leu demonstrated an 81% loss of the 18(O) label compared with a 33% decrease in [2H]Leu over 12 h. Loss of the 18(O) label was four times as great for Leu as for Phe. Loss of the 18(O) label was not decreased by addition of cycloheximide or by addition of a 3-fold excess of Ile, Val and Tyr; thus the loss of label was not due to protein synthesis alone or to misbinding to incorrect tRNAs. Infusion of the isotopes into pigs showed that the 18(O) label of Leu was not lost during transamination to alpha-ketoisocaproate (alpha-oxoisohexanoate). The most probable explanation is that the 18(O) label is lost as a result of the enzymic deacylation of tRNA, that this process is substantially faster for Leu than for Phe, and that this represents a potentially costly futile cycle for Leu.

Gas chromatographic/mass spectrometric analysis of stable isotopes of 3-methylhistidine in biological fluids: application to plasma kinetics in vivo

A simple and rapid method for measuring 3-methylhistidine (3MH) in plasma and urine is described. Internal standard, 1-methylhistidine (1MH), was added to plasma, acidified and absorbed onto cation-exchange columns. It was then eluted from columns, dried, and derivatized for gas chromatography/mass spectrometry. A major fragment of 3MH was monitored at 238 u and 3-methyl-(methyl-2H3)histidine (d3-3MH) (used for in vivo kinetics) at 241 u, whereas 1MH was monitored at 340 u and eluted 0.5 min later than 3MH. Standard curves for plasma analysis were linear and nanamole amounts of 3MH in plasma were determined with a precision of 3.5%. 3MH was also quantitated in urine; however, because of substantial amounts of 1MH, (18O2)1MH was used as the internal standard. Nanamole amounts of 3MH were determined in urine with a precision of 2.7%. Application of the 3MH analytical method was used to develop a kinetic compartmental model by using the stable isotope of 3MH, d3-3MH. Cattle, like humans, quantitatively excrete 3MH in the urine. A young bovine was injected with d3-3MH and the enrichment curve in plasma was evaluated in order to obtain a steady-state production rate of 3MH. The decay curve was modeled through the use of NIH-SAAM modeling program. The kinetics of d3-3MH from plasma were adequately described by a three-pool compartmental model. The de novo production rate of 3MH estimated in the calf was 665 mumol per day. This corresponded to an estimated fractional turnover rate of 1.56% per day, which was similar to estimates obtained from urine collections.(ABSTRACT TRUNCATED AT 250 WORDS)

Technical note: the use of a compartmental model to estimate the de novo production rate of N tau-methylhistidine in cattle

Urinary N tau-methylhistidine (NMH) excretion has been used as an index of muscle protein breakdown in cattle. An alternative means to estimate muscle proteolysis in cattle is to estimate the de novo production of NMH from plasma kinetics isotopically. Three crossbred steers (average 229 kg) were given a 5.0-mg bolus intravenous injection of [methyl-2H3-N tau-methylhistidine (d3-NMH), after which 16 serial blood samples and three consecutive 24-h urine samples were taken. The enrichment of NMH in plasma was determined by gas chromatography-mass spectrometry, and compartmental analysis of the kinetic data was performed using the SAAM modeling program. The NMH production rates per day (NMHPR, micromoles per day) were 732, 782, and 725, and the fractional breakdown rates (FBR, percentage per day) were 1.61, 1.72, and 1.58 as determined by urinary excretion of NMH, by a three-pool catenary model (plasma kinetics, Model A), and by a more descriptive, three-pool model with two response curves (both plasma and urine kinetics, Model B), respectively. Model A and B estimates of NMHPR and FBR were similar (P greater than .25) to those of estimates obtained from urinary NMH excretion. Kinetic modeling also allows calculation of compartment mass and flux of NMH between compartments and indicates that when NMH exists the muscle pool it is rapidly excreted via the urine. In conclusion, kinetic modeling offers an alternative approach to estimating the NMH production rate.

Leucine and its catabolites alter mitogen-stimulated DNA synthesis by bovine lymphocytes

This study determined effects of leucine and its catabolites on in vitro, mitogen-stimulated DNA synthesis by bovine lymphocytes. Cultures grown in leucine-free or leucine-replete (0.4 mmol/L leucine) medium were supplemented with 0-10.0 mmol/L leucine or individual catabolites. Leucine at greater than or equal to 0.08 mmol/L was necessary for normal DNA synthesis by mitogen-stimulated bovine lymphocytes. beta-Hydroxy-beta-methylbutyrate (HMB) and beta-hydroxy-beta-methylglutarate (HMG) had minimal effect on unresponsiveness of mitogen-stimulated bovine lymphocytes in leucine-free medium; however, alpha-ketoisocaproate (KIC) at 0.4 and 2.0 mmol/L partially or completely restored DNA synthesis. In leucine-replete medium, 0.016-0.4 mmol/L KIC and 0.016-2.0 mmol/L HMB and HMG did not affect DNA synthesis. At 2.0 and 10.0 mmol/L, KIC inhibited (P less than 0.01) DNA synthesis, whereas HMB and HMG at 10.0 mmol/L enhanced (P less than 0.01) DNA synthesis. Overall, these results suggest that leucine is necessary for mitogen-induced DNA synthesis by bovine lymphocytes, and that this requirement for leucine can be partially met by KIC. When leucine was not limiting, KIC, HMB and HMG at concentrations that might occur in vivo did not alter lymphocyte DNA synthesis in vitro.

Regulation of whole-body leucine metabolism with insulin during mixed-meal absorption in normal and diabetic humans

To determine the effects of insulin on dietary and endogenous leucine metabolism, five normal subjects, seven insulin-insufficient insulin-dependent (IDDM) diabetic patients, and five diabetic patients controlled with continuous subcutaneous insulin infusion (CSII) were studied before and for 8 h after ingestion of a chemically defined elemental test meal (10 cal/kg) containing crystalline amino acids. L-[1-14C]leucine was included in the meal to trace the entry and oxidation of the dietary leucine. Total (meal + endogenous) entry of leucine into the circulation was estimated with a constant infusion of [2H3]leucine. Postabsorptive and meal-related increases in the plasma leucine concentration were greater (P less than .05) in the insulin-insufficient IDDM than in the normal subjects but returned to near-normal values with CSII. Baseline leucine flux was approximately 40% greater in the insulin-insufficient IDDM than in normal subjects (2.17 +/- 0.17 vs. 1.55 +/- 0.15 mumol.kg-1.min-1, respectively; .05 less than P less than .01) but were near normal during CSII treatment (1.85 +/- 0.25 mumol.kg-1.min-1). Furthermore, total leucine entry during meal absorption was greater in the insulin-insufficient IDDM (1.41 +/- 0.10 mmol.kg-1.8 h-1) than in either normal (0.96 +/- 0.08 mmol.kg-1.8 h-1, P less than .01) or IDDM subjects during CSII treatment (1.09 +/- 0.11 mmol.kg-1.8 h-1, P less than .05). Fractional oxidation (approximately 40-50%) and entry of dietary leucine were similar in all three groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Inverse relationship of leucine flux and oxidation to free fatty acid availability in vivo

To determine the effect of fatty acid availability on leucine metabolism, 14-h fasted dogs were infused with either glycerol or triglyceride plus heparin, and 46-h fasted dogs were infused with either nicotinic acid or nicotinic acid plus triglyceride and heparin. Leucine metabolism was assessed using a simultaneous infusion of L-[4,5-3H]leucine and alpha-[1-14C]ketoisocaproate. Leucine, alpha-ketoisocaproate (KIC), and totalleucine carbon (leucine plus KIC) flux and oxidation rates were calculated at steady state. In 14-h fasted animals, infusion of triglyceride and heparin increased plasma free fatty acids (FFA) by 0.7 mM (P less than 0.01) and decreased leucine (P less than 0.01), total leucine carbon flux (P less than 0.02), and oxidation (P less than 0.05). The estimated rate of leucine utilization not accounted for by oxidation and KIC flux decreased, but the changes were not significant. During glycerol infusion, leucine and KIC flux and oxidation did not change. In 46-h fasted dogs, nicotinic acid decreased FFA by 1.0 mM (P less than 0.01) and increased (P less than 0.05) the rate of leucine and total leucine carbon flux, but did not affect KIC flux. Leucine oxidation increased (P less than 0.01) by nearly threefold, whereas nonoxidized leucine utilization decreased. Infusion of triglyceride plus heparin together with nicotinic acid blunted some of the responses observed with nicotinic acid alone. In that changes in oxidation under steady state condition reflect changes in net leucine balance, these data suggest that FFA availability may positively affect the sparing of at least one essential amino acid and may influence whole body protein metabolism.

Effects of [15N]leucine infused at low rates on leucine metabolism in humans

The present studies were carried out to determine whether infusions of [15N]leucine at low rates affect estimates of leucine oxidation and of proteolysis and protein synthesis in humans. Three groups of normal subjects were infused for 3 h with either [15N]leucine at a rate of 0.16 or 0.26 mumol X kg-1 X min-1 or saline using [2H3]leucine and alpha-[14C]ketoisocaproate as isotopic tracers of leucine metabolism. Data were analyzed at steady state using both single- and dual-isotope models. Preliminary studies were carried out to characterize the dual-isotope model in humans using infusions of [3H]leucine and alpha-[14C]ketoisocaproate. In the postabsorptive state estimates of leucine appearance, disappearance, and oxidation derived from the two isotope models were in good agreement. Infusion of stable isotope up to approximately 10% of the leucine carbon flux do not have a significant effect on leucine metabolism, but the data derived from such studies must be properly controlled and interpreted with care because these tracers are not massless.

Effects of epinephrine infusion on leucine and alanine kinetics in humans

Infusion of epinephrine in humans increases glucose production and decreases plasma concentrations of some essential amino acids such as leucine, while not affecting the plasma concentration of the potential gluconeogenic amino acid alanine. To determine whether epinephrine alters alanine and leucine metabolism, rates of appearance (Ra) and disappearance (Rd) of glucose, alanine, and leucine were determined in postabsorptive volunteers using [3H]glucose, [2H3]alanine, [15N]leucine, and [2H3]leucine during a 180-min infusion of epinephrine (50 ng X kg-1 X min-1). Plasma glucose (90 +/- 1 to 142 +/- 5 mg/dl) and insulin (10 +/- 1 to 16 +/- 2 micrograms/ml) increased (P less than 0.05), whereas plasma alanine concentrations did not change and plasma leucine concentrations increased (127 +/- 5 to 72 +/- 3 microM). Glucose Ra increased transiently and returned to basal values by 120 min. In contrast, alanine Ra and Rd increased identically and progressively from 5.7 +/- 0.5 to 14.5 +/- 1.9 mumol X kg-1 X min-1 by 180 min. Although leucine nitrogen Ra increased transiently and returned to basal values, leucine carbon Ra and Rd decreased (P less than 0.05) during the infusion of epinephrine. The calculated rate and percent of leucine nitrogen going to alanine increased, whereas the percent of alanine nitrogen derived from leucine remained constant. The increase in alanine Ra was entirely attributable to increased de novo synthesis because proteolysis, as estimated by leucine carbon flux, decreased.

Insulin binding on cultured chick muscle cells: decrease in binding associated with cell fusion

Binding of 125I-bovine and chicken insulin to cultured embryonic chick skeletal muscle cells was studied. Bovine and chicken insulin bound cultured cells with high affinities of 2.4 X 10(9)M-1 and 4.8 X 10(9)M-1 and low affinities of 2.4 X 10(7)M-1 and 3.7 X 10(7)M-1, respectively. Maximum insulin binding was achieved after 90 min of incubation at 20 degrees C and the maximum value was maintained for an additional 3 hr. Insulin binding increased in a linear manner with increasing nuclei number over a 5-fold range. Maximum insulin binding per nuclei decreased as cell fusion increased between 24 and 72 hr in culture, primarily due to a decrease in the number of low affinity insulin receptors.

Effects of free fatty acid availability, glucagon excess, and insulin deficiency on ketone body production in postabsorptive man

The present studies were undertaken to assess the relative effects of free fatty acid (FFA) availability, glucagon excess, and insulin deficiency on ketone body (KB) production in man. To determine whether an increase in FFA availability would augment KB production in the absence of insulin deficiency and glucagon excess, plasma insulin and glucagon were maintained at basal concentrations by infusion of somatostatin and exogenous insulin and glucagon, and plasma FFA were increased from 0.32 +/- 0.06 to 1.4 +/- 0.1 mM by a 2.5-h-infusion of a triglyceride emulsion plus heparin. KB production increased fivefold from 2.2 +/- 0.4 to 11.4 +/- 1.2 mumol . kg-1 . min-1, P less than 0.001. To determine whether insulin deficiency would further augment KB production, analogous experiments were performed but the replacement infusion of insulin was stopped. Despite a greater increase in plasma FFA (from 0.26 +/- 0.04 to 1.95 +/- 0.3 mM), KB production increased (from 1.5 +/- 0.3 to 11.1 +/- 1.8 mumol . kg-1 . min-1) to the same extent as in the absence of insulin deficiency. To determine whether hyperglucagonemia would augment KB production beyond that accompanying an increase in plasma FFA and, if so, whether this required insulin deficiency, similar experiments were performed in which the glucagon infusion rate was increased to produce plasma glucagon concentrations of 450-550 pg/ml with and without maintenance of the basal insulin infusion. When basal plasma insulin concentrations were maintained, hyperglucagonemia did not further increase KB production; however, when the basal insulin infusion was discontinued, hyperglucagonemia increased KB production significantly, whereas no change was observed in saline control experiments. These studies indicate that, in man, FFA availability is a major determinant of rates of KB production; insulin does not appear to influence ketogenesis rates by a direct hepatic effect, and glucagon can further augment KB production when FFA concentrations are increased but only in the setting of insulin deficiency.

Failure of infused beta-hydroxybutyrate to decrease proteolysis in man

Ketone bodies have been suggested to have a protein-sparing effect, since infusion of Na-beta-hydroxybutyrate in man decreases plasma alanine concentrations and urinary nitrogen (N) excretion. To test this hypothesis, six normal postabsorptive volunteers were infused with Na-beta-hydroxybutyrate for 3 h. Rates of glucose, leucine carbon, and alanine appearance and disappearance from the plasma space were traced with [3-3H]glucose, L-[6,6,6-2H3]leucine, and [2,3,3,3-2H4]alanine. Rates of leucine N appearance and disappearance and the rate of transfer of leucine N to alanine were assessed with [15N]leucine. During ketone body infusion, plasma alanine decreased (P less than 0.05), whereas plasma leucine increased (P less than 0.05). Rates of alanine appearance increased (5.3 +/- 0.3 to 7.8 +/- 0.6 mumol/kg X min), but the increase in its rate of disappearance was slightly greater, accounting for the decrease in plasma alanine concentration. Leucine N flux and the rate and percent of leucine N transferred to alanine increased, whereas leucine carbon flux was unchanged. To determine the effect of the alkalemia induced by Na-beta-hydroxybutyrate, four additional subjects were infused with NaHCO3. Alkalemia had no effect on leucine N or carbon flux or on the rate of appearance of alanine, but increased the rate of alanine disappearance, resulting in a decrease in the plasma alanine concentration. Since the rate of appearance of leucine carbon was unaltered during the infusion of Na-beta-hydroxybutyrate, it is unlikely that hyperketonemia per se decreases proteolysis in postabsorptive man.

Regulation of alpha-ketoisocaproate binding to albumin in vivo by free fatty acids

The importance of alpha-keto acid binding to plasma proteins was investigated both in vitro and in vivo using alpha-ketoisocaproate (KIC), the alpha-keto acid of leucine. Gel chromatography indicated that 65% of the radioactivity comigrated with serum albumin. An ultrafiltration assay was developed to estimate the percentage of free and bound KIC. These percentages, along with total plasma KIC concentrations, were used to calculate the circulating concentrations of free and bound KIC. KIC or free fatty acids (FFA) displaced [14C]KIC bound to bovine albumin or whole plasma. KIC was totally displaced from plasma proteins by 10 mM oleate, stearate, and myristate; whereas the alpha-keto acids of isoleucine and value were 50 and 85%, respectively, as effective as KIC. To determine whether increased plasma FFA concentrations alter the binding of KIC to plasma proteins in vivo, five postabsorptive humans were infused with triglyceride and heparin during the simultaneous administration of somatostatin, glucagon, and insulin. During the FFA elevation, plasma leucine decreased by 9% (P less than 0.02). Total plasma KIC remained constant, whereas free KIC increased (P less than 0.02) and bound KIC decreased (P less than 0.001). These results indicate that KIC is bound to plasma albumin in vivo and suggests that FFA, by altering circulating free KIC concentrations, may influence protein metabolism in man.