Biomedical subjects

S E Nelson

Publications and source records attributed to S E Nelson.

At least 37 records · Page 2Linked to original sources

PubMed1997

Expression of a murine gonadotropin-releasing hormone receptor-luciferase fusion gene in transgenic mice is diminished by immunoneutralization of gonadotropin-releasing hormone.

A line of transgenic mice harboring a fusion gene consisting of 1900 bp of proximal 5'-flanking region from the murine GnRH receptor gene linked to the complementary DNA encoding luciferase was established to determine whether this promoter can direct tissue-specific expression in vivo and serve as a model for identifying the molecular mechanisms underlying hormonal regulation of this gene. Of 10 tissues screened, luciferase was detected predominantly in pituitary gland, but also in brain and testis. To assess hormonal regulation, luciferase activity was measured in intact males and ovariectomized females treated with an anti-GnRH serum alone, and in combination with testosterone or 17beta-estradiol. No effect of steroid treatment on transgene expression was detected. However, immunoneutralization of GnRH resulted in decreased serum LH concentrations and suppressed pituitary expression of luciferase. Furthermore, the effects of GnRH antiserum could be prevented by the administration of a noncross-reactive GnRH agonist. Thus, 1900 bp of 5'-flanking DNA from the murine GnRH receptor gene are sufficient to target luciferase expression in transgenic mice to established sites of GnRH receptor gene expression. Furthermore, we suggest that GnRH regulation of GnRH receptor gene expression is mediated by regulatory elements residing within 1900 bp of the 5'-flanking region.

Animals↗

PubMed1997

The tripartite basal enhancer of the gonadotropin-releasing hormone (GnRH) receptor gene promoter regulates cell-specific expression through a novel GnRH receptor activating sequence.

The molecular mechanisms regulating restricted expression of GnRH receptor and gonadotropin subunit genes to gonadotrope cells have been the focus of intense interest. Using deletion and mutational analysis we have identified a tripartite enhancer that regulates cell-specific expression of the GnRH receptor gene in the gonadotrope-derived alphaT3-1 cell line. Individual elements of this enhancer include binding sites for steroidogenic factor-1; activator protein 1 (AP-1); and a novel element referred to as the GnRH receptor activating sequence (GRAS). Mutation of each element alone results in loss of approximately 60% of promoter activity. Combinatorial mutations of any two elements decreases promoter activity by approximately 80%. Finally, mutation of all three elements reduces promoter activity to a level not different from promoterless vector. Using 2-bp mutations, we have defined the functional requirements for transcriptional activation by GRAS. The core motif of GRAS is at -391 to -380 bp relative to the start site of translation and has the sequence 5'-CTAGTCACAACA-3'. Three copies of GRAS or GRAS with a 2-bp mutation (muGRAS) were cloned into a luciferase expression vector immediately upstream of the thymidine kinase minimal promoter (TK) and tested for expression in alphaT3-1 cells. When compared with TK promoter alone, activity of 3xGRAS-TKLUC was increased by more than 5-fold while activity of 3xmuGRAS-TKLUC was unchanged. When 3xGRAS-TKLUC was transfected into a variety of nongo-nadotrope cell lines, it did not increase activity of the TK promoter. We propose that basal activity of the GnRH receptor gene is regulated by a tripartite enhancer, and the key component of this enhancer is an element, GRAS, that activates transcription in a cell-specific fashion.

Animals↗

PubMed1996

Palm olein in infant formula: absorption of fat and minerals by normal infants.

Palm olein, a low-melting fraction of palm oil, and soy oil can be combined to obtain fat blends with proportions of palmitic and oleic acids similar to those of human milk. We compared the absorption of fat and calcium by infants fed a formula containing a blend of palm olein (53%) and soy oil (47%) (Formula PO/S) with that by infants fed a formula containing a blend of soy oil (60%) and coconut oil (40%) (Formula S/C). In a randomized crossover design, one study was performed with each formula in each of 11 normal infants ranging in age from 27 to 161 d. Six of the infants were admitted for 72-h metabolic balance studies. In the other five infants, feces (with some admixture of urine) were collected at home for 96 h by using acid-washed cloth diapers. Mean (+/- SD) absorption of fat was 90.6 +/- 1.6% of intake when Formula PO/S was fed and 95.2 +/- 1.1% of intake when Formula S/C was fed; the difference was significant (P < 0.001). The difference in excretion of fat by infants fed the two formulas was explained by the difference in excretion of palmitic acid. Absorption of calcium averaged 39.0 +/- 8.3% of intake with Formula PO/S and 48.4 +/- 10.3% with Formula S/C; the difference was significant (P < 0.01). We conclude that fat is less well absorbed from a mixture of 53% palm olein and 47% soy oil than from a mixture of 60% soy oil and 40% coconut oil, and that absorption of calcium is less from a formula containing palm olein, presumably because of the formation of insoluble calcium soaps of unabsorbed palmitic acid.

Absorption↗

PubMed1995

What is the safe protein-energy ratio for infant formulas?

Infants eat primarily to satisfy energy needs and the safe amount of protein in infant formulas (ie, the amount adequate for nearly all infants) is therefore expressed as the protein-energy ratio. We studied male infants aged 8-112 d fed milk-based formulas. One group (experimental group) was fed formulas that provided protein-energy ratios of 3.73 g/MJ (1.56 g/100 kcal) from 8 to 27 d of age, gradually decreasing to 2.99 g/MJ (1.25 g/100 kcal) from 84 to 111 d of age. Growth rates and serum albumin and urea nitrogen of these infants were compared with those of a concurrently studied control group and a previously studied large reference group. Gains in weight and concentrations of serum albumin of the three groups were not significantly different. Gains in length were significantly less for the experimental group than for the reference group. Serum urea nitrogen was significantly less in the experimental group than in the control group or reference group. We conclude that the protein-energy ratios of the experimental formula diet were below the safe level. Because the decrease in growth rate of the experimental group was rather small (demonstrable only in comparison with the large reference group), and because serum albumin of the experimental group increased with age as in normally nourished infants, we suspect that the safe protein-energy ratio of infant formulas lies closer to the ratios fed to the experimental group than to the ratio [approximately 5.0 g/MJ (2.1 g/100 kcal)] in currently marketed milk-based formulas.

Blood Urea Nitrogen↗

PubMed1995

Erythrocyte incorporation of iron by 56-day-old infants fed a 58Fe-labeled supplement.

In an effort to obtain information about absorption of supplemental iron by breast-fed infants during the early months of life, we determined erythrocyte incorporation of a stable iron isotope, administered to 56-d-old breast-fed infants in the form of a 58Fe-labeled vitamin-iron supplement. Infants of similar age fed a milk-based formula low in iron (approximately 4 mg/L) were also studied. The 58Fe-labeled vitamin-iron supplement was given between feedings. Fourteen days after administration of 58Fe, mean erythrocyte incorporation of the isotope was 7.8% of the dose by breast-fed infants and 4.4% of the dose by formula-fed infants. The feeding-related difference was statistically significant, probably reflecting the greater quantities of inhibitors of iron absorption in the intestines of formula-fed infants. With mean iron intake from the 58Fe-labeled vitamin-iron supplement of 7.99 mg for the breast-fed infants, erythrocyte incorporation of 7.8% of the dose corresponded to 0.62 mg, a value in the range of the estimated requirement for absorbed iron. We conclude that 2-mo-old breast-fed infants are able to absorb nutritionally significant amounts of iron from an iron supplement.

Breast Feeding↗

PubMed1994

Decreased treatment time due to changes in technique and practice philosophy.

A study was conducted to evaluate the impact of practice modifications on treatment time for patients in a private orthodontic office. Two patient groups were studied, consisting of Class I nonextraction, adult dentitions treated by one of the authors. One group (28 cases) was treated with the standard Begg technique and conventional motivation, hygiene, and finishing practices. The other (25 cases) was treated with the Tip-Edge appliance along with specific modifications to motivation, hygiene and finishing techniques. The average treatment time for the Tip-Edge group was 12.80 months versus 20.89 months for the Begg group. The use of motivational techniques and a specific mission and philosophy within a private orthodontic practice can help reduce total treatment time. The Tip-Edge appliance may reduce treatment time in Class I nonextraction therapy.

Adult↗

PubMed1994

Absorption and retention of dietary and supplemental fluoride by infants.

There is a widespread belief that an adequate intake of fluoride during the pre-eruptive stage of enamel formation (i.e., from the diet in frequent small doses throughout the day) will be protective against caries in later life. To obtain data on bio-availability and retention of fluoride in one age group (infants), we studied 3 treatment regimens: In Regimen A, small amounts of fluoride were obtained from the diet in frequent doses throughout the day; in Regimen B, a fluoride supplement (0.25 mg) was given once each day with a feeding; Regimen C was similar to regimen B except that the fluoride supplement was given 1 h before a feeding. For the 3 regimens, the respective mean absorptions of fluoride were 90.1, 88.9, and 96.0% of intake, and the respective retentions were 12.5, 47.1, and 52.3% of intake. Neither the difference in absorption nor the difference in retention between regimens B and C was statistically significant. By subtracting the background urinary excretion of fluoride (i.e., excretion of fluoride while diet was the sole source of fluoride) from the excretion after administration of the fluoride supplement, we calculated that 68.1% of the supplement was retained in Regimen B and 73.0% of the supplement in Regimen C. The difference was not significant.

Biological Availability↗

PubMed1994

Fluoride pharmacokinetics in infancy.

Fluoride pharmacokinetic data are presented for infants given a fluoride supplement. Seventeen infants participated in a total of 20 studies. On one day, 0.013 mmol (0.25 mg) fluoride was given as a supplement (fluoride supplement study), and on another day a placebo was given (control study). Samples of plasma and urine were collected for 5 h and analyzed for fluoride. During control studies fluoride intake averaged 0.15 mumol/kg (2.9 micrograms/kg), and plasma fluoride concentrations ranged from 0.05 to 0.11 mumol/L (10 to 20 micrograms/L). In nine instances, the quantity of fluoride excreted in the urine was more than twice that consumed. When the fluoride supplement was given, total fluoride intake averaged 1.93 mumol/kg (36.6 micrograms/kg). Plasma peak concentration was reached by 30 min in 14 studies and by 60 min in six studies. Mean plasma peak fluoride concentration was 3.3 mumol/L (63 ng/mL). Area under the plasma concentration curve averaged 236 nmol.m-1 x min (4479 ng.mL-1 x min) and was not related to the dose of fluoride. The rate of urinary excretion was significantly correlated with rate of urinary flow. When the dose of fluoride was expressed per unit of body weight, fluoride retention was strongly related to the dose. Retention of the fluoride absorbed from the fluoride dose ranged from 75.4 to 87.6%. Plasma clearance averaged 6.8 mL.kg-1 x min-1 and decreased significantly with age. Net fractional clearance (renal clearance of the fluoride dose/GFR) averaged 56.7%, which was significantly greater than the 29% observed during the control studies.(ABSTRACT TRUNCATED AT 250 WORDS)

Dental Caries↗

PubMed1994

Identification of a major prolactin-regulated protein as 20 alpha-hydroxysteroid dehydrogenase: coordinate regulation of its activity, protein content, and messenger ribonucleic acid expression.

We have previously reported that an abundant 37,000 mol wt protein with a pI of 6.15 (37K) is expressed specifically in the corpus luteum and is markedly inhibited by PRL. To identify the 37K, amino acid sequence analysis of the protein was performed. The 37K protein showed sequence similarity with rabbit 20 alpha-hydroxysteroid dehydrogenase (20 alpha HSD), chlordecone reductase, prostaglandin synthase, and 3 alpha-hydroxysteroid dehydrogenase, which are members of the aldo-keto reductase group of enzymes that catalyze the NADPH-dependent reduction of carbonyl compounds. Comparison of 20 alpha HSD activity with the level of 37K in the corpus luteum throughout pregnancy demonstrated a close correlation between enzyme activity and luteal levels of the protein. Both protein and enzyme activity were low early in pregnancy, reached a nadir between days 5-19, and reappeared abruptly between days 19-21 of pregnancy. To establish that the enzyme activity is intrinsic to the 37K, the protein was purified from sodium dodecyl sulfate-polyacrylamide electrophoresis gels (SDS-PAGE), renatured, and assayed for 20 alpha HSD activity. The renatured protein exhibited substantial 20 alpha HSD activity. As 20 alpha HSD is known to play a major role in the termination of pregnancy in the rat, it was of interest to examine whether the rapid appearance of the 37 K protein at the end of pregnancy is accompanied by the induction of 20 alpha HSD gene expression. Northern blot analysis using a rabbit cDNA for 20 alpha HSD indicated that the pattern of 20 alpha HSD mRNA expression in the corpus luteum closely paralleled the ontogeny of 20 alpha HSD enzyme activity as well as 37K protein levels. Our studies demonstrated that 20 alpha HSD protein and mRNA levels are coordinately regulated, and that the profound inhibitory effect of PRL on 20 alpha HSD activity is apparently due to inhibition of 20 alpha HSD gene expression, leading to the disappearance of the protein from the corpus luteum.

20-Hydroxysteroid Dehydrogenases↗

PubMed1994

Pregnancy increases guanosine 3',5'-monophosphate in the myometrium independent of nitric oxide synthesis.

The mechanism for myometrial quiescence during pregnancy is unknown. cGMP plays an integral role in the relaxation of smooth muscle, and nitric oxide (NO) is the most important endogenous activator of soluble guanylate cyclase. The purpose of this study was to determine the effect of gestational age on myometrial cGMP and NO synthase (NOS) activity in the guinea pig. Myometrial cGMP content (measured by RIA) rose slowly until 0.49 (fraction of pregnancy completed) gestation before abruptly increasing to 200 times the non-pregnant control value. It then declined precipitously after 0.87 gestation. Of the known isoenzymes of NOS, the messenger RNAs coding for both endothelial and neuronal NOS could be amplified from the myometrium of pregnant and nonpregnant animals using reverse transcriptase-polymerase chain reaction, but inducible NOS messenger RNA was not found. Myometrial calcium-dependent NOS activity (measured by the conversion of L-[U-14C]arginine to [U-14C]citrulline) declined slowly with advancing gestation (r2 = 0.096; slope = -0.34; P = 0.01), but never differed significantly from the activity in nonpregnant animals [31.1 +/- 11 (term pregnancy) vs. 56.9 +/- 16 (nonpregnant) pmol/min.g; P = NS]. Calcium-independent activity declined shortly after conception, and then rose toward the nonpregnant level (r2 = 0.19; slope = 0.45; P = 0.0009). However, at no time was it significantly different from that in the nonpregnant animal. Pregnancy had no effect on myometrial L-arginine and L-citrulline content. The administration of L-nitro-arginine methyl ester (200 mg/kg) to inhibit NOS dramatically increased blood pressure and reduced fetal renal NOS activity, but had no effect on the myometrial cGMP content. Estradiol (500 micrograms/kg for 5 days) modestly increased cGMP, but in contrast to many tissues in which estradiol increases NOS, it had no effect on myometrial NOS activity. We conclude that pregnancy dramatically increases cGMP by a mechanism independent of NOS. The stimulus remains to be identified. The temporal change in cGMP concentration is consistent with the hypothesis that cGMP mediates myometrial quiescence during pregnancy.

Animals↗

PubMed1993

Erythrocyte incorporation of ingested 58Fe by 56-day-old breast-fed and formula-fed infants.

As an index of iron absorption, erythrocyte incorporation of the stable isotope, 58Fe, was determined 14 and 42 d after the administration of 58Fe-labeled ferrous sulfate to 56-d-old exclusively breast-fed infants and to infants fed a low-iron (1.8 mg/L) formula. Each infant received a dose of 0.6 to 1.0 mg of iron with ascorbic acid between feedings on each of 3 consecutive d. Fourteen d after administration of the 58Fe-labeled iron doses (age 70 d), arithmetic mean incorporation of the 58Fe label into erythrocytes by breast-fed infants was 20.0% of the dose--only slightly less than that reported for erythrocyte incorporation of iron by fasting adults fed small quantities of 59Fe-labeled human milk. Erythrocyte incorporation of iron by the formula-fed infants was 6.9% of the dose, suggesting that, even between feedings, components of infant formula exerted a major inhibitory effect on iron absorption. For reasons that are not clear, the percentage of the administered label incorporated into erythrocytes was significantly greater in breast-fed (but not in formula-fed infants) at 112 d of age than at 70 d of age.

Absorption↗

PubMed1992

The cAMP-dependent signalling cascade in the two luteal cell types of the pregnant rat corpus luteum.

Corpora lutea of rats, like those of many other species, contain two sub-populations of luteal cells. In this report we sought to determine whether the luteinizing hormone (LH)- and beta-adrenergic cAMP signal transduction pathways known to be present in rat corpora lutea were segregated into separate luteal cell types. Results showed that large rat luteal cells, obtained on day 3 of pregnancy, exhibited elevated LH- and most notably epinephrine-stimulated adenylyl cyclase activities but equivalent cAMP-dependent catalytic protein kinase and total regulatory subunit cAMP binding activities compared to small luteal cells. Progesterone production by the large cell was greater than that by the small cell but both cells were equally sensitive to stimulation of progesterone by LH. However, neither the large nor the small rat luteal cell produced significant progesterone in response to epinephrine despite a marked epinephrine-stimulated adenylyl cyclase in both cell populations. The LH-stimulated progesterone synthetic response of the two sub-populations of rat luteal cells is more similar to that of the developing monkey corpus luteum and contrasts sharply with that of ruminants.

Adenylyl Cyclases↗

PubMed1992

Isolation, characterization, and culture of cell subpopulations forming the pregnant rat corpus luteum.

The aim of this investigation was to isolate, characterize, and culture the small and large luteal cell subpopulations forming the corpus luteum of the pregnant rat. Since the large luteal cells are extremely fragile and do not survive standard cell dispersion, a method which allows the survival and the long-term culture in serum-free media of small and large cells was developed. The two luteal cell populations differed not only by their size but also by their morphology in culture. The small luteal cells (12-20 mu in diameter) are characterized by a large oval nucleus, contain few lipid droplets and have a stellate shape. In contrast, the large luteal cells have a smaller spherical nucleus, high lipid content, and do not flatten out completely in culture, most probably due to the abundance of lipid droplets. Both luteal cell types express 3 beta HSD and the cytochrome P450 enzymes involved in steroidogenesis. However, it is the lipid filled large luteal cells that secrete the most progesterone, androgen, and estradiol; express greater amounts of P450scc and P450AROM; and possess more PRL and LH receptors. Despite the greater expression of LH receptor in the large luteal cells, small and large luteal cells responded to LH with equal increase in steroidogenic output. In serum free culture, luteal cells produced progesterone for up to 20 days; however, an exogenous source of cholesterol was a prerequisite for maximal progesterone secretion. The pattern of progesterone secretion by cultures of small and large luteal cells differed remarkably from that of mixed cell population. When nonsteroidogenic corpus luteum cells were cocultured with the large luteal cells, a severalfold increase in progesterone secretion was observed. This stimulation occurred even when cells were cocultured in the absence of exogenous source of cholesterol. In summary, a successful method was developed to disperse, isolate, and independently culture the two luteal cell populations forming the rat corpus lutem. The results indicate that the marked difference in the steroidogenic capacity of these two cell populations is due, in large part, to the difference in their size rather than to their origin in the follicle. In addition, the results have revealed an important effect of the nonsteroidogenic cells forming the corpus luteum on luteal cell steroidogenesis.

Androstenedione↗

PubMed1992

Differential capacity for cholesterol transport and processing in large and small rat luteal cells.

The aim of this investigation was to determine whether a specific luteal subpopulation is responsible for the hypertrophic development of the corpus luteum at midpregnancy in the rat and to determine whether there was an underlying cellular basis for the differential production of steroids by the luteal cell subtypes. To examine this, we have dispersed and separated rat luteal steroidogenic cell populations into small (< 20 microns) and large (> 30 microns) cell types by elutriation. Luteal cells were examined at early (day 3) and midpregnancy (day 14) for differences in protein content and for differential expression of proteins required for steroid production. Specific proteins examined include the P450side chain cleavage enzyme (P450scc), adrenodoxin and adrenodoxin reductase, proteins required for cholesterol conversion to progestagens in the corpus luteum, and sterol carrier protein-2 (SCP2), a protein thought to be involved in intracellular cholesterol transport. The cytochrome P450(17)alpha hydroxylase (P450(17)alpha), a key enzyme responsible for androgen biosynthesis was also examined in the isolated luteal cells. The large luteal cell population displayed an increase in total cellular protein content while the small cell type did not change with luteal development. In addition, the large luteal cells expressed proteins unique to or elevated in that cell type. Analysis by two-dimensional polyacrylamide gel electrophoresis revealed that the large cell-specific proteins had molecular masses of 23 K and 32 K and that a 14 kilodalton (kDa) protein was elevated in the large cell type relative to the small cells. The small luteal cell on day 3 of pregnancy expressed a 36 kDa protein which was barely detectable in the large cell. Immunocytochemical and Western analysis indicated that the large luteal cells contain 5.3-fold more SCP2 (P < 0.05) and 5.6-fold more P450scc (P < 0.001) relative to the small cell type. Immunocytochemical staining of adrenodoxin and adrenodoxin reductase indicate these proteins were elevated in the large cell as well. Human CG administration stimulated P450(17)alpha expression mainly in the large luteal cell population. The results of this investigation indicate, for the first time, that the large luteal cell of the rat, in contrast to the small cell type, undergoes a dramatic increase in protein content with luteal development, and that with this increase in cell size there is a concomitant increase in the large cell capacity to produce steroids. This occurs as a direct result of the enhanced expression of SCP2, P450scc, adrenodoxin and adrenodoxin reductase, proteins specifically required to transport and process cholesterol for steroid production in the large luteal cell.

Adrenodoxin↗

PubMed1992

Hormonal and immunological characterization of the 32 kilodalton ovarian-specific protein.

Recent studies from this laboratory have shown that the large luteal cell of the pregnant rat contains an abundant 32 kilodalton (32K) phosphoprotein which is up-regulated by estradiol. In order to assess the potential importance of this protein and to more fully understand its function, a specific polyclonal antibody was produced against the 32K and was used to examine its intraovarian localization, its tissue specificity, and its developmental regulation. Immunocytochemical localization of the 32K in the ovary of the pregnant rat found this protein to be selectively and abundantly expressed in the corpus luteum. Immunofluorescence study of small and large luteal cell populations clearly revealed an extensive localization of the 32K in the large luteal cells. Western blot analysis revealed that the 32K was absent from all steroidogenic and nonsteroidogenic tissues. Whereas this protein was absent from all other tissues examined in the rat, it was clearly expressed in corpora lutea of different animal species, including the mouse, hamster, cow, human, and pig. Although undetectable by immunohistochemistry, Western blot analysis showed this protein to be present in the follicle but at levels markedly lower than in the corpus luteum. Analysis of theca and granulosa cells revealed the presence of the 32K in both cell types. To further examine the developmental expression of this protein throughout gestation, Western blot analysis of microsomal fractions isolated from rat corpora lutea on days 3-21 of pregnancy was performed. The 32K was detected at low levels in early pregnancy, increased markedly on day 11, reached a peak on days 14-15, and remained elevated through day 21. Treatment with estradiol and PRL increased the content of the 32K in the corpus luteum. Human CG, known to cause follicular development to the preovulatory stage and to enhance luteal estradiol synthesis, also increased levels of the 32K in the corpus luteum, while it concomitantly decreased this protein in the follicle. In summary, the presence of a unique ovarian-specific 32 kilodalton protein has been established. This protein, which is present in low abundance in theca and granulosa cells, is localized to the large luteal cell and becomes abundantly expressed during midpregnancy, a time when there is a remarkable increase in luteal cell size and activity. Results of this study also demonstrate a multihormonal regulation of the 32K by tropic hormones. Thus, because of its apparent uniqueness and its timely and highly regionalized expression, the 32K may play a central role in the regulation of corpus luteum growth and function.

Animals↗

PubMed1991

Reference data on gains in weight and length during the first two years of life.

Serial data from studies of infants at the University of Iowa and from the Fels Longitudinal Study were used to develop sex-specific percentiles for increments in weight and recumbent length for selected intervals during the first 24 months of life. Weight increments are presented for 1-month intervals from birth to 6 months, 2-month intervals from birth to 12 months, and 3-month intervals from birth to 24 months. Length increments are presented for 2-month intervals from birth to 6 months, and for 3-month intervals from birth to 24 months of age. Weights and lengths at the target ages were obtained for the Iowa data by simple interpolation, and for the Fels data by fitting families of three-parameter mathematical functions to the serial data from ages 1 to 24 months. The tabular presentations are based on the Iowa data from birth to 3 months of age, on the combined Iowa and Fels data from 3 to 6 months of age, and on the Fels data from 6 to 24 months of age. We believe that these reference data will be useful in screening for deviations from normal growth and may aid in early detection of failure to thrive or excessive weight gain during early life.

Age Factors↗

PubMed1991

The development of virus-resistant alfalfa, Medicago sativa L.

We have generated more than 100 transgenic alfalfa plants, via Agrobacterium-mediated gene transfer, from genotypes selected from five alfalfa cultivars. These plants express the genes for kanamycin resistance and for the coat protein of alfalfa mosaic virus (AMV). The strongest expressers accumulated nearly 500 ng coat protein per mg soluble leaf protein. AMV inoculation of protoplasts from these strong expressers indicated that they were resistant to infection by AMV, while protoplasts from plants containing about a hundred-fold less coat protein and from control untransformed plants were not. Transgenic alfalfa plants containing large amounts of coat protein were, likewise, resistant to AMV. These plants did not develop systemic infections following inoculation with up to 50 micrograms/ml AMV, while inoculated control plants developed systemic infections following inoculation with as little as 10 micrograms/ml AMV. These results demonstrate that expression of the AMV coat protein gene confers resistance to AMV infection in transgenic alfalfa plants.

Capsid↗

PubMed1991

Gender-related differences in iron absorption by preadolescent children.

In a study of absorption of iron from meals by preadolescent children (Tanner stage 1), we had noted that erythrocyte incorporation of the extrinsic iron label was somewhat greater by girls than by boys. Although the difference was not significant, the observation seemed to warrant further study. Study A: A precisely determined quantity of ferrous sulfate enriched with the stable isotope 58Fe was given without food to 15 boys and 15 girls (Tanner stage 1) after an overnight fast and was immediately followed by a dose of 70 mg of ascorbic acid. 58Fe enrichment of the erythrocytes was determined by inductively coupled plasma mass spectrometry at baseline and 14 and 42 d after administration of the 58Fe dose. Geometric mean erythrocyte incorporation of the 58Fe label was 35.2% of intake by boys and 45.0% of intake by girls. The difference was significant (analysis of covariance with serum ferritin as covariate, p = 0.035). Study B: Fifteen boys and 15 girls (Tanner stage 1) were fed a breakfast labeled with 58Fe. Geometric mean erythrocyte incorporation of the 58Fe label was 14.8% of intake by boys and 24.7% of intake by girls. The difference was significant (analysis of covariance with serum ferritin as covariate, p = 0.004). Because serum ferritin concentrations were similar in boys and girls, the gender-related difference in iron absorption (as reflected by erythrocyte incorporation of the label) does not appear to be explained by a difference in body stores of iron. We hypothesize that hormonal differences between boys and girls in Tanner stage 1 favor iron absorption by girls.

Ascorbic Acid↗