Hyperthyroid Rats Research Articles

Effects of experimentally induced maternal hypothyroidism and hyperthyroidism on the development of rat offspring: I. The development of the thyroid hormones–neurotransmitters and adenosinergic system interactions

The adequate functioning of the maternal thyroid gland plays an important role to ensure that the offspring develop normally. Thus, maternal hypo- and hyperthyroidism are used from the gestation day 1 to lactation day 21, in general, to recognize the alleged association of offspring abnormalities associated with the different thyroid status. In maternal rats during pregnancy and lactation, hypothyroidism in one group was performed by antithyroid drug, methimazole (MMI) that was added in drinking water at concentration 0.02% and hyperthyroidism in the other group was induced by exogenous thyroxine (T4) (from 50μg to 200μg/kg body weight) intragastric administration beside adding 0.002% T4 to the drinking water. The hypothyroid and hyperthyroid states in mothers during pregnancy and lactation periods were confirmed by measuring total thyroxine (TT4) and triiodothyronine (TT3) at gestational day 10 and 10 days post-partum, respectively; the effect was more pronounced at the later period than the first. In offspring of control maternal rats, the free thyroxine (FT4), free triiodothyronine (FT3), thyrotropin (TSH) and growth hormone (GH) concentrations were pronouncedly increased as the age progressed from 1 to 3 weeks. In hypothyroid group, a marked decrease in serum FT3, FT4 and GH levels was observed while there was a significant increase in TSH level with age progress as compared with the corresponding control. The reverse pattern to latter state was recorded in hyperthyroid group. The thyroid gland of offspring of hypothyroid group, exhibited some histopathological changes as luminal obliteration of follicles, hyperplasia, fibroblastic proliferation and some degenerative changes throughout the experimental period. The offspring of hyperthyroid rats showed larger and less thyroid follicles with flattened cell lining epithelium, decreased thyroid gland size and some degenerative changes along the experimental period. On the other hand, the biochemical data revealed that in control offspring, the levels of iodothyronine 5′-monodeiodinase (5′-DI), monoamines, γ-aminobutyric acid (GABA), acetylcholinesterase (AchE), ATPase-enzymes (Na+,K+-ATPase, Ca2+-ATPase and Mg2+-ATPase) follow a synchronized course of development in all investigated brain regions (cerebrum, cerebellum and medulla oblongata). In addition, the depression in 5′-DI activity, monoamines levels with age progress in all investigated regions, was more pronounced in hypothyroid offspring, while they were increased significantly in hyperthyroid ones in comparison with their respective controls. Conversely, the reverse pattern was recorded in level of the inhibitory transmitter, GABA while there was a disturbance in AchE and ATPases activities in both treated groups along the experimental period in all studied regions. In conclusion, the hypothyroid status during pregnancy and lactation produced inhibitory effects on monoamines, AchE and ATPases and excitatory actions on GABA in different brain regions of the offspring while the hyperthyroid state induced a reverse effect. Thus, the maternal hypothyroidism and hyperthyroidism may cause a number of biochemical disturbances in different brain regions of their offspring and may lead to a pathophysiological state. These alterations were age dependent.

THYROID STATUS MODIFIES CARDIAC NITRIC OXIDE SYNTHASES DURING HEMORRHAGIC SHOCK: PP.22.400

The regulation of cardiac function is a complex process in which nitric oxide (NO) is a mediator and the thyroid status has a role. Objectives: To study the involvement of thyroid status and NO synthases (NOS) on hemodynamic changes induced by acute hemorragic shock. Animals euthyroid (E), hyperthyroid (H) and hypothyroid (h), are divided into two groups, control (C), and hemorrhaged rats (H) (withdrawal of 20 % of blood volume). Right atrium (A) and left ventricule (V) were removed at 120 min of hemorrhage. Histochemical NOS activity (NADPH-diaphorase technique), NOS, caveolin 1 and 3 (cav 1 and 3) protein levels (western blot) were evaluated. The results are expresed as X ± ES, n = 9/ group. Analysis of variance (ANOVA) followed by the ad hoc Bonferroni test was used for multiple comparisons. The 5% probability level was used as a criterion for biological significance. Results: Blood loss did not change neither eNOS and nNOS protein levels in A and V nor cav-3 protein levels in V. Conclusions: Acute blood loss increased NOS activity in A and V of euthyroid rats that correlated with changes in i-NOS protein levels. Hypovolemic state induced by acute hemorrhage induced changes in the cav-1 protein levels in A of hyperthyroid rats and in V of hyper and hypothyroid animals. The production of NO and its involvement in the cardiac adaptation to hemorrhage depend on the thyroid status. The coordinated expressional changes in NOS isoforms and their allosteric regulators, such as caveolin, may be viewed as a compensatory mechanism to maintain the production of bioactive NO.

Vasopressinergic network abnormalities potentiate conditioned anxious state of rats subjected to maternal hyperthyroidism

We have previously reported that a mild maternal hyperthyroidism in rats impairs stress coping of adult offspring. To assess anxiogenesis in this rat model of stress over-reactivity, we used two behavioural tests for unconditional and conditional anxious states: elevated plus maze test (EPM) and Vogel conflict test (VCT). In the latter one, arginine vasopressin (AVP) release was enhanced due to osmotic stress. With the EPM test no differences were observed between maternal hyperthyroid rats (MH) and controls. However, with the VCT, the MH showed increased anxiety-like behaviour. This behavioural difference was abolished by diazepam. Plasma AVP concentration curve as a function of water deprivation (WD) time showed a marked increase, reaching its maximal levels within half the time of controls and another significant difference after VCT. A general increase in Fos expression in hypothalamic supraoptic and paraventricular nuclei (PVN) was observed during WD and after VCT. There was also a significant increase of AVP immunoreactivity in anterior hypothalamic area. A large number of Herring bodies were observed in the AVP containing fibres of MH hypothalamic-neurohypophysial system. Numerous reciprocal synaptic connections between AVP and corticotropin releasing factor containing neurons in MH ventromedial PVN were observed by electron microscopy. These results suggest that a mild maternal hyperthyroidism could induce an aberrant organization in offspring's hypothalamic stress related regions which could mediate the enhanced anxiety seen in this animal model.

Alteration of guanylyl cyclase‐activated vasorelaxation in thoracic aorta from hyperthyroid rats

ObjectiveNitric oxide (NO) and C‐type natriuretic peptide (CNP) activate soluble (sGC) and particulate guanylyl cyclas e (pGC), respectively, and play important roles in the mainte nance of cardiovascular homeostasis. The purpose of the present study was to define the alteration of pGC‐ and sGC‐ac tivated vasorelaxation in the thoracic aorta from hyperthyroid rats.Methods and ResultsHyperthyroidism was induced by administering L‐thyroxine (T4, 0.05 mg/100 g, sc) daily for 16 days. Experiments were performed in isolated rat aortic rings. CNP (0.1–1000 nM) and SNAP (10‐10000 nM) induced vascular relaxation in a concentration‐dependent manner in aortic rings from eu‐and hyperthyroid rats. The responses were significantly attenuated in aortic rings from hyperthyroid rats. ODQ (10 uM), an inhibitor of sGC, blocked the SNAP ‐induced vasorelaxation of aortic rings from both eu‐ and hyperthyroid d rat. To define the changes in response to cGMP, 8‐Br‐Cgmp (1–100 uM), a cell‐permeable cGMP analog, was used. 8‐Br‐cGMP‐induced vasorelaxation was attenuated in aortic rings from hyperthyroid rats compared to those from euthyroid rats.ConclusionsThese data demonstrate that pGC‐ and sGC‐activated vaso relaxation is attenuated in thoracic aorta from hyperthyroid rats which may be a part of the pathophysiology of the disease. Supported by NSFC (No30570669; 30971080).

Thiol redox status critically influences mitochondrial response to thyroid hormone‐induced hepatic oxidative injury: A temporal analysis

Liver is a major target organ for thyroid hormone. The objective of the present study was to investigate temporal regulation of mitochondrial glutathione and protein-bound thiol redox status in hyperthyroid liver. Mitochondria were isolated from control and hyperthyroid rat liver tissues at different time intervals, i.e., 24, 72, and 120 h following treatment, and sub-fractionated into sub-mitochondrial particles (SMPs) and matrix fractions. Increased prooxidant levels were indicative of oxidative stress in hyperthyroid mitochondria. Sensitivity to membrane lipid peroxidation (LPx) was maximal after 24 h, which subsided with time. Oxidative damage to proteins was evident as high carbonylation after 72 h; thiol residue damage was an early phenomenon. Reduced and oxidized glutathione (GSH and GSSG) pools of mitochondria were progressively depleted, thereby, impairing matrix antioxidant capacity. However, adaptations to withstand oxidative challenge were elicited in both SMPs and matrix fractions over the long term. It is concluded that maintenance of appropriate intra-mitochondrial glutathione and protein-bound thiol redox status could be instrumental in attenuating thyroid hormone-induced oxidative stress.

Adenosine monophosphate-activated protein kinase activation, substrate transporter translocation, and metabolism in the contracting hyperthyroid rat heart.

Thyroid hormones can modify cardiac metabolism via multiple molecular mechanisms, yet their integrated effect on overall substrate metabolism is poorly understood. Here we determined the effect of hyperthyroidism on substrate metabolism in the isolated, perfused, contracting rat heart. Male Wistar rats were injected for 7 d with T(3) (0.2 mg/kg x d ip). Plasma free fatty acids increased by 97%, heart weights increased by 33%, and cardiac rate pressure product, an indicator of contractile function, increased by 33% in hyperthyroid rats. Insulin-stimulated glycolytic rates and lactate efflux rates were increased by 33% in hyperthyroid rat hearts, mediated by an increased insulin-stimulated translocation of the glucose transporter GLUT4 to the sarcolemma. This was accompanied by a 70% increase in phosphorylated AMP-activated protein kinase (AMPK) and a 100% increase in phosphorylated acetyl CoA carboxylase, confirming downstream signaling from AMPK. Fatty acid oxidation rates increased in direct proportion to the increased heart weight and rate pressure product in the hyperthyroid heart, mediated by synchronized changes in mitochondrial enzymes and respiration. Protein levels of the fatty acid transporter, fatty acid translocase (FAT/CD36), were reduced by 24% but were accompanied by a 19% increase in the sarcolemmal content of fatty acid transport protein 1 (FATP1). Thus, the relationship between fatty acid metabolism, cardiac mass, and contractile function was maintained in the hyperthyroid heart, associated with a sarcolemmal reorganization of fatty acid transporters. The combined effects of T(3)-induced AMPK activation and insulin stimulation were associated with increased sarcolemmal GLUT4 localization and glycolytic flux in the hyperthyroid heart.

Expression of hepatic antioxidant genes in l-thyroxine-induced hyperthyroid rats: Regulation by vitamin E and curcumin

Earlier we have demonstrated that oral supplementation of vitamin E and curcumin alleviates hyperthyroidism-induced oxidative stress and distorted histoarchitecture in rat liver [5]. To delineate the underlying mechanism of protection, the present study was undertaken to investigate the regulatory role of vitamin E and curcumin on antioxidant gene (AOG) expression in hyperthyroid rat liver. Adult male rats were rendered hyperthyroid by administration of 0.0012% l-thyroxine in their drinking water, while vitamin E (200 mg/kg body weight) and curcumin (30 mg/kg body weight) were supplemented orally for 30 days. l-Thyroxine-induced hyperthyroidism decreased the transcript levels of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx1) and glutathione reductase (GR) in liver. Alleviated message levels of SOD and CAT were noticed following simultaneous administration of curcumin and vitamin E to hyperthyroid rats. Moreover vitamin E or curcumin treatment ameliorated GPx1 and GR mRNA levels. Translated products of AOGs showed differential expression in the liver of hyperthyroid rats, where Cu/Zn SOD (SOD1), CAT and GR were decreased in contrast to Mn SOD (SOD2) and GPx1. Vitamin E administration was able to alleviate SOD1, CAT and GR translated products while only CAT protein was restored to normal level by curcumin. Co-administration of both antioxidants normalized GPx1 protein expression. Interestingly decreased activities of cytosolic CAT and GPx1 were alleviated following vitamin E and curcumin administration. Increased mitochondrial SOD1 and decreased GR activities were also normalized by antioxidant treatment. Above findings suggest that administration of vitamin E and curcumin may alleviate the hepatic AOG expression in hyperthyroid rats.

The CAAT‐binding transcription factor 1/nuclear factor 1 binding site is important in β‐myosin heavy chain antisense promoter regulation in rats

The rat heart expresses two myosin heavy chain (MHC) isoforms, beta and alpha; these genes are arranged in tandem on the same chromosome. We have reported that an antisense (AS) beta RNA starts in the intergenic (IG) region between beta and alpha genes and extends to overlap the beta gene. We propose that in adult rats, both the alpha sense and IG betaAS RNA expression are activated by an IG bidirectional promoter and that the transcription of betaAS RNA interferes with the sense beta, resulting in low levels of beta mRNA and high levels of alpha, a phenotype seen in a typical rat heart. A previous report examined the activity of the betaAS promoter and showed that a 559 bp fragment of the betaAS promoter (-2285 to -1726; relative to alphaMHC gene start site) injected into rat ventricle was activated in control heart, and decreased significantly in response to hypothyroidism (propylthiouracil induced) and diabetes (streptozotocin induced) and increased in hyperthyroid rats (T(3) induced), similar in pattern to the endogenous betaAS RNA. In the present paper, we demonstrate with electrophoretic mobility shift analyses that ventricular nuclear proteins are interacting with a nuclear factor 1/CAAT-binding transcription factor 1 (NF1/CTF1) binding site, and a supershift assay indicates that the protein binding at this site is antigenetically related to the CTF1/NF1 factor. Moreover, a mutation of the CTF1/NF1 site within the 559 bp promoter region nearly abolished promoter activity in vivo in control, STZ- and PTU-treated rats. Based on these findings, we conclude that the NF1 site is critical to betaAS promoter regulation.

Brain GABA-receptor systems in functional thyroid disorders

This experimental study was designed to evaluate effects of hypo- and hyperthyroidism on the density of 3H-muscimol and 3H-diazepam-binding sites in synaptic membranes of the rat brain. It was shown that density of both 3H-muscimol and 3H-diazepam-binding sites increases in animals with hypothyroidism and decreases in hyperthyroidism. This difference may account for the predominance of general inhibitory reaction in animals with hypothyroidism and general excitation in hyperthyroid rats.

Experimental hyperthyroidism in rats increases the expression of the ubiquitin ligases atrogin‐1 and MuRF1 and stimulates multiple proteolytic pathways in skeletal muscle

Muscle wasting is commonly seen in patients with hyperthyroidism and is mainly caused by stimulated muscle proteolysis. Loss of muscle mass in several catabolic conditions is associated with increased expression of the muscle-specific ubiquitin ligases atrogin-1 and MuRF1 but it is not known if atrogin-1 and MuRF1 are upregulated in hyperthyroidism. In addition, it is not known if thyroid hormone increases the activity of proteolytic mechanisms other than the ubiquitin-proteasome pathway. We tested the hypotheses that experimental hyperthyroidism in rats, induced by daily intraperitoneal injections of 100 microg/100 g body weight of triiodothyronine (T3), upregulates the expression of atrogin-1 and MuRF1 in skeletal muscle and stimulates lysosomal, including cathepsin L, calpain-, and caspase-3-dependent protein breakdown in addition to proteasome-dependent protein breakdown. Treatment of rats with T3 for 3 days resulted in an approximately twofold increase in atrogin-1 and MuRF1 mRNA levels. The same treatment increased proteasome-, cathepsin L-, and calpain-dependent proteolytic rates by approximately 40% but did not influence caspase-3-dependent proteolysis. The expression of atrogin-1 and MuRF1 remained elevated during a more prolonged period (7 days) of T3 treatment. The results provide support for a role of the ubiquitin-proteasome pathway in muscle wasting during hyperthyroidism and suggest that other proteolytic pathways as well may be activated in the hyperthyroid state.

Creatine Kinase in Hypo- and Hyperthyroid Rats under Consideration of the Circadian Oscillations

Thyroxine level (T4) and total creatine kinase-activity (CK) were measured in serum samples from male Wistar-rats to investigate the relationships of serum titers after exposure to cold and thyroidectomy (TX). 72 hours exposure to cold (10 degrees C) produced a statistically significant elevation of T4 and a diminuation of CK-activity. In contrast to this protocol, TX (90 days after operations) reduced the T4 level and enhanced the CK-activity. These reactions were likewise statistically significant. The presented results are in agreement with the previous proposal which consists in inverse correlation between the T4 level and the CK-activity at hypo- and hyperthyroid states. Additionally it was shown that the highest activity of the serum CK appears in the first half of the light phase of the day under normal ambient temperature (24 degrees C) as well as under exposure to cold (10 degrees C).

Ovarian LH/hCG receptors and plasma level of LH,17-beta estradiol and progesterone in gonadotropin--induced PCO syndrome in rats.

The aim of this work was to investigate the morphologic changes, LH/hCG receptor content in the ovaries and plasma levels of LH, progesterone and estradiol of hypo--and hyperthyroid rats injected with PMSG and hCG. The hypothyroid state was induced by thyreoidectomy (Tr-X) and the hyperthyroid condition by injections of 40 micrograms L-thyroxine daily during 21 days (T4). Gonadotropins were injected during 14 days in daily doses: PMSG--5 i.u. and hCG--10 i.u. The following 8 groups (n = 10-20) were established: control (euthyroid, no treatment), Tr-X, PMSG + hCG, Tr-X + hCG, Tr-X + PMSG, Tr-X + PMSG + hCG, T4 and T4 + PMSG. At the end of experiments rats were sacrificed, ovaries weighed, macroscopically inspected and concentration of LH/hCG receptors was estimated. In blood plasma the level of LH, progesterone and 17-beta estradiol was also analysed. The experiments showed that injections of PMSG alone, or PMSG + hCG in eu-or hypothyroid rats, appear the most effective in induction of PCO syndrome in rats. Low levels of thyroid hormones sensitized the ovaries to gonadotropin action, but a hyperthyroid status diminished or inhibited this response. Thyroid function is also essential in production of LH/hCG receptors in the ovaries. In hypothyroid animals the amount of these receptors was greatly increased, while in hyperthyroid animals they decreased. The level of plasma LH, progesterone, and estradiol showed insignificantly differences and various inconsiderable deviations from norm. These differences were not dependent on large doses of gonadotropins, altered thyroid function, or on cystic or luteinizing changes in the ovary.

Influence of thyroid dysfunction on liver lipid peroxidation and antioxidant status in experimental rats

The purpose of this study was to evaluate the effects of dysthyroidism on lipid peroxidation, antioxidants status, liver, and serum dysfunction parameters in the hypo-/hyperthyroidism-induced rats. Hypothyroidism and hyperthyroidism conditions were induced for 5 weeks by administration of 0.05% benzythiouracile (BTU) and l-thyroxine sodium salt (0.0012%), in drinking water, respectively. The enzymatic activities of glutathione peroxidase (GPx), superoxide dismutase (SOD), catalase (CAT) and the lipid peroxidation product; thiobarbituric acid reacting substances (TBARS) were measured in liver as indicators of oxidative damage. However, liver dysfunction parameters represented by the activities of aspartate transaminase (AST), alanine transaminase (ALT), alkaline phosphatase (ALP), lactate dehydrogenase (LDH), and gamma glutamyl transferase (GGT), were measured in serum. In hyperthyroidism rats, the TBARS contents of liver have significantly increased compared to those in hypothyroid rats and the controls (p<0.001), associated with a fall of the total antioxidant status (TAS) in the serum of the hyperthyroid rats. The SOD, CAT, and GPx activities in liver of hyperthyroid rats have significantly increased compared to hypothyroid rats and the controls (p<0.001). The AST, ALT, LDH, GGT, and ALP activities increased in the hyperthyroidism rats (p<0.05).We conclude that thyroid dysfunction induces oxidative stress and modifies some biochemical parameters of liver. Our results show the occurrence of a state of oxidizing stress in relation to hyperthyroidism.

Changes in vasoreactivity of rat large- and medium-sized arteries induced by hyperthyroidism

Although the excess of thyroid hormones has been found to be associated with many effects on the heart and vasculature, the adaptive changes of various conductive and resistance arteries from different vasculature are largely unknown. In this study, we compared changes in vascular reactivity between aortic and femoral arterial rings in hyperthyroidism rat model. Our results indicate that daily gastric feeding of euthyrox to rat with dosage of 100μg group (H1) or 200μg group (H2) for 25 days was sufficient to induce a thyrotoxicosis. The serum TT3 and TT4 levels, heart weight (HW), body weight (BW), HW/BW ratio and mean diameter of myocardiac cells of the rat were significantly greater (P<0.05) in that two hyperthyroidism groups than in control group (E). It demonstrates that the gastric feeding of euthyrox may provide a reliable, cheaper and convenient method to induce hyperthyroid state with varying severity and duration. Our results also suggest that the contractile responses to phenylephrine (PE) and the relaxation responses to acetylcholine (Ach) or sodium nitroprusside (SNP) were reduced and enhanced, respectively, in vascular rings from H1 and H2 rats compared with E rats (P<0.05). The above vasoconstriction and vasorelaxation responses to agonists at least in large, elastic and medium-sized muscular arteries, which might be important vascular changes accounting for the enhancement of ventriculoatrial coupling and the reduction in peripheral vascular resistance during hyperthyroidism.

Thyroid state and tolerance of mammalian myocardium to hypoxia

Thyroid hormone is known to affect myocardial glycogen stores and thereby possibly limit anaerobic performance of mammalian cardiac muscle. Thyroid hormone administration (3,5,3'-triiodo-L-thyroxine, 300 microg/kg/day, sc) for 10 days decreased left ventricle (LV) glycogen concentration relative to euthyroid animals (2.78+/-0.46 vs. 4.28+/-0.29 mg/g of LV (mean+/-SEM)) while increasing the percent of V(1) myosin isozyme, contractile activity and cardiac mass. In contrast, thyroidectomy increased myocardial glycogen stores (8.50+/-0.56 mg/g of LV) and shifted the myosin isozyme toward V(3), prolonged contractile activity and decreased LV mass. Thyroxine administration for 3, 7 and 10 days to thyroidectomized animals progressively decreased contractile duration and increased LV mass. Thyroxine administration for 3 or 7 days to thyroidectomized rats did not reduce glycogen stores (7.75+/-1.02 and 9.62+/-1.16 mg/g of LV, respectively), whereas myocardial glycogen declined to 3.30+/-0.58 mg/g of LV after 10 days of treatment. During hypoxia, cardiac muscle from thyroidectomized rats maintained greater active force and developed less contracture relative to euthyroid and, to a greater extent, than hyperthyroid rats. Removal of glucose from the bath decreased anaerobic performance and impaired recovery; however, myocardium from thyroidectomized rats remained more tolerant to hypoxia than the euthyroid group. Overall, the intrinsic LV glycogen content was positively correlated to anaerobic performance. These data demonstrate that the thyroid state profoundly affects myocardial growth, contractility and anaerobic performance of rat myocardium. Although energy demand may affect function during hypoxia, anaerobic substrate reserve (cardiac glycogen concentration) appears to be the primary factor determining tolerance to hypoxic stress.

Relationship of thyroid to estramustine binding protein (EMBP) concentration in rat prostate

Alternations of estramustine binding protein (EMBP) concentration in rat prostate in relation to androgen status under hypo- and hyperthyroid conditions was estimated by means of radioimmunoassay (RIA). In hyperthyroid rats, EMBP concentration in dorsal as well as in lateral prostate was not significantly changed, but significantly reduced in ventral prostate (P less than 0.01). Ventral tissue concentration of testosterone(T) + dihydrotestosterone (DHT), DHT and T, and the ventral tissue ratio of DHT to T + DHT were not significantly changed in hypo- and hyper-thyroid conditions compared with that of the control. In hyperthyroid rats, serum T level and EMBP concentration in ventral prostate were significantly reduced in comparison to ones of the control (P less than 0.05 and P less than 0.01, respectively), however, the ratio of ventral tissue (T + DHT) to serum T was significantly increased (P less than 0.05). Moreover, in contrast to the control, EMBP concentration expressed as microgram/microgram ventral DNA was significantly reduced in hyperthyroid rats (P less than 0.05). On the other hand, in hypothyroid rats, change of EMBP concentration in ventral prostate in relation to androgen status was not significant in comparison to the control. The results here obtained revealed that EMBP concentration in ventral prostate under hyperthyroid condition would be affected by (a) a modulation of endogenous androgen-dependency in EMBP synthesis or by (b) a reduction of cell numbers responsible for EMBP synthesis.

Thyroid hormone affects diabetes‐induced changes on cardiac myosin heavy chain gene expression

Ventricular muscle expresses two isoforms of myosin heavy chain (MHC) genes: beta and alpha; which are arranged in tandem on the chromosome. Endogenous mRNA of beta and alpha MHCs are expressed in an antithetical manner in control, diabetic, hypo‐ and hyperthyroid rat hearts. We have identified an intergenic region between the beta and alpha genes that modulates the transcription of alpha sense and beta antisense pre‐mRNAs, we believe the intergenic bidirectional promoter controls the antithetic expression of alpha and beta MHC genes. The alpha MHC gene is predominantly expressed in adult rat heart. However, in the diabetic state, the expression of alpha is decreased and beta is increased. Thyroid hormone treatment has been shown to have a large impact on cardiac MHC gene expression and is a positive regulator of alpha MHC and negative regulator of the beta MHC gene. The pathways that regulate MHC isoform expression are unclear. By examining the sequence of beta sense, beta antisense and alpha sense promoters, we hopefully can discern the factors that alter the MHC expression in response to diabetes and thyroid hormone. We attempt to "rescue" diabetic (STZ treated) adult and neonatal rats using low levels of thyroid hormone; and show an effective response on MHC isoform expression and antisense and sense promoter activity. Supported by Amer. Diabetes Assoc and NIHHL.

Hyperthyroid rats display increased adrenergic ‐mediated contraction in cavernosal tissue

IntroductionDisturbances in thyroid function lead to sexual dysfunction in humans. However, the mechanisms by which hyperthyroidism causes erectile dysfunction (ED) are unknown. Whereas nitric oxide (NO) is the mediator of erection, sympathetic activation causes detumescence.ObjectiveWe hypothesized that hyperthyroidism increases sympathetic‐mediated contractility in cavernosal tissue.Methods and ResultsWistar male rats were submitted to experimental hyperthyroidism (70ug/Kg T3 for 14 days). Thyroid hormone T3 plasmatic levels were increased in hyperthyroid animals (Hyper) (Control: 0.43±0.08 vs Hyper: 1.45±0.64, ng/mL). After euthanasia, penises were excised and dissected. Cavernosal strips were mounted in a myograph and stretched to a resting force of 3.0 mN. Cavernosal contractility to phenylephrine (PE) (Control: 1.72±0.2 vs Hyper: 3.06±0.2, mN) and sympathetic‐nerve stimulation (Control: 0.9±0.4 vs Hyper: 2.03±0.3, mN) were increased in Hyper rats. Cavernosal responses to nonadrenergic‐noncholinergic‐mediated relaxation and endothelium‐independent relaxation were not altered.ConclusionOur results suggest that increased sympathetic‐ mediated responses contribute to ED in hyperthyroidism.

IN VIVO PATHWAY ANALYSIS FOR THE EFFECT OF HYPERTHYROIDISM ON EJACULATION IN PHARMACOLOGICALLY-INDUCED EJACULATION IN ANAESTHETISED MALE RATS

INTRODUCTION AND OBJECTIVE: The aim of the current study is to determine the possible effects of hyperthyroidism on ejaculatory pathways in p-Chloroamphethamine(PCA) induced ejaculation in anaesthetised male rats. METHODS: Sixty male Wistar rats (300-350gr) were used in this study. Subcutaneous injection of L-Thyroxine for 14 days was performed to induce hyperthyroidism in thirty rats. Thyroid hormone status were evaluated by serum TSH measurements in all rats. Under intraperitoneally(i.p.) urethane anaesthesia; euthyroid and hyperthyroid rats underwent bilateral hipogastric nerve(HNx,n=6 for both groups), bilateral pelvic nerve(PNx,n=6 for both groups), bilateral paravertebral sympathetic chain (PSCx,n=6 for both groups) transections, complete spinal transection at the T8-T9 level (n=6 for both groups ) and no peripheral transection (Nonx) was performed for 6 rats in each group. After performing seminal vesicle (SV) catheterization and bulbospongiosus (BS) muscle dissection for SV pressure measuring and BS electromyographic (EMG) recordings we induced ejaculation with i.p. administration of 5 mg/kg PCA. Ejaculatory responses were recorded before and 30 min after PCA administration. RESULTS: After PCA administration SV pressure tonic amplitude, SV phasic contraction(SVPC) frequency, SVPC maximal amplitude and BS EMG area under curve values were higher in hyperthyroid Nonx rats than euthyroid Nonx rats. The time interval between PCA administration and first ejaculation, the time interval between first SVPC and first BS contraction of hyperthyroid Nonx rats were significantly shorter than euthyroid Nonx rats. In hyperthyroid rats bilateral HNx and bilateral PSCx significantly reduced SV tonic pressure ampitude, SVPC frequency and SVPC maximal amplitude. There were no differences in SVPC frequency and SVPC maximal amplitude values for HNx and PSCx between euthyroid and hyperthyroid rats. These values were higher in hyperthyroid PNx rats than euthyroid PNx rats. There were no significant differences between all parameters of emission and expulsion phases of ejaculation for euthyroid and hyperthyroid spinally transected rats. CONCLUSIONS: In this study we confirmed the recent data that hyperthyroidism effects both the emission and expulsion phases of ejaculation. The effect of hyperthyroidism on emission phase is probably by sympathetic pathways. However the overall effect of hyperthyroidism on ejaculation may take place in the central nervous system above T8 level

In hyperthyroid rats octylguanidine protects the heart from reperfusion damage

Hyperthyroidism sensitizes the heart for reperfusion injury. As known, mitochondrial permeability transition underlies reperfusion heart damage. This study was undertaken to explore the protective effect of octylguanidine (OG), an inhibitor of permeability transition, on hearts from hyperthyroid rats subjected to ischemia/reperfusion. Hyperthyroidism was induced by a daily injection of 2 mg T3/kg body weight for 5 days. OG was injected at a dose of 5 mg/kg body weight. It was found that the amine protects against reperfusion-induced permeability transition, i.e., mitochondria from hyperthyroid rats, treated with OG, retained accumulated Ca(2+), similarly to control mitochondria. OG maintained post reperfusion cardiac frequency in hyperthyroid rats at 429 +/- 16 in comparison to control and T3 treated rats (70 +/- 12 and 71 +/- 2, respectively). We also found that OG diminished the post reperfusion accumulation of IFNgamma from 34.3 +/- 2.5 to 18.7 +/- 1.35, IL-6 from 38.5 +/- 4.5 to 15.1 +/- 0.12, IL-1 from 16.78 +/- 0.73 to 12.19 +/- 1.54, and TNFalpha from 45.05 +/- 3.14 to 29.85 +/- 4.3 (pg/50 microg myocardial tissue). It is concluded that OG inhibits the hypersensitivity of the hyperthyroid myocardium to undergo reperfusion damage due to its inhibitory action on the permeability transition pore.