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TESTOSTERONE AND SEXUAL FUNCTION IN MEN

CHAPTER ONE

INTRODUCTION

1.1     Background of the Study

Testosterone is the principal sex hormone in men. It is important not only for normal sexual function but also for maintaining bone and muscle strength, mental and physical energy, and overall well-being. Due to the popular association one could understand why testosterone could play a major part in male sexual health. Low testosterone is associated with diminished libido, erectile dysfunction, increased fat mass, decreased muscle, bone mass and energy, depression, and anaemia (Wang et al., 2000).

Erectile dysfunction (ED) is a highly prevalent disorder among adult men and its incidence increases steadily with age. The ageing process in men is accompanied by a progressive decline in serum testosterone (T) levels and the various illnesses occurring in mid- to late adult life further contribute to lower circulating testosterone independently of age (Niclaas et al., 2005). The use of androgen measurement in the evaluation of ED has shown that up to 35% of adults presenting with ED have reduced or borderline circulating androgen levels. This has prompted many physicians to prescribe testosterone preparations to men with ED, even though a causal relationship between altered levels of androgens and erectile function has not yet been established. Several studies have investigated the effect of androgen replacement on sexual function in hypogonadal and eugonadal men, often with disparate findings. In published reports, (Sarosdy, 2007; Osifo and Ozor, 2013) the lack of discrimination between androgenic effects on the different domains of sexual function – erectile function, sexual desire, orgasmic function, intercourse satisfaction and overall satisfaction – along with inadequate sample sizes and statistical power contributed to misconceptions and misuse of testosterone in the treatment of ED.

Serum testosterone levels decline with age; thus, older men have lower testosterone levels than younger men. Some of the age-related changes in muscle mass, bone mineral density, fat mass, and sexual and cognitive functions resemble those observed in young, hypogonadal men. Consequently, the interest in treating older men with low testosterone levels with testosterone supplementation has grown rapidly. In older men, testosterone supplementation increases lean body mass, muscle strength, and hemoglobin levels and decreases whole body and visceral fat. One question of prime concern is how testosterone supplementation affects sexual function, mood, and cognition in older men (Niclaas et al., 2005).

Effects of testosterone interventions on sexual function, mood, and cognition have been obtained primarily from studies in young men. These data may not be extrapolated directly to older men. A handful of studies have examined the effects of testosterone supplementation on sexual function in older men. In a recent review it was found that testosterone supplementation in older men resulted in increased libido in seven of eight studies and improvement in erections in five of six studies (Osifo and Ozor, 2013). The studies reported in this review used only one or two testosterone replacement doses, limiting our understanding of the effects of a greater range of testosterone doses and concentrations on sexual function. Additional data are needed to elucidate whether older men receiving different doses, and thus achieving different concentrations of serum testosterone, experience changes in sexual function. A majority of the control of sexual functions in the male (and the female) begins with secretions of gonadotropin-releasing hormone (GnRH) by the hypothalamus (Osifo and Ozor, 2013). You may remember that the hypothalamus is driven by the limbic system, and therefore many psychological factors can influence the release of GnRH. GnRH stimulates the release of two other hormones, luteinizing hormone (LH) and follicle stimulating hormone (FSH) from the anterior pituitary (Peter et al., 2005).

Both LH and FSH are glycoproteins that exert their effect on the testes, which in turn activate specific enzyme systems in the testes. LH stimulates the interstitial cells of Leydig to synthesize and secrete testosterone. The majority of the circulating testosterone is made by the Leydig cells. FSH binds to the receptors on the Sertoli cells in the seminiferous tubules where it causes the Sertoli cells to grow and secrete spermatogenic substances. Testosterone and dihydroxytestosterone (DHT) enter into the interstitial spaces of the seminiferous tubules where they have a strong effect on spermatogenesis. Therefore, FSH and testosterone are the regulators of spermatogenesis (Wang et al., 2000). The Sertoli cells also secrete a glycoprotein hormone called inhibin in respond to spermatogenesis occurring to rapidly. This hormone decreases the secretion of FSH and GnRH. (inhibins are also secreted by the ovary).  There is a symbiotic relationship between the brain and testosterone. Many of the central nervous system functions are regulated by testosterone, among them is behavior and cognition (Sarosdy, 2007). The inputs to the central nervous system, such as psychological stress, can lower the release of GnRH, and therefore decrease serum testosterone levels. Low serum testosterone is also a component of insulin resistance. A previous research study concluded that low serum testosterone was independently associated with insulin resistance in non-diabetic older men (Osifo and Ozor, 2013).

From a functional medicine perspective, it’s important to assess for environmental factors that can influence testosterone level. Since over 90% of the testosterone is produced in the testis by the Leydig cells, it important to assess for factors that might inhibit Leydig cell production of testosterone. Disruption of androgen biosynthesis and actions by environmental endocrine disrupting compounds can inhibit critical cellular processes controlling steroidogenesis in the Leydig cells. Disruption can occur with the transport and delivery of cholesterol to the mitochondria, interference with the enzymatic activity along the steroidogenesis pathway, or by interfering with the androgen receptor (Seidman and  Roose, 2006).  

1.2     Statement of the Problem

Sexual function is an important component of human quality of life and subjective well being. Sexual problems are widespread and adversely affect mood, well being, and interpersonal functioning (Khera and Lipshultz, 2007). Main sexual problems are related to sexual desire and male erectile dysfunction. Erectile dysfunction is probably the most commonly recognized and treated sexual dysfunction. It affects more than 30% of men aged 40–70 years (Rosenthal et al., 2006). Successful treatment of sexual dysfunction may not only improve sexual relationships, but also overall quality of life. Alternatives for treatment of hypoactive sexual desire are scarcer. Testosterone is used because of its property to stimulate sexual desire in hypogonadal men. Other compounds are potent regulators of sexual behaviour in animals but not in healthy men (Peter et al., 2005).

Despite the broad use of oral agents for erectile dysfunction, and the use of testosterone for hypoactive sexual desire, many people in the world prefer the use of natural plants. Traditional herbs have been a revolutionary breakthrough in the management of erectile dysfunction and have become known worldwide as treatment. One example is the broad use of ginseng because of its supposed property to provoke sexuality (Wang et al., 2000).

1.3     Aim of the Study

The aim of this study is to summarize and critically discuss all available data supporting the role of testosterone on the regulation of erectile function in men. Other aspects of sexual function including libido and ejaculation will also be analyzed. In addition, the possible contribution of testosterone replacement therapy (TRT) to sexual outcomes as well as the role of the combined therapy with other erection disorder drugs such as phosphodiesterase type 5 inhibitors (PDE5i) will also be addressed.

1.4     Significance of the Study

This study will be of immense benefit to other researchers who intend to know more on this study and can also be used by non-researchers to build more on their research work. This study contributes to knowledge and could serve as a guide for other study.

1.5     Scope of the Study

This study is on testosterone and sexual function in men.

1.6     Limitations of the study

Financial constraint: Insufficient fund tends to impede the efficiency of the researcher in sourcing for the relevant materials, literature or information and in the process of data collection (internet, questionnaire and interview).

Time constraint: The researcher will simultaneously engage in this study with other academic work. This consequently will cut down on the time devoted for the research work.

1.7     Definition of Terms

Testosterone: This is the male sex hormone that is made in the testicles. Testosterone hormone levels are important to normal male sexual development and functions. During puberty (in the teen years), testosterone helps boys develop male features like body and facial hair, deeper voice, and muscle strength.

Sexual Function: This is how the body reacts in different stages of the sexual response cycle, or as a result of sexual dysfunction.

Erectile Dysfunction: can be a sign of a physical or psychological condition. It can cause stress, relationship strain and low self-confidence. The main symptom is a man's inability to get or keep an erection firm enough for sexual intercourse. Patients suffering from erectile dysfunction should first be evaluated for any underlying physical and psychological conditions. If treatment of the underlying conditions doesn't help, medication and assistive devices, such as pumps, can be prescribed.

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