Digitalis-like and vasoconstrictor effects of endogenous digoxin-like factor(s) from the venom of Bufo marinus toad

Digitalis glycoside-like properties of the Bufo marinus toad crude venom and one of its constituents, bufalin, were studied in various assay systems. In concentrations 0.3-30 micrograms/ml crude venom increased the contractility of isolated electrically driven rat atria, constricted rat aortic rings, inhibited ouabain-sensitive Na+,K(+)-ATPase in rat erythrocytes and the Na+,K(+)-pump in rat aorta, and cross-reacted with antidigoxin antibody from the dissociation enhanced lanthanide fluoroimmunoassay (DELFIA). These effects were unaffected by adrenoceptor blockers and the 5-HT antagonist, deseril, but were blocked by antidigoxin antibody. Bufalin (10-30 microM) increased myocardial contractility and inhibited Na+,K(+)-ATPase in rat erythrocytes similarly to crude Bufo marinus venom. In rat aorta bufalin showed weak and delayed vasoconstrictor activity which was antagonized by 2 microM phentolamine, and had a biphasic effect on the Na+,K(+)-pump; 0.5-1.0 microM bufalin stimulated the pump, while higher concentrations inhibited its activity. Although the effects of bufalin were blocked by antidigoxin antibody, bufalin showed very low digoxin-like immunoreactivity in the DELFIA. These observations suggest that, in addition to bufalin, Bufo marinus venom contains at least one more digitalis-like steroid with significant intrinsic vasoconstrictor activity which, unlike bufalin, constricts the blood vessels acting directly via inhibition of the sodium pump in the vascular smooth muscle membrane.     

Peculiarities in a composition of surface lipids in coniferous leaves

Composition on surface lipids of coniferous from Picea, Pinus and Larix genera (six plant species) are studied by spectral and chromatographic methods. Different content of carbonyl compounds in the summary fraction of surface lipids of coniferous, concerning componental content of hydrocarbon fraction and predominance of concrete fatty acids was shown. A substantial quantity of unethereficated fatty acids in surface lipids of plants is shown.     

The characteristics of exploratory behavior in Wistar rats in a permanent inhomogeneous magnetic field

The influence of weak perturbations (up to 300 microT) in the natural magnetic field (MF) (induced by the introduction of three constant magnets) on the problem task solving in complex maze was studied in two groups of Wistar rats. Under the action of inhomogeneous magnetic field there were no spontaneous change of the orienting for the explorative activity independently of the individual in the presence of the organization of goal-directed behaviour. Instead of the expected explorative activity, the stable and deep locomotor depression developed after orienting in a new environment. Such a phenomenon was manifested only against the background of informational loading. Nevertheless, under these conditions a short external stimulations resulted in even faster rat learning than in the control animals. It is suggested that the MF characteristics play a crucial role in the transformation of the orienting (unconditioned activity) into the explorative (cognitive) activity.     

A band-switched resonant quadrifilar helix

A technique is presented that can be used to multiple tune a resonant quadrifilar helix. An example of a design is given with an antenna that covers two frequency ranges: 250-270 MHz and 290-310 MHz.