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D Dondi

Publications and source records attributed to D Dondi.

At least 37 records · Page 2Linked to original sources
PubMed1994

Antiproliferative effects of luteinizing hormone-releasing hormone (LHRH) agonists on human androgen-independent prostate cancer cell line DU 145: evidence for an autocrine-inhibitory LHRH loop.

The therapeutic options for the treatment of androgen-independent prostatic cancers are rather limited; this is mainly because our understanding of the local mechanisms involved in the control of androgen-independent proliferation of the tumor is still very poor. The present experiments have been performed to verify whether luteinizing hormone-releasing hormone (LHRH) agonists may possess a direct effect on the growth of the human androgen-independent prostate cancer cells DU 145 and whether a LHRH growth regulatory system may be present in these cells. The data have shown that two potent LHRH agonists (Zoladex and Buserelin) exert a significant and dose-dependent antiproliferative action on DU 145 cells, after 4 days of treatment. The inhibitory action of Zoladex and Buserelin is completely counteracted by the simultaneous treatment of the cells with a potent LHRH antagonist, suggesting that the action of the LHRH agonists may be mediated by specific receptors. This hypothesis has been confirmed by the demonstration that low-affinity binding sites for 125I-Buserelin are present on DU 145 cell membranes, particularly when cells are cultured in serum-free conditions. By using the reverse transcription-polymerase chain reaction technique, in the presence of a pair of specific oligonucleotide primers complementary to the human LHRH complementary DNA, it has been demonstrated that a mRNA for LHRH is expressed in DU 145 cells. Taken together, these data seem to indicate that an autocrine/paracrine LHRH (or LHRH-like) loop is present in androgen-independent prostate cancer cells, and may participate in the regulation of tumor cell growth. To verify this hypothesis, DU 145 cells have been cultured in serum-free conditions, and treated with a LHRH antagonist for 4 days. The treatment resulted in a significant increase of cell proliferation, suggesting an inhibitory role for the LHRH system in the local regulation of cell growth. In conclusion, these data demonstrate that: (a) LHRH agonists exert a specific antiproliferative action on the human androgen-independent DU 145 cells; (b) an autocrine/paracrine LHRH (or LHRH-like) loop, which seems to be inhibitory on cell proliferation, is expressed in DU 145 cells.

Animals↗
PubMed1994

Androgen-dependent prostatic tumors: biosynthesis and possible actions of LHRH.

Testosterone (T) is the major exogenous stimulus for the growth of prostatic carcinoma. It is believed that the proliferative action of T may be mediated by locally expressed growth modulatory factors. Recent evidence from our laboratory suggests that a LHRH (or a LHRH-like) loop might be expressed in human prostatic tumor cells. To verify this hypothesis, we have studied whether a mRNA for LHRH is expressed in the human androgen-responsive prostatic cancer cell line LNCaP, using the reverse transcription-polymerase chain reaction technique in the presence of a pair of specific oligonucleotide primers. A cDNA band of the expected size was obtained from LNCaP cells; this band hybridized with a 32P-labeled LHRH oligonucleotide probe and its sequence showed a complete match with the reported sequence of the human placental LHRH cDNA. These observations indicate that the mRNA coding for LHRH is expressed in LNCaP cells and suggest that a LHRH (or a LHRH-like) peptide might be produced by these cells. To clarify the possible action of this peptide, LNCaP cells were grown in a steroid-free medium and treated with a LHRH antagonist. The treatment resulted in a significant increase of tumor cell growth. These data clearly indicate that the LHRH system expressed in LNCaP cells plays an inhibitory role on cell proliferation, and that this system seems to be regulated in a negative way by steroids. An EGF/TGF alpha autocrine stimulatory loop (peptides, receptors, intracellular signals) is also functional in these cells. Treatment of LNCaP cells grown in serum-free conditions (i.e. in the absence of exogenous growth factors) with a monoclonal antibody against the EGF receptor, or with immunoneutralizing antibodies against EGF or TGF alpha, resulted in a significant decrease of cell proliferation. T positively regulates this EGF/TGF alpha system by increasing the concentration of EGF binding sites. The present data indicate that an inhibitory LHRH (or LHRH-like) system is expressed in LNCaP cells and participates in the local mechanisms regulating tumor cell proliferation together with an EGF/TGF alpha stimulatory loop. Both systems appear to be modulated by T.

Androgens↗
PubMed1993

Characterization of a soluble LHRH-degrading activity in the rat ventral prostate.

Recent evidence supports the hypothesis of a direct action of LHRH at the level of the prostate. Since peptidases able to degrade the hormone are present in several LHRH target structures, it was deemed of interest to investigate whether the prostate of adult normal male rats might possess LHRH degrading activities (LHRH-DA). Through the use of RP-HPLC, it has been observed that LHRH-DA is present in the soluble fraction of the rat ventral prostate homogenate, and is able to hydrolyze synthetic LHRH and to generate fragments 1-3 and 1-5 of the decapeptide. The degradation of [pGlu-3H]LHRH is inhibited by LHRH itself, and affected by several LHRH agonists and antagonists with different kinetics and potencies. TRH, the enkephalin analog [D-Ala2-D-Leu5]enkephalin and rat prolactin do not inhibit the degradation of [pGlu-3H]LHRH by the soluble fraction of prostate homogenate; on the contrary, this is inhibited by graded doses of somatostatin. The prostatic LHRH-DA is also inhibited, in a dose dependent manner, by bacitracin, serine protease inhibitors (diisopropylfluorophosphate and phenylmethansulfonylfluoride), the metal chelating agent EDTA, HgCl2, and dithiothreitol. No inhibitory effect on [pGlu-3H]LHRH hydrolysis was observed after incubation of the prostatic extract in the presence of captopril. The prostatic LHRH-DA seems to be different from that present in other tissues of the rat (e.g., hypothalamus, pituitary, gonads), and to be decreased by castration performed 3 weeks before. These results suggest that (1) an LHRH-DA is found in the soluble fraction of rat prostate homogenate; (2) this enzymatic activity exhibits the characteristics of a metallo- and thiol-dependent neutral endopeptidase; (3) it appears to be different from similar hydrolytic activities found in other tissues; and (4) it is influenced by the hormonal milieu, since castration causes a significant decrease of its activity.

Animals↗
PubMed1993

Binding characteristics of hypothalamic mu opioid receptors throughout the estrous cycle in the rat.

This study presents a detailed analysis of the binding characteristics of hypothalamic mu opioid receptors during the different phases of the estrous cycle of the female rat. Different groups of adult female rats with a regular 4-day estrous cycle were killed by decapitation at 10.00 h of diestrus days 1 and 2, at 10.00, 12.00, 14.00, 16.00, 18.00 and 20.00 h of the day of proestrus and at 10.00, 12.00, 14.00, 16.00 and 18.00 h of the day of estrus. At sacrifice, the hypothalami of the animals were dissected out, plasma membrane preparations were obtained and the binding characteristics (Bmax, Kd) of the specific mu opioid ligand dihydromorphine (DHM) on mu opioid receptors were evaluated. Blood has been collected from the trunk vessels to monitor with specific radioimmunoassays serum levels of LH, estradiol and progesterone. The data obtained indicate that in the hypothalamus of female rats with a regular 4-day estrous cycle, the binding characteristics of DHM for mu receptors show important variations during the different phases of the estrous cycle. In general, the number of mu opioid receptors is elevated during the morning of diestrus day 2 and during the day of proestrus being maximal at 14.00 h and declining significantly at 18.00 and 20.00 h of the same day. At estrus, the number of mu receptors appears high at 10.00 and 16.00 h and low at 12.00, 14.00 and 18.00 h. All these variations take place without any significant change of the affinity (Kd) of DHM for the mu receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Expression of luteinizing hormone-releasing hormone mRNA in the human prostatic cancer cell line LNCaP.

Recent evidence suggests that LHRH or a LHRH-like peptide might be produced by human prostatic tumor cells. To test this hypothesis, we have studied whether a mRNA for LHRH is expressed in the human prostatic cancer cell line LNCaP, by means of the RT-PCR (reverse transcription-polymerase chain reaction) technique. For these experiments, mRNA was extracted from LNCaP cells, from rat hypothalami and from rat pituitaries, reverse transcribed to cDNA and amplified via the PCR utilizing a pair of oligonucleotide primers complementary to the LHRH cDNA. Following gel electrophoresis, a band of the expected size of 228 base pairs was found in LNCaP cells as well as in the rat hypothalamus, but not in the rat anterior pituitary. This 228 base pair band from LNCaP cells and from the rat hypothalamus specifically hybridized to a 32P-labeled LHRH oligonucleotide probe. The cDNA band obtained from LNCaP cells was subcloned into a plasmid vector, and the analysis of its sequence showed a complete match with the authentic human placental LHRH cDNA. These observations clearly demonstrate that a mRNA for LHRH is expressed in human prostatic cancer cells, and suggest that LHRH or a LHRH-like peptide may be produced by these cells. To test the hypothesis whether this material might act as a local growth regulating factor on tumor cell proliferation, LNCaP cells, grown in a steroid-free medium, were treated daily with a potent LHRH antagonist. After 9, 12 and 15 days, the treatment resulted in a significant increase of tumor cell proliferation. These data clearly suggest that the LHRH mRNA expressed in LNCaP cells is possibly translated into LHRH or a LHRH-like peptide which probably functions as a local growth inhibitory factor on prostatic tumor cell proliferation, by acting on LHRH receptors.

Animals↗
PubMed1993

Ageing of the neuroendocrine system in the brain of male rats: receptor mechanisms and steroid metabolism.

The work described in this article gives information on the effects of ageing on the hypothalamo-pituitary-testicular axis in rats. The hypothalami of young and old male rats contain similar amounts of luteinizing-hormone-releasing hormone (LHRH); when perifused in vitro they release comparable amounts of LHRH under basal conditions and in response to K+. The addition of an LHRH analogue to the perifusion medium blocks the release of LHRH induced by K+ from the hypothalami of young and old male rats, indicating that the ultrashort feedback mechanism controlling LHRH release functions normally in aged male rats. Ageing also exerts important effects on the density of mu- and kappa-opioid receptors in the brain. The number of hypothalamic mu-opioid receptors was significantly decreased in aged animals; a replacement treatment with testosterone does not reverse this decrease, indicating that the decline of hypothalamic mu receptors and of serum titres of testosterone in old rats are independent phenomena. The number of kappa-opioid receptors in the brain increases in the amygdala and in the thalamus with ageing. Apparently ageing does not influence the number of delta receptors in any of the brain areas investigated. The number of pituitary LHRH receptors decreases in old animals, which might explain the low serum concentration of gonadotrophins in aged rats caused by an inadequate response of the pituitary to hypothalamic LHRH. The impaired secretion of testosterone in aged male rats is accompanied by an increase in the number of testicular LHRH receptors, indicating that the intratesticular mechanisms controlling testosterone release also undergo significant alterations during ageing. The rate of conversion of testosterone to dihydrotestosterone (DHT) and 5 alpha-androstane-3 alpha, 17 beta-diol (3 alpha-diol) is the same in the hypothalami of young and old rats. However, the yields of DHT obtained from the pituitaries of aged male rats are significantly lower than those recorded in the pituitaries of young animals. These results show that the enzymes necessary for metabolizing testosterone via the 5 alpha-reductase pathway are maintained both in the hypothalamus and in the anterior pituitary of aged male rats. However, the 5 alpha-reductase activity of the anterior pituitary of senescent animals appears to be lower than that in the younger controls.

Aging↗
PubMed1992

Binding characteristics of delta opioid receptors in different regions of the brain of young and old male rats as studied with the highly selective ligand [D-Pen2-D-Pen5] enkephalin.

The present experiments were performed to study the binding characteristics of delta opioid receptors in membrane preparations obtained from the brain of adult male rats, and to analyze whether aging modifies these binding parameters. The binding characteristics of delta opioid receptors were evaluated on membrane preparations derived from dissected brain regions (hypothalamus, amygdala, mesencephalon, corpus striatum, hippocampus, thalamus, frontal poles, anterior and posterior cortex) collected from male rats of 3 and 24 months of age; the highly selective ligand 3H-[D-Pen2-D-Pen5] enkephalin (3H-DPDPE) was used. The results obtained in young rats show that the distribution of delta opioid receptors is different in the various brain areas examined; these receptors appear to be maximally concentrated in the frontal poles, anterior and posterior cortex; lower concentrations were found in the other structures considered. Kd (dissociation constant) for the delta sites was found very similar in all areas. The distribution of delta opioid receptors in the brain of 24-month-old rats was similar to that observed in young animals; this result was surprising in view of the fact that aging modifies the number of other types of brain opioid receptors (mu and kappa).

Aging↗
PubMed1992

Effects of ovarian hormones on brain opioid binding sites in castrated female rats.

These experiments were performed to analyze whether treatments of ovariectomized female rats with ovarian steroid regimens able to induce either an increase (positive feedback effect) or a decrease (negative feedback effect) of serum levels of luteinizing hormone (LH) have some impact on the characteristics of mu-opioid binding sites in circumscribed areas of the brain. The increase of serum levels of LH elicited by a treatment with estradiol benzoate (EB) plus progesterone (P; positive feedback effect) was accompanied by a significant decrease in the number of mu-binding sites in the hypothalamus and in the corpus striatum. The decrease in serum levels of LH induced by a treatment with EB alone (negative feedback effect) brought about a significant increase of the number of mu-binding sites in the thalamus and in the hippocampus. These results seem to suggest that the release of LH induced by EB plus P may involve a decrease of hypothalamic mu-binding sites. Apparently, the inhibitory effect on LH release exerted by EB alone does not involve any change of the density of these binding sites in the hypothalamus.

Animals↗
PubMed1992

Antiproliferative effects of luteinizing hormone-releasing hormone agonists on the human prostatic cancer cell line LNCaP.

Highly potent LH-releasing hormone (LHRH) agonists have been recently introduced in therapy for the treatment of the carcinoma of the prostate, an androgen-dependent pathology. These peptides are believed to act mainly by inhibiting the pituitary-testicular axis and, consequently, by reducing testosterone levels. The recent observation that binding sites for LHRH analogs are present on prostatic tumor tissue suggests that these drugs could also act directly on the tumor. To verify this hypothesis, the effects of two potent LHRH agonists [Zoladex (Z) and Buserelin (B)] have been studied on the proliferation of the human prostatic cancer cell line LNCaP (lymph node carcinoma of the prostate). LNCaP cells were treated for 9 days with different doses of either Z or B (concentrations from 10(-12)-10(-6) M). Both analogs significantly inhibited cell proliferation at doses between 10(-9)-10(-6) M. The antiproliferative action of the two LHRH agonists was shown to be dose dependent, with IC50 values of 0.82 and 1.79 nM for Z and B, respectively. A similar treatment with B was without any significant effect on the proliferation of a mouse embryo fibroblast cell line (Swiss 3T3), which was used as a nontumoral control. The inhibitory action of both LHRH agonists (10(-8) M) on LNCaP cell proliferation was completely antagonized by the simultaneous treatment of the cells with a potent LHRH antagonist (Nal-Arg-LHRH; 10(-8) M); when given alone at the dose selected, the antagonist did not affect cell growth. These results clearly suggest that the antiproliferative effect of LHRH agonists on LNCaP cells may be mediated by specific receptors. The presence of binding sites for [125I]B was consequently demonstrated on the membranes of LNCaP cells cultured in a medium containing charcoal-stripped fetal calf serum, i.e. in the absence of steroids. The affinity of these binding sites for the ligand was lower than that observed for the same receptors on rat pituitary membranes. To clarify the mechanism of the antiproliferative action of the LHRH agonists, the effects of both Z and B on the incorporation of [3H]thymidine and [14C]methionine into LNCaP cells were investigated. During a short incubation period (3 h), the two LHRH agonists rapidly inhibited [3H]thymidine incorporation into the cells. The same treatment did not affect the incorporation of [14C]methionine into proteins.(ABSTRACT TRUNCATED AT 400 WORDS)

Antineoplastic Agents↗
PubMed1991

Testosterone and postnatal ontogenesis of hypothalamic mu ([3H]dihydromorphine) opioid receptors in the rat.

Brain opioids modulate the activity of the hypothalamo-pituitary complex by binding to specific receptors which have been subdivided at least into 3 subclasses (mu, kappa, delta, etc). mu-Receptors and their ligands seem to be particularly involved in the control of gonadotropin and prolactin release. It is known that the neuroendocrine system, as well as the brain opioid systems and their receptors, are not fully mature at birth; it is also known that the postnatal maturation of many brain machineries is under the control of androgens secreted by the developing testes. Consequently, it has been investigated whether the presence or the absence of testosterone at time of birth may induce changes of the binding characteristics of hypothalamic mu-opioid receptors. The experiments have been performed by evaluating the maximal binding capacity (Bmax, an index of the number of receptors), and the affinity constant (Ka) of the specific mu-ligand dihydromorphine in hypothalamic plasma membrane preparations derived from normal male rats, normal female rats, male rats orchidectomized 2 days after birth and female rats treated 2 days after birth with 1.25 mg of testosterone propionate. Animals belonging to the 4 groups were killed at days 16, 26 and 60 of age. The results obtained show that, at 16 days of age, in the 4 groups of rats the number of hypothalamic mu receptors is identical. At 26 days a significant increase in the number of mu-receptors occurs in normal female animals, while their levels remain similar to those found at 16 days in the other 3 groups of animals. At 60 days of age, the number of mu-receptors in normal females remains elevated, while the number of mu-receptors increases to reach normal female levels in the hypothalamus of neonatally castrated males. At 60 days, there were no changes in normal males or in androgenized females. The variations here reported took place without any change of the Ka of dihydromorphine for the mu-receptors. These data show a sexual dimorphism of hypothalamic mu-receptors and suggest that their ontogenetic development may be linked to the presence or the absence of androgens at time of birth.

Animals↗
PubMed1991

Modulation of the binding characteristics of hypothalamic mu opioid receptors in rats by gonadal steroids.

Recent evidence suggests that the effects of the opioids on gonadotropin release may depend on the endocrine status existing in the experimental animal. In the brain, the effects of the opioids are exerted through the interaction with different classes of opioid receptors (mu, delta, kappa, etc.). Among these, the mu receptors appear to be particularly relevant to the control of gonadotropin secretion. Different groups of experiments have been performed in the rat in order to analyze whether changes of circulating levels of sex steroids may have an impact on the binding characteristics of hypothalamic mu opioid receptors, as evaluated by a receptor binding assay performed on plasma membrane preparations, using [3H]dihydromorphine as a mu ligand. In a first series of experiments, it has been observed that the ontogenesis of hypothalamic mu opioid receptors is different in male and in female rats: the concentration of mu sites, similar in animals of the two sexes at 16 days of age, increases in females, but not in males, between day 16 and day 26 of life. This sexual difference persists in 60-day old animals, when the brain is fully mature. It has also been observed that the pattern of maturation of hypothalamic mu receptors can be reversed by neonatal castration of males and by neonatal testosterone treatment of females. In a second series of experiments, it has been shown that in the hypothalamus of regularly cycling female rats the concentration of mu receptors varies during the different phases of the estrous cycle. In particular, a rather high density of mu sites during diestrus day 2 and the morning of the day of proestrus was found; this is followed by a progressive decline during the afternoon of the day of proestrus and the day of estrus, with a minimum value of the concentration of mu receptors being recorded in the first day of diestrus. These fluctuations seem to be linked to the physiological changes of serum levels of ovarian steroids: in fact, in a third series of experiments, it has been found that the positive feedback effect on LH release, exerted by the treatment of ovariectomized female rats with estrogens plus progesterone, is accompanied by a significant decrease of the concentration of hypothalamic mu opioid receptors; treatments with estrogens alone, able to induce a negative feedback effect on LH secretion, are not associated with modifications of hypothalamic mu receptors. These data seem to indicate that hypothalamic mu receptors may be involved in the positive but not in the negative feedback control of LH secretion.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Hypothalamic opiatergic tone during pregnancy, parturition and lactation in the rat.

The concentrations of beta-endorphin have been shown to change in the rat brain during pregnancy and lactation. This study has been performed in order to analyze whether also brain opioid receptors might undergo significant modifications during these two physiological situations. The maximal binding capacity (Bmax) and the constant of affinity (Ka) of the mu-subpopulation of opioid receptors have been evaluated in the hypothalami of female rats at different stages of pregnancy (7, 15 and 22 days), on the day of parturition (12-18 h after delivery) and 6-8 days postpartum (both in lactating and in nonlactating animals). Female rats killed on the day of estrus served as controls. The receptor binding assay has been performed utilizing [3H]-dihydromorphine [( 3H]-DHM) as the ligand for the mu-opioid receptors. Hypothalamic concentrations of beta-endorphin as well as serum levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and prolactin have also been evaluated by radioimmunoassay. The results showed that the concentration of hypothalamic mu-opioid receptors increased during pregnancy, being significantly higher than in the controls at days 15 and 22 of gestation. After delivery, the concentration of these receptors returned towards control values, regardless on whether the animals were lactating or not. The Ka values of [3H]-DHM for the mu-receptors did not change significantly in the different groups of experimental animals. Hypothalamic beta-endorphin content showed a modest though not significant increase at the end of gestation (day 22) and returned to control values 12-18 h after delivery.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Modulation by sex steroids of brain opioid receptors: implications for the control of gonadotropins and prolactin secretion.

Several experiments have been performed in order to analyze whether physiological or experimental changes of the endocrine environment might modify the binding characteristics of brain mu and kappa opioid receptors in the brain of the female and male rat. (a) In a first series of experiments, it has been observed that in the whole brain of regularly cycling female rats the number of mu receptors shows variation during the different phases of the estrous cycle. In particular a significant increase of the number of mu receptors has been observed in the morning of proestrus and in the afternoon of estrus. (b) In a second series of experiments, it has been shown that the administration of estrogens brings about a significant increase in the number of mu receptors in the hippocampus and in the thalamus of ovariectomized rats, while the administration of a regime including estrogen and progesterone induces a significant decrease of the number of mu receptors in the hypothalamus and in the corpus striatum. These data seem to indicate that hypothalamic mu receptors may be involved in the positive but not in the negative feedback control of LH secretion. (c) In a third series of experiments, it has been found that the number of mu receptors in the whole brain of 15- and 22-month-old male rats and in the hypothalamus of 22-month-old male rats is significantly lower than in the same tissues of young animals; moreover, the administration to old animals of testosterone does not modify the number of hypothalamic mu opioid receptors, indicating that the decline of brain mu receptors in old animals is not the consequence of the physiological decline of testosterone secretion but probably represents an autonomous phenomenon. (d) In a fourth series of experiments, it was shown that, in young male rats, the concentration of kappa receptors is extremely variable in different regions of the brain. The highest concentrations have been found in the hypothalamus and in the striatum; also in the mesencephalon and in the amygdala kappa receptors are present in rather elevated quantities; lower concentrations have been found in the thalamus, the frontal poles, the hippocampus and in the anterior and posterior cerebral cortex. These experiments have shown in addition that the process of aging induces an increase of the number of kappa receptors in the amygdala and in the thalamus; no age-linked modifications were observed in the other structures examined.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMed1989

Distribution of kappa opioid receptors in the brain of young and old male rats.

The experiments to be described have been designed in order to: (a) provide new information on the concentrations of opioid kappa receptors in different regions of the brain of the male rats; and (b) to analyze whether the density of brain kappa receptors might be modified by the process of aging. The concentration of kappa receptors was investigated in the hypothalamus, amygdala, mesencephalon, corpus striatum, hippocampus, thalamus, frontal poles, anterior and posterior cortex collected from male rats of 2 and 19 months of age. 3H-bremazocine (BRZ) was used as the ligand of kappa receptors, after protection of mu and delta receptors respectively with dihydromorphine and d-ala-d-leu-enkephalin. The results obtained show that: (1) in young male rats, the number of kappa opioid receptors is different in the various brain areas examined: the hypothalamus and the striatum have a concentration of kappa binding sites which is significantly higher than that found in the mesencephalon and in the amygdala; much lower concentrations of kappa binding sites have been found in the thalamus, the frontal poles, the hippocampus, the anterior and posterior cerebral cortex. (2) Aging exerts little influence on the number of kappa receptors in the majority of the brain structures considered. However in the amygdala and in the thalamus the number of kappa receptors was increased in old animals. To the authors' knowledge, the data here presented are the first ones which suggest that age may increase rather than decrease the number of neurotransmitter receptors in the brain.

Aging↗
PubMed1989

Neonatal organization of the brain opioid systems controlling prolactin and luteinizing hormone secretion.

It is known that the neural mechanisms which control PRL and gonadotropin secretion are different in male and female rats. The present experiments have been designed in order to analyze: 1) whether sexual differences exist in the responses of PRL and LH to the opioid antagonist naloxone; and 2) the mechanisms underlying these possible differences. To this purpose the responses of PRL and LH to the sc injection of either saline (0.5 ml) or naloxone (2.5 mg/kg) have been tested in the following four groups of animals: 1) normal male rats; 2) normal female rats; 3) female rats treated on the second day of life with 1.25 mg testosterone (androgenized female rats); and 4) male rats orchidectomized 2 days postnatally (demasculinized male rats). The naloxone challenge has been provided when the animals were 16, 26, and 60 days old; the animals were killed in the afternoon 20 min after treatment. The results obtained have shown that the acute injection of naloxone significantly decreases serum levels of PRL in normal males and in androgenized females at all ages considered. On the contrary, the opioid antagonist was always ineffective in normal females and in neonatally castrated males. The treatment of male rats with naloxone was without any effect on LH release before puberty (at 16 and 26 days of age), but induced a significant increase of serum LH titers after sexual maturation (60 days). In normal females, naloxone brought about a significant increase of serum LH only at 16 and 60 days (animals in estrus), but not at 26 days. Treatment with naloxone did not exert any significant effect on LH release in androgenized females and in deandrogenized males of any age. The present data suggest that, in the rat a sexual difference exists in the opiatergic control of PRL secretion; apparently, the central opioid systems which regulate PRL secretion develop towards a male pattern because of the presence of androgens in the neonatal period. On the contrary neonatal androgens do not seem to exert any important effect in directing the organization of the opiatergic mechanisms controlling LH release.

Aging↗
PubMed1988

Effects of aging on pituitary and testicular luteinizing hormone-releasing hormone receptors in the rat.

Aging exerts profound influences on the function of the hypothalamic-pituitary-testicular-axis. This work has been performed in order to verify whether, in male rats, the decreased secretion of LH and testosterone (T) occurring in old animals is reflected by modifications of luteinizing hormone-releasing hormone (LHRH) receptors at the level of the anterior pituitary and of the testes. To this purpose, the affinity constant (Ka) and the maximal binding capacity (Bmax) for the LHRH analog [D-Ser(tBu)6]des-Gly10-LHRH-N-ethylamide were evaluated, by means of a receptor binding assay, in membrane preparations derived from the anterior pituitary and testicular Leydig cells of male rats of 3 and 19 months of age. Serum levels of LH and T were measured by specific RIAs. The results obtained show that, in aged male rats, the concentration of pituitary LHRH receptors is significantly lower than that found in young animals. On the other hand, the concentration of LHRH binding sites is significantly increased on the membranes of Leydig cells of old rats. In no instance the Ka for the LHRH analog is significantly affected. Serum levels of LH and T are significantly lower in old than in young male rats. In conclusion, these results suggest that the reduced secretion of LH in old male rats may be linked, at least partially, to a decrease of the number of pituitary LHRH receptors. The impaired production of testosterone occurring in aged rats is accompanied by a significant increase of the number of testicular LHRH receptors, indicating that also the intratesticular mechanisms controlling testosterone release undergo significant alterations with aging.

Aging↗
PubMed1987

Decrease of mu opioid receptors in the brain and in the hypothalamus of the aged male rat.

Experiments have been designed in order to analyze whether the binding capability of mu opioid receptors in the brain of the male rat is modified by age. In a first experiment, the number of receptors (Bmax) and the constant of affinity (Ka) for the mu ligand 3H-dihydromorphine (3H-DHM) have been measured in the whole brain of male rats of 2, 15 and 22 months of age. In a second experiment the Bmax and the Ka for 3H-DHM have been evaluated in the hypothalamus of male rats of 2 and 22 months of age. In this experiment it was also investigated whether the administration of exogenous testosterone modifies the number and/or the affinity of the hypothalamic mu receptors. Serum levels of LH, FSH, prolactin and testosterone have been measured by specific RIAs. The results obtained show that: serum testosterone levels are significantly decreased in aged rats, while serum LH and FSH show only a small decline; serum prolactin is higher in old than in young animals; the number of mu receptors in the whole brain of 15 and 22 month old animals and in the hypothalamus of 22 month old rats is significantly lower than in the same tissues of young animals; the administration to old animals of testosterone, in doses able to bring back towards normal serum levels of testosterone, induces a decrease of LH and FSH, but has no effect on serum prolactin titers. Testosterone administration does not modify the number of hypothalamic mu opioid receptors, indicating that the decline of brain mu receptors in old animals is not the consequence of the physiological decline of testosterone secretion; in no instance the Ka for the mu ligand is significantly affected.

Aging↗