IGF-1 Levels are Significantly Correlated With Patient-reported Measures of Sexual Function

A W Pastuszak; J S Liu; A Vij; O Mohamed; K Sathyamoorthy; L I Lipshultz; M Khera

Disclosures

Int J Impot Res. 2011;23(5):220-226. 

In This Article

Abstract and Introduction

Abstract

Growth hormone (GH) supplementation may help to preserve erectile function. We assessed whether serum insulin-like growth factor 1 (IGF-1) levels, a surrogate for GH levels, correlate with sexual function scores in 65 men who completed the Sexual Health Inventory for Men (SHIM) and Expanded Prostate Cancer Index Composite (EPIC) questionnaires, and had serum IGF-1 and testosterone levels determined. Median±s.d. IGF-1 level, SHIM and EPIC scores were 235.0±86.4, 19.5±8.7 and 56.4±28.3 mg ml−1, respectively. IGF-1 levels and total SHIM score correlate significantly (r=0.31, P=0.02), as do IGF-1 levels and all individual SHIM question scores, and IGF-1 levels and the sexual domain of the EPIC questionnaire (r=0.30, P=0.02). No correlation was observed between IGF-1 levels and Gleason score, IGF-1 and testosterone level or SHIM score and testosterone level. These data support a potential role for the GH axis in erectile function.

Introduction

The male sexual cycle is regulated by a complex interplay between neuroendocrine, vascular and genital systems, and dysregulation of these systems can result in erectile dysfunction. The contributions of both vascular insufficiency and genital microstructural abnormalities to erectile dysfunction have been extensively studied, while the neuroendocrine axes have only recently come under scrutiny in the setting of male sexual function.[1,2] The aging process is associated with a decline in serum testosterone levels, which when present together with symptoms of androgen deficiency is termed late-onset hypogonadism (LOH).[3] The true prevalence of LOH remains uncertain, although a recent report suggests that LOH is present in 3.1–7.0% of men less than 70 years old, and up to 18.4% of men over the age of 70, when using total testosterone levels <300 ng dl−1 and symptomatic hypogonadism as diagnostic criteria.[4]

Testosterone replacement in men with LOH has been shown to ameliorate the symptoms of LOH and results in improvements in erectile function without significantly increasing the incidence of clinically significant prostate cancer, although the mechanism of this improvement in erectile function remains incompletely elucidated.[3,5,6] However, it does appear that this mechanism involves both local and central mechanisms.[7–13] Growth hormone (GH) levels, like testosterone, are also known to decline in an age-dependent manner.[14] This progressive decline has long been assumed to be physiological, although decline in GH secretion is associated with reduced lean body mass and bone density, an increased incidence of ischemic heart disease, dyslipidemia and erectile dysfunction, clinical outcomes that have also been observed in LOH.[15–21] An association between low GH levels and erectile dysfunction has been described in otherwise healthy male subjects, and recent in vitro and animal studies suggest that GH upregulates nitric oxide (NO) and may thus help to maintain erectile function.[20,22–24] The downstream effects of growth hormone are thought to be mediated in part by insulin-like growth factors 1 and 2 (IGF-1,-2), secretion of which is upregulated by GH. Given that the half-life of IGF-1 (12–15 h) is significantly longer than that of GH (less than 20 min), IGF-1 is considered to be a superior serum marker of growth hormone secretion and activity and is therefore used as a surrogate marker for GH levels, and has been validated as an accurate marker of GH levels over time.[25]

Studies have shown that GH and testosterone levels are closely related and that boys with delayed puberty and healthy older men with low-normal testosterone and IGF-1 have increased serum GH and IGF-1 levels with exogenous testosterone treatment.[2,26] IGF-1/GH and testosterone also appear to have similar clinical effects, with IGF-1/GH reversing endothelial progenitor cell dysfunction and testosterone increasing the number of endothelial progenitor cells.[27,28] Thus, it is reasonable to expect that low GH levels will correlate with sexual dysfunction, and a link between GH levels and male sexual dysfunction has been demonstrated.[20,29] This study builds on the current literature and examines a relationship between IGF-1 and validated measures of patient-reported sexual function, namely the Sexual Health Inventory for Men (SHIM) and the Expanded Prostate Cancer Index Composite (EPIC) questionnaires.[30,31]

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