Metabolic consequences of positive inotropy in rat and guinea-pig hearts

The metabolic and physiological responses of hearts from male rats and guinea-pigs to isoprenaline and SK&F 94120 (a phosphodiesterase III inhibitor), have been studied. Doses which gave similar chronotropic stimulation gave different inotropic responses. In both species, isoprenaline generated a greater increase in developed tension than SK&F 94120. With both drugs the inotropic response in the rat was less than than in the guinea-pig. 31P-NMR investigation of high-energy phosphate levels showed reduction in PCr concentration and an accompanying acidosis in the isoprenaline-perfused rat heart only. In both species, lactate production was stimulated by SK&F 94120 but not by isoprenaline. These results are discussed with reference to G-protein activation of ion channels and differences in Ca2+ handling by the two species.     

Clozapine induces hyperphagia in undeprived rats

Rats given either intragastric or intraventricular injections of clozapine showed a dose-dependent increase in food intake.     

Diffusion pathway for oxygen into highly thermogenic florets of the arum lily Philodendron selloum.

Thermogenic inflorescences of some arum lilies have the highest rates of respiration known among plants. Peak rates of oxygen consumption in the sterile male florets of Philodendron selloum Koch exceed 0.3 micromol x s(-1) x g(-1) when the inflorescence warms to 38 degrees C. This study describes the morphology of the oxygen diffusion pathway between the atmosphere and the parenchymal cells of the florets. Dimensions of the florets, stomata, interstitial gas network, and cells provide data for diffusion models of the PO2 profiles at each level of the 'oxygen cascade'. The lowest calculated PO2 of 4.7 kPa (35 mmHg) at the axis of the thickest part of the floret indicates that maximum respiration does not reach the point of diffusion-limitation, confirming earlier physiological measurements of the dependence of oxygen consumption rate on environmental PO2. Adequate aeration of all cells is achieved by appropriate floret size, despite a stomatal density less than 5%, and interstitial gas fraction less than 2%, of values commonly found in leaves.     

Thermodynamics of mucopolysaccharide–dye binding. III. Thermodynamic and cooperativity parameters of acridine orange–heparin system

Binding isotherms for acridine orange (AO)–heparin systems can be evaluated solely on the basis of quantitative fluorescence spectroscopic measurements. The evaluation of thermodynamic parameters indicates that the interactions of AO with heparins from several animal sources are similar to each other in magnitude. Binding is highly exothermic (ΔH = ?6 kcal mol^?1) and is stabilized by dye–polymer and dye–dye (coopertive) interactions, as well as by entropic factors (ΔS = +7 e.u.). The predominant stabilizing factor appears to be the electrostatic attraction between the AO cation and the heparin polyanion, although the other factors are important as well. At 24°C the value of the cooperative binding constants for the various heparins range from 8.8 to 11.3 × 10⁵M^?1, corresponding to a free energy of ?8 kcal mol^?1. The degree of cooperativity, which is a direct measure of dye–dye interaction, varies with polymer:dye ratio; the theoretical basis for this variation remains to be elucidated. Electrophoretic data indicate that each heparin sample consists of a mixture of species, each with its own charge density. This precludes definitive interpretation of observed small differences in the values of the thermodynamic parameters among the various samples until each sample can be resolved into its components.