Development of the adult-type Leydig cell population in the rat is affected by neonatal thyroid hormone levels.

We have investigated the effects of neonatal-prepubertal changes in thyroid hormone levels on the early phases of adult-type Leydig cell development in the rat testis. Hypothyroidism was induced by adding 6-propyl-2-thiouracil (PTU) to the drinking water, while hyperthyroidism was induced by daily injections with triiodothyronine (T3). The proliferative activity of the Leydig cells in PTU-treated animals was not different from that in age-matched controls through the age of 16 days. Nevertheless, the percentage of Leydig cells (i.e., the proportion of Leydig cells among the total interstitial cell population) was approximately 83% and 67% lower at the ages of 12 and 16 days, respectively. The proliferative activity of the Leydig cells in the T3-treated animals compared to the controls was increased approximately 3-fold at the ages of 12 and 16 days. The percentage of Leydig cells in T3-treated animals was also considerably increased at these two ages (400% and 725%, respectively). Concomitantly, the percentage of peritubular cells was decreased, suggesting that the increase in the percentage of Leydig cells may at least partially be the result of differentiation of peritubularly located precursor cells. Plasma testosterone levels fluctuated considerably at these ages. Hence, injection of T3 during the neonatal-prepubertal period not only affects Sertoli cell proliferation and differentiation but also directly or indirectly affects the onset of the formation of the adult-type Leydig cell population and its function.

Partial synchronization of spermatogenesis in the immature Djungarian hamster, but not in the immature Wistar rat.

The frequencies of the cellular associations of the seminiferous epithelium were determined at various ages after birth in immature Djungarian hamsters and Wistar rats. The frequencies of the cellular associations present in immature animals were then compared with the frequencies of the corresponding pooled stages in adult animals. At 15 days of age, the cellular associations present in Djungarian hamsters could be divided into four groups based on the presence of A3, intermediate (In), or B (B1 and B2) spermatogonia, or preleptotene-leptotene-zygotene spermatocytes. Compared with adult animals, the group containing spermatocytes was found to be enriched by 52%, while the frequency of the B spermatogonia was reduced by 55%. At 22 days of age, the cellular associations of spermatogenesis were classified into five groups: pachytene spermatocytes associated with A3 spermatogonia. In spermatogonia, B spermatogonia, or preleptotene-leptotene-zygotene spermatocytes, or the meiotic divisions. The stages containing preleptotene-leptotene-zygotene spermatocytes and those containing A3 spermatogonia were enriched by 35% and 59% compared with adult values, respectively. The meiotic divisions were enriched by 21%, but this increase was not significant. The frequency of the B spermatogonia was reduced by 62%. In addition, the synchronization factor, calculated with the computer program SYNTEST, was increased to 1.48 +/- 0.05 (mean +/- SEM) and 1.38 +/- 0.03 at 15 and 22 days of age, respectively, and was significantly higher (P < 0.001 at both ages) than the adult value of 1.08 +/- 0.02. However, after 22 days of age the synchronization factor did not differ from that in adult animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Spermatogenesis is accelerated in the immature Djungarian and Chinese hamster and rat.

The rate of progression of spermatogenesis was studied in immature Djungarian and Chinese hamsters and Wistar rats by scoring the most advanced cell types present at various ages after birth. From 15 days of age onward, the most advanced cell types in the Djungarian hamsters were formed at a rate compatible with the duration of the spermatogenic cycle in adult animals, i.e., 7.9 days. However, in Djungarian hamsters up to 15 days of age, the rate of spermatogenic development was accelerated. The estimated duration of the spermatogenic cycle ranged between 5.0 and 5.3 days. In the rats, spermatogenesis also was accelerated during the first 15 days of life, with an estimated duration of the seminiferous cycle of 4.5-5.3 days. From 15 days of age onward, the rate of progression was strongly reduced, being compatible with the adult value of 12.8 days. In the Chinese hamsters, a similar change in the rate of spermatogenesis occurred at 25 days. Before this age, spermatogenesis proceeded with an estimated duration of the cycle of 8.8-9.2 days. From 25 days onward, spermatogenesis advanced much more slowly, at a rate compatible with the adult value of 17.0 days. Despite the strong reduction in the rate of spermatogenic progression in the three species, the cellular associations in the stages of spermatogenesis were not affected. In the three species, the clear reduction in the rate of spermatogenic progression correlated with the process of testicular descent, with the appearance of pachytene spermatocytes associated with preleptotene spermatocytes, and with the onset of tubular lumen formation.(ABSTRACT TRUNCATED AT 250 WORDS)

High neonatal triiodothyronine levels reduce the period of Sertoli cell proliferation and accelerate tubular lumen formation in the rat testis, and increase serum inhibin levels.

T3 was injected daily in newborn rats from birth to 16 days of age. Control rats received daily injections of vehicle during the same period. The proliferative activity of the Sertoli cells was studied by means of bromodeoxyuridine incorporation, and tubular lumen formation and nuclear size were taken as markers of Sertoli cell differentiation. T3 treatment strongly reduced the proliferative activity of Sertoli cells from day 7 on, and on day 12, proliferation of Sertoli cells had ceased, while in control rats proliferating Sertoli cells were observed up to day 16. As a result of the reduced Sertoli cell proliferation, the final Sertoli cell number per testis at 23 days of age was reduced by 50% from 38 +/- 1 x 10(6) in control rats to 19 +/- 1 x 10(6) in T3-treated rats. Lumen formation in seminiferous tubules of T3-treated rats began at 12 days of age, while in controls lumen formation was first observed at 16 days. The area of the Sertoli cell nuclei was somewhat larger in T3-treated rats on day 16, but not at any other age examined. Body and testis weights in adult rats at 100 days of age were reduced by 46% and 48% of control values, respectively. The high neonatal T3 levels reduced serum levels of TSH on days 7 and 9, but not at any other age examined. FSH levels were reduced in T3-injected rats on days 5 and 7 and increased on day 23, after cessation of treatment. Immunoreactive inhibin-alpha levels were increased on days 5-9 and reduced on days 16 and 23. These findings indicate that T3 stimulates the production of immunoreactive inhibin by Sertoli cells, but also of bioactive inhibin, as indicated by the reduced FSH levels. It is concluded that the levels of thyroid hormones early in life are important for the terminal differentiation of Sertoli cells and, therefore, for determining adult testis size. The data indicate that this might be a direct effect of T3 on Sertoli cells.

Cycle of the seminiferous epithelium in the Djungarian hamster (Phodopus sungorus sungorus).

In this study, spermatogenesis in the adult Djungarian hamster is described. Undifferentiated spermatogonia topographically arranged as Asingle (A(s)), Apaired (Apr), and Aaligned (Aal) spermatogonia were observed, as were six generations of differentiating spermatogonia (A1, A2, A3, intermediate, B1, and B2). The differentiating spermatogonia divided at regular intervals during the cycle of the seminiferous epithelium. Mitosis of these cells was observed at the transition from stage IX to stage X (mitosis of A1 into A2 spermatogonia), at the transition from stage XII to stage I, at the transition from stage II to stage III, at the transition from stage IV to stage V, at the end of stage VI, and at approximately the middle of stage VII. Cellular associations in the cycle of the seminiferous epithelium are described. The seminiferous epithelium was divided into 12 stages, based upon the developmental steps in spermiogenesis, and the frequency of these stages was determined. The duration of the cycle of the seminiferous epithelium, determined by [3H]thymidine incorporation, was shown to be 7.90 +/- 0.01 (mean +/- SEM) days.

Effect of prenatal and postnatal photoperiod on spermatogenic development in the Djungarian hamster (Phodopus sungorus sungorus).

The effect of the pre- and postnatal daylength on the start of spermatogenesis and further testicular development from day 4 up to day 127 was investigated in Djungarian hamsters. Hamsters were either gestated under long (16 h light:8 h dark) photoperiod and reared under long or short (4 h light:20 h dark) photoperiod after birth (L/L and L/S hamsters, respectively), or gestated under short photoperiod and transferred to long photoperiod after birth (S/L hamsters). In L/L and L/S hamsters, spermatogenesis started between day 4 and day 5 (day of birth = day 1), when the first gonocytes entered the S-phase. A, Intermediate and B spermatogonia were first observed on days 6, 8 and 9, respectively. The proliferation pattern of gonocytes and Sertoli cells, studied between day 4 and day 9, did not differ between L/L and L/S hamsters. Hence, the duration of the postnatal photoperiod had no effect on the start of spermatogenesis. The first effect of postnatal photoperiod on spermatogenic development was observed on day 15, when testis weights and tubular diameters were reduced in L/S animals. From day 22 onwards, spermatogenesis was arrested mainly at the mid-pachytene stage, no tubular lumen was formed, and the number of preleptotene spermatocytes was reduced. The ultimate number of Sertoli cells per testis was not affected by postnatal short photoperiod. The duration of the prenatal photoperiod had a clear effect on spermatogenesis after birth. In S/L hamsters, the number of gonocytes per tubular cross-section was reduced on day 4 and 4.5. Gonocyte proliferation was reduced on day 5 and spermatogenesis started one day later. Consequently, A and Intermediate spermatogonia appeared on day 7 and 9, respectively. Sertoli cell proliferation was also shifted to later ages, but the ultimate number of Sertoli cells did not differ from L/L or L/S hamsters. From day 29 onwards, the number of preleptotene spermatocytes was increased in S/L hamsters, indicating that the Sertoli cells in these animals could support more germinal cells. In conclusion, a short postnatal photoperiod does not affect spermatogenesis before day 15 after birth, when further testicular development becomes arrested. A short prenatal photoperiod delays the start of spermatogenesis by one day, alters the proliferation pattern of Sertoli cells, and from day 29 onwards, enables the Sertoli cells to support more germinal cells. The duration of the pre- and postnatal photoperiod did not affect the ultimate number of Sertoli cells.

The effect of hypothyroidism on Sertoli cell proliferation and differentiation and hormone levels during testicular development in the rat.

In this study we show that 6-propyl-2-thiouracil (PTU) treatment of Wistar rats from birth up to day 26 p.p. retards the morphological differentiation of Sertoli cells, and prolongs the proliferation of these cells up to day 30. Sertoli cell numbers per testis, determined at day 36, were increased by 84% compared to controls. PTU treatment increased serum thyroid-stimulating hormone (TSH) levels and reduced serum levels of thyroxine (T4) from 5 days onwards, indicative of severe hypothyroidism. Follicle-stimulating hormone (FSH) levels were reduced from day 5 to 9, normal at day 12 and 16, and reduced again from day 20 to 36. Inhibin levels were decreased from day 9 to 20 and increased at 36 days of age. The increase in the number of Sertoli cells per testis in PTU treated rats, as has been reported in the present study, is likely to be responsible for the increased testis size observed by other groups (1) in these animals, when adult.

Visceral-endoderm-like cell lines induce differentiation of murine P19 embryonal carcinoma cells.

When P19 embryonal carcinoma (EC) cells were cocultured with cells from one of several established visceral-endoderm-like cell lines, the EC cells were rapidly induced to aggregate and differentiate, into cell types including mesoderm-derived cardiac and skeletal muscle. Neither parietal-endoderm- nor mesoderm-like cell lines induced aggregation or differentiation of EC cells in coculture, although a cell line with both parietal and visceral endoderm characteristics induced aggregation but not differentiation. Also, without the feeder cells aggregates of P19 failed to differentiate, provided that serum in the culture medium had been previously passed over dextran-coated charcoal to remove lipophilic substances, which may include endogenous retinoids. All experiments were carried out using serum treated in this way. Taken together, the results demonstrated that aggregation was necessary, but not sufficient, to make P19 EC cells differentiate. Direct contact between the two cell types was not necessary, since even when separated by an agar layer in cocultures, aggregates of P19 still differentiated. Medium conditioned by cells of the END-2 line, a visceral-endoderm-like derivative of P19, was particularly potent in inducing endodermal and mesodermal differentiation of single P19 aggregates, confirming the involvement of a diffusible factor secreted specifically by visceral-endoderm-like cells in this process.