Biological implications of the use of surfactants in medicines: and the biphasic effects of surfactants in biological systems

A survey of the biological effects of surface-active agents reveals that their affinity for membranes and in particular their ability to penetrate and increase the permeability of membranes is of prime importance. An increase in drug absorption from the gastrointestinal tract, from muscle, from the rectum and from topical preparations is frequently a result of an increase in membrane permeability; the effect of surfactants on enzyme activity can be also the result of changes in organelle permeability or to surfactant-induced changes in protein conformation. As anionic surfactants and cationic surfactants tend to exhibit too high a degree of toxicity, non-ionic agents are most commonly used in pharmaceuticals. Experiments to elucidate the mode of action of a range of commercially available non-ionic surfactants on the increase in drug absorption in model systems employing goldfish (Carassius auratus) are described. Emphasis is placed on the biphasic effects of the surfactants whereby an increase in membrane permeability is observed at low concentrations (frequently below the critical micelle concentration of the surfactant) and a decrease in overall absorption is found at higher concentration. Such biphasic effects are frequently encountered in the literature on surfactant effects in biological systems.     

Rodent species and their seasonal variations in Arusha,Northern Tanzania

A preliminary study was conducted at two areas in Arusha from July 1982 to December 1987 to assess the rodent species present and to determine their seasonal population trends at TPRI compound and at Selian Wheat Farm. The rodents were caught by using live and snap traps. Nine rodent species were captured and identified. Among themMastomys natalensis was dominant followed byArvicanthis spp. and shrews. There was a grater number ofM. natalensis at Selian wheat farm than at the TPRI compound (p<0.05). The rodent population density increased after the onset of short rains. This change is interpreted to be due to variations in food supply and plant cover.

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Zusammenfassung In den Jahren 1982–1987 wurden insgesamt 2614 Kleinsäuger auf zwei verschiedenen Versuchsflächen in Arusha, Tanzania, gefangen. Eine Fläche (TPRI compound) war von zahlreichen verschiedenen Wild-und Kulturpflanzen bedeckt. Hier war die nagetierabundanz insgesamt geringer, die Artendiversität jedoch beträchtlich größer als auf der kultivierten Ackerfläche (Selian Wheat Farm), die nur von Getreide und Mais bedeckt war. Die VielzitzenratteMastomys natalensis dominierte auf beiden Flächen während der gesamten Beobachtungsdauer. Die Fluktuation der Kleinsäugerdichte war mit den Niederschlägen in diesem Gebiet korreliert.

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With 2 figures     

Nursery diseases of Eucalyptus in Kerala1

Survey of Eucalyptus (E, grandis and E. tereticornis) nurseries in Kerala State indicates that the most prevalent diseases are damping-off, web blight and seedling blight in seedbeds and stem canker, leaf and shoot blights and Phaeoseptoria leaf spot in container plants. Cylindrocladium spp., Rbizoctonia solani and Pythium spp. arc the main serious pathogens. Pythium myriotylum, P. deliense, R. scilani, Cylindrocladium camellias, C. clavatum and Sclerotium rolfsii are recorded for the first time on Eucalyptus.     

Some diseases of forest tree seedlings in India caused by Sclerotium rolfsii and Rhizoctonia solani1

Leaf blight of Bombax ceiba and B. insigne caused by Sclerotium rolfsii and collar rot of B. ceiba and Ailanthus triphysa caused by Rhizoctonia solani are reported for the first time from India.     

Somatic embryogenesis inCephalotaxus harringtonia embryo-megagametophyte co-culture

Somatic embryogenesis was initiated fromCephalotaxus harringtonia (Forbes) K. Koch embryo culture. Explants consisted of embryo and megagametophyte halves both cut longitudinally. They were removed aseptically from mature seeds and grown together on a solid Murashige and Skoog modified medium supplemented with 5 mg·l ⁻¹ 2,4-dichlorophenoxyacetic acid. Embryogenic cultures started from callus after three or more months on the primary medium. The embryogenic callus originated from the suspensor region of the embryo. All chromosome counts made in the cells of the embryonic structures demonstrated a diploid stage, which suggest that they originated from zygotic embryo tissue. The early stages of somatic embryogenic development were achieved,i.e., formation of small clusters consisting of an embryonal region made up of isodiametric meristematic cells. A more advanced stage was reached in some cultures in which the distal embryonal end of the embryo appeared smooth and opaque. The ultrastructural characteristics of the embryos, the two types of embryo cells, embryonal and suspensor cells, as well as their contents were similar to those already reported in the case of somatic embryogenesis of other conifers.