Selective inhibition of pinacidil effects by estrogen in guinea pig heart

Sex-Specific Physiology and Cardiovascular Disease

Sex differences in cardiovascular diseases can be classified as those which are specific to one sex and those that differ in incidence, prevalence, etiology, symptomatology, response to treatment, morbidity, and mortality in one sex compared to the other. All sex differences in cardiovascular conditions have their basis in the combined expression of genetic and hormonal differences between women and men. This chapter addresses how understanding basic mechanisms of hormone responses, imaging diagnostics, and integration of genomics and proteomics has advanced diagnosis and improved outcomes for cardiovascular conditions, apart from those related to pregnancy that are more prevalent in women. These conditions include obstructive coronary artery disease, coronary microvascular dysfunction, spontaneous coronary artery dissection, diseases of the cardiac muscle including heart failure and takotsubo cardiomyopathy, and conditions related to neurovascular dysregulation including hot flashes and night sweats associated with menopause and effects of exogenous hormones on vascular function. Improvement in technologies allowing for noninvasive assessment of neuronally mediated vascular reactivity will further improve our understanding of the basic etiology of the neurovascular disorders. Consideration of sex, hormonal status, and pregnancy history in diagnosis and treatment protocols will improve prevention and outcomes of cardiovascular disease in women as they age.

Both Mitochondrial KATP Channel Opening and Sarcolemmal KATP Channel Blockage Confer Protection Against Ischemia/Reperfusion-Induced Arrhythmia in Anesthetized Male Rats

Aim: This study was performed to assess the effect of selective sarcolemmal adenosine triphosphate (ATP)-sensitive K+ channel (KATP) inhibition and the mitochondrial KATP channel activation on ischemia and reperfusion (I/R)-induced arrhythmias in different gender of rats. We compared the effect of a selective sarcolemmal KATP channel blocker HMR 1098, a selective mitochondrial KATP channel opener diazoxide, a nonselective KATP channel opener pinacidil, and the combination of pinacidil with HMR 1098 on the incidence and duration of ventricular arrhythmias in 2 groups: anesthetized males (n = 31) and females (n = 31). Main Methods: Ischemia and reperfusion was produced by occluding the left main coronary artery of Sprague-Dowley rats for 6 minutes followed by re-opening of the artery for 6 minutes. Key Findings: The arrhythmia score and the duration of arrhythmias were significantly reduced by HMR 1098, diazoxide, and pinacidil in male rats. The combination of the pinacidil with HMR 1098 did not change the antiarrhythmic effect of pinacidil. The duration of arrhythmas was shorter in females than that in the corresponding males. Drug treatments were not effective in decreasing arrhythmias in female groups to the same extent as in the male group. However, the mitochondrial K ATP channel activation that is provided by the combination of pinacidil with HMR 1098 significantly decreased the total length of arrhythmias in females. Significance: Results of the current study indicate that both mitochondrial KATP channel activation and sarcolemmal KATP channel inhibition exert antiarrhythmic action in male rats. The antiarrhythmic effect of pinacidil is not depend on the sarcolemmal KATP channel opening. These results also indicate that KATP channel modulators show no discernable effect in female rats due to the already low incidence of arrhythmias in females.

Cardiac sarcolemmal K(ATP) channels: Latest twists in a questing tale!

Reconstitution of K(ATP) channel activity from coexpression of members of the pore-forming inward rectifier gene family (Kir6.1, KCNJ8, and Kir6.2 KCNJ11) with sulfonylurea receptors (SUR1, ABCC8, and SUR2, ABCC9) of the ABCC protein sub-family, has led to the elucidation of many details of channel gating and pore properties, as well as the essential roles of Kir6.2 and SUR2 subunits in generating cardiac ventricular K(ATP). However, despite this extensive body of knowledge, there remain significant holes in our understanding of the physiological role of the cardiac K(ATP) channel, and surprising new findings keep emerging. Recent findings from genetically modified animals include the apparent insensitivity of cardiac sarcolemmal channels to nucleotide levels, and unenvisioned complexities of the subunit make-up of the cardiac channels. This topical review focuses on these new findings and considers their implications.

Pretreatment of male guinea pigs by 17-beta-estradiol induces hypersensitivity of beta-adrenoceptors in electrically driven left atria

BACKGROUND

It is well known that estrogen can modulate distribution and function of adrenergic receptors in the heart of different species. We reported here gender differences in adrenergic responsiveness of electrically driven guinea pig left atria.

METHODS

Experiments were performed on the guinea pigs divided in four groups: males control (MC), males treated by 17-beta-estradiol (MTE), females control (FC) and females treated by tamoxifen (FTT). After two weeks of treatment, the animals were sacrificed, the left atria were isolated and force of contraction (Fc), velocity of contraction (+dF/dt), velocity of relaxation (-dF/dt) and time to peak contraction (ttp) and relaxation time at 10% of amplitude (tt(10) ) were measured.

RESULTS

Apart from significantly lower Fc and longer tt10 in FC (0.97+/-0.12 mN, 233+/-7 ms, respectively) vs. MC (1.66+/-0.3, 176.3+/-18 ms, respectively, n=6, P<0.05), isoprenaline (ISO) and noradrenaline (NOR) (in the presence of prazosine) concentration-response curves were strongly shifted leftward in comparison with male group. Additionally, the maximal effects of. NOR was significantly lower in FC (about 40%) than in MC. Application of 17-beta-estradiol to males and tamoxifen to females guinea pigs confirmed crucial role of estrogen in observed phenomenon.

CONCLUSION

Our results indicate that estrogen not only downregulates beta1-adrenoceptors, but induces its hypersensitivity to catecholamines, at least in guinea pig left atria.