[On the mechanism of radioprotective effect of NO-synthase inhibitors].

We studied the influence on hemodynamics and radioprotective activity of two inhibitors of NO-synthase (NOS)--isothiourea derivatives with different NOS isoform selectivity: T1023--a selective inhibitor of endothelial and inducible NOS; and NTT2--a highly selective inhibitor of neuronal NOS. Both compounds at a dose of 1/7 LD50/15 caused a vasopressive effect and baroreflex response in normal Wistar rats. However, the nature of hemodynamic changes was qualitatively different. T1023 caused a prolonged elevation of vascular tone and reflex shift resulted in a significant and lasting reduction in the systemic blood flow (35-45%), which created conditions for the development of circulatory hypoxia. The use of NTT2 caused a reflex change in hemodynamics accompanied by vasodilation; and systemic blood flow was maintained at the initial level. T1023 effectively protected mice subjected to 10 Gy γ-irradiation and their bone marrow stem cells irradiated with 6 Gy, not yielding to the radioprotective effect of cystamine. NTT2 at these doses did not show any radioprotective effect. The obtained results support the leading mechanism of the radioprotective effect of NOS inhibitors is the induction of hypoxia. With this mechanism of action a significant radioprotective activity can be expected for the inhibitors which effectively suppress primarily endothelial NOS.

[The influence of some retarding agents NOS of dihydrothiazine-thiazoline rank on postradiational of recovery endogenous CFU-S-8 of mice].

In this work the attempt to estimate a nitric oxide (NO*) role in regulation of the number of pool haemopoietic stem cells at the irradiated mice was made. With this purpose the number of new compounds from dihydrothiazine-thiazoline line was synthesized, their NO-inhibiting activity was investigated in vivo by the method of ESR-spectroscopy of spin trap and their influence on an output endogenous spleen colonies (CFU-S-8) after the total sublethal y-irradiation of mice in a doze of 6 Gy was also investigated. Was shown, that the tested compounds reduced the contents of NO* in a liver tissue of mice which have received an injection of nitric oxide synthesis inductor - lipopolysaccharide, and also increased an output CFU-S-8 forming endogenous colonies in the spleen of the irradiated mice. Received data testify to perceptivity of search radioprotective agents among NO* synthesis inhibitors.

[NO-inhibiting activity of radioprotectors]. / NO-ingibiruiushchaia aktivnost' radioprotektorov.

The effect of radioprotectors of different structure on the syntheses of nitric oxide induced by endotoxin in mice was studied. Using ESR-spectroscopy and spin trap techniques, it was shown that compounds of different chemical structure, such as aminothiols, isothiuronium derivatives, thiazolines, indolylalkylamines and others, suppressed the nitric oxide production in a whole body. The analysis of the relevant literature has confirmed the phenomenon described by the authors: radioprotectors show NO-inhibiting activity.