Relationships between Leydig cell morphometry and plasma testosterone during postnatal development of the monkey, Macaca fascicularis

Histological Changes of the Testicular Interstitium during Postnatal Development in Microminipigs

Microminipigs have become an attractive animal model for the toxicology- and pharmacology-related studies because of their manageable size. In this study, the development of the testicular interstitium and steroidogenesis in microminipigs, from 0 to 12 months of age, were investigated. Testicular interstitium was mostly composed of two types of Leydig cells (large and small Leydig cells) and a few macrophages and mast cells. Large Leydig cells were observed in the peritubular area throughout all the ages. Small Leydig cells were present in the interlobular and subcapsular areas at an early age and then gradually converted into large Leydig cells. Testicular composition of the Leydig cells began to increase after 3 months of age, when spermatogenesis was completed, and reached approximately 35% at 12 months. Steroidogenic enzymes in Leydig cells were detected by immunohistochemistry from 0 month of age. Serum testosterone levels increased substantially from 1.5 to 4.5 months of age, which coincided well with the age of sexual development previously reported in microminipigs. Because the interstitial space of the testis has dramatic variations between species, the basic information obtained in the present study will be a useful reference for all the future toxicity evaluations in microminipigs.

Low testosterone in ApoE/LDL receptor double-knockout mice is associated with rarefied testicular capillaries together with fewer and smaller Leydig cells

The testis as a site for atherosclerotic changes has so far attracted little attention. We used the apolipoprotein E (ApoE)/low density lipoprotein (LDL) receptor deficient mouse model (KO) for atherosclerosis (20, 40, 60 and 87-week-old) to investigate whether Leydig cells or the capillary network are responsible for reduced serum testosterone levels previously observed in extreme ages of this model. In KO mice, overall testosterone levels were reduced whereas the adrenal gland-specific corticosterone was increased excluding a general defect of steroid hormone production. In addition to micro-CT investigations for bigger vessels, stereology revealed a reduction of capillary length, volume and surface area suggesting capillary rarefaction as a factor for diminished testosterone. Stereological analyses of interstitial cells demonstrated significantly reduced Leydig cell numbers and size. These structural changes in the testis occurred on an inflammatory background revealed by qPCR. Reduced litter size of the KO mice suggests hypo- or infertility as a consequence of the testicular defects. Our data suggest reduced testosterone levels in this atherosclerosis model might be explained by both, rarefication of the capillary network and reduced Leydig cell number and size. Thus, this study calls for specific treatment of male infertility induced by microvascular damage through hypercholesterolemia and atherosclerosis.

Time course and role of luteinizing hormone and follicle-stimulating hormone in the expansion of the Leydig cell population at the time of puberty in the rhesus monkey (Macaca mulatta)

In higher primates, development of the adult population of Leydig cells has received little attention. Here, the emergence of 3β-hydroxysteroid dehydrogenase (HSD3B) positive cells in the testis of the rhesus monkey was examined during spontaneous puberty, and correlated with S-phase labeling in the interstitium at this critical stage of development. In addition, the relative role of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in initiating the pubertal expansion of Leydig cells was studied by precociously stimulating the juvenile testis in vivo with pulsatile 11-day infusions of recombinant LH and FSH, either alone or in combination. At the time of castration, testes were immersion fixed in Bouin's, embedded in paraffin, and sectioned at 5 μm. Leydig cells/testis were enumerated using HSD3B as a Leydig cell marker. Leydig cell number per testis increased progressively during puberty to reach values in the adult approximately 10 fold greater than in early-pubertal animals. The rise in cell number was associated with an increase in nuclear diameter. That the pubertal expansion of Leydig cell number was driven primarily by the increase in LH secretion at this stage of development was suggested by the finding that precocious stimulation of mid-juvenile monkeys with LH, either alone or in combination with that of FSH, resulted in a 20-30 fold increase in the number of HSD3B-positive cells. Interestingly, precocious FSH stimulation, alone, also resulted in appearance of Leydig cells as indicated by the occasional HSD3B-positive cell in the interstitium. The nuclear diameter of these Leydig cells, however, was less than that of those generated in response to LH.

Functional assessment of sexual maturity in male macaques (Macaca fascicularis)

Selection of suitable criteria for assessing sexual maturity in the male long-tailed macaque (Macaca fascicularis) has yielded conflicting results. The present retrospective work investigates whether the sole presence of sperm in the baseline semen sample unequivocally (i.e. for every animal) hallmarks complete testicular maturation. For 956 animals providing the baseline semen sample, neither age, body weight nor testes volume unequivocally predicted the presence of sperm in that sample, and for 322 animals these parameters failed to predict testicular histology. In contrast, the presence of sperm in the baseline semen sample correlated with mature testis histology at study termination in every single animal (n=197/322). Surprisingly, for the 125/322 animals without sperm in the baseline semen sample, spermatogenesis was also mature in 95 animals. Thus, the mere provision of a semen sample without sperm--implying peripheral reproductive tract maturation--was associated with mature spermatogenesis in approx. 75% of animals. Interestingly, testicular maturation occurred approx. 2 years earlier in Mauritian compared to Asian mainland animals. In conclusion, a single semen sample that contains sperm provides unequivocal evidence for mature spermatogenesis and, thus, is suggested as a functional parameter for sexual maturity assessment in this species.

Effect of age, pubertal stage and season on testosterone concentration in male dromedary camel

The present study was conducted in the Laboratory of Animal Physiology and Biotechnology, Department of Animal Production, Faculty of Agriculture, Mansoura University, Egypt. The present investigation aimed at studying effects of ages, pubertal stages and seasons of the year on testosterone concentrations in blood plasma and tissue homogenate of the testes. The testes used in the current study were collected from a total of 104 one-humped male camels (Camelus dromedarius). Samples were taken from pre (1-3.5 years) and post (3.5-13 years) pubertal camels. Testes were studied for a two consecutive seasons. The freshly prepared homogenate of the testicular tissue and blood plasma were used for determining the concentrations of testosterone in plasma and testicular extract. The concentrations of testosterone in blood plasma and testicular tissue were significantly increased during the breeding season compared with that of non-breeding season; the concentration of testosterone was higher in testicular tissue than in blood plasma. Testosterone concentrations in plasma and testicular tissue were increased in breeding than in non-breeding season. In addition, the testosterone concentrations were closely related with seasonal changes, stage of puberty and advancing age.

Postnatal and pubertal development of the rhesus monkey (Macaca mulatta) testis

This review examines the neurobiology, endocrinology, and cell biology underlying the development of the testis from birth until puberty in the rhesus monkey, a representative higher primate.

Localization of immunoreactive testosterone and 3beta-hydroxysteroid dehydrogenase/delta5-delta4 isomerase in cynomolgus monkey (Macaca fascicularis) testes during postnatal development

The age-related expression of testosterone and 3beta-HSD in the testes of cynomolgus monkeys was detected using light-microscopic immunocytochemistry. Intense deposits of immunoreactive testosterone were labeled in parts of Leydig cells in neonatal, late infantile, pubertal, and adult testes, and only a few Leydig cells in early infantile testes. The immunoreactive 3beta-HSD was labeled in parts of Leydig cells and in all Sertoli cells in neonatal, late infantile, pubertal, and adult testes, whereas only a few Leydig cells, but no Sertoli cells, were labeled in early infantile testes. The fluctuations of testosterone and 3beta-HSD expression in testes correlated well with those already observed plasma testosterone levels during postnatal development in cynomolgus monkeys.

Blockade of the hypothalamic-pituitary-testicular axis with a GnRH antagonist in the neonatal marmoset monkey: changes in Leydig cell ultrastructure

Little is known of the cell biology of Leydig cells during the neonatal activation of the hypothalamic-pituitary-testicular (HPT) axis. The current study examined the effect of blockade of the HPT axis with a GnRH antagonist (antide) on the neonatal population of Leydig cells in the new world primate, the common marmoset. Three sets of twins, age 7 weeks, were studied: in each pair one twin was used as a control, while the other received treatment with GnRH antagonist from the day of birth to suppress pituitary gonadotrophin secretion. Leydig cells of treated animals were dramatically different from those of controls. The cells were atrophic and exhibited very irregular nuclei. The organelles involved in steroid synthesis were reduced to the extent to being barely evident. The smooth endoplasmic reticulum (SER) was greatly diminished in quantity and distribution. The usual form of the SER (anastomosing tubules) was not evident, but, instead, the SER was relatively unbranched. Peroxisomes, organelles involved in transfer of cholesterol to the mitochondria, were greatly reduced in number. Mitochondria were relatively sparse and exhibited a non-typical morphology, as tubular elements of the cristae were rarely evident. Thus, the central apparatus in steroid production, the SER, mitochondria and peroxisomes, was essentially shut down in the GnRH-antagonist-treated animals. Storage of cholesterol, the precursor of steroid biosynthesis, was also not in evidence, as lipid droplets were extremely rare. Two prominent features of control in neonatal marmoset Leydig cells, the membranofibrillar inclusion (MFI) and basal laminae, remain prominent in the Leydig cells of treated animals. Evidence of apoptosis was not observed. These results provide strong support that the gonadotrophic hormones are the primary regulator of neonatal Leydig cell development in primates, and also suggest cell regression, rather than apoptosis, being the mechanism of this inhibition.

Ultrastructure and morphometry of testicular Leydig cells and the interstitial components correlated with testosterone in aging rats

The ultrastructure of testicular interstitium in young and aged adult rats was analysed using morphometric methods, and the plasma testosterone concentration was measured. With increasing age there was an augmentation in the volume of collagen fibrils in the intercellular matrix and in blood vessels. During the aging process (approximately two years) the average volume of the Leydig cell decreased from 1364 microns 3 to 637 microns 3, but the number of Leydig cells in paired testes increased from 53 x 10(6) to 113 x 10(6). The absolute volume of smooth surfaced endoplasmic reticulum (SER) per Leydig cell amounted in aged rats to 78% of that in young adult rats. The total amount of SER in paired testes increased by 62% with aging. The present analysis suggests that the ability of SER to maintain peripheral testosterone concentration decreases with age. In young adult rats the absolute volume of peroxisomes per Leydig cell correlated significantly with the concentration of testosterone in blood and also with the absolute volume of SER per Leydig cell. These results combined with ultrastructural observations of close apposition of peroxisomes and SER suggest that peroxisomes have a role in testosterone secretion by Leydig cells.

Ultrastructural evidence of mature Leydig cells and Leydig cell regression in the neonatal human testis

The neonatal period in male development is characterized by an acute rise in serum testosterone, which peaks at 2 to 3 months of age. The purpose of this study is to examine the neonatal human testicular interstitium at 4 months for evidence of Leydig cell maturation, as well as any morphological criteria relating to the fate of Leydig cells during this period, specifically, for signs of cell regression. Leydig cells are described with impressive development of the steroid secreting apparatus, which are consistent with the mature Leydig cells found during early fetal development and in the adult. The outstanding feature of these cells is the "organelle association" of extensive, anastamosing tubules of smooth endoplasmic reticulum (SER), pleomorphic mitochondria with a component of tubular cristae, and abundant microperoxisomes associated with the SER. Well-developed Golgi elements, regionalized RER, and diverse cell inclusions are also characteristics of these cells. Reinke crystals and paracrystalline inclusions are absent. Gap junctions are common in this system and are notable in the asymmetric nature of the adjacent cytoplasmic components. These findings provide a morphologic correlate to the reported neonatal phase of testosterone production in man. Intermediate forms of Leydig cells are described with "organelle associations" including decreased SER with increased lipid droplets, and decreased SER with prominent cytoplasmic filaments and/or dramatic mitochondrial changes supportive of mitochondrial involution. Cells consistent with immature Leydig cells are also present. The rather impressive diversity in cell morphology present during this time frame of 4 months, slightly past the peak in testosterone production, provides evidence of Leydig cell regression and a continuity of the mature neonatal Leydig cells with the immature Leydig cells of childhood (Prince, 1984). There is also some evidence of cell degeneration. Although the developmental history of Leydig cells has been described for years as biphasic, it is time to view Leydig cell development in man as a triphasic event, fetal, neonatal, and pubertal.