Pieter Zandberg

Estrogen Receptor β Protects the Murine Heart Against Left Ventricular Hypertrophy

Background—Left ventricular hypertrophy (LVH) displays significant gender-based differences. 17&bgr;-estradiol (E2) plays an important role in this process because it can attenuate pressure overload hypertrophy via 2 distinct estrogen receptors (ERs): ER&agr; and ER&bgr;. However, which ER is critically involved in the modulation of LVH is poorly understood. We therefore used ER&agr;-deficient (ER&agr;−/−) and ER&bgr;-deficient (ER&bgr;−/−) mice to analyze the respective ER-mediated effects. Methods and Results—Respective ER-deficient female mice were ovariectomized and were given E2 or placebo subcutaneously using 60-day release pellets. After 2 weeks, they underwent transverse aortic constriction (TAC) or sham operation. In ER&agr;−/− animals, TAC led to a significant increase in ventricular mass compared with sham operation. E2 treatment reduced TAC induced cardiac hypertrophy significantly in wild-type (WT) and ER&agr;−/− mice but not in ER&bgr;−/− mice. Biochemical analysis showed that E2 blocked the increased phosphorylation of p38–mitogen-activated protein kinase observed in TAC-treated ER&agr;−/− mice. Moreover, E2 led to an increase of ventricular atrial natriuretic factor expression in WT and ER&agr;−/− mice. Conclusions—These findings demonstrate that E2, through ER&bgr;-mediated mechanisms, protects the murine heart against LVH.

Tibolone Prevents Atherosclerotic Lesion Formation in Cholesterol-Fed, Ovariectomized Rabbits

Tibolone (Org OD14), a synthetic steroid with estrogenic and progestogenic/androgenic properties, is clinically effective for the treatment of climacteric symptoms and the prevention and treatment of osteoporosis in postmenopausal women. The effect on atherogenesis, however, is not known. In the current study, we investigated the effect of tibolone in comparison with that of estradiol and norethisterone acetate on atherogenesis in 140 ovariectomized New Zealand White rabbits that had been induced by an atherogenic diet (0.4% cholesterol, 20 weeks). Tibolone at 18, 6, or 2 mg/d orally completely prevented cholesterol accumulation and fatty streak formation in the aorta; the impairment of endothelium-dependent smooth muscle relaxation of the aorta; and complex lesion formation after endothelial denudation in the carotid artery. Tibolone also reduced the increased postovariectomy plasma lipid concentrations. Analysis of the results, however, indicated that a substantial part of the strong, beneficial effects were plasma lipid independent. Compared with subcutaneous estradiol decanoate (150 microgram once weekly) and oral 17beta-estradiol (4 mg/d), the effects of tibolone were more pronounced at equipotent uterotropic activity. Norethisterone acetate (1 mg/d) did not affect atherosclerotic lesion formation. There are no indications that the progestogenic/androgenic properties of tibolone counteracted its atheroprotective effect on the vessel wall. Therefore, tibolone has the intrinsic potential to be a compound that protects the arterial vessel wall against atherosclerotic processes.

Oestrogen modulates cardiac ischaemic remodelling through oestrogen receptor-specific mechanisms.

Aim:  Observational and clinical studies suggest different responses upon sex hormone replacement therapy in ischaemic heart disease. Few studies, however, have examined the impact of oestrogen receptor‐dependent mechanisms on the extent of injury after myocardial infarction (MI). Therefore, we set out to evaluate the effect of oestrogen (E2) replacement on infarct size and remodelling, and the respective role of the oestrogen receptors (ER)α and ‐β in this process, using ERα‐ and ERβ‐deficient mice.

Comparison of the antiatherosclerotic effect of tibolone with that of estradiol and ethinyl estradiol in cholesterol-fed, ovariectomized rabbits.

Objective Tibolone is a synthetic steroid with tissue-specific estrogenic, progestogenic, and androgenic properties. The drug relieves climacteric symptoms and prevents osteoporosis but does not stimulate the endometrium. We have previously shown that in laboratory animals tibolone inhibits the atherogenesis induced by a high-cholesterol diet. Therefore, we compared the antiatherosclerotic effect of oral tibolone at different dose levels with that of oral 17&bgr;-estradiol (E2) and ethinyl estradiol (EE). Design Atherosclerotic lesion formation (increase in vessel wall cholesterol deposition and fatty streak formation) was measured in ovariectomized rabbits after 20 weeks on an atherogenic diet (fed daily 80 g of a rabbit chow containing 0.4% cholesterol, 3.75% peanut oil, and 3.75% coconut oil) in eight groups: group 1, placebo (n = 35); group 2, control (n = 34) received normal rabbit chow; group 3, E2 group (E2 4 mg, n = 12); group 4, EE group (EE 60 &mgr;g, n = 10); and groups 5–8, tibolone (6 mg, n = 12; 2 mg, n = 13; 0.6 mg, n = 25; and 0.15 mg, n = 11, respectively). During the study, blood samples were obtained for the evaluation of plasma triglycerides, cholesterol, lipoproteins, and glutamate pyruvate transaminase. After 20 weeks, the animals were killed, and cholesterol concentration and the formation of fatty streaks in the wall of the aortic arch were evaluated. Results In the placebo group, the atherogenic diet induced a mean increase in total plasma cholesterol concentration from 1.1 ± 0.1 mmol/L (control group) to 34.1 ± 1.8 mmol/L (mean ± SE). This resulted in an accumulation of cholesterol in the aortic arch from 48 ± 4 (control group) to 608 ± 44 nmol/mg protein and in the formation of fatty streaks (41.8 ± 3.2% of the surface of the aortic arch was covered with fatty streaks). Tibolone had strong dose-dependent antiatherosclerotic effects. It reduced the accumulation of cholesterol in the aortic arch at doses of 6 to 0.15 mg by 99, 97, 87, and 57% and the formation of fatty streaks by 98, 97, 81, and 38%, respectively. E2 had only a marginal antiatherosclerotic effect, whereas EE showed an effect comparable to that of tibolone at doses of 2 to 0.6 mg. With EE, the accumulation of cholesterol in the vessel wall was reduced by 93% and the formation of fatty streaks by 73%. Mean plasma cholesterol concentrations were also reduced by tibolone (64, 70, 61, and 47%) and EE (57%). This reduction was mainly mediated via a reduction in &bgr;-very-low-density lipoprotein cholesterol. Analysis, however, indicated that the observed antiatherosclerotic effects of tibolone and EE, at least partly, are due to a direct effect on the vessel wall and independent of the changes in plasma cholesterol. At equipotent antiatherosclerotic doses, EE showed a stronger uterotropic effect (measured as the increase in uterine weight) than tibolone. EE increased uterine weight from 0.57 g/kg body weight (BW) (control group) to 3.5 g/kg BW; tibolone at doses of 6, 2, 0.6, and 0.15 mg increased uterine weight to 2.5, 2.8, 2.2, and 1.3 g/kg BW, respectively. Conclusion Tibolone can protect the arterial vessel wall against atherosclerotic lesions induced by a hypercholesterolemic diet. However, it has much less estrogenic effects on the uterus compared with EE at equipotent doses, indicating tissue selectivity for tibolone. The clinical implications of these findings require investigation.

Protection by paracetamol against various gastric irritants in the rat

Four nonsteroid anti-inflammatory drugs (NSAID), indomethacin, phenylbutazone, ibuprofen, and glafenine, caused erosions in the rat stomach in a dose-dependent manner. Paracetamol, which has been shown to protect against the gastric erosive activity of aspirin, reduced the gastric toxicity of indomethacin but was ineffective against the erosive activity of phenylbutazone and glafenine. Only the high erosion score of a large dose of ibuprofen was partly decreased by paracetamol. The gastric damaging effects of necrotizing concentrations of ethanol and sodium hydroxide were strongly reduced by paracetamol, but the erosive activity of hydrochloric acid was only slightly decreased by paracetamol. Thus, although paracetamol protected the gastric mucosa against various noxious agents, this drug was not able to protect against every type of gastric damage. Paracetamol might be protective by stimulating the biosynthesis of prostaglandins in the stomach wall.

The influence of paracetamol on the erosive activity of indomethacin in the rat stomach.

Indomethacin induced erosions in the glandular part of the rat stomach in a dose-dependent manner. Gastric erosions became apparent about 15 min after administration of indomethacin and the damage was maximal at about 4 h. The erosive activity of indomethacin administered subcutaneously was similar to that after oral administration, confirming the data of other authors. The erosive activity of subcutaneously applied aspirin, however, was far less than that of oral administered aspirin and it was not dose dependent.In a dose-dependent manner, paracetamol reduced the incidence of gastric erosions induced with indomethacin; this effect was independent of the route of administration of either drug. Paracetamol was also effective when given 0.5 or 1 h before indomethacin.Orally administered paracetamol also reduced the incidence of gastric erosions induced with aspirin but after subcutaneous administration, paracetamol had no protective effect. The differences between the erosive activities of indomethacin and aspirin are discussed with emphasis on the differentiating influence of paracetamol on the incidence of gastric erosions. Direct contact with the mucosa is apparently more important for the erosive activity of aspirin than for that of indomethacin. Possible mechanisms by which paracetamol exerts its protective activity are proposed.