Short-term Physiological Changes Research Articles

Climate change and population persistence in a hibernating marsupial.

Climate change has physiological consequences on organisms, ecosystems and human societies, surpassing the pace of organismal adaptation. Hibernating mammals are particularly vulnerable as winter survival is determined by short-term physiological changes triggered by temperature. In these animals, winter temperatures cannot surpass a certain threshold, above which hibernators arouse from torpor, increasing several fold their energy needs when food is unavailable. Here, we parameterized a numerical model predicting energy consumption in heterothermic species and modelled winter survival at different climate change scenarios. As a model species, we used the arboreal marsupial monito del monte (genus Dromiciops), which is recognized as one of the few South American hibernators. We modelled four climate change scenarios (from optimistic to pessimistic) based on IPCC projections, predicting that northern and coastal populations (Dromiciops bozinovici) will decline because the minimum number of cold days needed to survive the winter will not be attained. These populations are also the most affected by habitat fragmentation and changes in land use. Conversely, Andean and other highland populations, in cooler environments, are predicted to persist and thrive. Given the widespread presence of hibernating mammals around the world, models based on simple physiological parameters, such as this one, are becoming essential for predicting species responses to warming in the short term.

Short-term physiological responses to moderate heat stress in grazing dairy cows in temperate climate.

Even in temperate climate regions, an increase in ambient temperature and exposure to solar radiation can cause heat stress in lactating dairy cows. We hypothesised that grazing dairy cows exhibit short-term physiological changes due to increasing heat load under moderate climate conditions. Over two consecutive summers, 38 lactating Holstein dairy cows were studied in a full-time grazing system. Data were collected in 10 experimental periods of up to three consecutive days with a moderate comprehensive climate index (CCI). The individual animals' vaginal temperature (VT), heart rate, and locomotor activity data were automatically monitored with sensors. Blood samples and proportional whole milk samples were collected at afternoon milking. The concentrations of beta-hydroxybutyrate, glucose, non-esterified fatty acids, urea nitrogen, plasma thyroxine and triiodothyronine were analysed in blood plasma, and fat, protein, lactose, urea nitrogen, cortisol, Na+, K+, and Cl- concentrations were analysed in milk. The daily distribution of VT recordings greater than 39°C showed a circadian rhythm with a proportion of recordings of 2% and lower during the night and a percentage of 10% or higher in the afternoon. The cows' maximal daily vaginal temperature (VTMAX) between 0830 and 1430h was positively related to the mean daily CCI in the same time period (CCIMEAN; mean and SD 23.6±5.4°C). Cows with greater VTMAX had an increased mean heart rate, plasma glucose and milk cortisol concentrations and decreased concentrations of plasma thyroxine and triiodothyronine. The concentration of Na+ in milk was lower, and the concentration of K+ in milk tended to be higher in cows with increased VTMAX. For beta-hydroxybutyrate, non-esterified fatty acids and urea nitrogen concentrations in plasma and fat and lactose concentrations in milk no relationships were found in terms of increasing VT. For milk urea nitrogen and protein concentrations, the proportion of total variance explained by inter-individual or -period variance was high. In conclusion, changes observed in milk and blood likely reflected short-term physiological responses to moderate heat stress. In particular, milk cortisol and Na+ may be useful traits for timely monitoring of heat stress in individual cows because their inter-individual variances were relatively small and samples can be collected non-invasively.

An updated review of cold shock and cold stress in fish.

Temperature is critical in regulating virtually all biological functions in fish. Low temperature stress (cold shock/stress) is an often-overlooked challenge that many fish face as a result of both natural events and anthropogenic activities. In this study, we present an updated review of the cold shock literature based on a comprehensive literature search, following an initial review on the subject by M.R. Donaldson and colleagues, published in a 2008 volume of this journal. We focus on how knowledge on cold shock and fish has evolved over the past decade, describing advances in the understanding of the generalized stress response in fish under cold stress, what metrics may be used to quantify cold stress and what knowledge gaps remain to be addressed in future research. We also describe the relevance of cold shock as it pertains to environmental managers, policymakers and industry professionals, including practical applications of cold shock. Although substantial progress has been made in addressing some of the knowledge gaps identified a decade ago, other topics (e.g., population-level effects and interactions between primary, secondary and tertiary stress responses) have received little or no attention despite their significance to fish biology and thermal stress. Approaches using combinations of primary, secondary and tertiary stress responses are crucial as a research priority to better understand the mechanisms underlying cold shock responses, from short-term physiological changes to individual- and population-level effects, thereby providing researchers with better means of quantifying cold shock in laboratory and field settings.

Characterizing Environmental and Occupational Exposures Associated to Kidney Function among Migrant Farm workers in Mexico

TPS 791: Occupational health 1, Exhibition Hall, Ground floor, August 26, 2019, 3:00 PM - 4:30 PM Chronic kidney disease of undetermined cause (CKDu) is an epidemic that is disproportionately affecting young workers in warm regions throughout the world. Even though the risk factors of CKDu are not fully understood, several factors, such as pesticides and heat exposure, have been proposed to explain the pattern of this disease. However, little is known about the impact of short-term physiological changes in intense work-environmental conditions on kidney functioning. In addition, no studies have evaluated kidney functioning in migrant farm workers in Northern Mexico, who are subject to strenuous working conditions in extreme heat environments when they migrate from Southern Mexico to semi-arid regions of Northern Mexico. Our objective is to characterize the renal function in migrant farm workers in relation to the environmental conditions in the semi-arid region of Sonora, Mexico. A longitudinal study of six-months (harvest season) duration will be conducted. One hundred and fifty participants will be recruited and followed for six months. Approximately 100 farm workers at a large-scale commercial grape farm will be randomly divided into 50 working in an organic area and 50 working in a conventional area. The two farm worker groups will be compared with 50 non-farmworkers (reference group). To determine kidney functioning at multiple points during the harvest season, urine and serum will be collected and analyzed for several biomarkers. The association between heat stress, measured using a Wet Bulb Globe Temperature (WBGT) instrument and the Physiological Strain Index (PSI), and kidney functioning will be examined. Similarly, several urinary pesticide biomarkers, including those for organophosphates and pyrethroids, will be analyzed during the harvest season to evaluate a possible association between pesticides and kidney function. At completion of this study, we expect to have a better understanding of the association between environmental risk factors and kidney functioning in migrant farm workers.

Diel patterns of microphytobenthic primary production in intertidal sediments: the role of photoperiod on the vertical migration circadian rhythm

Diel primary production patterns of intertidal microphytobenthos (MPB) have been attributed to short-term physiological changes in the photosynthetic apparatus or to diel changes in the photoautotrophic biomass in the sediment photic layer due to vertical migration. Diel changes in primary production and vertical migration are entrained by external factors like photoperiod and tides. However, the role of photoperiod and tides has not been experimentally separated to date. Here, we performed laboratory experiments with sediment cores kept in immersion, in the absence of tides, with photoperiod or under continuous light. Measurements of net production, made with O2 microsensors, and of spectral reflectance at the sediment surface showed that, in intertidal sediments, the photoperiod signal was the major driver of the diel patterns of net primary production and sediment oxygen availability through the vertical migration of the MPB photoautotrophic biomass. Vertical migration was controlled by an endogenous circadian rhythm entrained by photoperiod in the absence of tides. The pattern progressively disappeared after 3 days in continuous light but was immediately reset by photoperiod. Even though a potential contribution of a subjective in situ tidal signal cannot be completely discarded, Fourier and cross spectral analysis of temporal patterns indicated that the photosynthetic circadian rhythm was mainly characterized by light/dark migratory cycles.

The presence of females induces elevated cortisol levels in an alpha male: Experimental evidence in chimpanzees.

In group-living primates, it has been reported that the alpha male exhibits high concentrations of cortisol and testosterone in the context of mating competition. We investigated how the presence of females affected salivary cortisol and testosterone levels in males from a small captive group of chimpanzees (Pan troglodytes). Specifically, we assessed whether the presence of females resulted in a rapid increase in salivary cortisol and testosterone levels in the alpha male. We compared the social behavior and salivary hormone concentrations of four males before and after the presentation of receptive females. Three times a day, we collected saliva samples, a useful matrix for investigating short-term hormonal changes, and measured cortisol and testosterone concentration by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The frequency of inter-male aggression increased in the presence of females, indicating intense competition among males. Salivary cortisol levels increased in all males in the presence of females; however, the increase was significantly more pronounced in the alpha male. We found a complex three-way interaction among the presence of females, sampling timings, and male dominance rank in the analysis of salivary testosterone. Contrary to our prediction, a post hoc analysis revealed that salivary testosterone levels decreased after female introduction and that the alpha male did not show a higher level of salivary testosterone. Our study provides experimental evidence suggesting that the presence of females plays a significant role in the rank-related variation in the cortisol levels in male chimpanzees. Furthermore, our findings demonstrate the usefulness of salivary hormones for detecting short-term physiological changes in studies of socioendocrinology.

Short‐term Changes in Left Ventricular Dyssynchrony Leads to Congestive Heart Failure

Ventricular dyssynchrony (VD) may lead to congestive heart failure (CHF). VD is characterized by a difference in the timing of contractions in the ventricles of the heart and has become a prominent pathophysiological feature of CHF. While studies have been done to understand the long‐term effects of VD that lead to CHF, little is known on the short‐term changes associated with VD. This study explores the acute effects of induced VD in‐vivo. Animals will undergo left ventricular pacing to induce VD and changes in mitochondrial structure and function will be analyzed to determine if abnormalities lead to apoptosis and cardiac remodeling. In this study, tissue homogenates from control and paced animals will be used to perform western blot analysis to investigate the changes in expression of mitochondrial respiratory chain complexes and proteins involved in apoptosis. We will measure adenosine triphosphate levels (ATP) to assess overall mitochondrial function. It is expected that VD increases cell death as a result of mitochondrial dysfunction, leading to activation of a fibrotic response. Immunohistochemistry will be used to investigate neutrophil infiltration and myofibroblast formation to confirm the activation of a fibrotic response. We will also evaluate reactive oxygen species and matrix metalloproteinases activities, which implicate cell injury and death that results in cardiac remodeling. We hypothesize that induced left ventricular pacing in a non‐congestive heart failure model will create short‐term changes that alter cardiovascular structure and metabolism. It is important to understand the short‐term physiological changes that result from dyssynchrony because electro‐mechanical conditions found in the absence of CHF can result in long‐term effects that may eventually lead to CHF.Support or Funding InformationThis research project will be supported through FATSA funding by Dr. Katrina Yamazaki.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Environmental stress is the major cause of transcriptomic and proteomic changes in GM and non-GM plants

The approval of genetically modified (GM) crops is preceded by years of intensive research to demonstrate safety to humans and environment. We recently showed that in vitro culture stress is the major factor influencing proteomic differences of GM vs. non-GM plants. This made us question the number of generations needed to erase such “memory”. We also wondered about the relevance of alterations promoted by transgenesis as compared to environment-induced ones. Here we followed three rice lines (1-control, 1-transgenic and 1-negative segregant) throughout eight generations after transgenesis combining proteomics and transcriptomics, and further analyzed their response to salinity stress on the F6 generation. Our results show that: (a) differences promoted during genetic modification are mainly short-term physiological changes, attenuating throughout generations, and (b) environmental stress may cause far more proteomic/transcriptomic alterations than transgenesis. Based on our data, we question what is really relevant in risk assessment design for GM food crops.

Acute Aerobic Swimming Exercise Induces Distinct Effects in the Contractile Reactivity of Rat Ileum to KCl and Carbachol.

Aerobic exercise promotes short-term physiological changes in the intestinal smooth muscle associated to the ischemia-reperfusion process; however, few studies have demonstrated its effect on the intestinal contractile function. Thus, this work describes our observations regarding the influence of acute aerobic swimming exercise in the contractile reactivity, oxidative stress, and morphology of rat ileum. Wistar rats were divided into sedentary (SED) and acutely exercised (EX-AC) groups. Animals were acclimated by 10, 10, and 30 min of swimming exercise in intercalated days 1 week before exercise. Then they were submitted to forced swimming for 1 h with a metal of 3% of their body weight attached to their body. Animals were euthanized immediately after the exercise section and the ileum was suspended in organ baths for monitoring isotonic contractions. The analysis of lipid peroxidation was performed in order to determinate the malondialdehyde (MDA) levels as a marker of oxidative stress, and intestinal smooth muscle morphology by histological staining. Cumulative concentration-response curves to KCl were altered in the EX-AC with an increase in both its efficacy and potency (Emax = 153.2 ± 2.8%, EC50 = 1.3 ± 0.1 × 10−2 M) compared to the SED group (Emax = 100%, EC50 = 1.8 ± 0.1 × 10−2 M). Interestingly, carbachol had its efficacy and potency reduced in the EX-AC (Emax = 67.1 ± 1.4%, EC50 = 9.8 ± 1.4 × 10−7 M) compared to the SED group (Emax = 100%, EC50 = 2.0 ± 0.2 × 10−7 M). The exercise did not alter the MDA levels in the ileum (5.4 ± 0.6 μ mol/mL) in the EX-AC compared to the SED group (8.4 ± 1.7 μ mol/mL). Moreover, neither the circular nor the longitudinal smooth muscle layers thickness were modified by the exercise (66.2 ± 6.0 and 40.2 ± 2.6 μm, respectively), compared to the SED group (61.6 ± 6.4 and 34.8 ± 3.7 μm, respectively). Therefore, the ileum sensitivity to contractile agents is differentially altered by the acute aerobic swimming exercise, without affecting the oxidative stress and the morphology of ileum smooth muscle.

Saliva sampling in dogs: How to select the most appropriate procedure for your study

Saliva sampling is an easy, noninvasive method to assess short-term physiological changes, and as such is a valuable addition to behavioral studies in dogs. Different methods for collecting saliva samples in dogs have been reported in literature, and there appears to be no “standard operating procedure” that suits the needs of all studies. Hence, this review provides a clear overview of “considerations” to take into account when selecting the most appropriate saliva sampling procedure. Different collection devices, procedures, and practical considerations are discussed in light of available literature and the authors' practical experience, to guide researchers in this selection process. Additional factors that might influence the (interpretation of the) results are also discussed, so that these can be taken into account for optimization of the research protocol. This guidance should facilitate the initial selection of the most appropriate procedure, but each researcher is strongly recommended to conduct preliminary tests to detect and prevent possible biases or practical issues beforehand. Standardization is key to obtain reliable results that can be compared to other studies.

Short-term physiological changes in roots and leaves of sugarcane varieties exposed to H2O2 in root medium

The aim of this study was to evaluate the differential sensitivity of sugarcane genotypes to H2O2 in root medium. As a hypothesis, the drought tolerant genotype would be able to minimize the oxidative damage and maintain the water transport from roots to shoots, reducing the negative effects on photosynthesis. The sugarcane genotypes IACSP94-2094 (drought tolerant) and IACSP94-2101 (drought sensitive) were grown in a growth chamber and exposed to three levels of H2O2 in nutrient solution: control; 3mmolL−1 and 80mmolL−1. Leaf gas exchange, photochemical activity, root hydraulic conductance (Lr) and antioxidant metabolism in both roots and leaves were evaluated after 15min of treatment with H2O2. Although, root hydraulic conductance, stomatal aperture, apparent electron transport rate and instantaneous carboxylation efficiency have been reduced by H2O2 in both genotypes, IACSP94-2094 presented higher values of those variables as compared to IACSP94-2101. There was a significant genotypic variation in relation to the physiological responses of sugarcane to increasing H2O2 in root tissues, being root changes associated with modifications in plant shoots. IACSP94-2094 presented a root antioxidant system more effective against H2O2 in root medium, regardless H2O2 concentration. Under low H2O2 concentration, water transport and leaf gas exchange of IACSP94-2094 were less affected as compared to IACSP94-2101. Under high H2O2 concentration, the lower sensitivity of IACSP94-2094 was associated with increases in superoxide dismutase activity in roots and leaves and increases in catalase activity in roots. In conclusion, we propose a general model of sugarcane reaction to H2O2, linking root and shoot physiological responses.

A physiological comparison of three techniques for reviving sockeye salmon exposed to a severe capture stressor during upriver migration.

Capture of fish in commercial and recreational fisheries causes disruption to their physiological homeostasis and can result in delayed mortality for fish that are released. For fish that are severely impaired, it may be desirable to attempt revival prior to release to reduce the likelihood of post-release mortality. In this study, male sockeye salmon (Oncorhynchus nerka) undergoing their upriver migration were used to examine short-term physiological changes during the following three revival treatments after beach seine capture and air exposure: a pump-powered recovery box that provided ram ventilation at one of two water flow rates; and a cylindrical, in-river recovery bag, which ensured that fish were oriented into the river flow. Beach seine capture followed by a 3 min air exposure resulted in severe impairment of reflexes such that fish could not maintain positive orientation or properly ventilate. All three revival treatments resulted in significant reductions in reflex impairment within 15 min, with full recovery of reflex responses observed within 60-120 min. For most variables measured, including plasma lactate, cortisol and osmolality, there were no significant differences among revival treatments. There was some evidence for impaired recovery in the low-flow recovery box, in the form of higher haematocrit and plasma sodium. These data mirror published recovery profiles for a recovery box study in the marine environment where a survival benefit occurred, suggesting that the methods tested here are viable options for reviving salmon caught in freshwater. Importantly, with most of the benefit to animal vitality accrued in the first 15 min, prolonging recovery when fish become vigorous may not provide added benefit because the confinement itself is likely to serve as a stressor.

Differential effects of insemination volume and substance on reproductive changes in honey bee queens (Apis mellifera L.)

Mating causes dramatic changes in female insects at the behavioural, physiological and molecular level. The factors driving these changes (e.g. seminal proteins, seminal volume) and the molecular pathways by which these factors are operating have been characterized only in a handful of insect species. In the present study, we use instrumental insemination of honey bee queens to examine the role of the insemination substance and volume in triggering post-mating changes. We also examine differences in gene expression patterns in the fat bodies of queens with highly activated ovaries to determine if events during copulation can cause long-term changes in gene expression. We found that the instrumental insemination procedure alone caused cessation of mating flights and triggered ovary activation, with high-volume inseminated queens having the greatest ovary activation. Hierarchical clustering grouped queens primarily by insemination substance and then insemination volume, suggesting that while volume may trigger short-term physiological changes (i.e. ovary activation) substance plays a greater role in regulating long-term transcriptional changes. The results of gene ontology analysis and comparison with previous studies suggest that both insemination substance and volume trigger molecular post-mating changes by altering overlapping gene pathways involved in honey bee reproduction. We also discuss the effects on two genes (vitellogenin and transferrin) involved in reproduction and defence responses.

Introduction to the role of air pollution in heart disease

Major risk factors for atherosclerotic cardiovascular disease include hypertension, dyslipidemia, smoking, diabetes, obesity, and lack of physical exercise. While most of these factors act chronically, some of them (e.g., smoking) may acutely affect the cardiovascular system. Besides these major risk factors, there are also a number of triggers and risk factors that may produce acute short-term physiological changes (such as surge in arterial pressure or heart rate, an increase in coagulability, or vasoconstriction) that can lead to acute cardiovascular events. Air pollution has the potential to serve as both acute and chronic risk factor for cardiovascular disease. Some studies suggest that chronic exposure (months to years) may lead to or accelerate atherosclerotic disease. In addition, high air pollution days may also serve as a trigger whereby an acute increase in air pollution may result in deleterious physiologic changes that simulate acute cardiac events. This issue of Air Quality, Atmosphere & Health presents papers based on presentations given at a Continuing Medical Education Symposium entitled “The Role of Air Pollution in Heart Disease,” presented at the Heart Institute of Good Samaritan Hospital, an affiliate of the Keck School of Medicine at the University of Southern California, in Los Angeles, on September 11, 2009. The purpose of the symposium was to provide physicians, researchers, and health professionals with information regarding the adverse effects of air pollution on the cardiovascular system and the mechanisms responsible for air pollution-related cardiovascular toxicity.

Functional Magnetic Resonance Imaging

verthepast2decades,significantadvancesinmagneticresonance imaging (MRI) techniques have opened anentirely new field of evaluating regions of neural activitybased on focal metabolic changes. Nuclear medicine studieswithsingle-photonemissiontomographyandpositronemis-sion tomography, over many years, have shown that areas ofbrain activity have increased blood flow, and the ability tomeasure increases in oxygen concentration allows detectionof these regions of activity. Correlating imaging with specificneural activity is referred to as brain mapping. The ability toobserve brain function with MRI during specific tasks andmore recently in the resting state is called functional mag-netic resonance imaging (fMRI).fMRI reveals short-term physiological changes associatedwith active brain functioning, and in this way, fMRI canidentifythedifferentpartsofthebrainwhereparticularmen-tal processes occur and can characterize the patterns of acti-vation associated with those processes. This is a dynamiccomplementary modality to the static structural informationobtainedfromconventionalMRI.fMRIhasanincreasingrolein preoperative planning with delineation of eloquent brainareas in relation to intracranial pathologies. Furthermore,fMRIhasprovidedabetterunderstandingoftheneuralbasisfor major psychiatric disorders, neurologic disorders, andsubstance abuse. Numerous functional studies have identi-fiedneuralprocessingdifferencesoralterationsinfunctionalconnectivity on MRI between patient groups and healthyindividuals, such as regarding Alzheimer’s disease.

Denervation in murine fast-twitch muscle: short-term physiological changes and temporal expression profiling

Denervation deeply affects muscle structure and function, the alterations being different in slow and fast muscles. Because the effects of denervation on fast muscles are still controversial, and high-throughput studies on gene expression in denervated muscles are lacking, we studied gene expression during atrophy progression following denervation in mouse tibialis anterior (TA). The sciatic nerve was cut close to trochanter in adult CD1 mice. One, three, seven, and fourteen days after denervation, animals were killed and TA muscles were dissected out and utilized for physiological experiments and gene expression studies. Target cDNAs from TA muscles were hybridized on a dedicated cDNA microarray of muscle genes. Seventy-one genes were found differentially expressed. Microarray results were validated, and the expression of relevant genes not probed on our array was monitored by real-time quantitative PCR (RQ-PCR). Nuclear- and mitochondrial-encoded genes implicated in energy metabolism were consistently downregulated. Among genes implicated in muscle contraction (myofibrillar and sarcoplasmic reticulum), genes typical of fast fibers were downregulated, whereas those typical of slow fibers were upregulated. Electrophoresis and Western blot showed less pronounced changes in myofibrillar protein expression, partially confirming changes in gene expression. Isometric tension of skinned fibers was little affected by denervation, whereas calcium sensitivity decreased. Functional studies in mouse extensor digitorum longus muscle showed prolongation in twitch time parameters and shift to the left in force-frequency curves after denervation. We conclude that, if studied at the mRNA level, fast muscles appear not less responsive than slow muscles to the interruption of neural stimulation.

Physiological responses to different WEB page designs

Physiological indicators of arousal have long been known to be sensitive to mental events such as positive and negative emotion, changes in attention and changes in workload. It has therefore been suggested that human physiology might be of use in the evaluation of software usability. To this, there are two main approaches or paradigms: (i) comparisons of physiological readings across periods of time to indicate different arousal levels under different circumstances, and (ii) the detection of short-term (occurring in seconds) physiological changes in response to specific events. Both approaches involve methodological, analytical and interpretational difficulties. Also, the tight experimental controls usually adopted in psychophysiological experimentation can be at odds with the needs of applied usability testing. This paper reports initial investigations of these approaches and difficulties in the evaluation of software interfaces. From exploratory data, a preliminary model is proposed which combines the two paradigms for identifying significant HCI events. Explorations of the model within the context of a web-related task are then discussed. These explorations suggest techniques and procedures for applied usability testing, and the results point to ways in which physiological data may be informative about software usability. However, further investigations involving variations in task and procedure are required.

Short-Term Physiological Changes in Turbot and Seabream Juveniles Exposed to Exogenous Ammonia

Seabream and turbot juveniles (40-520 g) were exposed to constant exogenous NH5-N concentrations (1.27-4.27 mmol/l; pH, 8.15). In 96 hr acclimated fish, plasma TA-N (total ammonia nitrogen) contents were positively correlated to ambient ammonia concentrations. The LD50 were 2.2-2.5 mmol/l TA-N in both species. There were no marked osmoregulatory disturbances and plasma urea-N, thyroid hormones levels and gill (Na-K)-ATPase activities were only affected at the highest concentrations. Liver GOT, GPT and GIDH activity dose-response were low and species dependent. In cannulated and non-cannulated turbot exposed to half 96 hr LC50 (lethal ambient concentration for 50% of the population), there was a rapid, pronounced and prolonged increase in plasma TA-N, followed by an immediate decline when exogenous ammonia supply was stopped. Maximum loading and unloading were observed within 1-3 hr. Plasma cortisol levels indicated a stressful situation in exposed fish (150 ng/ml) and a quick recovery capacity. In dose and time response experiments, the most relevant physiological indicator of ammonia stress was blood TA-N content. Other parameters tested led either to transient or low amplitude responses except when fish approached death.

The influence of light/dark cycles in mixed algal cultures on their productivity

In mass algal cultures, some form of agitation is usually provided, which amongst others, moves the organisms though an optically dense profile. During this transport, fluctuations in the light energy supply are perceived by the algae, which are of the order of 1 Hz and less. Additional to these variations the cultures are subject to diurnal, seasonal and climatic light variations. It has been suggested that turbulence with the resultant light/dark cycles enhances their productivity. However, turbulence has two major influences on an organism, i.e. it facilitates fluctuating light regimes and decreases the boundary layer which results in an increased exchange rate between the organism and its environment. With the aid of oxygen liberation measurements, the influence of fluctuating light regimes on productivity was measured. No simple relation existed, but no enhancement of productivity could be shown at cycles of 1-0·0038 Hz. Short term physiological changes were found to influence productivity severely.

Regulation of short-term changes in hepatic beta-hydroxy-beta-methylglutaryl-CoA reductase activity.

Immunotitrations of rat liver hydroxymethylglutaryl-CoA (HOMeGlt-CoA) reductase activity were performed before and after short-term changes in the nutritional or hormonal state of the animals. Changes in enzyme activity (increase or decrease) within 1 h following cholesterol feeding or glucagon or mevalonolactone administration to normal rats, or insulin administration to diabetic rats were accompanied by no change in the specific activity of the enzyme, as determined from the quantity of enzyme activity inactivated by a fixed quantity of antibody. These results support the conclusion that the loss in enzyme activity was due to conversion of the enzyme to immuno-unreactive products. In agreement with this conclusion the enzyme activity lost after these short-term physiological changes was not restorable by phosphoprotein phosphatase action. On the other hand, incubation of rat liver microsomes with ATP and Mg2+ decreased the specific activity of HOMeGlt-CoA reductase about tenfold, as determined by immunotitration. The low specific activity produced under these conditions was increased by phosphatase action to nearly the original level. The above evidence suggests that the changes in HOMeGlt-CoA reductase activity that resulted from short-term physiological changes in hormonal or nutritional states of an animal were brought about by a change in the quantity of enzyme, and not by reversible phosphorylation of pre-existing enzyme.