Possible role of dopamine as transmitter to promote discharge of LH-releasing factor

The Increase in Signaling by Kisspeptin Neurons in the Preoptic Area and Associated Changes in Clock Gene Expression That Trigger the LH Surge in Female Rats Are Dependent on the Facilitatory Action of a Noradrenaline Input

In rodents, kisspeptin neurons in the rostral periventricular area of the third ventricle (RP3V) of the preoptic area are considered to provide a major stimulatory input to the GnRH neuronal network that is responsible for triggering the preovulatory LH surge. Noradrenaline (NA) is one of the main modulators of GnRH release, and NA fibers are found in close apposition to kisspeptin neurons in the RP3V. Our objective was to interrogate the role of NA signaling in the kisspeptin control of GnRH secretion during the estradiol induced LH surge in ovariectomized rats, using prazosin, an α1-adrenergic receptor antagonist. In control rats, the estradiol-induced LH surge at 17 hours was associated with a significant increase in GnRH and kisspeptin content in the median eminence with the increase in kisspeptin preceding that of GnRH and LH. Prazosin, administered 5 and 3 hours prior to the predicted time of the LH surge truncated the LH surge and abolished the rise in GnRH and kisspeptin in the median eminence. In the preoptic area, prazosin blocked the increases in Kiss1 gene expression and kisspeptin content in association with a disruption in the expression of the clock genes, Per1 and Bmal1. Together these findings demonstrate for the first time that NA modulates kisspeptin synthesis in the RP3V through the activation of α1-adrenergic receptors prior to the initiation of the LH surge and indicate a potential role of α1-adrenergic signaling in the circadian-controlled pathway timing of the preovulatory LH surge.

Role of the Ventricular System in Neuroendocrine Processes: Synthesis and Distribution of Thyrotropin Releasing Factor (TRF) in the Hypothalamus and Third Ventricle

In vitro biosynthesis of thyrotropin releasing factor (TRF) by different regions of the hypothalamus of mink was examined. Homogenates of hypothalamic tissue were incubated in Krebs-Ringer medium containing 200 mg% glucose, 10-5M ATP, 0.1 mM histidine and glutamic acid and 0.15 μ c 3H-proline (40 Cilmmol) per mg. tissue. Extraction, purification and estimation of 3H-TRF biosynthesis involved several steps of charcoal extraction, carboxymethylcellulose and sephadex chromatography. 3H-TRF was synthesized throughout the entire antero-posterior extent of the hypothalamus in its dorsal and medial portions. 3H-TRF was synthesized also in a more discreet region, the arcuate nucleus. In vitro biosynthesis of 3H-TRF was stimulated significantly by thyroxine, but not by TSH, estradiol, corticosterone or melatonin. A method is described for collection of cerebrospinal fluid of the third ventricle of the rat brain; TRF concentration in this fluid was approximately in normal animals.

The distribution of TRF-producing cells in the hypothalamus and presence of TRF in cerebrospinal fluid of the third ventricle is discussed with respect to the hypothesis that this releasing factor may be delivered to the median eminence and adenohypophysis in part, via the cerebrospinal fluid.

Aproteic diet decreases hypothalamic catecholamine turnover in adult male rats

Previous reports indicate that malnutrition reduces reproductive functions. We have demonstrated that protein deprivation in the diet also causes reproductive dysfunction by reducing hypothalamic GnRH secretion. Noradrenaline and nitric oxide are modulators of GnRH secretion. Noradrenaline stimulates GnRH secretion and nitric oxide inhibits catecholamine release. This work studies the hypothalamic catecholaminergic and nitrergic neuron activity in Wistar adult male rats fed on an aproteic diet (AP) during 21 days; this treatment was started when rats were 70 days old. Our first experiment studied catecholamine turnover rate after inhibition of tyrosine hydroxylase activity by injecting (i.p.) 400 mg/kg alpha-methyl-p-tyrosine. Our second experiment studied in vitro hypothalamic nitric oxide synthase (NOS) activity in animals under the same diet. AP diet significantly decreased both noradrenaline (P<0.05) and dopamine (P<0.05) hypothalamic turnover rate. Noradrenaline turnover in cerebral cortex was not altered by the aproteic diet. However, hypothalamic NOS activity was not affected in animals fed on an AP diet. These results indicate that the lack of protein in the diet reduces catecholaminergic neuron activity in adult male rats by a NO-independent mechanism, thus suggesting that a decrease in noradrenergic activity may be involved in the reduction of GnRH secretion induced by an AP diet.

Effect of morphine on hypothalamic tyrosine hydroxylase mRNA levels in dopaminergic neurons and on preoptic DOPAC levels measured by microdialysis

Morphine not only suppresses norepinephrine-induced increases in LHRH mRNA levels but, in these same animals, it simultaneously amplifies norepinephrine (NE)-induced LH release. These observations suggest that NE may activate parallel mechanisms which independently increase LHRH mRNA levels and LHRH release and suggest that some of these effects could be mediated indirectly via morphine's action on different components of the hypothalamic dopamine (DA) system. Accordingly, in the present studies we examined the effects of morphine on various components of this dopamine system using as our index of altered DA neuronal activity, the changes which occur in tyrosine hydroxylase (TH) mRNA levels following morphine. As an ancillary index of changes which occur in dopamine neuronal activity, we measured, by microdialysis, the changes which occur in preoptic dihydroxyphenylacetic acid (DOPAC) levels after either subcutaneous injections or following microinfusions of morphine into the zona incerta (ZI). In a final study, we evaluated whether DA when given alone (icv infusion) or prior to icv NE would altered LH release. Single cell levels of TH mRNA in preoptic A15 and periventricular anterior hypothalamic A14 DA neurons were not affected by morphine 1, 5 and 24 h later. In contrast, within 1 h after morphine, TH mRNA levels in ZI A13 neurons were significantly elevated and they remained high at 5 nd 24 h compared to controls. Morphine also resulted in a significant rise in TH mRNA levels in tuberoinfundibular DA neurons (TIDA) (A12) within 1 h and these levels remained high to 5 h. Thereafter, by 24 h, message levels had returned to control values. Morphine also resulted in a rapid rise in plasma prolactin (Prl) with peak values occurring at 20 min and then returning to baseline by 90 min. When morphine was given sc it resulted, within 15 min, in a rapid rise in preoptic DOPAC levels and these levels continued to rise such that they were 217% higher than pretreatment values by 105 min. Preoptic 5-hydroxyindoleacetic acid (5-HIAA) levels also increased by 25-75% after sc morphine. The microinfusion of morphine into ZI also resulted in elevated preoptic DOPAC but not 5-HIAA levels within 15 min. The icv infusion of DA alone had no effect on plasma LH whereas, NE (icv) produced a modest but significant increase in plasma LH. When DA was given 15 min prior to the infusion of NE, neither amplification nor inhibition of NE-induced LH release occurred. From these and other studies we conclude that the morphine-induced suppression of TIDA neuronal activity may allow NE to release greater amounts of LHRH from axon terminals in the median eminence.(ABSTRACT TRUNCATED AT 400 WORDS)

Luteinizing hormone-releasing hormone and gamma-aminobutyric acid neurons in the medial preoptic area are synaptic targets of dopamine axons originating in anterior periventricular areas

The aim of this study was to characterize further the transmitter content and the location of the parent cells of tyrosine hydroxylase-immunoreactive boutons terminating on luteinizing hormone-releasing hormone- and glutamic acid decarboxylase-immunoreactive neurons in the rat medial preoptic area. Electron microscopic immunostaining for luteinizing hormone-releasing hormone, tyrosine hydroxylase or glutamic acid decarboxylase was performed on desipramine-pretreated (to protect norepinephrine and epinephrine axons) rats which received a stereotaxic injection of 6-hydroxydopamine into the medial preoptic area anteroventral periventricular nucleus 48 h prior to sacrifice. This treatment induced acute degeneration of dopamine axon terminals characterized by the development of autophagous cytolysosomes, an early morphological sign of catecholamine axon degeneration. To further define the cells of origin of these dopamine boutons, the anterograde marker Phaseolus vulgaris leucoagglutinin was iontophoretically applied to the zona incerta. Six days later, rats received a 6-hydroxydopamine injection into the zona incerta or the lateral ventricle, and 48 h later, double immunostaining was performed for Phaseolus vulgaris leucoagglutinin and tyrosine hydroxylase, luteinizing hormone-releasing hormone, or glutamic acid decarboxylase on preoptic area vibratome sections. Following the 6-hydroxydopamine injection into the anteroventral periventricular nucleus, autophagous cytolysosome-containing degenerated axons were found in synaptic contact with both luteinizing hormone-releasing hormone and GABA neurons in the medial preoptic area, confirming that these are dopaminergic connections. Following the double injection treatment, 6-hydroxydopamine-induced degenerated, Phaseolus vulgaris leucoagglutinin-labeled dopamine axons originating in the zona incerta were not found to contact luteinizing hormone-releasing hormone-containing or GABA cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Dopamine regulation of gonadotropin-releasing hormone (GnRH) gene expression in the female rat brain

The effects of the dopaminergic antagonist haloperidol (HAL) as well as the D2 dopamine receptor agonist bromocriptine (BRO) on gonadotropin-releasing hormone (GnRH) mRNA levels in intact and hypophysectomized rats were investigated by quantitative in situ hybridization. In situ hybridization was performed using a 35S-labelled 48-base oligodeoxynucleotide complementary to the GnRH coding region of the GnRH DNA. In intact animals, a 14-day treatment with BRO increased by 70% the number of silver grains per neuron while HAL decreased by 20% the value of this parameter. Hypophysectomy which induced a 32% decrease in the hybridization signal could not prevent the effects of BRO or HAL. The present data clearly demonstrate that GnRH mRNA levels are positively regulated by dopamine and that the effects of BRO and HAL on GnRH mRNA are not mediated by variations in pituitary hormone secretion.

Effects of the antidopaminergic drug veralipride on LH and PRL secretion in postmenopausal women

Patterns of LH and PRL secretion have been evaluated in 15 postmenopausal women before and after the chronic blockage of the D2 dopamine receptors with veralipride (100 mg twice daily, for 30 days). In addition, the possible influence of the antidopaminergic drug on the activity of the endogenous opioid system has been evaluated by the infusion of the opioid antagonist naloxone, performed before and during veralipride administration. Mean plasma LH levels were significantly blunted (p less than 0.05) and mean plasma PRL levels were significantly increased (p less than 0.001) by veralipride administration. The frequency of both LH and PRL secretory pulses was not modified, while the mean pulse amplitude of both hormones was significantly increased (p less than 0.05 for LH; p less than 0.001 for PRL) by veralipride administration. In untreated postmenopausal women naloxone infusion did not modify LH secretion. Following veralipride, the infusion of naloxone significantly increased (p less than 0.05) the mean plasma LH levels, had no influence on the frequency and significantly reduced (p less than 0.01) the amplitude of LH pulses, expressed as the percent increase from the nadir to the peak. Both before and after veralipride administration, naloxone failed to modify the pattern of PRL secretion. In untreated postmenopausal women, the percentage of concomitant PRL and LH pulses was significantly higher (p less than 0.001) during naloxone than during saline infusion, and this effect was amplified by veralipride administration (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Methods for the study of somatostatin

It is clear from the above that there are a number of methods for study of SRIF release. From the standpoint of convenience, the in vitro static incubation of ME is the most practical technique at the present time. Using this preparation SRIF release has been found to be modified by a number of neurotransmitters and peptides, and studies on the mechanism of release of the peptide have been initiated. There is no doubt that such studies should be complemented by perifusion studies, by studies involving larger pieces of the hypothalamus which encompass the entire somatostatinergic neuron, and by in vivo studies to determine the correlation of in vivo and in vitro release. Among the in vivo techniques which have been utilized, the push-pull cannula technique employing cannulae implanted in hypothalamus or anterior pituitary gland offers the most promise. A summary of the effects of some neurotransmitters and neuropeptides on hypothalamic SRIF secretion is reported in Table. I.

Reversibility of the toxic effect of lead on the male reproductive axis

The present study investigates the reversibility of the toxic effects of lead on the hypothalamic-pituitary-testicular axis in prepubertal and pubertal male rats. Male Wistar rats, 27 days and 52 days old, were given ad libitum access to 0.0% or 0.6% lead acetate containing water. Groups of animals were sacrificed at the end of 30 days of exposure or after a 30-day recovery period. Blood lead and free erythrocyte porphyrin (FEP) levels in the lead-treated groups were significantly higher than in the control animals (P less than 0.001). The animals in the recovery groups had lower, albeit not normal, blood lead and FEP levels 30 days after discontinuing treatment. Serum testosterone, intratesticular sperm counts, and sperm production rates were suppressed in the lead-treated groups (P less than 0.001). Serum testosterone and sperm parameters normalized at the end of the recovery period in the prepubertal animals but not in the pubertal animals.

Luteinizing hormone response to domperidone in hyperprolactinaemic women with pituitary microadenomas

Administration of a dopamine (DA) antagonist, domperidone, increased circulating levels of LH in hyperprolactinaemic-amenorrhoeic women with pituitary microadenomas but not in normal women in the early follicular phase of the menstrual cycle. This drug does not readily cross the blood-brain barrier and therefore the site of action of domperidone could be the pituitary gland or the median eminence. As the simultaneous administration of GnRH and domperidone did not increase the GnRH-induced LH release in hyperprolactinaemic women, the site of action of domperidone is likely to be the median eminence.

Multifactorial control of pituitary hormone secretion: the "wheels" of the brain

An attempt is made to deal with the complexity of the nerve fibers in the median eminence. Visual aids are presented in the shape of "wheels" that depict a dynamic interplay of neurochemicals which result in the release of hormones from the anterior pituitary gland. The multiplicity of neurochemicals in the median eminence is perceived to be responsible for the integrated control of pituitary hormone releasing factors.

Apomorphine-induced behaviour during the oestrous cycle of the rat

The effect of various doses of apomorphine (APO) (25, 250, 400 and 750 micrograms/kg, s.c.) on open field behaviour, stereotyped behaviour, body temperature and concentrations of serum oestradiol was studied in cycling females and in ovariectomized rats. With the exception of grooming, the hormonal variations during the cycle, or the ovariectomy, did not have an effect on behaviour related to stimulation of presynaptic dopamine (DA) receptors. The endocrine status on proestrus (PE), characterized by an increase in serum oestradiol, did influence hyperlocomotion and hypothermia induced by apomorphine; the former being attenuated and the latter increased, as compared to the other phases of the cycle. Ovariectomy resulted in an increase in the stimulatory effect of apomorphine on locomotion. Stereotypy induced by apomorphine was unaltered by hormonal variations during the cycle and it was slightly attenuated by removal of the ovaries. During phases of low levels of oestrogen (oestrus, metestrus) apomorphine significantly increased the levels of serum oestradiol, determined 30 min after the administration of drug. It is concluded that the various DAergic mechanisms in brain are differentially affected by hormonal variations during the cycle and by ovariectomy.

Inhibition of the preovulatory LH surge after a catecholestrogen (2-hydroxyestrone) antiserum injection in the third ventricle of cycling female rats

Administration of a catecholestrogen (2-hydroxyestrone, 2-OHE1) antiserum (2-OHE1-AS) in the third ventricle of cycling female rats, on the morning of proestrus, leads to a significant reduction in the afternoon LH surge. These responses are dose-dependent and can be observed even when the 2-OHE1-AS is injected on the diestrus morning. Almost similar results were obtained with an antiserum against 17 beta-estradiol (17 beta-E2). Nevertheless, the fact that the central immunoneutralization of 2-OHE1 impedes the preovulatory surge of LH at a time of high peripheral levels of 17 beta-E2 strengthens the idea of a specific role for 2-OHE1 in the control of cycling LH release.

Effects of different dopamine agonists and antagonists on post-menopausal hot flushes

The dopaminergic system seems to be involved in both pulsatile luteinizing hormone (LH) secretion and hot flushes in post-menopausal women. With the aim of further clarifying its role, the effectiveness of dopaminergic and antidopaminergic drugs in the treatment of hot flushes was studied. Self-assessed scores for vasomotor symptoms were evaluated in 5 groups of 15 patients treated for 20 days with one of the following agents: placebo; the dopamine receptor agonist, bromocriptine; the indirect dopaminergic agent, Liposom; the antidopaminergic drug, veralipride or the peripheral antidopaminergic agent, domperidone. All of these treatment regimens were effective in alleviating hot flushes, but the pharmacological agents proved to be more effective than the placebo. A direct dopaminergic action is hypothesized in the case of bromocriptine and Liposom, while the antidopaminergic drugs might act through different indirect mechanisms such as the short-loop feedback exerted by hyperprolactinaemia on tuberoinfundibular dopamine (TIDA) neurons with a secondary dopamine-like activity, or stimulation of the opioid system.

The choice of a model for studying the hypothalamus-pituitary interactions in vitro

Comparative studies on the release of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and prolactin (Prl) by the whole pituitary, pituitary plus hypothalamus and pituitary-hypothalamus complex (PHC) were undertaken to choose an appropriate model for studying the hypothalamus-pituitary interactions in vitro and to relate the importance of the intact neural connections between pituitary and hypothalamus on hypothalamus-pituitary interactions. Also the effect of including dopamine (DA) at 1 X 10(-7) mol/1 in these different in vitro systems on the release of LH, FSH and Prl was investigated. The pituitary released increasing amounts of LH and FSH at 2, 4 and 6 h but the amount of Prl released remained unchanged. The rates of release of LH, FSH and Prl by the pituitary were different and were characteristic of each hormone. Co-incubation of pituitary with hypothalamus stimulated the release of LH and FSH but inhibited the release of Prl. Pituitary-hypothalamus complex behaved almost identical to behaved almost identical to pituitary plus hypothalamus system. Inclusion of 1 X 10(-7) M DA in the incubation medium stimulated the release of LH (80%) but inhibited the release of Prl (71%) by PHC. FSH was unaffected. DA had no significant effect on the release of LH, FSH and Prl by pituitary and pituitary plus hypothalamus systems. It is suggested that PHC is the system of choice for studying hypothalamus-pituitary interactions in vitro.

Influence of cerebroventricular injection of dopamine on plasma prolactin and LH levels of postlaying and broody turkey hens

Dopamine (DA), a well-known inhibitor of prolactin secretion in mammals, was injected into the third cerebroventricle of turkey hens in two distinct physiological states. Nonbroody postlaying turkeys had preinjection plasma prolactin (Prl) levels of about 68 ng/ml. Prolactin levels were significantly elevated 20 and 40 min after intraventricular injection of 10 micrograms of dopamine and then returned to basal levels. Incubating turkey hens, in contrast, showed the typical hyperprolactinemia characteristic of this physiological state. Mean preinjection Prl levels ranged from about 1290 to 1860 ng/ml. Injection of 10 or 30 micrograms of dopamine neither increased nor decreased plasma Prl levels over the 120-min time course of this experiment. Plasma luteinizing hormone (LH) levels were increased in nonbroody postlaying hens within 40 min after intraventricular injection of 10 micrograms of DA and then declined. Levels in vehicle-injected hens did not change significantly up to 120 min after injection. Dopamine injection had no effect on LH levels of broody turkey hens. These data clearly show that DA is not an inhibitor of Prl secretion in nonlaying turkeys with moderate Prl levels and in fact it appears to stimulate its release.

Dopamine decreases release of luteinizing hormone releasing hormone from superfused rat mediobasal hypothalamus

The effects of dopamine hydrochloride (DA) on the releases of LHRH and LH were examined in a serial sequential double chamber perifusion system by perifusing the mediobasal hypothalamus including the preoptic area and/or pituitaries excised from diestrus female rats. DA, perifused at a dose of 4.2 X 10(-4) M, significantly (p less than 0.05) lowered LH secretion from the pituitary in series with the hypothalamus 40-80% below the preinfusion level, but it had no effect on LH efflux from the pituitary perifused alone. DA also significantly (p less than 0.05) reduced the LHRH level 20-40% below the initial level. Perifusion with the DA receptor blocker haloperidol at a concentration of 10(-6) M abolished the suppressive effect of DA on LH secretion. These findings indicate that DA suppressed hypothalamic LHRH release, resulting in decrease in LH secretion from the pituitary in diestrus rats.

Demonstration of serotoninergic axons terminating on luteinizing hormone-releasing hormone neurons in the preoptic area of the rat using a combination of immunocytochemistry and high resolution autoradiography

The synaptic relationship between serotoninergic terminals and luteinizing hormone-releasing hormone-containing neurons was investigated in the medial preoptic area using a combined technique. Axon terminals selectively taking up 5-[3H]hydroxytryptamine were labelled autoradiographically and luteinizing hormone-releasing hormone-containing neuronal elements were identified by means of immunocytochemistry. Synaptic contacts were observed between tritiated 5-hydroxytryptamine-labelled boutons and luteinizing hormone-releasing hormone-immunoreactive dendrites. About 5% of the boutons which formed synapses with luteinizing hormone-releasing hormone-immunoreactive dendrites were found to be labelled by the tritiated indolamine. Luteinizing hormone-releasing hormone-immunoreactive axon terminals occurred as presynaptic elements in contact with unidentified dendritic spines, shafts or perikarya. These observations provide morphological basis for the idea that 5-hydroxytryptamine-containing neurons can act directly on luteinizing hormone-releasing hormone release. Further, they support the assumption that luteinizing hormone-releasing hormone is not only a neurohormone but may also function as a neurotransmitter or neuromodulator.

Dopamine antagonists do not block testosterone-induced decrease in luteinizing hormone

These studies were designed to test the hypothesis that testosterone might lower circulating levels of luteinizing hormone (LH) in castrated male rats by activating dopaminergic neuronal systems. Blood samples were drawn from conscious rats through an indwelling cannula during the fourth and eight hours after subcutaneous administration of testosterone (1 or 5 mg/kg, in corn oil). Testosterone caused a dose-dependent decrease in plasma LH levels eight hours after administration. This decrease was not blocked by prior administration of the dopaminergic antagonists haloperidol and flupenthixol. This lack of effect of dopaminergic antagonists indicates that testosterone does not act primarily via dopaminergic activation to lower LH.

Effects of increased central dopaminergic tonus on gonadotropin secretion

Gonadotropin secretion was investigated in 10 healthy volunteers (5 men and 5 women in the early follicular phase of cycle) by the following procedures: i) infusion of saline over 4 1/2 h period; ii) infusion of dopamine (DA) 4 microgram/kg bw/min over 4 h period; iii) oral administration of L-dopa (D) 100 mg plus carbidopa (C) 35 mg after 24 h pretreatment with C 50 mg every 6 h. This last pharmacological approach selectively enhances the central dopaminergic tonus. Blood samples were withdrawn every 15 min over 4 1/2 h period. No ultradian periodicity in LH and FSH secretion was observed. No significant modification in serum FSH levels was induced by any treatment at any time, while a significant decrease in serum LH concentration was observed from 45 to 240 min during DA infusion (-46.8%; p less than 0.005) and from 60 to 240 min after D + C administration -41.5%; p less than 0.05). These data demonstrate that, in humans, acute dopaminergic stimuli have an inhibitory action on LH release and suggest that this inhibition is exerted at the central level.

Amplification of LH response to LHRH by dopamine infusion in eugonadal women

Although the role of biogenic amines in the regulation of gonadotropin release has been studied extensively, the precise role of dopamine (DA) in stimulating LHRH and/or LH release is still controversial. In the present study 6 eugonadal women, aged 20-30, were given an LHRH infusion on day 6 of the menstrual cycle and the pattern and magnitude of LH and FSH responses were estimated. On day 6 of the next cycle, the experiment was repeated and DA was also infused beginning 60 min after the start of the LHRH infusion. Following LHRH infusion plasma LH showed a marked and significant rise with a mean peak increment at 4 h, and with a cumulative response (CR) of 9136 +/- 955 mIU/ml/6h. The pattern of FSH response tended to parallel that of LH; however, mean peak increment at 4 h and a CR of 2640 +/- 169 mIU/ml/6h were markedly lower. Plasma prolactin levels remained unchanged. Addition of DA to LHRH at 60 min evoked a significantly greater mean peak LH increment at 4 h and a CR of 15514 +/- 1836 mIU/ml/6h (p less than 0.001). There were no significant changes in either mean FSH peak at 4 h or in the CR (3257 +/- 309 mIU/ml/6h). As expected, a highly significant (p less than 0.001) decrease in circulating PRL from 12.1 +/- 3.1 to 3.0 +/- 1.5 ng/ml was seen during DA infusion. In conclusion, DA given by iv infusion enhancement LH response to LHRH in eugonadal women under the conditions of the present investigation, supporting a role for a dopaminergic component in the control of LH release in women.

Dopamine inhibits the naloxone induced gonadotrophin rise in man

Twenty milligrams of the opiate receptor antagonist naloxone were infused over 3 h to five young male volunteers. Naloxone produced a significant rise in both LH and FSH, but did not affect serum prolactin levels. The infusion of dopamine (4 microgram . kg-1 . min-1) completely abolished the naloxone effect on gonadotrophin release. The results suggest a possible interaction between dopamine, opioid receptors and gonadotrophin secretion in man.

Effects of sulpiride induced hyperprolactinaemia in patients with Turner's syndrome

In order to evaluate the interference of prolactin (PRL) on some aspects of pituitary-gonadal derangement observed in patients with hyperprolactinaemic amenorrhoea (HA), a GnRH stimulation test (100 micrograms i.v.) was performed on twenty-one patients with hyperprolactinaemia without evidence of pituitary tumour and in nine subjects with Turner's syndrome (TS) before and after sulpiride administration (200 mg/day orally, for 3 months). In patients with HA an enhanced response of gonadotrophins to GnRH was observed. In patients with TS a further increase of the gonadotrophin hyper-responsiveness to the releasing hormone occurred when hyperprolactinaemia was induced by chronic sulpiride administration. Since, in these patients, appreciable ovarian steroidogenesis is lacking, a direct effect of the increased plasma PRL at the hypothalamo-pituitary level is likely. In hyperprolactinaemic amenorrhoea pituitary hyper-responsiveness may not be due to PRL effects on ovarian steroidogenesis.

Evidence for central nervous system (CNS) involvement in inhibition of luteinizing hormone (LH) release by dopamine receptor stimulation

A pharmacologic study using 2-Br-alpha-ergocryptine (CB-154), a dopamine (DA) receptor agonist, the pimozide, a specific DA receptor antagonist, was undertaken to evaluate effects of manipulation of the DA system on plasma LH levels and on the ability of the pituitary to release LH following LHRH stimulation. Intraveneous administration of CB-154 lowered plasma LH levels in ovariectomized rats. Prior treatment with pimozide blocked the effect of CB-154, supporting dopaminergic system mediation in the observed response. Inhibition of LH release by pharmacologic stimulation of DA receptors did not appear to occur at the level of the pituitary, as pituitary release of LH following LHRH was not altered in CB-154 treated rats.

Factors altering the secretion of LHRH from superfused fragments of rat hypothalamus

This paper deals with the effect of temperature (t degrees), ions, prostaglandin (PGE2) and testosterone on the rate of release of LHRH from the superfused medial basal hypothalamus (MBH) of normal or castrated male rats in an effort to further validate the biological properties of this preparation. LHRH in the perfusate is nondetectable when the MBH is at 0 C, warming to 37 C produces a sharp rise in LHRH and then stabilization at a level at least threefold the one calculated for the 0 C experiment. Basal release rate of LHRH is t degrees and calcium dependent, as is the stimulatory action of potassium. Infusion of high K+ induces approximately a fivefold increase in the release rate of LHRH and stays at this high level for as long as the infusion lasts (50 min). LHRH stimulation by PGE2 (pulse) proceeds in the absence of external calcium, and the effect lasts longer than the potassium (pulse) action. Surprisingly, MBHs from long-ter castrated males (60-90 days) release less LHRH per minute than intact male MBHs during the steady state phase of LHRH secretion; testosterone propionate (TP, 200 microgram/100 g BW x 3 days) increases significantly the rate of release in castrate rats and is not related to the amount of LHRH assayed in the MBH. MBHs of untreated castrated rats or castrated rats treated with TP, show a reduced LHRH secretion in response to PGE2. It is concluded that this preparation can be used at advantage to study the rate of LHRH release in a variety of experimental paradigms.

Study of the effects of neurotransmitters on the hypothalamus-pituitary-testis function in in vitro cell suspension system

The effects of different neurotransmitters were tested in vitro on a hypothalamic tissue, collagenase-digested isolated anterior pituitary and Leydig cell suspension system by measuring the testosterone production of the Leydig cells. Neurotransmitters were used in concentrations of 0.25, 1.0, 2.5, 5.0, and 10.0 micrograms/ml incubation medium. Dopamine in doses of 1.0, 2.5, and 5.0 micrograms/ml increased the hypothalamic tissue-induced pituitary-testis activation, while it had no direct effect on pituitary and Leydig cells. Noradrenaline in the concentration range 2.5--10.0 micrograms/ml decreased the luteinizing-hormone-releasing-hormone (LHRH) sensitivity of the pituitary cells. 5.0 and 10.0 micrograms/ml 5-hydroxytryptamine decreased the testosterone production and the hCG sensitivity of the isolated Leydig cells. Carbamylcholine and pilocarpine had no action on the in vitro system at the different levels studied.

Studies on dopamine turnover in ovariectomized or hypophysectomized female rats. Effects of 17 beta-estradiol benzoate, ethynodioldiacetate and ovine prolactin

The effects of 17 beta-estradiol benzoate (EB), ethynodioldiacetate and ovine prolactin on dopamine (DA) turnover have been studied. As an index for a change in turnover, differences in DA depletion following tyrosine hydroxylase inhibition with alpha-methyl-tyrosine methylester were observed. DA was measured by means of mass fragmentographical analysis in the rat median eminence, the olfactory tubercle and the striatum. The actions of ethynodioldiacetate and ovine prolactin on DA turnover in various subregions of the rat median eminence were analysed by quantitative microfluorimetry. Repeated injections of EB to ovariectomized rats resulted in a significant increase of DA turnover in the median eminence. Administration of ethynodioldiacetate to ovariectomized rats almost significantly increased DA turnover in the olfactory tubercle. In the median eminence DA turnover was significantly increased only in the lateral palisade zone. In male hypophysectomized rats ovine prolactin increased DA turnover in both the lateral and the medial palisade zone of the median eminence. The results support the involvement of DA neurons in the control of prolactin and luteinizing hormone secretion. It is suggested that the tubero-infundibular DA neurons are involved in mediating the central inhibitory feedback actions of prolactin and gonadal steroids on prolactin and LH secretion, respectively.

L-dopa and oligozoospermia

A clinical investigation of L-Dopa on idiopathic oligozoospermia is carried out. Thirty nine male oligozoospermic patients with primary sterility were divided in two groups. The first group of 25 patients was treated with 500 mg a day during two months. The second group of 14 patients received 750 mg a day for the same time. In the first group we find 14 improvements, 9 at the first month and 5 at the second month. In the second group 8 improvements were observed, 5 in the first month and 3 in the second months. It would seem that L-Dopa has a stimulatory effect on spermatogenesis possibly through hypophysis when it is administered at these dosis and for these periods of time, and it was also observed similar results for longer terms of treatment.

The effect of marihuana (delta-9-tetrahydrocannabinol) on the secretion of luteinizing hormone in the ovariectomized rhesus monkey

Despite the widespread use of marihuana by large numbers of young adults in the reproductive years, little is known about the effects of this drug on reproductive function. information on the effect of the drug on the woman is particularly meager. The rhesus monkey provides an excellent animal model from which to generalize to man. While the primary purpose of the project is to determine the effect of long-term administration on the cycling female monkey, the initial studies were carried out in the ovariectomized monkey with resulting elevated gonadotropin levels under conditions of short-term administration of the drug. Marihuana causes a reversible depression in luteinizing hormone levels in the ovariectomized female rhesus monkey.

Current concepts of prolacting physiology in normal and abnormal conditions

Currently the physiology and pathophysiology of pituitary prolactin secretion are under intensive investigation. Development of sensitive, specific radioimmunoassays for hPRL and improved roentgenographic techniques have increased the diagnostic acumen for incipient pituitary microadenomas. Several modalities of treatment are available at the present time which can result in improvement in the clinical symptoms of the amenorrheagalactorrhea syndromes. Eponymic classification of amenorrhea-galactorrhea syndromes should be discarded and appropriate diagnostic studies initiated to determine the etiology of the inappropriate breast secretion and/or elevated serum hPRL level.

Catecholamine turnover alterations in discrete areas of the median eminence of the 4- and 5-day cyclic rat

Using quantitative microfluorimetry in combination with tyrosine hydroxylase inhibition (H44/68) the concentration and turnover of noradrenaline (NA) and dopamine (DA) was studied in the subependymal layer (SEL) and the medial (MPZ) and lateral palisade zone (LPZ) of the rat median eminence during the 4- and 5- day vaginal estrous cycle. Significant cyclic variations were only found in SEL and LPZ. The NA turnover in SEL was high on proestrous and low on all other days of the 4-day estrous cycle, whereas in the 5-day estrous cycle the NA turnover in SEL started to increase already on the second day of diestrous to reach a peak in the afternoon of proestrous. At that time also the NA concentrations in SEL were increased, although significantly only in the 5-day cyclic rats. The DA turnover in LPZ was low on proestrous and high on all other days in both 4-and 5-day cyclic rats. Apart from the median eminence cyclic variations in catecholamine metabolism were only found in the medial preoptic area, where NA turnover was high on proestrous and low on estrous-diestrous. The present findings give further support for the existence of a facilitatory noradrenergic and inhibitory dopaminergic mechanism in the control of gonadotrophin release. Furthermore, it is suggested that an acceleration of reticulo-hypothalamic NA turnover precedes the retardation of tubero-infundibular DA turnover found on proestrous and that the time lag between initial NA activation and subsequent DA inactivation is longer in the 5-than in the 4-day estrous cycle.

Effects of intraventricular 6-hydroxydopamine injections on serum prolactin and LH levels: absence of stress-induced pituitary prolactin release

The drug 6-hydroxydopamine (6-OHDA) has been reported to reduce hypothalamic norepinephrine (NE) content after administration into the lateral ventricle without altering the dopamine content of tubero-infundibular neurons. Serum prolactin levels in male rats injected with 2 X 250 mug 6-OHDA were significantly higher than in untreated control rats. Intraventricular injection of male rats with artificial cerebrospinal fluid resulted in elevated mean prolactin levels similar to those observed in 6-OHDA-treated animals. Further experimentation on animals decapitated at different times after removal from the animal quarters, indicates that prolcatin levels in 6-OHDA-treated rats are continuously elevated whereas they rise from basal levels to extremely high levels in CSF-treated rats, thus resulting in similar mean values. The CSF-treated controls ate hypersensitive to the stress of being removed from their normal environment. Such an effect was not observed in 6-OHDA-treated nor in untreated, and thus stress-inexperienced rats. In a long term study, serum prolactin and luteinizing hormone (LH) levels were followed over a period of 71 days after 6-OHDA treatment. Prolactin levels increased within one day after treatment and stayed at a high level for 15 days. Subnormal prolactin values were measured 37 days after 6-OHDA treatment. Serum LH levels were below normal 3 h and one day and were increased 37 and 71 days after 6-OHDA treatment. These results suggest that NE is important in the transmission of stressful stimuli to hypothalamic prolactin regulating centers. They further suggest functional recovery of LH and prolactin regulating mechanisms after 6-OHDA treatment.