Gonadotrophic hormones and testicular descent.

The effect of fetal decapitation on gubernacular development and testicular descent was studied in the pig. Gubernacular development was unaffected and testicular descent occurred normally in decapitated fetuses. Neither testicular descent nor gubernacular development could be induced by HCG or LH-RH, administered to naturally unilateral cryptorchid prepuberal pigs in doses comparable to those used in human therapy. Gubernacular development and, subsequently, testicular descent seem to be independent of gonadotrophic stimulation.     

Molecular and anatomical studies of testicular descent

The mechanism of testicular descent is multifactorial, and the process is known to occur in two steps accompanied by different anatomies and hormonal regulation. In the first step, the testis descends from the lower pole of the kidney to the pelvic cavity near the bladder neck as a result of the swelling reaction of the gubernaculum. Next, in the second step, the testis descends into the scrotum through the inguinal canal via the gubernacular migration. The first step is androgen-independent, whereas the second step depends on the androgen action. Recently, several molecular studies on testicular descent have been reported. Several factors, such as androgen, calcitonin gene-related peptide (CGRP), epidermal growth factor (EGF), Hoxa-10 and insulin-like factor 3 (INSL3) have been suggested to be possible regulators of testicular descent. Because cryptorchidism has been frequently shown in androgen-insensitive human and mice (TFM-mice), androgen has been thought to play an important role in testicular descent. CGRP, which is released from the genitofemoral nerve, has been suggested to mediate the inguinoscrotal testicular descent. The epidermal growth factor (EGF) may promote both testosterone-induced wollfian duct differentiation and testicular descent by activating the androgen responsive systems. In male mice, a targeted disruption of the HOXA 10 gene causes cryptorchidism and the cryptorchid testes in these mutant mice are located in the lower abdominal cavity, whereas the cryptorchid testes in male mice lacking the INSL3 gene or its receptor Lgr8 were located in the abdominal cavity high. Recently, estrogens or environmental endocrine disruptors have also been suspected to induce a down-regulated INSL3 expression and thus disturb testicular descent.     

Insulin-like 3 signalling in testicular descent

Undescended testis is one of the most common congenital defects in the newborn boys and the common cause of cryptorchidism. If left untreated, this condition is strongly associated with infertility and drastically increased risk of testicular cancer in adulthood. Testis position in developing males is defined by sexual dimorphic differentiation of two gonadal ligaments, gubernaculum and cranial suspensory ligament. Recent transgenic mouse studies identified testicular hormone insulin-like 3 (INSL3), and its receptor, GREAT/LGR8, as the critical regulators of the gubernacular differentiation. Mutation analysis of the two genes in patients with undescended testis revealed functionally deleterious mutations, which may be responsible for the abnormal phenotype in some of the patients.     

Crossed testicular ectopia in association with double incomplete testicular descent

Crossed testicular ectopia is a rare condition which usually presents as a hernia on the side of a fully descended testis and an impalpable testis on the contralateral side. At operation two testes are found on the side of the hernia. A case of crossed testicular ectopia where both testes had failed to reach the scrotum is described. The criteria for diagnosis of crossed testicular ectopia are listed and the appropriate management of the disorder is discussed.     

The role of the epididymis in testicular descent

In 54 patients with 70 undescended testes hospitalized for orchiopexy epididymal anatomy was examined intraoperatively. Of the testes 66 per cent had abnormal epididymides, which suggests a possibly significant role for the epididymis in the process of testicular descent.     

Endocrinological study of testicular descent in the rabbit

The process of testicular descent was investigated in the rabbit. In the rabbit, the testis descends on or about the sixth postnatal day and by 22 days of age, the testes are almost always (27 of 28 testes) found in the scrotum. The administration of 17β-estradiol (E₂) daily from Day 1 to Day 21 of age completely inhibits testicular descent ($\text{0}\text{26}$) at Day 22 of age. This inhibition of testicular descent by E₂ at Day 22 of age is completely reversible by the simultaneous treatment with 3α-androstanediol (3α-Diol) ($\text{12}\text{12}$) and only partially reversible by the simultaneous treatment with dihydrotestosterone (DHT) ($\text{12}\text{20}$) or human chorionic gonadotropin (hCG) ($\text{9}\text{18}$). Testosterone does not reverse the inhibition of testicular descent produced by E₂ ($\text{1}\text{20}$). The plasma testosterone level at Day 22 of age (600 ± 274, pg/ml ± SEM) was suppressed in the E₂-treated group (<100 pg/ml) and elevated in the group exposed to E₂ plus hCG (2367 ± 1224 pg/ml). From these data, it was concluded that in the rabbit (a) testicular descent appears to be an androgen-mediated event, (b) the active androgen involved in this event is most likely 3α-Diol or DHT, and (c) testicular descent appears to be under the regulation of the hypothalamic-pituitary-testicular axis.     

Leydig insulin-like hormone, gubernacular development and testicular descent

PURPOSE: Testicular descent is controlled by 2 morphological and hormonal steps. Transabdominal testicular descent is mediated by gubernacular swelling and regression of the cranial suspensory ligament. Müllerian inhibiting substance (MIS) has been proposed to stimulate the swelling but this remains controversial. Recently, a mouse mutant for Leydig insulin-like hormone (Insl3) was found to have undescended testis and deficient gubernaculum. We examine the testicular position of Insl3 mutant mice and the development of gubernacula. MATERIALS AND METHODS: Mice with Insl3 homozygotes (-/-), heterozygotes (+/-) and wild-types (+/+) were examined at embryonic day 16.5 and birth. Macroscopic dissections and measurements of the testicular position, as well as microscopic analysis (hematoxylin and eosin, and Masson's trichrome) were performed. RESULTS: Of the mice 11 Insl3 homozygote males had significantly impaired testicular descent at embryonic day 16.5 and birth (p <0.01), and the cord was thin and elongated, while 14 heterozygotes and 7 wild-types had normal testicular descent. Microscopically, the gubernaculum of Insl3 homozygotes was small with some muscle development but no central core of mesenchyme at embryonic day 16.5. On the other hand, heterozygotes and wild-types had normal gubernacular development with a swelling reaction. CONCLUSIONS: Insl3 mutants show feminized gubernaculum with deficient mesenchymal core. Insl3 appears to have some role in the gubernacular swelling reaction in mice.     

Testicular maldescent and infertility

Testicular maldescent is one of the causes of male infertility. This paper illustrates that it was possible to determine that this pathology was present in 8.96% of the cases in 212 men who consulted for infertility at our service during 1987. When we compared clinical, hormonal and seminal studies with infertile subjects without testicular maldescent and with a group of 20 fertile patients, statistically significant differences were established, suggesting a poorer prognosis of fertility to the group with maldescent testes.     

Hormonal regulation of testicular descent: experimental and clinical observations.

Hormonal regulation of testicular descent has been investigated. Based on experimental studies using the rat and on a review of clinical material it has been determined that testicular descent is an androgen-mediated event directly under the regulation of pituitary gonadotropin. Furthermore, the active androgenic metabolite involved in this process appears to be dihydrotestosterone, which is synthesized by the testis and must be present in high local concentrations to be effective. In addition to these hormonal requirements the anatomy of the inguinal canal must provide unimpeded migration of the testis into the scrotum. Any imbalance or anomaly of these prerequisites may lead to cryptorchidism.     

The gubernaculum during testicular descent in the pig fetus

The role of the gubernaculum during testicular descent was investigated in a study of 119 male pig fetuses obtained at gestational ages ranging from 53 to 116 days. Histologically the gubernaculum was shown to consist of primitive mesenchymal cells with an abundant intercellular material containing glycosaminoglycans (mucopolysaccharides). Rapid descent of the testis through the inguinal canal occurred between 77 and 88 days' gestation, while sustained but slower descent occurred up to 109 days. There was a dramatic increase in the total wet mass of the gubernaculum at the commencement of rapid testicular descent from 77 to 81 days, and a further increase in wet mass during sustained descent from 91 to 95 days. In the period just prior to rapid testicular descent (day 74-81) the percentage increase in the water content of the gubernaculum was larger than the percentage increase in the dry mass. After descent of the testis (day 95-109) there was a decrease in the water content, but also an increase in the dry mass of the gubernaculum. No comparable increase in the water content of umbilical cord or striated muscle tissue occurred during the period of testicular descent. Thus, the marked swelling of the gubernaculum, which dilates the inguinal canal and scrotum and may possibly exert traction on the testis by the force of its expansion, is due largely to an accumulation of water by the gubernaculum. This process may be mediated by the intercellular glycosaminoglycans, since these poly-anionic macromolecules are known to have a large hydrodynamic volume and can act as a "water trap."     

Improvement of semen quality by nocturnal scrotal cooling in oligozoospermic men with a history of testicular maldescent

For infertile men with a history of testicular maldescent only few therapeutic options exist beside assisted reproduction. The aim of our study was to evaluate the influence of nocturnal scrotal cooling on semen quality in such patients presenting with oligozoospermia. Twenty infertile men with a history of testicular maldescent and oligozoospermia were included for nocturnal scrotal cooling over 12 weeks for every night. To increase nocturnal periscrotal air circulation we used a membrane pump connected via plastic tubes to receptacles placed in both groins. Semen analysis was performed at the beginning of the cooling period and at weeks 4, 8 and 12. Another 20 infertile patients with a history of testicular maldescent and oligozoospermia were followed without specific treatment and served as a retrospectively built control group. Scrotal cooling at night by means of a perigenital air stream resulted in a scrotal temperature drop by 0.8 degrees C (median). A significant increase in sperm concentration and total sperm count was achieved by nocturnal cooling after 8 weeks (p < 0.01; p < 0.05; respectively) and 12 weeks (p < 0.01; p < 0.01; respectively). The improvement of sperm motility and sperm morphology was statistically insignificant. The present study suggests nocturnal scrotal cooling as a therapeutic option to improve semen quality. In a further controlled prospective study the influence on pregnancy rates should be evaluated.     

The role of a non-androgenic testicular factor in the process of testicular descent in the dog

Previous experiments with orchidectomized foetal and neonatal dogs have shown that the testis can induce outgrowth as well as regression of the gubernaculum testis and consequently, govern both the first and second phases of testicular descent. The aim of this study was to test whether it was possible to prevent the effects of orchidectomy on the gubernacular reaction and on epididymal migration by the administration of testosterone or by auto-transplantation of testicular tissue. In dogs, orchidectomized during foetal life and supplemented with testosterone, gubernacular regression was not completely prevented, and some descent of the remaining epididymis was obvious. However, the descent was less than in normal, intact animals. In dogs orchidectomized neonatally and supplemented with testosterone, the gubernacula showed normal regression and an almost normal descent of the epididymis. In dogs orchidectomized neonatally and supplemented with an auto-transplant of testicular tissue into to the scrotum, normal gubernacular development and normal epididymal descent were observed. We concluded that together with an unidentified non-androgenic testicular factor, testosterone from the testis appears to play a role in the outgrowth phase of the gubernaculum and consequently, in the first phase of testicular descent. In addition, testosterone was found to induce gubernacular regression in the second phase of testicular descent.     

Disturbed pituitary-testicular axis inhibits testicular descent in the prenatal rat

OBJECTIVE: To investigate whether prenatal stress affects the pituitary-testicular axis in relation to testicular descent in rat fetuses, as maternal stress can alter the plasma testosterone concentration and inhibit testicular descent in male rat fetuses. MATERIALS AND METHODS: Pregnant rats were divided into two groups and kept in reverse light-dark cycles, with lights-off at 08.00 hours and on at 20.00 hours. In group 1, 15 pregnant females were placed three times daily for 60 min each session in plastic rat-holders (13 x 6 x 8 cm) illuminated by two 150-W flood lights during the dark phase, from day 14 to 18 of gestation. In group 2, 10 pregnant females were not handled and thus were used as controls. At 19 days of gestation, five pregnant rats had a Caesarean section in each group, and both testes and the pituitary gland were removed from male fetuses at 10.00-11.00 hours. The tissue homogenates were analysed for testicular testosterone and pituitary luteinizing hormone (LH) by a radioimmunoassay. Thereafter, at 21 and 30 days of age, testicular descent was assessed in the remaining male offspring. Student's t- and the chi-square test were used to assess the results. RESULTS: The mean (sd) concentration of fetal testicular testosterone was significantly lower in group 1, at 312.9 (26.2) pg/mg, than in group 2, at 532.5 (18.2) pg/mg (P < 0.05); that of pituitary LH was also significantly lower in group 1, at 130.6 (22.7) and 295.6 (35.2) pg/mg, respectively (P < 0.05). The completion rate of testicular descent was 14% in group 1 (36 male rats) and 64% in group 2 (28 male rats) at 21 days old, and thereafter they were 81% and 100%, respectively, at 30 days old (P < 0.05). CONCLUSION: Maternal stress might inhibit the pituitary-testicular axis, thereby resulting in abnormal testicular descent in male fetuses.     

Hyperplasia and hypertrophy of the gubernaculum during testicular descent in the fetus

The role of the gubernaculum during testicular descent was investigated in 115 male pig fetuses ranging from 68 to 109 days of gestation. Descent of the testis through the inguinal canal occurred between 77 and 94 days. There was a marked increase in the total and relative wet mass as well as the wet/dry mass ratio of the gubernaculum, denoting an increase in the water content of this structure during descent of the testis. Similar changes were not seen in other fetal tissues. Asymmetrical descent of the testes occurred in seven of the 40 fetuses between 81 and 92 days of gestation. Descended testes had gubernacula with a greater relative wet mass than the gubernacula of undescended testes. These findings indicate that the increase in mass of the gubernaculum plays an important part in testicular descent. An increase in both the DNA content (hyperplasia) and the RNA/DNA ratio (hypertrophy) was noted in the gubernaculum during descent of the testis. Hyperplasia in the gubernaculum occurred at a rapid rate initially and ceased after the completion of descent. Hyperplasia was also seen in the testis and epididymis, but occurred at a slower rate initially, with a rapid acceleration after the completion of descent. Cellular hypertrophy was not noted in the testis and epididymis, but did occur in umbilical cord tissue. If gonadotropins acting via androgen secretion by the testis provide the stimulus for these changes, the observed difference in response between the gubernaculum and testis could be due to a difference in end-organ sensitivity. However, it is also possible that some unidentified non-androgenic gubernaculotropin, possibly secreted by the fetal testis, provides the stimulus for gubernacular growth.     

The gubernaculum shows rhythmic contractility and active movement during testicular descent.

Androgens are postulated to act indirectly on the gubernaculum via the genitofermoral nerve, which contains specific neuropeptide transmitters. We examined gubernacula in vitro and in vivo to see if these neuropeptides affected the gubernacular development directly. Gubernacula (n = 272) from male rats (aged 0 to 3 days) were incubated in organ culture with various different neurotransmitters. The cultures were examined daily with a dissecting microscope connected to a video camera and tape. Some rats were anaesthetized and the inguinoscrotal skin was excised to expose the gubernacula for in vivo video recording. Of 181 gubernacula treated with calcitonin gene-related peptide (CGRP) at concentrations of 7 to 714 nmol/L, 92 showed rhythmic contractions. The number of responsive gubernacula was proportional to CGRP concentrations (r = .685). This compared with 9 of 40 gubernacula treated with vasoactive intestinal peptide and 2 of 25 controls. Neither female gubernacula, skeletal muscle, nor umbilical cord showed CGRP-induced contractions. Gubernacula in vivo showed vigorous contractility and serpentine movements, which were accentuated by increased intraabdominal pressure. These studies demonstrate the gubernaculum to be highly motile during testicular descent. Rhythmic contractions suggest the presence of possible smooth muscle-like components that may be modulated by CGRP release from the genitofemoral nerve.     

Testicular feminization: a model for testicular descent in mice and men

The position of the testis was determined in patients and mice with the testicular feminization (TFM) syndrome, to answer the question, do androgens cause testicular descent? In 16 children with complete or partial TFM syndrome with androgen insensitivity, plus two children with a deficiency of androgen secretion, the testes were at or beyond the internal inguinal ring in 35 out of 36 instances. In male mice with TFM, the testes had descended normally to the internal ring by the time of birth but further descent was absent. These observations suggest testicular descent is a two-stage process comprising transabdominal and transinguinal phases. The first phase is not controlled by androgen, and hence is normal in TFM; by contrast the second phase is androgen-dependent, and absent in TFM. It is speculated that the first phase may be regulated by Müllerian Inhibiting Substance, although this is unproven. Because testicular descent in TFM can be separated into two stages, the TFM mouse should prove a useful model for studying the hormonal control of descent of the testis.     

The glycosaminoglycans of the gubernaculum during testicular descent in the fetus

Tissues were obtained from 387 male pig fetuses ranging from 60 to 120 days of gestation. The relative wet mass and water content of the gubernaculum increased during and decreased after the period of testicular descent. The extracellular glycosaminoglycans (GAG) were assayed to determine whether these polyanionic macromolecules are responsible for the increased water content of the gubernaculum. The total GAG/wet tissue mass in the gubernaculum decreased during and increased after descent, while the total GAG/dry mass decreased during and after descent, indicating an accumulation of water during descent, with a loss of water and an increase in less hydrated tissue components after descent. The major GAG fraction in the gubernaculum was dermatan sulfate, but the percentage hyaluronate in the gubernaculum was two times higher than in striated muscle or umbilical cord, indicating that this GAG fraction may be responsible for the increased water content of the gubernaculum, which probably serves to dilate the inguinal canal and scrotum, thus facilitating descent.