Estrogens, progestins, selective estrogen receptor modulators, and the arterial tree

A Review of the Actions of Endogenous and Exogenous Vasoactive Substances during the Estrous Cycle and Pregnancy in Rats

Vascular endothelium plays a key role in regulating cardiovascular homeostasis by controlling the vascular tone. Variations in sex hormones during the reproductive cycle of females affect the homeostasis of the cardiovascular system. Also, the evidence shows that estrogens show a cardioprotective effect. On this basis, this study describes some vascular responses induced by vasoactive substances during the estrous cycle in rats. We obtained the information available on this topic from the online databases that included scientific articles published in the Web of Science, PubMed, and Scielo. Many investigations have evaluated the vasoactive response of substances such as acetylcholine and norepinephrine during the estrous cycle. In this review, we specifically described the vascular response to vasoactive substances in rats during the estrous cycle, pregnancy, and in ovariectomized rats. In addition, we discussed the existence of different signaling pathways that modulate vascular function. The knowledge of these effects is relevant for the optimization and development of new treatments for some vascular pathologies.

Increases in serum estrogen levels during major illness are caused by increased peripheral aromatization

Although serum testosterone levels decrease acutely in critically ill patients, estrogen levels rise. We hypothesized that increased rates of aromatization of androgens to estrogens underlie the increase in serum estrogen levels. Eleven men and three women (age 42-69 yr) were prospectively studied before and again after elective coronary artery bypass graft surgery (CABG). Each patient received priming doses of [(14)C]androgen and [(3)H]estrogen that were immediately followed by peripheral infusions for 210 min. Eight men and three women received androstenedione (A(4))/estrone (E(1)) and three men received testosterone (T)/estradiol (E(2)). Adipose tissue biopsies were obtained in another six men before and after CABG to evaluate levels of P450 aromatase mRNA. Serum T levels decreased postoperatively in all 17 men (P < 0.001), whereas E(1) levels rose (P = 0.004), with a trend toward a rise in E(2) (P = 0.23). Peripheral aromatization rates of androgens to estrogens rose markedly in all 14 patients (P < 0.0001). Estrogen clearance rates rose (P < 0.002). Mean serum A(4) levels increased slightly postoperatively (P = 0.04), although no increase in A(4) production rates (PRs) was observed. T PRs decreased in two of three men, whereas clearance rates increased in all three. Adipose tissue P450 aromatase mRNA content increased postoperatively (P < 0.001). We conclude that the primary cause of increased estrogen levels in acute illness is increased aromatase P450 gene expression, resulting in enhanced aromatization of androgens to estrogens, a previously undescribed endocrine response to acute illness. Both increased T clearance and decreased T production contribute to decreased serum T levels. Animal studies suggest that these opposing changes in circulating estrogen and androgen levels may be important to reduce morbidity and mortality in critical illness.

Endothelial function in post-menopausal former elite athletes

OBJECTIVE

To characterize endothelial function in postmenopausal former elite athletes in comparison to sedentary controls and to study the influence of hormone replacement therapy (HRT) on endothelial function in these groups of women.

DESIGN

Cross-sectional study.

SETTING

Research unit at a university hospital.

PARTICIPANTS

Twenty postmenopausal former elite but still active endurance female athletes and 19 age-matched sedentary controls. The group of athletes and control subjects were each subdivided into two groups on the basis of utilization or non-utilization of HRT involving estrogen and gestagen.

METHODS

Flow-mediated vasodilatation (FMD) was employed as an indicator of endothelial function. Fasting blood samples were analyzed for lipids and body composition determined by dual-energy x-ray absorptiometry.

MAIN OUTCOME MEASURES

FMD, blood lipids and body composition.

RESULTS

Former elite athletes not utilizing HRT demonstrated the highest FMD of all four subgroups, their values being significantly higher than those of control subjects not utilizing HRT (P < 0.05), whereas this difference was not seen between the subgroups of athletes and control subjects using HRT. Serum levels of cholesterol and low-density lipoprotein (LDL) and the percentage of fat mass were significantly lower in the former elite athletes than in the control group (P < 0.05 in all cases). However, these variables were not related to FMD.

CONCLUSION

This investigation documents enhanced endothelial function in postmenopausal former elite endurance athletes not utilizing HRT, whereas the use of HRT equalizes FMD in former athletes and sedentary control subjects. Our findings suggest that long-term strenuous exercise has beneficial effects on endothelial function in postmenopausal women but that no further improvement can be obtained with HRT.

Hereditary and acquired defects in the fibrinolytic system associated with thrombosis

The fibrinolytic system plays a pivotal role in the regulation of hemostasis and the prevention of thrombosis. There are no drugs that will increase the plasma fibrinolytic activity for a lasting duration to prevent thrombotic events effectively. Despite the ability of vasoactive agents such as nicotinic acid and metformin to release PA from the vessel wall, this therapeutic effect has not been evaluated adequately. The PAs are short-acting and indicated only for thrombolysis and not for prophylaxis. Future directions are directed at finding, agents that can enhance plasminogen activator release or inhibit PAW-1 activity. As there are multiple factors involved in the pathogenesis of thrombosis, there are a number of conditions in which abnormal fibrinolysis is only a contributory factor. Examples are seen in pregnancy, especially during puerperium, when the thromboembolic risk is at its highest. The levels of inhibitors of fibrinolysis. both PAI-1 and PAI-2, are also at their highest. Another example was seen recently in the antiphospholipid syndrome, where antibodies against Annexin II, a receptor for tPA, were found to be higher than in healthy controls. Thus, a thorough investigation into other hereditary and acquired risk factors for thrombosis is recommended.

Nitric oxide synthase upregulation and the predelivery blood pressure decrease in spontaneously hypertensive rats

OBJECTIVE

The pregnant spontaneously hypertensive rat (SHR) exhibits a decrease in arterial blood pressure shortly before delivery; however, the mechanisms are unknown. Nitric oxide may be involved.

DESIGN

Blood pressure in stroke-prone SHR (SHRSP) and Wistar-Kyoto control rats (WKY) was telemetrically measured. Four groups were studied: pregnant and non-pregnant WKY and SHRSP rats, respectively. Mean blood pressure in pregnant SHRSP rats decreased from 148 +/- 2 mmHg at conception to 120 +/- 4 mmHg at day 15, compared to 112 +/- 1 mmHg in pregnant WKY rats. At delivery, we determined the vasodilatory responses of isolated preconstricted aortic strips.

RESULTS

Vasodilatory responses from late-term SHRSP rats were significantly greater following acetylcholine than either those from non-pregnant SHRSP or pregnant and non-pregnant WKY rats (acetylcholine IC50: 5, 22.8, 398, 1000 nmol/l, respectively), while contractile responses to increasing doses of norepinephrine were not different. Similar results were obtained with substance P. Indomethacin had no effect on the relaxation responses. Relaxation in response to sodium nitroprusside was not different in the groups. Western blot analysis showed that endothelial nitric oxide synthase (eNOS) levels were significantly increased in the pregnant SHRSP vessels compared to non-pregnant SHRSP, pregnant WKY, and non-pregnant WKY vessels.

CONCLUSION

Increased NOS may explain the blood pressure decrease during late pregnancy in genetically hypertensive rats.