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Biomedical subjects

K Leung

Publications and source records attributed to K Leung.

At least 55 records · Page 3Linked to original sources
PubMed1996

Genetic characterization of two phenotypically distinct North American ovine lentiviruses and their possible origin from caprine arthritis-encephalitis virus.

Ovine and caprine lentiviruses are closely related genetically and antigenically although the diseases that these viruses cause in their respective host animals can vary greatly. In sheep, syndromes consist primarily of interstitial pneumonia with rare occurrences of arthritis and encephalitis, whereas in goats, the disease expresses mainly as arthritis in adult animals with rare cases of encephalitis in newborns. Experimentally, viruses from either sheep or goats can infect animals of the reciprocal species and many field strains of ovine lentivirus have biological properties similar to those of caprine viruses. However, a molecular correlation for the phenotypic differences between ovine and caprine lentivirus strains is unknown. To investigate this, we examined genetic characteristics of two phenotypically distinct North American ovine lentiviruses. Nucleotide sequence analysis of the envelope regions from virus strains 85/34 and 84/28 showed that despite significant biological differences, these viruses are closely related to each other and are genotypically more homologous to caprine arthritis-encephalitis virus (CAEV) than to visna virus of sheep. Furthermore, analysis of the nucleotide substitutions in their env regions indicated that when differences between the two ovine viruses and CAEV were found, the changes often resulted in nucleotides homologous with visna virus. These results suggest that the two field strains of ovine lentivirus may have originated from a cross-species infection of sheep by a CAEV-like virus and, evolution of their genomes toward that of ovine lentivirus may be reflective of adaptation of these viruses to the new ovine host.

Animals↗
PubMed1996

Diurnal rhythms in cardiorespiratory function of the fetal baboon.

Diurnal periodicities of cardiorespiratory function were monitored between 144 and 156 days of gestation (term = 175 days) in six chronically instrumented fetal baboons. For each fetus, 5-11 days of electrocardiographic and tracheal fluid pressure data were summarized as hourly means of fetal heart rate (FHR), standard deviation of FHR, breath-to-breath interval (B-Bi) and percent time spent in fetal breathing activity (PFB). Summaries were evaluated by cosinor analysis to determine the least squares fit to a 24-h cycle. For all fetuses, FHR had a significant (P < 0.001) diurnal rhythm with peak to nadir fluctuations of 17.4 beats/min around a 24-h mean of 163.2 beats/min. The time of the peak FHR was similar across animals occurring in the mid-day between 10:49 h and 14:45 h. For each fetus, standard deviation of FHR also had a significant (P < 0.01) diurnal periodicity with highest values at night between 20:15 h and 02:04 h. The times of the acrophase for these heart rate parameters were correlated (R = 0.88, P < 0.02) across fetuses. Significant (P < 0.001) 24-h rhythms were found in four of six fetuses for B-Bi and five of six for PFB. These PFB rhythms accounted for a fluctuation of 14.4% around a mean of 36.9 +/- 4.5%. In contrast to heart rate, the acrophases of fetal breathing parameters were distributed throughout the entire 24-h cycle and not significantly correlated across fetuses. It is concluded that diurnal rhythms of fetal heart rate, which are synchronized with light/dark conditions in the environment, are evidence for a passive response or entrainment of fetal systems to maternal circadian influences. Alternately, the absence of synchronization across fetuses in daily rhythms of fetal breathing activity provides evidence for a functioning fetal pacemaker, and not simply the imposition of maternal rhythms on her fetus. This differential in the cardiac and breathing activity of the developing primate indicates that pathways for entrainment of fetal pacemaker function are subject to important maturational influences during late gestation.

Animals↗
PubMed1996

Variations in lentiviral gene expression in monocyte-derived macrophages from naturally infected sheep.

Seventy-nine 1-year-old lambs from three individual farms and a feedlot were examined for natural lentivirus infection. We used three different methods to detect infection and to identify the stage of the ovine lentivirus life cycle in blood-derived macrophages. Cytopathic infectious virus was obtained from 14/14 Border Leicester animals obtained from a naturally infected flock. Neither virus particles, virus proteins, virus specific antibodies nor viral DNA were detected in samples from 34 lambs from two South Kansas City farms. However, among 31 feedlot lambs, we identified 11 infected animals. Specific viral proteins were immunoprecipitated from macrophages of one animal, but no infectious cytopathic virus was isolated from these cells. Cells from ten of the other feedlot animals harboured viral DNA but neither viral particles nor proteins could be detected by our techniques. Thus, in these naturally infected animals, the virus life cycle either proceeded to completion, subject to differentiation of infected precursor cells in blood, or remained arrested at the DNA stage despite maturation of monocytes to macrophages. Sequence analysis of the env gene of viral genomes from two of the ten feedlot sheep showed sequences distinct from those of known ovine and caprine lentiviruses. Surprisingly, these sequences have a higher identity (of nucleotide and derived amino acid sequences) to caprine arthritis-encephalitis virus than to the ovine prototype, maedi-visna virus. These data suggest that the ovine and caprine lentiviruses found in North American sheep may have a common ancestral genotype that is closely related to the caprine virus.

Amino Acid Sequence↗
PubMed1996

Insulin-like growth factor I and insulin down-regulate growth hormone (GH) receptors in rat osteoblasts: evidence for a peripheral feedback loop regulating GH action.

The anabolic actions of GH are mediated by the production of insulin-like growth factor I (IGF-I) from the liver and by local production of IGF-I in extrahepatic tissues. Insulin facilitates the hepatic production of IGF-I by up-regulating GH receptors (GHRs) in the liver and augmenting the IGF-I response to GH. Although GHRs have also been identified in extrahepatic tissues that produce IGF-I, the possibility that IGF-I and insulin might partake in GHR regulation, thereby modulating the effects of GH locally has not received detailed study. The aim of this study was to investigate whether IGF-I and insulin are involved in the local regulation of GHRs, using osteoblasts as a model of GH-responsive extrahepatic tissues. We have used UMR106.06, a well differentiated rat osteoblast-like cell line that expresses GHRs and exhibits a mitogenic response to GH. IGF-I and insulin (0-10 nM) increased cell number and reduced [125I]GH binding in a concentration-dependent manner, with ED50 values of 0.8 and 0.3 nM, respectively. Although IGF-I increased cell number maximally by 36.9 +/- 1.2% (mean +/- SE) above the control value and insulin by 104.8 +/- 5.7% (P < 0.001), they decreased GH binding to 47.0 +/- 9.3% (P < 0.01) and 29.8 +/- 8.7% of the control value (P < 0.001), respectively. Scatchard analysis revealed that the down-regulation of GH binding was attributed to reduced receptor numbers and not binding affinity. The effects of IGF-I and insulin at submaximal concentrations were additive, although the combined effects did not exceed the maximal effect of either growth factor alone. Addition of an anti-IGF-I receptor antibody (alpha IR3) reversed the inhibition of GH binding induced by IGF-I, but not that caused by insulin; similarly, an antiinsulin receptor antibody (29B4) attenuated the inhibitory effect of insulin only. Addition of alpha IR3 alone or an ant-IGF-I antibody (Sm1.2) decreased cell number and increased GH binding in a concentration-dependent mode. GH at 1.5 nM significant increased cell number by 19.3 +/- 2.4% above the control level (P < 0.01), an increase that was reversed by alpha IR3. GH increased GH binding by 32.4 +/- 7.2% (P < 0.05) in cells treated with alpha IR3 to remove the secondary effect of IGF-I. In summary, IGF-I and insulin acted via specific receptors to stimulate cell proliferation and down-regulate GHRs in osteoblasts. GH stimulated cell proliferation, an action mediated by local production of IGF-I, and GH enhanced its own binding. The collective data suggest the presence of a peripheral negative feedback loop that allows IGF-I to limit locally the response of extrahepatic tissues to circulating GH.

Analysis of Variance↗
PubMed1996

Iodine, thyroid function, and very low birth weight infants.

OBJECTIVE: Research was undertaken to test two hypotheses. First, during the early neonatal period, thyroid function of very low birth weight (VLBW) infants is suppressed by exposure to iodine-containing antiseptic solutions and/or iodized contrast media. Second, this suppression is more pronounced in small for gestational age (SGA) infants. METHODS: Urinary iodine concentration and thyroid function measurements were obtained prospectively from 44 VLBW infants with gestational ages at birth of 30 +/- 2.3 weeks and weights of 1223 +/- 231 g. Eleven of these infants were SGA. The infants were grouped according to iodine exposure: 18 infants had no increased exposure and served as control infants; 9 infants were exposed to an iodine-containing antiseptic (povidone iodine); 12 infants were exposed to an iodized contrast medium (iopamidol); and 5 infants were exposed to both agents. Urinary iodine and serum free triiodothyronine, free thyroxine, and thyrotropin were measured on days 1, 7, 14, 21, and 28 of life. RESULTS: During the period of maximum exposure (days 1 to 7), the concentration of iodine in the urine of study infants was 2 to 4 orders of magnitude greater than that in the urine of control infants (123 +/- 141 micrograms/L). During the subsequent 3 weeks, levels of urinary iodine in study infants returned to levels that were not significantly different from controls. On day 7 of life, iodine-exposed infants had a significantly higher mean thyrotropin level than control infants, whereas on day 28, free triiodothyronine and thyroxine levels were lower. Of the 26 iodine-exposed infants, 6 had transient hyperthyrotropinemia and 2 had transient hypothyroidism. When exposed to iodine, SGA infants had more labile thyroid function than normally grown iodine-exposed or control infants. These SGA infants had significantly lower levels of thyroid hormones in umbilical cord blood, increased production of thyroid hormones on day 14 of life, and lower levels again at 1 month. CONCLUSION: In VLBW infants, the use of iodine-containing antiseptic solutions and iodized contrast media results in massive uptake of iodine that is associated with alterations in thyroid function. It is reasonable to suggest that, whenever possible, iodized products should be avoided in VLBW infants, because their routine use results in exposure to excessive loads of iodine, which can be associated with hyperthyrotropinemia and hypothyroidism.

Anti-Infective Agents, Local↗
PubMed1995

Cytokine induction of nuclear factor kappa B in cycling and growth-arrested cells. Evidence for cell cycle-independent activation.

Nuclear factor kappa B (NF-kappa B) is a pleiotropic transcription factor which regulates the expression of a large number of cellular and viral genes. Induction of NF-kappa B has been shown previously to occur during cell cycle transition from G0 to G1, but the relationship of cytokine induction of this transcription factor to cell cycling has not been directly addressed. Here we examine the inductions of NF-kappa B in serum-deprived and cycling cells in response to tumor necrosis factor-alpha (TNF-alpha). In 3T3 fibroblasts deprived of serum, and in the temperature-sensitive G2 phase mutant carcinoma line FT210, we find that NF-kappa B DNA binding activity is rapidly induced upon addition of TNF-alpha. In addition, NF-kappa B induction in cycling cells occurs without a significant change in cell cycle distribution. These data reveal that NF-kappa B is rapidly induced by TNF-alpha in both proliferating and arrested cells and suggest that distinct activation pathways can lead to cell cycle-dependent or -independent induction of NF-kappa B.

3T3 Cells↗
PubMed1995

Survival of and lacZ expression in recombinant Pseudomonas strains introduced into river water microcosms.

The lacZY gene cassette inserted into the chromosome of Pseudomonas aeruginosa UG2Lr and Pseudomonas aureofaciens Ps3732RNL11 was used as a genetic marker to study the fate of the Pseudomonas strains in river water microcosms. Expression of the lacZ marker in UG2Lr and Ps3732RNL11 was detected in microcosms containing as few as 12 and 14 colony-forming units (cfu)/mL of river water, respectively, by fluorimetric measurement of the beta-galactosidase activity against 4-methylumbelliferyl-beta-D-galactoside as the substrate. The persistence of and lacZ expression in the pseudomonas strains were monitored in sterile and nonsterile river water in the presence and absence of added nutrients by dilution plating and fluorimetry, respectively. After incubation for 10 d at 10 degrees C, culturable populations of strain UG2Lr in sterile water samples, with and without nutrient added, decreased from an initial density of 1.5 x 10(4) to 1.7 x 10(3) and 4.6 x 10(3) cfu/mL, respectively. Despite similar numbers of UG2Lr cells in the two treatments, expression of the lacZ marker in the surviving cells of the nutrient-supplemented sample was 24 times higher than in the cells of the unamended sample. In nonsterile water samples, the density of UG2Lr declined to less than 6 cfu/mL in 30 d regardless of the nutrient conditions. A nutrient supplement increased the growth of the native bacterial population but did not enhance growth of and lacZ expression in the bacteria. Polymerase chain reaction analysis showed a decrease in amplification signal indicating a genuine decline in viable UG2Lr cell density in the water samples.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed1994

The cytoplasmic domain of the interleukin-1 receptor is required for nuclear factor-kappa B signal transduction.

Interleukin-1 (IL-1) plays a central role in mediating immune and inflammatory responses. Binding of IL-1 to the type I 80-kDa receptor results in generation of intracellular signals and activation of the transcription factor NF-kappa B. However, the nature of the signals required to generate NF-kappa B binding activity remains unclear. In this paper, we show that NF-kappa B1 (p50) and RelA (p65) were specifically translocated to the nucleus following activation of intact type I IL-1 receptor (IL-1R). The C-terminal region of the type I IL-1R is required for this effect, and deletion of its cytoplasmic domain abrogates the activation of NF-kappa B by IL-1. These results provide evidence that IL-1 modulates the activity of NF-kappa B through the type I IL-1 receptor and identifies a domain required for signal transduction to this specific transcription factor.

Base Sequence↗
PubMed1994

Patterns of fetal breathing in the baboon vary with EEG sleep state.

This report examines the hypothesis that the characteristics of breathing activity of the fetal baboon are modulated with respect to sleep state in a fashion similar to that observed in the human fetus. The pattern of fetal breathing activity was examined in relationship to electroencephalographic (EEG) sleep state in studies of six fetuses of chronically monitored pregnant baboons at 143-148 days of gestation (term, 175-180 days). Fetal breaths were defined by fluctuations of tracheal fluid pressure. EEG sleep states were defined with an automated method for discrimination of EEG patterns that are standard indices of quiet and active sleep in immature primates. During more than 250 h of recorded data, the fetuses spent on average 33.3 +/- 3.9% of time in EEG quiet sleep. In comparisons across state the fetuses spent significantly (P = 0.001) less time breathing during quiet than active sleep (49.5 +/- 6.8 vs. 69.0 +/- 3.8%). The inspiratory and expiratory time intervals of fetal breaths were not differentiated by EEG state but, the mean breath to breath interval was significantly (P < 0.001) longer in EEG quiet sleep. In addition to these differences in incidence and time interval of breaths, during epochs of breathing, there was a significantly slower rate, lower amplitude, and lower variability of rate of breathing in quiet sleep (all P-values < 0.02). Thus, periodic breathing activity in the fetal baboon is present in both quiet and active EEG sleep states. Sleep states have a powerful influence on patterns of fetal breathing in the non-human primate, directly comparable to the human fetus.

Animals↗
PubMed1994

Serological and Ecological Characteristics of a Nodule-Dominant Serotype from an Indigenous Soil Population of Rhizobium leguminosarum bv. trifolii.

Although at least 13 antigenically distinct serotypes of Rhizobium leguminosarum bv. trifolii exist in an Abiqua silty clay loam soil, one serotype, AS6, occupies >/=50% of the root nodules formed on field-grown subclover and between 33 and 78% of the nodules formed on five annual clover species grown in the same soil under laboratory conditions. The dominance of subclover nodules by serotype AS6 was reproducible over a 4-year sampling period and throughout the entire 200- by 100-m pasture examined. Serotype AS6 was composed of three antigenically distinct subtypes (AS6-a, AS6-b, and AS6-c). Each subtype contributed about one-third of the AS6 isolates recovered from nodules of field-grown subclover plants and maintained similar population densities in nonrhizosphere and rhizosphere soil. Rhizobia with the AS6 antigenic signature accounted for from 20 to 100% of the soil populations of R. leguminosarum in arable and pasture soils under legumes throughout the state of Oregon. Over a 12-month period, the population densities of the serotype AS6 complex and three minor nodule-occupying serotypes (AG4, AP17, and AS21) were measured in the rhizospheres of field-grown subclover and orchard grass and in nonrhizosphere Abiqua soil. Regardless of season or serotype, the orchard grass rhizosphere effect was minimal, with the ratio between rhizosphere and nonrhizosphere serotype population densities ranging between 2.5 (midsummer) and 10.5 (spring). In contrast, the magnitude of the subclover rhizosphere effect varied seasonally and among serotypes. Between October and December the ratios for all serotypes were similar (12.5 to 25.5). However, in the spring (April and May), the magnitude of the rhizosphere effect varied among the indigenous serotypes (ratios, 10.5 to 442) and for minor nodule-occupying serotypes AS21 (ratio, 442) and AP17 (ratio, 47) was as great as, or even greater than, the magnitude of the rhizosphere effect observed with the AS6 complex (ratio, 65.5).

Journal Article↗
PubMed1994

Genotypic and Phenotypic Comparisons of Chromosomal Types within an Indigenous Soil Population of Rhizobium leguminosarum bv. trifolii.

The relative genetic similarities of 200 isolates of Rhizobium leguminosarum bv. trifolii recovered from an Oregon soil were determined at 13 enzyme loci by multilocus enzyme electrophoresis (MLEE). These isolates represented 13 antigenically distinct serotypes recovered from nodules formed on various clover species. The MLEE-derived levels of relatedness among isolates of R. leguminosarum bv. trifolii were found to be in good agreement with the levels of relatedness established by using repetitive (repetitive extragenic palindromic and enterobacterial repetitive intergeneric consensus) sequences and the PCR technique and with levels of relatedness from previously published DNA reassociation studies. BIOLOG substrate utilization patterns showed that isolates within an electrophoretic type (ET) were phenotypically more similar to each other than to isolates of other ETs. The soil isolates were represented by 53 ETs which could be clustered into seven groups (groups B, E, G, H1, H2, I, and J). Evidence for multilocus structure within the population was obtained, and group B was identified as the primary creator of the disequilibrium. Of 75 isolates belonging to the nodule-dominant serotype AS6 complex, 72 were found in group B. Isolates WS2-01 and WS2-02 representing nodule-dominant serotypes recovered from subclover grown at another Oregon site were also found in group B. Isolates representing the most numerous ETs in group B (ETs 2 and 3) were either suboptimally effective or completely ineffective at fixing nitrogen on six different clover species. Another four groups of isolates (groups A, C, D, and F) were identified when 32 strains of diverse origins were analyzed by MLEE and incorporated into the cluster analysis. Group A was most dissimilar in comparisons with other groups and contained strain USDA 2124 (T24), which produces trifolitoxin and has unique symbiotic characteristics.

Journal Article↗
PubMed1994

Symbiotic Characteristics of Rhizobium leguminosarum bv. trifolii Isolates Which Represent Major and Minor Nodule-Occupying Chromosomal Types of Field-Grown Subclover (Trifolium subterraneum L.).

The symbiotic effectiveness and nodulation competitiveness of Rhizobium leguminosarum bv. trifolii soil isolates were evaluated under nonsoil greenhouse conditions. The isolates which we used represented both major and minor nodule-occupying chromosomal types (electrophoretic types [ETs]) recovered from field-grown subclover (Trifolium subterraneum L.). Isolates representing four ETs (ETs 2, 3, 7, and 8) that were highly successful field nodule occupants fixed between 2- and 10-fold less nitrogen and produced lower herbage dry weights and first-harvest herbage protein concentrations than isolates that were minor nodule occupants of field-grown plants. Despite their equivalent levels of abundance in nodules on field-grown subclover plants, ET 2 and 3 isolates exhibited different competitive nodulation potentials under nonsoil greenhouse conditions. ET 3 isolates generally occupied more subclover nodules than isolates belonging to other ETs when the isolates were mixed in 1:1 inoculant ratios and inoculated onto seedlings. In contrast, ET 2 isolates were less successful at nodulating under these conditions. In many cases, ET 2 isolates required a numerical advantage of at least 6:1 to 11:1 to occupy significantly more nodules than their competitors. We identified highly effective isolates that were as competitive as the ET 3 isolates despite representing serotypes that were rarely recovered from nodules of field-grown plants. When one of the suboptimally effective isolates (ET2-1) competed with an effective and competitive isolate (ET31-5) at several different inoculant ratios, the percentages of nodules occupied by the former increased as its numerical advantage increased. Although subclover yields declined as nodule occupancy by ET2-1 increased, surprisingly, this occurred at inoculant ratios at which large percentages of nodules were still occupied by ET31-5.

Journal Article↗
PubMed1994

Genetic Structure of Rhizobium leguminosarum biovar trifolii and viciae Populations Found in Two Oregon Soils under Different Plant Communities.

An investigation was carried out to determine the genetic structure in soil populations of Rhizobium leguminosarum bv. trifolii and viciae at each of two Oregon sites (A and C) that were 1 km apart. Although the soils were similar, the plant communities were quite different because grazing by domestic animals had been allowed (site A) or prevented (site C). Analysis of allelic variation at 13 enzyme-encoding loci by multilocus enzyme electrophoresis delineated 202 chromosomal types (ETs) among a total of 456 isolates representing two populations of R. leguminosarum bv. trifolii (AT and CT) and two populations of R. leguminosarum bv. viciae (AV and CV). Regardless of their site of origin or biovar affiliation, isolates of the same ET were confirmed to be more closely related to each other than to isolates of other ETs by repetitive extragenic palindromic and enterobacterial repetitive intergeneric consensus sequences and the PCR technique. Despite the wide range in densities of the Rhizobium populations (<10 to >10/g of soil), their overall genetic diversities were similar (mean genetic diversity, 0.45 to 0.51), indicating that low-density populations of soil-borne bacterial species are not necessarily of little genetic diversity. Linkage disequilibrium analysis revealed significant multilocus structure (nonrandom associations of alleles) within each of the four populations. From a combination of cluster and linkage disequilibrium analyses, a total of eight distinct groups of ETs were defined in the four populations. Two groups (I and III) contributed significant numbers of ETs and isolates to each population. The two populations of R. leguminosarum bv. viciae (AV and CV) exhibited similar genetic structures despite existing at different densities, in different plant communities, and in the presence (CV) or absence (AV) of their local Vicia hosts. In contrast, total linkage disequilibrium was partitioned differently in two biovar populations occupying the same soil (AV and AT), with disequilibrium in the latter being due entirely to the presence of group V.

Journal Article↗
PubMed1994

Fetal hiccups in the baboon.

Bouts of hiccuping are recognized by pregnant women as distinct episodic movements of their fetuses. Ultrasound imaging of these fetuses has documented the occurrence of hiccups from early gestation through parturition. This study provides a systematic characterization of prenatal hiccuping in the fetal baboon (Papio species). Tracheal fluid pressure was recorded from 11 chronically instrumented fetal baboons for 21.5 +/- 7.3 consecutive days (mean +/- SD) over a range in gestation from 124 to 164 days (term 175 days). In an initial review of pressure recordings by visual inspection, hiccups were recognized as distinctive high-amplitude fluctuations in tracheal pressure that were readily discriminated from fetal breaths. Automated techniques were then developed and validated to detect hiccups and summarize their features. The mean hiccup amplitude was 23.0 +/- 3.1 mmHg, inspiratory time was 0.26 +/- 0.03 s, and expiratory time was 0.27 +/- 0.02 s. Each of these features discriminated hiccups from breaths (P < 0.001). Hiccuping incidence (1.8 +/- 0.4% of time), rate (26.2 +/- 6.2 min-1), bout duration (4.3 +/- 0.8 min), and the interval between bouts (3.35 +/- 0.60 h) were also different (P < 0.01) from breathing. These features of hiccups remained relatively constant over the latter third of gestation with the exception of an increase in duration of the expiratory time interval (r = 0.54, P < 0.01). Despite their vigorous nature, bouts of hiccuping were not associated with transitions in behavioral state. Moreover, the features of hiccups were not differentiated by state. Bouts of hiccuping recurred in a cyclic fashion, on average every 3-4 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Patterns of development in fetal breathing activity in the latter third of gestation of the baboon.

Patterns of fetal breathing activity were examined in a longitudinal study of the fetal baboon over the latter third of gestation. More than 1400 h of recorded tracheal fluid pressure in 16 or 24 h records from seven fetuses over a range in gestation from 121 to 172 days (term, 175-180 days) were analyzed. In these 81 records, there was a high degree of variability in the percent of time spent breathing by the fetuses (range, 14-83%) with no apparent influence of gestational age (mean +/- S.D., 45.6 +/- 17.6%). Nonetheless, the mean amplitude of fetal breaths increased with gestation from absolute values of about 5-10 mmHg (r = 0.73, P < 0.001) and the mean inspiratory time interval increased from about 0.45-0.55 s (r = 0.40, P < 0.001). During epochs of breathing, the mean rate decreased from about 42-36 breaths per min (r = -0.54, P < 0.001) and the indices of both short term (r = -0.54, P < 0.001) and long term (r = -0.73, P < 0.001) variability in rate decreased. These results demonstrate a clearly defined pattern of development in the breathing activity of the fetal baboon which is comparable to the pattern described for the human fetus in the third trimester of gestation. These similarities suggest that the progressive functional maturation of the mechanisms generating respiratory patterns are comparable among primate species.

Amniotic Fluid↗