Micropenis secondary to growth hormone deficiency: does treatment with growth hormone alone result in adequate penile growth?

Micropenis

Micropenis, i.e., a structurally normal but abnormally small penis is defined as stretched penile length (SPL) 2.5 SD below the mean for age and sexual stage. Several studies worldwide have published country-specific normative data on SPL; an appropriate cutoff for evaluation of micropenis as per international standards would be below 2 cm at birth and below 4 cm after 5 y of age. Testosterone production by fetal testes, its conversion to dihydrotestosterone (DHT) and its action on the androgen receptor is necessary for normal penile development. Hypothalamo-pituitary disorders (gonadotropin or growth hormone deficiencies), genetic syndromes, partial gonadal dysgenesis, testicular regression, disorders of testosterone biosynthesis and action constitute the various etiologies of micropenis. Associated hypospadias, incomplete scrotal fusion, and cryptorchidism are suggestive of disorders of sex development (DSD). Along with basal and human chorionic gonadotropins (HCG)-stimulated gonadotropins, testosterone, DHT, and androstenedione levels, karyotype assessment is equally important. Treatment aims at attaining penile length sufficient enough for urination and to perform sexual function. Hormonal therapy with intramuscular or topical testosterone, topical DHT or recombinant follicle stimulating hormone (FSH) and luteinizing hormone (LH) should be attempted in the neonatal or infancy period. The role of surgery for micropenis is limited and has variable patient satisfaction and complication outcomes. There is a need for long-term studies on the adult SPL achieved following treatment for micropenis in infancy and childhood.

Somatotropic-Testicular Axis: A crosstalk between GH/IGF-I and gonadal hormones during development, transition, and adult age

BACKGROUND

The hypothalamic-pituitary-gonadal (HPG) and hypothalamic-pituitary-somatotropic (HPS) axes are strongly interconnected. Interactions between these axes are complex and poorly understood. These interactions are characterized by redundancies in reciprocal influences at each level of regulation and the combination of endocrine and paracrine effects that change during development.

OBJECTIVES

To comprehensively review the crosstalk between the HPG and HPS axes and related pathological and clinical aspects during various life stages of male subjects.

MATERIALS AND METHODS

A thorough search of publications available in PubMed was performed using proper keywords.

RESULTS

Molecular studies confirmed the expressions of growth hormone (GH) and insulin-like growth factor-I (IGF-I) receptors on the HPG axis and reproductive organs, indicating a possible interaction between HPS and HPG axes at various levels. Insulin growth factors participate in sexual differentiation during fetal development, indicating that normal HPS axis activity is required for proper testicular development. IGF-I contributes to correct testicular position during minipuberty, determines linear growth during childhood, and promotes puberty onset and pace through gonadotropin-releasing hormone activation. IGF-I levels are high during transition age, even when linear growth is almost complete, suggesting its role in reproductive tract maturation. Patients with GH deficiency (GHD) and insensitivity (GHI) exhibit delayed puberty and impaired genital development; replacement therapy in such patients induces proper pubertal development. In adults, few studies have suggested that lower IGF-I levels are associated with impaired sperm parameters.

DISCUSSION AND CONCLUSION

The role of GH-IGF-I in testicular development remains largely unexplored. However, it is important to evaluate gonadic development in children with GHD. Additionally, HPS axis function should be evaluated in children with urogenital malformation or gonadal development alterations. Correct diagnosis and prompt therapeutic intervention are needed for healthy puberty, attainment of complete gonadal development during transition age, and fertility potential in adulthood.

Hormonal and Molecular Regulation of Phallus Differentiation in a Marsupial Tammar Wallaby

Congenital anomalies in phalluses caused by endocrine disruptors have gained a great deal of attention due to its annual increasing rate in males. However, the endocrine-driven molecular regulatory mechanism of abnormal phallus development is complex and remains largely unknown. Here, we review the direct effect of androgen and oestrogen on molecular regulation in phalluses using the marsupial tammar wallaby, whose phallus differentiation occurs after birth. We summarize and discuss the molecular mechanisms underlying phallus differentiation mediated by sonic hedgehog (SHH) at day 50 pp and phallus elongation mediated by insulin-like growth factor 1 (IGF1) and insulin-like growth factor binding protein 3 (IGFBP3), as well as multiple phallus-regulating genes expressed after day 50 pp. We also identify hormone-responsive long non-coding RNAs (lncRNAs) that are co-expressed with their neighboring coding genes. We show that the activation of SHH and IGF1, mediated by balanced androgen receptor (AR) and estrogen receptor 1 (ESR1) signalling, initiates a complex regulatory network in males to constrain the timing of phallus differentiation and to activate the downstream genes that maintain urethral closure and phallus elongation at later stages.

Why Do Normal Children Have Acromegalic Levels of IGF-I During Puberty?

CONTEXT

The rapid pubertal height growth is unique to humans, but why do we have it? Although the spurt contributes 13% to 15% to the final adult height, we hypothesized that the biological significance of the high acromegalic levels of GH and IGF-I, which are behind the pubertal growth spurt, might primarily occur to stimulate the reproductive organs.

EVIDENCE SYNTHESIS

Animal data have demonstrated that adult Igf1 and Igf2 gene knockout mice that survive show a dramatic reduction in the size of the reproductive organs and are infertile. In humans, case reports of mutations in the genes affecting the GH-IGF axis and growth (GH, GHRH, GH-R, STAT5b, IGF-I, IGF-II, IGF-1R, PAPPA2) are also characterized by delayed pubertal onset and micropenis. Furthermore, GH treatment will tend to normalize the penile size in patients with GH deficiency. Thus, the endocrine effects of high IGF-I levels might be needed for the transition of the sexual organs, including the secondary sex characteristics, from the "dormant" stages of childhood into fully functioning reproductive systems. The peak IGF-I levels, on average, occur 2 years after the peak height growth velocity, suggesting reasons other than longitudinal growth for the high IGF-I levels, and remain high in the years after the height spurt, when the reproductive systems become fully functional.

CONCLUSION

We suggest that the serum levels of IGF-I should be monitored in children with poor development of sexual organs, although it remains to be investigated whether GH should be added to sex steroids in the management of hypogonadism for some pubertal children (e.g., boys with micropenis).

Effects of combined growth hormone and testosterone treatments in a rat model of micropenis

Although it is well known that penile growth is dependent on androgens, few clinical studies have reported successful treatment of micropenis with testosterone, likely due to concerns regarding the efficacy and safety of prolonged testosterone use. Thus, we assessed the synergenic effects of growth hormone (GH) treatments with and without testosterone on phallic growth in a rat model of micropenis. Fifty Sprague-Dawley rats were assigned to control (C), microphallus (MP), testosterone (T), GH (G) and GH plus testosterone (GT) treatment groups, and microphallus was induced by secondary hypogonadism. Pre-pubertal treatments with testosterone, GH or the combination were initiated from 7 days after birth and were maintained until 12 weeks of age. To assess the efficacy of treatments, phallic dimensions were determined and histological markers of cavernosal integrity were evaluated. Skeletal and gonadal safety profiles of the treatments were then assessed according to right tibial lengths and testicular weights, respectively. No monotreatments normalised penile dimensions, whereas combination treatments led to complete restoration. The combination treatment also prevented decreases in histological indicators of cavernosal integrity, including smooth muscle actin and collagen III expression levels and fat globule accumulation and sinusoidal density. These synergenic effects of GH treatments on penile growth may follow changes in androgen receptor expression levels and were accompanied by decreased testicular volume losses. Although the physiological conditions of phallic growth differ between humans and rats, this proof-of-concept study provides a strategy for circumventing the problems of testosterone monotherapy for human micropenis.

Postnatal Changes in Testicular Position Are Associated With IGF-I and Function of Sertoli and Leydig Cells

CONTEXT

Despite clinical guidelines calling for repetitive examination of testicular position during childhood, little is known of normal changes in testicular position during childhood, let alone factors that control it.

OBJECTIVE

To assess changes in and factors associated with testicular position during childhood.

DESIGN

Testicular position (the distance from the pubic bone to the upper pole of the testes) at birth, 3 months, 18 months, 36 months, and 7 years and reproductive hormones at 3 months were measured.

SETTING

Prenatally recruited, prospective longitudinal birth cohort.

PARTICIPANTS

A total of 2545 boys were recruited prenatally in a Danish-Finnish birth cohort and had a testicular position examination available. A subset of 680 Danish and 362 Finnish boys had serum reproductive hormone concentrations and insulin-like growth factor I (IGF-I) determined at 3 months.

MAIN OUTCOME MEASURES

Testicular distance to pubic bone (TDP), serum reproductive hormone, and IGF-I concentrations.

RESULTS

TDP increased from birth to 3 months and decreased thereafter. Length, gestational age, weight for gestational age, and penile length were positively associated with larger TDP and thus lower testicular position in a linear mixed-effect model. Furthermore, IGF-I concentration, inhibin B/follicle-stimulating hormone ratio, and testosterone/luteinizing hormone ratio were all independently and positively associated with longer TDP.

CONCLUSIONS

We provide longitudinal data on postnatal changes in TDP. TDP is dynamic and associated with Leydig and Sertoli cell function as well as with IGF-I levels during the first months of life at mini-puberty of infancy. TDP may thus be a useful biomarker of postnatal testicular function.

Growth hormone and reproduction: a review of endocrine and autocrine/paracrine interactions

The somatotropic axis, consisting of growth hormone (GH), hepatic insulin-like growth factor I (IGF-I), and assorted releasing factors, regulates growth and body composition. Axiomatically, since optimal body composition enhances reproductive function, general somatic actions of GH modulate reproductive function. A growing body of evidence supports the hypothesis that GH also modulates reproduction directly, exerting both gonadotropin-dependent and gonadotropin-independent actions in both males and females. Moreover, recent studies indicate GH produced within reproductive tissues differs from pituitary GH in terms of secretion and action. Accordingly, GH is increasingly used as a fertility adjunct in males and females, both humans and nonhumans. This review reconsiders reproductive actions of GH in vertebrates in respect to these new conceptual developments.

[Micropenis]

Micropenis represents a clinical sign that should be diagnosed at birth (or in utero) by the detection of a normally structured penis with a length 2.5 SD below the mean for age. Micropenis can be classified as due to deficient testosterone secretion or action. Evaluation of the gonadotropic and testicular function during the mini-puberty is often helpful in evaluating the etiology. Management of micropenis should focus on achieving a suitable penis length, in order to allow an adequate urination, normal sexual intercourses and a good self-body image. Irrespective of the underlying cause, a short course of T should be tried in patients with micropenis to assess the ability of the penis to respond to it. Topical 5a-dihydrotestosterone gel has also been reported to be effective. Children with hypopituitarism and GH deficiency respond to appropriate hormonal therapy. Psychological counseling is helpful and often necessary.

Association between GH receptor polymorphism (exon 3 deletion), serum IGF1, semen quality, and reproductive hormone levels in 838 healthy young men

INTRODUCTION

GH activity may be involved in male reproductive function. A common genetic polymorphism in the gene encoding the GH receptor (GHR) results in deletion of the entire exon 3 sequence (GHRd3 isoform). The short GHRd3/d3 isoform seems more sensitive compared with full-length receptors (GHRfl/fl).

AIM

TO INVESTIGATE THE ASSOCIATIONS BETWEEN GH ACTIVITY, EVALUATED BY EXON 3 GHR POLYMORPHISM, AND SERUM IGF1 VS REPRODUCTIVE HORMONES, SEMEN QUALITY, AND PRE- AND POSTNATAL GROWTH IN HEALTHY YOUNG MALES (N=838, MEAN AGE: 19.4 years).

RESULTS

Compared with GHRfl/fl homozygous individuals (n=467) GHRd3/d3 homozygous individuals (n=69) tended to have larger semen volume (3.2 (2.4-4.3) vs 3.6 (2.6-4.7) ml, P=0.053) and higher serum inhibin-B levels (208 pg/ml (158-257) vs 227 pg/ml (185-264), P=0.050). Semen quality, levels of gonadotropins, testosterone, estradiol, sex hormone-binding globulin, and IGF1 were not associated with GHRd3 genotype. A twofold increase in serum IGF1 was associated with a 13% (4-23) increase in calculated free testosterone (P=0.004). By contrast IGF1 was inversely associated with serum inhibin-B (P=0.027), but showed no associations to semen quality. GHR genotype and serum IGF1 were not associated with size at birth or final height.

CONCLUSIONS

GHRd3 polymorphism seemed only to have a weak influence on male reproductive function of borderline significance. The sensitive GHRd3/d3 genotype may slightly increase testicular function, as evaluated by semen volume and levels of inhibin-B, but does not seem to influence Leydig cell steroidogenesis. GHR genotype did not influence pre- and postnatal growth.

Adult care of children from pediatric urology: part 2

PURPOSE

We describe the outcomes of undescended testes and sex development disorders in adolescence and young adulthood. We reviewed the requirements for the long-term care of children born with these and other major congenital anomalies of the genitourinary system.

MATERIALS AND METHODS

The current English language literature was retrieved with a PubMed® search for articles on these subjects. Only articles covering outcomes at ages past puberty were included in analysis. The material was supplemented from the database of the clinic for adults with sex development disorders at University College London Hospitals.

RESULTS

An undescended testis has impaired spermatogenesis. In men in whom a unilateral undescended testis was corrected before puberty the incidence of paternity is normal at around 90% of those who attempt it. The equivalent rate for those with bilateral undescended testes is about 65%. If surgery for bilateral undescended testes is delayed until after puberty, fertility is unlikely. The risk of testicular neoplasms is overestimated and the relative risk is between 2.5 and 8. Children born with a sex development disorder receive multidisciplinary treatment throughout childhood and require the same care as adults. Males who are under virilized likely have a micropenis (greater than 2 SD below the mean stretched length) but they may have normal sexual function. Fertility depends on the underlying condition. Virilized females, who most commonly have congenital adrenal hyperplasia, currently present to adult clinics with an inadequate vagina after infantile surgery. Reconstruction is required to allow intercourse.

CONCLUSIONS

The care of adults born with abnormalities of the genitalia is complex. Early management may define upbringing in childhood but requirements for sexuality and fertility in adult life are different. Multidisciplinary care is essential and a case can be made to establish a subspecialty of urology to coordinate it.

Maturation of the growth axis in marsupials occurs gradually during post-natal life and over an equivalent developmental stage relative to eutherian species

The separation of a nutrition-responsive insulin-like growth factor (IGF) system and a growth hormone (GH) responsive IGF system to control pre- and post-natal growth of developing mammals may originate from the constraints imposed by intra-uterine development. In eutherian species that deliver relatively precocial young, maturation of the GH regulatory system is coincident with the time of birth. We measured the hepatic expression of the four key growth axis genes GH-receptor, IGF-1 and -2, and IGFBBP-3, and plasma protein concentrations of IGF-1 from late fetal life through to adult stages of a marsupial, the tammar wallaby. The data clearly show that maturation of GH-regulated growth in marsupials occurs gradually over the course of post-natal life at an equivalent developmental stage to that of precocial eutherian mammals. This suggests that the timing of GH-regulated growth in marsupials is not related to parturition but instead to the relative developmental stage.

Penile hemodynamics in hypogonadal men with micropenis

OBJECTIVES

To document the penile vascular and erectile response to intracavernous injection (ICI) of vasoactive agent in hypogonadal men with micropenis.

METHODS

A total of 15, previously untreated, hypogonadal men with micropenis (stretched penis length less than 2.5 SD below the mean of the normal population) underwent a detailed urologic and endocrinologic evaluation. Their mean age was 21.2 +/- 4.2 years. Penile hemodynamics were assessed by color Doppler ultrasonography before and after ICI of 5 microg of prostaglandin E(1) combined with manual genital self-stimulation.

RESULTS

Endocrinologic evaluation revealed that hypogonadism was hypogonadotropic in 10 (66.7%) and hypergonadotropic in 5 (33.3%). Karyotype analysis showed 46XY in all. Their mean stretched penile length was 6.2 +/- 1.4 cm (range 3 to 7.5) and increased to a mean of 6.96 +/- 1.5 cm (range 4 to 8.5) after ICI. The serum free testosterone levels ranged from 0.2 to 3.2 pg/mL (mean 1.9 +/- 0.92). None had had any previous sexual experience, and 14 (93.3%) reported a history of nocturnal erections. Penile color Doppler ultrasonography demonstrated a normal penile vascular system in 7 (46.7%) and penile arterial insufficiency in 4 (28.6%). All 11 of these patients (73.3%) achieved an adequate erectile response to ICI combined with manual stimulation. Mixed vascular disease was observed in the remaining 4 patients (28.8%), and they did not have a sufficient erectile response to ICI. Color Doppler ultrasonography revealed similar results in the hypogonadotropic and hypergonadotropic men.

CONCLUSIONS

Our data suggest that the erectile response to ICI combined with manual genital self-stimulation is effective in most hypogonadal men having a micropenis with low serum androgen levels.

Growth hormone therapy

Since 1958 growth hormone (GH) has been used as substitution treatment for children with GH deficiency. At present, it is clear that a dose of 0.23 mg/kg/week can lead to a final height close to target height, but in view of the wide inter-individual variation, alternative regimens based on invidualizing the dosage with the help of prediction models are being investigated. The best strategy during puberty (increase the dosage, delay puberty) is still uncertain. The value of GH in idiopathic short stature is still heavily debated, although the average final height gain on 0.33 mg/kg/week is 5-7 cm. GH is efficacious in short stature due to chronic renal failure and Prader-Willi syndrome. In other conditions insufficient data are available. There are few side-effects.

Growth hormone treatment in adults: is there a true gender difference?

The importance of growth hormone (GH) deficiency in adults became evident at the end of the 1980s, when the first clinical studies on GH replacement therapy in adults were published. Since then, accumulated experience has shown a great individual variability in the response to GH replacement, including a potential difference in responsiveness between genders. The aim of this paper is to review the data regarding the effects of gender differences on GH pharmacokinetics, pharmacodynamics, and efficacy of replacement. In addition, we start with a short review of the possible role of GH in sexual development and sexual life.

Insulin-like growth factor-I promotes proliferation and migration of cavernous smooth muscle cells

To better understand the physiology of cavernous smooth muscle cells (CSMC), particularly their regulation by IGF-I, we isolated CSMC from rats of various ages and grew them as cell cultures. CSMC from very young (1 week of age) and very old (28 months of age) rats secreted the least amounts of IGF-I, and those from 16-week-old rats the most. IGF-I stimulated growth of CSMC at an optimal concentration of 12.5 ng/ml. At this concentration, CSMC from 11-week-old rats showed the highest growth rate and CSMC from 28-month-old rats showed the lowest. The optimal IGF-I concentration for migration of CSMC was 10 ng/ml. At this concentration, CSMC from 4-week-old rats showed the highest migratory rate and CSMC from 28-month-old rats showed the lowest. IGF-I also stimulated VEGF secretion from CSMC at an optimal concentration of 10 ng/ml. At this concentration, CSMC from 16-week-old rats secreted VEGF the most and CSMC from 28-month-old rats secreted the least. The expression levels of IGF-IR paralleled the IGF-I-regulated growth rates of these cells. Expression of IGF-IR was identified in the cavernous smooth muscle and the urethra epithelium of the penis.

The child with micropenis

Micropenis refers to an extremely small penis with a stretched penile length of less than 2.5 SD below the mean for age or stage of sexual development. It should be differentiated from a buried or hidden penis and aphallia. It is important to use a standard technique of stretched penile measurement and nomograms for age to identify children with micropenis. All children above 1 year of age with a stretched penile length of less than 1.9 cm need evaluation. Based on etiology they can be classified as hypogonadotropic hypogonadism (hypothalamic or pituitary failure), hypergonadotropic hypogonadism (testicular failure), partial androgen insensitivity syndrome and idiopathic groups. The help of a pediatric endocrinologist, geneticist, pediatric surgeon and/or urologist is often necessary. Growth velocity is an important determinant of associated hypothalamic or pituitary pathology. GnRH and/or hCG stimulation tests are often helpful in evaluating the etiology. Similarly chromosomal studies are indicated in a few. Often the diagnosis is inferred by the presence of clinical features suggestive of a syndrome usually associated with hypogonadotropic hypogonadism. Irrespective of the underlying cause a short course of testosterone should be tried in patients with micropenis and an assessment of the penis to respond should be made. Transdermal DHT has also been reported to be effective in prepubertal children. Children with hypopituitarism and GH deficiency respond to appropriate hormonal therapy. Surgical correction is not indicated in the common endocrine types of micropenis. Many studies have shown that most testosterone treated children have satisfactory gain in length of penis and sexual function. Thus sexual reassignment is done very infrequently now.

Micropenis and apparent micropenis--a diagnostic and therapeutic challenge

Micropenis should be diagnosed shortly after birth and differentiated from associated deformities and syndromes. Calling in a paediatric endocrinologist and a geneticist is obligatory. Endocrine treatment should be undertaken in the second and third months (25 mg testosterone enanthate per month) after a positive HCG test. Where there is a negative endocrine response and/or associated sex differentiation derangement, a sex change operation towards female should be discussed with the family at an early stage. Where male determination is already established and the androgen response is poor or absent, the indication is for plastic surgery to elongate the phallus using the Hinman or Johnston technique, performed by an experienced paediatric urologist.

Penile length of newborns in Singapore

Micropenis is an important sign in congenital hypopituitarism and various disorders. Documented norms for penile length exist only for babies of Caucasian and Middle-Eastern origin. This study was carried out to establish such norms for Asian newborns. We studied 228 male live births within their first three days of life. Stretched penile lengths were marked off on unmarked wooden spatulas, which were placed vertically along the dorsal aspect of the penis, with one rounded end on the pubic bone. The mean penile length +/- S.D. for the full-term Asian baby was 3.6 +/- 0.4 cm. Race had a significant effect: Chinese 3.5 cm, Malay 3.6 cm and Indian 3.8 cm. Penile length correlated with birth weight and gestational age. Asian babies thus have similar norms to Caucasian babies. An Asian newborn whose penis measures less than 2.6 cm has micropenis and may need prompt investigation for underlying endocrine disorders.

Congenital hypogonadotropic hypogonadism and micropenis: effect of testosterone treatment on adult penile size why sex reversal is not indicated

Micropenis is commonly due to fetal testosterone deficiency. The clinical management of this form of micropenis has been contentious, with disagreement about the capacity of testosterone treatment to induce a functionally adequate adult penis. As a consequence, some clinicians recommend sex reversal of affected male infants. We studied 8 male subjects with micropenis secondary to congenital pituitary gonadotropin deficiency from infancy or childhood to maturity (ages 18 to 27 years). Four patients were treated with testosterone before 2 years of age (group I) and four between age 6 and 13 years (group II). At presentation, the mean penile length in group I was 1.1 cm (-4 SD; range, 0.5 to 1.5 cm) and in group II it was 2.7 cm (-3.4 SD; range, 1.5 to 3.5 cm). All patients received one or more courses of 3 intramuscular injections of testosterone enanthate (25 or 50 mg) at 4-week intervals in infancy or childhood. At the age of puberty the dose was gradually increased to 200 mg monthly and later to an adult replacement regimen. As adults, both group I and II had attained a mean final penile length of 10.3 cm 2.7 cm with a range of 8 to 14 cm (mean adult stretched penile length for Caucasians is 12.4 2.7 cm). Six of 8 men were sexually active, and all reported normal male gender identity and psychosocial behavior. We conclude that 1 or 2 short courses of testosterone therapy in infancy and childhood augment penile size into the normal range for age in boys with micropenis secondary to fetal testosterone deficiency; replacement therapy at the age of puberty results in an adult size penis within 2 SD of the mean. We found no clinical, psychologic, or physiologic indications to support conversion of affected male infants to girls. Further, the results of this study do not support the notion, derived from data in the rat, that testosterone treatment in infancy or childhood impairs penile growth in adolescence and compromises adult penile length.

Establishment of a normal range of penile length in preterm infants

RATIONALE

Recognition of micropenis is important because it may be the only obvious manifestation of pituitary or hypothalamic hormone deficiencies. Alternatively it may indicate the presence of dysgenetic testicular tissue with malignant potential. Previously published normal ranges for premature males are based on small sample sizes, with few infants <30 weeks and none <28 weeks.

SETTING

Intensive and Special Care Nurseries, Royal Women's Hospital, Melbourne, Victoria.

SUBJECTS

188 consecutive male infants, inborn and outborn, with gestational age <37 completed weeks were examined in the first week of life. They included multiple births (n=51) and small for gestational age infants (n=16). Infants with hypospadias (n=3) or an endocrine disorder (n=1) were excluded from the study. MANOEUVRE: Stretched penile length was determined by a single examiner (RT) using a standardized measure.

RESULTS

A mean penile length with associated 95% confidence intervals is described for infants between 24 and 36 weeks inclusive. The relationship between penile length (PL, cm) and gestational age (GA, weeks) was: PL=2.27+0.16 GA.

CONCLUSION

This study confirms the normal range for penile length of premature male infants 30-36 weeks and defines the normal range <30 weeks. This should prove useful to paediatricians, paediatric surgeons and endocrinologists dealing with the increasing number of surviving male infants <30 weeks in whom penile size is questioned.

The effect of testosterone on androgen receptors and human penile growth

PURPOSE

Recent rat studies suggest that early exposure to exogenous testosterone accelerates the loss of androgen receptors and compromises eventual penile length. In humans we hypothesize that down regulation of the androgen receptor is not the mechanism that stops penile growth. To test this hypothesis we investigated the effects of androgen deprivation and supplementation on the developing human penis.

MATERIALS AND METHODS

A total of 15 normal human fetal penises at 7 to 19 weeks of gestation (mean plus or minus standard deviation 12 +/- 4.5) was divided in half sagittally. Specimens were grafted beneath the renal capsule of male athymic nude mice or nude rats. Three groups of host animals were prepared, including 10 with no testosterone that were castrated at grafting, 15 with testosterone and 5 with super testosterone in which 50 mg. testosterone propionate pellets were implanted subcutaneously at grafting. Each fetal penile specimen was its own control, since half was implanted into an intact animal and the other into a castrated or super testosterone host. Six weeks after grafting the specimens were analyzed for gross size (length), histology and expression of androgen receptors.

RESULTS

All human fetal penile specimens grew from the nadir size and appeared as white exophytic growths on the surface of the host kidneys. Normal grafts were larger than castrate specimens (mean 6.9 +/- 2.1 versus 3.9 +/- 2.1 mm., p = 0.014). Mean length of the super testosterone specimens (7.3 +/- 2.3 mm.) was not significantly greater than that of normal specimens (p = 0.797). Histological analysis revealed that all specimens were composed of viable penile tissue. Cellular density of the castrate penises was approximately 2 times greater than that of the normal and super testosterone specimens (40.6 +/- 5.9 versus 25.1 +/- 2.8 cells per cm.2, p > 0.001), as calculated on enlarged micrographs. Supraphysiological doses of testosterone did not change the histology compared to controls. Immunohistochemical localization revealed androgen receptors expressed throughout the corporeal bodies, surrounding stroma and penile skin with intracellular localization to nucleus. The mean proportion of cells expressing androgen receptors was higher in the castrate (29.4 +/- 5.2 cells per cm.2) than in the normal (24.0 +/- 3.7) and super testosterone (24.7 +/- 4.5) grafts (p = 0.005). However, in regard to growth there was no change in the proportion of androgen receptor positive cells among the groups.

CONCLUSIONS

Testosterone influences penile growth, possibly as a result of extracellular stromal expansion. The number of androgen receptor positive cells in the human fetal penis did not change among the castrate, normal and super testosterone hosts. These experiments support the hypothesis that penile growth cessation is mediated by mechanisms other than down regulation of the androgen receptor. Furthermore, these data support the hypothesis that early administration of androgen to prepubertal male individuals does not result in a shorter phallus in adulthood.