Calcium control of glycogen synthase activities in mouse diaphragms, rat adipocytes and rat hepatocytes

The following article provides evidence that cellular calcium controls the activity of glycogen synthase in all three major glycogen storage tissues; muscle, fat, and liver. Depletion of cellular calcium resulted in a moderate increase of glycogen synthase %I activities in intact mouse diaphragms, in isolated rat adipocytes, and in rat hepatocytes. The increase in %I activity of glycogen synthase was more pronounced when the uridine di-phosphoglucose concentration in the glycogen synthase assay was lowered from 4.4 mM to 0.2 mM. Calcium depletion resulted in an approximately two-fold decrease in the Ka values for glucose-6-phosphate in all three tissues. The activities of glycogen synthase also correlated well with the content of cell-associated calcium in rat hepatocytes. The glucose-6-phosphate independent activities of glycogen synthase in extracts of calcium-replete and calcium-depleted tissue approached the same value following the exposure to crude phosphoprotein phosphatase. The activities of glycogen phosphorylase decreased in calcium-depleted tissues and cells. Insulin stimulated the activity of glycogen synthase in muscle and fat in the absence of added sugar and in the absence of extracellular calcium. It is concluded that glycogen synthase is under the control of calcium in the three main glycogen storage tissues. The actions of calcium are probably mediated through the actions of calcium-sensitive protein kinase(s).     

Increasing saliva (free) oestriol to progesterone ratio in late pregnancy: a role for oestriol in initiating spontaneous labour in man?

Oestriol and progesterone concentrations were measured in samples of saliva obtained daily from six normal women during the final four weeks before the spontaneous onset of labour. Progesterone concentrations were found to plateau whereas oestriol concentrations continued to rise so that the mean ratio of saliva oestriol to progesterone increased from 0.80 to 1.43 between 29 days and one day before labour. Saliva oestriol concentrations were 15 times higher than saliva oestradiol concentrations. As saliva steroid concentrations reflect the unbound unconjugated (free) plasma steroid concentrations these data suggest that a changing ratio of oestriol to progesterone may play a part in initiating spontaneous labour in man.     

In vitro assessment of the selectivities of various beta-adrenergic blocking agents

Intrinsic sympathomimetic- and membrane activities of beta-adrenoceptor blocking agents are of little or no clinical significance. A selective blockade of cardiac receptors has important therapeutic consequences, especially in the treatment of patients with obstructive airways diseases. Profound depression of miocardial contractility can be deleterious in patients with cardiac muscle damage and the use of beta-adrenergic blockers with a quantitative selectivity towards chronotropism may become an important consideration. The effects of a number of beta-sympatholytics have been determined on isolated cardiac preparations (beta₁-adrenergic receptors) and tracheal preparations (beta₂-adrenergic receptors) of guinea-pigs. Results indicate that prindolol is the most selective blocker of the beta₁ chronotropic receptors whilst atenolol could be classified as being the most cardioselective beta-adrenergic blocker investigated. Butoxamine, on the other hand, proved to be the most beta₂-selective one.     

Heat exchanges in wet suits

Flow of water under foam neoprene wet suits could halve insulation that the suits provided, even at rest in cold water. On the trunk conductance of this flow was approximately 6.6 at rest and 11.4 W . m-2 . C-1 exercising; on the limbs, it was only 3.4 at rest and 5.8 W . m-2 . degrees C-1 exercising; but during vasoconstriction in the cold, skin temperatures on distal parts of limbs were lower than were those of the trunk, allowing adequate metabolic responses. In warm water, minor postural changes and movement made flow under suits much higher, approximately 60 on trunk and 30 W . m-2 . degrees C-1 on limbs, both at rest and at work. These changes in flow allowed for a wide range of water temperatures at which people could stabilize body temperature in any given suit, neither overheating when exercising nor cooling below 35 degrees C when still. Even thin people with 4- or 7- mm suits covering the whole body could stabilize their body temperatures in water near 10 degrees C in spite of cold vasodilatation. Equations to predict limits of water temperature for stability with various suits and fat thicknesses are given.     

Modelling Nitrogen Content and Distribution in Cauliflower (Brassica oleracea L.botrytis )

A model of nitrogen uptake and distribution is presented whichdescribes these processes in relation to the amount of availablesoil nitrate and the rate of plant growth. Nitrogen uptake iseither sink or source limited. Sink limitation is based on maximumN-concentrations of plant compartments. The N-uptake model iscombined with a photosynthesis model based on the productivity-nitrogenrelationship at the single-leaf level. The model is parameterizedusing cauliflower as an example crop. Applied to an independentdata set, the combined model was able to predict leaf, stemand inflorescence nitrogen concentrations with correlation coefficientsbetween predicted and simulated values of 0.89, 0.66 and 0.86,respectively. The influence of nitrogen supply and light intensityon leaf nitrate-N could also be predicted with good accuracy(r² = 0.87). Dry matter production based on the productivity-Nrelationship and the partitioning into leaf, stem and inflorescencewas also reproduced satisfactorily (r² = 0.91, 0.93 and 0.92,respectively). Copyright 2000 Annals of Botany Company Brassica oleracea L. botrytis, cauliflower, nitrogen, nitrate, nitrogen supply, nitrogen uptake, nitrogen distribution, model