Roberto Vargas

Effect of testosterone treatment on vasoconstrictor response of left anterior descending coronary artery in male and female pigs.

Summary Androgens may he risk factors in the pathogenesis of coronary artery disease by promoting coronary vasoconstriction. We studied the effect of testosterone treatment on coronary vascular reactivity of male and female domestic pigs treated for 2 weeks with either placebo or testosterone 10 mg/kg subcutaneous (s.c.) pellets. Vascular reactivity was studied in ring segments (4–5 mm) isolated from the left anterior descending coronary artery (LAD). No significant sex difference was noted in the response of LAD segments from placebo-treated male and female animals to KCI and prostaglandin F2α (PGF2α). Androgen treatment increased the maximum response (Tmax) of intact vessels to KC1 from 3,647 ± 689 mg in controls to 8.939 ± 1,284 mg in testosterone-treated males (p < 0.01) and from 3,405 ± 669 to 10.524 ± 1.663 mg in testosterone-treated female pigs (p < 0.01 ). Testosterone similarly increased the response to PGF2α 10 6M from a mean of 2.149 ± 1.036 to 3,163 ± 867 mg in males (p < 0.05) and from 2.076 ± 810 to 3.565 ± 578 mg in female segments (p < 0.05). Endothelial denudation significantly decreased the potentiating effect of testosterone treatment in males to both KC1 and PGF2α (p < 0.05). but not in segments from females. Our data show that testosterone treatment potentiates contractility of porcine LAD segments to both receptor- and nonreceptor-mediated agonists. In male pigs, this effect may be mediated by an effect on endothelium.

Effect of estradiol 17β on pressor responses of rat mesenteric bed to norepinephrine, K+, and U-46619

Summary We reinvestigated the effect of estradiol 17β on the responses of adrenergic and nonadrenergic vasoconstrictors characterized it in terms of steroid specificity, time course, and the role of classic estrogen receptors. We evaluated the effect of estradiol 17β on the pressor responses of isolated perfused rat mesenteric vascular bed (McGregors preparation). Estradiol 17β (7–700 nM) significantly increased the pressor response to bolus applications of norepinephrine (NE) (p < 0.05). However, estradiol 17β did not significantly increase the responses to endogenous NE release induced by electrical field stimulation. Other steroids, testosterone, and the 17α isomer of estradiol (7 and 700 nM) were ineffective. Estradiol 17β (700 nM) also significantly increased the maximum pressor response of rat mesenteric preparation to both the prostaglandin endoperoxide analogue U-46619 and to K+. The potentiation by estradiol 17β of mesenteric vasoconstriction elicited by NE, K+, and U-46619 was rapid (2–8 min), suggesting that a nuclear receptor may not be involved. This notion received further support in that significant potentiation of the NE-induced pressor response was also observed with estradiol 17β conjugated to albumin (700 nM), but not when electrical field stimulation was used. The conjugate increased the effect of all NE concentrations. Its effect was also more consistent (p < 0.01) than that elicited by free estradiol 17β. The dose-response curve was shifted to the left, and the maximum effect was increased. These data suggest that estradiol 17β may possess rapid nongenomic actions unrelated to nuclear receptor binding and gene transcription.

Estradiol effect on rate of proliferation of rat carotid segments: effect of gender and tamoxifen.

Using organ culture of carotid artery segments from sexually mature male and female rats, we examined the effect of estradiol 17 beta on proliferation. The index of cell proliferation was [3H]thymidine uptake. Estradiol 17 beta (0.18-0.36 microM) inhibited the uptake of thymidine in a concentration-dependent manner (p < 0.05). Estradiol 17 beta inhibited [3H]thymidine uptake only in the absence of the weak estrogen receptor agonist phenol red and in carotid artery segments from sexually mature female (p < 0.01) but not male rats. Tamoxifen (0.1 and 1 microM), a partial agonist of estrogen receptors, significantly inhibited thymidine uptake (p < 0.01). However, preincubation of the segments with tamoxifen (0.1 and 1.0 microM) for 4 h before the exposure to estradiol, blocked estradiol 17 beta-induced inhibition of thymidine uptake (p < 0.05 and p < 0.01 for 0.1 and 1.0 microM, respectively). The cyclooxygenase inhibitor indomethacin (5 microM) did not affect either the basal [3H]thymidine uptake or the estradiol 17 beta-induced inhibition of that uptake. This latter finding suggests that prostacyclin or prostaglandin E2 does not mediate the inhibitory response to estradiol 17 beta. The results of these experiments suggest that estradiol 17 beta-induced inhibition of proliferation of rat carotid artery segments is mediated through activation of estrogen receptors.

Vascular Non-genomic Effects of Estrogen

Studies of the cellular mechanisms of action of steroids lead to extensive investigation of DNA-binding and gene regulatory proteins. Steroids are thought to passively diffuse into the cell and bind to their nuclear receptor protein. Each receptor is both ligand and cell specific, and binds to its respective steroid with high affinity (K d: 0.1–1.0 nM). The ligand-receptor complex becomes an activated transcription factor, which binds gene regulatory elements on DNA to enhance transcription of several target genes. Protein synthesis and processing follows (Moudgil 1987).

The vasodilatation induced by hydroperoxy metabolites of arachidonic acid in the rat mesenteric and pulmonary circulation

1 The effects of 15‐hydroperoxy metabolites of arachidonic acid on vascular tone were evaluated in the perfused mesenteric preparation, the isolated perfused lung and segments of pulmonary arteries of the rat. 2 In the mesenteric preparation, precontracted with phenylephrine, both 15‐hydroperoxy‐5,8,11,13‐eicosatetraenoic acid (15‐HPETE, ED50 1.6 nmol) and 8,15‐dihydroperoxy‐5,9,11,13‐eicosatetraenoic acid (8,15‐diHPETE, ED50 0.3 nmol) induced dose‐dependent vasodilatation, whereas 5,15‐diHPETE (0.2–100 nmol) had no effect. Prostacyclin (ED50 0.01 nmol) was, however, more potent than the hydroperoxides. 3 In the rat isolated lung, precontracted with the stable thromboxane agonist U‐46619, dose‐dependent decrease in the perfusion pressure occurred with 15‐HPETE (ED50 40 nmol), 5,15‐diHPETE (ED50 30 nmol) and 8,15‐diHPETE (ED50 7 nmol) while 13‐hydroperoxide of linoleic acid had no effect. Prostacyclin was 10 times more potent than 8,15‐diHPETE. The vasodilator effects were not affected by indomethacin. 4 In both endothelium intact and denuded rat pulmonary arteries the hydroperoxides 15‐HPETE, 8,15‐diHPETE, and 5,15‐diPETE induced dose‐dependent relaxation. The hydroperoxide, 8,15‐diHPETE was at least 3 times more potent than 15‐HPETE or 5,15‐diHPETE. The hydroperoxides had no effect on the basal tone of vessel segments and the relaxation induced by 15‐HPETE was not attenuated by methylene blue (5 μm). 5 These data indicate that 8,15‐diHPETE may be a significant endothelium‐independent vasodilator product of arachidonate lipoxygenation.

Angiopeptin inhibits thymidine incorporation by explants of porcine coronary arteries

Angiopeptin, a stable octapeptide analog of somatostatin, inhibits proliferation in a variety of cancer cell lines. We studied the effect of angiopeptin on 3H-thymidine uptake into ring segments from the porcine coronary tree. The incorporation of 3H-thymidine into segments of porcine left anterior descending (LAD) coronary artery was time dependent and reached a plateau after 48 h. The addition of angiopeptin (48.1 and 96.2 nM) to the culture medium significantly inhibited 3H-thymidine incorporation into the segments by 36.7 +/- 10.1% and 48.3 +/- 2.3% of the control, respectively. Forskolin (100 microM), inhibited 3H-thymidine incorporation (52.7 +/- 10.1%) to the same degree as did angiopeptin (96.2 nM). Incubation of the segments with 125I-labeled angiopeptin, for 2 h at 37 degrees C, showed angiopeptin uptake to be time dependent and exhibited a first-order kinetics, reaching equilibrium after 30 min. Autoradiographic studies showed a uniform distribution of angiopeptin within the endothelium, media, and adventitia. Most of the labeling was associated with the nuclei of the cells. Angiopeptin, after 30-min incubation, did not significantly modify the basal levels of cyclic adenosine monophosphate (cAMP). In contrast, forskolin (100 microM) elicited a 50-fold increase of the basal levels of cAMP. These results indicate that in addition to its endocrine effects, angiopeptin reduces the rate of proliferation by acting directly on the vessel wall.