Reduction of long-term effects of local heating of the testis by treatment of rats with a GnRH agonist and an anti-androgen

Testicular heat stress, a historical perspective and two postulates for why male germ cells are heat sensitive

Herein, we compare the different experimental regimes used to induce testicular heat stress and summarise their impact on sperm production and male fertility. Irrespective of the protocol used, scrotal heat stress causes loss of sperm production. This is first seen 1-2 weeks post heat stress, peaking 4-5 weeks thereafter. The higher the temperature, or the longer the duration of heat, the more pronounced germ cell loss becomes, within extreme cases this leads to azoospermia. The second, and often underappreciated impact of testicular hyperthermia is the production of poor-quality spermatozoa. Typically, those cells that survive hyperthermia develop into morphologically abnormal and poorly motile spermatozoa. While both apoptotic and non-apoptotic pathways are known to contribute to hyperthermic germ cell loss, the mechanisms leading to formation of poor-quality sperm remain unclear. Mechanistically, it is unlikely that testicular hyperthermia affects messenger RNA (mRNA) abundance, as a comparison of four different mammalian studies shows no consistent single gene changes. Using available evidence, we propose two novel models to explain how testicular hyperthermia impairs sperm formation. Our first model suggests aberrant alternative splicing, while the second model proposes a loss of RNA repression. Importantly, neither model requires consistent changes in RNA species.

Amelioration of heat stress-induced damage to testes and sperm quality

Heat stress (HS) occurs when temperatures exceed a physiological range, overwhelming compensatory mechanisms. Most mammalian testes are ∼4-5 °C cooler than core body temperature. Systemic HS or localized warming of the testes affects all types of testicular cells, although germ cells are more sensitive than either Sertoli or Leydig cells. Increased testicular temperature has deleterious effects on sperm motility, morphology and fertility, with effects related to extent and duration of the increase. The major consequence of HS on testis is destruction of germ cells by apoptosis, with pachytene spermatocytes, spermatids and epididymal sperm being the most susceptible. In addition to the involvement of various transcription factors, HS triggers production of reactive oxygen species (ROS), which cause apoptosis of germ cells and DNA damage. Effects of HS on testes can be placed in three categories: testicular cells, sperm quality, and ability of sperm to fertilize oocytes and support development. Various substances have been given to animals, or added to semen, in attempts to ameliorate heat stress-induced damage to testes and sperm. They have been divided into various groups according to their composition or activity, as follows: amino acids, antibiotics, antioxidant cocktails, enzyme inhibitors, hormones, minerals, naturally produced substances, phenolic compounds, traditional herbal medicines, and vitamins. Herein, we summarized those substances according to their actions to mitigate HS' three main mechanisms: oxidative stress, germ cell apoptosis, and sperm quality deterioration and testicular damage. The most promising approaches are to use substances that overcome these mechanisms, namely reducing testicular oxidative stress, reducing or preventing apoptosis and promoting recovery of testicular tissue and restoring sperm quality. Although some of these products have considerable promise, further studies are needed to clarify their ability to preserve or restore fertility following HS; these may include more advanced sperm analysis techniques, e.g. sperm epigenome or proteome, or direct assessment of fertilization and development, including in vitro fertilization or breeding data (either natural service or artificial insemination).

Saponins derived from the stems and leaves of Panax ginseng attenuate scrotal heat-induced spermatogenic damage via inhibiting the MAPK mediated oxidative stress and apoptosis in mice

Heat stress (HS) reaction is a stress response caused by adverse conditions. Currently, the incidence of reproductive malignancies particularly in males has been constantly increasing. This work investigated the effects of saponins derived from the stems and leaves of Panax ginseng (GSLS) on testicular injury induced by scrotal hyperthermia in mice. GSLS (150, 300 mg/kg) were administered intragastrically to mice for 14 days, then exposed to a single scrotal heat treatment at 43°C for 18 min on seventh day. HS induced a significant loss of multinucleate giant cells, desquamation of germ cells in destructive seminiferous tubules. Moreover, HS reduced the serum testosterone, testicular tissue superoxide dismutase activity and glutathione (GSH) content, while significantly enhanced the production of malondialdehyde (p < .05). GSLS exhibited the protective potential against HS-induced injury not only by modulating Bcl-2 family and caspase protease family, but also by suppressing the protein levels of heme oxygenase-1 (HO-1), heat shock protein 70 (HSP70), hypoxia inducible factor-1α (HIF-1α) and activation of Mitogen-activated protein kinase (MAPK) signaling pathways (p < .05). In conclusion, we clearly demonstrated that GSLS exhibited a significant protective effect against HS-induced testicular dysfunction, mainly the inhibition of oxidative stress associated apoptosis partly via regulation of the MAPK signaling pathway.

Melatonin protects the mouse testis against heat-induced damage

Spermatogenesis, an intricate process occurring in the testis, is responsible for ongoing production of spermatozoa and thus the cornerstone of lifelong male fertility. In the testis, spermatogenesis occurs optimally at a temperature 2–4°C lower than that of the core body. Increased scrotal temperature generates testicular heat stress and later causes testicular atrophy and spermatogenic arrest, resulting in a lower sperm yield and therefore impaired male fertility. Melatonin (N-acetyl-5-methoxytryptamine), a small neuro-hormone synthesized and secreted by the pineal gland and the testis, is widely known as a potent free-radical scavenger; it has been reported that melatonin protects the testis against inflammation and reactive oxygen species generation thereby playing anti-inflammatory, -oxidative and -apoptotic roles in the testis. Nevertheless, the role of melatonin in the testicular response to heat stress has not been studied. Here, by employing a mouse model of testicular hyperthermia, we systematically investigated the testicular response to heat stress as well as the occurrence of autophagy, apoptosis and oxidative stress in the testis. Importantly, we found that pre-treatment with melatonin attenuated heat-induced apoptosis and oxidative stress in the testis. Also, post-treatment with melatonin promoted recovery of the testes from heat-induced damage, probably by maintaining the integrity of the Sertoli cell tight-junction. Thus, we for the first time provide the proof of concept that melatonin can protect the testis against heat-induced damage, supporting the potential future use of melatonin as a therapeutic drug in men for sub/infertility incurred by various testicular hyperthermia factors.

Korean Red Ginseng (Panax ginseng Meyer) with enriched Rg3 ameliorates chronic intermittent heat stress-induced testicular damage in rats via multifunctional approach

BACKGROUND

Panax ginseng Meyer, known as Korean Red Ginseng (KRG), is one of the important age-old traditional herbs used in boosting libido and improving male fertility. In this study, the effects of Rg3-enriched KRG extract (KGC04P) on heat stress-induced testicular damage in experimental rats was evaluated.

METHODS

Male rats (Sprague-Dawley) were divided into four groups (n = 10): normal control (NC), heat-stressed control (HC), heat-stressed plus KGC04P-100 mg/kg (HK100), and heat-stressed plus KGC04P-200 mg/kg (HK200) groups. Starting 1 week prior to heat stress, animals were administered orally with KGC04P (100 and 200 mg/kg) mixed with a regular pellet diet and continued for 25 weeks. Heat stress was induced to HC, HK100, and HK200 groups by intermittently exposing the animals to high temperatures (32 ± 1°C, 2 h/day). After 6 months, animals were euthanized under general anesthesia with carbon dioxide and evaluated for various parameters in serum and testicular tissue by using Western blotting, biochemical kits, and reverse transcription-polymerase chain reaction.

RESULTS

Significant (p < 0.05) alterations in several parameters, such as body/organ weight, sperm kinematics, and lipid metabolism marker levels, in the serum and testis of rats were observed. Further, the expression of testicular antioxidant enzymes, inflammatory cytokines, sex hormonal receptors, and spermatogenesis-related genes were also affected significantly (p < 0.05) in the heat-stressed group. However, KGC04P prevented the heat stress-induced changes in rats significantly (p < 0.05) at both concentrations.

CONCLUSION

KGC04P attenuated heat stress-induced testicular damage by a multifunctional approach and can be developed as an excellent therapeutic agent for hyperthermia-mediated male infertility.

Pectinase-treated Panax ginseng protects against chronic intermittent heat stress-induced testicular damage by modulating hormonal and spermatogenesis-related molecular expression in rats

Background

Elevated testicular temperature disrupts spermatogenesis and causes infertility. In the present study, the protective effect of enzymatically biotransformed Panax ginseng Meyer by pectinase (GINST) against chronic intermittent heat stress-induced testicular damage in rats was investigated.

Methods

Male Sprague–Dawley rats (4 wk old, 60–70 g) were divided into four groups: normal control (NC), heat-stress control (HC), heat-stress plus GINST-100 mg/kg (HG100), and heat-stress plus GINST-200 mg/kg (HG200) treatment groups. Each dose of GINST (100 mg/kg and 200 mg/kg) was mixed separately with a regular pellet diet and was administered orally for 24 wk. For inducing heat stress, rats in the NC group were maintained at 25°C, whereas rats in the HC, HG100, and HG200 groups were exposed to 32 ± 1°C for 2 h daily for 6 mo. At week 25, the testes and serum from each animal were analyzed for various parameters.

Results

Significant (p < 0.01) changes in the sperm kinematic values and blood chemistry panels were observed in the HC group. Furthermore, spermatogenesis-related molecules, sex hormone receptors, and selected antioxidant enzyme expression levels were also altered in the HC group compared to those in the NC group. GINST (HS100 and HS200) administration significantly (p < 0.05) restored these changes when compared with the HC group. For most of the parameters tested, the HG200 group exhibited potent effects compared with those exhibited by the HG100 group.

Conclusion

GINST may be categorized as an important medicinal herb and a potential therapeutic for the treatment of male subfertility or infertility caused by hyperthermia.

Leydig cells contribute to the inhibition of spermatogonial differentiation after irradiation of the rat

Irradiation with 6 Gy produces a complete block of spermatogonial differentiation in LBNF1 rats that would be permanent without treatment. Subsequent suppression of gonadotropins and testosterone (T) restores differentiation to the spermatocyte stage; however, this process requires 6 weeks. We evaluated the role of Leydig cells (LCs) in maintenance of the block in spermatogonial differentiation after exposure to radiation by specifically eliminating functional LCs with ethane dimethane sulfonate (EDS). EDS (but not another alkylating agent), given at 10 weeks after irradiation, induced spermatogonial differentiation in 24% of seminiferous tubules 2 weeks later. However, differentiation became blocked again at 4 weeks as LCs recovered. When EDS was followed by treatment with GnRH antagonist and flutamide, sustained spermatogonial differentiation was induced in >70% of tubules within 2 weeks. When EDS was followed by GnRH antagonist plus exogenous T, which also inhibits LC recovery but restores follicle stimulating hormone (FSH) levels, the spermatogonial differentiation was again rapid but transient. These results confirm that the factors that block spermatogonial differentiation are indirectly regulated by T, and probably FSH, and that adult and possibly immature LCs contribute to the production of such inhibitory factors. We tested whether insulin-like 3 (INSL3), a LC-produced protein whose expression correlated with the block in spermatogonial differentiation, was indeed responsible for the block by injecting synthetic INSL3 into the testes and knocking down its expression in vivo with siRNA. Neither treatment had any effect on spermatogonial differentiation. The Leydig cell products that contribute to the inhibition of spermatogonial differentiation in irradiated rats remain to be elucidated.

Electroacupuncture enhances spermatogenesis in rats after scrotal heat treatment

Spermatogenesis is regulated by a cascade of steroid regulated genes in the testis. Recent studies suggested that acupuncture may improve fertility in men with abnormal semen parameters. Yet, the underlying mechanisms in which acupuncture enhances spermatogenesis remain largely unknown. Here we used a scrotal heat-treated rat model to study the effect of electroacupuncture (EA) on recovery of spermatogenesis. In this model, spermatogenesis was disrupted by 30 min scrotal heat treatment at 43°C. Ten sessions of EA were given at Baihui (GV20), Guanyuan (CV4), Zusanli (ST36) and Sanyinjiao (SP6) from day 9 to day 36 post-treatment. Sperm motility and production, morphology of the germinal epithelium by Johnsen’s scoring, germ cell apoptosis by TUNEL staining, proliferation by proliferating cell nuclear antigen (PCNA) staining, as well as serum testosterone and inhibin B levels by immunoassays were evaluated on day 0, 1, 9, 25, 37, 46, 56 and 79. When compared with the heat-treated (H) group, the heat-treated plus EA (H⁺EA) group showed a significant increase (p < 0.05) in PCNA-positive cells and inhibin B levels on days 37 and 46, and a higher Johnsen’s score till day 56. On day 79, motile spermatozoa could be found in the vas deferens of H⁺EA group only. Consistently, there was a trend of improved motility and increased number of motile epididymal spermatozoa in the H⁺EA group than the H group; while apoptosis of germ cells and serum testosterone levels were similar between the two groups. Taken together, EA enhanced germ cell proliferation through improvement of Sertoli cell functions. This may facilitate the recovery of spermatogenesis and may restore normal semen parameters in subfertile patients.

Heat stress response of male germ cells

The vast majority of mammalian testes are located outside the body cavity for proper thermoregulation. Heat has an adverse effect on mammalian spermatogenesis and eventually leads to sub- or infertility. Recent studies have provided insights into the molecular response of male germ cells to high temperatures. Here, we review the effects of heat on male germ cells and discuss the mechanisms underlying germ cell loss and impairment. We also discuss the role of translational control in male germ cells as a potential protective mechanism against heat-induced germ cell apoptosis.

Heat stress decreases testicular germ cell proliferation and increases apoptosis in short term: an immunohistochemical and ultrastructural study

Scrotal hyperthermia has been known as a cause of male infertility but the exact mechanism leading to impaired spermatogenesis is unknown. This work was aimed to investigate the role of scrotal hyperthermia on cell proliferation and apoptosis in testes. The rats were randomly allotted into one of the four experimental groups: A (control), B (1 day after scrotal hyperthermia), C (14 days after scrotal hyperthermia), and D (35 days after scrotal hyperthermia); each group comprised 7 animals. Scrotal hyperthermia was carried out in a thermostatically controlled water bath at 43°C for 30 min once daily for 6 consecutive days. Control rats were treated in the same way, except the testes were immersed in a water bath maintained at 22°C. Hyperthermia-exposed rats were killed under 50 mg/kg ketamine anaesthesia and tissue samples were obtained for biochemical and histopathological investigations. Hyperthermia treatment significantly decreased the testicular antioxidant system, including decreases in the glutathione level, superoxide dismutase, and glutathione peroxidase activities. Moreover, exposure to hyperthermia resulted in lipid peroxidation increase in testes. Our data indicate a significant reduction in the expression of proliferating cell nuclear antigen and an enhancement in the activity of terminal deoxynucleotidyl transferase dUTP nick end labelling after scrotal hyperthermia. In scrotal hyperthermia, the mitochondrial degeneration, dilatation of smooth endoplasmic reticulum, and enlarged intercellular spaces were observed in both Sertoli and spermatid cells. Scrotal hyperthermia is one of the major factors that impair spermatogenesis in testis. This heat stress is shown to be closely associated with oxidative stress, followed by apoptosis of germ cells.

Effect of warm-rearing and heat acclimation on pituitary-gonadal axis in male rats

Plasma gonadotrophic and testicular hormones concentrations in both immature and adult male rats exposed to 34 degrees C of ambient temperature were determined. In vitro steroidogenic ability of interstitial cells from experimental rats was also studied. Four groups of rats (n = 45) were used. Warm-reared (WR) males were housed in 34 degrees C and control-reared rats in 20 degrees C from birth to adulthood. The other groups were acclimated to 34 degrees C [warm-acclimated (WA) group] or 20 degrees C [deacclimated (DA) group] as adults. Decreased body weight and testis weight (p < 0.05) was found in heat-exposed groups, but relative testis weight was unchanged in WA and increased (p < 0.05) in WR and DA males. Plasma luteinizing hormone (LH) concentration increased in WA and DA males. Increased (p < 0.05) follicle-stimulating hormone (FSH) and prolactin plasma levels were found in DA and WR groups respectively. WA males had decreased testosterone (T) and WR rats androstenedione (A(4)) plasma concentration (p < 0.05). Interstitial cells (43% of them were Leydig cells by 3beta-hydroxysteroid dehydrogenase activity) from heat-exposed males secreted less (p < 0.05) T compared with the control group when incubated without LH (basal conditions). Androstenedione secretion decreased (p < 0.05) in WA rats. Secretion of estradiol-17beta (E(2)) was higher in WR and lower in DA cells under basal conditions. Weaker responsiveness to LH was observed in WR cells. Androgen synthesis from pregnenolone by interstitial cells increased (p < 0.05) in the WA group. We concluded that heat exposure of neonatal and adult male rats caused different pituitary-testicular axis adjustments. It seemed that long-term heat exposure of neonatal rats is less deleterious concerning the activity of pituitary-testicular axis than heat acclimation of adults.

A single, mild, transient scrotal heat stress causes DNA damage, subfertility and impairs formation of blastocysts in mice

Infertility represents a major clinical problem and 50% of cases are attributable to the male partner. Testicular function is temperature dependent, and in both man and mouse the position of the testes in the scrotum ensures that they are kept at between 2 and 8 °C below core body temperature. We used a mouse model to investigate the impact of a single, transient, mild, scrotal heat stress (38, 40 or 42 °C for 30 min) on testicular function, sperm DNA integrity and embryo survival. We detected temperature-dependent changes in testicular architecture, number of apoptotic cells and a significant reduction in testis weight 7 and 14 days after heat stress at 42 °C. We report for the first time that DNA strand breaks (γ-H2AX-positive foci) were present in spermatocytes recovered from testes subjected to 40 or 42 °C. Fertility of heat-stressed males was tested 23–28 d after treatment (sperm at this time would have been spermatocytes at time of heating). Paternal heat stress at 42 °C resulted in reduced pregnancy rate, placental weight and litter size; pregnancies from the 40 °C group had increased resorptions at e14.5. Abnormalities in embryonic development were detected at e3.5 andin vitrofertilisation with sperm recovered 16 h or 23 d after scrotal stress at 42 °C revealed a block in development between the 4-cell and blastocyst stages. This study has provided evidence of temperature-dependent effects on germ cell DNA integrity and highlighted the importance of an intact paternal genome for normal embryo development.

Hormonal suppression for fertility preservation in males and females

Methods to restore fertility of men and women sterilized by medical treatments and environmental toxicant exposures are under investigation. Rendering spermatogenesis and ovarian follicular development kinetically quiescent by suppression of gonadotropins has been proposed to protect them from damage by cytotoxic therapy. Although the method fails to protect the fertility of male mice and monkeys, gonadotropin and testosterone suppression in rats before or after cytotoxic therapy do enhance the recovery of spermatogenesis. However, the mechanism involves not the induction of quiescence but rather the reversal, by suppression of testosterone, of a block in differentiation of surviving spermatogonia caused by damage to the somatic environment. In men, only one of eight clinical trials was successful in protecting or restoring spermatogenesis after cytotoxic therapy. In women, protection of primordial follicles in several species from damage by cytotoxic agents using GnRH analogs has been claimed; however, only two studies in mice appear convincing. The protection cannot involve the induction of quiescence in the already dormant primordial follicle but may involve direct effects of GnRH analogs or indirect effects of gonadotropin suppression on the whole ovary. Although numerous studies in female patients undergoing chemotherapy indicate that GnRH analogs might be protective of ovarian function, none of the studies showing protection were prospective randomized clinical trials and thus they are inconclusive. Considering interspecies differences and similarities in the gonadal sensitivity to cytotoxic agents and hormones, mechanistic studies are needed to identify the specific beneficial effects of hormonal suppression in select animal models that may be applicable to humans.

Testicular development of Zebu bulls after chronic treatment with a gonadotropin-releasing hormone agonist

The objective was to compare testis characteristics of Zebu bulls treated with the GnRH agonist, deslorelin, at different times and for different durations during their development. An additional objective was to determine the usefulness of a stain for the transcription factor GATA-binding protein 4 (GATA-4) as a specific marker for Sertoli cell nuclei in cattle. Bulls (54) were allocated to nine groups (n = 6) and received s.c. deslorelin implants as follows: G1 = from birth to 3 mo of age; G2 = from 3 to 6 mo; G3 = from 6 to 9 mo; G4 = from 9 to 12 mo; G5 = from birth to 15 mo; G6 = from 3 to 15 mo; G7 = from 6 to 15 mo; G8 = from 12 to 15 mo; and G9 (control) = no implant. Bulls were castrated at 19 mo of age. Paraffin sections (10 microm) were subjected to quantitative morphometry and GATA-4 immunohistochemistry. At castration, all bulls in the control group (6/6) had attained puberty (scrotal circumference > or = 28 cm), whereas a smaller proportion (P < 0.05) had reached puberty in G2 (2/5) and G6 (1/6). Bulls in G2 and G6 also had a lesser (P < 0.05) testis weight compared with the control group. Total volume of seminiferous epithelium and total daily sperm production in G2 and G6 were only half that observed in the control group. Spermatids were observed in less than 50% of seminiferous tubules in G2, G6, and G7 compared with 82% in the control group (P < 0.05). Staining for GATA-4 was specific for and abundant in the Sertoli cell nucleus in both pre- and postpubertal bulls, and no other cell nucleus inside the seminiferous tubule was positive for GATA-4. Total number of Sertoli cells was not affected by treatment (P = 0.45), but nuclear volume was smaller in G2 and G6 (P < 0.05) compared with the control group. In conclusion, treatment of Zebu bulls with deslorelin had no apparent beneficial effect on testis development and delayed puberty when treatment was initiated at 3 mo of age. Staining for GATA-4 was a useful method for identifying and quantifying Sertoli cell nuclei in both pre- and postpubertal bulls.

Spermatogonial differentiation in juvenile spermatogonial depletion (jsd) mice with androgen receptor or follicle-stimulating hormone mutations

The jsd mice experience a single wave of spermatogenesis, followed by an arrest of spermatogenesis because of a block in spermatogonial differentiation. Previous pharmacological and surgical studies have indicated that testosterone (T) and low scrotal temperatures but not FSH block spermatogonial differentiation in jsd mice. We sought to test these observations by genetic approaches by producing male jsd mutant mice with either defective androgen receptor (AR, Tfm mutation) or a deficiency of FSH (fshb(-/-)). In adult jsd-Tfm double-mutant mice, the tubule differentiation index was 95% compared with 14% in jsd littermates, suggesting that general ablation of AR function restored spermatogonial differentiation in jsd mice. The results indicated that this enhancement of differentiation was primarily a result of elevation of temperature caused by the cryptorchid position of the testis in jsd-Tfm double-mutant mice, which resulted from the lack of AR in the gubernaculum. The low levels of T were not a factor in the release of the spermatogonial differentiation block in the jsd-Tfm mice, but we were unable to determine whether inactivation of AR in the adult jsd testis had a direct effect on the restoration of spermatogonial differentiation because the elevated temperature bypassed the T-induced block in spermatogonial differentiation. Although spermatogonia were indeed present in adult jsd-fshb double-mutant mice and were capable of differentiation after androgen deprivation, these mice had a tubule differentiation index of 0%, ruling out the possibility that endogenous FSH inhibited spermatogonial differentiation in jsd mice. The results are consistent in support of the hypothesis that inhibition of spermatogonial differentiation in jsd mice is a result of T acting through the AR only at scrotal temperatures.

Hormones: what the testis really sees

Various barriers in the testis may prevent hormones from readily reaching the cells they are supposed to stimulate, especially the hydrophilic hormones from the pituitary. For example, LH must pass through or between the endothelial cells lining the blood vessels to reach the surface of the Leydig cells, and FSH has the additional barrier of the peritubular myoid cells before it reaches the Sertoli cells. The specialised junctions between pairs of Sertoli cells would severely restrict the passage of peptides from blood to the luminal fluid and therefore to the cells inside this barrier, such as the later spermatocytes and spermatids. There is evidence in the literature that radioactively labelled LH does not pass readily into the testis from the blood, and the concentration of native LH in the interstitial extracellular fluid surrounding the Leydig cells in rats is only about one-fifth of that in blood plasma. Furthermore, after injection with LHRH, there are large rises in LH in the blood within 15 min, at which time the Leydig cells have already responded by increasing their content of testosterone, but with no significant change in the concentration of LH in the interstitial extracellular fluid. Either the Leydig cells respond to very small changes in LH, or the testicular endothelial cells in some way mediate the response of the Leydig cells to LH, for which there is now some evidence from co-cultures of endothelial and Leydig cells. The lipophilic steroid hormones, such as testosterone, which are produced by the Leydig cells, have actions within the seminiferous tubules in the testis but also in other parts of the body. They should pass more readily through cells than the hydrophilic peptides; however, the concentration of testosterone in the fluid inside the seminiferous tubules is less than in the interstitial extracellular fluid in the testis, especially after stimulation by LH released after injection of LHRH and despite the presence inside the tubules of high concentrations of an androgen-binding protein. The concentration of testosterone in testicular venous blood does not rise to the same extent as that in the interstitial extracellular fluid, suggesting that there may also be some restriction to movement of the steroid across the endothelium. There is a very poor correlation between the concentrations of testosterone in fluids from the various compartments of the testis and in peripheral blood plasma. Determination of the testosterone concentration in the whole testis is also probably of little predictive value, because the high concentrations of lipid in the Leydig cells would tend to concentrate testosterone there, and hormones inside these cells are unlikely to have any direct effect on other cells in the testis. The best predictor of testosterone concentrations around cells in the testis is the level of testosterone in testicular venous blood, the collection of which for testosterone analysis is a reasonably simple procedure in experimental animals and should be substituted for tissue sampling. There seems to be no simple way of determining the concentrations of peptide hormones in the vicinity of the testicular cells.