Daniela Malnar

Fibre type composition of the human psoas major muscle with regard to the level of its origin

The aim of our study was to explore the fibre type composition of the human psoas major muscle at different levels of its origin, from the first lumbar to the fourth lumbar vertebra, and to compare the muscle fibre size and distribution of different fibre types between levels with respect to its complex postural and dynamic function. Muscle samples were collected from 15 young males (younger than 35 years). Serial transverse sections (5 μm) of the samples were cut by cryomicrotome. Type I, IIA and IIX muscle fibres were typed using myosin heavy chain identification. The serial sections were analysed using a light microscope with a magnitude of 100×. The differences between measurements were evaluated using a repeated‐measures anova and Scheffé test for post‐hoc analysis. Our study showed that the human psoas major muscle was composed of type I, IIA and IIX muscle fibres. It had a predominance of type IIA muscle fibres, whereas type I muscle fibres had the largest cross‐sectional area. Type IIX muscle fibres were present as a far smaller percentage and had the smallest cross‐sectional area. Moreover, the fibre type composition of the psoas major muscle was different between levels of its origin starting from the first lumbar to the fourth lumbar vertebra. We conclude that the fibre type composition of the psoas major muscle indicated its dynamic and postural functions, which supports the fact that it is the main flexor of the hip joint (dynamic function) and stabilizer of the lumbar spine, sacroiliac and hip joints (postural function). The cranial part of the psoas major muscle has a primarily postural role, whereas the caudal part of the muscle has a dynamic role.

Reg IV protein and mRNA expression in different rat organs.

The Reg IV gene has been documented in the human colon, small intestine, stomach and pancreas. Expression of the Reg IV in different cell types has been associated with regeneration, cell growth and cell survival, cell adhesion and resistance to apoptosis. Since the distribution of the Reg IV protein in normal rat tissues is unknown, the aim of this study was to reveal the expression of the Reg IV protein in structurally and functionally different rat organs. The expression of Reg IV gene was analyzed by Western blot and reverse transcription-polymerase chain reaction. Immunohistochemistry was used to localize Reg IV protein. Reg IV protein was expressed in pancreas, stomach, small intestine, colon, brain, spleen, kidney and urinary bladder in two-month-old male Wistar rats. In addition, the expression of Reg IV mRNA by reverse transcription-polymerase chain reaction was confirmed. Our study provides detailed information about the expression and localization of Reg IV protein in different rat organs. These findings provide an evidence of Reg IV expression in different rat organs, which may help elucidate a potential role in growth and proliferation of different cells like other members of the Reg family genes which act as growth factors in the different organs.

Segmental fibre type composition of the rat iliopsoas muscle

The iliopsoas of the rat is composed of two muscles – the psoas major muscle and the iliacus muscle. The psoas major muscle arises from all the lumbar vertebrae and the iliacus muscle from the fifth and sixth lumbar vertebrae and ilium. Their common insertion point is the lesser trochanter of the femur, and their common action is the lateral rotation of the femur and flexion of the hip joint. Unlike humans, the rat is a quadruped and only occasionally rises up on its hind legs. Therefore, it is expected that the fibre type composition of the rat iliopsoas muscle will be different than that of humans. The iliopsoas muscle of the rat is generally considered to be a fast muscle. However, previous studies of the fibre type composition of the rat psoas muscle showed different results. Moreover, very little is known about the composition of the rat iliacus muscle. The aim of our study was to examine the fibre type composition of the rat iliopsoas muscle in order to better understand the complex function of the listed muscle. The psoas major muscle was examined segmentally at four different levels of its origin. Type I, IIA, IIB and IIX muscle fibres were typed using monoclonal antibodies for myosin heavy chain identification. The percentage of muscle fibre types and muscle fibre cross‐sectional areas were calculated. In our study we showed that in the rat iliopsoas muscle both the iliacus and the psoas major muscles had a predominance of fast muscle fibre types, with the highest percentage of the fastest IIB muscle fibres. Also, the IIB muscle fibres showed the largest cross‐sectional area (CSA) in both muscles. As well, the psoas major muscle showed segmental differences of fibre type composition. Our results showed changes in percentages, as well as the CSAs of muscle fibre types in cranio‐caudal direction. The most significant changes were visible in type IIB muscle fibres, where there was a decrease of percentages and the CSAs from the cranial towards the caudal part of the muscle. From our results it is evident that the rat iliopsoas muscle has a heterogeneous composition and is composed of all four muscle fibre types. Primarily, it is a fast, dynamic muscle with a predominance of fast type IIB muscle fibres with the largest CSAs. The composition of the rat psoas major muscles changes in a cranio‐caudal direction, thus pointing to a more postural role of the caudal part of the muscle.