Experiment On The Effects Of Testosterone On Normalized Organ Mass In Rats

The purpose of this experiment was to investigate the effects testosterone has on normalized organ mass in male lab rats treated with cast/sham, cast/test, or intact/test. The various organ masses recorded for each rat included the heart, liver, kidneys, seminal vesicles, and the right gastrocnemius.

Based on previous research it was hypothesized that an increase in testosterone via implant, would lead to an increase in the normalized mass of the heart, liver, kidney, seminal vesicle, and gastrocnemius. Body mass percent change was not expected to be significantly different between the three treatment groups because adipose fat deposition was expected to counteract the increase in mass of several organs.

The results from this investigation suggest that testosterone has a significant impact on the normalized mass of wet seminal vesicles, dry kidneys, and dry seminal vesicles. Rats that received either cast/test or intact/test treatment had significantly higher normalized masses for wet seminal vesicles, dry kidneys, and dry seminal vesicles then rats that were treated with cast/sham. Normalized mass of wet kidneys, as well as, wet and dry heart, liver, and gastrocnemius resulted in no significant difference between treatment groups. Body mass percent change also showed no significant difference.

Contrary to several primary literature references, the results from this study identified no significant relationship between heart mass and increased testosterone levels. Perhaps if the length of the experiment was extended, a significant difference may have been revealed. Previous research has established a relationship between androgens, such as testosterone, and cardiac hypertrophy as well as increased ventricular performance. Androgen receptors have been identified in cardiac myocytes which modulate the cardiac phenotype and stimulate hypertrophy via direct, receptor-specific mechanisms and genome modulation (Marsh, et al., 1998). Today, little is still known about these underlying mechanisms, however differences in cardiac hypertrophy has been observed with sex hormone treatments (Huang, Lee, Chang, Pang, & Chang, 2016). The findings of this experiment were not consistent with the hypothesis that testosterone would have an effect on the mass of the heart.

Contrary to several primary literature references, the results from this study identified no significant relationship between liver mass and increased testosterone levels. Previous studies have established a relationship between testosterone and liver mass. Testosterone has been identified as a stimulant for hepatocyte proliferation, which is the mitotic division and differentiation of liver cells. The storage of hepatic glycogen has also been found to significantly increase after the administration of testosterone (Nucci et al, 2017). It is believed that testosterone plays an important independent role in the hepatic glycogen reserve however findings of this experiment were not consistent with literature and the hypothesis that testosterone would have an effect on the mass of the liver.

In agreement with several primary literature references, the results from this study identified a significant relationship between kidney mass and increased testosterone levels. Although there was not a statistical difference found between either treatment group for normalized wet kidney mass, the data was consistent with the general trend of increasing organ mass with testosterone levels. There were statistical differences found between treatment groups in normalized dry kidney mass. Previous studies have established that testosterone regulates transepithelial transport of organic cation in the kidney via modulation of OCT2 expression (Koya, Fujii, Yambe, & Tahara, 2015).

Organic cation transporters (OCTs) mediate facilitated diffusion of organic cation compounds at the basolateral membrane of renal tubular cells. OCT2 is most often expressed in the kidney and is upregulated in the presence of increased testosterone levels, which can explain the increased kidney mass (Meetam, Srimaroeng, Soodvilai, & Chatsudthipong, 2009). The findings of this experiment for the dry kidney mass were consistent with the hypothesis that testosterone would have an effect on the mass of the kidneys, however the findings for the wet kidney mass were not. Perhaps if the length of the experiment was extended, a significant difference may have been revealed for the wet kidney mass.

In agreement with several primary literature references, the results from this study identified a significant relationship between seminal vesicle mass and increased testosterone levels. Statistical analysis revealed a significant difference in both normalized wet and dry seminal vesicle mass. Previous research has established that the growth and development of seminal vesicles is androgen dependent. The synthesis of proteins contributing to seminal plasma is regulated by the seminal vesicles and when there is a deficiency in testosterone, there is a decrease in seminal vesicle growth and activity.

The opposite would be true if there is an increase in testosterone (Welsh, et al., 2010). Testosterone also contributes to the production of sperm, known as spermatogenesis. Increased testosterone leads to an increase in sperm production, which increases the volume of seminal plasma. Seminal plasma is a complex fluid composed of sperm, fructose, calcium, ascorbic acid, and certain enzymes (Smith, Walker, & O’Donnell, 2015). The findings of this experiment were consistent with the literature and hypothesis that testosterone would have an effect on the mass of the seminal vesicles.

Contrary to several primary literature references, the results from this study identified no significant relationship between gastrocnemius mass and increased testosterone levels. There was no statistical difference found between either treatment group for wet or dry normalized gastrocnemius mass, however both graphs are consistent with the general trend of increasing mass with testosterone levels. Perhaps if the length of the experiment was extended, a significant difference may have been revealed. Previous research has established that testosterone supplementation increases skeletal muscle mass by stimulating myogenic differentiation (Singh, Artaza, Taylor, Gonzalez-Cadavid, & Bhasin, 2003).

Testosterone has also been found to induce skeletal muscle hypertrophy and alter morphological development of sarcomeres by increasing myotube cross sectional area, actin mRNA and actin protein levels, as well as phosphorylation status of ERK1/2 and Akt which restrains PI3K/Akt and mTOR inhibition (Basualto-Alarcón, Jorquera, Altamirano, Jaimovich, & Estrada, 2013). The findings of this experiment were not consistent with literature and the hypothesis that testosterone would have an effect on the mass of the gastrocnemius.

In agreement with several primary literature references, the results from this study identified no significant relationship between increased testosterone levels and body mass percent change. Previous research has established that testosterone supplementation decreases fat mass by inhibiting adipogenic differentiation (Singh, Artaza, Taylor, Gonzalez-Cadavid, & Bhasin, 2003). With the expected mass increase of several internal organs, the decrease in fat mass should eliminate a difference between treatment groups. The findings of this experiment were consistent with the literature and hypothesis that testosterone would not have an effect on body mass percent increase.

Several design factors of this experiment could have been improved. The first one being the length of the experiment. Many of the investigated organs were expected to produce significant differences between treatment groups, however only the kidney and seminal vesicles revealed these differences. Another experimental improvement would be including a fourth treatment group that received no castration or implant.

This fourth group could be used as a control group and representative of average male lab rats in which the other treatment groups could be compared to. Along with adding another treatment group, increasing the sample size would also improve the experiment and reliability of the results. Post operation, the rats also showed signs of pica and the eating of their bedding could have altered our results. In the future a different procedure could be implemented here to improve data reliability.