No abstract

A number of drugs that are metabolized through the action of enzymes present in liver microsomes in the adult rabbit are not metabolized in livers of newborn rabbits. The development of metabolic pathways during a period of 4 weeks is presented. Evidence is given for the presence in livers of baby rabbits of inhibitors of some of these drug-enzyme systems.

No abstract

Two forms of cytochrome P-450 (P-450I and P-450II) have been shown by several techniques to be present in both nonciliated bronchiolar cells (Clara) and alveolar type II cells isolated from rabbit lung. In contrast, the alveolar macrophage contains little or none of these cytochromes. Cross-reactivity between antibodies to cytochrome P-450I or P-450II and detergent-digested microsomes prepared from 80% type II or 70% Clara cell fractions was shown by Ouchterlony double immunodiffusion. The presence of both cytochromes was also demonstrated by histochemical immunofluorescence in smears of type II cells stained by a modified Papanicolaou procedure and Clara cells stained with nitroblue tetrazolium. However, this same fluorescent antibody technique used for localization of rabbit pulmonary cytochromes P-450I and P-450II in tissue sections showed most of the immunofluorescence in the Clara cells of the bronchiolar epithelium. SDS-polyacrylamide gel electrophoresis of microsomes from either the type II or Clara cell fractions produced bands which corresponded to cytochrome P-450I (52,000 daltons) and cytochrome P-450II (58,000 daltons).

A procedure has been developed for the isolation of nonciliated bronchiolar epithelial cells (Clara cells) from rabbit lung. Following pulmonary lavage to eliminate macrophages, cells (5% Clara cells) were released by digestion with 0.1% Protease I in HEPES-buffered balanced salt solution containing 0.5 mM ethylene glycol-bis-(beta-aminoethyl ether)-N,N'-tetraacetic acid instilled through the trachea. These cells were then separated on the basis of size using the Beckman JE-6 elutriator rotor. The fourth fraction collected from the elutriator contained about 30% Clara cells. This fraction was then layered on a two-polymer aqueous phase system consisting of 5% dextran T500 (DT) and 3.8% polyethylene glycol 6000 (PEG) in sodium phosphate buffer. A cell fraction was obtained from the PEG phase, which included approximately 70% Clara cells. These cells were found to be greater than 90% viable by trypan blue dye exclusion. Identification of isolated Clara cells was confirmed by light microscopic observation of nitro blue tetrazolium staining and by ultrastructural characteristics as observed by electron microscopy.

No abstract

No abstract

Species variation in drug response is a well recognized pharmacological phenomenon. Strain variations within a given species, however, have been characterized to a much lesser degree. These problems assume importance not only when attempting to extrapolate results of animal experiments to man, but also in basic biological research.Law et a2( 1) have shown variations in beta-glucuronidase activity in various strains of mice. Jay(2) has also shown strain differences in mice with regard to hexobarbital sleeping time. The experiments of Yaffe(3) indicate that strain variation in drug response in mice is a genetic factor which is manifest soon after birth. Strain variation in drug response and hepatic drug metabolism in rats have been reported by Quinn et aZ(4). However, to our knowledge, no studies on strain differences in drug response have been reported using rabbits, a species commonly employed in research.We have attempted to determine whether the activity of several hepatic microsomal drug metabolizing enzyme systems varies in different rabbit strains. Studies were carried out on strains of rabbits commonly employed in research as well as on wild rabbits. We have also attempted to determine whether the stimulation of the hepatic drug metabolizing enzyme activity by phenobarbital dif-*This research was supported by a grant from Nat. Inst. Health ). fered in these strains. MateriaZs and methods. Dutch, New Zealand, English, and California strains were studied as representatives of commonly employed research animals. In addition, wild Jack rabbits were obtained from the Durant Animal Co., Ft. Sumner, New Mexico and wild Cottontails were obtained from the Earl Johnson Farms, Rago, Kansas. Rabbits were maintained on regular Purina Lab Chow and water ad libitum during the experiment, and constant conditions were maintained as nearly as possible. In all cases young adult bucks were employed.To study the effect of pre-treatment with phenobarbital, rabbits were injected intraperitoneally twice daily with 1 5 mg/kg phenobarbital sodium dissolved in normal saline. Injections were made for 3 days, on the 4th day the animals were not injected, and on the fifth day the animals were sacrificed and livers removed. Control animals were injected with normal saline on the same schedule. The livers were placed immediately on ice, blotted, weighed, and ground in the cold with a Potter homogenizer (teflon pestle) in 2 volumes of ice cold 1.15.h KCl solution. This homogenate was then centrifuged at 1-3 "C (International portable refrigerated centrifuge, model PR-2) at 9,0001 g for 30 minutes.The following metabolic pathways were studied: Side-chain oxidation of hexobarbital by guest on July 24, 2015 ebm.sagepub.com Downloaded from