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Summary. Male rats, aged 19 days, were injected with 1 mg cyproterone acetate, an antiandrogen, and killed 24 h later. In 9 out of 10 experiments this increased the apparent FSH-binding capacity by testicular tissue in vitro. In 4 out of 5 similar experiments, injection of 500 μg testosterone propionate caused a significant reduction in FSH binding. Observed changes were small but this does not preclude the possibility that androgens contribute to the physiological control of FSH receptor numbers.

Summary. Testes from mice aged 3, 15, 25, 30 or 60 days were incubated under basal conditions or in the presence of hCG. One testis from each animal was incubated at 37°C while the contralateral testis was incubated at 32 or 34°C. During development total androgen production in response to hCG (at 32°C) showed a marked increase between 15 and 30 days. The major androgens secreted at this time were testosterone and 5α-androstane-3α, 17β-diol. There was little change in total androgen production between 30 and 60 days but by 60 days testosterone was the dominant androgen. Both basal and hCG-stimulated androgen production were temperature sensitive. These effects were most pronounced at 30 and 60 days with androgen production significantly inhibited at 37°C. To examine the role of testicular descent in regulating steroidogenesis animals were rendered unilaterally cryptorchid at 19 days of age. At 25 days, when descent is normally completed in the mouse, there was no significant difference in steroidogenesis between scrotal and abdominal testes. By 30 days, however, the steroidogenic potential of the abdominal testis was significantly lower than that of the scrotal testis.

These results show that testicular steroidogenesis is sensitive to temperature changes around the time of testicular descent, although descent itself is not required to achieve an adult level of steroidogenesis. The results also show, however, that testicular descent is required to maintain the adult level of steroidogenesis.

Keywords: temperature; testis; androgen; mouse; development; cyrptorchid

Summary. Hypogonadal (hpg) mice were injected once daily with 10 ng, 50 ng or 1 μg GnRH for 5,10 or 20 days or 12 times daily with 4·2 ng GnRH for 5 days. Basal and hCG-stimulated production in vitro of androstenedione, testosterone and 5α-androstane-3α,17β-diol (androstanediol) were measured by radioimmunoassay. All doses of GnRH increased testicular weight and in-vitro androgen production although seminal vesicle weights were unchanged and serum testosterone concentrations remained undetectable. After 5 days' treatment androstenedione and androstanediol were the dominant androgens produced, the latter indicating the presence of high levels of 5α-reductase. By 20 days testosterone production was predominant after treatment with higher doses of GnRH. Total androgen production (androstenedione + testosterone + androstanediol) after 5 and 10 days was similar at all concentrations of GnRH used. After 20 days' treatment total androgen production was significantly greater with 50 ng GnRH/day than with 10 or 1000 ng/day. Multiple daily injections of 4·2 ng GnRH (total dose 50 ng/day) had no greater effect on androgen production in vitro compared to single daily injections of 50 ng. This suggests that under the conditions used in this study the testis does not require pulsatile release of the gonadotrophins. The pattern of [³H]pregnenolone metabolism was measured after 5 days injection of 50 ng GnRH/day. Compared to control hpg animals there was a significant increase in formation of C₁₉ steroids, synthesis being solely through the 4-ene pathway. These results show that GnRH treatment of hpg mice will induce testicular steroidogenesis. The changes which occur after GnRH treatment show similarities to those in the normal animal around puberty.

Keywords: hypogonadal; testis; GnRH; androgen; mouse

Summary. Bovine luteal cells cultured in the presence of lipoprotein-deficient serum (LPDS) produced less progesterone than did cells cultured in the presence of complete serum and, while dibutyryl cyclic AMP (dbcAMP) caused a marked stimulation of progesterone production in complete serum, it had only a small effect in LPDS. Lowdensity lipoprotein (LDL) and high-density lipoprotein (HDL) increased basal and dbcAMP-stimulated progesterone production. Cells were 7 times more sensitive to LDL than HDL although the maximum response to both lipoproteins did not differ significantly. Inhibition of de-novo cholesterol synthesis by compactin had no effect on dbcAMP-stimulated progesterone production by cells cultured with complete serum or LPDS plus lipoproteins. Basal progesterone production in complete serum was increased by compactin and this was associated with a marked inhibition of cell proliferation, both effects being reversed by mevalonic acid. Compactin caused a 50% reduction in dbcAMP-stimulated progesterone secretion by cells cultured in LPDS. These data show that bovine luteal cells are dependent upon lipoproteins to provide substrate for progesterone synthesis and that, while LDL is the preferred lipoprotein, both LDL and HDL may be of importance in vivo.

Summary. Ovarian steroid metabolism was investigated (i) during development in a normal inbred strain in which post-natal follicle growth has been described and (ii) in adult hypogonadal (hpg) mice which lack GnRH and have very low serum concentrations of gonadotrophins. Tissue was incubated with [³H]pregnenolone or [³H]androstenedione and metabolites separated by t.l.c. or h.p.l.c. Progesterone was the major metabolite formed at all ages while androstenedione was the major androgen. Between 7 and 21 days there was an overall increase in steroidogenic enzyme activity with a peak of 5α-reductase between 21 and 29 days. The major metabolite of progesterone around puberty was 5α-pregnane-3α-ol-20-one. A sharp increase in 20α-hydroxysteroid dehydrogenase was observed after 38 days due, presumably, to the appearance of corpora lutea. Unlike the rat, androstanediol levels were low at all ages. Oestradiol was the major oestrogen formed from androstenedione with a peak of production at 38 days. In the adult hpg mouse metabolism was similar to that of the 7-day normal mouse although 17-ketosteroid reductase and aromatase levels were very low compared to normal animals of any age, indicating that gonadotrophin stimulation is involved in the expression of activity by these enzymes.

Keywords: mouse; ovary; development; steroidogenesis; hypogonadal

Leydig cells in the rat testis can be specifically ablated with ethane dimethane sulfonate (EDS) and will subsequently re-generate. In this study, we have characterized Leydig cell re-generation and expression of selected cell-signaling molecules in a germ cell-free model of EDS action. This model offers the advantage that re-generation occurs on a stable background without confounding changes from the regressing and repopulating germ cell population. Adult rats were treated with busulfan to remove the germ cell population and Leydig cells were then ablated with EDS. Testicular testosterone levels declined markedly within 24 h of EDS treatment and started to recover after 8 days. After EDS treatment there were marked declines in levels of Leydig cell-specific mRNA transcripts coding for steroidogenic enzymes cytochrome P450 11a1 (Cyp11a1), cytochrome P450 17a1 (Cyp17a1), 3β-hydroxysteroid dehydrogenase type 1 (Hsd3b1), 17β-hydroxysteroid dehydrogenase type 3 (Hsd17b3) and the LH receptor. Levels of all transcripts recovered within 20 days of EDS treatment apart from Hsd17b3, which remained undetectable up to 20 days. Immunohistochemical localization of CYP11A1 during the phase of early Leydig cell re-generation showed that the Leydig cell precursors are spindle-shaped peritubular cells. Studies on factors which may be involved in Leydig cell re-generation showed there were significant but transient increases in platelet-derived growth factor A (Pdgfa), leukemia inhibitory factor (Lif), and neurofilament heavy polypeptide (Nefh) after EDS, while desert hedgehog (Dhh) levels declined sharply but recovered by 3 days. This study shows that the Leydig cell precursors are peritubular cells and that expression of Pdgfa and Lif is increased at the start of the re-generation process when precursor proliferation is likely to be taking place.

It has been shown that testicular germ cell development is critically dependent upon somatic cell activity but, conversely, the extent to which germ cells normally regulate somatic cell function is less clear. This study was designed, therefore, to examine the effect of germ cell depletion on Sertoli cell and Leydig cell transcript levels. Mice were treated with busulphan to deplete the germ cell population and levels of mRNA transcripts encoding 26 Sertoli cell-specific proteins and 6 Leydig cell proteins were measured by real-time PCR up to 50 days after treatment. Spermatogonia were lost from the testis between 5 and 10 days after treatment, while spermatocytes were depleted after 10 days and spermatids after 20 days. By 30 days after treatment, most tubules were devoid of germ cells. Circulating FSH and intratesticular testosterone were not significantly affected by treatment. Of the 26 Sertoli cell markers tested, 13 showed no change in transcript levels after busulphan treatment, 2 showed decreased levels, 9 showed increased levels and 2 showed a biphasic response. In 60% of cases, changes in transcript levels occurred after the loss of the spermatids. Levels of mRNA transcripts encoding Leydig cell-specific products related to steroidogenesis were unaffected by treatment. Results indicate (1) that germ cells play a major and widespread role in the regulation of Sertoli cell activity, (2) most changes in transcript levels are associated with the loss of spermatids and (3) Leydig cell steroidogenesis is largely unaffected by germ cell ablation.

This study was designed to identify genes that regulate the transition from FSH- to LH-dependent development in the bovine dominant follicle (DF). Serial analysis of gene expression (SAGE) was used to compare the transcriptome of granulosa cells isolated from the most oestrogenic growing cohort follicle (COH), the newly selected DF and its largest subordinate follicle (SF) which is destined for atresia. Follicle diameter, follicular fluid oestradiol (E) and E:progesterone ratio confirmed follicle identity. Results show that there are 93 transcript species differentially expressed in DF granulosa cells, but only 8 of these encode proteins known to be involved in DF development. Most characterised transcripts upregulated in the DF are from tissue development genes that regulate cell differentiation, proliferation, apoptosis, signalling and tissue remodelling. Semiquantitative real-time PCR analysis confirmed seven genes with upregulated (P≤0.05) mRNA expression in DF compared with both COH and SF granulosa cells. Thus, the new genes identified by SAGE and real-time PCR, which show enhanced mRNA expression in the DF, may regulate proliferation (cyclin D2; CCND2), prevention of apoptosis or DNA damage (growth arrest and DNA damage-inducible, β; GADD45B), RNA synthesis (splicing factor, arginine/serine rich 9; SFRS9) and unknown processes associated with enhanced steroidogenesis (ovary-specific acidic protein; DQ004742) in granulosa cells of DF at the onset of LH-dependent development. Further studies are required to show whether the expression of identified genes is dysregulated when abnormalities occur during DF selection or subsequent development.

The adult population of Leydig cells acts to secrete testosterone which is essential for reproductive health and fertility in the adult male. However, other physiological functions of these cells are uncertain, and to address this issue a cell ablation model has been used to identify Leydig cell-specific mRNA transcripts. Ethane dimethane sulphonate (EDS) was synthesised by a novel process and was used to ablate Leydig cells in adult male rats previously treated with butane dimethane sulphonate (busulphan) to delete the germ cell population. Levels of mRNA transcripts were measured in the testis using microarrays 1, 3, 5, 8 and 12 days after EDS injection. During this period, there was a significant change in the levels of 2200 different transcripts with a marked decline in the levels of canonical Leydig cell transcripts, such as Cyp11a1, Cyp17a1 and Insl3. A total of 95 transcripts showed a similar decline in expression after EDS treatment, suggesting that they have a Leydig cell-specific origin. Analysis of selected transcripts confirmed that they were expressed specifically in Leydig cells and showed that most had a late onset of expression during adult Leydig cell development. Apart from transcripts encoding components of the steroidogenic apparatus, the most common predicted function of translated proteins was endogenous and xenotoxicant metabolism. In addition, a number of transcripts encode acute-phase proteins involved in reduction of oxidative stress. Results show that, in addition to androgen secretion, Leydig cells may have a critical role to play in protecting the testis from damage caused by toxicants or stress.

FSH and androgen act to stimulate and maintain spermatogenesis. FSH acts directly on the Sertoli cells to stimulate germ cell number and acts indirectly to increase androgen production by the Leydig cells. In order to differentiate between the direct effects of FSH on spermatogenesis and those mediated indirectly through androgen action, we have crossed hypogonadal (hpg) mice, which lack gonadotrophins, with mice lacking androgen receptors (AR) either ubiquitously (ARKO) or specifically on the Sertoli cells (SCARKO). These hpg.ARKO and hpg.SCARKO mice were treated with recombinant FSH for 7 days and testicular morphology and cell numbers were assessed. In untreated hpg and hpg.SCARKO mice, germ cell development was limited and did not progress beyond the pachytene stage. In hpg.ARKO mice, testes were smaller with fewer Sertoli cells and germ cells compared to hpg mice. Treatment with FSH had no effect on Sertoli cell number but significantly increased germ cell numbers in all groups. In hpg mice, FSH increased the numbers of spermatogonia and spermatocytes, and induced round spermatid formation. In hpg.SCARKO and hpg.ARKO mice, in contrast, only spermatogonial and spermatocyte numbers were increased with no formation of spermatids. Leydig cell numbers were increased by FSH in hpg and hpg.SCARKO mice but not in hpg.ARKO mice. Results show that in rodents 1) FSH acts to stimulate spermatogenesis through an increase in spermatogonial number and subsequent entry of these cells into meiosis, 2) FSH has no direct effect on the completion of meiosis and 3) FSH effects on Leydig cell number are mediated through interstitial ARs.