The heterogeneity of arylhydrocarbon hydroxylase in fetal liver microsomes of rats

The characteristic of arylhydrocarbon hydroxylase system in fetal liver microsomes of rat was investigated. NADH-synergistic effect on NADPH-dependent arylhydrocarbon hydroxylase was observed in fetal liver microsomes of rat but not in maternal liver microsomes. NADH-synergistic effect decreased in parallel with the decrease of the ratio of cytochrome b5/cytochrome P-450 in liver microsomes. The cytochrome P-450 in arylhydrocarbon hydroxylase system in fetal liver microsomes of rat seemed to be different from that in offspring liver microsomes in respect of its dependency on cytochrome b5 system for its maximum activity.     

The enzymatic determination of bicarbonate and CO2 in reagents and buffer solutions

A method for the determination of bicarbonate in buffer solutions between pH 7.5 and 8.75 and in stock solutions of NaHCO3 is described. The HCO-3 is reacted with phosphoenolpyruvate (PEP) in the presence of PEP carboxylase (EC 4.1.1.31) and the oxaloacetate formed reduced to malate by NADH in the reaction catalyzed by malate dehydrogenase (EC 1.1.1.37). The extent of oxidation of NADH is measured spectrophotometrically. Experiments using standard solutions show that 1 mol of NADH is oxidized per mol of HCO-3 added. The method was used to establish the precautions needed to prepare buffer solutions containing less than 1% of the bicarbonate which would be present in the same buffers in equilibrium with air.     

Cerebral Blood Flow and Oxidative Metabolism in Conscious Fischer-344 Rats of Different Ages

Abstract: The cerebral metabolic rates for O₂ and for glucose were measured in conscious, fasted male Fischer-344 rats at the ages of 3, 12, and 24 months, and cerebral blood flow was determined with ¹⁴C-iodoantipyrine. The metabolic rates for oxygen and glucose were obtained by multiplying blood flow by the O₂ and glucose concentration differences, respectively, between blood in the femoral artery and in the superior sagittal sinus. Mean cerebral blood flow and the metabolic rates for oxygen and glucose did not differ significantly (p > 0.05) between 3 and 12 or between 12 and 24 months. Nor did the arteriovenous differences for O₂ and for glucose change significantly with age. Because the superior sagittal sinus drains blood mainly from the cerebral cortex, the results indicate that average cerebral cortical oxidative metabolism, and the coupling ratios between the cerebral metabolic rate for oxygen and cerebral blood flow and between the cerebral metabolic rate for glucose and cerebral blood flow, do not change significantly with age in the Fischer-344 rat.     

Pregnant mares' serum gonadotropin source influences fertilization and fresh or thawed embryo development,but the effect is genotype specific

The influence of the source of pregnant mares' serum gonadotropin (PMSG) on the num ber, quality, and in vitro development of mouse embryos before and after freezing was evaluated among three genotypes: N:NIH(S), C57BL/6N, and C3H/HeN-MTV^?. Immature females were given PMSG from one of five commercial sources. Following col lection ( 116 hr later), embryos were evaluated for stage of development, and four-to eight-cell embryos were pooled within genotype and assigned to standardized fresh or freeze-thaw culture trials. Different PMSG sources stimulated the production of different num bers of total embryos (P < 0.05) but not necessarily more embryos suitable for freezing. Differences in embryo production among genotypes indicated that absolute embryo num bers using a single mouse genotype may not accurately reflect the potency of a specific gonadotropin source. The PMSG source also affected the ability of an embryo to survive in culture either immediately after collection or after frozen storage. The effect, however, was genotype specific, with some mouse strains being relatively insensitive to PMSG source, whereas gonadotropin source played a major role in determining in vitro viability in others. Development rates for freshly collected embryos differed, often inconsistently, from those of thawed embryos regardless of the PMSG source used, demonstrating that fresh embryo development cannot be used to estimate expected post-thaw survival. In vitro development of thawed embryos is influenced not only by genotype, but also the source of the gonadotropin used to promote follicular development and oocyte maturation. These findings may explain, in part, the wide variation in embryo viability and culture rates reported among laboratories and intraspecies animal populations.     

Platelet activating factor (PAF) production by mouse embryos in vitro and its effect on embryonic metabolism

Factors affecting the production of platelet activating factor (PAF) by mouse embryos during culture in vitro were investigated. Detectable levels of embryo-derived PAF were produced within 1-4 hr with maximum PAF activity being observed after 6 hr of culture in vitro. The amount of PAF detected in media after 24 hr of culture of two-cell embryos was equivalent to 12.8 ng PAF/embryo. However, differences in activity were apparent with increased time in culture. Reduced synthesis of PAF during culture in vitro was supported by the observation that morulae stage embryos collected fresh from the reproductive tract displayed more PAF activity than morulae resulting from the 48 hr culture of two-cell embryos. In addition to determining production characteristics of PAF by embryos, we also show that the production of CO2 from carbon-1 position of lactate is positively correlated with the ability of embryos to develop during subsequent culture in vitro and therefore could be used as a measure of embryo viability. Furthermore, culture of embryos in media supplemented with PAF resulted in an increase in lactate utilization demonstrating a direct effect of PAF on the embryo. As PAF is produced by preimplantation embryos, an autocoid role of PAF in regulating embryo development is implicated. Therefore, the reduced production of PAF by embryos in vitro may explain the decreased viability of embryos commonly observed following their culture in vitro.     

The fish community structure in Tjeukemeer in relation to fishery and habitat utilization

The fish community in Tjeukemeer was monitored from 1971 to 1988 by trawling, and during the summer of 1988 the distribution of the more abundant species was determined in relation to size and location. Bream, pikeperch and smelt were the most dominant fishes, whereas roach, white bream, perch and ruffe comprised <10% of the total catches. After the termination in 1977 of the intensive gillnet fishery both pikeperch >50 cm and bream >30 cm increased in biomass, but roach >15 cm and perch >15 cm virtually disappeared and pikeperch <50 cm substantially decreased. Only smelt, ruffe, white bream and bream <30 cm hardly changed in biomass. Bream, pikeperch, perch and smelt were restricted to the open water zone, but roach <15 cm and 0 + bream were confined to the littoral zone. White bream and ruffe did not show a distinct habitat preference. Because the recruitment of smelt is largely dependent on immigration from the IJsselmeer, a feed-back between the smelt and pikeperch population is lacking. Because the carrying capacity of the pikeperch population is mainly determined by smelt, the other fish <15 cm are very vulnerable to predation when the smelt population is consumed, before a new year-class of smelt is recruited, or when the smelt fails to recruit. The vulnerability to predation of the different species and their feeding habits are discussed in relation to their distribution.     

Root respiration during grain filling in sunflower: The effects of water stress

Instantaneous rates of (soil + root) respiration were measured periodically during grain filling in sunflower crops that were i) irrigated at weekly intervals and ii) subjected to water stress for the last 25 days of the 40-day grain filling period. Daily (soil + root) respiration was calculated using instantaneous respiration rates, an empirically determined temperature response function, and diurnal records of soil temperature. Daily soil respiration was estimated using empirically determined functions linking soil respiration to soil temperature and water content. Between anthesis and maturity, daily root respiration of the irrigated crop dropped by about one half from ca. 1.8 g C m^-2 d^-1, exhibiting a strong association with daily crop gross photosynthesis. Water stress brought about a rapid decrease in root respiration, which fell to about 0.1 g C m^-2 d^-1 at maturity. Root respiration during grain filling was 46 and 30 g C m^-2 for irrigated and stressed crops, respectively.     

Monoterpene glycoside biosynthesis in detached grape berries grown in vitro

A procedure for the culture in vitro of isolated small berries of Vitis vinifera L. cv. Muscat of Alexandria in a Murashige and Skoog basal medium supplemented with N⁶-benzyladenine and indoleacetic acid is described. Berries developed well in culture during 60 days and tripled in size, but remained green and smaller than normal berries grown in vivo. Some callus formed on the distal end of the berry, and where major skin damage occurred, callus emerged from the cracked berries. In order to examine their biosynthetic competency, berries which were previously cultured in vitro for 60 days were incubated for 48 h in a Murashige and Skoog medium containing a [¹⁴C]-labelled water-soluble fraction. This fraction was isolated from grape berries located adjacent to a leaf that had been exposed to gaseous ¹⁴CO₂ in full sunlight for 5 h. The berries were then recultured for 48 h after which a glycosidic fraction was isolated on a C18 reversed phase column and further separated by thin layer chromatography (TLC). The major labelled band corresponded to the geranyl-β-rutinoside marker, indicating that grape berries have the ability to synthesize monoterpene glycosides. This band also consisted of other monoterpene glycosides as revealed by the gas chromatography-mass spectrometry (GC-MS) analysis of their aglycones (released by enzymatic hydrolysis).     

Seasonal nitrogen and carbon concentrations in white,brown and woody fine roots of sugar maple (Acer saccharum Marsh)

Small diameter (<1.0-mm) Acer saccharum Marsh roots were separated into white, brown and woody development state classes and analyzed for total N and C concentrations in April, July and October of 1988. White roots had greater concentrations of N and C than either brown or woody roots at each sampling date, and the N concentration of brown roots was consistently greater than that of woody roots. There were no temporal changes in N concentrations in any of the roots. C was slightly elevated in mid-summer in all three classes of roots. The data suggest the possible existence of an N translocation mechanism in ageing and developing fine roots. More research should be undertaken to establish the mechanisms of N loss in developing fine roots.