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Biomedical subjects

P F Tang

Publications and source records attributed to P F Tang.

16 recordsLinked to original sources
PubMed1999

Phase-dependent modulation of proximal and distal postural responses to slips in young and older adults.

BACKGROUND: Phase-dependent modulation of postural responses plays an important functional role in integrating reflexes into ongoing locomotion behaviors. This study tested the hypotheses that proximal and distal postural responses are modulated differently according to the phases of the gait cycle in young adults and that there is a decline in this modulatory ability with normal aging. METHODS: Thirty-three healthy young adults (age = 25 +/- 4 years) and 32 healthy older adults (mean age 74 +/- 14 years) participated. Subjects walked across a movable force plate with its movement timed to heel strike or midstance to simulate a forward slip occurring at different times during the gait cycle. Surface electromyography was recorded from bilateral leg, thigh, hip, and trunk muscles. Kinematic data were collected from the right (perturbed) side of the body. RESULTS: Postural responses to the heel strike slips occurred more frequently, and were of shorter latency, longer burst duration, and greater burst magnitude, than those in response to the midstance slips. Whereas the early and predominant postural responses came from bilateral tibialis anterior, rectus femoris, and biceps femoris muscles in heel strike slips, early postural responses were observed in bilateral erector spinae muscles in midstance slips. The late postural responses in midstance slips (from bilateral biceps femoris muscles and medial gastrocnemius and tibialis anterior of the nonperturbed leg) assisted in foot liftoff of the perturbed leg and earlier and safe landing with the nonperturbed leg. In response to the heel strike versus midstance slips, older adults preserved the phase-dependent modulatory abilities of the occurrence, onset latency, and burst duration of their postural responses, but not the ability to modulate burst magnitude, as compared to young adults. CONCLUSION: Postural responses from the proximal and distal muscles in reaction to different temporal phasing of slips during the step cycle showed differential modulation to meet the different task requirements. Older adults preserve this modulatory ability but with limited capacity. Physiological or psychological factors may influence older adults' phase-dependent modulatory capacity.

Accidental Falls↗
PubMed1998

Control of reactive balance adjustments in perturbed human walking: roles of proximal and distal postural muscle activity.

Studies on the proactive control of gait have shown that proximal (hip/trunk) muscles are the primary contributors to balance control, while studies on reactive balance control during perturbed gait, examining only activity in distal (leg/thigh) muscles, have shown that these muscles are important in compensating for a gait disturbance. This study tested the hypothesis that proximal muscles are also primary contributors to reactive balance control during perturbed gait. Thirty-three young adults participated in a study in which an anterior slip was simulated at heel strike by the forward displacement of a force plate on which they walked. Surface electromyographic data were recorded from bilateral leg, thigh, hip and trunk muscles. Kinematic data were collected on joint angle changes in response to the perturbation. The results did not support the hypothesis that the proximal muscles contribute significantly to balance control during perturbed gait. The proximal muscles did not demonstrate more consistent activation, earlier onset latency, longer burst duration or larger burst magnitude than distal muscles. Moreover, although proximal postural activity was often present in the first slip trial, it tended to adapt away in later trials. By contrast, the typical postural responses exhibited by young adults consisted of an early (90-140 ms), high-magnitude (4-9 times muscle activity during normal walking) and relatively long duration (70-200 ms) activation of bilateral anterior leg muscles as well as the anterior and posterior thigh muscles. Thus, postural activity from bilateral leg and thigh muscles and the coordination between the two lower extremities were the key to reactive balance control and were sufficient for regaining balance within one gait cycle. The adaptive attenuation of proximal postural activity over repeated trials suggests that the nervous system overcompensates for a novel balance threat in the first slip trial and fine-tunes its responses with experience.

Adult↗
PubMed1998

Correlation between two clinical balance measures in older adults: functional mobility and sensory organization test.

BACKGROUND: Functional mobility of older adults has been shown to correlate with stance stability to various extents. This variability could be due to the difference in the way sensory information is processed in these two types of balance tests. Correlations between functional mobility and stance stability under altered sensory conditions, such as those in the Sensory Organization Test (SOT), are needed to test this possibility. The present study investigated the correlation between the performance of older adults on a newly developed Sensory-Oriented Mobility Assessment Instrument (SOMAI) and on the various sensory conditions of the SOT. METHODS: Twenty-seven community-dwelling older adults (76 +/- 7 years) underwent tests of the six SOT conditions and 10 SOMAI mobility maneuvers performed under normal- and focal-vision (peripheral vision eliminated) conditions. Behavioral performance in the two SOMAI conditions and the amounts of postural sway in the six SOT conditions were ranked among the subjects. Correlations of performance rankings on these two tests were analyzed. RESULTS: Performance on the two SOMAI conditions significantly correlated with that on the SOT conditions in which accurate visual, vestibular, and somatosensory inputs were all present (p < .05). Performance on the focal-vision SOMAI condition was also significantly correlated with that on the SOT condition in which somatosensory input was unreliable for orientation while visual and vestibular inputs were reliable (p < .05). There were no correlations between the SOMAI performance and performance on the no-vision or unreliable-vision SOT conditions. CONCLUSIONS: The ability to use all visual, somatosensory, and vestibular inputs for balance was correlated with functional mobility. The moderate correlations between the performance on the normal-sensory SOT condition and the SOMAI conditions suggest that body systems other than balance senses also contribute to mobility performance.

Aged↗
PubMed1998

Inefficient postural responses to unexpected slips during walking in older adults.

BACKGROUND: Slips account for a high percentage of falls and subsequent injuries in community-dwelling older adults but not in young adults. This phenomenon suggests that although active and healthy older adults preserve a mobility level comparable to that of young adults, these older adults may have difficulty generating efficient reactive postural responses when they slip. This study tested the hypothesis that active and healthy older adults use a less effective reactive balance strategy than young adults when experiencing an unexpected forward slip occurring at heel strike during walking. This less effective balance strategy would be manifested by slower and smaller postural responses, altered temporal and spatial organization of the postural responses, and greater upper trunk instability after the slip. METHODS: Thirty-three young adults (age range=19-34 yrs, mean=25+/-4 yrs) and 32 community-dwelling older adults (age range=70-87 yrs, mean=74+/-14 yrs) participated. Subjects walked across a movable forceplate which simulated a forward slip at heel strike. Surface electromyography was recorded from bilateral leg, thigh, hip, and trunk muscles. Kinematic data were collected from the right (perturbed) side of the body. RESULTS: Although the predominant postural muscles and the activation sequence of these muscles were similar between the two age groups, the postural responses of older adults were of longer onset latencies, smaller magnitudes, and longer burst durations compared to young adults. Older adults also showed a longer coactivation duration for the ankle, knee, and trunk agonist/antagonist pairs on the perturbed side and for the knee agonist/antagonist pair on the nonperturbed side. Behaviorally, older adults became less stable after the slips. This was manifested by a higher incidence of being tripped (21 trials in older vs 5 trials in young adults) and a greater trunk hyperextension with respect to young adults. Large arm elevation was frequently used by older adults to assist in maintaining trunk stability. In an attempt to quickly reestablish the base of support after the slips, older adults had an earlier contralateral foot strike and shortened stride length. CONCLUSION: The combination of slower onset and smaller magnitude of postural responses to slips in older adults resulted in an inefficient balance strategy. Older adults needed secondary compensatory adjustments, including a lengthened response duration and the use of the arms, to fully regain balance and prevent a fall. The shorter stride length and earlier contralateral foot strike following the slip indicate use of a more conservative balance strategy in older adults.

Accidental Falls↗
PubMed1997

Balance control during walking in the older adult: research and its implications.

In this article, we highlight the unique nature of balance control during walking in humans. A control framework, including proactive and reactive balance control, is introduced to lay out age-related changes in different balance control mechanisms during walking. Clinical implications that may be useful for clinicians for assessment and treatment of balance problems that occur during walking are also discussed.

Accidental Falls↗
PubMed1989

Increased potency of antagonists of substance P having asparagine in position 6.

The general structure of antagonists of substance P (SP) which was found with the development of Spantide and analogs based on Spantide served for further refinement. The antagonistic potency was tested in vitro on guinea pig ileum and taenia coli. It was unexpectedly found that introduction of Asn6 gave rise to a considerable increase in potency. The exchange of Gln6 for Asn6 entails the shortening of the side chain by one CH2 unit and seems slight for steric advantages and potency increase. The analog [D-Arg1,D-Cl2Phe5,Asn6,D-Trp7,9,Nle11]SP had pA2 values of 7.4 (ileum) and 8.0 (taenia coli). We then used this sequence as a new lead to introduce new changes, which were made in positions 1, 3, 5, 7 and 9. It was found that Arg1 is important, but Lys3 can be exchanged. The Pal3 derivative had pA2 values of 8.1 and 8.0 and the Nle3 counterpart had 7.7 and 7.4 D-Cl2Phe is an effective substituent in position 5. D-Trp in positions 7 and 9 were superior to other alternatives.

Amino Acid Sequence↗
PubMed1987

Design, synthesis and bioassays of antagonists of LHRH which have high antiovulatory activity and release negligible histamine.

Potent antagonists of the luteinizing hormone releasing hormone have been achieved which release negligible histamine. [N-Ac-D-2-Nal1, D-pClPhe2, D-3-Pal3, NicLys5, D-NicLys6, ILys8, D-Ala10]-LHRH showed 100%AOA/1 microgram and 36%/0. 5 micrograms; ED50 greater than 300. [N-Ac-D-2-Nal1,D-pClPhe2,D-3-Pal3, PicLys5, D-PicLys6, ILys8, D-Ala10]-LHRH showed 100% AOA/0.5 micrograms and 40%/0.25 micrograms; ED50, 93 +/- 11, and is the most potent of 52 new peptides. These antagonists feature designs with weakly basic acylated D-Lys6, notably D-NicLys6 and D-PicLys6 and alkylated Lys8 or Orn8, e.g., ILys8 and IOrn8, and NicLys5 and PicLys5. Concepts included balanced overall basicity, superiority of ILys8 and IOrn8 which are sequence dependent and sensitivity of positions 5 and 6 for potency.

Animals↗
PubMed1986

Increased potency of antagonists of the luteinizing hormone releasing hormone which have D-3-Pal in position 6.

Ever increasing potency is an international goal for antagonists of the luteinizing hormone releasing hormone (LHRH). [N-Ac-D-2-Nal1,D-pClPhe2, D-3-Pal3,Ser4,Arg5,D-3-Pal6,Leu7,Arg8,Pro9,D- Ala10]-NH2 caused 60%/125 ng inhibition of ovulation in the rat, and appears to be the most potent antagonist yet described. Strategy of design was the replacement of D-Arg6 with D-3-Pal6 and of Tyr5 with Arg5. Replacing Arg5 with His5 reduced activity by 50% at 250 ng. Both the Arg5 and His5 analogs showed 100% inhibition of ovulation at 0.5 microgram. Of ten pairs of analogs with D-3-Pal6 and D-Arg6, 3/10 with D-3-Pal6 were more potent than those with D-Arg6. Histamine release was less for the D-3-Pal6 peptides of three pairs.

Alanine↗
PubMed1986

Cycloheximide analogues as potential anticonvulsants.

A series of 22 cycloheximide analogues in which the substituents on the cycloheximide ring and imide nitrogen were varied, the glutarimide ring was changed to a succinimide ring, and the ring and/or side-chain oxygens were present as ketone and/or alcohol groups were prepared and sent to the Anticonvulsant Drug Development program of the National Institute of Neurological and Communicative Disorders and Strokes for evaluation as anticonvulsants. Three compounds, namely cycloheximide (1a), 2-methyl dione 2c, and dihydrocycloheximide (4a), were further evaluated in Phase II testing for quantification of maximum activity with the latter eventually progressing to Phase IV and Phase VI screens.

Animals↗
PubMed1986

Decapeptides as effective agonists from L-amino acids biologically equivalent to the luteinizing hormone-releasing hormone.

Apparently, no agonist has been found that is comparable in potency to the luteinizing hormone-releasing hormone (LHRH) for release of LH and follicle-stimulating hormone (FSH) without substitutions with unnatural or D forms of natural amino acids. Of 139 known "agonist analogs" of LHRH, two were active in the range of 65%. The four LHRHs known to occur in nature involve a total of six amino acids (Tyr, His, Leu, Trp, Arg, Gln) in positions 5, 7, and 8. There are 16 possible peptides with these six amino acids in positions 5, 7, and 8, of which 4 are the known LHRHs, and 2 more were synthesized. We have synthesized the 10 new peptides and assayed 11 in vivo and in vitro, and we found not only 1 but a total of 5 that have activity equivalent to or greater than that of LHRH for the release of LH and/or FSH under at least one assay condition. These five are as follows: [His5,Trp7,Gln8]LHRH; [His5,Trp7,Leu8]LHRH; [His5,Trp7]LHRH; [Trp7]LHRH; [His5]LHRH. Two of these five agonists variably released relatively more FSH than LH. One or more of these five agonists may occur in nature and one may be follicle-stimulating hormone-releasing hormone. The two peptides with Gln8 and Leu8, if occurring in nature, may have different receptors according to radioreceptor assays and to the ratio of LH/FSH release in vivo. These structures are a basis for the design of antagonists without Arg8 toward avoiding histamine release. Complete inhibition of LH and FSH release in vivo may be induced by joint use of Arg8 and Gln8 or Leu8 antagonists. These potent agonists, related to LHRH, may be therapeutically useful in disorders of reproduction, the central nervous system, and for the control of hormone-dependent carcinomas.

Amino Acid Sequence↗
PubMed1986

Design and synthesis of antagonists of substance P.

Synthesis and bioassay of about 65 analogs of substance P (SP) over five years yielded the antagonist [D-Arg1,D-Trp7,9,Leu11]-SP, which was named Spantide, and which was used by many investigators as a "tool". Spantide served as a reference antagonist for the design of 47 new peptides toward the goal of more potent inhibitors. Designs emphasized analogs with D-Trp7, D-Trp9, D-Trp10, D-pClPhe10, Nle11, Leu11, Ile11 and Met11, etc. Twenty-one/47 antagonists were superior in potency to that of Spantide, the best was [D-Arg1,D-Na1(5), D-Trp7,9,Nle11]-SP which required a 255-fold increase in SP concentration to give 50% of the maximum response at a concentration of 10(-5)M of the antagonist; this potency is ca. 5 times that of Spantide. For certain, but not all pairs of undecapeptides and truncated analogs, the undecapeptides may be significantly more potent than the truncated counterparts.

Amino Acid Sequence↗
PubMed1985

Potential antineoplastic dihydroxy- fatty acids.

The fatty acid aglycones of two naturally occurring glycosides, one of which is reported to possess antitumor activity, were synthesized for biological evaluation. The preparation of 3,11-dihydroxyhexadecanoic acid and 3,12-dihydroxyhexadecanoic acid started with the monoethyl esters of nonanedioic acid and decanedioic acid, respectively, and proceeded through the corresponding C14 ketoesters, ketalesters, and ketalaldehydes and C16 ketalhydroxyesters and dihydroxyesters. Various products and intermediates were found to have no inhibitory action in the P388 lymphocytic leukemia screen. A rearrangement of the ethylene glycol ketal-protecting group from the initially protected ketone group to a newly formed aldehyde moiety was observed.

Antineoplastic Agents↗
PubMed1984

Antagonists of the luteinizing hormone releasing hormone (LHRH) with emphasis on the TRP7 of the salmon and chicken II LHRH's.

The sequences of four naturally occurring luteinizing hormone releasing hormones (LHRH's) differ only in positions 5, 7 and 8. Salmon and chicken II LHRH's have Trp7; porcine/ovine (P/O) and chicken I LHRH's have Leu7. The receptor for P/O LHRH might effectively bind certain antagonists with Trp7. Thirteen antagonists having Trp7 and eight antagonists with other substitutions in position 7 were synthesized. One of the thirteen antagonists with the natural Trp7, [N-Ac-D-2-Nal1,D-pClPhe2,D-3-Pal3,D-Arg6,Trp7,D- Ala10]-LHRH, not only maintained activity, but had increased potency (ca. 58%; 90% antiovulatory activity/250 ng; rats) in comparison with the companion analog with the natural Leu7 of P/O LHRH. The other twelve Trp7-antagonists had lower potency.

Amino Acid Sequence↗
PubMedDate not supplied

Constituents of Erysimum inconspicuum. Two sulfur-containing lactone compounds.

The alcohol extract of Erysimum inconspicuum fruits, which exhibited cytotoxic activity against the KB cell line and some activity against the P-388 lymphocytic leukemia in vivo, was studied. Strophanthidin, uzarigenin, and two sulfur-containing lactones, erysulfone[6-methylsulfonyl-4-hydroxyhexanoic acid lactone] and erysulfoxide[6-methylsulfinyl-4-hydroxyhexanoic acid lactone], were isolated and characterized by spectral data.

Antineoplastic Agents, Phytogenic↗
PubMedDate not supplied

Relative potencies of antagonists of the luteinizing hormone releasing hormone with Lys8 and Arg8 and substitutions in positions 3, 5, 6, 7 and 8.

Antagonists of the luteinizing hormone releasing hormone (LHRH) of increased potency is a goal for control of ovulation. In the design and synthesis of 26 decapeptides, emphasis was given to analogs with Lys8 and Arg8 and with various substitutions in positions 3, 5, 6, 7 and 8. Two antagonists, [N-Ac-D-2-Nal1,D-pClPhe2,D-3-Pal3,Ser4,Tyr5,D-Ar g6,Leu7,Lys8, Pro9,D-Ala10]-NH2 and [N-Ac-D-2-Nal1,D-pClPhe2,D-3-Pal3,Ser4,Arg5++ +,D-3-Pal6,Leu7,Arg8,Pro9, D-Ala10]-NH2 showed 80-85% antiovulatory activity (AOA) at 0.25 micrograms in the rat. The latter antagonist showed 60% AOA at 0.125 micrograms. Of four pairs of analogs with Arg8 and Lys8, respectively, two pairs favored Lys8 over Arg8 for potency. One pair showed negligible difference and another pair favored Arg8 over Lys8. There is specificity of substitution for potency. In other antagonists, D-3-Pal3, Tyr5 or Phe5, D-Arg6 and Leu7 or Nle7 or Val7 and Arg8 were variously effective substitutions for increase of potency and reduction of histamine release.

Animals↗