Use of GnRH agonist implants for long-term suppression of fertility in extensively managed heifers and cows

The ability of gonadotrophin releasing hormone (GnRH) agonist implants to suppress ovarian activity and prevent pregnancies, long-term, was examined in heifers and cows maintained under extensive management. At three cattle stations, heifers (2-year-old) and older cows (3- to 16-year-old) were assigned to a control group that received no treatment, or were treated with high-dose (12 mg, Station A) or low-dose (8 mg, Station B and Station Q GnRH agonist implants. The respective numbers of control and GnRH agonist-treated animals (heifers + cows) at each station were: Station A, 20 and 99; Station B, 19 and 89; Station C, 20 and 76. Animals were maintained with 4% bulls and monitored for pregnancy at 2-monthly intervals for approximately 12 months. Pregnancy rates for control heifers and control cows ranged from 60-90% and 80-100%, respectively, depending on the study site. The respective number of animals (heifers + cows) treated with GnRH agonist that conceived, and days to first conception, were: Station A, 9 (9%) and 336 3 days; Station B, 8 (10%) and 244 +/- 13 days; Station C, 20 (26%) and 231 +/- 3 days. Treatment with high-dose GnRH agonist prevented pregnancies for longer (similar to300 days) than treatment with low-dose GnRH agonist (similar to200 days). In the majority of heifers and cows treated with GnRH agonist, ovarian follicular growth was restricted to early antral follicles (2-4 mm). The findings indicate that GnRH agonist implants have considerable potential as a practical technology to suppress ovarian activity and control reproduction in female cattle maintained in extensive rangelands environments. The technology also has broader applications in diverse cattle production systems. (C) 2002 Elsevier Science B.V. All rights reserved.

The first strand transfer reaction of HIV-1 reverse transcription is more efficient in infected cells than in cell-free natural endogenous reverse transcription reactions

Background: In the presence of dNTPs, intact HIV-1 virions are capable of reverse transcribing at least part of their genome, a process known as natural endogenous reverse transcription (NERT). PCR analysis of virion DNA produced by NERT revealed that the first strand transfer reaction (1stST) was inefficient in intact virions, with minus strand (-) strong stop DNA (ssDNA) copy numbers up to 200 times higher than post-1stST products measured using primers in U3 and U5. This was in marked contrast to the efficiency of 1stST observed in single-round cell infection assays, in which (-) ssDNA and U3-U5 copy numbers were indistinguishable. Objectives: To investigate the reasons for the discrepancy in first strand transfer efficiency between intact cell-free virus and the infection process. Study design: Alterations of both NERT reactions and the conditions of cell infection were used to test whether uncoating and/or entry play a role in the discrepancy in first strand transfer efficiency. Results and Conclusions: The difference in 1stST efficiency could not be attributed simply to viral uncoating, since addition of very low concentrations of detergent to NERT reactions removed the viral envelope without disrupting the reverse transcription complex, and these conditions resulted in no improvement in 1stST efficiency. Virus pseudotyped with surface glycoproteins from either vesicular stomatitis virus or amphotrophic murine leukaemia virus also showed low levels of 1stST in low detergent NERT assays and equivalent levels of (-) ssDNA and 1stST in single-round infections of cells, demonstrating that the gp120-mediated infection process did not select for virions capable of carrying out 1stST. These data indicate that a post-entry event or factor may be involved in efficient HIV-1 reverse transcription in vivo. (C) 2002 Elsevier Science B.V. All rights reserved.

Endogenous angiotensin II modulates nNOS expression in renovascular hypertension

Nitric oxide (NO) influences renal blood flow mainly as a result of neuronal nitric oxide synthase (nNOS). Nevertheless, it is unclear how nNOS expression is modulated by endogenous angiotensin II, an inhibitor of NO function. We tested the hypothesis that the angiotensin II AT1 receptor and oxidative stress mediated by NADPH oxidase contribute to the modulation of renal nNOS expression in two-kidney, one-clip (2K1C) hypertensive rats. Experiments were performed on male Wistar rats (150 to 170 g body weight) divided into 2K1C (N = 19) and sham-operated (N = 19) groups. nNOS expression in kidneys of 2K1C hypertensive rats (N = 9) was compared by Western blotting to that of 2K1C rats treated with low doses of the AT1 antagonist losartan (10 mg·kg-1·day-1; N = 5) or the superoxide scavenger tempol (0.2 mmol·kg-1·day-1; N = 5), which still remain hypertensive. After 28 days, nNOS expression was significantly increased by 1.7-fold in the clipped kidneys of 2K1C rats and by 3-fold in the non-clipped kidneys of 2K1C rats compared with sham rats, but was normalized by losartan. With tempol treatment, nNOS expression increased 2-fold in the clipped kidneys and 1.4-fold in the non-clipped kidneys compared with sham rats. The changes in nNOS expression were not followed by changes in the enzyme activity, as measured indirectly by the cGMP method. In conclusion, AT1 receptors and oxidative stress seem to be primary stimuli for increased nNOS expression, but this up-regulation does not result in higher enzyme activity.

On the concept of endogenous volatility

Most financial and economic time-series display a strong volatility around their trends. The difficulty in explaining this volatility has led economists to interpret it as exogenous, i.e., as the result of forces that lie outside the scope of the assumed economic relations. Consequently, it becomes hard or impossible to formulate short-run forecasts on asset prices or on values of macroeconomic variables. However, many random looking economic and financial series may, in fact, be subject to deterministic irregular behavior, which can be measured and modelled. We address the notion of endogenous volatility and exemplify the concept with a simple business-cycles model.

Analysis of the interference of endogenous circadian rhythms on 3'- deoxy- 3'- [18F]Fluorothymidine physiological uptake at the human bone marrow

The main purpose of the present study is to determine if the circadian rhythms present in the human bone marrow are likely to influence 3’- deoxy- 3’-[18F] Fluorothymidine (18F-FLT) uptake in the same organ. The 18F-FLT is a Thymidine analogous proliferation agent. The relatively high physiological uptake of this tracer in the bone marrow diminishes the Tumor/Background (T/B) ratio, decreasing the detection accuracy of PET/CT and possibly affecting SUV quantifications.

Licensing endogenous cost-reduction in a differentiated Stackelberg model

In this paper we consider a differentiated Stackelberg model, when the leader firm engages in an R&D process that gives an endogenous cost-reducing innovation. The aim is to study the licensing of the cost-reduction by a two-part tariff. By using comparative static analysis, we conclude that the degree of the differentiation of the goods plays an important role in the results. We also do a direct comparison between our model and Cournot duopoly model.

Oxidative stress in pregnancy and fertility pathologies

Oxidative stress designates the state of imbalance between reactive oxygen species (ROS) production and antioxidant levels. In a healthy placenta, there is an increase in ROS production, due to formation of new tissues and inherent metabolism, but this is balanced by higher levels of antioxidants. However, this balance is lost in some situations, with a consequent increase in oxidative stress levels. Oxidative stress has been implicated in several placental disorders and pregnancy pathologies. The present review intends to summarize what is known about the relationship between oxidative stress and well-known pregnancy disorders.

Comparative study of the fecundity and fertility of Biomphalaria glabrata (Say, 1818) and Biomphalaria straminea (Dunker, 1848) in a laboratory through self-fertilization and cross-fertilization

The aim of this study was to compare the fecundity and fertility of B. glabrata and B. straminea by cross- and self-fertilization. To attain this objective, laboratory-raised strains of B. glabrata and B. straminea were used. The former originated from natural breeding grounds in the municipality Paulista, state of Pernambuco, Brazil. The latter originated from irrigation ditches in the municipality of Petrolândia, in the same state. Snail populations of B. glabrata and B. straminea were maintained for 240 days in laboratory. Their fecundity was evaluated by noting the number of egg-masses, eggs and eggs per mass. Their fertility was evaluated by the number of viable eggs and the hatching rate. B. straminea was markedly more fecund than B. glabrata through cross- and self-fertilization, namely: greater egg-mass; higher egg production and more eggs per mass. Regarding fertility, there seemed to be no preferential period for occlusion to occur or a trend in the rhythm of producing viable eggs.

Ovarian Borderline Tumor and Fertility-Sparing Surgery

Ovarian borderline tumors (OBTs) are frequently diagnosed in women of reproductive age. There is no consensus about their management, and it sometimes represents a dilemma aboutwhat should be done: fertility sparing surgery or a hysterectomy with salpingo-oophorectomy? Case: A 32-year-old nulligravida, diagnosed with a right ovarian borderline tumor is presented. She underwent pelvic washings, right salpingo-oophorectomy, appendectomy, and omental and peritoneal biopsies (laparotomic approach). Macroscopically, the left ovary was normal and subsequent exploration for staging was also normal, including the lymph nodes. Intraoperatively, frozen section examination was unclear, suggesting an OBT. Results: The final histopathologic diagnosis was ovarian borderline tumor, stage IIC (International Federation of Gynecology and Obstetrics [FIGO] staging). The patient expressed a desire to preserve her fertility. Thirty-six months postsurgery, she became pregnant spontaneously and delivered a healthy newborn at term. Conclusions: Conservative surgery can be performed in young patients treated for an OBT, provided they are closely followed up and that this surgery is performed after careful consideration and informed consent. It is, however, controversial with respect to performing hysterectomy and salpingo-oopherectomy upon the patient’s completion of childbearing.

Induction of male sterility through manipulation of genetic mechanisms present in vector species of Triatominae. II. Partial restoration of male fertility

The development of integrated measures which involve sterile mate release to supplement the conventional insecticidal techniques used in controlagainst insects of medical importance, raised the question, whether the vectors of Chagas'disease possess the natural mechanisms by manipulation of which they may be controlled. Results of earlier expenments, that had been published previously, were restricted to fragmentary information that raised various questions, the answer to which became available in the study herein described. Interspecific hybrids were produced from reciprocal crosses between T. pseudomaculata and T. sórdida and from unilateral crosses between female T. pseudomaculata and male. T. infestans. These females mated with males, laid less than the normal complement of eggs, but offspring was relatively abundant. When T. pseudomaculata females were paired with T. brasiliensis males, hybridization was more difficult because few of the females mated and those that did had a strongly reduced fertility. Adults emerged from ali crosses but exhibited sex disproportion, females predominating in all populations but one. The two Rhodnius species tested were also found to cross, but only when female R. prolixus were paired with male R. neglectus. These females laid a relatively high complement o f eggs, had a strongly reduced fertility, but 50% of the fertile eggs developed into vigorous adults, males predominating females. Neither type of hybrid male elicited fertilized eggs from either parental type of female, through their vesicula seminal is were found to be packed with spermatozoa, some normal looking and moving, others underdeveloped and motionless. Although, no artificial insemination was performed, the sperm in itself did not appear to be the prime inducer of sterility. Females paired with these hybrids did mate, sperm was transfered, as evidenced by the discharged spermatophores smeared with sperm, but did notcontain spermatozoa in their spermatecae. The failure of the sperm to migrate to the spermatecae indicate prezygotic pos-copulation incompatibility, thus the hybrid male can't be used to suppress populations. The female hybrids mated with parent males of either species had reduced fertility and ther sons were sterile as were those of their fertile daughters. However, continous backcrossing of the hybrid females and their female progeny to parental males partially restored fertility of the males and increased fertility of females, as scored by egg hatchability. Fertility of hybrid females, measured by the yield of adults capable to reproduce, indicated that the reproductive perfomance decreased when hybrid females and their daughters were backcrossed additional generations to parental males. It is tentatively suggested that hybrid females could be used for suppression if they compete efficiently with wild females.

R&D spillovers in an endogenous growth model with physical capital, human capital and varieties

There is a family of models with Physical, Human capital and R&D for which convergence properties have been discussed (Arnold, 2000a; Gómez, 2005). However, spillovers in R&D have been ignored in this context. We introduce spillovers in this model and derive its steady-state and stability properties. This new feature implies that the model is characterized by a system of four differential equations. A unique Balanced Growth Path along with a two dimensional stable manifold are obtained under simple and reasonable conditions. Transition is oscillatory toward the steady-state for plausible values of parameters.

Endogenous spillovers in the trade-off between centralization and decentralization

In this paper, we revisit the classical trade-off between centralized and decentralized provision of local public goods, in a setting where interregional spillovers depend on the level of a national public good. We compare the standard benevolent planner approach with a political economy in which decisions, in a centralized system, are undertaken by a non-cooperative legislature with no separation of powers. We observe that the policy-maker in a centralized system is able to play both with local public goods and spillovers, a mechanism that is not available under a decentralized system. When compared to the traditional exogenous spillovers assumption, this improves the case for centralization under the standard benevolent planner approach. However, the same is not necessarily true in the non-cooperative legislature, as in this case the interests of the legislator do not need to be aligned with those of the society. Finally, we extend the traditional political economy analysis by considering a legislature in which decisions are undertaken by different committees (separation of powers), and show that it performs better than the original non-cooperative legislature, greatly improving the case for centralization.

Making sense of the experimental evidence on endogenous timing in duopoly markets

The prediction of asymmetric equilibria with Stackelberg outcomes is clearly the most frequent result in the endogenous timing literature. Several experiments have tried to validate this prediction empirically, but failed to find support for it. By contrast, the experiments find that simultaneous-move outcomes are modal and that behavior in endogenous timing games is quite heterogeneous. This paper generalizes Saloner’s (1987) and Hamilton and Slutsky’s (1990) endogenous timing games by assuming that players are averse to inequality in payoffs. We explore the theoretical implications of inequity aversion and compare them to the empirical evidence. We find that this explanation is able to organize most of the experimental evidence on endogenous timing games. However, inequity aversion is not able to explain delay in Hamilton and Slutsky’s endogenous timing games.

Democracy and fertility

A Masters Thesis, presented as part of the requirements for the award of a Research Masters Degree in Economics from NOVA – School of Business and Economics

Absorption in human capital and r&d effects in an endogenous growth model

Until now, in models of endogenous growth with physical capital, human capital and R&D such as in Arnold [Journal of Macroeconomics 20 (1998)] and followers, steady-state growth is independent of innovation activities. We introduce absorption in human capital accumulation and describe the steady-state and transition of the model. We show that this new feature provides an effect of R&D in growth, consumption and welfare. We compare the quantitative effects of R&D productivity with the quantitative effects of Human Capital productivity in wealth and welfare.