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Dispersal-induced pattern formation is important from both fundamental and application points of view. Spatial pattern in an ecological system can strongly depend on exogenous factors like arrangement of the natural and artificial physical features of the habitat (topography) and distribution of resources. It is also influenced by endogenous factors (intrinsic biological forces) such as the ecological interactions of individuals. Here, we consider a discrete space–time host–parasitoid metapopulation model in the presence of both self-diffusion (due to endogenous factors) and cross-diffusion (due to exogenous factors). Dynamics of a metapopulation system consists of a dispersal stage and a reaction stage. In the dispersal stage, populations from an individual site can disperse to the nearest neighboring sites via dispersal and may cause variation in the host and parasitoid biomass of the node. In the reaction stage, hosts and parasitoids interact in each site and their local interaction is governed by the modified Nicholson–Bailey-type interaction. The conditions for the existence of pattern-forming instabilities (like Turing, Hopf and Hopf–Turing) in the reaction–diffusion discrete metapopulation model have been determined analytically, and the patterns have been visualized numerically. A wide range of complex spatiotemporal patterns (like periodic, quasi-periodic, chaotic) is observed with respect to the variation of diffusion coefficients and other local interacting parameters of the model.

Hematological studies of fishes are useful in the diagnosis of many diseases as well as investigation of the extent of damage to the blood. These parameters act as efficient and insightful index to examine health status, physiological and pathological changes occurring in various fishes, i.e., metabolic perturbations in fish body thereby acting as non-specific biomarkers in the field of environmental toxicology, deficiencies and chronic stress in natural as well as aquaculture systems and checking water quality. The assessments of these blood parameters help the biologists to understand the fish homeostasis and biomonitoring of severe and chronic patho-physiological changes inferable to nutrition, water quality, or disease so as to establish the normal reference values of different species and determine systematic relationships among them. Lot of work on various aspects of hematological parameters and their relation with ecological factors has been reported on several fish species from different parts of the world. Each study attributes one or other factors responsible for variation in hematological parameters among different fish species. Therefore, in the present study, an attempt has been made to compile the information about the hematological studies of various fish species reported from different parts of the world, and through this study, a general overview has been generated about the major factors responsible for the variation in hematological parameters of fish. The review provides an insight to the characteristics of hematological values showing that fluctuating internal environment of the fish, along with other intrinsic (age, body size, the cycle of sexual maturity, health condition, nutritional state, species) and extrinsic factors (temperature, stress, season, dissolved oxygen, water quality, lotic or lentic environment, stocking density, photoperiod, sampling conditions, laboratory techniques), are the reasons of huge variability of hematological parameters in fishes.

Mainstay haemophilia treatment, namely intravenous factor replacement, poses several clinical challenges including frequent injections due to the short half-life of recombinant factors, intravenous administration (which is particularly challenging in those with difficult venous access), and the risk of inhibitor development. These impact negatively upon quality of life and treatment compliance, highlighting the need for improved therapies. Several novel pharmacological therapies developed for haemophilia aim to rebalance the clotting cascade and potentially circumvent the aforementioned challenges. These therapies utilise a range of different mechanisms, namely: the extension of the circulating half-life of standard recombinant factors; the mimicking of factor VIII cofactor activity; rebalancing of coagulation through targeting of natural anticoagulants such as antithrombin and tissue factor pathway inhibitor; and inducing the production of endogenous factors with gene therapy. These therapies carry the potential of revolutionising haemophilia treatment by alleviating the current challenges presented by mainstay factor replacement. This review will provide an overview of the key trial findings related to novel therapies based on the mechanisms described above.

Juvenile to adult phase transition is a crucial part of plant life cycle. In potato, initiation of tuber development marks the beginning of such transition. Several environmental and endogenous factors have been implicated in tuber developmental process (tuberization) in potato. Photoperiod, temperature, plant age, activity of hormones, mobile RNAs and proteins are important cues that control potato tuberization. Recently, microRNAs (miRNAs) are shown to interact with these factors and play an integral role in determining the tuberization fate. This review discusses the current knowledge on function of miRNAs towards the tuberization process in potato.

A fundamental question in ecology is whether vegetation oscillations are merely a result of periodic environmental variability, or rather driven by endogenous factors. We address this question using a mathematical model of dryland vegetation subjected to annual rainfall periodicity. We show that while spontaneous oscillations do not exist in realistic parameter ranges, resonant response to periodic precipitation is still possible due to the existence of damped oscillatory modes. Using multiple time-scale analysis, in a restricted parameter range, we find that these endogenous modes can be pumped by the exogenous precipitation forcing to form sustained oscillations. The oscillations amplitude shows a resonance peak that depends on model parameters representing species traits and mean annual precipitation. Extending the study to bistability ranges of uniform vegetation and bare soil, we investigate numerically the implications of resonant oscillations for ecosystem function. We consider trait parameters that represent species with damped oscillatory modes and species that lack such modes, and compare their behaviors. We find that the former are less resilient to droughts, suffer from larger declines in their biomass production as the precipitation amplitude is increased, and, in the presence of spatial disturbances, are likely to go through abrupt collapse to bare soil, rather than gradual, domino-like collapse.

This paper attempts to conceptualize and examine regional productivity in terms of the regional endogenous development of Iran’s regions. The paper introduces a conceptual model for the study and then develops and tests the model with data for the primary regions of Iran. Large and positive correlation is found between measures of latent and explanatory independent and dependent variables in the regional productivity model. Specifically it is found that such endogenous factors as agglomeration and clustering is a critical driving force for achieving increased regional productivity and thus the tailoring of polices to support regional endogenous development and growth.

The pathogenesis of traumatic spinal cord disease involves two mechanisms causing injury to its neuronal apparatus: primary (necrosis) and secondary (apoptosis). This study assesses the involvement of a number of endogenous factors in the development of apoptosis in spinal cord and peripheral nerve trunk trauma; the role of these factors thus far remains unclear.

Epidemiological studies have shown that 70–90 % of all cancers are caused due to the chemicals present in environment. Exogenous exposure to carcinogens and their interaction with genetic sequences and endogenous factors, like exposures to products of metabolism which lead to acute stress, disruption of hormones and inflammation of tissues, are triggering factors. Due to relatively small risk of cancer following immediate exposure, the precise quantification of the burden of human cancer attributed to environmental exposure remains ambiguous, thereby leading to an assumption that a causal relationship is relatively large. Research suggests that 90–95 % of all cancers have their roots in the environmental effects on the DNA leading to genetic defects, whereas only 5–10 % can be attributed to inherited genetic defects. The hypothesis of the present review is that response of the cells to the environmental stimulants could be an evolutionary process of adaptation of the DNA. Carcinogenesis is considered as a process of adaptation of mammalian cells to sustained stress environment (SSE) by means of epigenetic alteration (EA) of the genome, mutations which arise due to EA and finally, natural selection of originated mutant cells evading apoptosis. Process of adaptation to SSE involves the emergence of senescent epigenetically reprogrammed cells with specific cancer-related EA in the genome.

This review examines the signaling pathways from the developmental and environmental point of view and the interactions among external conditions, hormonal regulations, and sugarsensing in wheat. Grain development is the key phase of reproductive growth that is closely associated with vegetative organ senescence, initiation of grain filling, pre-stored assimilates remobilization, and maturation. Senescence is characterized by loss of chlorophyll and the degradation of proteins, nucleic acids, lipids as well as nutrient exports to the sink. The initiation and progression of vegetative organ senescence are under the control of an array of environmental signals (such as biotic and abiotic stresses, darkness, and nutrient availability) and endogenous factors (including aging, multiple hormones, and sugar availability). This review will discuss the major breakthroughs in signal transduction for the wheat (Triticum aestivum) grain development achieved in the past several years, with focuses on the regulation of senescence, reserves remobilization and biosynthesis of main components of the grain. Different mechanisms of diverse signals in controlling different phrases of wheat grain development, and cross talks between different signaling pathways will also be discussed. For perspectives, key signaling networks for grain development remain to be elucidated, including cross talks and the interactions between various environmental factors and internal signals.

The endogenous factors that drive logistics performance have generated substantial literature. Our understanding of exogenous factors, such as national institutions, that determine logistics performance is still underdeveloped. We used a path analysis to examine the influence of six institutional constructs on logistics performance for 116 countries. Our findings show that five of the six institutional constructs—political risk, financial risk, economic freedom, political freedom, and competitiveness—have direct or indirect influences on logistics performance. Our model was tested using summated variables. Future research may aggregate manifest variables to ascertain relevant institutional variables for a parsimonious model.

The growing tumor employs various strategies to establish its growth, progression and spread in the host. Angiogenesis or formation of new blood vessels from existing ones and escape from immune surveillance are the two critical steps that ensure proper establishment and growth of the newly formed tumor. Thus understanding the novel pathways associated with tumor angiogenesis and immunity may lead to the development of newer therapeutic strategies using the regulators of these pathways to improve patient outcomes. These two pivotal steps in the process of tumorigenesis are governed by plethora of endogenous factors. The neuroendocrine molecules, which include the catecholamine neurotransmitters, dopamine, norepinephrine and epinephrine are of growing interest considering their varied and diverse regulatory roles both in the process of tumor angiogenesis and tumor immunity. This review focuses on the emerging roles of catecholamines in modulating tumor angiogenesis and immunity, and also discusses the probable molecular mechanisms of their actions. Understanding of this new group of endogenous regulators of tumor growth may lead to the development of newer therapeutic approaches for the treatment of cancer.

Brain injury during development can have severe, long-term consequences. Using an array of animal models, we have an understanding of the etiology of perinatal brain injury. However, we have only recently begun to address the consequences of endogenous factors such as genetic sex and developmental steroid hormone milieu. Our limited understanding has sometimes led researchers to make over-generalizing and potentially dangerous statements regarding treatment for brain injury. Therefore this review acts as a cautionary tale, speaking to our need to understand the effects of sex and steroid hormone environment on the response to brain trauma in the neonate.

Central to the survival and reproduction of social insect queens is the size of colonies at maturity. The influence of exogenous factors such as predation, food abundance, and seasonal changes in temperature on colony size are well studied. Less well studied are endogenous life-history factors such as a queen’s fertility and lifespan, duration of worker development from egg to adult and worker lifespan. Endogenous factors regulating the rate of colony growth and colony size were simulated using the fire ant, Solenopsis invicta. Assuming ideal environmental conditions of no predation, abundant food and uniform temperature, the simulation showed unequivocally that colony size is determined by two endogenous factors: a queen’s egg-laying rate (R q) and worker longevity (L w) (Colony size = R q × L w). Thus, we are left with an unanswered question: if worker longevity contributes directly to colony size, why is the lifespan of workers so short—in most cases, a small fraction of a queen’s lifespan?

Urosepsis is one of the most frequent sepsis entities. Mortality from urosepsis is nowadays mostly lower than from other entities. Sepsis syndrome is pathophysiologically characterized by a generalized infection and immune dysregulation. Exogenous microbiological and active or passive endogenous factors released from body cells initiate and accompany the immune dysregulation. Diagnosis and therapy of urosepsis need to be instigated as early as possible (within the first hour), in order to prevent cell and tissue damage in the early phase. For this reason a series of measures is started, aimed at achieving early control of the focus of infection, providing antibiotic treatment, and stabilizing respiratory and cardiovascular function in order to optimize tissue oxygenation. A significant clinical problem ensues due to increasing antibiotic resistance mainly of enterobacteria. The choice of antibiotic therefore is made on the basis of local antibiotic resistance statistics. Dosage is determined on an individual basis, as well as according to current pharmacokinetic/pharmacodynamic knowledge. The intensive care of the septic patient needs to be started as early as on patient admission and, where necessary, continued on the intensive care ward.

Neurodegenerative diseases are featured by progressive dysfunction and death of cells in selected areas in the nervous system, determining clinical presentation. Neuronal loss is associated with conformational changes in proteins that result in extra- and intra-cellular accumulation of misfolded proteins, representing the hallmarks of many neurodegenerative disorders, summarized as proteinopathies. Intermediate forms such as oligomers and protofibrils are thought to have cytotoxic effects to neurons. Major basic processes, caused by genetic, environmental, and endogenous factors, in addition to abnormal protein dynamics with defective degradation due to deficiency of the ubiquitin-proteosomal-autophagy system, include oxidative stress and free radical formation, impaired bioenergetics and mitochondrial dysfunction, disruption of neuronal Golgi apparatus and transport, molecular chaperones, neurotrophins and "neuroinflammatory" processes. These mechanisms are interrelated in vicious circles finally leading to programmed cell death. A common feature of these conditions is a long run until sufficient protein accumulates, followed by a cascade of symptoms over many years with increasing disability leading to death. This provides a wide therapeutic window, especially in groups at risk identified early and preclinical diagnosis becomes feasible. Neurodegenerative disorders are classified according to known genetic mechanisms or to the major components of protein deposits. Although this has been a productive paradigm for the development of diagnostic consensus criteria, recent molecular biologic and genetic approaches have revealed that there are both overlap and intraindividual diversities between different phenotypes, related to synergistic mechanisms between major pathologic proteins (beta-amyloid, tau, alpha-synuclein, TDP-43), suggesting common pathogenic mechanisms. The nature, time course, and molecular causes of cell degeneration and demise, and the role of various pathogenic factors are a matter of considerable debate, but recent studies have provided insight into the basic processes in neurodegeneration and the roles of cell death programs common to this complex group of disorders, offering new ways for future prevention and treatment strategies.

An econometric model is developed to help explain uncertain yields from processes that generate inherently skewed outcomes. The yield is modeled as the interaction of potential and effort functions, where potential represents maximum yield that would be observed, if the effort was infinite. The potential function is determined by some endogenous factors, and the effort function is determined by an exogenous input and allows for increasing and decreasing marginal returns to effort. A non-linear model incorporating these features is theoretically derived and empirically tested using data on outcomes from sales-tax audits. The results document the superiority of the proposed model in capturing the underlying relationships, and providing a better out-of -sample fit to the data compared to two OLS models. The proposed model can be applied in various business and non-business settings.

Venous thromboembolism (VTE) is a common cause of morbidity and mortality with an estimated annual incidence of 1 : 1,000. Patients show individual risk profiles with regard to recurrent VTE and treatment-associated bleeding, which are characterized by the presence of endogenous factors (such as hereditary thrombophilic disorders), but much more by exogenous factors (underlying disease). This results in risk-adapted therapeutic recommendations, which will be discussed in the following review.

Flowering in rice is influenced by not only endogenous factors that comprise an autonomous pathway, but also environmental effects, such as photoperiod, water availability, and temperature just before floral initiation. Recent molecular genetics studies have elucidated the functional roles of genes involved in the photoperiod pathway, e.g., photoreceptors, circadian clock components, and short-day (SD) promotion factors. Although these molecular players are well conserved between rice andArabidopsis, their actual genetic functions are distinct. This is exemplified byHd1 (aCO counterpart) and phytochromes, in particular, ricePHYA. Hd1 has a dual role in regulating flowering time and the expression ofHd3a (anFT counterpart) repression under long-day (LD) conditions while promotion under SDs. Models have been proposed to explain these photoperiod-dependent antagonistic activities. Some regulatory factors are present in only one of the model systems, e.g.,FLC inArabidopsis orEhd1 in rice. Furthermore, epistatic relationships vary among such flowering regulators asHd3a (FT), OsMADS50 (SOCT), andOsMADS14 (AP1). Further experiments to probe these differences will be essential to enlarging our understanding of the diversified flowering regulation mechanisms in rice.

The induction of antigen-specific tolerance is essential to maintain immune homeostasis, control autoreactive T cells, prevent the onset of autoimmune diseases and achieve tolerance of transplants. Inflammation is a necessary process for eliminating pathogens, but can lead to serious deleterious effects in the host if left unchecked. Identifying the endogenous factors that control immune tolerance and inflammation is a key goal in the field of immunology. In the last decade, various neuropeptides that are produced by immune cells with potent anti-inflammatory actions were found to participate in the maintenance of tolerance in different immunological disorders.

Several animal species are considered to exhibit what is called negligible senescence, i.e. they do not show signs of functional decline or any increase of mortality with age, and do not have measurable reductions in reproductive capacity with age. Recent studies in Naked Mole Rat (NMR) and long- lived sea urchin showed that the level of gene expression changes with age is lower than in other organisms. These phenotypic observations correlate well with exceptional endurance of NMR tissues to various genotoxic stresses. Therefore, the lifelong transcriptional stability of an organism may be a key determinant of longevity. However, the exact relation between genetic network stability, stress-resistance and aging has not been defined. We analyze the stability of a simple genetic- network model of a living organism under the influence of external and endogenous factors. We demonstrate that under most common circumstances a gene network is inherently unstable and suffers from exponential accumulation of gene-regulation deviations leading to death. However, should the repair systems be sufficiently effective, the gene network can stabilize so that gene damage remains constrained along with mortality of the organism, which may then enjoy a remarkable degree of stability over very long times. We clarify the relation between stress-resistance and aging and suggest that stabilization of the genetic network may provide a mathematical explanation of the Gompertz equation describing the relationship between age and mortality in many species, and of the apparently negligible senescence observed in exceptionally long-lived animals. The model may support a range of applications, such as systematic searches for therapeutics to extend lifespan and healthspan., 8 pages, 2 figures

Historically, inappropriate lifestyle with an inadequate dietary intake of vitamin C has been associated with poor wound healing as a clinical manifestation of scurvy. In modern times, clinical evidence produced over the past few decades indicates that a modern lifestyle factor, such as smoking, together with biologic characteristics, like old age and male gender, are risk factors for abdominal wall hernia and recurrence. The pathologic pathways for these clinical observations are unclear. Yet, evidence from animal and human studies suggests that these exogenous and endogenous factors may have a negative impact on collagen metabolism, enhancing degradation and impairing formation.

Venous thromboembolism is a common cause of morbidity and mortality with an estimated annual incidence of 1:1,000. Several patient groups at risk can be differentiated, according to the presence of endogenous factors (such as hereditary thrombophilic disorders), but much more by exogenous factors (underlying disease). This results in risk-adapted recommendations for prophylaxis and therapy, which will be discussed in the following overview.

Physical growth and development of children, determined by endogenous factors (genetic and paragenetic) is modified by numerous exogenic ones. This affects differentiation of ways of growth in individual children. In order to estimate the individual growth patterns and changes in growth rate as well as differences in growth of boys and girls, one must observe the process of growth of the same children and over a period of many years (longitudinal study). Such longitudinal study is the only way to provide information about the variability of growth and growth velocity at each age.

The investigation is concerned with slow oscillations of the intracellular calcium concentration, fast oscillations of the membrane potential, and their interactions during bursting generation. The question associated with functioning of the bursting mode is considered: how is the condition of simultaneous existence of the slow and fast membrane potential oscillations (necessary for the bursting mode) realized under exo- and endogenous actions that result in changes in the neuron membrane parameters? To answer the question the regions of existence of fast, slow and bursting oscillations have been constructed on different parameter planes. The study has revealed that in spite of the fact the regions of the existence of the slow and fast oscillations are sensitive to parameter variations, the condition of the bursting mode existence remains due to invariance of the spatial vicinity of these regions. Furthermore, it has been demonstrated that there exists the possibility to enhance the maximal conductances of the calcium-dependent currents simultaneously such that even strong variations of their values do not induce changes of the oscillations mode (i.e. it remains bursting).

In normal human cells there is a steady accumulation of mutations with time. We argue that the great majority of these mutations arise spontaneously and are due to endogenous factors or processes that damage DNA. A small fraction of these mutations converts a normal cell into a cell that is initiated towards the development of cancer. We propose that, in general, these initiated cells are more susceptible to the mutagenic effects of exogenous carcinogenic agents than to the mutagenic effects of endogenous factors. Indeed, it can be assumed that in most instances the initiation event is due to a mutation which causes inactivation or loss of a mutation avoidance gene, such as the p53 gene, or a gene which is involved in the repair of damaged DNA. Recent studies have shown that most of such mutations lead to a considerable enhancement in the mutagenicity of many exogenous agents, whereas the mutagenicity of endogenous factors is less affected. Furthermore, the progressive accumulation of mutations with increasing age implies that more initiated cells are likely to be found in older individuals. Therefore, sensitivity to the carcinogenic effect of exogenous mutagens can generally be assumed to increase in older people.

The vasculature suffers damage as a result of diabetes, often leading to conditions such as kidney failure. In bench to bedside, Christian Rask-Madsen and George King examine endogenous factors that protect against damage of the vasculature, such as vascular-endothelial growth factor (VEGF). Recent studies report that VEGF is expressed by kidneys and fends off renal failure; such findings have implications for the development of treatments that harness endogenous factors and sound a note of caution for the therapeutic use of VEGF inhibitors. People with end-stage renal disease often die of cardiovascular complications and clinical studies have shown that one popular class of drugs, statins, does not work in this population. In bedside to bench, S. Ananth Karumanchi and Ravi Thadhani show how this clinical finding is spurring research into the biological mechanisms behind cardiovascular death in people with kidney disease.

Cortisol is the principal corticosteriod in teleost fishes and its plasma concentrations rise dramatically during stress. The relationship between this cortisol increase and its metabolic consequences are subject to extensive debate. Much of this debate arises from the different responses of the many species used, the diversity of approaches to manipulate cortisol levels, and the sampling techniques and duration. Given the extreme differences in experimental approach, it is not surprising that inconsistencies exist within the literature. This review attempts to delineate common themes on the physiological and metabolic roles of cortisol in teleost fishes and to suggest new approaches that might overcome some of the inconsistencies on the role of this multifaceted hormone. We detail the dynamics of cortisol, especially the exogenous and endogenous factors modulating production, clearance and tissue availability of the hormone. We focus on the mechanisms of action, the biochemical and physiological impact, and the interaction with other hormones so as to provide a conceptual framework for cortisol under resting and/or stressed states. Interpretation of interactions between cortisol and other glucoregulatory hormones is hampered by the absence of adequate hormone quantification, resulting in correlative rather than causal relationships.

Coronary artery disease is a complex disease influenced by modifiable risk factors as well as genetic susceptibility. The genetics of coronary artery disease and myocardial infarction have long been enigmatic. Recent advances in molecular genetics and biology, bioinformatics, and statistics have allowed us to study the interaction of exogenous and endogenous factors. Recent genome-wide association studies and their meta-analyses have included thousands of patients and healthy individuals and provided the statistical power to identify genetic variants, each associated with a rather small increase in risk. Thus far, more than 45 risk loci have been identified. Nevertheless, the search for genetics-based improvements in therapy and prevention has just begun. Hitherto unrecognized mechanisms may provide promising drug targets and early interventional strategies. Furthermore, the sum of risk alleles may facilitate risk assessment as they provide complementary information to traditional risk scores.

There is increasing recognition of the potential contribution of local small and medium enterprises (SMEs) towards employment and economic growth in Singapore. Unfortunately, SMEs tend to have a high mortality rate. A survey was conducted among owners or managers of local SMEs to identify factors perceived as important in affecting business failures. The research results indicate that endogenous factors were viewed by respondents as more critical in causing SME failures than exogenous factors. Important exogenous and endogenous factors in specific areas were identified.

The present report describes a systematic study comparing and combining methods currently used for the removal of endogenous factors known to affect the interaction of GABA with its receptor. The effects of these methods were analyzed by performing [3H]GABA binding studies, and by measuring the amount of residual GABA left in the different membrane preparations. The effectiveness of these methods were also applied to different developmental stages. The results show that: 1) an exhaustive buffer washing procedure is necessary to accurately measure the maximal binding capacity (Bmax) of the low-affinity GABA binding site, and 2) the use of more drastic methods, including freeze-thawing and Triton treatment allows a clear demonstration of receptor heterogeneity and a precise measurement of the Bmax of the high-affinity GABA binding site as well as increases the affinity of the low-affinity site. The analysis of the Bmax values obtained with these different procedures in relation to the values of GABA removal, strongly indicates that the exhaustive washing procedure removes some unknown endogenous substances required for Triton treatment to exhibit its maximal effectiveness. Finally, a detailed analysis of Kd and Bmax values obtained with these three methods in the developing nervous tissue shows the existence of significant differences with regard to their effectiveness in removing endogenous substances when applied in different developmental stages.

This paper highlights the difficulty of developing HT firms in a peripheral region of Spain. Although the endogenous development of HT firms in these regions is possible, their evolution depends on more central regions. The firm's geographical location and the type of HT production are the most important endogenous factors governing the firm's success.

Until now the day/night and seasonal rhythmicity in the synthesis of 5-methoxyindoles (MI) is thought to be regulated by environmental factors, especially photoperiod and temperature. Endogenous factors are also implicated in the generation of N-acetyltransferase and hydroxyindole-O-methyltransferase activity rhythms. In the present experiments seasonal rhythmicity in the synthesis of MI in the pineal gland was investigated in hamsters kept under the same artificial conditions throughout the year. Though the environmental conditions were the same, day/night and seasonal rhythmicity in the production of MI in the pineal were observed indicating the existence of endogenous factors influencing the rhythmicities. In November, most of the MI showed the highest synthesis, MA and ML excepted, which were especially produced in July and September. The results obtained sustain the hypothesis that aMT is synthesized from MT rather than from aHT. Moreover, the rhythmicities in aMT synthesis are not identical to those found in aMT concentration as described in the literature. This indicates that synthesis and concentration of a compound are not comparable. At the end of the light period, when aMT injections have an antigonadotropic effect, a peak of aMT synthesis was always present. Although MI synthesis showed seasonal rhythmicity, no reproductive cycle occurred in the hamsters. At present, the concept that the pro- and/or antigonadal effects of the pineal are mediated by aMT seems to be the most acceptable. The present results, however, indicate that aMT and perhaps other MI, often regarded as factors influencing gonadal growth in golden hamsters, are not the only factors involved.