Characterization of circadian oscillations in alanine dehydrogenase activity in non-dividing populations of Euglena gracilis (z)

Possible factors that could generate the circadian oscillations in alanine dehydrogenase (EC 1.4.1.1.) activity observed in cultures of non-dividing Euglena gracilis (Z) have been examined in an effort to learn more about the basic timekeeping mechanism of biological clocks. No differences in K_m, pH optimum or electrophoretic mobility could be demonstrated between enzyme extracted from the minimum part of the 24-h oscillation in activity and that extracted from the maximum part. Also, no evidence for the presence of activators or inhibitors was found in mixing experiments. The effect of cycloheximide on the rhythm was examined; it was shown that the oscillation ceases in the presence of the inhibitor, but that if the inhibitor is removed after 12 h, the rhythm resumes with no apparent change in phase. Analyses of gel scans of enzyme preparations partially purified by (NH₄)₂SO₄ fractionation and polyacrylamide gel electrophoresis indicated that there was more alanine dehydrogenase protein present at the maximum part of the cycle than there was at the minimum part. In view of these and other data, an operational model of a circadian biological clock is discussed.     

Relationship between Growth and Ageing in <Emphasis Type="Italic">Drosophila</Emphasis>

THERE are two principal groups of theories of ageing—those which hold that random cell damage is chiefly responsible for the events characteristic of ageing, which culminate in death and those which hold that ageing and death are genetically controlled. It is too soon to decide between these points of view and in any case Bullough¹ has shown that they are not mutually exclusive. So far experiments to test the random error theories of ageing, involving exposure of organisms to unnaturally large or even small amounts of agents such as X-rays and mutagenic agents (for reviews, see refs. 2 and 3), have been controversial and inconclusive.     

Parallel dose-response curves in combination experiments

A possible experimental design for combination experiments is to compare the doseresponse curve of a single agent with the corresponding curve of the same agent using either a fixed amount of a second one or a fixed dose ratio. No interaction is then often defined by a parallel shift of these curves. We have performed a systematic study for various types of doseresponse relations both for the dose-additivity (Loewe additivity) and for the independence (Bliss independence) criteria for defining zero interaction. Parallelism between doseresponse curves of a single agent and those of the same agent in the presence of a fixed amount of another one is found for the Loewe-additivity criterion for linear doseresponse relations. For nonlinear relations, one has to differentiate between effect parallelism (parallel shift on the effect scale) and dose parallelism (parallel shift on the dose scale). In the case of Loewe additivity, zero-interaction dose parallelism is found for power, Weibull, median-effect and logistic doseresponse relations, given that special parameter relationships are fulfilled. The mechanistic model of competitive interaction exhibits dose parallelism but not effect parallelism for Loewe additivity. Bliss independence and Loewe additivity lead to identical results for exponential doseresponse curves. This is the only case for which dose parallelism was found for Bliss independence. Parallelism between single-agent doseresponse relations and Loewe additivity mixture relations is found for examples with a fixed doseratio design. However, this is again not a general property of the design adopted but holds only if special conditions are fulfilled. The comparison of combination doseresponse curves with single-agent relations has to be performed taking into account both potency and shape parameters. The results of this analysis lead to the conclusion that parallelism between zero interaction combination and single-agent doseresponse relations is found only for special cases and cannot be used as a general criterion for defining zero-interaction in combined-action assessment even if the correct potency shift is taken into account.     

Venography in the evaluation of the results of surgical treatment of varicocele in children]

The paper is concerned with analysis of the results of intraoperative phlebotesticulography, performed in 50 patients with varicocele of degree I-II during Ivanissevich's operation. The effect of surgical intervention was shown to depend upon the quality of ligation of the testicular vein, some parts of which are anastomosed between themselves. The localization of this anastomosis is revealed by means of intraoperative phlebotesticulography, which permits increasing the results of surgical treatment and predicting a course of a postoperative period.     

Dietary restriction causes chronic elevation of corticosterone and enhances stress response in red-legged kittiwake chicks

Release of corticosterone in hungry kittiwake chicks facilitates begging and allows them to restore depleted energy reserves by increasing parental food provisioning. However, in order to avoid detrimental effects of chronic elevation of corticosterone, chicks might suppress adrenocortical activity in response to prolonged food shortages. In this study we examined temporal dynamics of corticosterone release in red-legged kittiwake (Rissa brevirostris) chicks exposed to prolonged restrictions in energy content and/or nutritional quality (low versus high lipid content) of their food. Starting at the age of 15 days, chicks were fed either high- or low-lipid fish at 40%, 65%, and 100% of ad libitum energy intake. Body mass measurements and baseline plasma samples were taken on a weekly basis after beginning of the treatment. After 3 weeks of treatment, chicks were exposed to a standardized acute handling and restraint stress protocol, where in addition to a baseline sample, three plasma samples were taken at intervals up to 50 min. We found that food-restricted chicks had lower body mass, chronically (during 2-3 weeks) elevated baseline and higher acute stress-induced levels of corticosterone compared to chicks fed ad libitum. Low lipid content of food further exacerbated these effects. An increase in baseline levels of corticosterone was observed within a week after energy requirements of food-restricted chicks exceeded their daily energy intake. A tendency for suppression of adrenocortical activity was observed in treatments fed low-lipid diets only at the end of the experiment. We suggest that nest-bound chicks, if food-stressed, might suffer deleterious effects of chronic elevation of corticosterone.