Recently, we have established that slow soleus (SOL) and fast extensor digitorum longus (EDL) muscles of euthyroid (EU) Lewis rats posses the same proportions between their four myosin heavy chain (MyHC) mRNAs , protein isoforms and fiber types as determined by real time RT-PCR, SDS-PAGE and 2-D stereological fiber type analysis, respectively. In the present paper we investigated if these proportions are maintained in adult Lewis rats with hyperthyroid (HT) and hypothyroid (HY) status. Although HT and HY states change MyHC isoform expression, results from all three methods showed that proportion between MyHC mRNA-1, -2a, -2x/d, -2b , protein isoforms MyHC-1, -2a, -2x/d, -2b and to lesser extent also fiber types 1, 2A, 2X/D, 2B were preserved in both SOL and EDL muscles. Furthermore, in the SOL muscle mRNA expression of slow MyHC-1 remained up to three orders higher compared to fast MyHC transcripts, which explains the predominance of MyHC-1 isoform and fiber type 1 even in HT rats. Although HT status led in the SOL to increased expression of MyHC-2a mRNA, MyHC-2a isoform and 2A fibers, it preserved extremely low expression of MyHC-2x and -2b mRNA and protein isoforms, which explains the absence of pure 2X/D and 2B fibers. HY status, on the other hand, almost completely abolished expression of all three fast MyHC mRNAs , MyHC protein isoforms and fast fiber types in the SOL muscle. Our data present evidence that a correlation between mRNA , protein content and fiber type composition found in EU status is also preserved in HT and HY rats., T. Soukup, M. Diallo., and Obsahuje bibliografii
Expression of the muscle phenotype is the result of interaction between intrinsic and extrinsic factors, the latter including innervation, mechanical influences and hormonal signals. This minireview summarizes some of the current knowledge regarding the regulation of myosin heavy chain (MHC) isoform transitions during muscle development and regeneration. It describes the role of genetic factors, neural and mechanical influences and it focuses on the contribution of thyroid hormones to the differentiation of muscle fiber phenotypes as shown by the regulation of the expression of MHC isoforms and development of myofibrillar ATPase activity. Finally, it shortly summarizes results regarding the differentiation of MHC isoforms in regenerated muscle fibers of the graft after heterochronous isotransplantation in rats with different thyroid status., T. Soukup, I. Jirmanová., and Obsahuje bibliografii
The purpose of this study was to compare the daytime hourly responses of total thyroxine (T4) and triiodothyronine (T3) during an 8-hour recovery period following aerobic and anaerobic exercise to an equivalent non-exercise, control period. The data were examined for hourly mean differences as well as by determination of the integrated area under the curve (AGC) responses. Significant persistent elevations (hourly concentrations and AGC) from control levels in total T4 following both aerobic and anaerobic exercise were found. Total T3, however, was transiently elevated (only in the hourly concentration immediately following exercise) compared with the control following aerobic exercise, but remained unaffected by anaerobic exercise. No significant changes in the total T3 AGC responses were found due to exercise. The present findings demonstrate that exercise, aerobic and anaerobic, disrupts the daytime hourly pattern for total T4 in the blood, but apparently has minimal effect on total T3.