17Beta-estradiol rapid stimulation of rat aorta NOS activity is prevented by oestrogen deficiency

The purpose of this study was to determine the effects of chronic oestrogen deficiency on rat aorta rapid response to 17beta-estradiol treatment.

Rat aortic strips (RAS) were isolated from Wistar female rats of three different groups: rats 6-7-month old with normal oestrogen levels (NER); aged rats, 24-month old, with low oestrogen levels (LER); and young rats after 2 months of bilateral ovariectomy (OVX). Platelet aggregation was measured after incubation of RAS in a platelet rich plasma by addition of 10 microM ADP. NO production by RAS was measured by 3H-citrulline technique.

RAS obtained from NER treated with 17beta-estradiol produced an inhibition of platelet aggregation specific for ovarian hormones, since testosterone was devoid of any effect. In aortic tissue isolated from male rats no increment in nitric oxide (NO) production was found. RAS from LER and OVX treated with 1-10 nM failed to induce a significant inhibition of platelet aggregation compared with NER (5 and 17%; 6 and 20% vs. 45 and 77% inhibition of platelet aggregation respect to control, respectively). In contrast to NER, 5 min treatment of LER and OVX aortic tissue with 1 nM 17beta-estradiol did not incremented NO production (NER 1.14 vs. 2.3 (P < 0.05); LER 1.14 vs. 1.42; OVX 1.24 vs. 1.52 pmol NO per mg protein).

These results suggest that chronic oestrogen deprivation impairs the inhibition of platelet aggregation and suppresses the rapid stimulation of aortic NOS induced by acute 'in vitro' treatment with 17beta-estradiol.