*2.4. Biochemical Analysis*

As shown in Figure 7, *EC* tissues had, on average, much higher elastin concentrations than the *Xenopus* samples. On the other hand, there are minimal differences between the elastin content in male and female *EC* tissues. As summarized in Table 2, there was an average of 58.5 ± 16.9 and 64.5 ± 9.8 μg/mg of wet tissue in male and female gular skin, respectively. The elastin content found in *EC* gular tissues was higher than the *Xenopus* gular tissues, with 22.1 ± 5.2 and 42.1 ± 11.9 μg/mg of wet tissue for *XL* and *XM,* respectively. In general, leg tissues contained less elastin than the gular tissues, and, once again, *EC* samples contained more elastin than *Xenopus* samples (Figure 7A). Collagen assays show the opposite trend, with *EC* tissues containing less collagen than *Xenopus*. Male *EC* gular tissue contained an average of 202.0 ± 41.3 μg/mg of wet tissue and female *EC* had 234.5 ± 86.7 μg/mg of wet tissue. These values were much lower than those of *XL* and *XM*, with 377.8 ± 86.7 μg/mg and 400.8 ± 36.5 μg/mg of wet tissue, respectively (Figure 7B). As expected, male *EC* leg tissue contained more collagen than the gular tissues; however, this trend was not found in the other samples. Although *EC* tissues had more elastin than *Xenopus* tissues, the similar concentrations of elastin between male and female *EC* further imply the importance of the collagen structure in the extensibility of the tissue. Lastly, the average elastin to collagen ratio was calculated to show that the *EC* gular tissue had higher elastin to collagen ratios of 0.29 and 0.27 for males and females, respectively. In stark contrast, *Xenopus* gular tissues were 0.06 and 0.1 for *XL* and *XM,* respectively. As a comparison, the male rat bladder had significantly more elastin and less collagen, with averages of 484.8 ± 121.9 and 96.1 ± 19.4 μg/mg of wet tissue, respectively. Rat bladder has approximately eight times more elastin than the male EC. As expected, the rat bladder had five times more elastin than collagen, unlike frog tissues, where the opposite is observed.

**Figure 7.** (**A**) Elastin content and (**B**) collagen content for the respective tissue sample. M: male, F: female. *p* < 0.05 (\*) and *p* < 0.01 (\*\*).


**Table 2.** Summary of elastin and collagen content in tissue samples.
