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PubMed1986

Inducing fertility change: a game-theoretic approach.

This paper explores the inducement of fertility change in situations where actual fertility levels do not coincide with socially optimal fertility levels. The motivating example is that of higher than socially optimal levels of fertility in less developed countries (LDCs), but the approach is equally applicable to contexts of lower than socially optimal levels of fertility in developed countries. The paper proposes a prisoner's dilemma characterization of higher than socially optimal levels of fertility in LDCs and offers a resolution of the dilemma, and hence a possible route to fertility-reduction policies, through the generation of mutual altruism. The prisoner's dilemma characterization hinges on the assumption that there is some social sharing of the costs associated with a given level of fertility but less or none with respect to the benefits. The mutual altruism solution depends on representing an agent's preferences as a specific convex combination of his/her and the other agent's original utilities. The unique critical level of such altruism is identified and hence a stopping rule is provided. Several examples from the array of extensions and possible implications of this approach are discussed briefly.

Behavior↗
PubMed1985

A simplified fertility test in the dairy bull utilizing superovulated dairy cows.

Dairy bull fertility level has received less attention than production transmitting ability. A simplified fertility test may be beneficial. A study was designed to test the use of tris-(1-aziridinyl)-phosphine oxide (TEPA) treated sperm, which arrests early cell division of the fertilized egg, in heterospermic insemination of superovulated cows. Semen samples were collected and pooled from University of Illinois dairy bulls. Semen samples were washed once, suspended in Illini Variable Temperature diluent (IVT) and incubated with or without TEPA (1.0 to 5.0 mg/ml) for 15 min. Samples were then washed again to remove excess TEPA. Additions of 1.0 to 5.0 mg/ml TEPA to sperm concentrations of 8 x 10(8) sperm/ml had no adverse effect on motility or morphology. The first part of the study utilized superovulated cows inseminated with treated (six cows) or untreated (six cows) sperm in different samples from the same bulls. Secondly, superovulated cows (eight cows) were artificially inseminated with treated and untreated split ejaculates from the same bulls. Lastly, superovulated cows (five cows) were heterospermically inseminated with treated (bull No. 1) and untreated (bull No. 2) spermatozoa. Out of 54 and 39 ova recovered in control and test cows, 40 blastocysts and 31 embryos arrested at the one- to five-cell stage resulted, respectively. Out of a predicted 123 ovulations, 78 fertilized ova were recovered; 40 of these were fertilized by control spermatozoa and 36 by TEPA-treated spermatozoa for parts one and two of the study respectively. These results indicated no significant difference in fertilizability of ova between control and TEPA-treated spermatozoa. Of 41 fertilized ova recovered (part 3), bull No. 1 fertilized significantly more ova (mean +/- standard deviation 5.0 +/- 2.3) than bull No. 2 (2.6 +/- 1.8). Results indicate a difference in fertility between bulls.

Journal Article↗
PubMed1991

In vitro fertilization of sheep oocytes matured in vivo.

Incubating washed ram spermatozoa in a modified Brackett's defined medium buffered with Hepes (DM-H) containing 20% of heat-inactivated sheep serum appears to be a reliable method of capacitating sperm for in vitro fertilization. Raising the Ca(++) concentration in the fertilization medium (DM-H-SS) to 10 mM stabilized the fertilization rate of various rams (2). This study was designed to determine if the developmental competence of the oocytes fertilized under such conditions was normal. Thirty-seven ewes, treated with progestagen sponges, were superovulated with porcine follicle stimulating hormone (pFSH: 16 mg). An intramuscular injection of gonadotropin releasing hormone (GnRH: 100 mug); given 24 to 26 h after sponge removal, induced the synchronization of ovulations 24 h later. Ovulated oocytes (n = 229) recovered with flushing of the oviducts were inseminated in vitro and 17 h later either fixed in acetic/alcohol (n = 115) to evaluate fertilization or transferred (n = 114) into 38 synchronized recipients (three oocytes/recipient) to evaluate their developmental competence. Of the fixed oocytes, 82.6% were fertilized and 61.7% were monospermic. Nineteen of the recipient ewes (50%) were pregnant at Day 18, and 16 ewes produced a total of 26 live young (mean: 1.63/ewe). The results showed a high efficiency of in vitro fertilization of ovulated oocytes in sheep following a pFSH-GnRH treatment and the in vivo developmental competence of oocytes fertilized in the presence of elevated Ca(++) concentration.

Journal Article↗
PubMed1994

The initial fertilizing capacity of longerm-stored liquid boar semen following pre- and postovulatory insemination.

In pigs, high variation is seen in the duration of estrus and in the time of ovulation. This is one of a wide range of factors not related to semen quality, which possibly influences the results of field insemination trials. Experiment 1 (n=81 gilts) was performed to determine the influence of the time of ovulation on the fertilizing capacity of liquid boar semen stored up to 118 h. The objective of Experiment 2 (n=102 gilts) was to study the fertilizing potential of semen stored up to 120 h in 2 different extenders, Androhep and Beltsville Thawing Solution (BTS), by means of postovulatory AI. Inseminations were performed 0 to 4 h after ovulation in order to standardize the trial conditions. Fertilization rates based on Day-2 to Day-4 embryos, and the number of accessory spermatozoa per zona pellucida did not differ between semen stored for 0 to 48 and 48 to 87 h in gilts ovulating within 12 after insemination (Experiment 1). Gilts with an interval of 12 to 24 h between AI and ovulation had lower fertility results using semen stored for more than 48 h. A further decrease was observed when semen storage exceeded 87 h in those gilts ovulating later than 24 h after insemination. The time of ovulation has to be considered as being a major factor of variation in the fertility results of AI trials. In Experiment 2, fertilization rates and numbers of accessory spermatozoa decreased between semen stored for 0 to 24 and 24 to 48 h in BTS, and between semen stored for 0 to 24 and 48 to 72 h in Androhep. Significant differences in fertility between diluents were seen only when using semen stored for more than 96 h, with semen extended with Androhep giving the higher results. The results indicate that the decrease in fertilizing capacity due to in vitro aging of spermatozoa cannot be prevented even during the first days of storage.

Journal Article↗
PubMed2005

Differences between Belclare and Suffolk ewes in fertilization rate, embryo quality and accessory sperm number after cervical or laparoscopic artificial insemination.

Ewe breed has been shown to have a major effect on pregnancy rates following cervical AI using frozen-thawed semen. The main objective of this study was to examine the differences between purebred Belclare and Suffolk ewes (multiparous) in fertilization rate, number of accessory sperm and stage of embryo development on day 6 after cervical or laparoscopic AI with frozen-thawed semen. In experiment 1, Belclare and Suffolk ewes were synchronized for 12 days and were either cervically inseminated (year 1: n=28 and 31; year 2: n=16 and 15, respectively) or laparoscopically inseminated (year 2: n=13 and 14). In experiment 2, superovulated Belclare (n=4) and Suffolk (n=13) ewes were laparoscopically inseminated. All ewes were slaughtered 6 days after AI; oocytes/embryos were recovered, morphologically graded and stained to assess the number of cells and accessory spermatozoa. Data from both experiments were combined for statistical analysis. The proportion of ewes with fertilized oocytes was significantly higher following laparoscopic AI compared with cervical AI (54% versus 19%). More Belclare than Suffolk ewes yielded fertilized oocyte(s) after cervical AI (34% versus 10%, P<0.02) but there was no difference after laparoscopic AI (62% versus 60%). From the ewes that yielded at least one fertilized oocyte the proportion of Belclare ewes with embryos at the morula/blastocyst stage was significantly greater than for Suffolk ewes (94% versus 59%, P<0.02). A higher proportion of Belclare than Suffolk ewes had evidence of sperm reaching the site of fertilization following cervical AI (39% versus 15%, P<0.02) but there was no difference after laparoscopic AI (62% versus 64%, P>0.8). Amongst the ewes with evidence of sperm at the site of fertilization, laparoscopic AI resulted in a higher number of sperm per oocyte/embryo or per ewe than cervical AI (P<0.01). These results suggested that the difference in pregnancy rate between Suffolk and Belclare ewes following cervical AI was due to: (i) sperm traversing the cervix and uterus in a higher proportion of Belclare than Suffolk ewes, leading to a higher incidence of fertilization and (ii) the lower developmental competence of fertilized oocytes from Suffolk ewes.

Animals↗
PubMed2000

Sperm deposition site during ICSI affects fertilization and development.

OBJECTIVE: To evaluate the effects of sperm placement during ICSI relative to the M-II spindle location on fertilization and preimplantation development. DESIGN: Retrospective analysis of oocyte fertilization and embryo development with respect to sperm deposition site during ICSI. SETTING: A program of IVF-ET. PATIENT(S): Seven hundred seventy-six patients. INTERVENTION(S): Egg quality, sperm deposition site, and polar-body position were recorded during ICSI; fertilization was assessed on day 1; embryo development was evaluated on days 2 and 3. MAIN OUTCOME MEASURE(S): Fertilization, embryo development, and implantation rates. RESULT(S): Normal fertilization is not affected by polar-body orientation, with the exception of a significantly lower fertilization rate from a 9 o'clock polar-body orientation. Injections with the polar-body positioned at 7 or 11 o'clock result in the greatest number of high-quality embryos, significantly more than the adjacent 6 or 12 o'clock polar-body orientations and irrespective of oocyte anomaly frequency. Embryos originating from the 7 or 11 o'clock polar-body category implant at a higher rate, although the data are not significant. CONCLUSION(S): The placement of the sperm during ICSI relative to the presumed location of the meiotic spindle significantly impacts fertilization and high-quality embryo development. Sperm deposition in the M-II spindle area should be avoided. It appears that development, and not fertilization, is improved by decreasing the distance between the sperm cell and the spindle.

Cell Nucleus↗
PubMed1988

Fertilization rates in superovulating cows after deposition of semen on the infundibulum, near the uterotubal junction or after insemination with high numbers of sperm.

Three experiments were conducted with 105 superovulating Holstein dairy cows in attempts to improve the fertilization rate. Cows were superovulated with follicle-stimulating hormone (FSH) and time of estrus was regulated with prostaglandin F(2)alpha (PGF(2)alpha). Semen was deposited on each infundibulum through a laparoscope inserted through the flank (Experiment 1) or near the uterotubal junctions through flexible tubing passed through the cervix and uterine horns (Experiment 2). In the third experiment, high numbers of sperm in fresh semen were deposited in the uterus. Cows were necropsied and ova were recovered and examined about 3.5 d after the beginning of estrus. Deposition of 0.5 ml of frozen-thawed semen on each infundibulum (Experiment 1) reduced both ovum recovery and fertilization. In ten cows inseminated on the infundibulum, ova representing 43% of ovulation points were recovered and 9% of these recovered ova were fertilized. In ten control cows, ova representing 80% of ovulation points were recovered and 62% of them were fertilized. In a 2 x 2 experiment with 36 superovulating cows (Experiment 2), 1 ml of diluted fresh or frozen semen was deposited either near the uterotubal junction or in the uterine body. The overall fertilization rate was 61%, with no significant effect of site of semen deposition or type of semen used. In Experiment 3, 2 or 3 ml of neat semen (average of 4.4 billion sperm) was deposited in the uterus of 12 cows; 183 of 197 intact ova (93%) were fertilized. In 56 control cows inseminated with 0.5 to 1.5 ml of frozen diluted semen (average of 70 million sperm), 502 of 947 intact ova were fertilized (53%, P<0.001). Insemination with high numbers of fresh sperm overcame problems of sperm loss or sperm transport and improved the fertilization rate.

Journal Article↗
PubMed1998

Outcome of in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) using human sperm prepared via a new standardized swim-up technique fit for office use.

Objective: Recent developments in the assisted reproductive technology (ART) areas necessitate the use of new and more efficient and acceptable modes of gamete in vitro manipulation techniques. As established via the use of various forms of ART, the natural process of fertilization has been largely bypassed and the gametes are obtained and manipulated outside of the normal means of conception. For the male, improvements in sperm quality have involved the use of various techniques that aim to recover a small percentage of healthy spermatozoa that can be further used for the different ART procedures. Previous IVF results showed no differences in fertilization rates between ZSC and Percoll recovered sperm (Zarmakoupis-Zavos et al. ACOG, 1997). The current study was designed to study the fertilizing capacity of ZSC recovered spermatozoa and subsequent embryonic development and pregnancy rates established via IVF and ICSI procedures.Methods: Sperm specimens (n = 30) were prepared via the use of the standardized ZSC swim-up technique, which was designed to harvest almost all overlayered media at the end of the procedure to maximize the sperm recovery. The ZSC device consists of a column with a conical cavity where the semen is placed, and from where the sperm swim-up into the overlayered media and are subsequently recovered at the end of the procedure. Semen specimens were initially assessed and then prepared (0.5 mL each) via the ZSC swim-up technique. The enhancement of the routine semen parameters was assessed and the recovered specimens were used for either conventional IVF or ICSI.Results: The results of the fertilization and pregnancy via IVF and ICSI are shown below:The generated results point out that ZSC recovered specimens yielded acceptable levels of fertilization and pregnancy rates in our IVF and ICSI program. Furthermore, the IVF inseminations yielded higher fertilization rates with a slight increase in polyspermic oocytes when compared to the ICSI inseminations.Conclusion: The data generated in this study tend to point out that the ZSC, besides being a simple one-step standardized system, can also be effectively employed in an ART program and can generate adequate fertilization and pregnancy rates. We have previously shown that the quality and fertilizing capacity of ZSC recovered sperm is comparable to that recovered via Percoll gradients. However, the ZSC when compared to the Percoll method was less time consuming (5 minutes of actual labor) and less tedious by eliminating the dilution and centrifugation steps of Percoll preparation, since it washes the sperm while simultaneously selecting it. The ZSC is a standardized semen preparation method and could be the method of choice in an ART program.

Journal Article↗
PubMed1994

The end of fertility: age, fecundity and fecundability in women.

Onset of capacity for childbearing in women is dated biologically by menarche, although actual onset may be delayed. The end of childbearing is less understood but recent demographic and biological research on fertility at older ages in clarifying the end of fertility. The demographic view of declining fertility with age is based on age-specific fertility in natural fertility populations, artificial insemination and pregnancy rates by age and World Fertility Survey data. New data from the Demographic and Health Surveys on exposure to the risk of pregnancy shows that whereas older women biologically need longer exposure to pregnancy, exposure declines on behavioural grounds such as duration of marriage. Actual fecundity is obscured by factors of fecundability. Recent research on medically assisted conception is adding to the understanding of declining fecundity with age, especially the relative contributions of endometrial and ovarian ageing. This paper reviews the available information on declining fertility with age and discusses the implications of the extension of fertility through new medical technologies.

Adult↗
PubMed1997

Binding of antibiotics to glycoproteins of the vitelline and fertilization envelopes of cherry salmon eggs.

The binding of antibiotics (gentamicin, oleandomycin and chloramphenicol) to vitelline and fertilization envelopes and their extracts was investigated by immunohistochemical and immunocytochemical techniques and immunoblot analysis using mature and artificially activated eggs of the fish Oncorhynchus masou. Binding of antibiotics was detected in the vitelline and fertilization envelope outermost layers, the fertilization envelope inner surface and cortical alveolus exudates, with differences in immunoreactive intensity and deposition. The fertilization envelope outermost layer had the capacity to bind much greater amounts of the antibiotics than the vitelline envelope outermost layer. The greater capacity was caused by the deposition of cortical alveolus exudates, which were known to be responsible for functional roles of protection against bacteria, fungi and noxious materials. Treatment of the vitelline and fertilization envelopes with neuraminidase markedly reduced the binding of gentamicin and chloramphenicol but slightly increased that of oleandomycin; binding of the latter to the vitelline and fertilization envelope outermost layers was considerably reduced after treatment with alpha-fucosidase. Treatment of the two envelopes with alpha-mannosidase, beta-galactosidase or beta-D-glucosaminidase did not cause any alteration in immunoreactive intensity or number of immunoreactive deposits. Immunoblot analysis of the vitelline or fertilization envelope extracts indicated that many of the antibiotic-binding substances were glycoproteins, and several major bands were bound by all three antibiotics. These results suggest that the vitelline or fertilization envelopes may have the ability to protect the egg itself, or the embryo, respectively, by trapping antibiotics, and the trapping may be related to the presence of carbohydrate moieties, such as sialyl or fucosyl residues.

Animals↗
PubMed1996

A mutation that allows endosperm development without fertilization.

The mechanisms that initiate reproductive development after fertilization are not understood. Reproduction in higher plants is unique because it is initiated by two fertilization events in the haploid female gametophyte. One sperm nucleus fertilizes the egg to form the embryo. A second sperm nucleus fertilizes the central cell to form the endosperm, a unique tissue that supports the growth of the embryo. Fertilization also activates maternal tissue differentiation, the ovule integuments form the seed coat, and the ovary forms the fruit. To investigate mechanisms that initiate reproductive development, a female-gametophytic mutation termed fie (fertilization-independent endosperm) has been isolated in Arabidopsis. The fie mutation specifically affects the central cell, allowing for replication of the central cell nucleus and endosperm development without fertilization. The fie mutation does not appear to affect the egg cell, suggesting that the processes that control the initiation of embryogenesis and endosperm development are different. FIE/fie seed coat and fruit undergo fertilization-independent differentiation, which shows that the fie female gametophyte is the source of signals that activates sporophytic fruit and seed coat development. The mutant fie allele is not transmitted by the female gametophyte. Inheritance of the mutant fie allele by the female gametophyte results in embryo abortion, even when the pollen bears the wild-type FIE allele. Thus, FIE carries out a novel, essential function for female reproductive development.

Journal Article↗
PubMed2005

Fertility and hatchability in RIR and WL breeds as functionally modified by crossing them in alternate sex combinations (Gallus domesticus).

(1) Four breeding groups of Rhode Island Red and White Leghorn domestic fowl (RIR (female) x RIR (male), RIR (female) x WL (male), WL (female) x RIR (male) and WL (female) x WL (male)) were compared for fertility, hatchability, and their post-insemination sustainability, egg weight loss during incubation and uncovered yolk in abdominal cavity of dead in shell in order to understand the problems associated with the RIR breed in these respects. (2) Crossing RIR (female) with WL (male) or in reverse sex combinations did not improve fertility in comparison to pure RIR chickens and all these groups were less fertile than the pure WL. (3) Unlike fertility, hatchability in RIR improved with the change to either sex partner of the WL breed but the WL (female) x RIR (male) combination was similar to the pure WL (97.72 and 97.12%, respectively). In contrast, crossing RIR (female) with WL (male) resulted in an improvement (86.67%) as compared to pure RIR (76.67%) but still lower than the pure WL and WL (female) x RIR (male) cross. (4) Egg weight loss during incubation was more (20.16%) in pure RIR as compared to RIR (female) x WL (male) (17.13%), followed by WL (female) x RIR (male) (10.28%) and pure WL (9.57%). (5) There were more dead-in-shell embryos with yolks outside their abdominal cavity in pure RIR and their crosses as compared to pure WL breeds. (6) Fertility was sustained for longer in WL than other combinations with post-artificial insemination using constant number of spermatozoa. Fertility after a week of insemination tended to decrease more rapidly than hatchability on a fertile egg basis. (7) It is concluded that both sexes are responsible for the poor fertility in RIR but the female is responsible for poor hatchability and this poor performance is mainly due to greater egg weight loss during incubation.

Animals↗
PubMed2002

Tillering in grain sorghum over a wide range of population densities: identification of a common hierarchy for tiller emergence, leaf area development and fertility.

Most studies of tiller development have not related the physiological and morphological features of each culm to its subsequent fertility. This introduces problems when trying to account for the effects of tillering on yield in crop models. The objective of this study was to detect the most likely early determinants of tiller fertility in sorghum by identifying hierarchies for emergence, fertility and grain number of tillers over a wide range of assimilate availabilities. Emergence, phenology, leaf area development and dry weight partitioning were quantified weekly for individual tillers and main culms of tillering and uniculm plants grown at one of four densities, from two to 16 plants m(-2). For a given plant in any given density, the same tiller hierarchy applied for emergence of tillers, fertility of the emerged tillers and their subsequent grain number. These results were observed over a range of tiller fertility rates (from 7 to 91%), fertile tiller number per plant at maturity (from 0.2 to 4.7), and tiller contribution to grain yield (from 5 to 78 %). Tiller emergence was most probably related to assimilate supply and light quality. Development, fertility and contribution to yield of a specific tiller were highly dependent on growing conditions at the time of tiller emergence, particularly via early leaf area development of the tiller, which affected its subsequent leaf area accumulation. Assimilate availability in the main culm at the time of tiller emergence was the most likely early determinant of subsequent tiller fertility in this study.

Edible Grain↗
PubMed1992

Influence of nitrogen fertilization on minerals, carbohydrates, amino acids and phenolic compounds in beech (Fagus sylvatica L.) leaves.

Beginning in 1985, plots in a 120-year-old beech (Fagus sylvatica L.) stand in the province of Scania, southern Sweden were fertilized annually with ammonium nitrate. In August 1989, leaves from both fertilized and unfertilized trees were analyzed for mineral nutrients, soluble carbohydrates, amino acids and phenolic compounds. Leaf concentrations of total nitrogen were increased by N fertilization. Ammonium was not detected in the leaves, but NO(3) (-) was increased by up to 65% as a result of N fertilization. Nitrogen fertilization decreased foliar concentrations of P and Cu, leading to a nutrient imbalance relative to N. Of the free amino acids, glutamic acid and aspartic acid predominated and, together with glutamine and asparagine, were significantly increased by N fertilization. The concentrations of amides were 2-4 times higher in fertilized trees than in unfertilized trees. Soluble carbohydrates did not change in response to N fertilization, but total phenolic compounds decreased markedly. The reduced concentration of phenolics may explain the greater susceptibility to parasite attacks of trees exposed to N deposition and excess N.

Journal Article↗
PubMed1999

Fine root biomass of Scots pine stands differing in age and soil fertility in southern Finland.

The biomass of small and large fine roots (</= 2 mm and 2-5 mm in diameter, respectively) in mineral soils of southern Finland was compared with estimated foliage biomass in the same stands. Study material was collected from stands differing in site fertility and age. The humus layer was deeper at the more fertile sites than at the less fertile sites. Fine root density was greater in humus than in mineral soil, and the fine root density in mineral and humus layers was greater at the less fertile sites than at the more fertile sites. Although the amount of fine root biomass was not correlated with any commonly recorded stand characteristic, small fine root biomass was proportional to foliage biomass for both site types. The coefficient of proportionality was larger for the less fertile sites than for the more fertile sites, supporting the theory of functional balance. A similar relationship could not be established for the large fine roots. A trend of increasing fine root:needle mass ratio with stand age was observed for stands on the less fertile sites.

Journal Article↗
PubMed1986

Site fertility affects seasonal carbon reserves in loblolly pine.

Concentrations of nitrogen, phosphorus and total non-structural carbohydrates were examined in loblolly pine foliage from control stands and stands fertilized with sludge containing 450 kg N ha(-1). Needles from the fertilized sites had higher N concentrations regardless of needle age. Fertilization increased P concentration in needles relative to the control sites. Seasonal patterns of change in sugar concentrations were similar among sites for both current-year and one-year-old needles, the highest concentration (126 mg g(-1)) occurring in February. Sugar concentrations were lowest in June and were generally lower in current needles than year-old needles. Starch concentrations and the amount of starch per fascicle varied both seasonally and among sites. Fertilization increased starch reserves in current needles at the end of the growing season (7 mg g(-1) and 14 mg g(-1) for the control and fertilized sites, respectively), and increased the rate of starch mobilization during the initiation of needle growth. In the growing season, starch concentrations were lower in current foliage from high fertility sites than low fertility sites. Carbon reserves accumulated during the growing season in mature one-year-old needles from control sites indicating a lower sink strength for carbon under low nutrient conditions. There was a positive relationship between starch and nitrogen concentrations during the dormant season whereas the relationship was negative during the growing season. The magnitude and direction of change in starch reserves with the onset of growth following the dormant season may indicate nutrient limitation and potential growth response to fertilization.

Journal Article↗
PubMed1990

Seasonal changes in amino acids, protein and total nitrogen in needles of fertilized Scots pine trees.

Seasonal changes in amino acids, protein and total nitrogen in needles of 30-year-old, fertilized Scots pine (Pinus sylvestris L.) trees growing in Northern Sweden were investigated over two years in field experiments. The studied plots had been fertilized annually for 17 years with (i) a high level of N, (ii) a medium level of N, or (iii) a medium level of N, P and K. Trees growing on unfertilized plots served as controls. In control trees, glutamine, glutamic acid, gamma-aminobutyric acid, aspartic acid and proline represented 50-70% of the total free amino acids determined. Arginine was present only in low concentrations in control trees throughout the year, but it was usually the most abundant amino acid in fertilized trees. Glutamine concentrations were high during the spring and summer in both years of study, whereas proline concentrations were high in the spring but otherwise low throughout the year. In the first year of study, glutamic acid concentrations were high during the spring and summer, whereas gamma-aminobutyric acid was present in high concentrations during the winter months. This pattern was less pronounced in the second year of investigation. The concentrations of most amino acids, except glutamic acid, increased in response to fertilization. Nitrogen fertilization increased the foliar concentration of arginine from < 1 micromol g(dw) (-1) in control trees to a maximum of 110 micromol g(dw) (-1). Trees fertilized with nitrogen, phosphorus and potassium had significantly lower arginine concentrations than trees fertilized with the same amount of nitrogen only. Protein concentrations were similar in all fertilized trees but higher than those in control trees. For all treatments, protein concentrations were high in winter and at a minimum in early spring. In summer, the protein concentration remained almost constant except for a temporary decrease which coincided with the expansion of new shoots. Apart from arginine, the amino acid composition of proteins was similar in all treatments.

Journal Article↗
PubMed1999

Fertility and infant mortality trends in Nicaragua 1964-1993. The role of women's education.

OBJECTIVES: To assess trends in fertility and infant mortality rates (IMR) in León, Nicaragua, and to examine the effect of women's education on these trends during 1964-1993, a period of rapid social change. DESIGN: Cross sectional survey, based on random cluster sampling. A retrospective questionnaire on reproductive events was used. SETTING: The municipality of León, which is the second largest city in Nicaragua, with a total population of 195,000 inhabitants. SUBJECTS: 10,867 women aged 15-49 years, corresponding to 176,281 person years of reproductive life. Their children contributed 22,899 person years under 12 months of age to the IMR analysis. MAIN OUTCOME MEASURES: Fertility rate (number of pregnancies per 1000 person years) for specific age groups and calendar periods, total fertility rate, and IMR. RESULTS: Fertility rates and IMR declined in parallel, especially during the 1980s. However, education specific fertility rates did not decline, but the proportion of educated young women increased from 20% to 46%. This had also an impact on the overall IMR decline, although IMR reduction mainly took place among infants of women without formal education, decreasing from 118 to 69 per 1000 during the observation period. CONCLUSIONS: In this demographic transition over three decades, fertility and IMR declined simultaneously. The decreasing trend in fertility was mainly explained by an increase in women's education, while the IMR decline seemed to be the result of health interventions, specially targeted to poorer groups of women and their infants. Thus, social differences in fertility rates remained unchanged, while equity in chances of child survival increased.

Adolescent↗