A histologic analysis of three-dimensional versus two-dimensional tissue expansion in the porcine model.

OBJECTIVE: Recently, a two-dimensional Silastic Dacron stretching skin device has been developed for scalp reduction surgery. Attached subgaleally, this device stretches skin over time, while avoiding the visible volumetric distention that is typical of three-dimensional tissue expanders. Unlike three-dimensional expanders, the histological changes observed with a two-dimensional stretching device have not been described in the literature. The present study compares the histological effects of two-dimensional and three-dimensional skin tissue expansion in the porcine model. STUDY DESIGN: A university Institutional Review Board-approved study in which 16 domestic piglets were used. The 16 piglets were divided evenly into four cohorts as follows: 1, 1-week control cohort; 2, 1-week experimental cohort; 3, 4-week control cohort; and 4, 4-week experimental cohort. METHODS: Tissue expanders (three-dimensional) and Dacron Silastic tissue stretchers (two-dimensional) were surgically inserted into the lateral skin of 16 domestic pigs. Animals were killed at either 1 or 4 weeks based on group assignment. Light microscopic ocular micrometry and stereological point counting were used to determine the depth of the epidermis, dermis, and subdermal adipose tissue layer; width of the panniculus muscle; diameter of sweat gland follicles; percentage ratio of dermal collagen, blood vessels, and tissue space; and epidermal mitotic index in 100 specimens. One-way ANOVA was used to evaluate statistical differences. RESULTS: Both tissue expanders yielded increased values compared with control subjects, with respect to epidermal, dermal, and fat widths and blood vessel counts, whereas adnexal structures in the panniculus muscle width were unaltered. CONCLUSIONS: Although statistically the two types of expansion produced histologically similar changes, the degree of change varied according to the type of expander that was used and the duration of tissue expansion. Most notably, three-dimensional expansion produced more tissue gain per unit area expanded at both the 1-week and the 4-week time intervals, and early (1-week) two-dimensional tissue expansion stimulated a greater angiogenic response than three-dimensional expansion. These findings will assist the surgeon in understanding the physical changes that occur with these two forms of tissue expansion, as well as the potential clinical advantages and shortcomings of each method.

Reduction of glutamine synthetase mRNA in hypertrophied skeletal muscle.

Skeletal muscle glutamine synthetase (GS) expression is reduced by endurance exercise and is increased when normal innervation is interrupted. This investigation was undertaken to determine whether GS expression is downregulated by the increased contractile activity associated with functional overload. Plantaris muscles overloaded for 30 days by synergist ablation were 70% heavier than those in sham-operated and unoperated control muscles. GS mRNA levels from hypertrophied muscles, measured by Northern and dot-blot hybridization, were reduced to 30% of controls. Changes in total RNA concentration and the proportion of poly(A)+ RNA in the total RNA pool did not account for the decline in GS mRNA. Despite reduced levels of GS mRNA, GS enzyme activity (nmol.h-1.mg protein-1) was unchanged in the hypertrophied muscles (overload, 79 +/- 5; control, 82 +/- 4). To further examine the lack of relationship between GS mRNA and enzyme activity, the concentration of glutamine, a known posttranslational modifier of GS activity, was measured. Consistent with the observed enzyme activities, muscle glutamine was unchanged in hypertrophied muscle (overload, 6.2 +/- 0.3; control, 5.8 +/- 0.4 mumol/g tissue). These results suggest that translational or posttranslational regulation, other than through alterations in glutamine concentration. may play a role in maintaining GS enzyme levels in hypertrophied muscle. Moreover, the regulation of GS activity in muscle hypertrophy may differ from the regulation with endurance training, in which changes in enzyme activity parallel changes in mRNA.