Biomedical subjects

Melanie Walton

Publications and source records attributed to Melanie Walton.

3 recordsLinked to original sources

PubMed2006

Calculated free testosterone in men: comparison of four equations and with free androgen index.

BACKGROUND: Serum testosterone remains the most important investigation in the diagnosis of androgen deficiency in men. Most of the circulating testosterone is bound to albumin and sex hormone-binding globulin (SHBG), whereas free testosterone accounts for approximately 2% of total testosterone. Because direct measurement of free testosterone is impractical in routine practice, several equations are used to provide clinically useful estimates of free testosterone concentration. This study aimed to (1) obtain locally derived reference limits for total testosterone and calculated free testosterone (CFT) concentrations, and (2) critically evaluate the equations commonly used to estimate free testosterone. METHODS: Serum total testosterone, SHBG and albumin were assayed in morning blood samples obtained from 126 healthy men (aged 20-45 years) known to have normal semen analysis. CFT concentrations calculated using four published methods (i.e. the Sodergard, Nanjee-Wheeler, Vermeulen and Ly-Handelsman equations) were compared with one another and the free androgen index. RESULTS: Reference intervals for total testosterone and CFT by the Vermeulen equation were 9.4-31.0 nmol/L and 0.245-0.785 nmol/L (2.5-97.5 percentile), respectively. CFT values varied considerably with the four equations examined. Mean biases ranged from 5.8 to 56.0%; the Nanjee-Wheeler and Ly-Handelsman equations yielded positive and negative biases, respectively, against the other equations. Free androgen index was shown to correlate poorly with CFT (r2=0.21-0.46) and over-estimate the CFT at low SHBG concentrations. CONCLUSIONS: We have used various equations to derive reference ranges for CFT in healthy men aged 20-45 years. We suggest that CFT be incorporated into the investigation regimen for suspected hypogonadism when total testosterone results are equivocal.

Adult↗

PubMed2005

Hormonal contraception in men.

All major advances in the development of hormonal methods of contraception over the past 40 years have been exclusively female orientated with male hormonal contraception forever "just around the corner". Despite this, the last few years have seen a significant increase in the pace of research and increased involvement from the pharmaceutical industry. This is essential if the progress derived from the public sector is to be translated into a real product for widespread use. Current male methods of contraception, condoms and vasectomy, are relied on by 30% of couples throughout the world but there have been no new male contraceptive methods introduced in the last century. There is currently an increasing emphasis on male involvement in family planning, and evidence both that some men would be keen to shoulder this responsibility and that their partners would trust them to do so. There are several potential novel approaches to male contraception, but the hormonal one is the only one at the stage of clinical research. This method is based on the normal regulation of spermatogenesis by the pituitary gonadotrophins: suppression of gonadotrophin secretion results in a reduction in the rate of spermatogenesis, and azoospermia, the absence of sperm from the ejaculate, can be achieved. Current approaches are now getting close to the ideal of inducing azoospermia in all men. This approach also results in suppression of testicular testosterone production, thus androgen 'add-back' is an essential component of a contraceptive regime. Many different steroids and delivery methods -oral, buccal, transdermal, subcutaneous implants- are under exploration at present, each with their own advantages and drawbacks. The use of synthetic androgens is also starting to be explored: these have the potential advantage of offering tissue-specific actions.

Androgens↗

PubMed2004

Update on the male hormonal contraceptive agents.

There remains a need for new acceptable and effective male contraceptives to increase the choice for couples throughout the world. There have been no recent advances in available male contraceptive methods although a number of promising approaches have been identified, of which the hormonal approach is currently undergoing clinical investigation. In recent years the pace of research in this area has quickened significantly with increasing interest and now investment by the pharmaceutical industry. This is vital if the work undertaken so far by the public sector is to be transformed into a commercial reality. The hormonal approach is based on suppression of pituitary gonadotropin secretion resulting in a reversible reduction in spermatogenesis with azoospermia in all men being the ultimate aim. Without stimulation by luteinising hormone from the pituitary, testicular testosterone production also ceases. Therefore, androgen administration to restore physiological levels is an essential component of all male hormonal contraceptive regimes. Male hormonal contraceptives can consist of testosterone alone, or either a progestogen or gonadotropin-releasing hormone antagonist with 'add-back' testosterone. This article reviews the current state of progress in this field.

Androgens↗