Primary, secondary and compensated hypogonadism: a novel risk stratification for infertile men

Recently, the cohort of men from the European Male Ageing Study has been stratified into different categories distinguishing primary, secondary and compensated hypogonadism. A similar classification has not yet been applied to the infertile population. We performed a cross-sectional study enrolling 786 consecutive Caucasian-European infertile men segregated into eugonadal [normal serum total testosterone (≥3.03 ng/mL) and normal luteinizing hormone (≤9.4 mU/mL)], secondary (low total testosterone, low/normal luteinizing hormone), primary (low total testosterone, elevated luteinizing hormone) and compensated hypogonadism (normal total testosterone; elevated luteinizing hormone). In this cross-sectional study, logistic regression models tested the association between semen parameters, clinical characteristics and the defined gonadal status. Eugonadism, secondary, primary and compensated hypogonadism were found in 80, 15, 2, and 3% of men respectively. Secondary hypogonadal men were at highest risk for obesity [OR (95% CI): 3.48 (1.98-6.01)]. Primary hypogonadal men were those at highest risk for azoospermia [24.54 (6.39-161.39)] and testicular volume <15 mL [12.80 (3.40-83.26)]. Compensated had a similar profile to primary hypogonadal men, while their risk of azoospermia [5.31 (2.25-13.10)] and small testicular volume [8.04 (3.17-24.66)] was lower. The risk of small testicular volume [1.52 (1.01-2.33)] and azoospermia [1.76 (1.09-2.82)] was increased, although in a milder fashion, in secondary hypogonadal men as well. Overall, primary and compensated hypogonadism depicted the worst clinical picture in terms of impaired fertility. Although not specifically designed for infertile men, European Male Ageing Study categories might serve as a clinical stratification tool even in this setting.

[Androgens stimulate the expression of SOCS-3 and inhibits their effect on proliferation and secretion]

PURPOSE

Suppressors of cytokine signalling (SOCS) are induced by interleukins and peptide hormones. These molecules prevent the activation of diverse signalling pathways in benign and malignant cells. In previous studies, we showed that SOCS-3 is expressed in most prostate cancer cell lines and tissue specimens. In the present study we investigated the effects of androgen on the regulation of SOCS-3 in prostate cancer cell lines.

MATERIALS AND METHODS

SOCS-3 expression was determined with PCR and Western blot techniques. The activity of the SOCS-3 promoter was measured with the luciferase test. We measured proliferation with (3)H-thymidine assay.

RESULTS

We show that androgen induces the expression of SOCS-3 in two prostate cancer cell lines. The non-steroidal anti-androgen bicalutamide is able to block the induction of SOCS-3 -expression. Androgenic hormones did not induce the expression of SOCS-3 mRNA or its promoter activity. In LNCaP-IL-6- cells transfected with the inducible Tet-On construct SOCS-3 expression was induced. The effects of androgenic hormones on the proliferation and induction of PSA were -diminished in the presence of SOCS-3.

CONCLUSIONS

Our results show that androgenic -regulation of SOCS-3 leads to inhibition of prolif-eration and secretion in human prostate cancer.

Neuroactive steroids influence peripheral myelination: a promising opportunity for preventing or treating age-dependent dysfunctions of peripheral nerves

The process of aging deeply influences morphological and functional parameters of peripheral nerves. The observations summarized here indicate that the deterioration of myelin occurring in the peripheral nerves during aging may be explained by the fall of the levels of the major peripheral myelin proteins [e.g., glycoprotein Po (Po) and peripheral myelin protein 22 (PMP22)]. Neuroactive steroids, such as progesterone (PROG), dihydroprogesterone (5alpha-DH PROG), and tetrahydroprogesterone (3alpha,5alpha-TH PROG), are able to stimulate the low expression of these two myelin proteins present in the sciatic nerve of aged male rats. Since Po and PMP22 play an important physiological role in the maintenance of the multilamellar structure of PNS myelin, we have evaluated the effect of PROG and its neuroactive derivatives, 5alpha-DH PROG and 3alpha,5alpha-TH PROG, on the morphological alterations of myelinated fibers in the sciatic nerve of 22-24-month-old male rats. Data obtained clearly indicate that neuroactive steroids are able to reduce aging-associated morphological abnormalities of myelin and aging-associated myelin fiber loss in the sciatic nerve.

Effects of neuroactive steroids on myelin of peripheral nervous system

Peripheral nervous system (PNS) possess both classical (e.g. progesterone receptor, PR, androgen receptor, AR) and non-classical (e.g. GABA(A) receptor) steroid receptors and consequently may represent a target for the action of neuroactive steroids. Our data have indicated that neuroactive steroids, like for instance, progesterone, dihydroprogesterone, tetrahydroprogesterone, dihydrotestosterone and 3alpha-diol, stimulate both in vivo and in vitro (Schwann cell cultures), the expression of two important proteins of the myelin of peripheral nerves, the glycoprotein Po (Po) and the peripheral myelin protein 22 (PMP22). It is important to highlight that the mechanisms by which neuroactive steroids exert their effects on the expression of Po and PMP22 involve different kind of receptors depending on the steroid and on the myelin protein considered. In particular, at least in culture of Schwann cells, the expression of Po seems to be under the control of PR, while that of PMP22 needs the GABA(A) receptor. Because Po and PMP22 play an important physiological role for the maintenance of the multilamellar structure of the myelin of the PNS, the present observations might suggest the utilization of neuroactive steroids as new therapeutically approaches for the rebuilding of the peripheral myelin.

Interactions between growth factors and steroids in the control of LHRH-secreting neurons

How the gene expression and the release of luteinizing hormone releasing hormone (LHRH) are controlled in LHRH-secreting neurons is a very crucial and still debated topic of the neuroendocrinology. Several observations present in literature have recently indicated that glial cells may influence the activity of hypothalamic LHRH-secreting neurons, via the release of growth factors. The present review will summarize data obtained in our laboratory indicating that: (a) type 1 astrocytes, a kind of glial cells, are able to release in vitro growth factors belonging to the transforming growth factors beta (TGFbeta) family (i.e. TGFbeta1 and TGFbeta2) which influence the gene expression and the release of the decapeptide in immortalized LHRH-secreting neurons; (b) glial cells are also able to influence the steroid metabolism occurring in these neurons and in some cases this effect is exerted by TGFbeta1; (c) the mRNA levels of TGFbeta1 and of basic fibroblast growth factor (bFGF), another growth factor involved in the control of LHRH-secreting neurons, are modified in the rat hypothalamus during the different phases of the estrous cycle; (d) steroid hormones are able to modulate the gene expression of TGFbeta1 and bFGF both in vivo (i.e. in the whole hypothalamus of ovariectomized rats) and in vitro (cultures of type 1 astrocytes). On the basis of these results a possible functional correlation in the control of LHRH-secreting neurons between growth factors and gonadal steroids will be discussed and proposed.

Neuroactive steroids and peripheral myelin proteins

The present review summarizes observations obtained in our laboratories which underline the importance of neuroactive steroids (i.e., progesterone (PROG), dihydroprogesterone (5alpha-DH PROG), tetrahydroprogesterone (3alpha, 5alpha-TH PROG), testosterone (T), dihydrotestosterone (DHT) and 5alpha-androstan-3alpha,17beta-diol (3alpha-diol)) in the control of the gene expression of myelin proteins (i.e. glycoprotein Po (Po) and the peripheral myelin protein 22 (PMP22)) in the peripheral nervous system. Utilizing different in vivo (aged and adult male rats) and in vitro (Schwann cell cultures) experimental models, we have observed that neuroactive steroids are able to stimulate the mRNA levels of Po and PMP22. The effects of these neuroactive steroids, which are able to interact with classical (progesterone receptor, PR, and androgen receptor, AR) and non-classical (GABA(A) receptor) steroid receptors is further supported by our demonstration in sciatic nerve and/or Schwann cells of the presence of these receptors. On the basis of the observations obtained in the Schwann cells cultures, we suggest that the stimulatory effect of neuroactive steroids on Po is acting through PR, while that on PMP22 needs the GABA(A) receptor. The present findings might be of importance for the utilization of specific receptor ligands as new therapeutical approaches for the rebuilding of the peripheral myelin, particularly in those situations in which the synthesis of Po and PMP22 is altered (i.e. demyelinating diseases like Charcot-Marie-Tooth type 1A and type 1B, hereditary neuropathy with liability to pressure palsies and the Déjérine-Sottas syndrome, aging, and after peripheral injury).

Corticosteroids protect oligodendrocytes from cytokine-induced cell death

The present data show that the simultaneous exposure to tumor necrosis factor-alpha (TNFalpha) and interferon-gamma (IFNgamma) induces cell death with characteristics of apoptosis in cultured rat oligodendrocytes; TNFalpha alone was ineffective. We have also demonstrated that different corticosteroids (aldosterone, deoxycorticosterone, dexamethasone and corticosterone) protect rat oligodendrocytes in culture from apoptosis induced by TNFalpha plus IFNgamma. This effect seems to be exerted via the interaction with both type I and type II corticosteroid receptors since all steroids considered are effective. Since oligodendrocyte apoptosis represents an important event in multiple sclerosis and in several demyelinating diseases, the present observations might be considered an interesting background for further researches directed to the possibility of controlling in vivo the death of these cells.

Testosterone metabolites in patients reduce the levels of very long chain fatty acids accumulated in X-adrenoleukodystrophic fibroblasts

Testosterone metabolites (dihydrotestosterone, DHT) and 5 alpha-androstan-3 alpha,17 beta-diol (3 alpha-diol), but not testosterone itself, were shown to reduce the levels of very long chain fatty acids which accumulate in cultured skin fibroblasts from X-adrenoleukodystrophic patients (X-ALD). In addition, in X-ALD fibroblasts, testosterone is less actively converted into DHT vs. controls (skin fibroblasts retrieved from normal subjects) whereas the additional conversion of DHT to the final product 3 alpha-diol is enhanced. This is the first report of altered testosterone metabolism in X-ALD fibroblasts and of the effects of androgens in lowering the abnormal accumulation of very long chain fatty acids in this type of cells.

Corticosteroids regulate the gene expression of FGF-1 and FGF-2 in cultured rat astrocytes

The present data show that the gene expression of FGF-1 and FGF-2 is regulated by corticosteroids in rat type 1 astrocytes. In particular, the gene expression of FGF-1 is modulated by corticosteroids acting both on type I (minerocorticoid) and type II (glucocorticoid) receptors. In fact, at short times of exposure (2 h) a slight decrease in FGF-1 mRNA levels is induced by deoxycorticosterone, a steroid able to interact with the type I receptors; a similar effect is observed at 6 h following exposure to corticosterone or its 5alpha-reduced metabolite, dihydrocorticosterone. Conversely, at longer times of exposure (24 h) corticosterone is able to strongly increase FGF-1 mRNA levels. Both effects of corticosterone (inhibition and stimulation) were duplicated by dexamethasone, indicating that both effects occur via the type II receptors. Interestingly, the 5alpha-3alpha-reduced metabolite of deoxycorticosterone, tetrahydrodeoxycorticosterone, which does not interact with either corticosteroid receptors, is able to stimulate (at 6 and 24 h of exposure) the gene expression of FGF-1. It is possible that this effect might be induced via the GABA(A) receptor, since muscimol, an agonist of this receptor, exerts a similar effect. The situation is different in the case of FGF-2. The mRNA levels of this growth factor are only stimulated by steroids interacting with type II receptors. Altogether, these observations indicate that corticosteroids modulate the levels of FGF-1 and FGF-2 gene expression in astroglial cells by interaction with classical (type I and II) or nonclassical (GABA(A) receptor) steroid receptors.

Interactions between type 1 astrocytes and LHRH-secreting neurons (GT1-1 cells): modification of steroid metabolism and possible role of TGFbeta1

The hypothesis that type 1 astrocytes (A1) might modify the activities of the enzymes 5alpha-reductase (5alpha-R) and 3alpha-hydroxysteroid dehydrogenase (3alpha-HSD) present in the GT1-1 cells has been tested. The data obtained indicate that, utilizing a co-culture technique, A1 are able to: (1) decrease the formation of dihydrotestosterone (DHT) from testosterone (T); (2) increase the formation of dihydroprogesterone (DHP) from progesterone (P); (3) decrease the conversion of DHP into tetrahydroprogesterone (THP) in GT1-1 cells. Moreover, GT1-1 cells are able to increase the formation of DHP in A1; that of DHT was unchanged. The present data might suggest the possible existence of a third isoform of the enzyme 5alpha-R; details on this hypothesis are provided in the text. Interestingly, the inhibitory effect exerted by A1 on the formation of DHT in GT1-1 cells can be mimicked by transforming growth factor beta1 (TGFbeta1). Since TGFbeta1 had been previously shown to be directly involved in the stimulatory control of LHRH secretion by GT1-1 cells, acting both on LHRH release [R.C. Melcangi, M. Galbiati, E. Messi, F. Piva, L. Martini, M. Motta, Type 1 astrocytes influence luteinizing hormone-releasing hormone release from the hypothalamic cell line GT1-1: is transforming growth factor-beta the principle involved? Endocrinology 136 (1995) 679-686.] and gene expression [M. Galbiati, M. Zanisi, E. Messi, I. Cavarretta, L. Martini, R.C. Melcangi, Transforming growth factor-beta and astrocytic conditioned medium influence LHRH gene expression in the hypothalamic cell line GT1, Endocrinology 137 (1996) 5605-5609], the present data also show that TGFbeta1 might intervene in modulating feedback signals reaching hypothalamic LHRH producing neurons. The present findings underline once more the importance of the physiological cross-talk between A1 and neurons.

Po gene expression is modulated by androgens in the sciatic nerve of adult male rats

The present results show that androgens are able to modulate the Po gene expression in different models. In particular, we have shown that: (1) the messenger for the androgen receptor (AR) is present in the rat sciatic nerve but not in cultured Schwann cells; (2) castration induces a decrease of Po mRNA levels in the sciatic nerve of male rats, which is counteract by the subsequent treatment with dihydrotestosterone (DHT), the 5alpha-reduced metabolite of testosterone; (3) castration is also able to significantly decrease in the sciatic nerve the activity of the enzyme 5alpha-reductase (which converts testosterone into DHT); and (4) DHT is able to stimulate Po gene expression in cultured Schwann cells. These observations seem to indicate that androgens may exert their effect on Po gene expression via indirect mechanisms; modulation of neuronal influences reaching the Schwann cells through the binding of the androgen to the AR present in neurons may be postulated. However, alternative mechanisms may also be taken in consideration. The data presented suggest indeed that androgens might act on Schwann cells via the progesterone receptor (PR) rather than the AR. It has been observed that: (1) the messenger for PR is present in Schwann cells; (2) DHT may activate the transcriptional activity of a PR-responsive gene by binding to the PR; and (3) putative steroid responsive elements have been described in this paper to be present in the Po promoter region.

Progesterone derivatives are able to influence peripheral myelin protein 22 and P0 gene expression: possible mechanisms of action

The present study has analyzed the effect of progesterone and its derivatives (dihydroprogesterone and tetrahydroprogesterone) on the gene expression of the peripheral myelin protein 22 utilizing in vivo and in vitro models. The data obtained indicate that tetrahydroprogesterone is able to stimulate the gene expression of peripheral myelin protein 22 both in vivo (in adult but not in old animals) and in Schwann cell cultures. An effect of this steroid, which is known to interact with the GABA(A) receptor, would not be surprising, since in the present study we show the presence in Schwann cells and in the sciatic nerve of the messengers for several subunits (alpha2, alpha3, beta1, beta2, and beta3) of the GABA(A) receptor. An effect of tetrahydroprogesterone is also evident on the gene expression of another myelin protein, the peripheral myelin protein zero. However, in this case also dihydroprogesterone, which is able to bind the progesterone receptor, is involved, both in old and adult animals, in the stimulation of messengers levels of this myelin protein. In conclusion, the present data show that the gene expression of two important peripheral myelin proteins can be influenced by progesterone derivatives. The hypothesis has been put forward that part of their effects might occur not through the classical progesterone receptor, but rather via an interaction with the GABA(A) receptor.

Effects of steroid hormones on gene expression of glial markers in the central and peripheral nervous system: variations induced by aging

The present article summarizes our data regarding: (a) the effect of sex steroids on the expression of a specific astrocytic marker in glial cell cultures (GFAP); (b) the effects of aging on two markers of the peripheral myelin (glycoprotein Po and the myelin basic protein, MBP); (c) the possible modification of the damaging effects of aging on these two markers by the in vivo administration of progesterone and its derivatives; and, finally, (d) the effect of progesterone derivatives on the gene expression of Po in cultures of rat Schwann cells. The data obtained have indicated that progesterone and its 5 alpha-reduced metabolites may play an important role in the control of gene expression of GFAP and Po, respectively, in type 1 astrocytes and Schwann cells. It has also been found that the gene expression of Po and MBP is dramatically decreased in the myelin of the sciatic nerve of aged male rats and that the aged-linked decrease of the gene expression of Po is partially reversible with steroid treatment.

Age-induced decrease of glycoprotein Po and myelin basic protein gene expression in the rat sciatic nerve. Repair by steroid derivatives

The data here reported show that the gene expression of the glycoprotein Po and of the myelin basic protein, the major components of myelin in the peripheral nervous system, dramatically decreases with ageing in the sciatic nerve of normal male rats. A one-month treatment with dihydroprogesterone, the 5alpha-reduced derivative of progesterone, is able to partially restore the fall in Po gene expression occurring in the sciatic nerve of aged male rats, without significantly modifying the gene expression of the myelin basic protein. In cultures of neonatal Schwann cells (the peripheral nervous system elements involved in the synthesis of myelin), the addition of progesterone and of dihydroprogesterone significantly increases Po gene expression; the 3alpha-reduced metabolite of dihydroprogesterone, tetrahydroprogesterone proved to be even more effective. These data suggest that the effect of progesterone is linked to its conversion into dihydroprogesterone and especially into tetrahydroprogesterone, since Schwann cells possess the 5alpha-reductase-3alpha-hydroxysteroid dehydrogenase system. The data provide the first demonstration that ageing decreases the gene expression of two major components of the peripheral myelin in the sciatic nerve; they also show that this phenomenon may be partially reversed by progesterone derivatives, which might act by stimulating Po gene expression in the Schwann cells.

The 5alpha-reductase in the central nervous system: expression and modes of control

The present paper will summarize two important aspects of the interactions between steroids and the brain, which have recently been studied in the authors' laboratory. In particular the paper will consider data on: (1) the significance of the two isoforms of the 5alpha-R during brain ontogenesis and development, and (2) the cross-talk between glial and neuronal elements, particularly in relation to the metabolism of sex hormones. (1) The data obtained have shown that the 5alpha-R type 1 enzyme is constitutively expressed in the rat CNS at all stages of brain development. Moreover, the expression of the 5alpha-R type 1 is similar in males and in females, and does not appear to be controlled by androgens. The gene expression of the 5alpha-R type 2 is totally different. This isoform appears to be expressed in the rat brain almost exclusively in the late fetal/early post-natal life and is controlled by testosterone. (2) The present data show that two cell lines derived respectively from a rat glioma (C6 cell line) and from a human astrocytoma (1321N1 cell line) are able to convert testosterone and progesterone into their corresponding 5alpha-reduced metabolites dihydrotestosterone and dihydroprogesterone. The possibility that secretory products of normal and tumoral brain cells might be able to influence steroid metabolism occurring in the two glial cell lines previously mentioned has been considered.

Crosstalk between normal and tumoral brain cells. Effect on sex steroid metabolism

The present article shows for the first time that two cell lines derived respectively from a rat glioma (C6 cell line) and from a human astrocytoma (1321N1 cell line) are able to convert testosterone and progesterone into their corresponding 5 alpha-reduced metabolites dihydrotestosterone and dihydroprogesterone. Moreover, both cell lines are also able to convert these metabolites further into their corresponding 3 alpha-OH derivatives, 5 alpha-androstan-3 alpha, 7 beta-diol (3 alpha-diol) and tetrahydroprogesterone. On the basis of these observations, the possibility that secretory products of normal and tumoral brain cells might be able to influence steroid metabolism occurring in the two glial cell lines previously mentioned as well as in fetal rat neurons and in neonatal rat type 1 astrocytes has been considered. To this purpose, cultures of the different cellular types have been exposed to the conditioned medium in which the other cells were grown. The results obtained indicate that: 1. Neurons are able to stimulate, in a statistically significant fashion, the formation of dihydrotestosterone (DHT), 3 alpha-diol, and tetrahydraprogesterone (THP) in C6 cells. 2. Type 1 astrocytes, on the contrary, are unable to modify steroid metabolism in C6 cells. 3. C6 cell product(s) decrease(s) the formation of DHP in type 1 astrocytes, without modifying that of DHT. 4. C6 cells do not influence the metabolism of testosterone (T) and progesterone (P) in neurons. In conclusion, the present observations show that the conditioned medium of normal neurons is able to increase the metabolism of testosterone and progesterone occurring in a tumoral glial cell line, and that the conditioned media of the two tumoral cell lines analyzed are able to decrease the conversion of P into DHP occurring in normal type 1 astrocytes. The surprising result that these conditioned media do not alter the formation of DHT is discussed. Work is presently in progress to identify the principle(s) responsible respectively for the activating and inhibiting actions here described.

Astrocyte-neuron interactions in vitro: role of growth factors and steroids on LHRH dynamics

The data here reviewed, obtained with in vitro models, indicate that growth factors and steroids play a significant role in astrocyte-neuron interactions. Different designs have been adopted: (1) GT1-1 cells (a cell line derived from a mouse hypothalamic LHRH-producing tumor) were cocultured with type 1 rat astrocytes; and (2) GT1-1 cells were exposed to the conditioned medium (CM) in which type 1 rat astrocytes had been grown for 24 h. LHRH release and mRNA LHRH levels were measured respectively in the medium and in cell homogenates, at different time intervals (LHRH release, by RIA; LHRH mRNA by Northern blot analysis). The data obtained show that type 1 astrocytes secrete in the medium TGFbeta, which is able to modulate the release and the gene expression of LHRH in GT1-1 cells; and that one or more LHRH-degrading enzymes is/are present in the conditioned medium of type 1 astrocytes. A second part of the experiments have indicated that type 1 astrocytes are also able to affect, in different directions, the metabolism of testosterone and progesterone into their 5alpha-reduced metabolites occurring in the GT1-1 cells. In particular, it has been observed that the conversion of testosterone into DHT is decreased by the coculture with type 1 astrocytes, while the conversion of progesterone into DHP is increased by the same coculture conditions. Moreover, type 1 astrocytes are sensitive to steroid hormones, and in particular to the 5alpha-reduced metabolites of progesterone; this has been shown by analyzing the effects exerted by different steroids on the gene expression of the typical astrocyte marker GFAP.

Corticosteroid effects on gene expression of myelin basic protein in oligodendrocytes and of glial fibrillary acidic protein in type 1 astrocytes

The paper describes the effects of corticosterone and deoxycorticosterone (DOC), used in their native or in their 5 alpha-reduced molecular forms (dihydrocorticosterone, DHC; dihydrodeoxycorticosterone, DHDOC; and tetrahydrodeoxycorticosterone, THDOC) on the gene expression of the myelin basic protein (MBP) and of the glial fibrillary acidic protein (GFAP) in pure cultures, respectively, of oligodendrocytes and type 1 astrocytes obtained from the neonatal rat brain. Among the different steroids tested (corticosterone, DHC, DOC, DHDOC and THDOC), only DHDOC was effective on the gene expression of MBP in the oligodendrocyte cultures; the mRNA levels of this typical oligodendrocyte marker were decreased following exposure to this steroid for 24 h. In the case of the astrocytic marker GFAP, its gene expression was increased by the exposure to corticosterone for 6 and 24 h, while DHC was ineffective; the mineralocorticoid DOC was also ineffective, while its 5 alpha-reduced derivative, DHDOC, strongly inhibited GFAP gene expression, starting at 6 h after beginning of the treatment. In conclusion, the present data show that: (1) adrenal steroids possessing gluco- and mineralocorticoid activities may influence the gene expression of the astrocytic marker GFAP; (2) the 5 alpha-reduced metabolite of DOC, DHDOC is able to influence the gene expression not only of GFAP but also that of MBP, which are, respectively, typical markers of the astrocytes and the oligodendrocytes; (3) the metabolic conversion of hormonal steroids into their 5 alpha-reduced metabolites, which also occurs in the glia, could be implicated in the biochemical control of oligodendrocyte and astrocyte functions.

Transforming growth factor-beta and astrocytic conditioned medium influence luteinizing hormone-releasing hormone gene expression in the hypothalamic cell line GT1

On the basis of our previous observations indicating that a principle [possibly transforming growth factor-beta1 (TGFbeta1)] secreted by type 1 astrocytes may increase the release of LHRH in the GT1 cell line, it was deemed of interest to analyze whether TGFbeta1 might influence LHRH gene expression in addition to LHRH release in GT1-1 neurons. The effects of TGFbeta1 on the levels of LHRH messenger RNA (mRNA) present in GT1-1 cells have been compared to those found after either coculture of these cells with type 1 astrocytes or exposure of GT1-1 cells to the conditioned medium in which type 1 astrocytes were grown for 24 h. The data obtained indicate that 1) TGFbeta1 increases LHRH mRNA levels 1 and 6 h after the beginning of treatment; longer exposures (24 h) bring about a decrease in LHRH gene expression; 2) a significant stimulatory effect of TGFbeta1 (1 and 6 h of exposure) is also evident on LHRH release; 3) the exposure to the conditioned medium of type 1 astrocytes is able to increase LHRH gene expression in GT1-1 cells at 1 h; LHRH mRNA levels show a small decrease after 6 h of exposure, which becomes more evident at 24 h; and 4) the coculture of GT1-1 cells with type 1 astrocytes is not able to modify LHRH mRNA levels at any time considered. The present data support the concept that glial cells are able to control, possibly through the release of TGFbeta, the gene expression of LHRH in hypothalamic neurons.