Thyroid hormone modulates the responsiveness of rat aorta to alpha1-adrenergic stimulation: an effect due to increased activation of beta2-adrenergic signaling.

AIM: The ability of the thyroid hormone to increase cardiac output and to lower systemic vascular resistance may provide a novel treatment for cardiovascular diseases. Therefore, understanding the mechanisms of thyroid hormone action on the heart and peripheral vasculature could be of clinical importance. We previously found that thyroid hormone modulates the alpha1-adrenergic effect on vascular reactivity of rat aortas. In the present study we further investigated possible mechanisms of this response. METHODS: Hyperthyroidism was induced on Wistar-Kyoto male rats with L-Thyroxine, (THYR) treatment for two weeks, N.=18 while untreated rats used as controls (NORM), N.=16. The thoracic aorta was dissected and cut into rings that were suspended in an isolated organ bath with Krebs-Henseleit buffer. Maximal tension, Tmax, in g was measured in response to Potassium Chloride (KCl) and Phenylephrine (PE) in rings in the presence of Ritodrine, a beta-2 agonist (NORM-RITO, N:=8, THYR-RITO, N.=9), or in the absence of Ritodrine (THYR, N.=9, NORM, N.=8). RESULTS: With KCL, Tmax was not different between the THYR, NORM, NORM-RITO, and THYR-RITO groups. With PE, there was a difference in Tmax between NORM-RITO and NORM, 0.66 (0.056) g vs 1.00 (0.066) g, P<0.05 and THYR and NORM, 0.75 (0.055) g vs 1.00 (0.066) g, P<0.05. No significant difference was observed between THYR-RITO AND THYR. Furthermore, Relax % was not significantly different between the NORM and the THYR, NORM-RITO, and THYR-RITO groups, 64.5%(3.7) vs 67.3%(6.7), 73.5% (4.3) and 81.8 %(4.7), P>0.05. CONCLUSIONS: PE induced vasoconstriction in isolated rat aortic rings was reduced after both ritodrine and thyroxine treatment. However, co-administration of thyroid hormone and ritodrine did not result in a synergistic reduction of PE induced vasoconstriction. Thus, thyroxine may modulate the alpha1-adrenergic vascular responsiveness by enhancing beta2-adrenergic stimulation.

Narrow-band imaging with magnification in Barrett's esophagus: validation of a simplified grading system of mucosal morphology patterns against histology.

BACKGROUND AND STUDY AIMS: Validation of a simplified classification of mucosal morphology in prediction of histology in Barrett's esophagus using narrow-band imaging with magnification (NBI-Z) and assessing its reproducibility by endoscopists experienced in the use of NBI (NBI-experts) and by endoscopists who were new to NBI (non-NBI-experts). PATIENTS AND METHODS: In a prospective cohort study of 109 patients with Barrett's esophagus at a single tertiary referral center, mucosal patterns visualized in Barrett's esophagus on NBI-Z were classified into four easily distinguishable types: A, round pits with regular microvasculature; B, villous/ridge pits with regular microvasculature; C, absent pits with regular microvasculature; D, distorted pits with irregular microvasculature. The NBI-Z grading was compared with the final histopathological diagnosis, and positive (PPV) and negative predictive values (NPV) were calculated. The reproducibility of the grading was then assessed by NBI-expert and non-NBI-expert endoscopists, and interobserver and intraobserver agreement were calculated using kappa statistics. RESULTS: Per-biopsy analysis: In 903 out of 1021 distinct areas (87.9%) the NBI-Z grading corresponded to the histological diagnosis. Per-patient analysis: The PPV and NPV for type A pattern (columnar mucosa without intestinal metaplasia) were 100% and 97% respectively; for types B and C (intestinal metaplasia) they were 88% and 91% respectively, and for type D (high-grade dysplasia) 81% and 99% respectively. Inter- and intraobserver agreement: The mean kappa values in assessing the various patterns were 0.71 and 0.87 in the non-expert group; 0.78 and 0.91 in the expert group. CONCLUSIONS: This study has validated a simplified classification of the various morphologic patterns visualized in Barrett's esophagus and confirmed its reproducibility when used by NBI-expert and non-NBI-expert endoscopists.

Decreased vascular reactivity to alpha1 adrenergic stimulation in the presence of hypothyroid state: a part of an adaptive response?

AIM: A hypothyroid state frequently accompanies cardiac illnesses but its physiological significance for the cardiovascular hemodynamics remains largely unknown. Therefore, the present study investigated possible physiological consequences on vascular function in an experimental model of low thyroid hormone state. METHODS: Hypothyroidism was induced in rats by the administration of 6-n-propyl-2-thiouracil in drinking water (final concentration of 0.05%) for 3 weeks, HYPO rats, and untreated rats served as controls (Control). Isolated aortic rings with or without endothelium (E+, E-) were contracted with KCl (10 to 60 mM) and phenylephrine (PE) (10(-10) to 10(-5) M). Maximal tension (Tmax) in g and EC(50) in response to PE and KCl were measured. RESULTS: Tmax was significantly lower while EC(50) was significantly higher in response to PE in HYPO(E+) than in Control(E+). Upon endothelium removal, Tmax was not significantly different between the groups but EC(50) was still significantly higher in HYPO(E-) than in Control(E-). EC(50) in response to KCl was significantly higher in HYPO with or without endothelium and no difference was found in Tmax. CONCLUSIONS: Hypothyroid aortic rings respond less to a1 adrenergic stimulation probably due to the endothelium modulatory effect as well as to intrinsic smooth muscle defect. This seems to be of important clinical relevance.

Blockade of angiotensin II type 1 receptor diminishes cardiac hypertrophy, but does not abolish thyroxin-induced preconditioning.

Growth and stress seem to share common intracellular pathways and activation of growth signaling can increase resistance to stress. Thyroid hormone induces cardiac hypertrophy and preconditions the myocardium against ischemia reperfusion injury. The present study investigated whether this response is mediated by renin-angiotensin system (RAS). RAS is shown to be activated in hyperthyroidism and is involved in the development of cardiac hypertrophy. Male Wistar rats were treated with L-thyroxin (25 microg/100 g, sc, od) for fourteen days, while normal rats served as controls. In addition, irbesartan (150 mg/kg po), a potent blocker of angiotensin II type 1 receptor (AT1), was given with L-thyroxin for fourteen days. Isolated hearts were perfused in Langendorff mode; after stabilization, they were subjected to 20 min zero-flow global ischemia and 45 min of reperfusion. Thyroxin induced cardiac hypertrophy, which was diminished with irbesartan administration. Post-ischemic recovery of function was increased in thyroxin-treated hearts as compared to controls while ischemic contracture was accelerated and intensified. Irbesartan did not abolish this response. In conclusion, blockade of angiotensin II type 1 receptor with irbesartan preserves thyroxin-induced cardioprotection while diminishing cardiac hypertrophy. It is likely that thyroxin-induced cardioprotection is due to a direct effect of thyroid hormone.

Increased resistance to activated protein C and factor V Leiden in recurrent abortions. Review of other hypercoagulability factors.

OBJECTIVE: To evaluate hereditary and acquired hemostatic abnormalities associated with recurrent spontaneous early (first-trimester) abortions. METHOD: A group of 56 Greek women with two or more unexplained primary spontaneous abortions, and a reference group of 148 women without a history of recurrent abortions, were screened for hypercoagulability. A randomly selected population of first-trimester pregnant women was also chosen for factor V Leiden genetic screening. RESULTS: A total of 21% of the women with recurrent abortions, compared with 12% of the reference group, showed increased activated protein C resistance. Fourteen per cent had positive lupus anticoagulant, compared with 11.5% of the reference group. For the rest of the parameters, there was no difference between the two groups. Of 22 women studied for factor V Leiden, one was homozygous and one was heterozygous. Results were compared using Fisher's exact test and two-tailed Student's t tests. CONCLUSIONS: Increased activated protein C resistance appears to be an important factor in women with recurrent abortions. These data indicate the need for routine investigation of activated protein C resistance in women with recurrent abortions.