Pharmacological inhibition of TRalpha1 receptor potentiates the thyroxine effect on body weight reduction in rats: potential therapeutic implications in controlling body weight.

It has been previously reported that thyroid hormone receptor alpha1 (TRalpha1) is involved in the regulation of food intake and heart rhythm. Herein, we show that pharmacological inhibition of TRalpha1 by dronedarone, an amiodarone like compound (shown to antagonize thyroid hormone binding to TRalpha1), prevented the thyroid hormone induced increase in food intake and heart rate acceleration in rats. This resulted in a marked reduction in body weight. It is likely that thyroid analogs may prove potential therapeutic agents for controlling body weight.

Hyperthyroid hearts display a phenotype of cardioprotection against ischemic stress: a possible involvement of heat shock protein 70.

Hyperthyroid hearts are shown to display a phenotype of cardioprotection against ischemic stress, but the underlying signaling mechanisms remain largely unknown. The present study investigated the possible relation of HSP70 to the thyroid hormone induced cardioprotection. HSP70 is a redox-regulated molecular chaperone, and enhances cell survival under stress. Thyroxin (25 microg/100 g body weight) was administered to Wistar male rats for four days (THYR-4d) and two weeks (THYR-14d), respectively, while untreated animals served as controls (CON-4d, CON-14d). Isolated hearts from control and thyroxin treated rats were subjected to 20 min zero-flow ischemia followed by 45 min of reperfusion (I/R). The amount of HSP70 in the myocardium for THYR-14d was 1.85 times the levels of CON-14d (p < 0.05). The levels of HSP70 expression were no different between THYR-4d and CON-4d, p > 0.05. This was only accompanied by an increase in MDA levels (used as an index of oxidative stress) in THYR-14d compared to untreated hearts. These changes corresponded to a differential response of the heart to I/R; post-ischemic recovery of function was significantly increased in THYR-14d compared to CON-14d, and was no different between the THYR-4d and CON-4d hearts. In conclusion, long-term thyroxin administration results in increased tolerance of the myocardium to I/R and enhances the expression of HSP70 which may, at least in part, account for this response.

Thyroid hormone receptors alpha1 and beta1 are downregulated in the post-infarcted rat heart: consequences on the response to ischaemia-reperfusion.

There is accumulating evidence that thyroid hormone metabolism is altered after myocardial infarction (AMI) but its physiological relevance remains largely unknown. The present study investigated the possible role of thyroid hormone signaling in the response of the post-infarcted heart to ischaemia-reperfusion. Wistar rats were subjected to left coronary artery ligation (AMI), or sham operation (SHAM). After 8 weeks, hearts from AMI and SHAM rats were perfused in Langendorff mode and subjected to 20 min of zero-flow global ischaemia (I) and 45 min of reperfusion (R); AMI(I/R), n = 7 and SHAM(I/R), n = 7. Basal left ventricular pressure (LVDP), +dp/dt, and -dp/dt were significantly reduced. Left ventricular weight of the viable myocardium was increased by 14% in the AMI as compared to SHAM hearts, P < 0.05. T(3) and T(4) plasma levels in nM were 1.83 (0.08) and 53.3 (2.9) for SHAM and 1.76 (0.06) and 59.4 (5.2) for AMI rats, respectively, P > 0.05. TRalpha1 and TRbeta1 expression levels were 1.3- and 1.8-fold less in AMI than in SHAM hearts, P < 0.05. Furthermore, SERCA and NHE1 expression levels were 2.1- and 1.8-fold less in AMI than in SHAM, P < 0.05. PKCepsilon was 1.35-fold more in AMI compared to SHAM, P < 0.05. Myocardial glycogen content (in micromol/g) was 7.8 (1.2) in AMI as compared to 4.4 (0.5) for SHAM hearts, P < 0.05. After I/R, left ventricular end-diastolic pressure at 45 min of R (LVEDP45 in mmHg) was 20.3 (3.2) for AMI(I/R) vs 50.6 (4.8) mmHg for SHAM(I/R), P < 0.05. LDH release per gram of tissue was 251 (103) for AMI(I/R) and 762 (74) for SHAM(I/R), P < 0.05. In conclusion, TRalpha1 and TRbeta1 are downregulated after myocardial infarction and this was associated with altered expression of thyroid hormone responsive genes and increased tolerance of the post-infarcted heart to ischaemia-reperfusion injury.

Propylthiouracil-induced hypothyroidism is associated with increased tolerance of the isolated rat heart to ischaemia-reperfusion.

The present study investigated the response of the hypothyroid heart to ischaemia-reperfusion. Hypothyroidism was induced in Wistar rats by oral administration of propylthiouracil (0.05%) for 3 weeks (HYPO rats), while normal animals (NORM) served as controls. Isolated hearts from NORM and HYPO animals were perfused in Langendorff mode and subjected to zero-flow global ischaemia followed by reperfusion (I/R). Post-ischaemic recovery of left ventricular developed pressure was expressed as % of the initial value (LVDP%). Basal expression of protein kinase C epsilon (PKCepsilon) and PKCdelta and phosphorylation of p46 and p54 c-jun NH(2)-terminal kinases (JNKs) in response to I/R were assessed by Western blotting. LVDP% was found to be significantly higher in HYPO hearts than in NORM. At baseline, PKCepsilon expression was 1.4-fold more in HYPO than in NORM hearts, P<0.05, while PKCdelta was not changed. Furthermore, basal phospho-p54 and -p46 JNK levels were 2.2- and 2.6-fold more in HYPO than in NORM hearts, P<0.05. In response to I/R, in NORM hearts, phospho-p54 and -p46 JNK levels were 5.5- and 6.0-fold more as compared with the baseline values, P<0.05, while they were not significantly altered in HYPO hearts. HYPO hearts seem to display a phenotype of cardioprotection against ischaemia-reperfusion and this is associated with basal PKCepsilon overexpression and attenuated JNK activation after I/R.

Phenylephrine induced aortic vasoconstriction is attenuated in hyperthyroid rats.

BACKGROUND: Abnormal vascular responsiveness to vasoconstrictors may play an important role in peripheral vascular resistance in hyperthyroidism. The aim of the present study was to evaluate whether the vascular response to potassium chloride and phenylephrine is abnormal in a rat model of thyroxine-induced cardiac hypertrophy. METHODS: Left ventricular hypertrophy was induced in Wistar rats by subcutaneous administration of L-thyroxine for two weeks ("THYR"), n=17. Animals treated with normal saline served as controls, ("NORM"), n=20. 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 KCl and PE at the highest concentration in rings with endothelium (+E) and without endothelium (-E) in both groups. Relaxation response (Relax percent) to acetylcholine administration was expressed as percent of the maximal tension induced by phenylephrine. RESULTS: Left ventricular weight was 0.9 (SEM, 0.04) g for THYR group vs 0.7 (0.02) g for the NORM group, p<0.05. With KCl, Tmax was not different between the THYR and NORM groups with and without endothelium. With PE, there was a difference in Tmax between THYR+E and NORM+E, 1.2 (0.05) g vs 1.5 (0.09) g, p<0.05. Tmax was also different between THYR-E and NORM-E, 1.5 (0.08) g vs 1.7 (0.07) g, p<0.05. Relax percent was not significantly different between THYR+E and NORM+E (45.9 percent vs 42.8 percent, p>0.05). CONCLUSIONS: We conclude that: a) Vascular tension of the thoracic aorta in response to PE is lower in thyroxine-treated rats as compared to controls, probably due to enhanced PE-induced vasorelaxation at high concentration. b) Relaxation response of the thoracic aorta to acetylcholine is not different between THYR and NORM groups.

Long-term thyroxine administration increases heat stress protein-70 mRNA expression and attenuates p38 MAP kinase activity in response to ischaemia.

The present study was undertaken to investigate heat stress protein (HSP)-70 mRNA induction and p38 MAP kinase (MAPK) activity in response to ischaemic stress in the hyperthyroid rat heart. L-Thyroxine (T(4)) (25 microg/100 g body weight) was administered to Wistar rats for 2 days (THYRacute) or 14 days (THYR), while animals treated similarly with normal saline served as controls (NORMacute and NORM). In addition, abdominal aortic banding was performed in another group of rats to produce constriction-induced hypertrophy (HYP), while sham-operated (SOP) animals served as controls. Isolated rat hearts were perfused in a Langendorff mode. Hearts from NORMacute (n=6), THYRacute animals (n=8), NORM (n=6), THYR (n=6), SOP (n=5) and HYP (n=7) animals were subjected to 20 min of zero-flow global ischaemia followed by 45 min of reperfusion. HSP70 mRNA expression and phosphorylated p38 MAPK protein expression were detected in response to ischaemia and protein kinase C-epsilon (PKCepsilon) protein expression was detected at baseline. Thyroid hormones were measured in plasma. Long-term T(4) administration and aortic constriction resulted in the development of cardiac hypertrophy. Thyroid hormones were increased in both THYR and THYRacute as compared with normal groups (P<0.05). HSP70 mRNA induction was increased 2.3-fold in THYR as compared with NORM hearts (P<0.05), whereas there was not any difference between THYRacute and NORMacute hearts (P>0.05). Phosphorylated p38 MAPK protein expression was 2.2-fold more in NORM than in THYR hearts (P<0.05), but it was not different between NORMacute and THYRacute hearts (P>0.05). HSP70 mRNA induction was 1.8-fold greater in HYP than in SOP hearts (P<0.05), whereas phosphorylated p38 MAPK protein expression was similar between the two groups (P>0.05). PKCepsilon protein expression at baseline was 1.7-fold more in NORM than in THYR hearts (P<0.05), and not different between NORMacute and THYRacute hearts (P>0.05) as well as HYP and SOP hearts (P>0.05). This study shows that HSP70 mRNA expression is increased, whereas p38 MAPK activation is attenuated in response to ischaemia in long-term T(4)-treated rat hearts as compared with normal and acute hyperthyroid hearts.

Propranolol diminishes cardiac hypertrophy but does not abolish acceleration of the ischemic contracture in hyperthyroid hearts.

This study was undertaken to define the contributions of left ventricular hypertrophy (LVH) and increased adrenergic activity to the acceleration of ischemic contracture (IC) that occurs in chronic hyperthyroid rat heart. Acute and chronic hyperthyroidism (THYR) were induced by thyroxine administration for 2 and 14 days, respectively, and normal animals (NORM) served as controls. Isolated hearts were perfused in a Langendorff mode. NORM alpha acute, n = 6; THYR alpha acute, n = 8; and THYR alpha, n = 13; and NORM alpha, n = 13 were subjected to 20-min zero-flow global ischemia (I) and 45-min reperfusion (R). Additional THYR and NORM hearts treated with propranolol (prop) were subjected to 30-min I; THYR beta prop, n = 6 and NORM beta prop, n = 8, and THYR beta, n = 6, NORM beta, n = 8 served as controls. Acceleration of IC was measured by the time to peak contracture (Tmax). Left ventricular hypertrophy (LVH) was assessed by the ratio of left ventricular weight in milligrams (LVW) to animal body weight (BW) in grams. Cardiac hypertrophy developed in chronic but not acute hyperthyroidism. Propranolol reduced the extent of LVH. Contracture occurred earlier in chronic than in acute hyperthyroid and normal hearts. Propranolol did not alter contracture. In conclusion, IC is accelerated by thyroxine administration, and this is probably not due to LVH or increased beta-adrenergic activity. Propranolol diminishes LVH in hyperthyroidism.

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.

Hyperthyroidism is associated with preserved preconditioning capacity but intensified and accelerated ischaemic contracture in rat heart.

BACKGROUND: The present study was undertaken to define the effects of thyroxine administration on ischaemic preconditioning (PC) and the ischaemic contracture. METHODS: Hyperthyroidism was induced by administration of L-thyroxine in rats (THYR) while normal animals served as controls (NORMa). Isolated rat hearts were perfused in a Langendorff preparation. NORMa control (n = 16) and THYR control (n = 9) hearts underwent 20 min of ischaemia and 45 min reperfusion while NORMa PC (n = 16) and THYR PC (n = 14) were subjected to PC before ischaemia. Additional normal hearts were subjected to 30 min of ischaemia with and without PC, NORMb control, n = 8 and NORMb PC, n = 6. Postischaemic recoveries of left ventricular (LV) developed pressure were expressed as % of the initial value (LVDP%). Severity of contracture was measured by the time (Tmax) and magnitude (Cmax) of peak contracture. RESULTS: LVDP% was significantly higher after PC, both in NORMa and THYR rats. In NORMa control hearts, ischaemic contracture had not yet reached a plateau at 20 min of ischaemia. Contracture appeared earlier in THYR control and PC than in NORMa control and PC groups. Tmax was 22.1 (0.9) vs 16.8 (1.4) min for NORMb control and PC, p < 0.05 and 12.5 (1.0) vs 9.3 (1.1) min for THYR control and PC hearts, p < 0.05. Tmax was earlier in both THYR groups compared to NORMb groups, p < 0.05. Cmax was significantly higher in both THYR groups compared to both NORMb groups. CONCLUSION: Ischaemic contracture is both accelerated and accentuated in thyroxine treated hearts while preconditioning capacity is preserved. Preconditioning and thyroxine administration shorten Tmax in an additive way, whereas Cmax in hyperthyroid hearts did not further increase by preconditioning.

Diethylbarbiturate potentiation of 2,4,6-trinitrobenzenesulphonate-induced rhodanese inactivation.

The rate of rhodanese inactivation by 2,4,6-trinitrobenzenesulphonate is increased in the presence of diethylbarbiturate in the reaction medium. A "rate saturation effect" indicates the formation of a rhodanese-diethylbarbiturate complex, prior to modification-induced enzyme inactivation. The dissociation constant of this complex is 19.0 mM. Diethylbarbiturate has no effect on the trinitrophenylation rate of the free amino groups of rhodanese. When rhodanese modification, in the presence of diethylbarbiturate in the reaction medium, is carried out by the use of a 2,4,6-trinitrobenzenesulphonate concentration much lower than the concentration of rhodanese modifiable amino groups, reaction stoichiometry indicates that 3 to 5 moles of rhodanese are rendered inactive for each mole of 2,4,6-trinitrobenzenesulphonate utilized. This finding indicates the existence of a chain-reaction type mechanism of rhodanese inactivation.

Inactivation of rhodanese from human gastric mucosa and stomach adenocarcinoma by 2,4, 6-trinitrobenzenesulphonate and by 4,4'-diisothiocyanatostilbene-2,2'-disulphonate.

Rhodanese (thiosulphate sulphurtransferase, EC 2.8.1.1) was partially purified from normal human gastric mucosa and from gastric adenocarcinoma by DEAE-cellulose column chromatography. Rhodanese inactivation by 2, 4, 6-trinitrobenzenesulphonate and by 4,4'-diisothiocynatostilbene-2-2'-disulphonate was studied by an analysis of the time-dependence of rhodanese activity loss. Rhodanese inactivation by 2, 4, 6-trinitrobenzenesulphonate was, under all conditions tested, found to be first-order with regard to enzyme residual activity. In contrast to this, rhodanese inactivation by 4, 4'-diisothiocyanatostilbene-2, 2'-disulphonate was found to be biphasic, when log residual enzyme activity was plotted vs reaction time. The first-order rate constant, k, for rhodanese inactivation by 2, 4, 6-trinitrobenzenesulphonate was, at all pH values tested, higher with the gastric adenocarcinoma enzyme than with the normal mucosa enzyme: at pH 8.00, k is 27.0 per hour, for the normal mucosa enzyme, while for the adenocarcinoma enzyme k is 69.0 per hour. In contrast to this, no difference in the inactivation profile of the normal mucosa enzyme and the gastric adenocarcinoma enzyme was to be observed with 4,4'-diisothiocyanatostilbene-2,2'-disulphonate.