Effect of puberty on coronary arteries from female pigs

Endothelial impairment evaluation by peripheral arterial tonometry in pediatric endocrinopathies: A narrative review

Endothelial dysfunction (ED) is characterized by an imbalance between vasodilator and vasoconstriction agents. Several pathological conditions clinically diagnosed in childhood and adolescence are characterized by ED and increased risk for early development of microangiopathic and macroangiopathic impairment, in particular type 1 diabetes mellitus (T1DM), T2DM, obesity, metabolic syndromeand pituitary dysfunction associated to various endocrinopathies. More recently insulin resistance following chemotherapy or radiotherapy for tumors, bone marrow transplantation for hematological malignancies (i.e., cancer survivors), or immunosuppressive treatment for solid organ transplantation has been observed. Assessment of ED by means of non-invasive techniques is the gold standard for early ED detection before clinical manifestation. It is aimed to recognize patients at risk and to avoid the development and progression of more serious illnesses. Reactive hyperemia-peripheral artery tonometry is a noninvasive technique to assess peripheral endothelial function by measuring modifications in digital pulse volume during reactive hyperemia, and represents a non-invasive, reproducible and operator-independent tool able to detect precocious ED. This narrative review aimed to provide an overview of the most important papers regarding ED detection by EndoPat 2000 in children and adolescents with different endocrine diseases. A comprehensive search of English language articles was performed in the MEDLINE database without using other search filters except the publication interval between 2005 and 2020.

17β-estradiol reduces Cav 1.2 channel abundance and attenuates Ca2+ -dependent contractions in coronary arteries

One mechanism by which the female sex may protect against elevated coronary vascular tone is inhibition of Ca²⁺ entry into arterial smooth muscle cells (ASMCs). In vitro findings confirm that high estrogen concentrations directly inhibit voltage‐dependent Ca_v1.2 channels in coronary ASMCs. For this study, we hypothesized that the nonacute, in vitro exposure of coronary arteries to a low concentration of 17β‐estradiol (17βE) reduces the expression of Ca_v1.2 channel proteins in coronary ASMCs. Segments of the right coronary artery obtained from sexually mature female pigs were mounted for isometric tension recording. As expected, our results indicate that high concentrations (≥10 μmol/L) of 17βE acutely attenuated Ca²⁺‐dependent contractions to depolarizing KCl stimuli. Interestingly, culturing coronary arteries for 24 h in a 10,000‐fold lower concentration (1 nmol/L) of 17βE also attenuated KCl‐induced contractions and reduced the contractile response to the Ca_v1.2 agonist, FPL64176, by 50%. Western blots revealed that 1 nmol/L 17βE decreased protein expression of the pore‐forming α_1C subunit (Ca_vα) of the Ca_v1.2 channel by 35%; this response did not depend on an intact endothelium. The 17βE‐induced loss of Ca_vα protein in coronary arteries was prevented by the estrogen ERα/ERβ antagonist, ICI 182,780, whereas the GPER antagonist, G15, did not prevent it. There was no effect of 1 nmol/L 17βE on Ca_vα transcript expression. We conclude that 17βE reduces Ca_v1.2 channel abundance in isolated coronary arteries by a posttranscriptional process. This unrecognized effect of estrogen may confer physiological protection against the development of abnormal Ca²⁺‐dependent coronary vascular tone.

Oestrogen upregulates the sarcoplasmic reticulum Ca(2+) ATPase pump in coronary arteries

The presence of circulating plasma 17β-oestradiol (E2) is beneficial in women against abnormal vascular tone development, such as coronary arterial vasospasms. Several vascular diseases have demonstrated that increased expression of the sarcoplasmic reticulum Ca(2+) -ATPase pump (SERCA2b) serves to limit the excessive accumulation of intracellular Ca(2+) . Therefore, the hypothesis of the present study was that E2 would increase SERCA2b expression in the coronary vasculature. Coronary arteries were dissected from hearts obtained from mature female pigs. Artery segments were cultured for 24 h in E2 (1 pmol/L or 1 nmol/L) and homogenized for western blot analysis. At 1 nmol/L, E2 induced an approximate 50% increase in immunoreactivity for SERCA2b. In addition, E2 increased the protein expression of the known SERCA regulatory proteins, protein kinase A (PKA) and protein kinase G (PKG). The E2-induced increase in SERCA2b was attenuated when the culture medium was supplemented with the oestrogen receptor (ER) α/β antagonist ICI 182,780 and the PKG antagonist KT5823 (10 μmol/L, 24 h for both). The PKA antagonist (KT5720; 10 μmol/L, 24 h) had no effect on SERCA2b expression. Removal of the endothelium (using a wooden toothpick) from artery segments prior to culture decreased the E2-mediated increase in SERCA2b and PKG expression by 45% and 47%, respectively. Overall, the findings suggest that one of the potential cardiovascular benefits of E2 in women is upregulation of SERCA2b, via activation of the classic ERα and ERβ pathway.

Strategies and methods to study sex differences in cardiovascular structure and function: a guide for basic scientists

Background

Cardiovascular disease remains the primary cause of death worldwide. In the US, deaths due to cardiovascular disease for women exceed those of men. While cultural and psychosocial factors such as education, economic status, marital status and access to healthcare contribute to sex differences in adverse outcomes, physiological and molecular bases of differences between women and men that contribute to development of cardiovascular disease and response to therapy remain underexplored.

Methods

This article describes concepts, methods and procedures to assist in the design of animal and tissue/cell based studies of sex differences in cardiovascular structure, function and models of disease.

Results

To address knowledge gaps, study designs must incorporate appropriate experimental material including species/strain characteristics, sex and hormonal status. Determining whether a sex difference exists in a trait must take into account the reproductive status and history of the animal including those used for tissue (cell) harvest, such as the presence of gonadal steroids at the time of testing, during development or number of pregnancies. When selecting the type of experimental animal, additional consideration should be given to diet requirements (soy or plant based influencing consumption of phytoestrogen), lifespan, frequency of estrous cycle in females, and ability to investigate developmental or environmental components of disease modulation. Stress imposed by disruption of sleep/wake cycles, patterns of social interaction (or degree of social isolation), or handling may influence adrenal hormones that interact with pathways activated by the sex steroid hormones. Care must be given to selection of hormonal treatment and route of administration.

Conclusions

Accounting for sex in the design and interpretation of studies including pharmacological effects of drugs is essential to increase the foundation of basic knowledge upon which to build translational approaches to prevent, diagnose and treat cardiovascular diseases in humans.

Endothelial function as measured by peripheral arterial tonometry increases during pubertal advancement

BACKGROUND/AIMS

Sex steroids, such as estrogens, are known to influence endothelial function by their vasodilator action. The aim of this study was to study the relation of puberty and sex steroids with endothelial function using peripheral arterial tonometry (PAT).

METHODS

In 89 healthy school boys and girls, we determined height, weight, waist circumference, percent body fat, BMI, BMI z-score, blood pressure (BP), BP percentiles, lipid profile, insulin, and glucose levels after overnight fast. Estrone (E(1)), estradiol (E(2)), DHEAS and E(1)-sulfate were measured using ultrasensitive assays. Participants were divided into 3 pubertal groups on the basis of their estrogen levels: group 1 (Tanner stage I), group 2 (Tanner stages II-III), and group 3 (Tanner stages IV-V). Endothelial function was measured by Endo-PAT 2000® and expressed as PAT index. A higher PAT index represents a higher reactive hyperemia response.

RESULTS

The PAT index was lowest at 1.42 ± 0.44 (mean ± SD) in group 1 and significantly increased in group 2 at 1.71 ± 0.35 (p = 0.02) and group 3 at 1.92 ± 0.38 (p < 0.001). The PAT index correlated positively with E(2), DHEAS and age.

CONCLUSION

Enhancement of the PAT index was associated with an increment in Tanner stages. The changes in E(2) and DHEAS levels may contribute to increasing endothelial response to shear stress or arterial blood flow.

Differential effects of chronic treatment with estrogen receptor ligands on regulation of nitric oxide synthase in porcine aortic endothelial cells

In cultured endothelial cells, estrogen increases expression and activity of endothelial nitric oxide synthase (eNOS). This study was designed to determine whether estrogenic treatments increase eNOS similarly in vivo. Aortic endothelial cells were collected from adult ovariectomized pigs which were untreated (8wk-OVX) or treated with oral 17beta-estradiol (E2, 2 mg/day), conjugated equine estrogen (CEE, 0.625 mg/day), or raloxifene (60 mg/day) for 4 weeks. Plasma NOx, estrogen receptors (ERalpha and ERbeta), eNOS, eNOS regulatory proteins, and eNOS mRNA in endothelial cells were determined by Griess reaction, Western blot, and real-time polymerase chain reaction, respectively. Ovariectomy decreased, whereas all treatments restored plasma NO(x) to pre-OVX levels. On the contrary, eNOS protein and mRNA increased with ovariectomy; E2 and CEE but not raloxifene reduced mRNA; eNOS protein was reduced by CEE and raloxifene treatments. Tyrosine phosphorylation of eNOS and expression of calmodulin increased, but Hsp90 decreased with all treatments and only raloxifene treatment increased caveolin-1 compared with OVX. Expression of ERalpha/ERbeta increased with ovariectomy and was reversed by treatments such that raloxifene>CEE>E2. Three clinically relevant estrogen treatments restore plasma NO after ovariectomy, but do not affect eNOS mRNA, posttranslational regulation of eNOS or expression of estrogen receptors in the same way.

Changes in coronary resistance related to the stages of the female life cycle

BACKGROUND

Estrogen is known to dilate the coronary vascular system mainly through nitric oxide (NO) release. However, it has not been determined whether or not this effect occurs equally throughout all stages of the female life cycle. We examined the changes in coronary flow properties in adolescent, adult and ovariectomized (OVX) female rats using the endothelial NO synthetase blocker, L-N (omega) nitroarginine (L-NNA).

METHODS AND RESULTS

Female rats were divided into 3 groups: adolescent (13 weeks, n=6), adult (19 weeks, n=8) and OVX (20 weeks, n=7, 12 weeks after oophorectomy). Coronary effluent was measured using the Langendorff non-working heart model before and 15 min after the use of L-NNA. In OVX rats, coronary effluent was significantly decreased in comparison with adolescent and adult rats (adolescent vs OVX: p<0.001; adult vs OVX: p<0.05). After treatment with L-NNA, coronary effluent was significantly higher in the adolescent group compared with the adult and OVX groups (adolescent vs adult: p<0.01; adolescent vs OVX: p<0.0005).

CONCLUSIONS

Oophorectomy brought about an increase in coronary vascular resistance. L-NNA exacerbated coronary vascular resistance in relation to maturation. It is suggested that the effect of estrogen on vascular dilatation in adolescents is largely dependent on a non-NO pathway, whereas adults are largely dependent on an NO pathway.

Differential effects of 17beta-estradiol and raloxifene on VSMC phenotype and expression of osteoblast-associated proteins

Several studies demonstrate an association between osteoporosis and arterial calcific disease, both of which being common in elderly women. Estradiol and raloxifene, a selective estrogen receptor modulator, prevent bone loss in postmenopausal women. Little is known regarding how these agents affect arterial calcification. The aim of this study was to determine whether or not 17beta-estradiol and raloxifene reduced vascular smooth muscle cell (VSMC) differentiation and expression of bone-associated proteins during phosphate-induced calcification in vitro. Aortic VSMC were cultured from adult, gonadally intact, and ovariectomized (OVX) female pigs. Calcifying medium was added, and cells were treated with solvent (control), 17beta-estradiol (E(2)), or raloxifene. Extent of calcification and phenotypic expression of bone-associated proteins [matrix gla protein (MGP), osteoprotegerin (OPG), and bone sialoprotein (BSP)] were examined at 3-day intervals over 2 wk. Calcium content increased in all groups but was greater in VSMC derived from intact compared with OVX animals. E(2) reduced calcification and preserved a contractile phenotype. Expression of OPG significantly decreased with time; this decrease was significantly greater in VSMC derived from OVX compared with gonadally intact pigs. E(2) and raloxifene preserved expression of OPG only in VSMC from intact pigs. Expression of MGP increased significantly with time and was not affected by E(2) or raloxifene treatments. E(2) treatment significantly inhibited synthesis of BSP in cells from both groups. In conclusion, E(2) slows differentiation of VSMC induced by excess phosphate. Effectiveness of raloxifene to preserve expression of bone cell-associated proteins depends on the hormonal status of the tissue donor.

Differential effects of 17beta-estradiol, conjugated equine estrogen, and raloxifene on mRNA expression, aggregation, and secretion in platelets

Changes in platelet functions could contribute to thrombotic risk associated with estrogen treatments. This study was designed to test the hypothesis that three clinically relevant estrogenic treatments affect platelet function comparably. Adult female pigs were ovariectomized and randomized to either no treatment or treatment with oral 17 beta-estradiol (2 mg/day), conjugated equine estrogen (0.625 mg/day), or raloxifene (60 mg/day) for 4 wk. Platelet turnover, aggregation, and secretion were assessed before and after treatment. Platelet turnover and mRNA increased significantly only in pigs treated with 17 beta-estradiol. Expression of estrogen receptors increased with ovariectomy and decreased with all treatments. Platelet aggregation and secretion of ATP, platelet-derived growth factor, and matrix metalloproteinase-2 increased with ovariectomy. All treatments reduced both aggregation and secretion. Expression of mRNA for constitutive endothelial nitric oxide synthase (eNOS), but not eNOS protein, increased with ovariectomy. Only eNOS mRNA decreased with all treatments, but only treatment with 17 beta-estradiol increased secretion of nitric oxide from intact platelets. Platelets from 17 beta-estradiol-treated animals caused relaxation of coronary arteries, which was sensitive to inhibition of nitric oxide. Although three different estrogenic treatments reversed increases in platelet aggregation caused by ovariectomy, only 17 beta-estradiol increased platelet RNA and release of platelet-derived nitric oxide. These differences reflect transcriptional and posttranscriptional regulation of protein synthesis in bone marrow megakaryocytes and circulating platelets.

Sex-specific changes in platelet aggregation and secretion with sexual maturity in pigs

Cardiovascular disease may begin early in adolescence. Platelets release factors contributing to vascular disease. Experiments were designed to test the hypothesis that hormonal transitions associated with sexual maturity differentially affect platelet aggregation and secretion in males and females. Platelets were collected from juvenile (2-3 mo) and sexually mature (adult; 5-6 mo) male and female pigs (n=8/group). Maturation was evidenced by increased weight of reproductive tissue and changes in circulating levels of gonadal hormones. Aggregation to ADP (10 microM) and collagen (6 microg/ml) and ATP secretion to 50 nM thrombin were determined by turbidimetric analysis and bioluminescence, respectively. Total platelet counts, platelet turnover, and mean platelet volume did not change with maturity. Platelet aggregation and ATP secretion decreased in females but increased in males with maturity, whereas total ATP content remained unchanged in platelets from females but increased in platelets from males. Platelet fibrinogen receptor, P-selectin expression, and receptors for sex steroids did not change with sexual maturation. Plasma C-reactive protein and brain-type natriuretic peptide also did not change. Results indicate that changes in platelet aggregation and secretion change with sexual maturity differently in females and males. These observations provide evidence on which clinical studies could be designed to examine platelet characteristics in human children and young adults.