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Biomedical subjects

M H Maxwell

Publications and source records attributed to M H Maxwell.

At least 19 recordsLinked to original sources
PubMed1992

Differential leucocyte responses to various degrees of food restriction in broilers, turkeys and ducks.

1. White blood cell responses of broilers, turkeys and ducks were examined at regular intervals after being subjected to various degrees of food restriction. 2. Restricted-fed broilers showed increases in heterophil and basophil numbers, together with a corresponding decrease in lymphocytes. The heterophil/lymphocyte ratio was raised. There were no differences between broiler strains. 3. After only one week of feeding restricted diets, heterophils were significantly raised in selected and unselected 2-week-old ducks. At 21 weeks of age, those ducks receiving 50% of food required to achieve their ad libitum-fed body weight had raised heterophils. 4. Ducks receiving food to achieve 25% of ad libitum-fed birds produced a marked basophilia, but no heterophilia. 5. After two weeks of food restriction, turkeys responded with significant heterophil/lymphocyte ratios following two degrees of restricted feeding. 6. It was concluded that in some poultry, a heterophilia may be the response to mild to moderate stress but a basophilia may result after severely stressing birds.

Animals↗
PubMed1992

Whole blood and plasma viscosity values in normal and ascitic broiler chickens.

1. Whole blood and plasma viscosity values in normal and ascitic broiler chickens were measured. 2. The mean blood viscosity value in ascitic broilers was greater than that of the controls. There was a small but significant difference in the opposite direction between plasma viscosity values of the respective groups of birds. 3. Although the haematocrit and arterial pressure index values in the ascitic birds were raised, there was a fall in the concentration of total plasma protein. 4. The data suggest that the raised viscosity in the ascitic birds was caused by a polycythemia and not by any influence of plasma protein. 5. The cumulative effect of these factors, such as raised blood viscosity values and larger deformed red cells flowing through constricted lung arterioles, may contribute to the pulmonary hypertension and ascites seen in some young commercial broilers.

Animals↗
PubMed1991

Fine structure of secondary granule inclusions in fowl heterophils after ruthenium tetroxide fixation.

Bone marrow from domestic fowls was initially fixed for electron microscopy in glutaraldehyde and post-fixed with either ruthenium tetroxide or osmium tetroxide. Inclusions with distinct outlines were revealed in the secondary granules of heterophil leucocytes after ruthenium tetroxide but not with osmium tetroxide fixation. In longitudinal orientation, these inclusions were rod-shaped and composed of microfilaments measuring 3.7 nm in diameter. In transverse section, the outline of some of these inclusions was hexagonal and therefore the inclusions may be crystalline in nature.

Animals↗
PubMed1991

Red cell size and various lung arterial measurements in different strains of domestic fowl.

Red cell size and various lung arterial measurements were examined in different strains of young commercial broiler and layer fowls. The broilers were: Marshall, Cobb, Ross 'selected', Ross 'relaxed' and the layers were: Isa Brown, Ross Brown and Hisex Brown. The Ross relaxed bird had a significantly larger red cell than any other strain. Overall, broilers had larger red cells than layers. The internal elastic lamina, a measure of arterial size, was small in the Ross relaxed bird (138 microns) and was at its maximum (163 microns) in the selected Ross strain. The medial area (muscle coat) was least in the Ross relaxed bird (984 microns2) and greatest in the Cobb strain (1516 microns2). In some strains there was a slight correlation among birds between red cell and arterial size but not with the medial area. The results appeared to indicate that red cell size may not be the only important correlating factor in the aetiology of pulmonary hypertension in fowls.

Animals↗
PubMed1991

Haematology and histopathology of seven-week-old broilers after early food restriction.

The haematology and histopathology of seven-week-old broilers were examined after periods of early food restriction, for six, 10 or 14 days from six days old. After several weeks on an ad libitum diet the birds failed to compensate for the weight lost during early food restriction. Immediately after the periods of food restriction, the birds demonstrated significantly increased heterophil/lymphocyte ratios, reduced eosinophils and slightly raised basophil counts. At seven weeks old, a significant reduction was seen in red and white blood cells and thrombocyte numbers together with significant increases in mean cell haemoglobin and mean cell volume. The haematological profile demonstrated a macrocytic normochromic anaemia caused possibly by a folic acid deficiency as a result of the food restriction. Histopathological lesions were seen in the heart, lungs and liver from birds on all diets but there were more lesions the longer the food had been restricted. Lung disease was more marked where there was inadequate ventilation. Cartilaginous and osseous lung nodules were significantly fewer after food restriction. It was postulated that the increase in pathological lesions in the food-restricted birds may be associated with a stress response.

Animals↗
PubMed1991

Dietary restriction on serum thyroid hormone levels.

To determine the long term effects of a protein sparing fast on serum thyroid hormone levels, the authors studied 38 obese patients ingesting a diet of 320 kcal for up to 13 weeks. The high baseline serum triiodothyronine (T3) levels decreased significantly by the first week, further decreased by the third week, and this lower level persisted for the duration of the fast until realimentation. Serum free T3 index followed the same general pattern as did serum T3 levels. Serum reverse T3 increased significantly by the first week, but by week three, the reverse T3 level had begun to fall, although still significantly increased above baseline. By week seven, reverse T3 had decreased to almost baseline and remained not significantly changed from the baseline to 13 weeks. Serum thyroxine (T4) increased significantly by the first week in all patients, but by the third week had returned to baseline levels which persisted to 13 weeks. The free T4 index and free T4 concentrations showed the same increment at week one and then returned to baseline levels. There were no significant changes in serum thyroxine-binding globulin (TBG) or thyroid-stimulating hormone (TSH) concentrations. The changes in serum T3 and reverse T3 levels are attributable to alterations in peripheral 5'-monodeiodination of T4 and reverse T3 induced by the protein sparing fast.

Body Weight↗
PubMed1991

Differentiation of cancellous bone and medullary bone in laying hens: a novel technique for image analysis.

A selective staining technique for the identification and differentiation of cancellous bone from medullary bone of the laying hen by image analysis is described. Undecalcified Polymaster resin sections were oxidized in acidified potassium permanganate and oxalic acid before being immersed in an ammoniacal silver solution. The sections were reduced in formalin, fixed in sodium thiosulfate and counterstained in naphthalene black 10B which was dissolved in picric and acetic acids. Intensely stained cancellous bone was prominent with this technique compared with a paler medullary bone component which permitted the former to be easily recognized and measured by image analysis.

Animals↗
PubMed1991

Hormonal correlates of weight loss associated with blood pressure reduction.

This study investigated changes in plasma norepinephrine and the renin-angiotensin-aldosterone system during weight loss. Subjects were maintained on a hypocaloric and low sodium diet for 12 weeks. During weight loss statistically significant decreases in blood pressure, aldosterone, plasma renin activity, and norepinephrine were evident. Plasma renin substrate was suppressed from week one to eight and returned to control levels by week twelve. The data indicate that a reduction in the activity of the renin-angiotensin-aldosterone system, modulated by circulating norepinephrine and plasma renin substrate, may significantly contribute to the fall in blood pressure associated with weight loss.

Adult↗
PubMed1990

Comparison of haematological values in restricted- and ad libitum-fed domestic fowls: white blood cells and thrombocytes.

1. White blood cells and thrombocyte values were examined in normal domestic fowls of layer and broiler strains fed restricted or ad libitum diets. 2. Basophils were the only white blood cells to increase significantly in number after the period of food restriction. It is suggested that the increase may have been associated with stress. 3. There were more basophils in broilers than layers, in males than females and in younger than older birds. 4. In contrast, a decrease in the total number of white blood cells was seen in birds maintained on a restricted diet compared with those fed ad libitum. 5. Stress may also have been responsible for an increased thrombocyte count in the restricted birds as well as a slightly lowered eosinophil count. 6. Heterophil/lymphocyte ratios were not significantly altered by the restriction of food.

Age Factors↗
PubMed1990

Comparison of haematological values in restricted- and ad libitum-fed domestic fowls: red blood cell characteristics.

1. A haematological study of the red blood cell characteristics in domestic fowls fed restricted and ad libitum diets was examined. The characteristics included Hb (haemoglobin), PCV (Packed Cell Volume), Rbc (Red blood cell count), MCH (Mean Cell Haemoglobin), MCV (Mean Cell Volume), MCHC (Mean Cell Haemoglobin Concentration) and reticulocytes. 2. The investigation showed that Hb, PCV, MCH and MCV were all reduced when broilers were fed a restricted diet. The number of Rbc's in these birds also increased significantly compared with control ad libitum-fed broilers. MCHC and reticulocyte numbers did not alter significantly. 3. It is proposed that some of the red cell characteristics may be restored to within "normal" ranges by food restriction. However, the results did show that there was a tendency to induce a microcytic normochromic anaemia in these restricted-fed birds.

Animal Feed↗
PubMed1990

Modified staining techniques for avian blood cells.

1. Two routine staining methods for domestic fowl blood cells have been modified with superior results. 2. Type of anticoagulant had a major effect on staining quality: EDTA gave excellent results whereas lithium heparin was unsatisfactory. 3. Unfixed blood smears were preferred to smears fixed in methanol before staining with May Grunwald and Giemsa's stain. Intact heterophil and basophil granules were clearly demonstrated. 4. Staining for 60 min in Natt and Herrick's haemocytometer diluent improved the differentiation between small lymphocytes and thrombocytes.

Animals↗
PubMed1990

Ultrastructural abnormalities in seven-day-old broilers reared at high altitude.

Fine structural abnormalities in seven-day-old broilers reared at high altitude are described. Tissue changes were seen in the heart, kidney and lung that resembled those previously reported in four-week-old broilers reared at altitude with an ascitic syndrome. Almost half of the hearts examined had myofibril disorganisation and mitochondrial hyperplasia. Renal changes occurred principally in tubule morphology and the lungs showed capillary congestion as well as engorged parabronchi. Increased levels of cartilaginous and osseous nodules in the lungs of 28-day-old ascitic birds reared at high altitude supported observations from a previous study conducted at low altitude. The observations in this study of seven-day-old chicks, may indicate that the embryo is at greater risk of developing abnormalities following exposure to low oxygen tension.

Altitude↗
PubMed1990

Haematological and histopathological findings in young broilers reared in poorly and well ventilated environments.

Two strains of broilers, a modern commercial strain and a strain which has not recently been selected for economic traits, were reared in adjacent rooms which were identical except that one had good ventilation and the other poor ventilation. Mean cell volume (MCV) of erythrocytes was studied in relation to plasma viscosity and the incidence of lung nodules. Poor ventilation was associated with an increased incidence of lung nodules and increased plasma viscosity but there was no correlation between MCV and the number of nodules. Although environmental factors may influence MCV the genotype of the bird appears to be of major importance.

Animals↗
PubMed1989

Efficacy and safety of triamterene/hydrochlorothiazide combinations in mild systemic hypertension.

After a 3-week placebo lead-in (Period 1), 78 patients with sitting diastolic blood pressures (BPs) of greater than or equal to 90 and less than or equal to 105 mm Hg entered a 4-week period (Period 2) during which they received triamterene (TMT) 37.5 mg/hydrochlorothiazide (HCTZ) 25 mg/day. Four weeks of therapy with TMT 37.5 mg/HCTZ 25 mg resulted in a statistically significant decrease in mean BP of -15.0/-9.6 mm Hg. Mean BP changed from 145/95 to 130/85 mm Hg. Fifty-nine percent of patients were classified as responders as defined by study criteria. An additional 4 weeks of therapy (Period 3) for responders produced no further change in BP. Nonresponders as a group continued to have a further decrease in BP in Period 3. However, only patients in whom therapy was transferred to TMT 75 mg/HCTZ 50 mg had a statistically significant decrease. All patients who changed to the higher dose combination achieved goal BP by the end of the study. Of the nonresponders who continued to take TMT 37.5 mg/HCTZ 25 mg, 69% achieved goal diastolic BP by the end of Period 3. Three patients were withdrawn because of adverse experiences, 1 of which was considered treatment related. Of 58 reports of adverse experiences, 8 were considered possibly related and 2 probably related to therapy. There was a total of 8 clinically significant abnormal laboratory values, 1 of which was considered to have a possible relation to therapy.

Antihypertensive Agents↗
PubMed1988

Haematological and tissue abnormalities in chicks caused by acute and subclinical folate deficiency.

1. Haematological, histological and ultrastructural findings in young chicks fed on a purified diet severely deficient in folate are reported. 2. Growth of the birds was greatly depressed and they had a macrocytic anaemia. Other haematological changes included abnormal nuclear formations in erythrocytes, numerous mitoses and hypersegmented granulocytes. 3. Megaloblasts were observed in bone marrow and their fine structure is described for the first time in an avian species. 4. Morphological changes occurred also in the liver. The parenchyma had damaged sinusoidal endothelium, inflammatory cells and no glycogen. Mitochondria were damaged and many were associated with unusual crystalline structures. 5. Chickens fed on a semi-purified diet of low folate content showed no growth depression or clinical signs of deficiency but had abnormal haematological values and morphological changes that resembled those seen in birds fed on the purified diet. 6. These abnormalities responded to dietary supplements of pteroylmonoglutamic acid in a dose-related manner and may be useful in diagnosing subclinical folate deficiency.

Animals↗
PubMed1988

The relation between degree of blood pressure reduction and mortality among hypertensives in the Hypertension Detection and Follow-Up Program.

The relation between degree of diastolic blood pressure reduction and mortality was examined among hypertensive persons in the Hypertension Detection and Follow-up Program. This program, conducted from 1973-1979, was a multicenter community-based trial, which followed 10,940 hypertensive participants for five years. The one-year annual visit was the first occasion on which change in blood pressure could be measured on all participants. During the subsequent four years of follow-up on 10,053 participants, 568 deaths occurred. With time-dependent life tables and time-dependent Cox life table regression analyses, the existence of a quadratic function which modeled the relation between diastolic blood pressure reduction and mortality was supported, even after adjusting for other risk factors. The minimum mortality hazard ratio, based on a particular model, occurred at a diastolic blood pressure reduction of 26.2 mmHg (standard error = 13.4) in the whole population and 10.0 mmHg (standard error = 5.3) in the baseline diastolic blood pressure stratum 90-104 mmHg. After this reduction, there was a small increase in the risk of death. There was no evidence of the quadratic function after fitting the same model with systolic blood pressure. Methodological issues involved in studying a particular degree of blood pressure reduction were considered. The confidence interval around the change corresponding to the minimum hazard ratio was wide, and the obtained blood pressure level should not be interpreted as a goal for treatment. Blood pressure reduction was attributed not only to pharmacologic therapy but also to regression to the mean, and to other factors unrelated to treatment.

Actuarial Analysis↗
PubMed1988

Beyond blood pressure control. Effect of antihypertensive therapy on cardiovascular risk factors.

Mild hypertension accounts for approximately 60% of the mortality associated with high blood pressure. In addition to hypertension, other major cardiovascular risk factors include left ventricular hypertrophy (LVH), dyslipoproteinemia, and glucose intolerance. Thus, the effects of agents used to treat hypertension on these risk factors are of considerable importance. Large therapeutic intervention trials have shown that while adequate treatment of mild hypertension significantly and consistently reduces all-cause mortality as well as the risk of stroke and congestive heart failure, an anticipated reduction in coronary heart disease (CHD) has not been demonstrated. It is possible adverse metabolic side effects (hypercholesterolemia, hyperglycemia, hypokalemia) of widely used agents, such as diuretics and beta-blockers may be partially offsetting the beneficial effects of blood pressure reduction, with the net result being a failure of these agents to reduce the risk of CHD. Angiotensin-converting enzyme inhibitors (ACEIs) and calcium channel blockers do not produce these adverse metabolic derangements. The use of antihypertensive agents that have favorable or neutral metabolic effects should further reduce the risk of cardiovascular morbidity and mortality attributable to high blood pressure, including CHD.

Antihypertensive Agents↗