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Biomedical subjects

C J Nelson

Publications and source records attributed to C J Nelson.

At least 55 records · Page 3Linked to original sources
PubMed1988

Diurnal Growth of Tall Fescue Leaf Blades : II. Dry Matter Partitioning and Carbohydrate Metabolism in the Elongation Zone and Adjacent Expanded Tissue.

The spatial distributions of net deposition rates of water soluble carbohydrate-free dry matter (WSC-free DM) and WSC were evaluated within and above the elongation zone of tall fescue (Festuca arundinacea Schreb.) leaf blades during light and darkness. Imported DM used for WSC-free DM synthesis during darkness (67% of the total in experiment I and 59% in experiment II) was greater than during light (47% in both experiments), suggesting that the 65% higher leaf elongation rate during darkness was accompanied by higher rates of synthesis of cellular structural components. Deposition rates of WSC in the basal and central part of the elongation zone (0-20 mm from the ligule) were similar during light and darkness, but above 20 millimeters WSC deposition occurred during light and WSC loss occurred during darkness. WSC deposition and loss throughout the elongation zone and the recently expanded tissue were mostly due to net synthesis and degradation of fructan. Fructan was predominantly low molecular weight and contributed about 50% of the total osmotic partial pressure of WSC. In the most actively growing region, where fructan synthesis was most rapid, no diurnal change occurred in molecular weight distribution of fructan. WSC solute concentrations were diluted in the most actively growing tissue during darkness because net monosaccharide and fructan deposition were unaltered and sucrose deposition was decreased, but growth-associated water deposition was increased by 77%. Net rates of fructan synthesis and degradation were not related to tissue sucrose concentration, but appeared to respond to the balance between assimilate import and assimilate use in synthesis of cellular structural components (i.e. WSC-free DM) and deposition of monosaccharides. Fructan synthesized in tissue during most active elongation was degraded when the respective tissue reached the distal limit of the elongation zone where assimilate import in darkness was insufficient to maintain synthetic processes associated with further differentiation of cells.

Journal Article↗
PubMed1988

Characterization of fructan from mature leaf blades and elongation zones of developing leaf blades of wheat, tall fescue, and timothy.

Water-soluble carbohydrate composition of mature (ceased expanding) leaf blades and the elongation zone of developing leaf blades was characterized in wheat (Triticum aestivum L.), tall fescue (Festuca arundinacea Schreb.), and timothy (Phleum pratense L.). These species were chosen because they differ in mean degree of polymerization (DP) of fructan in the mature leaf blade. Our objective was to compare the nature and DP of the fructan. Vegetative plants were grown with a 14-hour photoperiod and constant 21 degrees C at the leaf base. Gel permeation chromatography of leaf blade extracts showed that the apparent mean fructan DP increased in the order wheat < tall fescue < timothy. Apparent mean DP of elongation zone fructan was higher than that of leaf blade fructan in wheat and timothy, but the reverse occurred for tall fescue. Low DP (</=10) and high DP (>10) pools were found in both tissues of tall fescue and wheat, but concentration of low DP fructan was very low in either tissue of timothy. All three species have high DP fructan. Comigration with standards on thin-layer chromotography showed that wheat contained 1-kestose and a noninulin fructan oligomer series. Tall fescue contained neokestose, 1-kestose and higher oligosaccharides that comigrated with neokestose-based compounds and inulins. Thin-layer chromatography showed that small amounts of fructose-containing oligosaccharides were present in timothy.

Journal Article↗
PubMed1987

Assessment of spatial distribution of growth in the elongation zone of grass leaf blades.

Knowledge about the spatial distribution of growth is essential for understanding the leaf growth process. In grasses the elongation zone is located at the base of the leaf blade and is enclosed by sheaths of older leaves. Assessment of spatial growth distribution, therefore, necessitates use of a destructive method. We used a fine needle to make holes through bases of tillers at the location of the leaf elongation zone of tall fescue (Festuca arundinacea Schreb.), then measured the displacement of the holes after a 6 or 24 h interval. Needle holes caused a 22 to 41% decrease in daily leaf elongation so experiments were conducted to investigate if the spatial distribution of growth in the elongation zone was altered. Leaf elongation rate was reduced similarly when needle holes were made within or above the zone where cell elongation occurs. Distribution of elongation within the zone was the same when estimated by displacement of needle holes or ink marks placed on the epidermis of the elongation zone after surrounding tissue had been removed. Making holes at different locations within the elongation zone did not differentially affect the relative contribution of the damaged or undamaged parts to leaf elongation. These findings demonstrate that needle holes or ink marks in paired leaves can be used to estimate the relative distribution of growth in the elongation zone of undamaged tall fescue leaf blades.

Journal Article↗
PubMed1987

Growth Rates and Carbohydrate Fluxes within the Elongation Zone of Tall Fescue Leaf Blades.

Investigations were performed to better understand the carbon economy in the elongation zone of tall fescue leaf blades. Plants were grown at constant 21 degrees C and continuous 300 micromoles per square meter per second photosynthetic photon flux density where leaf elongation was steady for several days. Elongation occurred in the basal 20 mm of the blade (0-20 millimeters above the ligule) and was maximum at 9 to 12 millimeters. Eight 3-millimeter long segments were sampled along the length of the elongation zone and analyzed for water-soluble carbohydrates. Sucrose concentration was high in the zone of cell division (0-6 millimeters) whereas monosaccharide concentration was high at and distal to the location where cell elongation terminated (20 millimeters). Fructan concentration increased in the basal part, then remained constant at about 85% of the total mass of water-soluble carbohydrates through the remainder of the elongation zone. Data on spatial distribution of growth velocities and substance contents (e.g. microgram fructan per millimeter leaf length) were used to calculate local net rates of substance deposition (i.e. excess rates of substance synthesis and/or import over substance degradation and/or export) and local rates of sucrose import. Rates of sucrose import and net deposition of fructan were positively associated with local elongation rate, whereas net rates of sucrose deposition were high in the zone of cell division and those of monosaccharide were high near the termination of elongation. At the location of most active elongation imported sucrose (29.5 milligrams per square decimeter per hour) was used largely for synthesis of structural components (52%) and fructan (41%).

Journal Article↗
PubMed1985

Influence of genetic composition of test-animal populations on chronic toxicity studies used for risk estimation.

A lifespan exposure of mice to benzidine dihydrochloride was conducted for 33 m using both sexes of two populations of mice with the same gene pool. One population was the genetically homogeneous F1 hybrid produced by crossing BALB/cStCrlC3Hf/Nctr males with C57BL/6jfC3Hf/Nctr females. The second population consisted of genetically heterogenous monohybrid cross (MC) offspring produced by mating the F1 hybrids inter se. Data comparisons were made to determine if gene distribution among members of a population affects the response to a toxic insult. Endpoints tested consisted of mortality, liver tumor incidence and time of tumor onset, mortality from reticulum-cell sarcoma, and body weights. In most instances it was noted that among animals not dosed (controls), the F1 population had lower background incidence of lesions and lived longer than the MC population. However, among the dosed animals, the F1 mice were generally more susceptible to the toxic agent and developed higher incidences of the chemically induced lesions than did the MC population. The F1 hybrid population gave a more conservative estimate of risk than did the MC population. The calculation of the liver tumor risk for these two populations showed that lifespan exposure to benzidine would be predicted to result in a larger number (higher risk) when using the F1 data. A 4.5-fold difference in the toxic response was observed between the F1 females and the MC males. This emphasizes the importance of gene distribution in risk estimation studies.

Animals↗
PubMed1985

The postnatal ontogeny of rat uterine glands and age-related effects of 17 beta-estradiol.

In the uterus of the newborn rat, only the luminal epithelium is differentiated. Differentiation of musculature and glandular epithelium occurs postnatally, the latter originating as invaginations of the luminal epithelium into the stroma. Using unambiguous criteria for quantification of uterine glands, we find that uterine glands first appear on postnatal day 9 after which the increase in the number of glands is rapid and synchronous, with approximately 4.4 glands per uterine section reached by day 15. Between days 15 and 35, the number of glands per uterine section varied in a cyclic manner with an amplitude of approximately one gland per uterine section and a period of 6-7 days. Although exogenous 17 beta-estradiol (E2) administered on postnatal days 1-5 induced slight premature gland genesis, the number of glands per uterine section was approximately 30% lower between days 15-26 compared to untreated animals. Administration of E2 during the period of normal gland genesis (days 10-14) induced a dose-related delay in the onset of appearance of glands. After this, gland genesis proceeded at a normal rate; however, the maximum levels reached were again generally below those observed in untreated controls. E2 administered after uterine glands were established (days 20-24) induced a small increase in gland number compared to controls. E2 also induced temporary hypertrophy, hyperplasia, and cellular degeneration in the luminal epithelium during each of the dosing periods without corresponding changes in the stroma or myometrium. These data demonstrate that uterine gland genesis occurs between postnatal days 9-15 and that exogenous estrogen can alter, in an age-specific manner, both uterine gland genesis and the number of glands per uterine section.

Age Factors↗
PubMed1985

Inhibition of rat uterine gland genesis by tamoxifen.

We have previously shown that rat uterine gland genesis occurs rapidly and synchronously between postnatal days 9-15. Exogenous estrogens either stimulate or inhibit gland genesis depending on dose and age at administration. We therefore examined the developmental effects of the triphenylethylene antiestrogen tamoxifen, which exhibits both estrogen agonist and antagonist properties, in the postnatal rat uterus. Tamoxifen administered sc in oil on postnatal days 1-5 or days 10-14 caused dose-related inhibition of uterine gland genesis which persisted to day 26 or day 60, respectively. Tamoxifen administered on postnatal days 20-24, which is after the age of normal gland genesis, did not alter the number of preexisting glands. A 24-h exposure to tamoxifen inhibited 17 beta-estradiol (E2)-induced ornithine decarboxylase (ODC) activity measured 6 h after E2 administration in 14-day-old rats. Treatment with tamoxifen before or during the period of gland genesis also reduced uterine responsiveness to a single dose of E2 as measured by both uterine weight gain (after a 24-h exposure on days 14, 19, 22, and 26) and the pattern of E2-induced ODC activity in 26-day-old rats. Control rats respond to E2 with peaks of ODC activity at 6 and 18 h after administration. Treatment with tamoxifen on either postnatal days 1-5 or 10-14 reduced the 18-h peak to approximately half of controls but did not affect the 6-h E2-induced ODC peak. Analysis of both nuclear and translocatable cytosol estrogen receptor in uteri from 26-day-old rats indicate that neither the dissociation constant (KD) nor the number of binding sites was affected by tamoxifen treatment on postnatal days 1-5 or 10-14.

Age Factors↗
PubMed1984

Sex and strain differences in the developmental activity profile of the rat tested over clean vs home cage bedding.

In the first of two experiments, CD rat litters were used to characterize activity patterns obtained in a size-adjustable, single photodetector chamber. Beginning on postnatal Day 10 or 12, pups were tested repeatedly over clean bedding (C) or over bedding removed from each pup's home cage (HC). In C rats of both sexes and in HC females, short-term activity levels peaked on Day 16. However, HC males displayed an earlier and even greater elevation in activity from Day 12 to 16. This overall pattern was found in rats tested either every second or fourth day. In the second experiment, Long-Evans pups were assigned to each testing condition (C vs HC) and activity measured beginning on Day 12. Peak levels were seen in all Long-Evans rats on Day 16 and only females showed significant alterations as a function of bedding condition. When overall activity levels of the two strains were compared, significant differences were found on Days 12, 24, 30, and 120 in males, and 12, 24, and 30 in females. Significant differences between strains in activity as a function of bedding condition were found in males on Days 12, 20, 24, and 120 and in females on Days 12, 30, and 60. These data confirm the generality of a developmental hyperactivity phase in isolated juvenile rats. However, different patterns of hyperactivity were found in male vs female rats across strains. CD males were more active in the presence of HC olfactory cues, while in Long-Evans rats, female activity was affected more by bedding condition.

Age Factors↗
PubMed1984

Blood flow changes and conceptal development in pregnant rats in response to caffeine.

Alterations in blood flow to the uterus and its contents during pregnancy have been suggested to account for the teratogenicity and/or embryotoxicity of several agents, including caffeine. Using a radioactive microsphere technique, blood flow to several maternal organs, including ovary, uterus, decidua, and chorioallantoic placenta (CAP), was measured following a single dose of 0 or 120 mg/kg caffeine by gavage to pregnant CD rats on Day 12 of gestation. At 1 or 4 hr after treatment, animals were anesthetized and strontium 85-labeled microspheres (25 micrometers diam) were infused into the left ventricle. Whole body and tissue radioactivity were determined. Maternal cardiac output (CO) and absolute flow (f1; ml/min), relative flow (f2; ml/min/g tissue), and flow as %CO (f3) to each tissue were calculated. Maternal CO was not altered. All blood flow parameters for ovaries, uterus, and bladder were reduced in treated animals at both time points except for absolute flow (f1) to the ovaries at 1 hr. Decidual changes included reduced weight at 1 hr, reduced f2 at 4 hr, and reduced f1 and f3 at both times. However, CAP weight and blood flow wre not significantly altered by caffeine treatment. Examination of conceptuses from thse litters, and from other animals at 24 hr after treatment or at term did not reveal any significant effect of this dose of caffeine on viability, growth, or physical development. The ratio of embryo to maternal blood caffeine concentrations was approximately 1, indicating free transfer of caffeine to the embryos.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Benzidine dihydrochloride: risk assessment.

Benzidine, recognized as a bladder carcinogen in man and as a liver carcinogen in experimental animals, is the chemical basis of as many as 200 commercial dyes. Physiological processes can metabolize these dyes to release benzidine, thereby creating a potential exposure hazard. To assess this hazard, both sexes of F1 hybrid (genetically homogeneous) and monohybrid (genetically heterogeneous) mice from a BALB/c male and C57BL/6 female cross were exposed for their respective lifespans to benzidine dihydrochloride in their drinking water at concentrations of 0, 30, 40, 60, 80, 120, and 160 ppm for males, and 0, 20, 30, 40, 60, 80, and 120 ppm for females. Animals were removed from the study when they were dead or moribund. This study was terminated after 33 months of exposure. Using the endpoint of hepatocellular adenomas and carcinomas, the Armitage Doll multistage model was used to describe the tumor rates in the experimental dose range and to obtain the upper confidence level on tumor rates. Linear interpolation was used between zero dose and the upper confidence level of the lowest experimental dosage for predicting potential low dose tumor rates. Dose-response effects on body weight, survival, and liver neoplasms were noted in both stocks. For each of the endpoints, the females were more susceptible than males and the F1 (homogeneous) stock was more susceptible than the monohybrid cross (heterogeneous). The calculated virtually "safe" dose predicted to produce less than one per million F1 female mice with a liver tumor is 0.045 ppb. One part per billion of benzidine dihydrochloride in the drinking water of these mice is estimated to produce liver tumors in less than 2.23 mice per 100,000 population.

Animals↗
PubMed1984

Carbohydrate metabolism in leaf meristems of tall fescue : I. Relationship to genetically altered leaf elongation rates.

The physiological bases for genetic differences in leaf growth rates were examined in two genotypes of tall fescue (Festuca arundinacea Schreb.) selected for a 50% difference in leaf elongation rate. Genotypes had similar dark respiration rates and concentrations of carbohydrate fractions in the leaf meristem and in each daily growth segment above the meristem. Dark respiration rates and concentrations of nonreducing sugars, fructans, and takadiastase-soluble carbohydrates were highest in leaf intercalary meristems and declined acropetally with tissue age. Concentrations of reducing sugars were 1.0% of dry weight in leaf meristems, 3.7% of dry weight in tissue adjacent to the meristem, then decreased progressively with distance from the meristem. Glucose, fructose, and myo-inositol comprised over 90% of the monosaccharides present in leaf meristems. Soluble protein concentration was 9.7 milligrams per gram fresh weight in leaf meristems, 5.5 milligrams per gram in tissues immediately above the meristem and, thereafter, increased linearly with distance from the meristem.Leaf meristems of the genotype exhibiting rapid leaf elongation contained 30% more soluble protein than those of the genotype selected for slow leaf elongation. The 4-fold difference in size of the leaf meristem appeared to be more important in influencing leaf elongation than were other characteristics examined.

Journal Article↗
PubMed1984

Carbohydrate Metabolism in Leaf Meristems of Tall Fescue : II. Relationship to Leaf Elongation Rates Modified by Nitrogen Fertilization.

Our objective was to examine alterations in carbohydrate status of leaf meristems that are associated with nitrogen-induced changes in leaf elongation rates of tall fescue (Festuca arundinacea Schreb.). Dark respiration rates, concentrations of nonstructural carbohydrates, and soluble proteins were measured in leaf intercalary meristems and adjacent segments of elongating leaves. The two genotypes used differed by 43% in leaf elongation rate. Application of high nitrogen (336 kilograms per hectare) resulted in 140% higher leaf elongation rate when compared to plants receiving low nitrogen (22 kilograms per hectare). Leaf meristems of plants receiving high and low nitrogen had dark respiration rates of 5.4 and 2.9 microliters O(2) consumed per milligram structural dry weight per hour, respectively. Concentrations of soluble proteins were lower while concentrations of fructan tended to be slightly higher in leaf meristems of low-nitrogen plants when compared to high-nitrogen plants. Concentrations of reducing sugars, nonreducing sugars, and takadiastase-soluble carbohydrate of leaf meristems were not affected by nitrogen treatment. Total nonstructural carbohydrates of leaf meristems averaged 44 and 39% of dry weight for low- and high-nitrogen plants, respectively. Within the leaf meristem, approximately 74 and 34% of the pool of total nonstructural carbohydrate could be consumed per day in high- and low-nitrogen plants, respectively, assuming no carbohydrate import to the meristem occurred. Plants were able to maintain high concentrations of nonstructural carbohydrates in leaf meristems despite a 3-fold range in leaf elongation rates, suggesting that carbohydrate synthesis and transport to leaf intercalary meristems may not limit leaf growth of these genotypes.

Journal Article↗
PubMed1984

Postnatal toxicity following prenatal reserpine exposure in rats: effects of dose and dosing schedule.

Pregnant CD rats were treated subcutaneously with 0, 0.1, 0.33, or 1.0 mg reserpine/kg/day either on Days 12-15 or on Days 16-19 of gestation. Dams were allowed to deliver and litters (4 +/- 1 of each sex) were weighed weekly and held to 21 days of age. Basal ornithine decarboxylase (ODC) activity and neurochemical determinations were made on hearts and brains, respectively, from pups culled from litters on postnatal Day 1, and from two males and two females/litter at 21 days of age. Following both treatment schedules, the high dose of reserpine resulted in maternal weight loss during dosing, increased stillborn pups, reduced pup weight at birth, retarded postnatal growth, and decreased survival to 21 days of age. Basal cardiac ODC activity was reduced to 33% of control levels only on Postnatal Day 1 in both high-dose groups, while absolute heart weight decreased and relative heart weight increased in these pups. Whole-brain concentrations of two neurotransmitter metabolites, 3-4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA), were increased only at Postnatal Day 1 in the high dose group treated on Days 12-15 of gestation. No other changes were found in concentrations of these metabolites or in the transmitters dopamine and serotonin. The only effect found following administration of 0.33 mg/kg reserpine was a reduction in maternal weight gained during both dosing periods. No signs of toxicity were observed following low-dose exposure on either schedule. Most previously reported postnatal functional studies following reserpine exposure have used mid- to late-gestational treatment with 1.0 mg/kg, a dose shown here to result in marked overt maternal and fetal toxicity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Impotence in medical clinic outpatients.

One thousand one hundred eighty men in a medical outpatient clinic were screened as to the presence of impotence. Four hundred one men (34%) were impotent, and of those, 188 (47%) chose to be examined for their problem. After a comprehensive evaluation the following diagnoses were obtained: medication effect, 25%; psychogenic, 14%; neurological, 7%; urologic, 6%; primary hypogonadism, 10%; secondary hypogonadism, 9%; diabetes mellitus, 9%; hypothyroidism, 5%; hyperthyroidism, 1%; hyperprolactinemia, 4%; miscellaneous, 4%; and unknown causes, 7%. The mean age of the impotent patients was 59.4 years, and the prevalence of alcoholism was 7%. Luteinizing hormone, follicle-stimulating hormone, testosterone, thyroxine, triiodothyronine (T3), T3 resin uptake, and prolactin studies were necessary to diagnose individual cases. We conclude that erectile dysfunction is a common and often overlooked problem in middle-aged men followed in a medical clinic.

Alcoholism↗
PubMed1983

Photosynthesis in Tall Fescue : IV. Carbon Assimilation Pattern in two Genotypes of Tall Fescue Differing in Net Photosynthesis Rates.

We previously reported that the net photosynthetic rate of a decaploid genotype (I-16-2) of tall fescue (Festuca arundinacea Schreb.) was 32 to 41 versus 22 milligrams CO(2) per square decimeter per hour in a hexaploid genotype (V6-802) (Randall, Nelson, Asay Plant Physiol 59: 38-41). The high rate was later correlated with increases in total ribulose 1,5-bisphosphate carboxylase protein (17%) and activity (27%) (Joseph, Randall, Nelson Plant Physiol 68: 894-898). This report characterizes photosynthesis with respect to light saturation and early products of photosynthesis in an attempt to identify regulatory metabolic site(s) in these two genotypes. Analysis of the early products of photosynthesis indicated that both genotypes fixed CO(2) via the Calvin-Benson cycle with phosphoglyceric acid as the initial primary product. Both genotypes had similar (14)C-labeled intermediates. Sucrose was the primary sink of (14)CO(2) assimilation. After 10 min of (14)CO(2) assimilation with attached leaves, sucrose accounted for 89% (decaploid) and 81% (hexaploid) of the total (14)C incorporated. In 10 min, this amounted to 1.3 (decaploid) and 0.8 (hexaploid) mumol [(14)C]sucrose formed g fresh weight(-1) and reflected the observed differences in photosynthetic rates. There was limited labeling of starch (1%) and fructan (1%). Results of total nonstructural carbohydrates and P(i) analysis also demonstrated sucrose was the predominant carbohydrate in fescue leaves. Quantitative differences in sucrose and P(i) between the two genotypes may reflect changes in partitioning and this possibility is discussed.

Journal Article↗
PubMed1982

Blood flow during pregnancy in the rat: I. Flow patterns to maternal organs.

Normal blood flow patterns to several maternal organs were characterized in individual CD rats, nonpregnant (NP) or on day 6, 7, 8, 10, 11, 12, 13, 16, 18, or 20 of gestation using the radioactive microsphere technique. Weights and flow values were determined for several uterine tissue samples as well as maternal organs. No significant changes were found in blood flow to the stomach, spleen, and urinary bladder of these animals. There also were no remarkable changes as pregnancy progressed in blood flow to the lungs, suggesting that no marked arterial-venous shunting occurs in maternal placental tissues over gestation. Slight but consistent decreases in absolute (ml/min) and relative (ml/min/g tissue) blood flow to the brain were noted, and percent cardiac output (CO) was significantly decreased on all days of gestation except day 7. Complex changes were observed in blood flow to the kidneys, liver, adrenals, and heart. Absolute flow to the kidneys and liver reached maximum values on day 11, although percent CO delivered to both organs was consistently reduced throughout gestation. Absolute flow to the heart and adrenals peaked on day 13 and days 11-12, respectively. Absolute flow to the ovaries increased nearly 5-fold from the NP state (0.36 +/- 0.11) to day 20 of pregnancy (1.61 +/- 0.33). Interlitter differences in ovarian blood flow during midgestation were found to be a result of differences in litter size and distribution of embryo/fetuses between the two uterine horns. The fact that the majority of changes observed in maternal organ flow coincide with placental development, rapid augmentation of total uterine flow, and/or maternal hormonal changes suggests that these patterns may be important indicators of the dynamic physiology of pregnancy.

Animals↗