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Biomedical subjects

R M Leach

Publications and source records attributed to R M Leach.

At least 55 records · Page 3Linked to original sources
PubMed1994

Effect of growth hormone, insulin-like growth factor I, basic fibroblast growth factor, and transforming growth factor beta on cell proliferation and proteoglycan synthesis by avian postembryonic growth plate chondrocytes.

We examined the in vitro effects of pituitary-derived chicken growth hormone (cGH), recombinant human insulin-like growth factor-I (rhIGF-I), recombinant human basic fibroblast growth factor (rhbFGF), and porcine transforming growth factor beta (pTGF-beta) on proliferation ([3H]thymidine uptake) and matrix proteoglycan synthesis (35SO4 incorporation) by chicken epiphyseal growth plate chondrocytes. Factorial experiments were used to study the effect of these substances in a serum-free culture system. Basic FGF had to be present in the culture medium for mitogenesis to take place. In the presence of this peptide, TGF-beta, TGF-beta + IGF-I, and newborn calf serum (NCS) stimulated mitogenesis. The mitogenic activity of NCS could be duplicated by adding platelet-derived growth factor (PDGF) to the culture medium. For matrix synthesis, IGF-I was the key factor, with the addition of TGF-beta, TGF-beta+bFGF, or serum producing further stimulation in matrix synthesis. Using this culturing system, homologous cGH did not stimulate cell proliferation or proteoglycan synthesis. The lack of stimulatory activity of cGH was consistent, regardless of the age of the birds from which the chondrocytes were isolated, the zone of the growth plate, or the level of cGH used. None of the growth factors used in this study or several other systemic hormones were found to be permissive factors for GH to be active. Either other factors must be present for a direct effect of GH on growth plate chondrocytes, or the avian species differ from their mammalian counterpart.

Animals↗
PubMed1994

Isolation and localization of basic fibroblast growth factor-immunoreactive substance in the epiphyseal growth plate.

Previous research in our laboratory has shown basic fibroblast growth factor (bFGF) to be a permissive mitogen for isolated avian growth plate chondrocytes. The present study was conducted to determine whether bFGF is present in avian growth plate and, if present, to determine its localization within the tissue. Immunohistochemical studies revealed that bFGF is present in the resting proliferative and hypertrophic calcifying zones of the growth plate but is absent from the prehypertrophic zone. Basic FGF appears to be associated with the extracellular matrix of the proliferative zone, but it is predominantly intracellular in the hypertrophic and mineralizing zone chondrocytes. Partial purification of cartilage-derived bFGF was performed on crude extracts of cartilage using heparin-Sepharose affinity chromatography. The presence of bFGF in the heparin-Sepharose column fractions was confirmed by immunoblotting and radioimmunoassay. Furthermore, western blot analysis of the extracts showed multiple protein bands having bFGF immunoreactivity, in the molecular weight range 14.4-18 kD. The data support the hypothesis that bFGF has a dual role in the growth plate. In the proliferative zone it acts as a chondrocyte mitogen, whereas when released from terminal hypertrophic chondrocytes, bFGF may serve as a chemotactic signal for metaphyseal blood vessel proliferation.

Animals↗
PubMed1994

Reduced sciatic nerve substance P and calcitonin gene-related peptide in rats with short-term diabetes or central hypoxaemia co-exist with normal messenger RNA levels in the lumbar dorsal root ganglia.

Endoneurial hypoxia of ischaemic origin is believed to cause the reduction in sciatic nerve substance P levels in experimentally diabetic rats. The first part of this study was designed to determine whether the changes seen extended to another neuropeptide, calcitonin gene-related peptide, and to reveal any correlation between substance P and calcitonin gene-related peptide levels in the sciatic nerve of both diabetic and centrally hypoxaemic rats. Comparison of streptozotocin diabetic rats (four-week duration) with their control group showed clear reductions in both substance P-like immunoreactivity (control = 225 +/- 20 pg/mg protein, diabetic = 139 +/- 19; P < 0.01) and calcitonin gene-related peptide-like immunoreactivity (control = 9.08 +/- 0.65 ng/mg protein, diabetic = 4.43 +/- 0.44; P < 0.001). A similar pattern was seen with the comparison of five-week centrally hypoxaemic rats (housed in 10% O2) with their controls for both substance P-like immunoreactivity (control = 222 +/- 10 pg/mg protein, hypoxic = 148 +/- 13; P < 0.001) and calcitonin gene-related peptide-like immunoreactivity (control = 6.58 +/- 0.42 ng/mg protein, hypoxic = 3.01 +/- 0.45; P < 0.001). Calcitonin gene-related peptide levels correlated closely with substance P levels in both the diabetes and central hypoxaemia studies (r2 = 0.69 and 0.62, respectively). The second part of this study measured the messenger RNA levels of the substance P precursor, preprotachykinin-A, and calcitonin gene-related peptide messenger RNA in the L4 and L5 dorsal root ganglia of control, diabetic and centrally hypoxaemic rats. There was no change in preprotachykinin-A or calcitonin gene-related peptide messenger RNA levels between any of the groups, suggesting that the sciatic nerve decreases in substance P and calcitonin gene-related peptide described above are post-transcriptional in origin.

Animals↗
PubMed1994

Vitamin K deficiency does not functionally impair skeletal metabolism of laying hens and their progeny.

The purpose of this research was to determine the effect of vitamin K deficiency on indices of skeletal metabolism in laying hens, developing embryos and young growing chickens. Laying hens were fed a vitamin K-deficient diet for 28 wk, which resulted in impaired blood clotting and reduced bone gamma-carboxyglutamic acid (Gla) concentration compared with vitamin K-sufficient hens. However, this treatment did not influence egg production, eggshell deposition or other reproductive performance criteria. Vitamin K-deficient embryos were able to mobilize sufficient quantities of calcium for normal skeletal development, although they exhibited severe reduction in blood clotting and bone Gla concentration. Similar results were obtained from progeny of both vitamin K-sufficient and -deficient hens fed deficient diets for 4 wk after hatching. These results indicate that a severe reduction in skeletal protein Gla concentration does not interfere with normal development of this tissue.

1-Carboxyglutamic Acid↗
PubMed1994

Hypoxic vasoconstriction in rat pulmonary and mesenteric arteries.

Hypoxic vasoconstriction was investigated in isolated pulmonary and mesenteric arteries of the rat. Experiments were performed on large (approximately 2 mm pulmonary, approximately 0.8 mm mesenteric) and small (100-350 microns) arteries. Hypoxia [oxygen partial pressure (PO2) approximately 33 mmHg] elicited a biphasic response in arteries precontracted with prostaglandin F2 alpha (10 microM). A transient contraction reaching a peak within 2-3 min was observed in both large and small pulmonary and mesenteric arteries (phase 1). In pulmonary arteries, this was followed by a slowly developing contraction over 45 min (phase 2). In mesenteric arteries, there was no phase 2 but instead a profound relaxation. Mechanical disruption of the endothelium had no significant effect on phase 1 in preconstricted large pulmonary arteries but reduced phase 1 in small arteries by 40%. Phase 2 was abolished in both large and small arteries. Inhibition of endothelium-derived relaxing factor synthesis or cyclooxygenase pathways had no effect on either phase. Verapamil substantially reduced phase 1 but abolished phase 2. In conclusion, we have found a clear biphasic response to hypoxia in pulmonary arteries of the rat, but, in contrast to some previous reports, phase 1 was only partially dependent on the endothelium, whereas phase 2 was entirely dependent on the endothelium. Small and large arteries had qualitatively similar responses. These results are consistent with the involvement of at least two mechanisms for hypoxic vasoconstriction, one of which may involve release of an as yet unidentified endothelium-derived constrictor factor.

Animals↗
PubMed1994

Influence of manganese deficiency on the characteristics of proteoglycans of avian epiphyseal growth plate cartilage.

The need for manganese for normal skeletal development appears to be related to its role in proteoglycan biosynthesis. The purpose of this research was to characterize the proteoglycans synthesized under conditions of manganese deficiency. The proteoglycans were extracted from epiphyseal growth plate cartilage and the monomers separated by cesium chloride density gradient centrifugation followed by column chromatography. The proteoglycan monomers from normal cartilage contained primarily (92%) chondroitin sulfate side chains with keratan sulfate being a minor (8%) component. Manganese deficiency reduced the total amount of cartilage proteoglycans. Of the monomers present in deficient cartilage, the majority (75%) were similar to those found in normal cartilage. Cartilage from deficient chicks also contained a second monomer fraction (25%) characterized by a reduced carbohydrate content. Thus, in addition to a reduction in total proteoglycan content, manganese deficiency results in qualitative changes in the proteoglycans present in epiphyseal growth plate cartilage.

Animals↗
PubMed1994

Autocrine, paracrine, and hormonal signals involved in growth plate chondrocyte differentiation.

Longitudinal bone growth depends upon intricate steps in the metabolism and differentiation of epiphyseal growth plate chondrocytes. These steps involve cell proliferation followed by the synthesis of gene products that are characteristic of the subsequent stages of differentiation. Until recently, the major control of growth plate metabolism was thought to reside with systemic hormones, principally growth hormone. However, it is now apparent that locally produced peptide growth factors play important autocrine and paracrine roles in normal growth plate physiology. Investigations with cultured chondrocytes have demonstrated the importance of the peptide growth factors insulin-like growth factor-I, transforming growth factor-beta, and basic fibroblast growth factor for cell proliferation, extracellular matrix biosynthesis, and changes in morphology associated with the progressive stages of chondrocyte differentiation. All three of these factors have been shown to be present in specific zones of the epiphyseal growth plate. A preliminary map of the epiphyseal growth plate is proposed, which delineates the site and mode of action of systemic and locally produced factors involved in longitudinal bone growth.

Animals↗
PubMed1994

The relationship between oxygen delivery and consumption.

The primary function of the heart and lungs is to generate a flow of oxygenated blood to respiring tissues to sustain aerobic metabolism. Teleologically, such a transport system has several basic requirements. It should be energy efficient, avoiding unnecessary cardiorespiratory work, but it should be sensitive to the fluctuating demands of cellular metabolism. Ideally, metabolic demand and oxygen distribution should be matched regionally when at rest, during exercise, and in different disease states. Finally, oxygen should pass efficiently across the extravascular tissue matrix. The mechanisms that control oxygen distribution are complex and not completely understood. In the critically ill patient, these mechanisms may have an important role in determining the clinical outcome. The relationship between oxygen delivery and consumption has not been clearly established despite considerable investigation during the last decade. However, these variables are often measured to define a population of critically ill patients in whom oxygen consumption is limited by oxygen delivery, the state of so-called delivery-dependent oxygen consumption or pathologic supply dependency. The recent literature in critical care and many leading intensive care units has emphasized the importance of raising oxygen delivery to "supranormal" levels in an attempt to satisfy the increased metabolic demands of these patients. This practice has been justified by the observation that increasing oxygen delivery improves oxygen debt and outcome in postoperative surgical patients requiring intensive care. In the severely hypovolemic patient, most physicians would agree that volume replacement to improve oxygen delivery must be beneficial. However, in patients with more complex problems, including sepsis, cardiovascular collapse, and hypoxic hypoxemia, controlled trials to examine the influence of such strategies on clinical outcome have produced conflicting data. Several methodologic factors may have contributed to these contradictory and often controversial results. These factors include failure to define the disease and patient population adequately, the relationship between the time of investigation and the evolution of the disease process, and the accuracy and frequency of measurement.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Antitussive effects of levodropropizine in the dog.

The antitussive activity of levodropropizine (S(-)3-(4-phenyl-piperazine-1-yl)-propane-1,2-diol, DF 526, CAS 99291-25-5) was evaluated after oral administration to the conscious dog. Levodropropizine had a good antitussive activity, comparable with, but having a longer duration of action than dropropizine, the racemate from which it is derived. The antitussive activity of levodropropizine in the dog was approximately 1/20 of that of codeine phosphate.

Animals↗
PubMed1993

Chicken tibial dyschondroplasia: a limb mutant with two growth plates and possible defects of collagen crosslinking.

In the cartilaginous epiphyseal growth plate, extracellular matrix molecules such as collagens are believed to play important roles during both normal and abnormal development. One defect of the epiphyseal plate occurs in chickens with a condition termed tibial dyschondroplasia (TD). This abnormality occurs in certain strains of juvenile chickens and other rapidly developing animals. It is characterized by the presence of a mass of avascular, uncalcified cartilage which is retained in the proximal metaphysis of the tibiotarsus. To elucidate the developmental events which may be involved in this lesion, we have performed both immunohistochemistry and in situ hybridizations for collagen types II and X, known components of the extracellular matrix of the growth plate. By immunohistochemical analyses, the TD lesion contains both of these collagen types; therefore, the presence of these molecules per se is not sufficient for calcification of vascularization to occur. Since type X collagen is expressed exclusively in hypertrophic cartilage, the chondrocytes in the lesion must have undergone hypertrophy before their developmental arrest. The matrix of the lesion also reacted with a monoclonal antibody which is directed against an epitope in the NH2-terminal telopeptide of the alpha 1(II) chain. Our previous data suggest that this epitope is rendered unavailable in type II collagen which has undergone crosslink formation; its availability in the lesion suggests that crosslinking may be abnormal. Lastly, analyses by in situ hybridization failed to detect mRNA for either type II or type X collagen within the lesion, but chondrocytes distal to the lesion do contain mRNAs for these collagens in a spatial pattern suggesting the presence of a second growth plate.

Animals↗
PubMed1993

Insulin-like growth factor-I gene expression is increased in the right ventricular hypertrophy induced by chronic hypoxia in the rat.

Rats were maintained in chambers and breathed air (control, n = 8) or an atmosphere containing 10% oxygen (hypoxic, n = 10) for 35 days. On completion of the experiment the hypoxic animals weighed less than the controls (hypoxic, 290 +/- 11.7g; control, 339 +/- 19.2g; means +/- S.E.M., p < 0.05). No differences in the left ventricular weights were found between groups but the right ventricular weights were greater in the hypoxic rats (hypoxic, 0.39 +/- 0.02g; control, 0.27 +/- 0.08g; p < 0.01). The amount of mRNA for IGF-I in the ventricles was quantified by Northern blot analysis. There was no difference between groups in IGF-I mRNA levels in the left ventricles (hypoxic, 1.07 +/- 0.41 absorbance units (AU); control, 0.73 +/- 0.33 AU). In the right ventricles, IGF-I mRNA was greater in hypoxic than in control rats (hypoxic, 2.37 +/- 0.75 AU; control, 0.64 +/- 0.11 AU; p < 0.05). This study demonstrates that expression of IGF-I mRNA is increased in the hypertrophied right ventricle of hypoxic rats; IGF-I may play a central role in the initiation and maintenance of this process.

Animals↗
PubMed1993

Liquid methionine hydroxy analog (free acid) and DL-methionine attenuate calcium-induced kidney damage in domestic fowl.

To evaluate the possibility that kidney damage may be induced by the commercial practice of feeding high-Ca (HCa) prelayer rations, and to evaluate the protective efficacy of supplementing HCa diets with liquid methionine hydroxy analog free acid or DL-methionine, 12-wk-old female Single Comb White Leghorn pullets were fed one of the following corn-soybean meal-based diets until they reached 22 wk of age: normal-Ca (NC, 1% Ca); HCa (HC, 3.5% Ca); HCa supplemented with .34 or .68% liquid methionine hydroxy analog free acid (HC3A or HC6A); or HCa supplemented with .3 or .6% DL-methionine (HC3DL or HC6DL). The unsupplemented HC diet caused a significant reduction in kidney mass and a significant increase in the incidence of gross kidney damage and urolithiasis in pullets necropsied at 22 wk of age. Calcium-induced kidney damage was attenuated in a dose-response fashion by supplementing the HC diet with liquid methionine hydroxy analog and DL-methionine. None of the diets caused a significant metabolic acidosis. Plasma uric acid concentrations were not predictive of the extent of Ca-induced kidney damage. Analyses of glomerular size distributions indicated that subclinical or "hidden" kidney damage may not progressively develop into urolithiasis as hens mature. When compared with hens reared on the NC diet, rearing hens on the HC, HC3A, HC3DL, HC6A, or HC6DL diets did not consistently affect hen-day egg production, egg mass, eggshell mass, percentage eggshell, or bone mineralization.

Animals↗
PubMed1992

Development of a serum-free system to study the effect of growth hormone and insulinlike growth factor-I on cultured postembryonic growth plate chondrocytes.

We have developed a serum-free system to culture postembryonic growth plate chondrocytes while maintaining some important phenotypic characteristics of their tissue of origin. This serum-free medium was as effective as medium containing 10% newborn bovine serum (NBS) for recovering the cells from enzymatic isolation. Surface secretory activity of chondrocytes cultured in monolayer, assessed through scanning electron microscopy, was also comparable to cells grown in medium containing serum. The effects of growth hormone (GH) and insulinlike growth factor-I (IGF-I) were also studied using the serum-free medium. GH had no effect on cell density and morphology of the cells compared to the control without the hormone. In contrast, chondrocytes grown in medium containing IGF-I had a marked increase in cell density after 3 days and presented similar morphologic characteristics to cells grown in the presence of NBS. The growth factors required for proliferation of chondrocytes cultured in the serum-free medium are IGF-I and fibroblast growth factor (100 ng/ml, respectively). Addition of ascorbic acid to the serum-free medium (0 to 50 micrograms/ml) produced a dose-dependent decrease in cell proliferation. This medium should provide a useful tool for studying the effects of different growth factors/hormones in the regulation of longitudinal bone growth and their interactions.

Animals↗
PubMed1992

Interactions of plant zinc and plant species on the bioavailability of plant cadmium to Japanese quail fed lettuce and spinach.

Many cadmium-contaminated environments contain high levels of zinc. The effects of plant Zn and plant species on plant Cd bioavailability were tested in Japanese quail fed lettuce and spinach. Four groups of birds received 10% of their diets as lettuce or spinach leaves intrinsically labeled with 109Cd and containing low or high intrinsic Zn. Two other groups were fed control diets containing 109Cd as CdSO4 and low or high Zn as ZnCO3. Cadmium concentrations in diets ranged from 0.857 to 1.05 micrograms/g dry wt. Zinc concentrations in low-Zn diets ranged from 21.2 to 22.8, and in high-Zn diets from 56.0 to 63.3 micrograms/g dry wt. Increased lettuce and spinach Zn decreased plant Cd retention in kidney, liver, and jejunum-ileum of Japanese quail. Spinach Cd was less absorbed than lettuce Cd at both Zn levels. Inorganic Zn produced a lesser decrease in Cd retention in kidney, liver, and jejunum-ileum than did plant Zn. We conclude that (1) crops that transport Zn and Cd readily into edible tissues show lower Cd bioavailability when grown in Zn-Cd contaminated environments than in Cd-only polluted sites, (2) plant species differ in Cd bioavailability for identical concentrations of Zn and Cd in edible tissues, and (3) toxicological studies with animals exposed to Cd salts and Zn supplements do not assess Cd bioavailability of Zn-Cd contaminated crops.

Absorption↗
PubMed1992

A comparison of the pharmacological and mechanical properties in vitro of large and small pulmonary arteries of the rat.

1. The mechanical and pharmacological properties of small pulmonary arteries (100-300 microns normalized lumen diameter) were directly compared with those of the left main pulmonary artery (1-2 mm) from the rat. The active and passive length-tension characteristics and responses to a variety of agonists and antagonists were dependent on arterial diameter. 2. Maximum contractile function was obtained in both groups of vessels when stretched so as to give an equivalent transmural pressure of 30 mmHg. This is substantially lower than that found for systemic vessels, and reflects the normal low pulmonary arterial pressure. 3. Noradrenaline was a powerful vasoconstrictor in large but not small pulmonary arteries (P less than 0.001). In contrast, bradykinin produced a significantly greater response in the small arteries (P less than 0.001). In comparison with large pulmonary arteries, small arteries were more sensitive to noradrenaline (P less than 0.05) and 5-hydroxytryptamine (P less than 0.001), less sensitive to endothelin-1 (P less than 0.001) and had the same sensitivity to prostaglandin F2 alpha. 4. The mechanism that maintains the low arterial tone of the pulmonary circulation is unknown, but it may involve the release of relaxing factors from the endothelium. In this preparation, basal resting tone could not be demonstrated in either large or small arteries. 5. Acetylcholine-induced relaxation of pre-contracted pulmonary arteries was reduced or absent in the small artery, despite histological evidence of an intact endothelium. In large arteries pre-contracted with prostaglandin F2 alpha, acetylcholine (100 mumol/l) caused 88.2% relaxation compared with 25.2% in the small artery.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1992

The use of avian epiphyseal chondrocytes for in vitro studies of skeletal metabolism.

Chondrocytes from the postembryonic avian epiphyseal growth plate are easily obtained and can be successfully cultured for a considerable length of time. Under the proper culture conditions, the chondrocytes will become confluent and achieve a hypertrophic morphology followed by mineralization of the extracellular matrix. Although this can be accomplished with a serum-free medium, the process is accelerated in the presence of serum. Minimal growth factor requirements for the serum-free medium include fibroblast growth factor and insulin-like growth factor. Transforming growth factor-beta and parathyroid hormone are also mitogenic for chondrocytes. Chondrocytes may have more critical requirements for amino acids because further supplementation of a conventional medium such as Dulbecco's modified Eagle's medium results in improved performance of the cultured cells. Ascorbic acid in the medium is very important for matrix vesicle production and mineralization of cartilage nodules.

Animals↗
PubMed1992

Portable liquid oxygen and exercise ability in severe respiratory disability.

BACKGROUND: The development of portable liquid oxygen systems, capable of delivering high flow rate oxygen for long periods, justifies reassessment of the value of supplemental oxygen to aid exercise tolerance in patients with chronic respiratory insufficiency. The type of exercise test and the low oxygen flow rates previously used may account for the variable and often poor responses to supplemental oxygen reported in earlier studies. METHODS: The walking tolerance of 30 patients with severe respiratory disability was measured while they were breathing air and increasing doses of supplemental oxygen (2, 4, 6 1/min) by using both the standard six minute walking test and an endurance walking test. To assess the initial learning effect and repeatability of the walking tests, three six minute walks and three endurance walks were performed on day 1 and a single walk of each type on days 2, 3, and 14. In addition, oxygen dosing studies were performed on days 2 and 3 after the initial baseline walking tests. Each dosing study comprised four endurance walking tests or four six minute walking tests with patients breathing either air at a flow rate of 4 1/min from a portable cylinder or supplemental oxygen at a flow rate of 2, 4 or 6 1/min from a portable liquid oxygen supply. The order of the tests was randomised. Walking distance with each flow rate of oxygen was compared with walking distance with patients carrying cylinder air and for the initial unburdened walks. Breathlessness was assessed by visual analogue scoring on completion of each walk. RESULTS: Exercise ability and breathlessness were significantly improved with supplemental oxygen and this benefit outweighed the reduction in performance resulting from carrying the portable device. Supplemental oxygen at flow rates of 2, 4, and 6 1/min increased mean endurance walking distances by 37.9%, 67.7% and 85.0% and six minute walking distances by 19.2%, 34.5%, and 36.3% by comparison with distances when the patient was carrying air with a flow rate of 4 1/min. The additional work of carrying the portable gas supply reduced endurance walking distance by 22.2% and six minute walking distance by 14.1% by comparison with a baseline unburdened walk. Comparison of supplemental oxygen at 2, 4, and 6 1/min with the baseline unburdened performance showed increased endurance walking distances of 7.3%, 30.4%, and 43.9% and six minute walking distances of 2.3%, 15.5%, and 17.0%. Walking distance was increased by more than 50% by comparison with an unburdened walk in seven patients with the endurance walking test but in only three patients with the six minute walking test. The benefit was similar in patients with obstructive and with interstitial lung disease. Individual responses were variable and only desaturation during the baseline walk in patients with obstructive lung disease had any predictive value for benefit with oxygen. CONCLUSION: As there was no clear relation between response to oxygen therapy and the patients' characteristics, assessment for supplemental oxygen therapy will depend on exercise testing. It is suggested that portable oxygen should be considered only if a patient shows a 50% improvement in exercise ability with high flow rate oxygen (4-6 1/min) by comparison with an unburdened walk.

Ambulatory Care↗