Showing papers by "University of Nairobi published in 1989"

Urea excretion as a strategy for survival in a fish living in a very alkaline environment.

Abstract: Ammonia is toxic to all vertebrates. It can be converted to the less toxic urea, but this is a metabolically expensive process found only in terrestrial vertebrates that cannot readily excrete ammonia and marine fish that use urea as an osmotic filler. Freshwater fish mostly excrete ammonia with only a small quantity of urea. It seems the ornithine cycle for urea production has been suppressed in all freshwater teleosts except for some airbreathers which, when exposed to air, increase urea synthesis via the cycle. Here we show that the tilapia fish Oreochromis alcalicus grahami, the only fish living in Lake Magadi, an alkaline soda lake (pH = 9.6-10) in the Kenyan Rift Valley, excretes exclusively urea and has ornithine-urea cycle enzymes in its liver. A closely related species that lives in water at pH 7.1 lacks these enzymes and excretes mainly ammonia with small amounts of urea produced via uricolysis. It dies within 60 min when placed in water from Lake Magadi. We suggest that urea production via the ornithine-urea cycle permits O. a. grahami to survive the very alkaline conditions in Lake Magadi.

The spatial and temporal patterns of the East African seasonal rainfall derived from principal component analysis

Abstract: In this study, rotated principal component analysis (RPCA) was used to study the spatial and temporal characteristics of seasonal rainfall over East Africa during the period 1922–1983. The RPCA solutions were derived from both spatial and temporal correlation matrices. The spatial correlation matrices described intercorrelation between pairs of stations, while the temporal matrices gave correlations between pairs of map patterns. Results obtained with the spatial correlation matrices indicated seasonal shifts in the patterns of the dominant RPCA modes which closely resembled the seasonal migration patterns of the rainfall belts induced by the Inter Tropical Convergence Zone (ITCZ). The influence of the large water bodies, especially Lake Victoria and the Indian Ocean, were however, outstanding throughout the year. Twenty-six homogeneous regional groups were delineated from the spatial characteristics of the dominant eigenvectors. Solutions based on the temporal correlation matrices clustered together some of the wet and dry episodes. Some of the map patterns clustered together could be associated significantly with the El-Nino/Southern Oscillation events.

Primary productivity of natural grass ecosystems of the tropics: A reappraisal

Abstract: Studies of net primary production in four contrasting tropical grasslands show that when full account is taken of losses of plant organs above- and below-ground these ecosystems are far more productive than earlier suggested. Previous values have mainly been provided by the International Biological Programme (IBP), where estimates of production were based on a change in vegetation mass alone and would not necessarily have taken full account of organ losses and turnover. Calculation at three of our sites based on estblished methodology using changes in plant mass alone (i.e. that used by the International Biological Programme, IBP) proved to be serious underestimates of when acount was taken of losses simultaneously with measurement of change in plant mass. Accounting for the turnover of material at these three sites resulted in productivities up to five times higher than were obtained using the standard IBP procedure. An emergent C4 grass stand at a fourth site in the Amazon achieved a productivity which approached the maximum recorded for agricultural crops. In this case, productivity values, when organ losses were taken into account, only slightly exceeded that obtained with IBP methods. The findings reported here have wider implications, in prediction of global carbon cycling, remote sensing of plant productivity and impact assessment of conversion to arable cropping systems.

An Allometric Study of Pulmonary Morphometric Parameters in Birds, with Mammalian Comparisons

Abstract: Comprehensive pulmonary morphometric data from 42 species of birds representing ten orders were compared with those of other vertebrates, especially mammals, relating the comparisons to the varying biological needs of these avian taxa. The total lung volume was strongly correlated with body mass. The volume density of the exchange tissue was lowest in the charadriiform and anseriform species and highest in the piciform, cuculiform and passeriform species. The surface area of the blood-gas (tissue) barrier, the volume of the pulmonary capillary blood and the total morphometric pulmonary diffusing capacity were all strongly correlated with body mass. The harmonic mean thickness of both the blood-gas (tissue) barrier and the plasma layer were weakly correlated with body mass. The mass-specific surface area of the blood-gas (tissue) barrier (surface area per gram body mass) and the surface density of the blood-gas (tissue) barrier (i.e. its surface area per unit volume of exchange tissue) were inversely correlated (though weakly) with body mass. The passeriform species exhibited outstanding pulmonary morphometric adaptations leading to a high specific total diffusing capacity per gram body mass, consistent with the comparatively small size and energetic mode of life which typify passeriform birds. The relatively inactive, ground-dwelling domestic fowl (Gallus gallus) had the lowest pulmonary diffusing capacity per gram body mass. The specific total lung volume is about 27% smaller in birds than in mammals but the specific surface area of the blood-gas (tissue) barrier is about 15% greater in birds. The ratio of the surface area of the tissue barrier to the volume of the exchange tissue was also much greater in the birds (170-305%). The harmonic mean thickness of the tissue barrier was 56-67% less in the birds, but that of the plasma layer was about 66% greater in the birds. The pulmonary capillary blood volume was also greater (22%) in the birds. Except for the thickness of the plasma layer, these morphometric parameters all favour the gas exchange capacity of birds. Consequently, the total specific mean morphometric pulmonary diffusing capacity for oxygen was estimated to be about 22% greater in birds than in mammals of similar body mass. This estimate was obtained by employing oxygen permeation constants for mammalian tissue, plasma and erythrocytes, as avian constants were not then available. Recalculations using recent values for the rate of oxygen uptake by avian whole blood indicate that the superiority of the avian pulmonary diffusing capacity for oxygen is even greater, the value for birds exceeding that of mammals by about 82%. However, because of the small numbers of some of the avian species investigated and the lack of representatives of many important groups of birds, our allometric computations should be regarded as essentially a preliminary basis for comparing the pulmonary morphometric characteristics of birds and mammals. It is suggested that the greater physiological efficiency of the avian pulmonary system compared with that of mammals can be attributed partly to the pulmonary morphometric differences between these two vertebrate classes. Other major factors are the cross-current relation of parabronchial gas and blood, the auxiliary counter-current relation of air capillary gas and blood, and the bellows action of the air sacs.

Combined oral contraceptives and liver cancer

Abstract: A multi-national, hospital-based, case-control study was conducted to evaluate the possible relationships of steroid contraceptives to 6 neoplasms. Based on data from 122 newly diagnosed cases of primary liver cancer and 802 matched controls, the relative risk of liver cancer in women who had ever used combined oral contraceptives was estimated to be 0.71 (95% Cl 0.4–1.2). No consistent trend in risk with months of use or time since first or last use was observed. Separate analyses also revealed no association between use of combined oral contraceptives and hepatocellular carcinoma (RR = 0.60) or cholangiocarcinoma (RR = 1.22). Most women in this study came from areas in which hepatitis B is endemic and rates of liver cancer are relatively high, and in most cases use of oral contraceptives was of short duration. These results provide no evidence that short-term use of oral contraceptives enhances risk of liver cancer in countries where the determinants of this disease are similar to those observed in the countries where this study was conducted.

Distribution of Cr, Pb, Cd, Zn, Fe and Mn in Lake Victoria sediments, East Africa

Abstract: The presence of many metals at trace or ultra-trace levels in the human environment has received increased global attention. Sediments as a sink for pollutants are widely recognized pollution sources and diagenesis and biochemical transformations within the sediment may mobilize pollutants posing a threat to a wider biological community. The natural (background) concentrations of heavy metals in lake sediments can be estimated either by analysis of surface sediments in non-polluted regions or by analysis of core samples antedating modern pollution. The distribution pattern of heavy metals in tropical freshwater systems has been little studied. The authors found increased concentrations of lead and other trace metals in Lake Victoria. Thus this study was initiated in order to further investigate the distribution patterns of lead and other metals in Lake Victoria.

Placebo-controlled trial of potassium supplements in black patients with mild essential hypertension

Abstract: Forty-eight black patients with mildly increased blood pressure (BP) that had not yet been subjected to treatment took part in a double-blind clinical trial of the efficacy and tolerability of oral potassium supplements (64 mmol daily) versus a matching placebo (made of starch with coating) in a 16-week study. Potassium supplements produced a significant decrease in mean supine and standing BP within 4 weeks after treatment inception. Urinary potassium excretion increased significantly in the 24 patients who received potassium supplements (p less than 0.001). No significant changes occurred in plasma sodium and potassium concentrations or in urinary excretion of sodium during the study. All patients completed the trial without experiencing any notable untoward effects. These results are consistent with the premise that oral potassium supplements may exert hypotensive effects of clinically significant degree in patients with mild hypertension.

Feline anaemia associated with Ehrlichia-like bodies in three domestic short-haired cats.

Abstract: Three domestic short-haired cats with a history of anorexia and loss of body condition had high rectal temperatures, and a normocytic, normochromic anaemia. Two of them were also dyspnoeic, and thoracic radiographs revealed a diffuse, unstructured increase in radio-opacity involving all the lung lobes. Examination of Giemsa-stained blood smears and culture of blood monocytes revealed purplish-staining intracytoplasmic inclusions, in monocytes and lymphocytes, which occurred either singly or in aggregates. Electron micrographs of a buffy coat smear from one of the cats revealed round intracytoplasmic inclusions, with electron dense and lucid areas morphometrically similar to those found in other members of the genus Ehrlichia. An attempt to culture chlamydia from one of the cats was unsuccessful. The cats were treated successfully, one with tetracycline hydrochloride and the other two with imidocarb dipropionate.

Salmonella septicaemias in Kenyan children.

Abstract: In a 5-month study of Salmonella septicaemias in Kenyan children carried out during the annual peak infection period, Salmonella typhimurium septicaemias occurred seven times more frequently than typhoid or other non-typhoid infections. Salmonella typhimurium infections were predominantly community acquired, malnourished infants from rural malaria endemic areas with poor water supply were especially vulnerable. Typical clinical features of fever, diarrhoea, and severe anaemia resembled P. falciparum malaria which often co-existed. Mortality was 18 per cent. Isolates exhibited a wide range of multidrug resistance. Typhoid affected older children, was less severe and drug sensitive.

Low prevalence of oral mucosal lesions in HIV-1 seropositive African women.

Abstract: In Nairobi (Kenya) 334 women prostitutes of whom 80.5% were HIV-1 positive, were examined for oral mucosal lesions; 15.6% of seropositive, and 4.6% of seronegative, women had oral mucosal lesions, predominantly oral candidiasis. In the seropositives, 8.6% had erythematous, 1.1% had hyperplastic candidiasis, and 0.4% had hairly leukoplakia as the only oral lesions; 0.4% had a combination of erythematous and hyperplastic candidiasis, and 1.5% had combinations of pseudomembranous and erythematous candidiasis in the presence of hairly leukoplakia. Of the 211 seropositive women for whom we knew the first date on which a positive serologic test was obtained, the likelihood of developing an oral mucosal lesion was found to be dependent on the duration of seropositivity. The low incidence of oral mucosal lesions in this population may be due to the relatively recent acquisition of HIV-1 infection.

Maturity, fecundity and the effect of reduced rainfall on the spawning rhythm of a siluroid catfish, Clarias mossambicus (Peters)

Abstract: . Five maturity stages in the male and six in the female Clarias mossambicus (Peters) are described based on macroscopic and histological analysis of the gonads. During the study period (September 1984-August 1985) the species spawned only once instead of the usual biannual spawnings which coincide with the two rainy seasons in the gulf region. The reduction in the spawning rhythm is associated with the reduced rainfall which the Nyanza district experienced during October-December 1984. Rainfall, therefore, acts as a spawning stimulus in the species. Ripe ovaries which could not be released due to lack of spawning underwent atresia. The fecundity of fish measuring 46 0-87-Ocm TL ranged from 7966-229648 with a mean of 78152 eggs and it increased lineariy with total length (r = 0-9165) and body weight (r = 0.9371). The overall ratio of male to female was 1:1. First sexual maturity is attained in the length range of 41-45cm TL in both sexes.

Light microscopic morphometry of the kidneys of fourteen avian species.

Abstract: Kidney volume and the volume proportions of the cortex, medulla, blood vessels larger than capillaries and ureter and ureteral ducts were investigated in 61 birds from 14 species representing passeriformes, psittaciformes, podicipediformes, anseriformes, galliformes, and columbiformes. The kidneys were fixed in situ by perfusion via their arterial supply. Kidney volume and body weight were strongly correlated (r = 0.991); the allometric function relating kidney volume (Vk) to body weight (W) was: Vk = 13.96W0.902. Histological sections of one kidney from each bird were analysed by point counting with a Zeiss integrating eyepiece to estimate the volume proportions and subsequently the absolute volumes of the main components of the kidney. The avian kidney was found to consist of a very large cortex (range 71-81%), a relatively small medulla (range 5-15%), blood vessels larger than capillaries (range 10-13%). For all the birds, the mean volume proportions of the kidney components were as follows: cortex, 77%; medulla, 10%; blood vessels larger than capillaries, 12%; ureter and ureteral ducts, 1%. The values for the absolute volume of each of the main components of the kidney were well correlated with body weight. The allometric equations and correlation coefficients (r) relating: (a) the volume of cortex (Vc) and the body weight (W) was Vc = 10.06W0.914, r = 0.991; (b) the volume of medulla (Vm) and body weight was Vm = 2.27W0.795, r = 0.974; (c) the volume of blood vessels larger than capillaries (Vb) and body weight was Vb = 1.76W0.894, r = 0.988. All the birds were divided into two groups in the following five sets: (a) passeriform and non-passeriform orders; (b) galliform and non-galliform orders; (c) small and large birds weighing less than and more than 500 g respectively; (d) aquatic and non-aquatic birds; (e) desert and non-desert birds. In the two groups of each set the differences between kidney volume per gram body weight and those between the respective percentage proportions of cortex, medulla and blood vessels larger than capillaries were assessed by Student's t-test. The differences between kidney volume per gram body weight were significant for all sets except desert and non-desert birds; those between the respective percentage proportions of cortex and medulla were significant for all sets; those between the percentage proportions of blood vessels larger than capillaries were significant only in desert and non-desert birds.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of phenylbutazone and indomethacin on the post-operative course following experimental orthopaedic surgery in dogs.

Abstract: Randomized placebo-controlled crossover studies were carried out in dogs to evaluate how two non-steroidal anti-inflammatory drugs (NSAID) might modulate an acute post-traumatic inflammatory reaction. Two "identical" surgical interventions were performed on the forelimbs of each animal with an interval of 28 days, to enable a paired comparison of the inflammatory signs and the wound/bone healing processes. At one operation 8 dogs received 300 mg phenylbutazone twice daily for 8 days starting on the day before surgery, and at the other operation matching placebo tablets were given. In a similar placebo-controlled trial another group of 8 dogs received 5 mg indomethacin twice daily. With phenylbutazone the post-operative swelling was not significantly reduced compared to placebo, but there was less pain and limping. With indomethacin the swelling was somewhat reduced, but there was no consistent difference to placebo in the pain and limping assessments. None of the drugs appeared to distinctly effect the wound or fracture healing, as evaluated by clinical inspection, comparison of radiographs and comparison of bone sections from the sites of surgery. It proved difficult to select an appropriate dosage of indomethacin due to its high potential to induce GI ulceration and bleeding in dogs. In this experimental surgical model with an acute inflammation, neither phenylbutazone nor indomethacin showed impressive anti-inflammatory or analgesic properties. In the same model paracetamol has proved to significantly and more efficiently, reduce both swelling and pain without any noticeable adverse effects, and appears to be a better alternative than the two presently tested NSAID.

The lung of the emu, Dromaius novaehollandiae: a microscopic and morphometric study.

Abstract: Qualitative and quantitative characteristics suggest that the lung of the emu is poorly adapted for gas exchange when compared with that of other birds. The granular epithelial cells extend over the air capillaries, and the squamous epithelial cells have microvilli indicating a poor differentiation of the epithelium of the exchange tissue. The surface area of the blood-gas tissue barrier per unit body mass was only 5.4 cm2/g, the volume of the pulmonary capillary blood per unit body mass was only 0.93 cm3/kg, and the tissue barrier was unusually thick (0.232 micron). These parameters produce a relatively small total morphometric pulmonary diffusing capacity for oxygen of 0.014 ml O2/sec/mbar/kg. The findings conform to the evolution of a very large flightless bird in a warm environment lacking effective predators.

Nutritive value of papyrus (Cyperus papyrus, Cyperaceae), a tropical emergent macrophyte

Abstract: Papyrus (Cyperus papyrus, Cyperaceae) covers large areas in tropical African wetlands. Analysis of its nutritive value has revealed that crude protein is higher in umbels than culms. Ruminai dry matter digestibility of papyrus is, however, higher in culms than umbels. Both the crude protein and ruminai dry matter digestibility decrease with increasing age of the plant. Values for crude protein and ruminai dry matter digestibility are similar to those reported for the range grasses that constitute the greatest percentage of forage in East Africa. In general, papyrus has some grazing potential and could be used as fodder especially in the dry season when other forage is scarce and of low nutritive value.

Prevalence and presentation of depressive illness in a primary health care setting in Kenya.

Abstract: Using a two-stage screening procedure, ICD-9 diagnostic criteria, and the Hamilton Rating Scale for Depression, the authors diagnosed depressive disorders in 81 (9.2%) of 881 patients in a primary care setting in Kenya. All depressed patients had somatic symptoms, and all of the 27 depressed patients assessed with the Hamilton scale scored higher than 2 on the work and activities item. These findings contradict the earlier reports that Africans do not admit to being depressed. Nearly one-third of the depressed patients were moderately or severely ill and would have benefited from psychiatric assessment and treatment.

Alcoholism among outpatients of a rural district general hospital in Kenya.

Abstract: Summary This article presents the results of a study of alcoholism among outpatients of a rural district hospital in Kenya. One hundred and twelve outpatients aged 18 years or over attending Kisii District Hospital were interviewed using the alcohol section of the Diagnostic Instrument Schedule (DIS). The participants consisted of 56 males and 56 females. Of these, 54% of the males and 25% of the females met the DIS criteria for alcohol abuse and/or alcoholism. Those classified as alcoholics differed significantly from the non-alcoholics on variables associated with sex, age, past marital state, religion and types of alcoholic drinks consumed. No significant differences were found with respect to present marital state, education, occupation, family size, age of first intoxication or physical illness.

Field Studies of Larval Anopheles Arabiensis Patton of Mwea Irrigation Scheme, Kenya

Abstract: Between May 1984 and December 1985, the population of immature stages of Anopheles arabiensis was sampled by the dip method at sites close to two villages in Mwea Irrigation Scheme, Kenya. Larval presence corresponded to rainy seasons and the flooding phase of the rice cycle. No larvae were found during the postharvest dry season. The instar composition, age distribution and survivorship curves for the different stages were determined. Pupal productivity for Mwea rice fields was estimated to be 1% of the total immature population.

Scanning and transmission electron microscopic study of the tracheal air sac system in a grasshopper Chrotogonus senegalensis (Kraus)--Orthoptera: Acrididae: Pyrgomorphinae.

Abstract: The morphology of the trachea-air sac system in a species of grasshopper Chrotogonus senegalensis has been studied by using scanning and transmission electron microscopes. Capacious air sacs were formed as dilatations along the primary tracheal trunks. Narrower secondary trachea arose either directly from the primary trachea that bypassed the air sacs or from the air sacs themselves. At or close to the organ or tissue supplied with air, the secondary trachea gave rise to the notably smaller tertiary trachea that penetrated the tissue, giving rise terminally to the extremely small tracheoles that indent some cells. The trachea and the air sacs were basically made up of an inner cuticular lining, helical taenidial rings, and an overlying epithelial cell cover. The air sacs may be important in efficient ventilation of the respiratory system. The supply of air directly to the tissue cells was viewed as an exemplary efficient design when compared to that prevailing in the nontracheate air-breathing animals, where the vascular system is interposed between the respiratory organ and the target tissue cells. A similarity in the general morphological design of the insect and avian respiratory systems has been observed, mainly in respect to the presence of the air sacs and that of the respiratory shunts. This, together with the reported functional features like the unidirectional mode of ventilation, has been interpreted as a classic case of structural and functional convergent evolution leading to the evolution of similar and comparably efficient respiratory systems capable of providing the large amount of oxygen demanded by flight.

Mefloquine disposition in normals and in patients with severe Plasmodium falciparum malaria

Abstract: Mefloquine pharmacokinetics were studied in Kenyan African normal volunteers and in patients with severe acute attack ofPlasmodium falciparum malaria. Peak concentrations were achieved in both groups at 20 – 24 hours. The mean half-life of elimination was 385±150 hours (mean±SD) in normal subjects while in severe malaria it was 493 ±215 hours which was significantly longer (P<-0.001).

Scanning electron microscope study of the morphology of the reptilian lung: the Savanna monitor lizard Varanus exanthematicus and the pancake tortoise Malacochersus tornieri.

Abstract: The morphology of the langs of two reptilian species, Varanus exanthematicus and Malacochersus tornieri, have been studied on gross preparations, latex casts, and critical-point-dried tissues. The shape of these lungs was observed to conform with that of the body, the lung of the monitor lizard (Varanus) being long and ovoid while that of the pancake tortoise (Malacochersus) was rounded and laterally indented. With respect to the size distribution of the gas exchange compartments, the lungs were observed to be notably heterogenous. In both species these units were generally smaller in diameter in the cranial region of the lung while those in the caudal region were larger. The gas exchange compartments in the tortoise were more profusely compartemented with the primary, secondary, and tertiary septa being well developed white in the lizard only the primary and secondary septa were observed. The tertiary septa in the tortoise lung and the secondary septa in that of the monitor lizard defined the terminal gas exchange units, the favoli. The cast impressions closely resembled the actual lung tissue and convincingly revealed the hierarchical design of the gas exchange compartments as they radiate from the air chambers and ducts, terminally giving rise to the faveoli. This stratification clearly increases the surface area available for gas exchange in these lungs. Disparate refinements of the basic reptilian lung design, as noted here, may lead to differing anatomic pulmonary diffusing capacities for oxygen to which characteristics like energetics and mode of respiration in this taxon may be attributed.

Variation in seedling predation and herbivory in Prunus africana in the Kakamega Forest, Kenya

Abstract: SUMMARY Variation in seedling predation and herbivory was studied in three Prunus africana adult trees in the Kakamega forest, Kenya. Percentage predation varied inversely with percentage herbivory and both changed from one tree to another. Smaller seedlings were more likely to be killed by predators while larger seedlings could only be damaged by herbivores. Although it was hard to predict percentage predation given percentage herbivory, it was possible to predict the likely cause of seedling mortality or damage given a seedling stage. The effects of predation and herbivory on seedling dynamics are also discussed. Resume On a etudie la variation de la predation et de l'herbivorie sur les jeunes pousses de trois arbres adultes de Prunus africana, dans la foret de Kakamega, au Kenya. Le pourcentage de predation variait inversement par rapport a celui des dommages causes par les herbivores. Les plus petites pousses etaient plus susceptibles d'etre attaquees par des predateurs tandis que les plus grandes ne pouvaient etre endommagees que par les herbivores. Ces deux pourcentages variaient d'un arbre a l'autre. S'il etait difficile de predire le pourcentage de predation au su des dommages causes par les herbivores, il etait possible de prevoir la cause vraisemblable de mortalite des jeunes pousses ou des dommages selon l'âge de la pousse. On discute des effets de predation et d'herbivorie sur la dynamique de la repousse.

African soil erosion — nature undone and the limitations of technology

Abstract: A wide range of mechanical soil conservation techniques commonly used in Africa are reviewed in a politico-economic framework. Three factors within this framework play a significant role in the adoption of mechanical soil conservation techniques. These are: (a) land considerations, such as land availability and tenure, and farm size; (b) capital and labour constraints; and (c) access to, and functioning of, institutions. Hypotheses which are concerned with the relationships between these factors and the likelihood of farmers adopting soil conservation techniques are introduced. Case studies drawn from Kenya, Lesotho, Malawi, Swaziland and Sierra Leone, as well as from Jamaica, are used to test these hypotheses in relationship to such techniques as terracing, grass strip cultivation, bunding, and contour cultivation. Greater reliance on local knowledge and indigenous soil conservation techniques seems to provide the best solution to the introduction of mechanical soil conservation techniques.