The low prevalence of
coronary heart disease in premenopausal women and its increase after menopause are well established. Many studies have suggested that
steroid hormones can inhibit platelet aggregation, reducing the cardiovascular risk. In addition, a number of studies have shown an effect of
estrogen on vascular function. The process of haemostasis and
thrombus formation can be also affected by
adenine nucleotides and
adenosine. Consequently, the regulation of
enzymes that hydrolyze these
nucleotides in the bloodstream is essential in the modulation of the processes of platelet aggregation, vasodilatation and coronary flow. Thus, in this study, we examined the effect of
ovariectomy (OVX),
estradiol replacement
therapy and the in vitro administration of 17beta-estradiol,
dehydroisoandrosterone 3-sulfate (DHEAS) and
pregnenolone (PREG) on the activity of the
enzymes that degrade
adenosine triphosphate (
ATP),
adenosine diphosphate (
ADP) and
adenosine monophosphate (
AMP) in the blood serum of female rats. OVX significantly increased the hydrolysis of
ATP,
ADP and
AMP, whilst
phosphodiesterase activity was unchanged.
Estradiol replacement
therapy significantly decreased the hydrolysis of the
adenine nucleotides and of the substrate marker of
phosphodiesterase. In vitro, the addition of
steroid hormones did not have any effect on the
nucleotide hydrolysis by rat serum. These results suggest the presence of a strong relation between these
enzymes and the hormonal system. In addition, the alterations observed are important, because these
enzymes control the
nucleotides/
nucleosides ratio in the circulation and thus the events related to haemostasis.