Control and production of leukotriene B4 in rat tumour and testicular Leydig cells

Immunology of the Testis and Male Reproductive Tract

A large body of evidence points to the existence of a close, dynamic relationship between the immune system and the male reproductive tract, which has important implications for our understanding of both systems. The testis and the male reproductive tract provide an environment that protects the otherwise highly immunogenic spermatogenic cells and sperm from immunological attack. At the same time, secretions of the testis, including androgens, influence the development and mature functions of the immune system. Activation of the immune system has negative effects on both androgen and sperm production, so that systemic or local infection and inflammation compromise male fertility. The mechanisms underlying these interactions have begun to receive the attention from reproductive biologists and immunologists that they deserve, but many crucial details remain to be uncovered. A complete picture of male reproductive tract function and its response to toxic agents is contingent upon continued exploration of these interactions and the mechanisms involved.

Signal transduction involving cyclic AMP-dependent and cyclic AMP-independent mechanisms in the control of steroidogenesis

The control of steroidogenesis via signal transduction mechanisms involving cAMP-dependent and cAMP-independent mechanisms is reviewed. Several structurally unrelated factors that are potent stimulators of steroidogenesis whose actions do not require cAMP and/or synthesis of proteins have been identified. These include various interleukins, a lipophilic factor from macrophages, a steroidogenic inducing protein from follicular fluid and an imidazole compound, calmidazolium. All of these factors are capable of inducing maximum steroidogenesis. Calcium is required for steroidogenesis in all steroidogenic cells. With the exception of the effects of angiotensin II, there is little evidence for a role of IP3 in the stimulation of the release of calcium from intracellular stores in steroidogenic cells under physiological conditions. There may however, be a cAMP-mediated activation of a plasma membrane calcium channel. Chloride channels that can be regulated by cAMP-dependent and -independent mechanisms, are present in steroidogenic cells. Chloride ions exert a negative effect on steroidogenesis because exclusion of chloride from the extracellular medium markedly enhances cAMP-stimulated steroidogenesis. Arachidonic acid and its lipoxygenase products are involved in the control of steroidogenesis via cAMP mediated processes. An arachidonic acid related thioesterase has been isolated that is activated by ACTH and which may be involved in the release of arachidonic acid. It is concluded that while cAMP is a second messenger for LH/ACTH in the control of steroidogenesis, other signalling systems exist which are potentially equally effective in controlling steroidogenesis. In addition, the action of cAMP requires other signalling pathways involving calcium and chloride ions, as well as arachidonic acid and its lipoxygenase products.

Involvement of arachidonic acid and the lipoxygenase pathway in mediating luteinizing hormone-induced testosterone synthesis in rat Leydig cells

Evidence has been introduced linking the lipoxygenase products and steroidogenesis in Leydig cells, thereby supporting that this pathway may be a common event in the hormonal control of steroid synthesis. On the other hand, it has also been reported that lipoxygenase products of arachidonic acid (AA) may not be involved in Leydig cells steroidogenesis. In this paper, we investigated the effects of PLA2 and lipoxygenase pathway inhibitors on steroidogenesis in rat testis Leydig cells. The effects of two structurally unrelated PLA2 inhibitors (4-bromophenacyl bromide (BPB) and quinacrine) were determined. BPB blocked the LH- and Bt2cAMP-stimulated testosterone production but had no effect on 22(4)-OH-cholesterol conversion to testosterone. Quinacrine caused a dose-dependent inhibition of LH- and Bt2cAMP-induced steroidogenesis. The effects of different lipoxygenase pathway inhibitors (nordihydroguaiaretic acid (NDGA), 5,8,11,14-eicosatetraynoic acid (ETYA), caffeic acid and esculetin) have also been determined. Both NDGA and ETYA inhibited LH- and Bt2cAMP-stimulated steroid synthesis in a dose-related manner. Furthermore caffeic acid and esculetin also blocked the LH-stimulated testosterone production. Moreover, exogenous AA induced a dose-dependent increase of testosterone secretion which was inhibited by NDGA. Our results strongly support the previous concept that the lipoxygenase pathway is involved in the mechanism of action of LH on testis Leydig cells.

Arachidonic acid and its metabolites effects on testosterone production by rat Leydig cells

Arachidonic acid (AA) seems to play an important role in testicular steroidogenesis, although controversial data exist in the literature. In the present study AA induced a dose related increase of testosterone (T) formation and, at the highest dose, stimulated the production of prostaglandin E2 (PGE2), leukotrienes B4 (LTB4) and C4 (LTC4) by purified rat Leydig cells. The contemporary addition of the prostaglandin synthesis blocker, indomethacin (IND), and AA further increased T formation, decreased PGE2 levels and did not modify LTB4 and LTC4 concentrations. The addition of a lipoxygenase inhibitor, nordihydroguaiaretic acid (NDGA, 5 microM), did not influence the stimulatory effect of AA on T and PGE2 formation while it decreased the output of LTB4 and LTC4. When 20 microM NDGA was used in addition to AA the expected reduction of leukotrienes release was observed together with a surprising impairment of T and PGE2 secretion. PGE2 and PGF2 alpha did not modify basal T production but reduced HCG-stimulated T secretion at the 10 nM dose. When 5-12- and 15-HETE were tested an enhancement of basal T formation was observed at the 10nM dose. 5-HETE (10nM) stimulated HCG-induced T production. LTA4, LTB4 and LTE4 did not influence basal T output while LTC4 and LTD4 inhibited it. LTC4 (10nM) induced a decrease of HCG-stimulated T production. These findings suggest that: 1) exogenous AA stimulates T secretion; 2) conversion of AA to cycloxygenated and lipoxygenated metabolites is not required for its steroidogenic effect; 3) cycloxygenated and lipoxygenated compounds play a diverse modulatory role on testicular steroidogenesis.

Cell-cell interactions in the control of spermatogenesis as studied using Leydig cell destruction and testosterone replacement

This review centers around studies which have used ethane dimethane sulphonate (EDS) selectively to destroy all of the Leydig cells in the adult rat testis. With additional manipulations such as testosterone replacement and/or experimental induction of severe seminiferous tubule damage in EDS-injected rats, the following questions have been addressed: 1) What are the roles and relative importance of testosterone and other non-androgenic Leydig cell products in normal spermatogenesis and testicular function in general? 2) What are the factors controlling Leydig cell proliferation and maturation? 3) Is it the Leydig cells or the seminiferous tubules (or both) which control the testicular vasculature? The findings emphasize that in the normal adult rat testis there is a complex interaction between the Leydig cells, the Sertoli (and/or peritubular) cells, the germ cells, and the vasculature, and that testosterone, but not other Leydig cell products, plays a central role in many of these interactions. The Leydig cells drive spermatogenesis via the secretion of testosterone which acts on the Sertoli and/or peritubular cells to create an environment which enables normal progression of germ cells through stage VII of the spermatogenic cycle. In addition, testosterone is involved in the control of the vasculature, and hence the formation of testicular interstitial fluid, presumably again via effects on the Sertoli and/or peritubular cells. When Leydig cells regenerate and mature after their destruction by EDS, it can be shown that both the rate and the location of regenerating Leydig cells is determined by an interplay between endocrine (LH and perhaps FSH) and paracrine factors; the latter emanate from the seminiferous tubules and are determined by the germ cell complement. Taken together with other data on the paracrine control of Leydig cell testosterone secretion by the seminiferous tubules, these findings demonstrate that the functions of all of the cell types in the testis are interwoven in a highly organized manner. This has considerable implications with regard to the concentration of research effort on in vitro studies of the testis, and is discussed together with the need for a multidisciplinary approach if the complex control of spermatogenesis is ever to be properly understood.

Exogenous action of 5-lipoxygenase by its metabolites on luteinizing hormone release in rat pituitary cells

The stimulatory effect of exogenously administered potato 5-lipoxygenase (0.1-0.3 U/2 ml) on luteinizing hormone (LH) release was demonstrated in rat anterior pituitary cells in a superfusion system. Nordihydroguaiaretic acid (NDGA), an inhibitor of 5-lipoxygenase, abolished the effect of the enzyme on LH secretion. The secretory effect on LH after 5-lipoxygenase administration was biphasic and dependent on Ca2+ indicating that 5-lipoxygenase affects LH release through its oxygenation reaction. Another series of experiments demonstrated that activation of 5-lipoxygenase, expressed as production of leukotriene (LT) B4 and C4 (728 +/- 127 pg/10(6) cells and 178 +/- 23 pg/10(6) cells, respectively) occurs in rat pituitary cells after addition of Ca2+ ionophore A23187. However, LTB4 and LTC4 were not formed by pituitary cells that had previously been desensitized by gonadotropin-releasing hormone (GnRH), the physiological ligand of LH release. These results are consistent with a role of 5-lipoxygenase metabolites in the mechanism of GnRH-induced LH secretion.

Mechanism of LHRH-stimulated steroidogenesis in rat Leydig cells: lipoxygenase products of arachidonic acid may not be involved

Luteinizing hormone releasing hormone agonist, [(imBzl)-DHis6,Pro9,NEt]-LHRH (LHRH-A), caused a two to threefold increase in in vitro testosterone (T) secretion by rat Leydig cells. This LHRH-A-induced T secretion was completely blocked by quinacrine and chloroquine, inhibitors of phospholipase A2. Addition of phospholipase A2, however, was ineffective in stimulating basal or LHRH-A-induced T secretion. Phospholipase C, on the other hand, significantly stimulated both basal and LHRH-A-induced T secretion. Exogenously added arachidonic acid stimulated basal T secretion in a dose dependent manner, the maximum increase being about 100% over basal at a dose of 100 microM. Higher doses of arachidonic acid had no stimulatory effect. In the presence of LHRH-A, the stimulatory effect of arachidonic acid was additive up to a concentration of 100 microM; but higher concentrations of arachidonic acid (200 microM) were inhibitory. LHRH-A-induced steroidogenesis was inhibited by 5, 8, 11, 14 Eicosatetraynoic acid (ETYA), an inhibitor of all the three known pathways of arachidonic acid metabolism, and by nordihydroguaiaretic acid, and inhibitory of the lipoxygenase pathway of arachidonic acid metabolism. LHRH-A-stimulated T secretion was not inhibited by indomethacin, an inhibitor of the cyclo-oxygenase pathway of arachidonic acid metabolism. ETYA inhibited arachidonic acid-induced T secretion. Nordihydroguaiaretic acid, on the other hand, augmented basal, arachidonic acid-, phospholipase C-, or phorbol 12, myristate 13 acetate-induced testosterone secretion. These results suggest that arachidonic acid, whose release is influenced by phospholipase C, is involved in LHRH-A-induced T secretion by rat Leydig cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Focal disruption of spermatogenesis in the testis of adult rats after a single administration of human chorionic gonadotrophin

The effect of a single injection of 100 i.u. human chorionic gonadotrophin (hCG) upon the morphology of the rat testis was studied by light and electron-microscopy from 12-48 h after treatment. Twelve hours after injection of hCG, emigration of leukocytes occurred across the intertubular blood vessels and, both at this time and at 24 h, infiltrations of leukocytes were observed within the extracellular tissue spaces. Furthermore, 12 h after hCG, the seminiferous epithelium showed focal disruption of spermatogenesis involving germ cell degeneration and pyknosis. Focal damage to the seminiferous epithelium persisted at 24 h and 48 h after injection of hCG, the affected seminiferous tubules showing failure of spermiation, accumulation of extracellular vacuoles and degeneration or partial loss of spermatogonia and primary spermatocytes. The observations show that, after stimulation of the Leydig cells with hCG, the intertubular tissue exhibits an inflammatory-type response and this is associated with focal tissue destruction in the seminiferous tubules. It is concluded that a high dose of hCG exerts anti-spermatogenic effects upon the testis and raises the possibility of unexpected interference with tests of normal Leydig cell function in both laboratory and clinical investigations.

Assessment of the role of Leydig cell products other than testosterone in spermatogenesis and fertility in adult rats

Adult male rats were treated with ethane dimethanesulphonate (EDS) to destroy the Leydig cells and were then supplemented for 3-10 weeks with testosterone esters (TE) by injection every 3 days. The latter treatment prevented Leydig cell regeneration but maintained quantitatively the androgen-dependent aspects of spermatogenesis, as judged by germ cell counts at stage VII of the spermatogenic cycle. Other than the absence of Leydig cells, the testes of EDS-treated, TE-supplemented rats showed only two morphological changes, (1) the appearance of mast cells throughout the interstitium, and (2) a 3- to 4-fold increase in the number of degenerating germ cells (secondary spermatocytes) at stages XIV-I; this was reflected in a significant decrease in the ratio of spermatids to pachytene spermatocytes at stage VII. These changes were not observed in either oil-treated or TE-treated control rats although similar, but less marked, changes in cell degeneration at stages XIV-I were observed in rats actively immunized against oxytocin. Epididymal sperm number was reduced marginally (approximately 15%) in EDS-treated, TE-supplemented rats while sperm motility was affected even less. In a serial mating trial, some of these treated rats showed evidence of subfertility/infertility, but this was mostly transient and may have been the result of epididymal effects of EDS. These results suggest that Leydig cell products other than testosterone are not essential for maintenance of spermatogenesis and fertility in rats, although because of increased germ cell degeneration during the final stages of meiosis (perhaps as the result of oxytocin withdrawal), a small reduction in sperm count may occur.

Role of prostaglandins and leukotrienes in volume regulation by Ehrlich ascites tumor cells

PGE2 and LTC4 syntheses in Ehrlich ascites cells were measured by radioimmunoassay. Hypotonic swelling results in stimulation of the leukotriene synthesis and a concomitant reduction in the prostaglandin synthesis. If the cells have access to sufficient arachidonic acid there is a parallel increase in the synthesis of both leukotrienes and prostaglandins following hypotonic exposure. PGE2 significantly inhibits regulatory volume decrease (RVD) following hypotonic swelling in Na-containing medium but not in Na-free media, supporting the hypothesis that the effect of PGE2 is on the Na permeability. PGE2 also had no effect on RVD in Na-free media in the presence of the cation ionophore gramicidin. Since the Cl permeability becomes rate limiting for RVD in the presence of gramicidin, whereas the K permeability is rate limiting in its absence, it is concluded that PGE2 neither affects Cl nor K permeability. Addition of LTD4 accelerates RVD and since the K permeability is rate limiting for RVD this shows that LTD4 stimulates the K permeability. Inhibition of the leukotriene synthesis by nordihydroguaiaretic acid inhibits RVD even when a high K conductance has been ensured by the presence of gramicidin. It is, therefore, proposed that an increase in leukotriene synthesis after hypotonic swelling is involved also in the activation of the Cl transport pathway.

Leucocytes mediate the hCG-induced increase in testicular venular permeability

Human chorionic gonadotrophin (hCG) treatment of adult male rats induces microvascular changes in the testis consisting of abolished vasomotion, an accumulation of leucocytes in postcapillary venules and increased vascular permeability. To study the role of leucocytes, rats were made leucopenic with a specific antineutrophil serum (ANS). Testicular interstitial fluid volume was decreased in leucopenic rats. Leucopenic rats also failed to show an hCG-induced increase in venular permeability as in saline-treated rats. The normally pulsatile blood flow pattern (vasomotion) persisted in leucopenic rats but was abolished after hCG treatment both in saline-treated and leucopenic rats. Plasma testosterone concentration after hCG treatment was not affected by elimination of circulating polymorphonuclear (PMN) leucocytes. It is concluded that PMN leucocytes mediate in part the hCG-induced increase in testicular venular permeability but not the hCG-induced inhibition of vasomotion.

Sertoli-cell prostaglandin synthesis. Effects of (follitropin) differentiation and dietary vitamin E

The synthesis of prostanoids by the Sertoli cell was assessed as part of a study on the role of vitamin E in maintaining spermatogenesis. Analyses of eicosanoid synthesis from endogenous substrate were carried out using freshly isolated Sertoli-cell-enriched preparations from both pre-pubertal and adult rats fed purified diets with and without vitamin E, as well as cells carried in primary culture. Freshly isolated cells from both the immature and fully differentiated adult testes produced PGI2 (prostaglandin I2) and PGE2, but PGF2 alpha was produced only by cells of the adult vitamin E-deficient rat. Cells from adult controls synthesized PGF2 alpha after primary culture. In contrast with other hormone responses of this cell, which are refractory in the adult, FSH (follitropin) potentiated prostaglandin production by freshly isolated cells of both immature and adult rats. The FSH response of Sertoli cells from immature animals did not change after primary culture. Adult cells were refractory to the hormone after culture, but the total amounts of prostaglandins produced by these cells were 10-fold higher than by either freshly isolated or cells of the immature in culture. Analogues of cyclic AMP did not potentiate prostaglandin synthesis. However, mepacrine, a phospholipase inhibitor, blocked the FSH effect. The finding that Sertoli cells synthesize prostaglandins and FSH enhances prostaglandin production implicates a potential role for eicosanoids in spermatogenesis and suggests that vitamin E may affect intratesticular regulators.