Mapping and Predicting Non-Linear Brassica rapa Growth Phenotypes Based on Bayesian and Frequentist Complex Trait Estimation

Predicting phenotypes based on genotypes and understanding the effects of complex multi-locus traits on plant performance requires a description of the underlying developmental processes, growth trajectories, and their genomic architecture. Using data from Brassica rapa genotypes grown in multiple density settings and seasons, we applied a hierarchical Bayesian Function-Valued Trait (FVT) approach to fit logistic growth curves to leaf phenotypic data (length and width) and characterize leaf development. We found evidence of genetic variation in phenotypic plasticity of rate and duration of leaf growth to growing season. In contrast, the magnitude of the plastic response for maximum leaf size was relatively small, suggesting that growth dynamics vs. final leaf sizes have distinct patterns of environmental sensitivity. Consistent with patterns of phenotypic plasticity, several QTL-by-year interactions were significant for parameters describing leaf growth rates and durations but not leaf size. In comparison to frequentist approaches for estimating leaf FVT, Bayesian trait estimation resulted in more mapped QTL that tended to have greater average LOD scores and to explain a greater proportion of trait variance. We then constructed QTL-based predictive models for leaf growth rate and final size using data from one treatment (uncrowded plants in one growing season). Models successfully predicted non-linear developmental phenotypes for genotypes not used in model construction and, due to a lack of QTL-by-treatment interactions, predicted phenotypes across sites differing in plant density.

An On-line Computer System for a Rehabilitation Hospital

An on-line computer system has been implemented for processing medical information at the Texas Institute for Rehabilitation and Research. The major objectives of the system are: 1. to improve the process of patient care by expediting the flow of information among members of the rehabilitation team, 2. to facilitate the utilization of medical data for research purposes, 3. to enhance efficient hospital management, and 4. to obtain accurate data for an effective study of the cost of hospitalization.

The system consists of the following interrelated programs: a) recording of physiological monitoring, b) on-line processing of data collected at the bedside, c) processing of laboratory data, d) on-line processing of results of physiological studies, e) processing of data pertaining to treatments administered to patients, f) on-line calculation of fluid and electrolyte requirements, and g) statistical analysis of the hospital census.

The on-line computer facility is based on a time-shared teleprocessing system located at Baylor University College of Medicine and time-shared with various departments of the College. Remote terminal units installed at the Texas Institute for Rehabilitation and Research are connected by cable with the computer at the College of Medicine.

An On-line Computer System for a Rehabilitation Hospital

An on-line computer system has been implemented for processing medical information at the Texas Institute for Rehabilitation and Research. The major objectives of the system are: 1. to improve the process of patient care by expediting the flow of information among, members, of .the rehabilitation team, 2. to facilitate the utilization of medical data for research purposes, 3. to enhance efficient hospital management, and 4. to obtain accurate data for an effective study of. the cost of hospitalization.

The system consists of the following interrelated programs: a) recording- of physiological monitoring, b) on-line processing of data collected at the bedside, c) processing of laboratory data, d) on-line processing of results of physiological studies, e) processing of data pertaining to treatments administered to patients, f) on-line calculation of fluid and electrolyte requirements, and g) statistical analysis of the hospital census.

The on-line computer facility is based on a time-shared teleprocessing system located at Baylor University College of Medicine and time-shared with various departments of the College. Remote terminal units installed at the Texas Institute for Rehabilitation and Research are connected by cable with the computer at the College of Medicine.

Identification of quantitative trait loci affecting resistance to gastrointestinal parasites in a double backcross population of Red Maasai and Dorper sheep

A genome-wide scan for quantitative trait loci (QTL) affecting gastrointestinal nematode resistance in sheep was completed using a double backcross population derived from Red Maasai and Dorper ewes bred to F(1) rams. This design provided an opportunity to map potentially unique genetic variation associated with a parasite-tolerant breed like Red Maasai, a breed developed to survive East African grazing conditions. Parasite indicator phenotypes (blood packed cell volume - PCV and faecal egg count - FEC) were collected on a weekly basis from 1064 lambs during a single 3-month post-weaning grazing challenge on infected pastures. The averages of last measurements for FEC (AVFEC) and PCV (AVPCV), along with decline in PCV from challenge start to end (PCVD), were used to select lambs (N = 371) for genotyping that represented the tails (10% threshold) of the phenotypic distributions. Marker genotypes for 172 microsatellite loci covering 25 of 26 autosomes (1560.7 cm) were scored and corrected by Genoprob prior to qxpak analysis that included Box-Cox transformed AVFEC and arcsine transformed PCV statistics. Significant QTL for AVFEC and AVPCV were detected on four chromosomes, and this included a novel AVFEC QTL on chromosome 6 that would have remained undetected without Box-Cox transformation methods. The most significant P-values for AVFEC, AVPCV and PCVD overlapped the same marker interval on chromosome 22, suggesting the potential for a single causative mutation, which remains unknown. In all cases, the favourable QTL allele was always contributed from Red Maasai, providing support for the idea that future marker-assisted selection for genetic improvement of production in East Africa will rely on markers in linkage disequilibrium with these QTL.

Dynamics of maternal and paternal effects on embryo and seed development in wild radish (Raphanus sativus)

BACKGROUND AND AIMS

Variability in embryo development can influence the rate of seed maturation and seed size, which may have an impact on offspring fitness. While it is expected that embryo development will be under maternal control, more controversial hypotheses suggest that the pollen donor and the embryo itself may influence development. These latter possibilities are, however, poorly studied. Characteristics of 10-d-old embryos and seeds of wild radish (Raphanus sativus) were examined to address: (a) the effects of maternal plant and pollen donor on development; (b) the effects of earlier reproductive events (pollen tube growth and fertilization) on embryos and seeds, and the influence of embryo size on mature seed mass; (c) the effect of water stress on embryos and seeds; (d) the effect of stress on correlations of embryo and seed characteristics with earlier and later reproductive events and stages; and (e) changes in maternal and paternal effects on embryo and seed characteristics during development.

METHODS

Eight maternal plants (two each from four families) and four pollen donors were crossed and developing gynoecia were collected at 10 d post-pollination. Half of the maternal plants experienced water stress. Characteristics of embryos and seeds were summarized and also compared with earlier and later developmental stages.

KEY RESULTS

In addition to the expected effects of the maternal plants, all embryo characters differed among pollen donors. Paternal effects varied over time, suggesting that there are windows of opportunity for pollen donors to influence embryo development. Water-stress treatment altered embryo characteristics; embryos were smaller and less developed. In addition, correlations of embryo characteristics with earlier and later stages changed dramatically with water stress.

CONCLUSIONS

The expected maternal effects on embryo development were observed, but there was also evidence for an early paternal role. The relative effects of these controls may change over time. Thus, there may be times in development when selection on the maternal, paternal or embryo contributions to development are more and less likely.

A maize trypsin inhibitor (ZmTIp) with limited activity against Aspergillus flavus

Infection of maize both pre- and postharvest by Aspergillus flavus is a severe agricultural problem in the southern United States. Aflatoxins are secondary metabolites produced by A. flavus and are carcinogenic to humans and animals upon ingestion. Extensive research has been conducted to identify sources of resistance to A. flavus in maize. Some maize genotypes exhibit greater resistance to A. flavus than others. Many research groups have validated the role of plant trypsin inhibitors (TIs) as a means of plant defense against fungal infection. Research consisting of the cloning, expression, and partial characterization of one previously uncharacterized TI protein has been conducted. The overexpressed protein displayed TI activity, as expected, and some ability to alter germination of conidia (8%) from several fungal pathogens and to inhibit hyphal growth (30%). This effect on fungal growth, although less than that of previously investigated TIs, marks this protein as a potential source of resistance to aflatoxin accumulation in maize.

A maize lectin-like protein with antifungal activity against Aspergillus flavus

The filamentous fungus Aspergillus flavus causes an ear rot on maize and produces a mycotoxin (aflatoxin) in colonized maize kernels. Aflatoxins are carcinogenic to humans and animals upon ingestion. Aflatoxin contamination results in a large loss of profits and marketable yields for farmers each year. Several research groups have worked to pinpoint sources of resistance to A. flavus and the resulting aflatoxin contamination in maize. Some maize genotypes exhibit greater resistance than others. A proteomics approach has recently been used to identify endogenous maize proteins that may be associated with resistance to the fungus. Research has been conducted on cloning, expression, and partial characterization of one such protein, which has a sequence similar to that of cold-regulated proteins. The expressed protein, ZmCORp, exhibited lectin-like hemagglutination activity against fungal conidia and sheep erythrocytes. Quantitative real-time PCR assays revealed that ZmCOR is expressed 50% more in maize kernels from the Mp420 line, a type of maize resistant to A. flavus, compared with the expression level of the gene in the susceptible B73 line. ZmCORp exhibited fungistatic activity when conidia from A. flavus were exposed to the protein at a final concentration of 18 mM. ZmCORp inhibited the germination of conidia by 80%. A 50% decrease in mycelial growth resulted when germinated conidia were incubated with the protein. The partial characterization of ZmCORp suggests that this protein may play an important role in enhancing kernel resistance to A. flavus infection and aflatoxin accumulation.

Effects of non-genetic factors on responses to gastro-intestinal nematode infections in Ethiopian sheep

The effects of non-genetic factors on responses to gastrointestinal nematode infections were examined in artificially infected indigenous Horro and Menz lambs in the central highlands of Ethiopia. The experiment involved lambs of two sexes, infection and monitoring regimens (3 levels), dam parity (4 levels) and birth types (2 levels). A total of 152 weaner lambs (103 Menz and 49 Horro) were used. Endoparasite challenge involved three infection periods (primary, secondary and tertiary) each separated by an anthelmintic treatment. Data were collected on faecal egg counts (FEC), packed cell volume (PCV), worm count, and weight gain. Female lambs were found to harbor lower numbers of T. colubriformis counts and had lower (p < 0.01) FEC in tertiary infection compared to males. Younger animals were more susceptible to the nematode infections than older animals as measured by all the parameters studied (p < 0.01). Twins had higher FEC in both secondary and tertiary infections compared to singles. Lambs born to dams of first parity had higher PCV and lower FEC values during the tertiary infection compared to other parities. These results would be used as basic information in designing a more rational control strategy and should also help to advise on better management care for less resistant sheep.

Genetic variation in resistance to repeated infections with Heligmosomoides polygyrus bakeri, in inbred mouse strains selected for the mouse genome project

Since the publication of the mouse genome, attention has focused on the strains that were selected for sequencing. In this paper we report the results of experiments that characterized the response to infection with the murine gastrointestinal nematode Heligmosomoides polygyrus of eight new strains (A/J, C57BL/6, C3H, DBA/2, BALB/c, NIH, SJL and 129/J), in addition to the well-characterized CBA (poor responder) and SWR (strong responder) as our controls. We employed the repeated infection protocol (consisting of 7 superimposed doses of 125L3 each administered at weekly intervals, faecal egg counts in weeks 2, 4 and 6 and assessment of worm burdens in week 6) that was used successfully to identify quantitative trait loci for genes involved in resistance to H. polygyrus. SWR, SJL and NIH mice performed indistinguishably and are confirmed as strong responder strains to H. polygyrus. CBA, C3H and A/J mice all tolerated heavy infections and are assessed as poor responders. In contrast, DBA/2, 129/J and BALB/c mice performed variably between experiments, some tolerating heavy worm burdens comparable to those in poor responders, and some showing evidence of resistance, although only in one experiment with female 129/J females and one with female BALB/c was the pattern and extent of worm loss much like that in SWR mice. Because the genetic relationships between six of the strains exploited in this study are now well-understood, our results should enable analysis through single nucleotide polymorphisms and thereby provide more insight into the role of the genes that control resistance to H. polygyrus.

Evaluation of the phenotypic performance of a Red Maasai and Dorper double backcross resource population: indoor trickle challenge with Haemonchus contortus

Six F(1) Dorper (D) x Red Maasai (R) rams were mated to both D and R ewes to produce backcross lambs. These six double backcross resource families are being analysed to identify quantitative trait loci that may be controlling resistance to gastro-intestinal (GI) nematode parasites, mainly Haemonchus contortus. After assessing the phenotypic performance of the lambs following exposure to natural infections, the surviving lambs were drenched and moved indoors for an artificial challenge with H. contortus along with straightbred D and R lambs. A total of 1317 lambs were included in the analyses consisting of 523 3/4D, 580 3/4R, 87 D and 127 R. The D lambs were significantly and consistently heavier than R lambs and 3/4D were significantly heavier than the 3/4R lambs. The difference between the backcrosses was about half of that between the straightbreds. Resistance was assessed in terms of faecal egg counts (FEC) and total worm counts (TWC) at necropsy while packed cell volume (PCV) was used to assess resilience to weekly oral doses of 2500 infective larvae of H. contortus. No significant breed differences were observed for log transformed FEC (LFEC). A significant breed difference in PCV was recorded. The backcrosses had the higher values and while no differences were observed between the straightbreds, 3/4D had significantly higher PCV than the 3/4R. Despite the absence of breed differences in FEC the R and the 3/4R had significantly fewer worms than the D and the 3/4D. The D had significantly longer worms than the R and the 3/4D had significantly longer worms than the 3/4R. Worms recovered from D had more eggs than those recovered from R. Similarly worms from 3/4D contained more eggs than those from 3/4R. Thus, on a breed basis the breed with more worms had longer worms. In contrast, when, in a small part of the experiment two doses of larvae were used to check for any breed by dose interactions, worms from the low dose (and hence fewer worms) animals were longer. We postulate that in fast growing hosts like the D, worms also have a better potential for growth and reproduction than in hosts that have less potential for growth. The overall correlation coefficient between PCV and LFEC was -0.67 while that between LFEC and LTWC was 0.72. From these results it is clear that the R do not respond to the artificial challenge the way they do to natural infection suggesting that phenotyping of R and R cross lambs for purposes of selecting those that are resistant or susceptible is best done under natural challenge.

Evaluation of anthelmintic properties of some plants used as livestock dewormers against Haemonchus contortus infections in sheep

Gastrointestinal helminth infections remain a major constraint to livestock production globally. This study evaluated anthelmintic efficacy of 7 plants used as dewormers by farmers and pastoralists in Kenya. Thus 3 commercial anthelmintics and 7 plant preparations were tested in lambs infected with 5000 or 3000 L3 Haemonchus contortus in 4 experiments. In the first experiment, ivermectin, levamisole and albendazole were tested in 46 lambs. Seven plant preparations of Hagenia abyssinica, Olea europaea var. africana, Annona squamosa, Ananas comosus, Dodonea angustifolia, Hildebrandtia sepalosa and Azadirachta indica were tested in 151 lambs in 3 experiments. All 3 anthelminitics were highly effective in reducing faecal egg counts (FEC) and total worm counts (TWC) in lambs. Plant preparations had varying levels of crude proteins from 2.6% for O. europaea to 18.4% for A. indica. Compared with controls, no significant reductions in FEC were observed for any of the treated groups either 2 or 3 weeks post-treatment. Lambs treated with A. squamosa and A. comosus were slaughtered 4 weeks post-treatment. No significant differences were observed in mean TWC or number of eggs per female worm between treated animals and the controls. No significant improvements in weight gain were observed in treated lambs.

Chasing the genes that control resistance to gastrointestinal nematodes

The host-protective immune response to infection with gastrointestinal (GI) nematodes involves a range of interacting processes that begin with recognition of the parasite's antigens and culminate in an inflammatory reaction in the intestinal mucosa. Precisely which immune effectors are responsible for the loss of specific worms is still not known although many candidate effectors have been proposed. However, it is now clear that many different genes regulate the response and that differences between hosts (fast or strong versus slow or weak responses) can be explained by allelic variation in crucial genes associated with the gene cascade that accompanies the immune response and/or genes encoding constitutively expressed receptor/signalling molecules. Major histocompatibility complex (MHC) genes have been recognized for some time as decisive in controlling immunity, and evidence that non-MHC genes are equally, if not more important in this respect has also been available for two decades. Nevertheless, whilst the former have been mapped in mice, only two candidate loci have been proposed for non-MHC genes and relatively little is known about their roles. Now, with the availability of microsatellite markers, it is possible to exploit linkage mapping techniques to identify quantitative trait loci (QTL) responsible for resistance to GI nematodes. Four QTL for resistance to Heligmosomoides polygyrus, and additional QTL affecting faecal egg production by the worms and the accompanying immune responses, have been identified. Fine mapping and eventually the identification of the genes (and their alleles) underlying QTL for resistance/susceptibility will permit informed searches for homologues in domestic animals, and human beings, through comparative genomic maps. This information in turn will facilitate targeted breeding to improve resistance in domestic animals and, in human beings, focused application of treatment and control strategies for GI nematodes.

Double potentials along the ablation line as a guide to radiofrequency ablation of typical atrial flutter

OBJECTIVES

The purpose of this study was to determine the characteristics of double potentials (DPs) that are helpful in guiding ablation within the cavo-tricuspid isthmus.

BACKGROUND

Double potentials have been considered a reliable criterion of cavo-tricuspid isthmus block in patients undergoing radiofrequency ablation of typical atrial flutter (AFL). However, the minimal degree of separation of the two components of DPs needed to indicate complete block has not been well defined.

METHODS

Radiofrequency ablation was performed in 30 patients with isthmus-dependent AFL. Bipolar electrograms were recorded along the ablation line during proximal coronary sinus pacing at sites at which radiofrequency ablation resulted in incomplete or complete isthmus block.

RESULTS

Double potentials were observed at 42% of recording sites when there was incomplete isthmus block, compared with 100% of recording sites when the block was complete. The mean intervals separating the two components of DPs were 65 +/- 21 ms and 135 +/- 30 ms during incomplete and complete block, respectively (p < 0.001). An interval separating the two components of DPs (DP(1-2) interval) <90 ms was always associated with a local gap, whereas a DP(1-2) interval > or =110 ms was always associated with local block. When the DP(1-2) interval was between 90 and 110 ms, an isoelectric segment within the DP and a negative polarity in the second component of the DP were helpful in indicating local isthmus block. A DP(1-2) interval > or =90 ms with a maximal variation of 15 ms along the entire ablation line was an indicator of complete block in the cavo-tricuspid isthmus.

CONCLUSIONS

Detailed analysis of DPs is helpful in identifying gaps in the ablation line and in distinguishing complete from incomplete isthmus block in patients undergoing radiofrequency ablation of typical AFL.

Prevalence of central venous occlusion in patients with chronic defibrillator leads

BACKGROUND

Many patients with previously implanted ventricular defibrillators are candidates for an upgrade to a device capable of atrial-ventricular sequential or multisite pacing. The prevalence of venous occlusion after placement of transvenous defibrillator leads is unknown. The purpose of this study was to determine the prevalence of central venous occlusion in asymptomatic patients with chronic transvenous defibrillator leads.

METHODS

Thirty consecutive patients with a transvenous defibrillator lead underwent bilateral contrast venography of the cephalic, axillary, subclavian, and brachiocephalic veins as well as the superior vena cava before an elective defibrillator battery replacement. The mean time between transvenous defibrillator lead implantation and venography was 45 +/- 21 months. Sixteen patients had more than 1 lead in the same subclavian vein. No patient had clinical signs of venous occlusion.

RESULTS

One (3%) patient had a complete occlusion of the subclavian vein, 1 (3%) patient had a 90% subclavian vein stenosis, 2 (7%) patients had a 75% to 89% subclavian stenosis, 11 (37%) patients had a 50% to 74% subclavian stenosis, and 15 (50%) patients had no subclavian stenosis.

CONCLUSIONS

The low prevalence of subclavian vein occlusion or severe stenosis among defibrillator recipients found in this study suggests that the placement of additional transvenous leads in a patient who already has a ventricular defibrillator is feasible in a high percentage of patients (93%).

Incidence and clinical significance of inducible atrial tachycardia in patients with atrioventricular nodal reentrant tachycardia

INTRODUCTION

The purpose of this prospective study was to determine the prevalence and clinical significance of inducible atrial tachycardia in patients undergoing slow pathway ablation for AV nodal reentrant tachycardia who did not have clinically documented episodes of atrial tachycardia.

METHODS AND RESULTS

Twenty-seven (15%) of 176 consecutive patients who underwent slow pathway ablation for AV nodal reentrant tachycardia were found to have inducible atrial tachycardia with a mean cycle length of 351+/-95 msec. The atrial tachycardia was sustained in 7 (26%) of 27 patients and was isoproterenol dependent in 20 patients (74%). The atrial tachycardia was not ablated or treated with medications, and the patients were followed for 9.7+/-5.8 months. Six (22%) of the 27 patients experienced recurrent palpitations during follow-up. In one patient each, the palpitations were found to be due to sustained atrial tachycardia, nonsustained atrial tachycardia, recurrence of AV nodal reentrant tachycardia, paroxysmal atrial fibrillation, sinus tachycardia, and frequent atrial premature depolarizations. Thus, only 2 (7%) of 27 patients with inducible atrial tachycardia later developed symptoms attributable to atrial tachycardia.

CONCLUSION

Atrial tachycardia may be induced by atrial pacing in 15% of patients with AV nodal reentrant tachycardia. Because the vast majority of patients do not experience symptomatic atrial tachycardia during follow-up, treatment for atrial tachycardia should be deferred and limited to the occasional patient who later develops symptomatic atrial tachycardia.

Electrogram polarity and cavotricuspid isthmus block during ablation of typical atrial flutter

INTRODUCTION

The atrial activation sequence around the tricuspid annulus has been used to assess whether complete block has been achieved across the cavotricuspid isthmus during radiofrequency ablation of typical atrial flutter. However, sometimes the atrial activation sequence does not clearly establish the presence or absence of complete block. The purpose of this study was to determine whether a change in the polarity of atrial electrograms recorded near the ablation line is an accurate indicator of complete isthmus block.

METHODS AND RESULTS

Radiofrequency ablation was performed in 34 men and 10 women (age 60 +/- 13 years [mean +/- SD]) with isthmus-dependent, counterclockwise atrial flutter. Electrograms were recorded around the tricuspid annulus using a duodecapolar halo catheter. Electrograms recorded from two distal electrode pairs (E1 and E2) positioned just anterior to the ablation line were analyzed during atrial flutter and during coronary sinus pacing, before and after ablation. Complete isthmus block was verified by the presence of widely split double electrograms along the entire ablation line. Complete bidirectional isthmus block was achieved in 39 (89%) of 44 patients. Before ablation, the initial polarity of E1 and E2 was predominantly negative during atrial flutter and predominantly positive during coronary sinus pacing. During incomplete isthmus block, the electrogram polarity became reversed either only at E2, or at neither E1 nor E2. In every patient, the polarity of E1 and E2 became negative during coronary sinus pacing only after complete isthmus block was achieved. In 4 patients (10%), the atrial activation sequence recorded with the halo catheter was consistent with complete isthmus block, but the presence of incomplete block was accurately detected by inspection of the polarity of E1 and E2.

CONCLUSION

Reversal of polarity in bipolar electrograms recorded just anterior to the line of isthmus block during coronary sinus pacing after ablation of atrial flutter is a simple, quick, and accurate indicator of complete isthmus block.

Complete atrioventricular block after valvular heart surgery and the timing of pacemaker implantation

The natural history of patients who developed complete atrioventricular block after valvular heart surgery was investigated to determine the optimal timing for pacemaker implantation. Patients who developed complete atrioventricular block within 24 hours after operation, which then persisted for > 48 hours, were unlikely to recover; such patients could potentially undergo earlier pacemaker implantation if otherwise ready for discharge.

Role of transisthmus conduction intervals in predicting bidirectional block after ablation of typical atrial flutter

INTRODUCTION

Complete bidirectional cavotricuspid isthmus block is the endpoint for ablation of typical atrial flutter. The purpose of this study was to determine whether the extent of prolongation of the transisthmus interval after ablation predicts complete bidirectional block.

METHODS AND RESULTS

Fifty-seven consecutive patients underwent 60 ablation procedures for isthmus-dependent atrial flutter. The clockwise and counterclockwise transisthmus intervals were determined before and after ablation during pacing from the low lateral right atrium and the coronary sinus. Bidirectional block was achieved with ablation in 55 (96%) of 57 patients. The transisthmus intervals before ablation and after complete transisthmus block were 100.3 +/- 21.1 msec and 195.8 +/- 30.1 msec, respectively, in the clockwise direction (P < 0.0001), and 98.2 +/- 24.7 msec and 185.7 +/- 33.9 msec, respectively, in the counterclockwise direction (P < 0.0001). An increase in the transisthmus interval by > or = 50% in both directions after ablation predicted complete bidirectional block with 100% sensitivity and 80% specificity. The positive and negative predictive values were 89% and 100%, respectively. The diagnostic accuracy of a > or = 50% prolongation in the transisthmus interval was 92%.

CONCLUSION

Prolongation of the transisthmus interval by > or = 50% in the clockwise and counterclockwise directions is associated with a high degree of diagnostic accuracy and an excellent negative predictive value in determining complete bidirectional transisthmus block. This may be a useful and simple adjunctive criterion for assessment of complete transisthmus conduction block.

Effects of digoxin on acute, atrial fibrillation-induced changes in atrial refractoriness

BACKGROUND

Atrial fibrillation (AF) shortens the atrial effective refractory period (ERP) and predisposes to further episodes of AF. The acute changes in atrial refractoriness may be related to tachycardia-induced intracellular calcium overload. The purpose of this study was to determine whether digoxin, which increases intracellular calcium, potentiates the acute effects of AF on atrial refractoriness in humans.

METHODS AND RESULTS

In 38 healthy adults, atrial ERP was measured at basic drive cycle lengths (BDCLs) of 350 and 500 ms after autonomic blockade. Nineteen patients had been treated with digoxin for 2 weeks. After a several-minute episode of AF, atrial ERP was measured serially at alternating BDCLs. Compared with pre-AF ERPs, the first post-AF ERPs were significantly shorter in both the digoxin and the control groups (P:<0.001). The post-AF ERP at a BDCL of 350 ms shortened to a greater degree in the digoxin group (37+/-16 ms) than in the control group (20+/-13 ms, P:<0.001); similar changes occurred at a BDCL of 500 ms. During post-AF determinations of the atrial ERP, secondary AF episodes occurred significantly more often in the digoxin group (32% versus 16%; P:<0. 04).

CONCLUSIONS

After a brief episode of AF, digoxin augments the shortening that occurs in atrial refractoriness and predisposes to the reinduction of AF. These effects occur in the setting of autonomic blockade and therefore are more likely to be due to the effects of digoxin on intracellular calcium than to its vagotonic effects.

Lack of preference for low-predation-risk habitats in larval damselflies explained by costs of intraspecific interactions

Many studies indicate prey organisms select microhabitats with high structural complexity as a way of reducing risk of predation. We used laboratory experiments to show that damselfly larvae, Ischnura verticalis, suffer higher predation rates from pumpkinseed sunfish in low-density vegetation. However, larvae do not preferentially occupy microhabitats with high vegetation density in either the presence or absence of sunfish; when given a choice, the number of larvae per stem of vegetation was equal across all densities of vegetation. That larvae do not congregate in dense vegetation may reflect costs of aggressive interactions. Results from laboratory experiments indicated larval interactions increase conspicuous behaviours (most notably swimming) and consequently increase fish predation. A subsequent experiment indicated that frequency of larval interactions increases with increased vegetation density when number of larvae/stem is constant. Thus, larval microhabitat selection may reflect a trade-off between reduced risk of predation in areas of high vegetation density, caused by reduced fish foraging ability, and increased aggressive larval interactions, due to decreased proximity of larvae. Copyright 2000 The Association for the Study of Animal Behaviour.

Cost analysis of transthoracic cardioversion of atrial fibrillation with and without ibutilide pretreatment

BACKGROUND

Ibutilide may result in chemical cardioversion of atrial fibrillation and facilitates transthoracic cardioversion by lowering the defibrillation energy requirement. Whether routine pretreatment with ibutilide increases or decreases the cost of cardioversion is unknown. The purpose of this study was to compare the cost of outpatient transthoracic cardioversion of atrial fibrillation with and without ibutilide pretreatment.

METHODS

Using a model based on published literature and hospital accounting information, a hypothetical group of 100 patients with atrial fibrillation and a left ventricular ejection fraction >0.30 underwent 2 strategies of outpatient cardioversion: transthoracic cardioversion with and without routine pretreatment with 1 mg ibutilide, and with and without involvement of an anesthesiologist for sedation. If transthoracic cardioversion was unsuccessful in patients who did not receive ibutilide, transthoracic cardioversion was repeated after administration of ibutilide.

RESULTS

If an anesthesiologist was involved, transthoracic cardioversion with ibutilide was associated with incremental cost-savings as the efficacy of ibutilide alone in restoring sinus rhythm increased above the critical values of 20%, 27%, and 35% when the efficacy of transthoracic cardioversion alone was 60%, 80%, and 100%, respectively. In the absence of an anesthesiologist, routine pretreatment with ibutilide increased the cost of cardioversion at all success rates of transthoracic cardioversion.

CONCLUSIONS

In the presence of an anesthesiologist, whether or not routine pretreatment with ibutilide lowers the mean cost of cardioversion is determined by the success rates of chemical cardioversion with ibutilide and transthoracic cardioversion. In the absence of an anesthesiologist, ibutilide pretreatment increases the cost of cardioversion.

CNS toxicity after topical application of EMLA cream on a toddler with molluscum contagiosum

EMLA (eutectic mixture of local anesthetics) cream is used topically to provide local anesthesia for a variety of painful superficial procedures. Although the side effects of EMLA are usually mild and transient local skin reactions, potential life threatening complications can be encountered. We report a case of central nervous toxicity after EMLA application for curettage of molluscum contagiosum lesions in a pediatric patient. This complication was the result of a therapeutic misadventure that led to an excessive application of EMLA cream over an extensive area causing an overdose of lidocaine and prilocaine with their subsequent systemic toxicities.

Effects of a mite, Limnochares americana (Hydrachnida: Limnocharidae), on the life-history traits and grooming behaviour of its damselfly host, Enallagma ebrium (Odonata: Coenagrionidae)

We examined whether experimental parasitism by a mite Limnochares americana (Lundblad) affected survivorship and maturation of adult damselflies Enallagma ebrium (Hagen). We then tested whether differences in grooming activity between control and exposed individuals (within different age or sex categories of host) mirrored reductions in fitness that resulted from experimental parasitism. We based our choice of experimental numbers of mites on our finding that adult damselflies had between 0 and 12 mites (71% had 0 mites), and mature adults had a higher prevalence and intensity of parasitism than did prereproductive damselflies in two of three field surveys. Low numbers of mites did not affect survivorship of teneral or mature males and females; however, high numbers of mites significantly depressed survivorship of teneral males and females and mature males, and were associated with a delay in maturation of females. Of teneral individuals, only females groomed more than controls when challenged with low numbers of mites; mature individuals of both sexes groomed more than controls in response to high numbers of mites but not in response to low numbers. Our results suggest that variation in grooming behaviour partially reflects variation in fitness costs, due to mite parasitism, across age and sex categories of hosts.

Grooming decisions by damselflies, age-specific colonisation by water mites, and the probability of successful parasitism

We examined whether host damselflies (Ischnura verticalis) in different stages of development were differentially susceptible to parasitism by larval water mites (Arrenurus pseudosuperior). We found that mites were successful in reaching the parasitic phase more often if they colonised hosts closer to emergence. Thus, we predicted that more mites should colonise damselflies closer to emergence and damselflies closer to emergence should spend more time defending against mites. We found that mites colonised damselflies closer to emergence in one of two experiments, but that damselflies in different stages of development did not differ in time spent defending against mites.

Resistance of Galla and Small East African goats in the sub-humid tropics to gastrointestinal nematode infections and the peri-parturient rise in faecal egg counts

A study was carried out from 1994 to 1996 to compare the resistance to naturally acquired gastrointestinal (GI) nematode infections (predominantly Haemonchus contortus) of 88 Galla and 114 Small East African (SEA) goats (does) in the sub-humid coastal region of Kenya. Live weights (LWT), blood packed cell volume (PCV) and faecal egg counts (FEC) were recorded each year at mating, 3-4 months after mating, 1-2 weeks before kidding and 1-4 months after kidding. There was a significant increase in FEC and a decline in PCV in lactating does compared to non-lactating does over the peri-parturient period. This peri-parturient rise in FEC occurred in both breeds but was more marked and persistent in the Galla than in the SEA. The SEA does were more resistant to GI nematode infections than Galla does as shown by their significantly lower FEC and higher PCV at all sampling times over the reproductive cycle, but this breed difference was particularly marked over the lactation period.

Breed and season effects on the peri-parturient rise in nematode egg output in indigenous ewes in a cool tropical environment

A study was carried out at the International Livestock Research Institute (ILRI) Debre Berhan Research Station in Ethiopia from 1992 to 1995 to compare the peri-parturient rise (PPR) in faecal nematode egg counts (FEC) in ewes of two indigenous sheep breeds. A total of 1439 Menz and 1347 Horro ewes were single sire mated following oestrus synchronization to lamb in the wet and dry season. Three ewe treatment groups were constituted as mated/lactating/undrenched; mated/lactating/drenched; unmated/undrenched for three wet and three dry lambing seasons. All ewes grazed naturally contaminated pasture. Levels of faecal egg output were monitored at mating, 3 months after mating, 2 weeks before lambing, 4, 8 and 12 weeks post-lambing. A significant PPR in FEC occurred 2 weeks before lambing and peaked at 4 weeks post-parturition in ewes lambing just before the beginning of the dry season (October/November). There was no significant increase in FEC when lambing occurred before the onset of the long rainy season (May/June). The PPR in this study was associated with both lactation and seasonal availability of third-stage infective larvae on pasture. There was no consistent breed difference in FEC during the six sampling periods from mating to weaning. Faecal cultures and worm counts from both breeds confirmed the presence of Longistrongylus (Pseudomarshallagia) elongata, Trichostrongylus spp.and Haemonchus contortus. The role of the peri-parturient rise of FEC in ewes in gastrointestinal nematode transmission is discussed.

The epidemiology of nematode infections in sheep in a cool tropical environment

The epidemiology of nematode infections in Menz sheep was studied in the highlands of Ethiopia at the International Livestock Research Institute (ILRI), Debre Berhan Research Station, using a series of tracer lambs grazing contaminated pasture for either 4, 16, 32 or 48 weeks from July 1992 to June 1994. The basic nematode seasonal infectivity pattern was expressed in terms of relative numbers of third-stage larvae (L3) available on pasture for different months. Data from faecal nematode egg counts, pasture larval recoveries and worm counts from the tracer lambs were used to investigate the infectivity pattern. Four nematode species of economic importance: Longistrongylus (Pseudomarshallagia) elongata, Trichostronglylus colubriformis, Haemonchus contortus, and Dictyocaulus filaria, were recovered from sheep. The largest numbers were recovered during the wet season (i.e. July to November) with peaks in late August and early September. During this 2 year study period, the seasonal pattern of sheep gastrointestinal nematodes was clearly defined. An important finding was that conditions during the short rainy season (i.e. March-May) were not conducive to the development and survival of nematode eggs and the free-living stages, hence little or no transmission occurred. Rainfall and humidity seemed to be the most important factors for the development of eggs and free-living stages. The period of acquisition of third-stage larvae from pasture was found to be relatively short, suggesting that a strategic control programme is feasible with minimal anthelmintic use. Results from the studies are discussed in relation to control strategies.

Controlling the spread of vancomycin-resistant enterococci with a rehabilitation cohort unit

Enterococci are common to the human gastrointestinal tract. Recently there has been an emergence of vancomycin-resistant enterococci (VRE); infection requires strict contact isolation. Patients with VRE infections are at higher risk for morbidity and mortality. As a result of the high prevalence of VRE, it was recommended that a cohort unit be established to control its spread within our metropolitan community hospital. We report the development of a rehabilitation VRE cohort unit. We present case studies of five patients who developed nosocomial colonization and one with an infection with VRE; all were treated on the rehabilitation cohort unit. Protocols for VRE isolation and procedures for decontamination in the cohort unit were developed. If a cohort unit is necessary, it is feasible to conduct a rehabilitation program in a cohort unit with strict adherence to contact isolation.

Prospects of breeding small ruminants for resistance to internal parasites

Resistance to nematode parasites can be improved by selection, but efforts to include appropriate traits in commercial livestock breeding programs are only a recent development. Procedures for including resistance in breeding programs are similar to those involving other traits. The steps are described with special reference to sheep, and areas are highlighted where particular considerations exist. Three approaches are described and contrasted: breeding for resistance (reduced parasite numbers, as determined by faecal worm egg count); resilience (production during parasitism); or number of treatments required during parasitism. It is necessary, but difficult, to assess the economic benefits of improving resistance relative to other traits. Disease costs vary widely depending on the prevalence of the disease and on the availability, effectiveness and sustainability of alternative control measures. Costs of treatment and control are relatively simple to estimate for a given situation, but production losses are more difficult. Methods of dealing with this problem are discussed. Breeding for disease resistance usually requires that either selection candidates, or their relatives, are exposed to the pathogen so that resistance levels can be compared. Parasitic diseases generally create no special ethical problems in a breeding program unless natural challenge levels are insufficient to enable discrimination between hosts in their susceptibility. In the longer term, it is desirable that selection criteria for all major diseases be developed that will be informative in healthy animals. Molecular genetic markers offer promise, but simple genetic markers have so far been as elusive as physiological traits to predict resistance in undiseased animals. In the longer term, useful genetic markers will be found and techniques for combining these with phenotypic information need to be developed. Commercial breeding programs for sheep which include resistance to gastrointestinal roundworms are now operating in Australia and New Zealand, and issues related to breeding in the tropics are discussed.

Evidence for multiple anthelmintic resistance in sheep and goats reared under the same management in coastal Kenya

Four experiments, two with sheep and two with goats, were carried out to determine the efficacy of ivermectin, fenbendazole, levamisole, closantel and some of their combinations by faecal egg count reduction tests. In the first experiment, injectable ivermectin, oral ivermectin, fenbendazole and levamisole were tested in 6-month-old lambs, and their reduction percentages were 77%, 13%, 42% and 92%, respectively. In the second experiment, with yearling sheep, the reduction percentages were 35% for injectable ivermectin, 32% for fenbendazole, 99% for levamisole, 48% for closantel, 92% for injectable ivermectin combined with fenbendazole, 99% for injectable ivermectin combined with levamisole, and 100% for fenbendazole combined with levamisole. In the study with 18-month-old goats given the same dose rates as those recommended for sheep, the reduction percentages were 73% for injectable ivermectin, 25% for fenbendazole, and 78% for levamisole. Another group of 14-month-old goats was treated with dose rates 1.5 times those recommended for sheep and the reduction percentages were 93% for levamisole, 92% for injectable ivermectin, and 97% for a combination of levamisole and ivermectin. In all experiments with sheep and goats the gastrointestinal nematode parasites identified by larval cultures were Haemonchus contortus, Trichostrongylus spp. and Oesophagostomum spp. The gastrointestinal nematodes of both sheep and goats on this farm are resistant to ivermectin and fenbendazole, whereas levamisole is still effective in sheep, but not in goats. The results are discussed in relation to the farm as a source of breeding stock to smallholder farmers and its potential to spread anthelmintic resistance.

Efficient quadtree coding of images and video

The quadtree data structure is commonly used in image coding to decompose an image into separate spatial regions to adaptively identify the type of quantizer used in various regions of an image. The authors describe the theory needed to construct quadtree data structures that optimally allocate rate, given a set of quantizers. A Lagrange multiplier method finds these optimal rate allocations with no monotonicity restrictions. They use the theory to derive a new quadtree construction method that uses a stepwise search to find the overall optimal quadtree structure. The search can be driven with either actual measured quantizer performance or ensemble average predicted performance. They apply this theory to the design of a motion compensated interframe video coding system using a quadtree with vector quantization.

The heritability of gingival crevice depths in sheep

The gingival crevices of the four central incisor teeth of 396 sheep with known sires were measured at the mid-labial, mid-mesial and distal (interproximal), and mid-lingual aspects to test the hypothesis that gingival crevice depths were heritable. In total, 6336 gingival crevices were examined. Mean crevicular depths were 1.50 mm (labial), 3.16 mm (interproximal) and 6.52 mm (lingual). Within breedstrain genetic variation was examined and paternal half-sib heritability estimates were found to be high for the interproximal crevice depth (0.66 +/- 0.20) and the lingual crevice depth (0.69 +/- 0.21), but lower, and non-significant, for the labial crevice depth (0.24 +/- 0.17).

Delivery of preterm and small for gestational age infants across generations

Two generations of women were studied to clarify the influence of a woman's own preterm delivery or intrauterine growth retardation on her later risk of delivering preterm or growth-retarded infants. The first generation consists of the cohort of women who gave birth at the National University Hospital (Rigshospitalet) in Copenhagen from 1959 to 1961 and the second, those of their daughters that have delivered themselves. The background of the study and the procedures involved are described. The percentage of data obtained and the preliminary findings concerning the relationship between social and demographic factors and the willingness of subjects to participate are included.

Second generation follow-up of the Danish perinatal study women: study design and factors affecting response

To study the mother-infant correlation of fetal growth and duration of pregnancy, women who were born as subjects in the Danish Perinatal Study (1959-61) were traced and interviewed, and the pregnancy and birth records of their children were abstracted. The study population consisted of 159 women who were small-for-gestational age (SGA) at birth, 162 who were preterm, 38 who were both preterm and SGA, and 939 term, appropriately-grown control women. Methods for sample selection, measuring gestational age and fetal growth in both generations, locating and interviewing the women, abstracting the records of their children, and obtaining paternal birth and adult stature are described. A total of 84.5% of the selected women were successfully interviewed; the fraction interviewed did not differ by maternal birth status. The medical records of over 98% of pregnancies to the study women were abstracted, making it possible to study various factors associated with completion of an interview. By a variety of measures, women of higher socio-economic status were more likely to be interviewed. Birthweight and adult weights were available for 63 and 73% of the children's fathers.

A diabetes control program in a public health care setting

The Houston Diabetes Control Program is part of an effort by the State of Texas and approximately 30 other programs throughout the United States to ensure that persons with diabetes-related complications receive ongoing state-of-the-art preventive care and treatment. For the past 5 years, this program has served an urban, high-risk patient population with special cultural, ethnic, and economic challenges. The intervention has included the development and implementation of protocols for the prevention and care of diabetes-related complications of the eyes, lower extremities, and cardiovascular system, as well as general management of diabetes and patient and professional education. The program is ongoing in nine community health centers located in low-income neighborhoods of a large metropolitan area. The results thus far indicate an increase in sensitive eye examinations from 8 percent to 26 percent of the patient population, a reduction in incidence of legal blindness from 9.5 to 2.7 per 1,000 during a 4-year period, an increase in foot examinations from 18 percent to 44 percent of the patient population, and 77 percent of hypertensive patients in good control of blood pressure at less than 160 over 95 mmHg (millimeters of mercury). On the average, there have not been significant long-term improvements in weight reduction or blood glucose control. The major challenges for this program are (a) improvement in control of glycemia, hypertension, and cholesterol; (b) more effective diet and physical activity interventions; and (c) more effective education approaches that help patients to understand metabolic and cardiovascular functions. These challenges will require collaboration of health care professionals in constructive and imaginative ways through their unselfish commitment toward common goals.

Carcass composition in weight-selected and control bulls from a serial slaughter experiment

Bull calves were sampled at random at weaning from the 17th calf crop of an Angus herd selected for yearling weight (AS1) and from its contemporary control herd (ACO). Thirty animals per herd were slaughtered in groups of five per herd at intervals, from 7 to 25 months of age. Live weight and scrotal circumference were taken on the day before slaughter, along with a blood sample for analysis of plasma insulin-like growth factor-1 (IGF-1) and testosterone concentration. The left side of each carcass was dissected into saleable meat, bone and trimmed fat components. Live weights and hot carcass weights of AS1 animals were, on average, 16.8 and 17- 6% greater respectively than those of ACO animals. Allometric comparisons of the carcass composition data (log-log regressions) showed no significant herd differences in the rate at which saleable meat, bone or trimmed fat weights increased with carcass weight. Adjusted weights of bone, however, were significantly greater in the AS1 than ACO herds (P < 0.05). There were significant herd differences in the weights of kidney, liver and testes, in scrotal circumference and in the concentration of IGF-1, but these disappeared after adjustment for live weight. On an adjusted basis, heart weight was 6.1% greater in the AS1 than the ACO herd (P < 0.05).

Recursive optimal pruning with applications to tree structured vector quantizers

A pruning algorithm of P.A. Chou et al. (1989) for designing optimal tree structures identifies only those codebooks which lie on the convex hull of the original codebook's operational distortion rate function. The authors introduce a modified version of the original algorithm, which identifies a large number of codebooks having minimum average distortion, under the constraint that, in each step, only modes having no descendents are removed from the tree. All codebooks generated by the original algorithm are also generated by this algorithm. The new algorithm generates a much larger number of codebooks in the middle- and low-rate regions. The additional codebooks permit operation near the codebook's operational distortion rate function without time sharing by choosing from the increased number of available bit rates. Despite the statistical mismatch which occurs when coding data outside the training sequence, these pruned codebooks retain their performance advantage over full search vector quantizers (VQs) for a large range of rates.

Replicated selection for insulin-like growth factor-1 and body weight in mice

Five generations of divergent selection for plasma concentration of insulin-like growth factor-1 (IGF-1) and for 12-week body weight were carried out in mice, including randomly selected control lines for each trait. All lines were replicated once (12 lines in total). Each replicate line consisted of eight male and eight female parents per generation. Litter size was standardized to eight pups at birth. Mass selection was applied in the selected lines and within-family random selection in the control lines. Blood was taken from the orbital sinus of individual mice at 12 weeks of age for IGF-1 assay. Realized heritabilities were 0.10±0.01 for IGF-1 and 0.41 ± 0.02 for 12-week weight. The realized genetic correlation between IGF-1 and 12-week weight was 0.58 ± 0.01, with a phenotypic correlation of 0.38. Although the genetic correlation between IGF-1 and body weight in mice is moderately positive, 12-week weight responded 3.5 times as fast to weight selection as to selection for IGF-1.

Disseminated histoplasmosis in the acquired immune deficiency syndrome: clinical findings, diagnosis and treatment, and review of the literature

Histoplasmosis is a serious opportunistic infection in patients with AIDS, often representing the first manifestation of the syndrome. Most infections occurring within the endemic region are caused by exogenous exposure, while those occurring in nonendemic areas may represent endogenous reactivation of latent foci of infection or exogenous exposure to microfoci located within those nonendemic regions. However, prospective investigations are needed to prove the mode of acquisition. The infection usually begins in the lungs even though the chest roentgenogram may be normal. Clinical findings are nonspecific; most patients present with symptoms of fever and weight loss of at least 1 month's duration. When untreated, many cases eventually develop severe clinical manifestations resembling septicemia. Chest roentgenograms, when abnormal, show interstitial or reticulonodular infiltrates. Many cases have been initially misdiagnosed as disseminated mycobacterial infection or Pneumocystis carinii pneumonia. Patients are often concurrently infected with other opportunistic pathogens, supporting the need for a careful search for co-infections. Useful diagnostic tests include serologic tests for anti-H. capsulatum antibodies and HPA, silver stains of tissue sections or body fluids, and cultures using fungal media from blood, bone marrow, bronchoalveolar lavage fluid, and other tissues or body fluids suspected to be infected on clinical grounds. Treatment with amphotericin B is highly effective, reversing the clinical manifestations of infection in at least 80% of cases. However, nearly all patients relapse within 1 year after completing courses of amphotericin B of 35 mg/kg or more, supporting the use of maintenance treatment to prevent recurrence. Relapse rates are lower (9 to 19%) in patients receiving maintenance therapy with amphotericin B given at doses of about 50 mg weekly or biweekly than with ketoconazole (50-60%), but controlled trials comparing different maintenance regimens have not been conducted. Until results of such trials become available, our current approach is to administer an induction phase of 15 mg/kg of amphotericin B given over 4 to 6 weeks, followed by maintenance therapy with 50 to 100 mg of amphotericin B given once or twice weekly, or biweekly. If results of a prospective National Institutes of Allergy and Infectious Disease study of itraconazole maintenance therapy document its effectiveness, alternatives to amphotericin B may be reasonable.

In vivo tyrosine hydroxylation rate in retina: effects of phenylalanine and tyrosine administration in rats pretreated with p-chlorophenylalanine

p-Chlorophenylalanine was administered to rats to inhibit hepatic phenylalanine hydroxylase activity. Two days later, phenylalanine injection was noted to produce substantial increases in serum phenylalanine levels, and relatively modest increments in serum tyrosine levels. Rats injected with p-chlorophenylalanine 2 days earlier showed a normal light-induced activation of retinal tyrosine hydroxylase activity in vivo, measured as dihydroxyphenylalanine accumulation following pharmacologic inhibition in vivo of aromatic L-amino acid decarboxylase activity. In addition, tyrosine injection into p-chlorophenylalanine-treated rats in the light produced anticipated increments in retinal tyrosine hydroxylation rate, showing the enzyme to be functionally normal. The acute administration of phenylalanine (62.5-500 mg/kg i.p.) to p-chlorophenylalanine-treated rats produced dose-related increments in retinal phenylalanine. In vivo tyrosine hydroxylation rate in retina was normal at all doses below 300 mg/kg. However, at the highest dose (500 mg/kg), when retinal phenylalanine levels were almost 5-times normal tyrosine hydroxylation rate consistently fell (to about half-normal values). These results demonstrate that very large elevations in tissue phenylalanine levels do not stimulate tyrosine hydroxylation in vivo, and that at extremely high levels phenylalanine inhibits tyrosine hydroxylation rate.

Interrelationships of vitamin D, bone metabolism and blood calcium concentration in the chick

It is not known if the effects of vitamin D deficiency on chick bone are due to direct actions of the vitamin or if they are secondary to other changes, such as hypocalcemia. Day-old cockerels were fed either a rachitogenic diet containing no Ca (-D-Ca), 1.4% Ca (-D), or 3% Ca (-DHiCa) and given corn oil (-D groups) or vitamin D3 in corn oil (+D and +D-Ca) p.o. for up to 21 days. Radii were harvested and incubated for 6-8 h in a defined medium. Medium samples were taken every 2 h and analysed for Ca, Pi and lactate. Some bones were incubated in a respirometer to measure O2 consumption. Compared to +D, -D birds showed evidence of D deficiency by decreased plasma Ca concentration (35%), bone and body weight (43%) and Ca release from bone (70%) and by histological changes in bone characteristic of rickets. Increases were seen in total and bone alkaline phosphatase activity in plasma (270 and 706%, respectively), Pi release (23%), O2 consumption (23%) and lactate production (52%) by the -D radii. The marked hypocalcemia seen in the -D chicks did not occur in -DHiCa birds. Nevertheless, bone and body weights were decreased in this group and bone lactate production, O2 consumption and total and bone alkaline phosphatase in plasma were increased. Rachitic bone lesions were only partially corrected by the high-Ca diet. Release of Ca and Pi from the -DHiCa bone was not different than from +D radii. Comparing +D-Ca and -D-Ca groups with +D chicks, both were hypocalcemic with decreased bone weight, body weight and bone Ca release, while showing elevated lactate production and Pi release. The only difference between the +D-Ca and -D-Ca groups was a 50% decrease in Ca release by -D-Ca bone. The results suggest that in chicks: (1) some, but not all, of the effects of vitamin D deficiency on bone can be corrected by normalizing plasma Ca and (2) evaluation of the effects of vitamin D deficiency on bone may require hypocalcemia, since some responses are masked by normocalcemia.