Failure of spermatogenesis in mice lacking connexin43

Connexin43 (Cx43), a gap junction protein encoded by the Gja1 gene, is expressed in several cell types of the testis. Cx43 gap junctions couple Sertoli cells with each other, Leydig cells with each other, and spermatogonia/spermatocytes with Sertoli cells. To investigate the role of this communication pathway in spermatogenesis, we studied postnatal testis development in mice lacking Cx43. Because such mice die shortly after birth, it was necessary to graft testes from null mutant fetuses under the kidney capsules of adult males for up to 3 wk. Grafted wild-type testes were used as controls. In our initial experiments with wild-type testes, histological examination indicated that the development of grafted testes kept pace with that of nongrafted testes in terms of the onset of meiosis, but this development required the presence of the host gonads. When excised grafts were stimulated in vitro with cAMP or LH, there was no significant difference in androgen production between null mutant and wild-type testes, indicating that the absence of Cx43 had not compromised steroidogenesis. Previous research has shown that Cx43 null mutant neonates have a germ cell deficiency that arises during fetal life, and our analysis of grafted testes demonstrated that this deficiency persists postnatally, giving rise to a "Sertoli cell only" phenotype. These results indicate that intercellular communication via Cx43 channels is required for postnatal expansion of the male germ line.

CD45 modulation of CXCR1 and CXCR2 in human polymorphonuclear leukocytes

All leukocytes express the cell surface glycoprotein CD45, which has intrinsic intracellular protein tyrosine phosphatase activity. CD45 is known to play a regulatory role in activation-induced signaling in lymphocytes; however, little is known of its role in non-lymphoid leukocytes. Therefore, we examined the potential effect of CD45 on chemokine-induced signaling in human neutrophils (polymorphonuclear cells, PMN). Treating isolated PMN for 2 h with an anti-CD45RB antibody (Bra11) down-modulated expression of the chemokine receptors CXCR1 and CXCR2 to 44 +/- 10% and 47 +/- 9% of their respective controls. The tyrosine kinase inhibitors genistein and herbimycin A significantly inhibited the Bra11-induced down-modulation of CXCR1 and CXCR2. Furthermore, Bra11-treated PMN were functionally inhibited in their capacity to exhibit IL-8-induced transient intracellular Ca2+ increases. Selected targeting of CXC receptors is indicated by the fact that N-formyl-Met-Leu-Phe (fMLP) receptor expression and function were not lost following Bra11 treatment. The effect of Bra11 on IL-8-mediated function and receptor expression was paralleled by decreased tyrosine phosphorylation of a 54- to 60-kDa protein. These findings indicate that CD45 can act to modulate PMN responses to chemokines; thus agents regulating CD45 can potentially modulate leukocyte traffic and may represent a novel therapeutic approach towards the treatment of inflammatory diseases.

Nitric oxide is a mediator of the inhibitory effect of activated macrophages on production of androgen by the Leydig cell of the mouse

We hypothesized that macrophage activation results in nitric oxide (NO) production and that this NO acts directly on Leydig cells (LC) to alter androgen synthesis. Both peritoneal macrophages and a murine macrophage cell line (RAW 264.7) were activated in vitro by sequential exposure to interferon-gamma (50 U/ml) and then bacterial lipopolysaccharide (LPS; 100 ng/ml) for 24 h each. At various times after initiation of activation, selected wells were harvested for identification of messenger RNA for inducible NO synthase by RT-PCR. Amplicons of the predicted 651-bp product were isolated, cloned, and sequenced to validate the PCR procedure. Such amplicons first appeared between 2-4 h after exposure to LPS, and staining increased in intensity for the rest of the study. Nitrite accumulation followed a similar time course. Similarly treated wells were washed after 24-h activation and cocultured with purified LC for a final 24-h incubation in the absence of interferon-gamma and LPS. Basal and LH-stimulated production of androgen was estimated by RIA. In some experiments the NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester or the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (C-PTIO) was added during activation and coculture. Coculture of LC with quiescent macrophages altered neither basal nor LH-stimulated androgen production. Coculture with either type of activated macrophage did not alter basal, but significantly reduced (by 50%) LH-stimulated, androgen production. N(omega)-Nitro-L-arginine methyl ester and C-PTIO blocked the inhibitory effect. The NO donor S-nitroso-N-acetyl penicillamine at concentrations greater than 10(-5) M significantly inhibited LH-stimulated androgen production by purified LC (P < 0.01). The inhibitory effect of S-nitroso-N-acetyl penicillamine was evident when exposure exceeded 4 h. Intermediates of steroidogenesis were added to elucidate the site of NO inhibition. The enzymatic inhibition occurred at least in part at 17alpha-hydroxylase/C(17/20) lyase (P450c17). Enzyme inhibition was reversed by C-PTIO. Northern blot analysis indicated that accumulation of messenger RNA for P450c17 was not significantly altered. Therefore, activation of macrophages results in decreased androgen production by cocultured LC. The inhibition is mediated in part by macrophage-derived NO acting directly on the LC via inhibition of at least one of the P450 steroidogenic enzymes.

Neuroimmune mechanisms in health and disease: 2. Disease

In the second part of their article on the emerging field of neuroimmunology, the authors present an overview of the role of neuroimmune mechanisms in defence against infectious diseases and in immune disorders. During acute febrile illness, immune-derived cytokines initiate an acute phase response, which is characterized by fever, inactivity, fatigue, anorexia and catabolism. Profound neuroendocrine and metabolic changes take place: acute phase proteins are produced in the liver, bone marrow function and the metabolic activity of leukocytes are greatly increased, and specific immune reactivity is suppressed. Defects in regulatory processes, which are fundamental to immune disorders and inflammatory diseases, may lie in the immune system, the neuro endocrine system or both. Defects in the hypothalamus-pituitary-adrenal axis have been observed in autoimmune and rheumatic diseases, chronic inflammatory disease, chronic fatigue syndrome and fibromyalgia. Prolactin levels are often elevated in patients with systemic lupus erythematosus and other autoimmune diseases, whereas the bioactivity of prolactin is decreased in patients with rheumatoid arthritis. Levels of sex hormones and thyroid hormone are decreased during severe inflammatory disease. Defective neural regulation of inflammation likely plays a pathogenic role in allergy and asthma, in the symmetrical form of rheumatoid arthritis and in gastrointestinal inflammatory disease. A better understanding of neuroimmunoregulation holds the promise of new approaches to the treatment of immune and inflammatory diseases with the use of hormones, neurotransmitters, neuropeptides and drugs that modulate these newly recognized immune regulators.

Neuroimmune mechanisms in health and disease: 1. Health

A novel scientific discipline that examines the complex interdependence of the neural, endocrine and immune systems in health and disease has emerged in recent years. In health, the neuroimmunoregulatory network is fundamental to host defence and to the transfer of immunity to offspring; the network also plays important roles in intestinal physiology and in tissue regeneration, healing and reproduction. The proliferation of lymphocytes in primary lymphoid organs (bone marrow, bursa of Fabricius [in birds] and thymus) and in secondary lymphoid organs (spleen, lymph nodes and mucosal lymphoid tissue) depends on prolactin and growth hormone. These hormones allow immune cells to respond to antigen and to soluble mediators, called cytokines. Immune-derived cytokines are capable of inducing fever and of altering neuro-transmitter activity in the brain and hormone secretion by the pituitary gland. The activation of the hypothalamus-pituitary-adrenal axis by cytokines leads to immunosuppression. Lymphoid organs are innervated, and tissue mast cells respond to neurologic stimuli. In general, acetylcholine and substance P exert immunostimulatory and proinflammatory effects, whereas epinephrine and somatostatin are immunosuppressive and anti-inflammatory. In this article, the authors predict that novel approaches to immunomodulation will be possible by altering the level or efficacy of immunoregulatory hormones and neurotransmitters.

Relationship between decidual leukocyte infiltration and spontaneous abortion in a murine model of early fetal resorption

The relationship between the early cellular response to embryo implantation and subsequent embryo survival was explored. Immunohistochemistry using the anti-CD11b antibody (Mac-1) was used to localize and quantify maternal inflammatory cells present at the fetoplacental interface. CD 11b is expressed mostly on macrophages, but is also present on natural killer (NK) cells, neutrophils, and B cells. The occurrence of CD11b-positive cells at the fetoplacental interface was quantified in CBA/J females mated by DBA/2 males (20-30% embryo loss) and CBA/J females mated by BALB/c males (5-10% embryo loss) in order to investigate the relationship between infiltration by these types of cells and subsequent embryo loss. CD11b-positive cells were found to infiltrate decidua of each embryo starting at Day 6 of gestation. Their numbers sharply increased on Days 7 and 8, to a plateau on Days 8 to 10, well before any damage to the embryo is macroscopically visible on Days 10 to 12 of gestation. The resorption-prone mating of CBA/J female by DBA/2 male showed a significantly elevated number of CD11b-positive cells in 26% of the embryos on the eighth day of gestation compared to CBA/J female by BALB/c male matings which were taken as the reference mating. Moreover, experimental conditions modulating fetal survival in CBA/J mothers such as poly (I:C) treatment of DBA/2-mated females (lower survival) or mating with BALB/c males (higher survival than with the mating with DBA/2 males), were found to be associated with high or low numbers numbers of CD11b-positive cells at the fetoplacental interface. Furthermore, injection of anti-CD 11b into pregnant mice at Day 6 of gestation significantly reduced the subsequent incidence of resorption in the resorption prone CBA/J x DBA/2 mating. These results suggest that CD11b-positive cells are associated with the etiology of spontaneous abortion in this system.

Effects of sensory stimuli on the incidence of fetal resorption in a murine model of spontaneous abortion: the presence of an alien male and postimplantation embryo survival

Pregnancy outcome may be altered by both genetic and environmental factors. The mating of CBA/J female mice with DBA/2 males normally results in pregnancies characterized by a relatively high incidence of early embryo compared with most other syngeneic or allogeneic matings. This study addressed the role of normal laboratory stress in the induction of early embryo loss. The previously studied 'Bruce effect' describes the total loss of preimplantation embryos (pregnancy block) that is apparently caused by the stress induced by the presence of an alien male and mediated by neuroimmunological effects on prolactin activity. To determine whether this effect could be responsible for the high incidence of postimplantation embryo losses in the CBA/J x DBA/2 model, the original DBA/2 male was replaced on day 6 of gestation by another DBA/2 male, a CBA/J, a C57Bl/6 or a BALB/c male. The relatively high incidence of embryo loss was not affected by removing the original DBA/2 male or introducing another DBA/2 or a CBA/J male, indicating that stress induced by an alien male did not increase the postimplantation losses in this model. Furthermore, the introduction of a DBA/2 male to a CBA/J female that had been mated with a BALB/c male did not elicit early embryo loss. However, the replacement of the original DBA/2 male by a BALB/c male dramatically reduced the incidence of early embryo loss in pregnant CBA/J female mice. The introduction of a C57Bl/6 male also reduced embryo loss but to a lesser extent.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of the role of exogenous pathogens on the incidence of embryo loss during early pregnancy in mice

The mating of CBA/j female mice (H2k) by DBA/2j male mice (H2d) typically results in an elevated incidence of spontaneous embryo loss thus providing an ideal genetically controlled laboratory model for the study of the factors causing early embryo loss during pregnancy. There is now considerable data on the cells and factors involved in fetal resorption but little is known about the events which activate this process. While the activation of the maternal response to the fetal implant could have endogenous or genetic origins, a role for exogenous factors including microbial pathogens could also be involved. In order to investigate these possibilities, the reproductive success of CBA/j female x DBA/2j male matings in a conventional animal care facility were compared with matings in a specific pathogen free (SPF) animal facility. All animals housed under these conditions were routinely screened by immunoassay and culture, for the presence of a number of viral and bacterial pathogens of mice. The incidence of spontaneous embryo loss in specific pathogen free CBA female mice mated by DBA and other male strains was found to be virtually identical to that of CBA female mice infected with multiple viral pathogens and housed under otherwise identical conditions (non-SPF). However, the numbers of implantation per pregnancy was significantly greater in an SPF facility. Therefore, exposure of mating mice to exogenous viral and bacterial pathogens did not appear to alter the overall incidence of spontaneous embryo resorption. It was concluded that the immunomodulatory effects of infection by common murine pathogens neither augmented nor reduced post-implantation embryo losses.

Improved sensitivity of the mouse interstitial cell testosterone assay with the addition of forskolin

Modification of the mouse interstitial cell testosterone assay by the addition of 1.5 microM forskolin to the incubation medium has improved the sensitivity of this luteinizing hormone bioassay from approximately 100 to 3 pg/tube of NIH rLH RP-2. Luteinizing hormone can be clearly detected in 1 microL of serum from rats castrated 1 week previously and 5 microL of serum from intact rats. Parallelism was noted between dilution curves of serum from intact and castrated rats, and the luteinizing hormone standard curve. Luteinizing hormone detected in serum samples from 30 intact rats by the improved bioassay and by radioimmunoassay was significantly correlated (r = 0.85). Secretion patterns of circulating luteinizing hormone in individual rats were similar when detected by either bioassay or radioimmunoassay. Thus, with the addition of forskolin, the mouse interstitial cell testosterone assay has been improved so that luteinizing hormone can be detected in small volumes of serum or plasma from male rats.

An investigation of the requirement for increased LH secretion during the compensatory response in androgen secretion after unilateral castration of the adult rat

The endocrine mechanisms underlying the response to unilateral castration were examined by determining systemic androgen and luteinizing hormone (LH) concentrations, as well as testicular vein androgen at 3, 6, 12, and 24 hours after sham surgery and castration. Systemic androgen was significantly depressed 3 hours after unilateral castration, but had recovered to concentrations observed in sham operated rats at 6, 12, and 24 hours. The recovery of serum androgen after castration was apparently due to increased testicular secretion of androgen, seen as a significant increase in testicular vein androgen. Systemic concentrations of bioactive and immunoactive LH were significantly increased only at 6 hours after castration. The authors next examined whether the increase in LH was necessary for the compensatory secretion of androgen seen after castration. This was accomplished by examining the response to castration when circulating LH was prevented from changing by suppressing endogenous LH secretion with subcutaneous steroid implants and maintaining circulating LH with subcutaneous osmotic pumps containing ovine LH. The compensatory increase in testicular vein androgen was observed 1 and 7 days after castration in rats bearing sham implants. When circulating LH was prevented from changing by using the combination of steroids and LH, however, compensatory secretion of androgen did not occur 1 and 7 days after castration.(ABSTRACT TRUNCATED AT 250 WORDS)

Initial characterization of factors from testicular fluid which alter in vitro androgen secretion by normal rat Leydig cells

It is known that testicular interstitial fluid (TF) contains thermolabile factors that can alter in vitro production of androgens by the Leydig cells. The net stimulatory activity of this fluid increases in association with the disruption of spermatogenesis. The identity of the active agent(s) in TF is not known. Therefore, the authors used gel-liquid chromatography to initially characterize TF from control and bilaterally cryptorchid animals. The stimulatory activity of TF was retained on Concanavalin A Sepharose columns. Gel filtration on Ultrogel AcA 44 suggested a molecular size between 40 and 90 kD. The unfractionated fluid from control and bilaterally cryptorchid rats, as well as the chromatographic fractions containing stimulatory activity, were further resolved by SDS-PAG electrophoresis. At least three bands representing glycoproteins with apparent molecular size between 57 and 75 kD were seen in all samples containing stimulatory activity. No difference in the pattern of protein bands was seen between TF from control and bilaterally cryptorchid testes. However, samples reduced with beta-mercaptoethanol showed protein bands with apparent molecular size of 78 and 118 kD which were present only in unpurified control TF. These data support the possibility that the stimulatory substance in TF from control and bilaterally cryptorchid testes is a glycoprotein with a molecular size between 57 and 75 kD. Differences in the bioactivity of the unfractionated TF may be due in part to the presence of additional larger protein molecules in the control TF.

Plasma LH, FSH, testosterone, prolactin and androstenedione in male white-tailed deer after ACTH and dexamethasone administration

1. In order to investigate the role of the adrenocortical system in the regulation of plasma levels of reproductive hormones, adult male white-tailed deer (five intact and one castrated) from a captive herd were sedated with xylazine and ketamine and then challenged with various doses of ACTH with and without dexamethasone (DX) pretreatment. 2. Plasma levels of LH, testosterone (T), FSH, prolactin (PRL) and androstenedione (A) were determined by RIA in serial samples taken from the jugular vein. 3. An increase of A levels detected after ACTH in both intact and castrated deer indicated stimulation of secretion of adrenal androgens by ACTH. 4. No effect on FSH and PRL levels was observed in either group. 5. A significant decline of LH and T observed in various treatments could not be attributed to ACTH or DX administration. It is speculated that the decrease may be caused by anaesthetics which alleviate the stress induced in deer by the pre-immobilization activities.

Effect of a traditional Chinese herbal medicine (san zhuang wan) on the hypothalamus-pituitary-testis axis of the immature rat

San Zhuang Wan (SZW) is a traditional Chinese herbal medicine used to treat male impotence. The mechanism of its therapeutic effect is not known nor have any of its potential physiologic actions been investigated. We examined the effect of SZW administered by gavage, on the reproductive system of the prepubertal male rat. After 10 days treatment of 21-day-old rats the concentration of testosterone in serum and testicular weight had decreased whereas the serum concentration of luteinizing hormone (LH) had significantly increased. When administered to gonadectomized rats SZW partially restored the weight of the accessory sex organs and concentration of LH toward normal, but serum androgen concentration was not changed. In vitro assessment of fragments of testicular tissue or purified Leydig cells for responsiveness to maximal doses of LH or cyclic AMP showed that SZW significantly reduced testosterone secretion in response to either stimulant. The data demonstrate that SZW has potent effects on the reproductive axis of the pubertal male rat. At least one locus for such action is on the Leydig cell at a point distal to the formation of cyclic AMP. Further study is necessary to determine whether these effects could be involved with or independent of the mechanism of the therapeutic action of SZW.

Disruption of spermatogenesis is associated with decreased concentration of immunoreactive arginine vasopressin in testicular fluid

We have previously shown that testicular fluid contains factors that can inhibit luteinizing hormone (LH)-stimulated androgen production by Leydig cells, and others have reported the presence of immunoreactive vasopressin (iAVP) in the testes as well as in vitro inhibition by vasopressin of Leydig cell-androgen production. In the current report, we have used an established radioimmunoassay (RIA) to measure the concentration of iAVP in testicular fluid and have related changes in iAVP concentration to disruption of the seminiferous tubules. Spermatogenesis was disrupted in adult rats by surgically establishing bilateral cryptorchidism. The concentration of iAVP decreased progressively from 349 +/- 52 to 61 +/- 5 pg/ml during 4 wk. When cryptorchidism was unilaterally established, the concentration of iAVP in fluid from that testis decreased to 116 +/- 19 pg/ml while the concentration of iAVP in the contralateral scrotal testis remained unaffected. Unilateral ligation of the ductuli efferentes also caused an equivalent unilateral decrease in iAVP to 110 +/- 15 pg/ml. The osmotic pressure of the testicular fluid was not altered by disruption of gametogenesis, and the extracellular "albumin space" was not increased. Therefore, the decrease in concentration of iAVP was probably not due to dilution with increased amounts of interstitial fluid. We conclude that the disruption of spermatogenesis is associated with a decrease in the concentration of iAVP in testicular fluid and suggest that AVP or a similar peptide may be involved in the intratesticular mechanisms associated with increased production of androgen by Leydig cells after disruption of spermatogenesis.

The effect of spermatogenic disruption on the ability of testicular fluid to stimulate androgen production by normal Leydig cells

Reports from this and other laboratories have concluded that unilateral disruption of spermatogenesis induces a predominantly ipsilateral increase in the responsiveness of Leydig cells to stimulation with luteinizing hormone (LH) and have suggested that if such effects were mediated by locally produced hormones then such "factors" should be detectable in testicular interstitial fluid. We sought to demonstrate such factors in testicular fluid from gonads subjected to a variety of treatments that disrupt gametogenesis. Fluid (TF) was drained from testes of adult rats that had been sham treated, irradiated, or treated with busulfan in utero, made unilaterally or bilaterally cryptorchid, or were unilaterally or bilaterally efferent-duct-ligated. Leydig cells obtained from normal rats basally produced 8 +/- 1 ng androgen/10(6) Leydig cells/2 h and, when maximally stimulated with LH, produced 66 +/- 3 ng. The addition of the various TFs to the incubations significantly increased both basal and LH-stimulated androgen production. TF from lesioned testes was more effective in increasing androgen production than TF from control rats. Unilateral lesions caused an increase in the ability of TF from the disrupted testes to increase the androgen production by normal Leydig cells, as compared to TF from contralateral testes. Thus, locally produced "factor(s)" do appear to modify Leydig cell function. Additional studies using TF from control and bilaterally cryptorchid animals suggest that the ""factor'' in TF is heat-labile; has a molecular size between bovine serum albumin and ovalbumin; exerts a portion of its action independently of cAMP formation; and does not appear to be LH, follicle-stimulating hormone, prolactin, or gonadotropin-releasing hormone.

The role of androstenedione and testosterone in the reproduction and antler growth of a male white-tailed deer

Seasonal levels of androstenedione and testosterone were investigated in plasma of mature intact and castrated male white-tailed deer. In four intact bucks, androstenedione concentrations were low in February and March (around 1 nmol/l) and then increased significantly (P less than 0.05) from April to November (peak 2.34 nmol/l). Testosterone remained low (below 3.5 nmol/l) from February to August and then rose significantly (P less than 0.01) till November (peak 36.78 nmol/l). Both hormones declined from November to February. In three castrates, androstenedione levels remained virtually unchanged (averaging around 0.5 nmol/l) between January and September. After a rapid significant increase (P less than 0.05) till November (peak value 2.45 nmol/l), androstenedione concentrations declined quickly to a baseline level. Testosterone in castrates remained around 0.3 to 0.7 nmol/l for most of the year with a non-significant peak (1.45 nmol/l) in October. These data indicate that the spring and summer increase in androstenedione in the intact deer is of testicular origin; the fall peak, however, may be a result of increased production in the adrenal glands. It can be speculated that the increase in androstenedione in the blood of the male deer during the spring may be responsible for the seasonal initiation and support of antler growth as well as being supportive to the re-activation of the reproductive system.

A comparison of Leydig cell function after unilateral and bilateral cryptorchidism and efferent-duct-ligation

Surgical induction of cryptorchidism or ligation of the efferent ducts disrupts spermatogenesis. The response of Leydig cells to disrupted gametogenesis was studied in vitro in tissue and collagenase dispersed Leydig cells obtained from the testes of rats that were made unilaterally or bilaterally cryptorchid or had been efferent-duct-ligated. Four wks after surgery, androgen secretion per mg of tissue or per Leydig cell in response to maximal luteinizing hormone (LH) stimulation was greater in tissue from damaged than from sham-operated testes. It was concluded that disruption of spermatogenesis resulted in Leydig cells that were hyperresponsive to LH stimulation in vitro. Unilateral lesions produced different responsiveness of Leydig cells from the testes ipsilateral and contralateral to the lesion, supporting the hypothesis that intragonadal modulation of Leydig cells function occurs when the function of seminiferous tubules is impaired. Stimulated androgen production of Leydig cells from the contralateral nonligated testis did not differ from that of the sham-operated controls. With unilateral cryptorchidism, which is accompanied by an increase in the temperature of the operated testis, Leydig cells from the scrotal testis were also hyperresponsive compared to those from sham-operated controls. This suggests a possible intergonadal influence of aspermatogenesis caused by cryptorchidism.

Characteristics of pulsatile luteinizing hormone secretion in middle-aged ovariectomized rats

Experiments were performed to characterize the pulsatile patterns of circulating luteinizing hormone (LH) in the middle-aged ovariectomized (OVX) rat. Frequent blood samples were taken from OVX rats at 6, 7-8, and 9-10 mo of age, and LH was measured by radioimmunoassay. Rats had been OVX either 2 wk (STO) or 10-20 wk (LTO) previously. Mean LH levels were significantly lower with increasing age, reflecting effects on both pulse amplitude and pulse frequency. Mean LH levels were higher in LTO than STO groups, reflecting primarily an increase in pulse amplitude, but there was also a small, significant decrease in pulse frequency with increased time following OVX. In a second experiment, a random selection of the rats in the STO groups was tested again 10 wk after OVX. A significantly higher number of 9- to 10-mo-old rats had pulsatile patterns at 10 wk than at 2 wk following OVX. Furthermore, mean plasma LH concentrations were higher in all three groups. We conclude that decreases in several parameters of LH secretion are seen in middle-aged OVX rats, at the time when irregularities are first seen in the estrous cycle in the intact rat.

The effect of prenatal treatment with busulfan on in vitro androgen production by testes from rats of various ages

Treatment of rats with busulfan in utero severely depletes the germ cell population of the seminiferous tubules. These studies have examined the in vitro capacity of testicular tissue and Leydig cells from such testes to secrete androgens. Leydig cells were identified by staining for 3 beta-hydroxy steroid dehydrogenase. Rats were studied at several ages to identify any developmental changes in the androgen-secreting capacity of control and treated gonads. At 30 days of age, no effect of treatment on serum androgen was found. At 60 and 90 days of age, treatment caused decreased androgen and increased LH content of the serum. At 12, 30, 60, and 90 days of age, the amount of androgen secreted per milligram of testicular tissue in response to LH was higher in busulfan-treated rats. Leydig cells from 60- and 90-day-old rats which had received busulfan were also hyperresponsive to LH. It was concluded that Leydig cells from testes essentially devoid of germ cells were hyperresponsive to LH. Serum androgen levels were decreased yet androgen production per Leydig cell was increased. A possible explanation of this apparent paradox is that busulfan treatment resulted in decreased numbers of Leydig cells in the gonads.

Fetal irradiation increases androgen production by dispersed leydig cells of the rat

Damage to the seminiferous epithelium of the rat has been shown to decrease the concentration of serum testosterone. In these animals, compared to controls, the structure of the Leydig cells suggests hyperactivity. In an attempt to understand the functional changes at the Leydig cell level, we measured in vitro androgen production by whole testes, testicular fragments, and Leydig cell preparations. The androgen production of adult rats that had received 1.6 Gy of gamma radiation on day 20 of gestation was compared to that of nonirradiated controls. Leydig cells obtained from fetally-irradiated adult rats demonstrated increased basal (1.3 X) and LH-stimulated (4.4 X) testosterone production and increased hCG binding (4.8 X) per histochemically identified Leydig cell, as compared to cells obtained from nonirradiated control animals. Although the irradiated testicular tissue showed an increased responsiveness per mg/tissue compared to controls, basal and stimulated in vitro testosterone production per irradiated testis calculated from this data was diminished because of the five-fold decrease in testis size. In addition, the circulating levels of testosterone were reduced in irradiated animals. We suggest that fetal irradiation is associated with an increase of hCG binding and testosterone production per Leydig cell, and a decrease in the number of these Leydig cells per testis.

Developmental change in the ability of estradiol to suppress testosterone secretion by the testis of the rat

An intratesticular site of action has been proposed for the ability of estradiol (E2) to suppress testosterone secretion. Because testicular testosterone and E2 secretion as well as E2 receptors change during development, a physiologic role for E2 is possible. The present experiments compared the testes from 12-day-old and adult rats for the capacity of in vivo estradiol treatment to change in vitro androgen secretion in response to luteinizing hormone (LH) and dibutyryl cyclic AMP (Bt2cAMP). After 5 days in vivo treatment, in vitro responsiveness was estimated by radioimmunoassay (RIA) measurement of androgen secretion elicited by various doses of NIAMDD-LH-24 or 1.0 mM Bt2cAMP. Five days of E2 alone (500 ng/g BW s.c. once daily) markedly inhibited basal, LH-stimulated and Bt2cAMP-stimulated androgen production at both ages. Similar treatment of infant rats with LH (100 ng NIAMDD-LH-24/g BW) caused an increase in basal and LH-stimulated androgen secretion in vitro, but had no effect on the response to Bt2cAMP. The same pretreatment of adults with LH had no effect on basal, but inhibited LH- or Bt2cAMP-stimulated androgen secretion. Combined treatment of infants with E2 and LH for 5 days had no effect on basal or maximally stimulated androgen production; the in vitro response to submaximal stimulation with LH was significantly inhibited. Combined E2/LH treatment of adults significantly decreased the basal production of androgens and the response to LH or Bt2cAMP. These results suggest a major difference between the response to E2 of the Leydig cells from the rats of the two ages tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms involved in the ability of human chorionic gonadotropin to increase the responsiveness of the infant rat's testis to follicle-stimulating hormone

Pretreatment of 9-day-old rats for 3 days with human chorionic gonadotropin (hCG) increases the amount of estradiol secreted by the testis in response to in vivo or in vitro stimulation with follicle-stimulating hormone (FSH). Potential mechanisms for this sensitizing effect were studied by treating infant rats with a variety of agents and then using radioimmunoassay to determine testicular estradiol secretion. Substitution of 3 days priming with estradiol for hCG did not enhance subsequent in vitro responsiveness to FSH. Subcutaneous capsules of 1,4,6-androstatriene-3,17-dione (ATD) blocked stimulation of testicular aromatization in vivo by hCG or FSH. ATD capsules alone, or when combined with the antiestrogen tamoxifen, were not able to alter the ability of hCG pretreatment to increase responsiveness to in vitro FSH. It was concluded that estradiol was not involved in the sensitization caused by hCG in this model system. When gonadal tissue from 12-day-old rats was incubated in the presence or absence of 0.6 microM testosterone and various concentrations of FSH, more estradiol was secreted by testes in the containing testosterone. The amount secreted was not different from that noted after hCG priming. Priming of 9-day-old rats for 3 days with the nonaromatizable androgen 5 alpha-dihydrotestosterone did not influence the amount of estradiol secreted in response to FSH. It is further concluded that hCG augments the testicular aromatization response of infant rats to FSH by providing additional substrate for these reactions.

Interactions of follicle-stimulating hormone and luteinizing hormone in controlling estradiol synthesis by the testis of the infant rat

Experiments were conducted to assess the relative contribution of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) to the regulation of estradiol secretion by the testis of the 12-day-old rat. In an in vivo model system, stimulation of the whole testis with NIH-FSH-S13 (5% LH activity) caused an 8-fold increase in testosterone secretion within 1 h followed by a 5-fold increase in estradiol secretion. Qualitatively, similar findings were obtained from whole testes incubated in tissue culture medium 199. The in vitro system was used to further examine the response of the testes to LH and FSH. Testes exposed to a variety of doses of LH or 10 ng/ml of highly purified FSH (3 X 13, 1% LH activity) showed no change in estradiol secretion. However, a synergistic effect was observed when purified FSH and LH were combined, provided the LH concentration exceeded 25 pg/ml. It is suggested that FSH secretion in infant rats maintains the aromatizing capacity of the seminiferous tubule at a level such that availability of aromatizable substrate becomes a major factor in the rate of tubular estrogen formation.

Control of estrogen synthesis in the testis of the infant rat by FSH and androgen

The experiments studied the ability of androgens to stimulate in vivo the production of estradiol by the testes of the 12-day-old rat as well as interactions between FSH and androgens in this regard. The content of testosterone and estradiol in the testes was measured by RIA of methanolic extracts which were purified on columns of Sephadex LH-20. It was found that androstenedione, testosterone and 19-hydroxytestosterone were able to stimulate estradiol formation in the testes; the response was optimal 3 h after s.c. injection. The stimulatory effect was absent after injection of 5 alpha-reduced androgens. It was concluded that the ability of a single injection of androgen to increase the content of estradiol in the testes was due to provision of additional substrate for aromatization by the Sertoli and/or Leydig cells. Priming of rats for 2 days with testosterone (60 microgram/g bw daily) resulted in a reduction of concentration of LH and FSH in plasma and was associated with an inhibition of the estradiol response to a subsequent injection of testosterone. If priming with testosterone was followed by an injection of FSH, more estradiol was formed than when the FSH injection was preceded by an oil or dihydrotestosterone priming regimen. It was concluded that the inhibition of testosterone-induced aromatization noted after testosterone priming was due to low gonadotropin secretion rather than a direct effect on the testis and that priming of the infant rat with androgen enhanced the response to FSH because such treatment provided additional substrate for aromatization.

Effect of porcine follicular fluid injection on FSH secretion in the immature female rat

Porcine ovarian follicular fluid (pFF) contains a substance capable of selectively suppressing FSH secretion in adult rats. The effectiveness of this material in prepubertal female rats was examined. Steroids were removed from pFF or pig serum by adsorption to charcoal. Twenty-four hours after sham or bilateral ovariectomy, at 17 days of age, the rats received an intraperitoneal injection of 0.4 ml charcoal-extracted pFF or serum. Eight hours after injection animals were killed by cervical dislocation and blood collected. Serum estrogen and FSH concentrations were estimated by radioimmunoassay. Ovariectomy reduced total serum estradiol from 181 ± 25 to 77 ± 18 pg/ml (mean ± SEM) and pFF had no effect on this response. Ovariectomy caused an increase of serum FSH from 1275 ± 239 to 2392 ± 122 ng FSH (RP – 1)/ml in control and gonadectomized rats, respectively. Post-ovariectomy hypersecretion of FSH was completely Mocked when animals were treated with pFF. in sham-ovariectomized animais pFF was unable to suppress FSH secretion. These results support the notion that the relatively high levels of FSH found in intact female rats of this age might be explained in part by a low responsiveness to the inhibin-like component of follicular fluid.

Plasma luteinizing hormone and testosterone in the adult male pig: 24 hour fluctuations and the effect of copulation

Secretory patterns of LH and testosterone were characterized in the intact male miniature pig. All blood samples were taken from indwelling catheters. Hourly sampling was carried out over 24 h and during a morning period blood was collected for 2 h at 10 min intervals. No significant difference was detected in the plasma LH concentration on the basis of hourly sampling. Plasma testosterone was significantly (P less than 0-05) lower during the evening and night when compared with morning values. The second experiment was concerned with the pattern of plasma LH and testosterone concentrations before and after copulation. Blood sampling was performed at 10 min intervals. Plasma LH was significantly (P less than 0-001) raised for 30 min after copulation when compared with any 30 min period (0-120 min) before copulation. Plasma testosterone was not significantly altered for any 30 min period of the experiment (0-270 min). The data are interpreted as a possible mechanism for endocrine control of testicular function.

Androgen level in the sheep fetus during gestation

The androgen content of amniotic fluid, plasma, and gonads from 107 fetal lambs was determined by radioimmunoassay in an attempt to understand the ontogeny of gonadal function. Testosterone (T) was too low to be reliably measured in the amniotic fluid from fetuses of either sex. Ovaries were without T activity at any of the stages of gestation studied. Testicular T-5alpha-dihydrotestosterone (T-DHT) concentration steadily decreased from 1.4/ml near term. It is suggested that nongonadal testosterone production increases during fetal life and that T secretion by the fetal testis may contribute steadily less to the plasma pool of T as gestation proceeds.

Effects of estradiol-17beta on LH-RH/FSH-RH-induced, and spontaneous, LH release in prepubertal female pigs

The effect of estrogen (E2) on pituitary response to LH-RH/FSH-RH (LH-RH) was examined in immature female pigs (gilts). Eight gilts (9-10 weeks old) received iv injections of 2.5, 5.0, 10.0, 20.0, and 40.0 mug LH-RH, beginning 4 days after placement of indwelling jugular cannulae. Blood samples were drawn at 5-min intervals following LH-RH injection and plasma LH was determined by RIA and expressed as ng R786-3/ml. Pituitary responses were expressed as the increment in LH levels above baseline (delta LH). Pretreatment LH levels were 0.45-1.25 ng/ml. Responses to LH-RH (delta LH plus or minus SE) ranged from 3.7 plus or minus 0.6 (at 5 min) to 8.4 plus or minus 1.4 ng/ml (at 20 min) for 2.5 and 40 mug doses, respectively. Three additional prepubertal gilts were cannulated and implanted with E2. After 3 days plasma estrogens rose from approximately 30 pg/ml to 289 plus or minus 34 pg/ml and the dose-response studies were repeated. Prestimulation LH concentration was consistently below 0.4 ng/ml and delta LH levels ranged from 1.4 plus or minus 0.5 (at 10 min) to 5.7 plus or minus 1.3 ng/ml (at 20 min) for the 2.5 and 40.0 mug doses, respectively. Analysis of the regression equations for delta LH on log LH-RH dose showed that the adjusted means for LH response were significantly lower (P less than 0.02) in E2 implanted animals. However, the regression coefficients were not different (P greater than 0.5). On the basis of these and other analyses, it is concluded that chronic E2 treatment depresses both basal LH secretion and pituitary responsiveness, but that pituitary sensitivity to LH-RH is not modified. Several nonimplanted females showed bursts of LH release subsequent to the LH-RH induced peak, but multiple peaks were never observed in E2 implanted gilts. An explanation was sought and 7 of the nonimplanted gilts were used to study spontaneous LH release by determining plasma LH at 10-min intervals for 20 h. During this period spontaneous episodes of LH release were observed in control animals with a mean frequency of 1.3 LH peaks/h. When 4 animals were given 5 mug E2 iv and then sampled for 12 h, episodic secretion was suppressed and the latency to the first spontaneous LH release was 9.6 plus or minus 0.8 h, significantly greater (P less than 0.02) than the latency to the first peak after saline injections (4.2 plus or minus 1.5 h) in the controls. It is suggested that "multiple" LH peaks occurring after initial LH-RH stimulation may represent the superimposition of spontaneous episodic release upon the induced response.

Acute and chronic estradiol-17beta inhibition of LH release in prepubertal female pigs: time course and site of action

It has been demonstrated that 5.0 mug estradiol-17beta (E2) iv inhibits spontaneous episodic release (SER) of LH from 3-9 h after injection in immature female pigs (gilts). To understand this phenomenon we tested pituitary response (PR) to synthetic LH-RH/FSH-RH (LH-RH) for 13 h after identical E2 treatment in eight 7-8-week-old gilts. Using chronic cannulae PR was determined by measuring the change in plasma LH (delta LH) by RIA after iv injection of 2.0 mug LH-RH. PR was determined every 2 h starting 1 or 2 h before E2 or saline treatments. The PR prior to treatment was 4.3 plus or minus 0.3 ng/ml. By the second releasing-hormone challenge PR in controls was depressed, remaining at about 2.5 ng/ml thereafter. Compared with controls PR depression was greater (P less than 0.005) 1 h following E2 (delta LH = 1.0 plus or minus 0.4 ng/ml). Responsiveness then returned toward pretreatment levels and from 6 h post-treatment onward PR was not different from controls. Initial inhibition of SER may therefore be located in the pituitary and brain. However, after 4 h inhibition appears to be purely neural. Earlier studies showed that subcutaneous (SC) implants of E2 for 3 days in prepubertal gilts depressed PR to LH-RH. We further examined the effect upon PR of implants releasing physiologic levels of E2. PR was evaluated as above at 2-h intervals for 12 h after SC implantation of silastic capsules containing E2 (n = 6) or sham implant (n = 1); then every 6 h up to 54 h post-treatment. For the first 12 h PR depression in the control was identical to controls in the acute experiment; after 36 h PR was similar to pretreatment levels. In E2 implanted animals PR fell to a mean of 1.8 plus or minus 0.1 ng/ml, 4-12 h after implantation, then recovered, stabilizing at 2.3 plus or minus 0.1 ng/ml after 18 h. It is concluded that estrogen treatment rapidly causes a depression of pituitary response to exogenous LH-RH. This rapid effect may not be dependent on E2 dosage. The extent of recovery of pituitary responsiveness probably depends upon the level and persistence of the E2 treatment.