Effects of thyroxine on myosin isoform expression and mechanical properties in guinea-pig smooth muscle

Pharmacological and mechanical properties of isolated pig coronary veins

Recent successful cardiac transplantation from pig to non-human primates and the first pig-to-human transplantation has put the focus on the properties of the pig heart. In contrast to the coronary arteries, the coronary veins are less well characterized and the aim was to examine the mechanical and pharmacological properties of coronary veins in comparison to the arteries. Vessel segments from the left anterior descending coronary artery (LAD) and the concomitant vein were isolated from pig hearts in cardioplegia and examined in vitro. The wall thickness, active tension and active stress at optimal circumference were lower in coronary veins, reflecting the lower intravascular pressure in vivo. Reverse transcription polymerase chain reaction (RT-PCR) analysis of myosin isoforms showed that the vein could be characterized as having a slower smooth muscle phenotype compared to the artery. Both vessel types contracted in response to the thromboxane agonist U46619 with EC50 values of about 20 nM. The artery contracted in response to acetylcholine. Precontracted arteries relaxed in noradrenaline and substance P. In contrast, the veins relaxed in acetylcholine, contracted in noradrenaline and were unresponsive to substance P. In conclusion, these results demonstrate significant differences between the coronary artery and vein in the smooth muscle properties and in the responses to sympathetic and parasympathetic stimuli.

Thyroid Hormone in the Pathogenesis of Congenital Intestinal Dysganglionosis

INTRODUCTION

The objective of this study is to investigate the role of thyroid hormone (TH) in the pathogenesis of intestinal dysganglionosis (ID).

METHODS

A zebrafish model of congenital hypothyroidism (CH) was created by exposing the larvae to the 6-propyl-2-thiouracil (PTU). The enteric neurons were labeled with anti-HuC/D antibodies. The number of enteric neurons was counted. The larval intestine was dissociated and stained with anti-p75 and anti-α4 integrin antibodies. Mitosis and apoptosis of the p75⁺ α4 integrin⁺ enteric neural crest cells (ENCCs) were studied using flow cytometry. Intestinal motility was studied by analyzing the transit of fluorescent tracers.

RESULTS

PTU (25 mg/L) significantly reduced TH production at 6- and 9-days post fertilization without changing the body length, body weight, and intestinal length of the larvae. Furthermore, PTU inhibited mitosis of ENCCs and reduced the number of enteric neurons throughout the larval zebrafish intestine. Importantly, PTU inhibited intestinal transit of fluorescent tracers. Finally, thyroxine supplementation restored ENCC mitosis, increased the number of enteric neurons, and recovered intestinal motility in the PTU-treated larvae.

CONCLUSIONS

PTU inhibited TH production, reduced the number of enteric neurons, impaired intestinal motility, and impeded ENCC mitosis in zebrafish, suggesting a possible role of CH in the pathogenesis of ID.

DOES GRAVES' DISEASE AFFECT ESOPHAGEAL MOTILITY?

CONTEXT

The gastrointestinal tract is one of the most affected systems in hyperthyroidism. Although thyrotoxicosis is thought to be associated with gastrointestinal dysmotility, there are limited studies focused on motility disorders in hyperthyroidism.

OBJECTIVES

We aimed to investigate the manometric measurements to determine if esophageal motility is affected in Graves' disease.

MATERIALS AND METHODS

Thirty patients with Graves' disease (18 female and 12 male) and 30, age and sex matched, healthy controls (22 female and 8 male) were recruited to the study between 2015 and 2016. Esophageal manometry was performed using MMS (Medical Measurement Systems bv. The Netherlands) Solar GI - Air Charged Intelligent Gastrointestinal Conventional Manometry.

RESULTS

The mean lower esophageal sphincter pressure (LESP) was 16.9 ± 5.3 mmHg in hyperthyroid patients and 20.1 ± 8.8 mmHg in the control group and there was no significant difference (p>0.05). It was observed that the duration of contraction was 3.9 ± 0.7 s in healthy subjects and, significantly shorter 3.2 ± 0.5 s in hyperthyroid patients (p<0.001). Duration of contraction was negatively correlated with TSH receptor Ab titer in patients (p=0.006, r= -0.48). Also, it was observed that the duration of relaxation was negatively correlated with fT4 levels in the patient group (p<0.05, r= -0.46).

CONCLUSION

In this study, we observed that esophageal motility can be affected via shortened duration of contraction in Graves' disease. The gastrointestinal symptoms due to possible motility dysfunctions should be considered in the evaluation of hyperthyroid patients.

Radionuclide Esophageal Transit Scintigraphy in Primary Hypothyroidism

Background/Aims

Esophageal dysmotility is associated with gastrointestinal dysmotility in various systemic and neuroregulatory disorders. Hypothyroidism has been reported to be associated with impaired motor function in esophagus due to accumulation of glycosaminoglycan hyaluronic acid in its soft tissues, leading to changes in various contraction and relaxation parameters of esophagus, particularly in the lower esophageal sphincter. In this study we evaluated esophageal transit times in patients of primary hypothyroidism using the technique of radionuclide esophageal transit scintigraphy.

Methods

Thirty-one patients of primary hypothyroidism and 15 euthyroid healthy controls were evaluated for esophageal transit time using 15-20 MBq of Technetium-99m sulfur colloid diluted in 10-15 mL of drinking water. Time activity curve was generated for each study and esophageal transit time was calculated as time taken for clearance of 90% radioactive bolus from the region of interest encompassing the esophagus. Esophageal transit time of more than 10 seconds was considered as prolonged.

Results

Patients of primary hypothyroidism had a significantly increased mean esophageal transit time of 19.35 ± 20.02 seconds in comparison to the mean time of 8.25 ± 1.71 seconds in healthy controls (P < 0.05). Esophageal transit time improved and in some patients even normalized after treatment with thyroxine. A positive correlation (r = 0.39, P < 0.05) albeit weak existed between the serum thyroid stimulating hormone and the observed esophageal transit time.

Conclusions

A significant number of patients with primary hypothyroidism may have subclinical esophageal dysmotility with prolonged esophageal transit time which can be reversible by thyroxine treatment. Prolonged esophageal transit time in primary hypothyroidism may correlate with serum thyroid stimulating hormone levels.

Esophagus motility in overt hypothyroidism

PURPOSE

Gastrointestinal tract is one of the most affected systems in hypothyroidism. Despite decreased esophageal emptying, prolonged esophageal and gastric transit time have been indicated in previous reports, the mechanism of thyroid hormones activity and antibodies on the esophagus motility is not yet fully understood. This study was conducted to evaluate the esophagus motility by manometry in hypothyroid patients.

METHODS

The study enrolled with 28 overt, newly diagnosed hypothyroid patients and 29 age- and sex-matched healthy controls. Twenty-one females and 7 males with overt hypothyroidism and 22 females and 7 males with healthy control subjects were recruited to study. Esophageal manometry was performed using MMS (Medical Measurement Systems bv. The Netherlands) Solar GI-Air-Charged Intelligent Gastrointestinal Conventional Manometry.

RESULTS

The lower esophageal sphincter pressure (LESP) was 19.5 ± 6.5 mmHg in hypothyroid patients and 17.48 ± 4.65 mmHg in controls, and there was no significant difference (p = 0.18). Percentage of relaxation was 61.5 and 80.9 %, and it was significantly lower in hypothyroid patients than controls (p < 0.001). Additionally, duration of relaxation was found 3.85 ± 2.3 and 5.5 ± 2.28 s in patients and controls, respectively (p = 0.009). In patient group, LESP was positively correlated with fT3 (p = 0.033), and the duration of the contraction was negatively correlated with fT4 (p = 0.044).

CONCLUSION

In this study, we observed that hypothyroid state can affect esophagus motility via shortened duration of relaxation and reduced percentage of relaxation even if in patients without any gastrointestinal symptoms. Further studies are needed to clarify the effect of thyroid hormones on esophagus motility.

Vascular smooth muscle phenotypic diversity and function

The control of force production in vascular smooth muscle is critical to the normal regulation of blood flow and pressure, and altered regulation is common to diseases such as hypertension, heart failure, and ischemia. A great deal has been learned about imbalances in vasoconstrictor and vasodilator signals, e.g., angiotensin, endothelin, norepinephrine, and nitric oxide, that regulate vascular tone in normal and disease contexts. In contrast there has been limited study of how the phenotypic state of the vascular smooth muscle cell may influence the contractile response to these signaling pathways dependent upon the developmental, tissue-specific (vascular bed) or disease context. Smooth, skeletal, and cardiac muscle lineages are traditionally classified into fast or slow sublineages based on rates of contraction and relaxation, recognizing that this simple dichotomy vastly underrepresents muscle phenotypic diversity. A great deal has been learned about developmental specification of the striated muscle sublineages and their phenotypic interconversions in the mature animal under the control of mechanical load, neural input, and hormones. In contrast there has been relatively limited study of smooth muscle contractile phenotypic diversity. This is surprising given the number of diseases in which smooth muscle contractile dysfunction plays a key role. This review focuses on smooth muscle contractile phenotypic diversity in the vascular system, how it is generated, and how it may determine vascular function in developmental and disease contexts.

Ontogenetic profile of the expression of thyroid hormone receptors in rat and human corpora cavernosa of the penis

Introduction

In the last few years, various studies have underlined a correlation between thyroid function and male sexual function, hypothesizing a direct action of thyroid hormones on the penis.

Aim

To study the spatiotemporal distribution of mRNA for the thyroid hormone nuclear receptors (TR) α1, α2 and β in the penis and smooth muscle cells (SMCs) of the corpora cavernosa of rats and humans during development.

Methods

We used several molecular biology techniques to study the TR expression in whole tissues or primary cultures from human and rodent penile tissues of different ages.

Main Outcome Measure

We measured our data by semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) amplification, Northern blot and immunohistochemistry.

Results

We found that TRα1 and TRα2 are both expressed in the penis and in SMCs during ontogenesis without development-dependent changes. However, in the rodent model, TRβ shows an increase from 3 to 6 days post natum (dpn) to 20 dpn, remaining high in adulthood. The same expression profile was observed in humans. While the expression of TRβ is strictly regulated by development, TRα1 is the principal isoform present in corpora cavernosa, suggesting its importance in SMC function. These results have been confirmed by immunohistochemistry localization in SMCs and endothelial cells of the corpora cavernosa.

Conclusions

The presence of TRs in the penis provides the biological basis for the direct action of thyroid hormones on this organ. Given this evidence, physicians would be advised to investigate sexual function in men with thyroid disorders. Carosa E, Di Sante S, Rossi S, Castri A, D'Adamo F, Gravina GL, Ronchi P, Kostrouch Z, Dolci S, Lenzi A, and Jannini EA. Ontogenetic profile of the expression of thyroid hormone receptors in rat and human corpora cavernosa of the penis. J Sex Med 2010;7:1381–1390.

(+)Insert smooth muscle myosin heavy chain (SM-B): From single molecule to human

In smooth muscle, alternative mRNA splicing of a single gene produces four myosin heavy chain (SMMHC) isoforms. Two of these isoforms differ by the presence [(+)insert] or absence [(-)insert] of a seven amino acid insert in the motor domain. This insert enhances the kinetic properties of myosin at the molecular level but its exact role at the cell and tissue levels still has to be elucidated. This review focuses on the expression and biological functions of the (+)insert isoform. Current knowledge is summarized regarding its tissue distribution in animals and humans. Studies at the molecular, cellular and tissue levels that aimed at understanding the contribution of this isoform to smooth muscle mechanical function are presented with a particular focus on velocity of shortening. In addition, the altered expression of the (+)insert isoform in diseases and models of diseases and the compensatory mechanisms that occur when the (+)insert is knocked out are discussed. The need for additional studies on the relationship of this isoform to contractile performance and how expression of this isoform is regulated are also considered.

Urinary bladder contraction and relaxation: physiology and pathophysiology

The detrusor smooth muscle is the main muscle component of the urinary bladder wall. Its ability to contract over a large length interval and to relax determines the bladder function during filling and micturition. These processes are regulated by several external nervous and hormonal control systems, and the detrusor contains multiple receptors and signaling pathways. Functional changes of the detrusor can be found in several clinically important conditions, e.g., lower urinary tract symptoms (LUTS) and bladder outlet obstruction. The aim of this review is to summarize and synthesize basic information and recent advances in the understanding of the properties of the detrusor smooth muscle, its contractile system, cellular signaling, membrane properties, and cellular receptors. Alterations in these systems in pathological conditions of the bladder wall are described, and some areas for future research are suggested.

Smooth, slow and smart muscle motors

Smooth muscle is a slow and economical muscle with a large variability in contractile properties. This review describes results regarding the relation between expression of myosin isoforms and the contraction of smooth muscle. The focus of the review is on studies of the organised contractile system in the smooth muscle tissue. The role of the myosin heavy chain variants formed by alternative splicing in the myosin heavy chain tail (SM1, SM2 isoforms) and head (SM-A SM-B isoforms) regions, as well as the role of essential light chains (LC17a, LC17b isoforms) for the variability of contractile properties are discussed. Smooth muscle also has the ability to alter its contractile properties in response to altered functional demands in vivo, e.g. during hypertrophic growth of urinary bladder, intestine, uterus and vessels and in response to altered hormone levels. These alterations involve changes in myosin expression and altered contractile kinetics. Non-muscle myosin has been shown to have a contractile function in some smooth muscle tissues and recent data on the kinetic properties of non-muscle myosin filaments in smooth muscle tissue are described.

Decreased shortening velocity and altered myosin isoforms in guinea-pig hypertrophic intestinal smooth muscle

The aims of this study were to investigate whether hypertrophy of the small intestinal smooth muscle leads to alterations of myosin isoform composition and shortening velocity and whether possible changes correlate with a change in the sensitivity to ADP of shortening velocity in this tissue. A partial occlusion was introduced in the distal part of the ileum of guinea-pigs. After 2 weeks, the part of the small intestine just proximal of the stenosis was hypertrophied (indicated by a significantly increased cross-sectional area). The most proximal part of the small intestine was used as control, thus enabling comparisons between hypertrophic and normal tissue from the same animal. The outer longitudinal layer of the intestinal wall was gently peeled off and used for biochemistry, RT-PCR and mechanical experiments. The desmin/actin ratio was significantly increased following hypertrophy, although myosin and actin expression were similar in control and hypertrophic tissue. In hypertrophic tissue, the myosin heavy chain mRNA with a 21 base pair insert decreased significantly. The composition of the mRNA encoding the myosin essential light chains changed towards more of the basic type (LC17b). No change in the expression of non-muscle myosin heavy chains A and B was detected. The maximal shortening velocity (V(max)) of maximally activated skinned preparations was significantly lower in the hypertrophic tissue (~50 % of control). The sensitivity of V(max) to ADP was increased in the hypertrophic smooth muscle tissue. We conclude that myosin expression is altered following intestinal hypertrophy and that these alterations affect reactions in the cross-bridge interaction, leading to a slower and more economical contractile function.