[Role of the inositol phosphate cycle in the cardioprotective effect of adaptation to intermittent hypoxia].

The impact of adaptation to intermittent hypoxia of different duration (for 20 and 40 days) on the inositol triphosphate-diacylglycerol (ITP-DAG) regulatory contour in the heart was investigated. For this, isolated heart alpha 1-adrenoreactivity to phenylephrine and phospholipase (PhL-C) activities were studied in cardiac plasma membranes. On day 20 of adaptation, the heart inotropic response to phenylephrine stimulation was somewhat reduced and the activity of Ca(2+)-dependent PhL-C did not differ from that in the controls within the range of Ca2+ physiological concentrations. Forty days after adaptation, both positive inotropic responses of the heart to phenylephrine and activity of Ca(2+)-dependent PhL-C were enhanced, i.e. activation of the ITP-DAG regulatory cascade occurred. Early studies have shown that a phenomenon of adaptive stabilization develops at this stage of adaptation. The phenomenon appears as a significant increase in heart resistance to thermal injury, toxic catecholamine levels, Ca2+ paradox and high Ca2+ concentrations. Thus, the revealed activation of the ITP-DAG regulatory contour was accompanied by the development of a phenomenon of adaptive structure stabilization (PhASS) in the hearts of adapted animals. The findings suggest that the ITP-DAG regulatory cascade plays an important role in the cardioprotective effect of adaptation to intermittent hypobaric hypoxia and in PhASS formation.