A simple yet effective method (iso-density percoll centrifugation) has been developed for consistently preparing isolated rat liver parenchymal cells with over 98% initial viability. The method has been applied to cells isolated by a variety of collagenase digestion techniques. This procedure involves the low-speed centrifugation (50 X g) of the initial cell suspension through a percoll medium having a density of 1.06 g/ml and results in the separation of single and viable parenchymal cells from cell aggregates, debris, and nonparenchymal cells. The enriched parenchymal cells have been shown to be superior to untreated cells by a number of criteria including: preparation homogeneity, cell morphology, maintenance of cytochrome P-450, hormonal responsiveness (measured by the induction of tyrosine aminotransferase after treatment with glucagon or dexamethasone, or both), plasma membrane integrity (determined by both trypan blue exclusion and leakage of glutamic-oxaloacetic transaminase), and the DNA repair capability after treatment with benzo[a]pyrene or 2-acetylaminofluorene.

Subspecies of the eastern tiger swallowtail butterfly exhibit striking differences in their ability to use quaking aspen (Populus tremuloides) and other members of the Salicaceae as larval host plants. Papilio glaucus canadensis survives and grows well on aspen, whereas Papilio glaucus glaucus does not. In earlier studies we isolated a crude fraction of aspen compounds that exhibited activity against P. g. glaucus and identified the components as a suite of four phenolic glycosides (salicin, salicortin, tremuloidin, and tremulacin). This study was designed to identify the specific phenolic glycosides, or interactions among glycosides, responsible for the differential abilities of Papilio subspecies to utilize quaking aspen. We bioassayed the glycosides individually and in combination against both Papilio subspecies, using neonate survival trials and fourth—instar feeding trials. None of the compounds or combinations of compounds negatively affected the survival, growth, consumption rates, or digestibility/conversion efficiencies of P. g. canadensis, or 72—h survival rates of P. g glaucus. Salicortin and tremulacin significantly increased fourth—instar duration and decreased growth rates for P. g. glaucus, primarily by reducing consumption rates. Salicin and tremuloidin showed no negative effects. Combinations of glycosides containing salicortin and tremulacin decreased larval survival and a dramatically lowered growth rates by decreasing both consumption rates and food conversion efficiencies. Observations of treated larvae indicated that these glycosides may have caused gut lesions. The active component of salicortin and tremulacin is a cyclohexeone saligenin ester, and its activity is synergized in tremulacin by the presence of a benzoyl ester on the same molecule. We propose that differences in the susceptibilities of P. g. canadensis and P. g. glacus to the active phenolic glycosides are due to differences in activity of their carboxylesterase detoxication systems.

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Two subspecies of the eastern tiger swallowtail butterfly, Papilio glaucus, exhibit reciprocal inabilities to survive and grow on each other's preferred foodplant. P. g. canadensis R. & J. performs well on quaking aspen (Populus tremuloides Michx.) but not on tulip tree (Liriodendron tulipifera L.); P. g. glaucus L. performs well on tulip tree but not on quaking aspen. This study was designed to test the hypothesis that secondary metabolites in tulip tree and quaking aspen are responsible for these differential utilization abilities. We extracted and fractionated leaf constituents into different chemical classes, applied them to a mutually acceptable diet (black cherry, Prunus serotina, leaves), and bioassayed them against neonate larvae (survival) and penultimate instar larvae (survival, growth, digestibility and conversion efficiencies). For each plant species, one fraction in particular showed activity against the unadapted subspecies. One tulip tree fraction dramatically reduced survival of P. g. canadensis neonates, and reduced consumption rates, growth rates, and ECI's of fourth instar larvae. The tulip tree constituents most likely responsible for these effects are sesquiterpene lactones. One quaking aspen fraction greatly lowered survival of P. g. glaucus neonates, and decreased survival, consumption rates, growth rates and ECD's of fourth instar larvae. The compounds responsible for these results are probably simple phenols or phenolic glycosides. Surprisingly, P. g. glaucus and P. g. canadensis showed slightly poorer performance on the active tulip tree and quaking aspen fractions, respectively, indicating that even adapted insects incur a metabolic cost in the processing of their host's phytochemicals.

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