Microvascular transplant of the gastrocnemius muscle in rats

Suitability of denervated muscle flaps as recipient sites for pancreatic islet cell transplantation

BACKGROUND

Extensive research has been conducted on islet transplantation as a possible cure for diabetes. Islet transplantation in the liver via the portal vein has shown remarkable results, but numerous other recipient sites are currently being investigated. We aimed to show the effectiveness of using a muscle flap as a recipient site for islet transplantation.

METHODS

Islet cells were harvested from 12 isogenic Lewis rats, and then diabetes was induced in another 12 isogenic Lewis rats by streptozotocin injection. In six rats, 3,000 islets were transplanted into gastrocnemius muscle flaps, and in the other six rats, the same number of islets were transplanted into the gastrocnemius muscle. The transplanted islet cell function between the two groups was compared by means of blood glucose tests, glucose tolerance tests, immunohistochemistry, and real-time reverse transcription polymerase chain reaction.

RESULTS

In the muscle flap group, blood glucose levels significantly decreased after islet transplantation. Blood glucose levels were significantly different between the two groups at 3 weeks after transplantation. The muscle flap group showed nearly normoglycemic results upon the glucose tolerance test, whereas the muscle group was hyperglycemic. Immunohistochemical evaluation showed positive results against insulin and glucagon in biopsies of both groups, and the islet cell density was higher in the muscle flap group. There were no statistically significant differences between the two groups in real-time reverse transcription polymerase chain reaction results.

CONCLUSIONS

Our results suggest that muscle flaps are promising candidates for islet cell transplantation.

Efficacy and Safety of the Babysitter Procedure With Different Percentages of Partial Neurectomy

BACKGROUND

After 2 months of denervation, the number of motor units in the muscle decreases; after 6 months of denervation, muscle atrophy and weakness are irreversible and successful nerve reconstruction does not generally restore function. The babysitter procedure was reported to successfully avoid muscle atrophy. One study found that the babysitter procedure with a 40% neurectomy was most suitable; however, the amount of donor nerve that can be borrowed for the babysitter procedure in peripheral nerve injury is unknown.

METHOD

One hundred adult female Sprague-Dawley rats were used in this study. The rats were randomly allocated to 5 groups (groups A-E; n = 20 each). The rats underwent different surgeries based on their grouping. At 6, 12, 18, and 24 weeks after surgery, 5 rats in each group were selected for electrophysiology and muscle force tests. These rats were then killed, and the gastrocnemius and tibialis anterior muscles were harvested for weight measurement and cross-sectional muscle measurement.

RESULT

The results of the effects on the peroneal nerves and tibialis anterior muscles after the babysitter procedure with 40% and 80% neurectomies showed that the functional ability of the recipient nerves was maintained and the muscle was effectively prevented from atrophy, whereas the 20% neurectomy and end-to-side procedures showed relatively poor performance. The results of the effects on the tibial nerve and gastrocnemius muscles after the babysitter procedure with 20% and 40% neurectomies showed that there was little effect on the donor nerve. By contrast, 80% neurectomy strongly and negatively affected the donor nerve.

CONCLUSIONS

Our results indicate that the babysitter procedure using a donor nerve with a partial neurectomy of 40% was the best choice for effectively treating peripheral (peroneal) nerve injury in rats.

A Model of Free Tissue Transfer: The Rat Epigastric Free Flap

Free tissue transfer has been increasingly used in clinical practice since the 1970s, allowing reconstruction of complex and otherwise untreatable defects resulting from tumor extirpation, trauma, infections, malformations or burns. Free flaps are particularly useful for reconstructing highly complex anatomical regions, like those of the head and neck, the hand, the foot and the perineum. Moreover, basic and translational research in the area of free tissue transfer is of great clinical potential. Notwithstanding, surgical trainees and researchers are frequently deterred from using microsurgical models of tissue transfer, due to lack of information regarding the technical aspects involved in the operative procedures. The aim of this paper is to present the steps required to transfer a fasciocutaneous epigastric free flap to the neck in the rat.

This flap is based on the superficial epigastric artery and vein, which originates from and drain into the femoral artery and vein, respectively. On average the caliber of the superficial epigastric vein is 0.6 to 0.8 mm, contrasting with the 0.3 to 0.5 mm of the superficial epigastric artery. Histologically, the flap is a composite block of tissues, containing skin (epidermis and dermis), a layer of fat tissue (panniculus adiposus), a layer of striated muscle (panniculus carnosus), and a layer of loose areolar tissue.

Succinctly, the epigastric flap is raised on its pedicle vessels that are then anastomosed to the external jugular vein and to the carotid artery on the ventral surface of the rat's neck. According to our experience, this model guarantees the complete survival of approximately 70 to 80% of epigastric flaps transferred to the neck region. The flap can be evaluated whenever needed by visual inspection. Hence, the authors believe this is a good experimental model for microsurgical research and training.

A gastrocnemius heterotopical transplant model with end-to-side neurorraphy

PURPOSE

To present an animal model to assess the effects of end-to-side innervation in the heterotopically transplanted model with reduced chances of neural contamination.

METHODS

The medial portion of the gastrocnemius muscle in wistar male rats was isolated and its pedicle dissected and performed a flap in the abdominal portion. To prevent neural contamination in the abdominal region, the muscle was wrapped with a Goretex(r) sheet. The specimens were divided into 2 groups (G). In G1 was performed an end-to-end suture between tibial nerve of the gastrocnemius and femoral motor nerve and between the saphenous sensory nerve and the motor nerve. In G2 was performed a end-to-side suture between the tibial nerve and the motor femoral and between the tibial nerve and saphenous motor nerve. The specimens were evaluated 60 days later to check the structure of the neurorraphy. Sections were obtained proximal and distal to the coaptation site.

RESULTS

The medial gastrocnemius muscle had the advantage of maintaining visible mass after 60 days. No disruption of the coaptation site was found. No major injury to the donor nerve was seen in group 2.

CONCLUSION

The proposed model is simple, reproduciple and prevent the neural contamination in the flap in end-to-side suture.

The effect of suture coated with mesenchymal stem cells and bioactive substrate on tendon repair strength in a rat model

PURPOSE

Exogenously administered mesenchymal stem cells and bioactive molecules are known to enhance tendon healing. Biomolecules have been successfully delivered using sutures that elute growth factors over time. We sought to evaluate the histologic and biomechanical effect of delivering both cells and bioactive substrates on a suture delivery vehicle in comparison with sutures coated with bioactive substrates alone.

METHODS

Bone marrow-derived stem cells were harvested from Sprague-Dawley rat femurs. Experimental cell and substrate-coated, coated suture (CS) group sutures were precoated with intercellular cell adhesion molecule 1 and poly-L-lysine and seeded with labeled bone marrow-derived stem cells. Control (substrate-only [SO] coated) group sutures were coated with intercellular cell adhesion molecule 1 and poly-L-lysine only. Using a matched-paired design, bilateral Sprague-Dawley rat Achilles tendons (n = 105 rats) were transected and randomized to CS or SO repairs. Tendons were harvested at 4, 7, 10, 14, and 28 days and subjected to histologic and mechanical assessment.

RESULTS

Labeled cells were present at repair sites at all time points. The CS suture repairs displayed statistically greater strength compared to SO repairs at 7 days (12.6 ± 5.0 N vs 8.6 ± 3.7 N, respectively) and 10 days (21.2 ± 4.9 N vs 16.4 ± 4.8 N, respectively). There was no significant difference between the strength of CS suture repairs compared with SO repairs at 4 days (8.1 ± 5.1 N vs 6.6 ± 2.3 N, respectively), 14 days (22.8 ± 7.3 N vs 25.1 ± 9.7 N, respectively), and 28 days (40.9 ± 12.4 N vs 34.6 ± 15.0 N, respectively).

CONCLUSIONS

Bioactive CS sutures enhanced repair strength at 7 to 10 days. There was no significant effect at later stages.

CLINICAL RELEVANCE

The strength nadir of a tendon repair occurs in the first 2 weeks after surgery. Bioactive suture repair might provide a clinical advantage by jump-starting the repair process during this strength nadir. Improved early strength might, in turn allow earlier unprotected mobilization.

End-to-end versus end-to-side motor and sensory neurorrhaphy in the repair of the acute muscle denervation

BACKGROUND

The aim of this study was to experimentally compare end-to-end and end-to-side neurorrhaphy in perineural window model after motor nerve lesion, evaluating which one was the most effective to preserve nerves. Also, differences in motor and sensorial nerve regeneration were tested to verify differences in nerve regeneration.

METHODS

A total of 20 adult male Wistar rats were randomly assigned to 5 groups, and, in each one, a different treatment was performed: besides the control group, and end-to-end or end-to-side graft with motor or sensorial nerves was performed. Silastic sheet was used as a mechanical barrier to prevent innervation from adjacent nerves. After 16 weeks, the specimens were histologically assessed and wet weight was evaluated as a direct parameter of atrophy.

RESULTS

The end-to-end neurorrhaphy group presented the best results in terms of mass preservation, but it did not differ significantly from the control group. Motor nerves presented similar results in muscular atrophy. The end-to-side neurorrhaphy group with sensory nerve as donor showed the worst results.

CONCLUSIONS

The use of sensory nerves to preserve skeletal muscle trophism is not justified, since, according to our model, it affects 50% to 80% of the muscle mass in a period of 16 weeks. End-to-side neurorrhaphy was demonstrated to be an option for re-enervation of a nerve-deprived motor muscle in selected cases.

Different angiogenic behaviour of ligated saphenous and epigastric vascular bundles in avascular environment: an in-vivo experimental study

The purpose of the study was to compare angiogenic response of isolated saphenous and epigastric arteriovenous bundles in avascular environment, in an in-vivo model. Saphenous and epigastric bundles of 20 rats were dissected and ligated distally. The bundles were implanted into silicone tubing to create a biologically neutral environment. Gross and histologic examination was performed at different intervals. No thrombus was detected in any of bundles prior to 24 hours. An adherent thrombus was seen at 24 hours in all ligated saphenous bundles; it persisted at three weeks with no evidence of neovascular sprouting. The ligated epigastric bundles remained patent with evidence of neovascular sprouting. The saphenous vessels are more likely to thrombose and do not show vascular proliferation when placed in an isolated environment, whereas the epigastric vessels are likely to remain patent and show vascular proliferation.

Cold storage of rat skeletal muscle free flaps and pre-ischemic perfusion with modified UW solution

We used the rat medial gastrocnemius free flap, based on a pedicle of the femoral artery and vein, in order to test the tolerance of skeletal muscle to cold ischemia-reperfusion (IR) injury, and to determine whether tolerance can be enhanced by pre-ischemic perfusion with tissue/organ preservation solutions. Muscle flaps (n = 6 per group) were subjected to variable periods of cold storage (0, 1, 2, 3, or 4 days) and 24-h normothermic reperfusion. Muscle viability, as determined by nitroblue tetrazolium (NBT) histochemical staining of viable mitochondria and supported by histological examination, was 100%, 26%, 11%, 4%, and 1%, respectively. Using 24-h cold storage/24-h reperfusion as the experimental conditions, groups of muscle flaps (n = 5 per group) were perfused immediately before cold storage with either modified, colloid-free University of Wisconsin (UW) solution, a solution described by Kohout et al. (Br J Plast Surg 1995;48:132-144) or normal saline. Perfusion with modified UW solution or Kohout's solution increased survival to 33% (P < 0.05) and 28% (not statistically significant), respectively, compared with the 19% viability of separate groups of nonperfused or saline-perfused controls. These findings indicate that cold-stored skeletal muscle is highly susceptible to cold IR injury and that the viability can be increased by prior perfusion with a tissue preservation solution such as modified UW solution.

Experimental model for transplantation of a modified free myocutaneous gracilis flap to an irradiated neck region in rats

In 102 Wistar rats (male, weight 300-500 g), a modified free myocutaneous gracilis flap was obtained from the groin and transplanted to the neck. To create a pre-irradiated transplant bed, a local area of the neck was irradiated preoperatively with 30 Gy (fractionation: 3 x 10 Gy) in 30 animals, and with 50 Gy (fractionation: 5 x 10 Gy) in a further 30 animals. The interval between preoperative irradiation and transplantation was 4 weeks. Forty-two animals received no such preoperative radiation. The evaluation of healing and the success of the transplanted flap was based on a clinical assessment, carried out on postoperative days 1 7. Testing for significant differences was done nonparametrically using the Kruskal-Wallis test. The survival rate in the nonirradiated animals was 86%. In contrast, the healing of the free flaps in the pre-irradiated transplant bed was significantly lower (P=0.003) 76%, after irradiation with 30 Gy and 50% after 50 Gy. The significant difference (P=0.020) in survival rates after irradiation with 30 and 50 Gy was evidence for the dependence of successful healing on the preoperative radiation dose. Transplantation of the free myocutaneous gracilis flap to a previously irradiated transplant bed in the region of the neck is a suitable model for investigating the healing of free transplants to irradiated tissue. The success rate observed in non-irradiated transplant beds is comparable to that seen with other flap models in rats.

Pectoralis major muscle free flap in rat model

The rat pectoralis muscle can serve as a vascularized, innervated muscle flap model. The muscle, consisting of superficialis and profundus portions, is supplied by separate neurovascular systems. The vessels to pectoralis profundus (averaging 0.3 mm in diameter) can be taken in continuity with the axillary vessels (averaging 11 mm in diameter), which are used for transplantation. The profundus portion of muscle weighed an average of 1.8 g, and the average pedicle length was 0.9 cm. Nine of 11 transplanted muscles were viable, with intact circulation at 72 hours. An example of muscle transplantation for tissue defect coverage was attempted. The pectoralis profundus transplant was technically reliable, and the muscle bulk and contour could allow biochemical and functional studies.

The greater omentum transplantation model in the rat

Dissection of the rat omentum were performed to study the feasibility of rat omental free transfer. The right epiploic vessels were found to be adequate for anastomosis in transfer. Twelve omental free flaps were transferred to the groin, with 100% survival of flaps in the 10 animals that survived the operation. The artery and vein averaged 0.3 and 0.4 mm in diameter, respectively. The average pedicle length was 5 mm, and the average flap weight was 136.9 mg. This omental transplant offers a new experimental means of studying lymphedema, neovascularization, and tissue revascularization.