CHANGES IN THE VASOACTIVE EFFECTS OF NITRIC OXIDE, HYDROGEN SULFIDE AND THE STRUCTURE OF THE RAT THORACIC AORTA: THE ROLE OF AGE AND ESSENTIAL HYPERTENSION

Several studies have already confirmed the specific vasomotor effect of hydrogen sulfide (H2S) and its interaction with the nitric oxide (NO) system in normotensive rats, but results in spontaneously hypertensive rats (SHRs) are limited The aim of this study was to describe the age- and blood pressure-dependent effects of endogenous NO and exogenous Na2S and their interaction in vasomotor responses of the thoracic aorta (TA) in normotensive Wistar rats and SHRs. The systolic blood pressure (sBP), vasoactivity, NO-synthase (NOS) expression and activity, cystathionine gamma-lyase (CSE) expression, and geometry of the isolated TA were evaluated at 4 and 16 weeks of age. Although hypertrophy of the heart was observed in young and adult SHRs, the sBP was increased only in adulthood. The contractile responses were decreased in young as in adult SHRs with the key participation of the endogenous NO system. However, the hypotrophy in the young and the hypertrophy (mainly at the expense of extracellular matrix) in the adult SHRs were found in the TA. While unchanged in young SHRs, in adult SHRs, partially impaired endothelial function was confirmed. Nevertheless, the NO-dependent component of acetylcholine-induced relaxation was higher in both young and adult SHRs. Consistently, even though there was an age-dependent decrease in NOS activity in both strains, NOS activity was higher in both young and adult SHRs compared to age-matched normotensive rats. Application of exogenous Na2S evoked a concentration-dependent dual vasoactive effect of TAs in both strains, regardless of age. Increased sensitivity in favor of vasorelaxant responses of Na2S in prehypertensive SHRs, and an enhanced maximal vasorelaxation in adult SHR was observed. The acute NO inhibition generally increased the relaxant phase of Na2S responses; nevertheless, the development of hypertension potentiated this effect. The TA of the SHRs is endowed with a unique inherent predisposition of vasoactive mechanisms, which serve as compensatory processes during the developed stage of hypertension: the NO component and H2S signaling pathways are implicated. The decreased contractility seems to be a deleterious effect. The increased participation of the H2S system on vasorelaxation after acute NO inhibition could be considered a reserved mechanism in case of endogenous NO deficiency.