Normal Lambs Research Articles

Feeding high levels of vitamin D3 does not improve tenderness of callipyge lamb loin chops.

The objective of this study was to determine whether feeding high doses of vitamin D3 7 d before slaughter would increase muscle Ca++ levels and result in more tender loin chops. Market lambs (n = 4 callipyge and 4 normal in Exp. 1, and n = 16 calipyge and 16 normal in Exp. 2) were randomly and equally assigned to feeding groups based on callipyge genotype and experimental diet, (vitamin D3 or control). Serum Ca++, muscle Ca++, Warner-Bratzler shear force, and troponin-T degradation data were analyzed. In Exp. 1, vitamin D3 was supplemented at 1 or 2 x 10(6) IU/d. The 2 x 10(6) IU dose resulted in the greatest serum Ca++ reponse and was chosen for Exp. 2. In Exp. 2, serum Ca++ concentration was higher (P < 0.05) for normal and callipyge lambs fed the vitamin D3 diet than for the control diet fed lambs. Muscle Ca++ concentrations, however, were not higher (P = 0.28) for the vitamin D3-fed lambs. Warner-Bratzler shear values were higher (P < 0.05) for callipyge than for normal lambs, but no differences were observed with vitamin D3 supplementation. These data were supported by results from Western blot analysis of troponin-T degradation, in which no differences were observed for vitamin D3 vs control diet lambs at 14 d postmortem. This experiment showed that feeding 2 x 10(6) IU/d of vitamin D3 to market lambs, callipyge or normal, raised serum Ca++ concentration, but did not increase muscle Ca++ concentration. This lack of response in muscle Ca++ was likely the reason that no differences were observed for Warner-Bratzler shear force values or troponin-T degradation data between the vitamin D3 and control loin chops. A higher dose of vitamin D3 may be required to improve tenderness.

Pulmonary hypertension alters soluble guanylate cyclase activity and expression in pulmonary arteries isolated from fetal lambs.

The nitric oxide (NO)-guanosine 3',5'-cyclic monophosphate (cGMP) signaling pathway plays an important role in the pulmonary vascular transition at birth. We studied pulmonary arteries and veins isolated from normal late-gestation fetal lambs and from fetal lambs with persistent pulmonary hypertension (PPHN) following prenatal ligation of the ductus arteriosus. We additionally used double immunolabeling and immunoblot analysis to determine relative vascular contents of endothelial nitric oxide synthase (NOS-III) and soluble guanylate cyclase (sGC). Cyclic GMP content and sGC activity were significantly lower in arteries from hypertensive lambs than controls. A rank order for contents of both soluble guanylate cyclase and NOS-III was observed by both immunolabeling and immunoblotting: Control vein = Hypertensive vein > Control artery > Hypertensive artery. Our data demonstrate that the relative expression of sGC correlates well with the relative expression of NOS-III, and indicate the potential importance of soluble guanylate cyclase in the regulation of the perinatal pulmonary circulation. These data may help us understand vascular mechanisms producing PPHN, as well as patterns of response to exogenous NO.

Fetal surgery for congenital heart disease.

Certain congenital heart defects, which present at birth as complex morphologic defects, are actually the result of a relatively simple primary lesion and the subsequent acquired development of a complex secondary lesion during gestation. Moreover, fetal heart approach during gestation can prevent simple cardiac lesions from such development. Specific structural lesions can be diagnosed before 12 weeks of gestation by transvaginal fetal echocardiography, and animal experiments have shown that direct or indirect fetal cardiac approach and fetal cardiac bypass are technically feasible. A number of fetal bypass models have resulted in long-term survivors, with for example, the delivery of normal lambs at full-term gestation. Also, successful full-term delivery has been obtained after fetal cardiac intervention. The success of fetal cardiac bypass was accomplished by the use of total spinal anesthesia and the administration of indomethacin. Moreover, a 42 % long-term survival after fetal cardiopulmonary bypass in a fetal lamb model has been reported. Maternal risk related to fetal bypass should be considered carefully alongside fetal risks and benefits. Most fetal malformations do not directly threaten maternal health, yet the procedures required to address fetal malformations can produce significant maternal risk and discomfort and subsequent pregnancies may be jeopardized. Further investigation of maternal outcome is required. Deep exploration of fetal and maternal pathophysiologic responses to intervention and comprehensive investigation is required to overcome current limitations, and should precede clinical trials as many problems remain to be solved before these techniques can be applied to human beings.

Histology of longissimus muscle from 2-week-old and 8-week-old normal and callipyge lambs

There were no differences in proportion or sizes of myofiber types in longissimus from 2-wk-old lambs of the callipyge and normal genotypes. In 8-wk old lambs, the type I ovine myofibers were oxidative, the majority of type IIA myofibers were glycolytic, and the majority of type IIB myofibers were oxidative. Key words: Callipyge, lamb, muscle, histology

Congenital arthrogryposis: an inherited limb deformity in pedigree Suffolk lambs

Thirty of 52 pedigree Suffolk lambs (58 per cent) were born with arthrogryposis characterised by bilateral flexion rigidity of the metacarpophalangeal and carpal joints. The recent introduction of a breeding...

Growth and differentiation of cultured satellite cells from callipyge and normal lambs

We tested whether the muscle enlargement found in callipyge sheep is linked to increased proliferation, differentiation, and protein accrual of cultured satellite cells. Satellite cells were isolated from the longissimus muscle of three callipyge and three normal lambs. The satellite cells were grown using serum from horse, normal lambs, and callipyge lambs and cultured under conditions that promoted differentiation into myotubes and accumulation of myofibrillar protein. There was no difference in the population doubling times (PDT) or fusion percentages for callipyge and normal satellite cells, but PDT was longer (P &lt; 0.05) for satellite cells grown in callipyge serum (pooled mean PDT = 22 h) than for cells grown in normal sheep serum (PDT = 20 h) or horse serum (PDT = 18 h). The protein:DNA ratios of the cultures increased during 96 h in differentiation media (P &lt; 0.01), but there was no difference in protein:DNA ratios between cells from callipyge and normal lambs. These results suggest that muscle hypertrophy of callipyge sheep is not linked to the inherent capacity of their cultured satellite cells to proliferate, fuse or accrue protein, but hypertrophy may be linked to the influence of serum-born factors on satellite cell proliferation. Key words: Satellite cell, callipyge, sheep, cell culture

Hematologic evaluation of normal and anemic lambs with the Technicon H*1 using EDTA or heparin as anticoagulants.

A study was performed to evaluate blood from young lambs using the Technicon H*1 hematology analyzer, with emphasis on RBC parameters, comparison of tripotassium EDTA and heparin, and the effects of storage on heparinized blood. Blood samples from lambs 2 days to 18 weeks of age were analyzed within 6 hours, revealing a high precision, except for WBC counts in heparinized blood. The HCT values estimated by the H*1 correlated well (r(2)=.90) with those obtained by the microhemotocrit method. Mean hematologic values obtained for heparinized blood differed by up to 4% from values obtained from blood collected into EDTA. WBC counts decreased 8.5% in heparinized blood stored at 4 degrees C for 1 day, but differences observed in RBC counts were </= 2%. Problems occurred when analyzing blood from young lambs with low hemoglobin values because the H*1 incorrectly counted microcytes with volumes of < 10 fL as platelets. When the necessary corrections were performed, the H*1 was useful for analyzing RBC parameters in lamb blood collected both into EDTA and into heparin.

Morphometric analysis of preterm fetal pulmonary development in the sheep model of congenital diaphragmatic hernia.

Congenital diaphragmatic hernia (CDH) in humans carries high mortality/morbidity attributed to associated pulmonary hypoplasia. An understanding of the effects of CDH on fetal lung growth is important for development of successful treatments. This study aimed to quantitate structural differences between normal and CDH-affected preterm lamb lungs. We hypothesized that (a) pulmonary hypoplasia is present in preterm CDH-affected lungs; (b) the relative degree of pulmonary hypoplasia increases with gestation; and (c) the left upper lobe (LUL) is affected most. Fetal lambs were allocated to two groups. One group underwent surgery (72-74 days gestation) inducing CDH. Both groups (n = 7, n = 7) were delivered by cesarean section at 129 days (term: 145-149). Lungs were obtained at autopsy, were inflation-fixed, processed for histology, and morphometry was performed. Preterm lungs of CDH-affected lambs in comparison to those of normal lambs demonstrated a reduction in the following: lung weight (37.7 g vs. 116.3 g); lung weight:body weight (0.012 vs. 0.040); fixed lung volume (33.6 ml vs. 96.9 ml); gas-exchange surface area (4.56 m(2) vs. 13.70 m(2)); parenchyma:nonparenchyma (59:41 vs. 72:28); and parenchymal airspace:tissue (16:84 vs. 35:65). Non-parenchyma connective tissue was increased (58%), airspaces were more numerous (1077/mm(2)) and smaller (perimeter 76.6 microm), gas-exchange surface density (2394 cm(-1)) was greater and capillary loading (0.04 ml/m(2)) was reduced compared to preterm normal lung (49%; 778/mm(2); 108.7 microm; 2003 cm(-1), 0.11 ml/m(2), respectively). The LUL was affected most. These data quantitate pulmonary hypoplasia in preterm CDH-affected lambs. Comparisons with published data indicate increasing relative hypoplasia as gestation proceeds. Fetal interventions will affect lung development, depending on timing, with intervention still likely to be worthwhile during late gestation.

Effect of the callipyge gene on muscle growth, calpastatin activity, and tenderness of three muscles across the growth curve.

Changes in muscle growth, calpastatin activity, and tenderness of three muscles were assessed in 20 callipyge and 20 normal wether lambs slaughtered at live weights (LW) of 7, 20, 36, 52, and 69 kg. At 24 h postmortem, the longissimus (LM), semimembranosus (SM), and supraspinatus (SS) muscles were removed and weighed and samples were obtained for calpastatin activity (CA; 24 h) and Warner-Bratzler shear force (WBS; aged 6 d). For muscle weights and calpastatin activity, the weight group x muscle x phenotype interaction was significant (P < 0.05). Muscle weights were similar (P > 0.05) between phenotypes for all three muscles at 7 kg LW. At 20 kg LW, the LM and SM muscles from the callipyge lambs were heavier (P < 0.05) than those from normal lambs; however, the SS did not differ (P > 0.05) between phenotypes at 7, 20, or 52 kg. From 20 to 69 kg LW, the LM and SM weights were 42 and 49% heavier (P < 0.05) for callipyge than for normal lambs. Calpastatin activity of the callipyge LM was greater (P < 0.05) than that of normal LM at 36, 52, and 69 kg. In the callipyge LM, CA was similar (P > 0.05) at 20, 36, and 52 kg LW and did not differ (P > 0.05) from 7-kg or 69-kg values. Calpastatin activity declined (P < 0.05) across the growth curve for the SM and SS, but values were higher (P < 0.05) in the SM in callipyge than in normal lambs. Shear force values of the LM were lower (P < 0.05) for normal lambs at 36, 52, and 69 kg LW than for callipyge lambs. In the SM and SS, WBS values decreased (P < 0.05) across the growth curve, but values were higher (P < 0.05) for callipyge lambs in the SM only. These data indicate that the selective muscular hypertrophy of the callipyge phenotype develops during the postnatal growth period between 7 and 20 kg LW (19 and 100 d of age). Longissimus and semimembranosus muscles in the callipyge lambs were over 40% heavier from 20 to 69 kg LW; however, they also had higher levels of calpastatin activity and Warner-Bratzler shear force during this time period, indicating the need for postmortem tenderization treatments to improve palatability.

Protein kinetics in callipyge lambs.

The objectives for this experiment were to determine the effect of the callipyge phenotype on protein kinetics. We studied callipyge and normal lambs (n = 37) at 5, 8, and 11 wk of age (n = 4 to 7/ group) to determine how protein kinetics are altered by this trait. Total protein, DNA, and RNA and calpastatin activity were measured in five skeletal muscles and in the heart, kidneys, and liver, and protein accretion rates were calculated. At 8 wk, the fractional synthesis rates of proteins in these tissues were measured in vivo using a primed, continuous 8-h infusion of [2H5]phenylalanine. Fractional rates of protein degradation were estimated by differences. At 5 wk of age, muscle weights, protein mass, protein:DNA, RNA:DNA, and calpastatin activity were higher (P < .05) for callipyge, and protein mass differences continued to increase through 11 wk. At 8 wk, fractional rates of protein synthesis and degradation were lower (P < .05) in callipyge than in normal lambs. The organs of callipyge lambs exhibited reduced growth at 11 wk. Thus, enhanced muscle growth seems to be maintained in callipyge lambs by reduced protein degradation rather than increased protein synthesis. However, we cannot exclude the possibility that the initial onset of the callipyge condition may be caused by an increase in the fractional rate of protein synthesis.

Offspring from one-month-old lambs: studies on the developmental capability of prepubertal oocytes.

A wave of follicular growth in lamb ovaries occurs at about 4 weeks of age, generating a life-time peak in follicle numbers. In order to take advantage of the large number of oocytes available, and to substantially decrease the generation interval, embryos were derived from oocytes collected from 1-mo-old lambs. Animals were subjected to one of 3 regimes of hormonal stimulation: groups 1 and 2 were treated to obtain germinal vesicle-stage oocytes, and group 3 to produce mature metaphase II oocytes. Adult sheep stimulated by an appropriate dose of FSH served as control. The developmental ability of collected oocytes was evaluated by either in vivo or in vitro culture to the blastocyst stage after in vitro maturation and/or fertilization. Blastocysts were transferred immediately or after cryopreservation to suitable recipient sheep. In order to investigate the full developmental potential of these embryos, pregnancies were allowed to go to term. The results show significant differences (P < 0.001) between all experimental groups in blastocyst numbers produced. Embryos derived from group 1 animals produced the greatest number of blastocysts, under both in vivo (36. 7%), and in vitro (22.9%) culture systems. Group 2 gave lowest blastocyst production (5.0%), while group 3 yielded 13.2% blastocysts. The number of pregnant recipients carrying to term lamb-derived embryos was severely reduced for both in vivo- (2 of 9; 22.2%) and in vitro-cultured, fresh (3 of 10; 30.0%) and cryopreserved (1 of 6; 16.7%) lamb embryos. This study is the first report of the birth of live lambs derived from oocytes obtained from donors as young as 4 wk. Defects in the competence of lamb-derived embryos may account for the increased fetal loss during pregnancy and the occurrence of mummified fetuses delivered alongside normal healthy lambs.

The pathogenesis of dysplastic kidney in a urinary tract obstruction in the female fetal lamb

Background/Purpose : The type of renal dysplasia resulting from obstructive uropathy depends on the completeness of the obstruction and its timing with respect to the stage of glomerulogenesis at the time of the obstruction. The authors created a successful obstructive uropathy model in the female fetal lamb to demonstrate the differing pathogenesis of renal dysplasia. Methods : Female fetal lambs at 60 and 90 days' gestation had their urethra and urachus ligated transabdominally and were delivered by cesarean section at 145 days (full term). Kidney length and cortical thickness were measured, and samples were examined histologically. In the lambs operated on at 90 days, the urine was collected at delivery and Na and Cl were measured and compared with the results obtained from normal full-term lambs. Results : Seven of 10 female lambs had hydronephrosis or dysplastic kidneys. The cortext to kidney length ratio was 10 ± 3% in the 90-days hydronephrotic group versus 29 ± 6% in the controls ( P < .001). Morphologically, the 90-day model had dilatation of the collecting tubules with normal glomerular numbers. The 60-day model had tubular cysts with fibromuscular cuffing and reduced glomerular numbers. The fetal urine Na was 47 ± 3.3 mmol/L in controls versus 78 ± 24 mmol/L in the hydropnephrotic lambs ( P < .05). The urine Cl in these lambs was 38 ± 8.6 mmol/L in controls versus 55 ± 14.5 mmol/L in the hydronephrotic lambs ( P < .05). Conclusions : An obstructive uropathy model was created in female fetal lambs. There were no dysplastic changes in the kidneys in lambs operated on at 90 days' gestation, but there were definite dysplastic changes in those operated on at 60 days. Concentrations of Na and Cl in the fetal urine are higher than normal in the 90-day model.

EXPERIMENTAL FETAL VESICOURETERAL REFLUX INDUCES RENAL TUBULAR AND GLOMERULAR DAMAGE, AND IS ASSOCIATED WITH PERSISTENT BLADDER INSTABILITY

Purpose We assessed renal function and urodynamic status in animals with experimental congenital vesicoureteral reflux. Materials and Methods Vesicoureteral reflux was surgically induced in male sheep fetuses at 95 days of gestation. After birth the animals were maintained on antibiotic prophylaxis. At ages 1 week and 6 months reflux was assessed by fluoroscopic voiding cystography. Cystometrography was performed with the animals awake. Serum creatinine, inulin clearance and the excretion of urinary N-acetyl-beta-D-glucosaminidase were measured at ages 1 week, 1 month and 6 months by surveillance urine cultures. Urinary concentrating capacity was assessed by desmopressin testing at ages 1 and 6 months. Results Nine animals (18 renal units) were born after the induction of reflux. There was no reflux in 2 renal units, while reflux was mild in 2, moderate in 5 and severe in 9. In the 6 animals available for followup at age 6 months only severe reflux persisted. Reflux resolution was associated with normalization of bladder urodynamics. Surveillance urine cultures were negative until age 6 months, when infection developed in 3 of the 6 lambs. In all animals serum creatinine was normal during followup. Glomerular filtration rate in the lambs with reflux was no different from normal at age 1 week but it was significantly less than normal independent of infection at age 6 months (2.7 versus 3.9 ml./kg. per minute, p = 0.002). As an indicator of renal tubular injury the ratio of N-acetyl-beta-D-glucosaminidase-to-creatinine remained significantly higher in animals with reflux than in normal animals from ages 1 week to 6 months (51.0 versus 10.2 IU/mg., p = 0.03). Maximal concentrating ability after desmopressin testing was already less than normal by age 1 month with a maximal increase of 98 versus 435 mOsm./l. in lambs with reflux versus normal lambs (p <0.0001). It was further impaired by age 6 months. Urodynamic evaluation of the animals with reflux revealed decreased bladder compliance at age 1 week with normal voiding pressure. In addition, in those with reflux there was a more pronounced immature voiding pattern with multiple phasic contractions due to sphincteric activity as well as a post-void bladder contraction. Conclusions Our model of fetal vesicoureteral reflux induces alterations in renal function that are consistent with clinical observations and marked by altered tubular function but a relatively mild decrease in glomerular filtration. Bladder dynamics are altered, consistent with observations in human neonates with high grade reflux and bladder instability. Whether this represents cause or effect remains unclear. Our model permits focused study of the interaction of these factors in neonatal reflux and may allow the application of more specific therapies, particularly those directed toward mechanisms of renal and bladder dysfunction.

Experimental fetal vesicoureteral reflux induces renal tubular and glomerular damage, and is associated with persistent bladder instability.

We assessed renal function and urodynamic status in animals with experimental congenital vesicoureteral reflux. Vesicoureteral reflux was surgically induced in male sheep fetuses at 95 days of gestation. After birth the animals were maintained on antibiotic prophylaxis. At ages 1 week and 6 months reflux was assessed by fluoroscopic voiding cystography. Cystometrography was performed with the animals awake. Serum creatinine, inulin clearance and the excretion of urinary N-acetyl-beta-D-glucosaminidase were measured at ages 1 week, 1 month and 6 months by surveillance urine cultures. Urinary concentrating capacity was assessed by desmopressin testing at ages 1 and 6 months. Nine animals (18 renal units) were born after the induction of reflux. There was no reflux in 2 renal units, while reflux was mild in 2, moderate in 5 and severe in 9. In the 6 animals available for followup at age 6 months only severe reflux persisted. Reflux resolution was associated with normalization of bladder urodynamics. Surveillance urine cultures were negative until age 6 months, when infection developed in 3 of the 6 lambs. In all animals serum creatinine was normal during followup. Glomerular filtration rate in the lambs with reflux was no different from normal at age 1 week but it was significantly less than normal independent of infection at age 6 months (2.7 versus 3.9 ml./kg. per minute, p = 0.002). As an indicator of renal tubular injury the ratio of N-acetyl-beta-D-glucosaminidase-to-creatinine remained significantly higher in animals with reflux than in normal animals from ages 1 week to 6 months (51.0 versus 10.2 IU/mg., p = 0.03). Maximal concentrating ability after desmopressin testing was already less than normal by age 1 month with a maximal increase of 98 versus 435 mOsm./l. in lambs with reflux versus normal lambs (p <0.0001). It was further impaired by age 6 months. Urodynamic evaluation of the animals with reflux revealed decreased bladder compliance at age 1 week with normal voiding pressure. In addition, in those with reflux there was a more pronounced immature voiding pattern with multiple phasic contractions due to sphincteric activity as well as a post-void bladder contraction. Our model of fetal vesicoureteral reflux induces alterations in renal function that are consistent with clinical observations and marked by altered tubular function but a relatively mild decrease in glomerular filtration. Bladder dynamics are altered, consistent with observations in human neonates with high grade reflux and bladder instability. Whether this represents cause or effect remains unclear. Our model permits focused study of the interaction of these factors in neonatal reflux and may allow the application of more specific therapies, particularly those directed toward mechanisms of renal and bladder dysfunction.

Perinatal myocardial DNA and protein changes in the lamb: effect of cortisol in the fetus.

Myocardial growth during fetal life is accomplished by proliferation of the number of myocytes (hyperplasia). Shortly after birth, normal growth of the heart is predominantly due to increase in cell size (hypertrophy), and myocytes largely lose the capability to replicate. This change is characterized by a decrease in myocardial DNA concentration and an increase in protein/DNA concentration ratio. Among many of the events associated with birth is an increase in plasma cortisol concentrations in the few days before delivery of the fetus. To determine the possible role of cortisol in the postnatal change in myocardial growth, we measured DNA and protein concentrations in the free walls of the left (LV) and right (RV) ventricles in normal fetal lambs, normal newborn lambs, and in fetal lambs in which cortisone was infused for 72-80 h into the left coronary artery, which we showed does not perfuse the RV free wall. Normally, fetal RV DNA is higher than LV DNA concentration, and DNA/protein ratio is lower in RV than in LV. It is suggested that this could be related to the greater load on the RV. Postnatally, protein concentrations increase progressively, but DNA remains the same in both ventricles, and protein/DNA ratios increase. Cortisol, infused to achieve normal prenatal levels in LV myocardium, markedly decreases LV DNA without affecting RV DNA concentrations. The present study indicates that cortisol inhibits myocyte replication and that cortisol simulates the change in myocardial growth pattern normally occurring after birth. It raises concerns regarding prenatal administration of glucocorticoids to mothers to mature the fetal lungs before preterm delivery.

Localization of Nitric Oxide Synthase I and III and the α1 Subunit of Soluble Guanylate Cyclase (sGC) in the Pulmonary Vasculature of Normal and Hypertensive Fetal Lambs

Localization of Nitric Oxide Synthase I and III and the α1 Subunit of Soluble Guanylate Cyclase (sGC) in the Pulmonary Vasculature of Normal and Hypertensive Fetal Lambs

Repetitive abortion in Neospora-infected ewes

Pregnant ewes inoculated with cultured Neospora caninum tachyzoites in 1995, 1996, or 1995 and 1996 aborted or delivered weak or clinically normal lambs in 1996. Nine of 11 ewes in the study had previously produced infected lambs or fetuses after being experimentally infected in 1995. Fetuses and lambs produced in 1996 showed histologic lesions and zoites indicative of Neospora. Serologic responses and production of infected fetuses/lambs indicated systemic neosporosis in the ewes during gestation, although tachyzoites could not be cultured from maternal tissues. The repetitive infection of fetuses, and resulting clinical and histopathologic findings in the present study are similar to those reported in naturally infected cattle, adding to the already established similarities of neosporosis between sheep and cattle.

Determinants Of The Pulmonary Input Impedance Spectrum: Theoretical Considerations Based On A Mathematical Model

The determinants of the shape of the pulmonary input impedance spectrum were investigated using a mathematical model based on Womersley’s equations for pulsatile flow in constrained viscoelastic tubes and structural data (morphometry, elasticity, and rheology) provided for the entire cat lung by Zhuang et al. Mean distending pressures and diameters of vessels were determined from the struc-tured data and four independent variables: cardiac output and left atrial, pleural, and alveolar pressures. Studies were performed in a control model and a model whose structure was designed to imitate that of a subject with pulmonary vascular impairment. Model simplifications were investigated. Increasing left atrial pressure or cardiac output caused passive distention of vessels that increased total blood volume and decreased vascular resistance, creating a slight spectral shift downward and to the right. Increasing pleural pressure decreased total blood volume and increased vascular resistance, creating a spectral shift upward and to the right. Increasing levels of alveolar pressure resulted in increased vascular resistance and pressures find a shift in blood volume from the capillaries to the arteries without significant change in total blood volume, creating a spectral shift that was slightly downward and to the right. Model simplification studies demonstrated that (1) all vessels distal to the tenth generation (arteries with zero distending pressure diameters < 50 μM) can be modelled as a simple resistor or (2) all vessels distal to the fourth generation can be modelled as a modified Windkessel. Results obtained from the passive studies were consistent with those obtained from normal lambs and lam be with chronically elevated pulmonary blood flow. To model a hypertensive state created by ifljury to the lung microvasculature, the number and size of small vessels and the compliance constants of all arteries were decreased and the viscoelastic constant was increased, which created the requisite shift to the right and upward. To better match the modulus fluctuation and negative phase angles at higher frequencies in the hypertensive animals, the development of a major reflection site between the main and branch arteries was hypothesized.

The effects of bovine respiratory syncytial on normal ovine lymphocyte responses to mitogens or antigens in vitro

In the present study peripheral blood mononuclear cells (MNC) obtained from normal uninfected lambs were used to study the possible effects of bovine respiratory syncytial virus (BRSV) on lymphocyte responses to the mitogens, phytohaemagglutinin (PHA), concanavalin A (Con A) and pokeweed mitogen (PWM) in vitro. Live BRSV had a depressive effect on the proliferative responses of normal MNC to PHA, Con A and PWM. Inactivated BRSV and a commercial preparation of prostaglandin E 2 were also found to depress the proliferative responses of normal ovine MNC to PHA but recombinant tumour necrosis factor-alpha (TNF-α) had no such effect. Serum samples obtained from BRSV-infected lambs contained substances inhibitory to PHA-driven lymphocyte blastogenesis. Memory blastogenic responses to border disease virus (BDV) of lymphocytes obtained from lambs previously primed with BDV were significantly reduced when lymphocytes were exposed to infectious BRSV.

Prominence of gammadelta T cells in the elicitation phase of dinitrochlorobenzene-induced contact hypersensitivity in lambs.

Immunohistochemical techniques were used to identify T-cell subpopulations in the ear skin of lambs during the elicitation phase of dinitrochlorobenzene (DCNB)-induced contact hypersensitivity. Thirty lambs (21-26 weeks of age) were divided into groups of 10. The shaved right ear of one group was treated with DNCB. Two weeks later, this group was challenged with DNCB. One group was treated with the vehicle alone, and the remaining group was left untreated. The lambs were killed 48 hours after challenge, and tissue specimens were collected from the ears of the three groups. There was an increase in T-cell populations in the skin of the DNCB-treated lambs 48 hours after challenge. The majority of the T cells were CD8+ and associated predominantly with the blood vessels and adnexa of the superficial dermis. There was also an increased presence of CD4+ cells and gammadelta T cells in the superficial dermis. In the epidermis, clusters of gammadelta T cells and CD4+ cells were associated with microlesions. Computer-assisted morphometric analysis was used to estimate the relative presence of the T-cell subpopulations in the superficial and deep dermis and the entire dermis. Statistical analysis of the relative area of immunostaining showed that the significant increases in all T-cell subpopulations (CD4+, CD8+, and gammadelta T cells) in the entire dermis were accounted for by changes in the superficial dermis. The prominence of gammadelta T cells in delayed-type hypersensitivity in the skin of domestic ruminants has been the subject of conflicting reports. In the present study, CD4+ cell and gammadelta T-cell populations were of similar size in the normal and DNCB-treated lambs, suggesting an equal participation in the elicitation phase of contact hypersensitivity.