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Fig. 32.6 The levels of NOS and NO in the penis tissue: Results are presented as meanĀ±SE
( n = 8). **: significantly different from the control group ( p < 0.01)
In the present study, we firstly found that taurine can significantly reduce the EL and
ML and obviously increase the ERF, MF, IF, and EJF in male aged rats. The results
indicated that taurine can increase the sexual response and mating ability in aged
male rats.
Normal male reproductive function depends on the intermittent secretion of LH
and FSH by the pituitary gland that was stimulated by hypothalamic GnRH. LH
stimulates the testicular Leydig cells to secrete T. Testosterone is necessary in libido
and sexual behavior, and can increase sexual interest and frequency of sexual acts
(Mulliqan and Schmitt 1993 ). Any dysfunction of the hypothalamic-pituitary-testis
axis can result in productive and sexual dysfunction. The function of hypothalamic-
pituitary-testis axis will degrade with aging, which is due to the decrease in GnRH,
FSH, LH, and T (Lamberts et al. 1997 ; Tenover 1997 ). Our results showed that the
concentrations of GnRH, LH, and T in male aged rats were obviously increased by
taurine administration, which implies that the enhancement of reproductive func-
tion may be partly attributed to more T secretion. Although taurine is known as a
GnRH inhibitor in the central nervous system, we think that taurine may increase
GnRH secretion by means of LH or other ways rather than direct effect on
hypothalamus.
Penile erection is a highly regulated physiologic event, involving increased arte-
rial inflow and restricted venous outflow, coordinated with corpus cavernosum
smooth muscle relaxation (Andersson and Wagner 1997 ). NO has been demon-
strated as a crucial mediator of penile erection, because NOS, the synthetic enzyme
for NO, was localized to the penile innervation and NOS inhibitors selectively block
erections (Burnett et al. 1992 ). Our laboratory had previously reported that taurine
can increase the levels of serum NOS and NO in aged male rats (Yang et al. 2010b ).
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