Effects of testosterone replacement on serotonin levels in the prostate and plasma in a murine model of hypogonadism

Abstract

Benign prostate hyperplasia is a dysfunctional disease with an elevated prevalence. Despite the accepted impact of aging and testosterone (TES) in its pathophysiology, its aetiology remains unknown. Recent studies described that serotonin (5-HT) inhibits benign prostate growth through the modulation of the androgen receptor, in the presence of TES. Accordingly, this work aimed to determine the impact of castration and TES replacement in plasmatic and prostatic 5-HT regulation. C57BL/6 mice were submitted to surgical castration and divided into three groups, continually exposed to either vehicle or different TES doses for 14 days. Plasmatic 5-HT concentration was measured before and after castration, and after TES reintroduction. Finally, total prostatic weight and intra-prostatic 5-HT were determined in the different groups. Our results demonstrate that mice prostate exhibits high 5-HT tissue levels and that intra-prostatic total 5-HT was independent of castration or TES reintroduction, in all studied groups. Also, 5-HT plasmatic concentration significantly increased after castration and then normalized after TES administration. Our findings revealed that mice prostate has a high 5-HT content and that total prostatic 5-HT levels do not depend on androgens' action. On the other hand, castration induced a significant increase in plasmatic 5-HT concentration, raising the hypothesis that androgens might be regulating the production of extra-prostatic 5-HT.

Figure 1

Schematic representation of the experimental design. Timeline for surgical castration, vehicle, TES 2.5 mg/kg or TES 7.5 mg/kg continuous administration and sacrifice of C57BL/6 mice. Plasma and tissue analysis at each time point, is also indicated. 5-HT, serotonin; TES, testosterone. (Fig. 1 was constructed by Barbosa-Martins, J.).

Figure 2

Effect of castration or TES administration in mice prostatic 5-HT (A) Quantification of total 5-HT in prostatic tissue by ELISA assay, after 14 days of continuous administration of vehicle (n = 5), 2.5 mg/kg (n = 5) or 7.5 mg/kg of TES (n = 7). (B) Absolute levels of 5-HT were normalized to the corresponding prostate weight. Data are presented as mean ± SEM. A one-way ANOVA, followed by a Bonferroni post-hoc, was used to compare data. n.s.—non-significant; **p = 0.006, 2.5 mg/kg vs. castration; **p = 0.001, 7.5 mg/kg versus castration.

Figure 3

Effect of castration and TES re-introduction in plasmatic 5-HT concentration. (A) Quantification of plasmatic 5-HT concentration by ELISA assay in mice before and after 21 days of castration (n = 17). **p = 0.001. A paired samples T-test was used to compare each time point. (B) Quantification of 5-HT plasmatic concentration before, and after 7 and 14 days of continuous administration of vehicle (n = 6), 2.5 mg/kg (n = 4) or 7.5 mg/kg (n = 5) of TES, by ELISA assay. Data are presented as mean ± SEM. A one-way ANOVA, followed by a Bonferroni post-hoc test was used to compare Day 14 5-HT concentrations between groups. A mixed factorial ANOVA, followed by a Bonferroni post-hoc test was used to compare each time point and groups. *p = 0.043, Day 14 versus Day 0 to castration + 2.5 mg/kg group; #p = 0.038, castration versus castration + 2.5 mg/kg at Day 14.

Figure 4

5-HT plasmatic concentration in experimental groups. (A) Quantification of plasmatic 5-HT concentration by ELISA assay in mice before castration (n = 17) and after 14 days of TES 2.5 mg/kg (n = 4) and TES 7.5 mg/kg (n = 5) re-introduction. Data are presented as mean ± SEM. A one-way ANOVA, followed by a Bonferroni post-hoc was used to compare data. n.s.—non-significant; **p = 0.002. (B) Comparison between 5-HT concentration levels of control (n = 6) and both TES-receiving groups (n = 9), at Day 14. Data are presented as mean ± SEM. An independent samples T-test was used to compare each data. *p = 0.012.

Figure 5

Correlation between plasmatic and prostatic 5-HT, to similar prostatic masses. A scatter diagram and Pearson’s bivariate correlation was used to compare plasmatic and prostatic 5-HT levels of TES group at day 14 (n = 11). r = 0.607; p = 0.048.

Figure 6

Effect of TES in mice prostatic size and weight. (A) Representative examples of mice prostatic tissue for the three experimental groups. (B, C) Dissected prostate weight (mg) and prostatic index for control (n = 5), 2.5 mg/kg (n = 5) and 7.5 mg/kg (n = 7) of TES receiving groups. Data are presented as mean ± SEM. A one-way ANOVA, followed by a Bonferroni post-hoc, was used to compare each data. ***p < 0.001. (Photos of (A) were taken by Mota, P. and Carvalho-Dias, E.).

Figure 7

TES effect on mice body weight. (A) Representation of total body weight before and after 21 days of surgery (n = 20). Data are presented as mean ± SEM. A paired samples T-test was used to compare each time point. **p = 0.005. (B) Representation of total body weight before castration (n = 20) and after 14 days of continuous administration in both TES-receiving groups (n = 12). Data are presented as mean ± SEM. An independent samples T-test was used to compare each data. n.s.—non-significant.