Rat Pars Tuberalis Research Articles

Adenosine stimulates neuromedin U mRNA expression in the rat pars tuberalis

Neuromedin U (NMU) shows circadian expression in the rat pars tuberalis (PT), and is known to be suppressed by melatonin. Here we examined the involvement of adenosine in the regulation of Nmu expression. We found that the rat PT expressed adenosine receptor A2b and that an adenosine receptor agonist, NECA, stimulated Nmu expression in brain slice cultures. In vitro promoter assays revealed that NECA stimulated Nmu promoter activity via a cAMP response element (CRE) in the presence of adenosine receptor A2b. NECA also increased the levels of phosphorylated CRE-binding protein. These findings suggest that adenosine stimulates Nmu expression by activating the cAMP signaling pathway through adenosine receptor A2b in the rat PT. This is the first report to demonstrate that Nmu expression in the PT is regulated by adenosine, which acts as an intravital central metabolic signal, in addition to melatonin, which acts as an external photoperiodic environmental signal.

Identification of an endocannabinoid system in the rat pars tuberalis-a possible interface in the hypothalamic-pituitary-adrenal system?

Endocannabinoids (ECs) are ubiquitous endogenous lipid derivatives and play an important role in intercellular communication either in an autocrine/paracrine or in an endocrine fashion. Recently, an intrinsic EC system has been discovered in the hypophysial pars tuberalis (PT) of hamsters and humans. In hamsters, this EC system is under photoperiodic control and appears to influence the secretion of hormones such as prolactin from the adenohypophysis. We investigate the EC system in the PT of the rat, a frequently used species in endocrine research. By means of immunocytochemistry, enzymes involved in EC biosynthesis, e.g., N-arachidonoyl-phosphatidylethanolamine-phospholipase D (NAPE-PLD) and diacylglycerol lipase α (DAGLα) and enzymes involved in EC degradation, e.g., fatty acid amide hydrolase (FAAH) and cyclooxygenase-2 (COX-2), were demonstrated in PT cells of the rat. Immunoreactions (IR) for FAAH and for the cannabinoid receptor CB1 were observed in corticotrope cells of the rat adenohypophysis; these cells were identified by antibodies against proopiomelanocortin (POMC) or adrenocorticotrophic hormone (ACTH). In the outer zone of the median eminence, numerous nerve fibers and terminals displayed CB1 IR. The majority of these were also immunolabeled by an antibody against corticotropin-releasing factor (CRF). These results suggest that the EC system at the hypothalamo-hypophysial interface affects both the CRF-containing nerve fibers and the corticotrope cells in the adenohypophysis. Our data give rise to the hypothesis that, in addition to its well-known role in the reproductive axis, the PT might influence adrenal functions and, thus, the stress response and immune system.

Negative regulation of neuromedin U mRNA expression in the rat pars tuberalis by melatonin.

The pars tuberalis (PT) is part of the anterior pituitary gland surrounding the median eminence as a thin cell layer. The characteristics of PT differ from those of the pars distalis (PD), such as cell composition and gene expression, suggesting that the PT has a unique physiological function compared to the PD. Because the PT highly expresses melatonin receptor type 1, it is considered a mediator of seasonal and/or circadian signals of melatonin. Expression of neuromedin U (NMU) that is known to regulate energy balance has been previously reported in the rat PT; however, the regulatory mechanism of NMU mRNA expression and secretion in the PT are still obscure. In this study, we examined both the diurnal change of NMU mRNA expression in the rat PT and the effects of melatonin on NMU in vivo. In situ hybridization and quantitative PCR analysis of laser microdissected PT samples revealed that NMU mRNA expression in the PT has diurnal variation that is high during the light phase and low during the dark phase. Furthermore, melatonin administration significantly suppressed NMU mRNA expression in the PT in vivo. On the other hand, 48 h fasting did not have an effect on PT-NMU mRNA expression, and the diurnal change of NMU mRNA expression was maintained. We also found the highest expression of neuromedin U receptor type 2 (NMUR2) mRNA in the third ventricle ependymal cell layer, followed by the arcuate nucleus and the spinal cord. These results suggest that NMU mRNA expression in the PT is downregulated by melatonin during the dark phase and shows diurnal change. Considering that NMU mRNA in the PT showed the highest expression level in the brain, PT-NMU may act on NMUR2 in the brain, especially in the third ventricle ependymal cell layer, with a circadian rhythm.

Glutamine and glutamic acid enhance thyroid-stimulating hormone β subunit mRNA expression in the rat pars tuberalis

Thyroid-stimulating hormone (TSH)-producing cells of the pars tuberalis (PT) display distinct characteristics that differ from those of the pars distalis (PD). The mRNA expression of TSHβ and αGSU in PT has a circadian rhythm and is inhibited by melatonin via melatonin receptor type 1; however, the detailed regulatory mechanism for TSHβ expression in the PT remains unclear. To identify the factors that affect PT, a microarray analysis was performed on laser-captured PT tissue to screen for genes coding for receptors that are abundantly expressed in the PT. In the PT, we found high expression of the KA2, which is an ionotropic glutamic acid receptor (iGluR). In addition, the amino acid transporter A2 (ATA2), also known as the glutamine transporter, and glutaminase (GLS), as well as GLS2, were highly expressed in the PT compared to the PD. We examined the effects of glutamine and glutamic acid on TSHβ expression and αGSU expression in PT slice cultures. l-Glutamine and l-glutamic acid significantly stimulated TSHβ expression in PT slices after 2- and 4-h treatments, and the effect of l-glutamic acid was stronger than that of l-glutamine. In contrast, treatment with glutamine and glutamic acid did not affect αGSU expression in the PT or the expression of TSHβ or αGSU in the PD. These results strongly suggest that glutamine is taken up by PT cells through ATA2 and that glutamic acid locally converted from glutamine by Gls induces TSHβ expression via the KA2 in an autocrine and/or paracrine manner in the PT.

Cell organization of the rat pars tuberalis. Evidence for open communication between pars tuberalis cells, cerebrospinal fluid and tanycytes

The pars tuberalis (PT) is the only pituitary region in close contact with the medial-basal hypothalamus and bathed by cerebrospinal fluid (CSF). Although PT has long been recognized as an endocrine gland, certain aspects of its structure remain obscure. The present investigation has been designed to gain information concerning (1) the cellular organization of PT, (2) the PT/median eminence spatial relationship and (3) the exposure of various cell compartments of PT to CSF. Non-endocrine cells (S100-reactive) appear as the organizer of the PT architecture. The apical poles of these cells line large cistern-like cavities and the processes of these cells establish a close spatial relationship with PT-specific secretory cells, portal capillaries and tanycytes. The cisterns are also endowed with clusters of ciliated cells and with a highly electron-dense and PAS-reactive content. The unique spatial organization of endocrine and non-endocrine cells of the PT supports a functional relationship between both cell populations. PT endocrine cells display a hallmark of PT-specific cells, namely, the paranuclear spot, which is a complex structure involving the Golgi apparatus, a large pool of immature secretory granules and a centriole from which originates a single 9+0 cilium projecting to the intercellular channels. Horseradish peroxidase (HRP) injected into the CSF readily reaches the intercellular channels of PT and the inner channel of the single cilium and is incorporated by the endocytic machinery of the secretory cells. The PT endocrine cells, through their single 9+0 cilium, may act as sensors of the CSF. HRP also reaches the lumen of the cisterns, indicating that this PT compartment is also exposed to CSF. PT endocrine cells establish direct cell-to-cell contacts with hypothalamic beta(1) tanycytes, suggesting a second means of brain-PT communication.

Diurnal Change of Thyroid‐Stimulating Hormone mRNA Expression in the Rat Pars Tuberalis

Thyroid-stimulating hormone (TSH)-producing cells (TSH cells), which account for a large fraction of the cells in the rat pars tuberalis (PT), have been found to express MT1 melatonin receptor and mammalian clock genes at high densities. Although these findings suggest that TSH production in the rat PT is regulated by melatonin and/or the biological clock, there have been no studies focusing on the diurnal change and regulation mechanism of TSH production in the rat PT. Therefore, in the present study, we examined diurnal changes of in TSH beta and alpha-glycoprotein subunit (alpha GSU) mRNA expression and TSH immunoreactivity (-ir) in the rat PT, and also examined the relationship between melatonin and TSH production in vivo. Both TSH beta mRNA expression and alpha GSU mRNA expression in the PT showed diurnal variations: the expression levels were lowest at the light phase [Zeitgeber time (ZT)4] and high at the dark phase (ZT12 and ZT20). TSH-ir in the PT showed the lowest level at ZT4, as was found for mRNA expression. Interestingly, TSH-ir, which was confined to the Golgi apparatus at ZT4, spread to the cytoplasm, and most of the TSH cells in the PT were uniformly immunostained in the cytoplasm at ZT20. Despite the fact that chronic administration of melatonin suppressed TSH beta and alpha GSU mRNA expression, TSH-ir in the PT was significantly enhanced. These findings results clearly show that there are diurnal changes in TSH expression and accumulation in rat PT-TSH cells and suggest that these fluctuations are regulated by melatonin.

Negative energy balance and leptin regulate neuromedin-U expression in the rat pars tuberalis

Central neuromedin U (NMU) functions in energy balance, the hypothalamic-pituitary-adrenal axis, LH release and circadian rhythmicity. In rats, high levels of NMU occur in the hypothalamic suprachiasmatic nuclei and the pars tuberalis of the pituitary. NMU expression in the pars tuberalis appears to be downregulated in the Zucker fatty (fa/fa) rat, lacking functional leptin receptors. In contrast, in the dorsomedial (DMH) nuclei of the mouse, NMU expression is higher in the ob/ob mouse, lacking leptin, and is upregulated by fasting. However, leptin appears not to change NMU gene expression in either the mouse DMH or the rat pars tuberalis. Thus, the present study aims to better identify factors influencing central NMU expression in the rat pars tuberalis. Sprague-Dawley rats were fasted and/or challenged with intracerebroventricular leptin or ghrelin and gene expression was measured using real-time reverse transcriptase-PCR and quantitative in situ hybridisation with riboprobes specific for NMU and NMU receptor (NMU-R2). NMU expression in the rat pars tuberalis was elevated by fasting. Ghrelin administration had no effect on the level of NMU expression, but leptin was found to diminish the expression in a concentration- and time-dependent manner. NMU-R2 expression was unchanged in any of the groups measured. These results suggest that NMU expression in rat pars tuberalis is upregulated in states of negative energy balance, and this may be mediated indirectly by changes in leptin levels. These results demonstrate a link between energy balance and NMU expression in the pars tuberalis of the pituitary.

Melatonin stimulates thyroid-stimulating hormone accumulation in the thyrotropes of the rat pars tuberalis.

We have reported that the unique thyroid-stimulating hormone-immunoreactive cells (TSH cells) in the intact adult and fetal rat pars tuberalis (PT) show an intense spot-like TSH immunoreaction in the perinuclear region. The present study was designed to investigate the relationship between melatonin and these unique TSH cells. We classified TSH cells in the PT (PT-TSH cells), on the basis of immunoreactivity, into spot-like stained cells (SC) and whole cytoplasm stained cells (WC), and estimated the proportion of each TSH cell type to total cells in the experimental rats by morphometry. Chronic administration of melatonin to control rats leads to an increase of WC in number but a decrease of SC. On the other hand, the intensity of TSH immunoreactivity and the number of rat PT-TSH cells significantly decreased after pinealectomy and recovered by melatonin administration. Radioimmunoassay showed that melatonin treatment increased the TSH content in the PT. Moreover, electron microscopy showed that the number of TSH secretory granules in the PT-TSH cells increased in the melatonin-replaced rats. These results demonstrated that melatonin stimulates the accumulation of TSH in the rat PT-TSH cells via secretory granule formation and suggest that melatonin regulates TSH release from PT-TSH cells.

Melatonin Regulates the mRNA Expression of the mt1 Melatonin Receptor in the Rat Pars tuberalis

The pars tuberalis (PT) of the pituitary is a major neuroendocrine target site for melatonin as it contains a large number of high-affinity melatonin receptors. We have previously shown that melatonin autoregulates the density of its own receptors in the PT. However, whether melatonin regulation includes mRNA expression in vivo is unclear. In the present study we have used quantitative in situ hybridization to (1) follow the daily profile of mt₁ mRNA expression in the rat PT and (2) investigate whether mt₁ mRNA expression could be regulated in vivo by melatonin. We found clear diurnal variations of mt₁ mRNA expression that persist in constant darkness. We also showed, on pinealectomized animals, that the rhythmic pineal melatonin secretion is necessary for the expression of these daily variations. In a second step, we studied the effect of an acute suppression of endogenous melatonin synthesis on mt₁ melatonin receptors by applying a 1-hour light pulse during the night. We found that light induced a dramatic increase in mt₁ mRNA which was totally prevented by a melatonin injection showing that the acute effect of melatonin on the receptor mRNA is strongly inhibitory. A light pulse applied to animals with a chronic absence of melatonin was ineffective showing that light only affects melatonin receptors via the light-induced plasma melatonin suppression. Altogether our results show that melatonin regulates mt₁ melatonin receptor mRNA expression. However, this regulation seems to be complex: acute changes in plasma melatonin concentration regulate negatively the gene transcription, even if the daily endogenous nocturnal melatonin peak seems a prerequisite for variations in its receptor expression.

Characterization of TSH-positive cells in foetal rat pars tuberalis that fail to express Pit-1 factor and thyroid hormone beta2 receptors.

The thyroid stimulating hormone (TSH)-immunoreactive cells (TSH cells) in the pars tuberalis (PT-TSH cell) of the male rat pituitary gland show an intense spot-like TSH immunoreaction in the paranuclear cytoplasm. However, the ontogenic origin and characteristics of these spot-like stained PT-TSH cells remain to be elucidated. The present study was designed to investigate the distribution and characteristics of PT-TSH cells in the foetal and adult rat pituitary by immunostaining for Pit-1 factor and thyroid hormone receptors (TRs) and reverse transcriptase-polymerase chain reaction (RT-PCR). TSH cells first appeared in the PT at 15.5 days of gestation and were either stained diffusely throughout the cytoplasm or displayed a strongly stained, spotty appearance in the paranuclear region. By 15.5 days of gestation, the rostral part of the PT consisted of columnar epithelium, in which TSH immunoreactivity was spot-like in the apical region of cytoplasm corresponding to the Golgi apparatus. At the 16.5 days of gestation, TSH cells were present in the pars distalis (PD); however, the cells were mostly larger and polygonal with strong staining throughout the cytoplasm. These differences between the PT and PD were retained throughout foetal and neonatal rat development. The TSH cells in the PD of the adult or gestational rat were observed to contain Pit-1 factor by double immunostaining. However, TSH cells in the PT lacked Pit-1 factor. RT-PCR confirmed the absence of Pit-1 and TRbeta2 mRNA in the PT of the adult and late gestation rat pituitary gland. These results suggest that apparently distinct types of TSH cells in the PT develop independently from TSH cells in the PD.

Daily and circadian expression patterns of mt1 melatonin receptor mRNA in the rat pars tuberalis.

The mammalian pineal gland transduces lighting conditions into an endocrine message, the nocturnal synthesis and secretion of melatonin (17,20). Photoperiod is then coded hormonally by the duration of the nocturnally elevated plasma melatonin levels (7,14,23). Herewith, melatonin is involved in the regulation of seasonal biological rhythms, like reproduction (14,15,23). Among the large number of structures containing melatonin receptors, the pars tuberalis (PT) of the pituitary is the only one presenting a high number of 2-I-melatonin binding sites in all the mammalian species studied so far (14). To date, in mammals, two different melatonin receptor cDNAs have been cloned, called Mel1a and Mel1b (mt1 and MT2, respectively) (18,19). These authors showed also that the distribution of mt1 mRNA is coincident with that of 2-125Imelatonin binding. In response to the photoperiodic changes, seasonal variations of 2-125I-melatonin binding in the PT of seasonal breeders have been described (2,4,13,16,21,22,23). At present time, these receptors are thought to be involved in mediating the photoperiodic effects of melatonin in the seasonal control of prolactin secretion (8,9,10,12).

Effects of two melatonin analogues, S-20098 and S-20928, on melatonin receptors in the pars tuberalis of the rat.

By using quantitative autoradiography, we studied the effects of two drugs related to melatonin on the 2-(125)I-melatonin binding in the pars tuberalis (PT) of rats. The drugs tested were two naphthalenic analogues of melatonin, S-20098 (N-[2-(7-methoxy-1-naphthyl) ethyl] acetamide), an agonist, and S-20928 (N-[2-(1-naphthyl) ethyl] cyclobutyl carboxamide), a putative antagonist. Melatonin (s.c. and i.p.), S-20098 (s.c.), and S-20928 (i.p.) were injected 4 hr before sacrifice. Acute administration of both melatonin and S-20098 decreased melatonin receptor density. In contrast, the putative antagonist S-20928, at a low dose (1 mg/kg), was ineffective on melatonin receptors. It neither affected the 2-(125)I-melatonin specific binding observed in the control group nor did it prevent the decrease in binding induced by melatonin when injected 5 min before the hormone. At a high dose (10 mg/kg), S-20928 totally blocked the effect of melatonin on melatonin receptor density and induced a decrease in binding capacity as melatonin did when injected alone. These results indicate that in the rat pars tuberalis, the melatonin agonist, S-20098, is able to down-regulate melatonin receptors, whereas S-20928 seems to behave as a partial agonist.

Melatonin receptors in the suprachiasmatic nuclei and pars tuberalis of testosterone induced photoresponsive rats

The sexual axis of rats can be rendered photoresponsive by testosterone implants. We have studied in these conditions whether rat pars tuberalis (PT) melatonin receptor density would be decreased after exposure to short photoperiod (SP) like as observed in long day seasonal breeders. The answer is no, but we observed that testosterone induced a photoperiod independent decrease in PT melatonin receptor density. These results show that testosterone-induced photosensitivity in rat is not linked to an SP-induced decrease in PT melatonin receptor density. However, testosterone regulates PT melatonin receptors independently of the photoperiod.

Melatonin receptors in the suprachiasmatic nuclei and pars tuberalis of testosterone induced photoresponsive rats

The sexual axis of rats can be rendered photoresponsive by testosterone implants. We have studied in these conditions whether rat pars tuberalis (PT) melatonin receptor density would be decreased after exposure to short photoperiod (SP) like as observed in long day seasonal breeders. The answer is no, but we observed that testosterone induced a photoperiod independent decrease in PT melatonin receptor density. These results show that testosterone-induced photosensitivity in rat is not linked to an SP-induced decrease in PT melatonin receptor density. However, testosterone regulates PT melatonin receptors independently of the photoperiod.

Daily variations in melatonin receptor density of rat pars tuberalis and suprachiasmatic nuclei are distinctly regulated

Suprachiasmatic nuclei (SCN) and pars tuberalis (PT) are two structures in the rat exhibiting high affinity receptors for melatonin. Melatonin receptor density in these two structures was previously shown to be inversely related to endogenous ligand concentration, thus elevated at daytime. We now demonstrate that, in the PT, these daily variations are directly induced by the circadian rhythm of plasma melatonin concentration. Variations persist in constant darkness and can only be blocked by pinealectomy. Thus, autoregulation loop of melatonin receptors determines the circadian rhythm in PT melatonin receptor de density. However, this process of densensitization does not determine the daily variations in SCN melatonin receptor density. Indeed, in the SCN, the light/dark cycle is the regulatory factor: melatonin receptor density was shown to be specifically reduced during the night even in pinealectomized animals, while one h light was shown to reverse this nocturnal decrease in the SCN. Moreover, this darkness-induced down-regulation of SCN melatonin receptors has a masking effect on the earlier shown ligand-dependent desensitization process in this structure. This explain why, in constant darkness, SCN melatonin receptor density did not show any variation throughout the 24 h subjective day and night, although the circadian rhythm of melatonin persisted. These results thus clearly show that although daily rhythms in the density of melatonin receptors are identical in the PT and in the SCN, their regulation is totally different in each of these two structures.

Seasonal changes in melatonin binding sites in the pars tuberalis of male European hamsters and the effect of testosterone manipulation.

Seasonal changes in specific 2-[125I]iodo-melatonin binding were assessed in the pars tuberalis of male European hamsters (Cricetus cricetus) kept under natural environmental conditions. Saturation studies were performed on pars tuberalis membrane preparations every 5-7 weeks for 13 months. The maximum number of melatonin binding sites occurred in spring and summer (Bmax, 4.0 +/- 0.3 fmol/mg protein, n = 9) with significantly reduced binding in winter (Bmax, 1.2 +/- 0.2 fmol/mg protein, n = 2). As an assay control, simultaneous saturation studies were performed on rat pars tuberalis membranes. No summer-winter difference in binding site density was observed in the rat studies. In both hamsters and rats no seasonal changes in binding affinity were found. Although an apparent correlation between Bmax, values and paired testes weight of the hamsters was noted, in early spring the increase in the number of melatonin binding sites preceded the elevation in testicular weight. Castration during the period of sexual activity or sexual inactivity also failed to reduce the elevated number of binding sites observed in the spring and summer. In addition, testosterone implanted sc 5 weeks before had no effect on the low 2-[125I]iodo-melatonin binding site density found in winter (November). These results suggest that the observed seasonal variation in the number of melatonin binding sites is independent of seasonal changes in circulating testosterone concentrations.

Seasonal changes in melatonin binding sites in the pars tuberalis of male European hamsters and the effect of testosterone manipulation

Seasonal changes in specific 2-[125I]iodo-melatonin binding were assessed in the pars tuberalis of male European hamsters (Cricetus cricetus) kept under natural environmental conditions. Saturation studies were performed on pars tuberalis membrane preparations every 5-7 weeks for 13 months. The maximum number of melatonin binding sites occurred in spring and summer (Bmax, 4.0 +/- 0.3 fmol/mg protein, n = 9) with significantly reduced binding in winter (Bmax, 1.2 +/- 0.2 fmol/mg protein, n = 2). As an assay control, simultaneous saturation studies were performed on rat pars tuberalis membranes. No summer-winter difference in binding site density was observed in the rat studies. In both hamsters and rats no seasonal changes in binding affinity were found. Although an apparent correlation between Bmax, values and paired testes weight of the hamsters was noted, in early spring the increase in the number of melatonin binding sites preceded the elevation in testicular weight. Castration during the period of sexual activity or sexual inactivity also failed to reduce the elevated number of binding sites observed in the spring and summer. In addition, testosterone implanted sc 5 weeks before had no effect on the low 2-[125I]iodo-melatonin binding site density found in winter (November). These results suggest that the observed seasonal variation in the number of melatonin binding sites is independent of seasonal changes in circulating testosterone concentrations.

Melatonin receptor density is regulated in rat pars tuberalis and suprachiasmatic nuclei by melatonin itself

The pineal hormone melatonin interacts with the neuroendocrine system via high affinity binding sites. The density of these receptors is increased after 72 h constant light or pinealectomy in both rat pars tuberalis and suprachiasmatic nuclei. The present results show that, in rat PT and SCN, this increase can be inversed by a single melatonin injection (50 μg s.c. in 0.1 ml NaCl, 4 h before sacrifice). At the time of sacrifice, plasma melatonin concentrations of injected animals were no longer significantly different when compared to control values. Thus, this observed effect is not a result of a receptor occupation, but demonstrates a direct regulation of melatonin receptors by melatonin itself.

Daily rhythms of melatonin binding sites in the rat pars tuberalis and suprachiasmatic nuclei; evidence for a regulation of melatonin receptors by melatonin itself.

Using quantitative autoradiography, the density of melatonin binding sites has been measured in the rat pars tuberalis (PT) and suprachiasmatic nuclei (SCN) every 4 h throughout a 24-hour period in animals kept in a light regime of 12L/12D (with lights on at 07.00 h). Slices of PT and SCN were incubated in the presence of 180 and 172 pM, respectively, of 2-125I-melatonin. In both structures investigated, specific 2-125I-melatonin binding sites showed similar rhythms throughout the 24-hour period with a maximum at 16.00 h (PT: 46.9 +/- 2.8 fmol/mg protein, n = 5 and SCN: 5.12 +/- 0.30 fmol/mg protein, n = 5) and a minimum at 4.00 h (PT: 28.5 +/- 4.5 fmol/mg protein, n = 5 and SCN: 3.07 +/- 0.39 fmol/mg protein, n = 5). Similar experiments performed on PT of animals kept in constant light (LL) for 3 days revealed a lack of variations of melatonin binding site density, all the values being significantly higher than those of the respective 12L/12D group (concentration of 2-125I-melatonin used: 180 pM). All these preliminary results were confirmed by saturation studies performed at 16.00 and 4.00 h using quantitative autoradiography and in 12L/12D animals, using radioreceptor binding assays on isolated PT membranes. In 12L/12D animals, the maximum number of melatonin binding sites (Bmax) of both SCN and PT was significantly higher at 16.00 h than at 4.00 h. In all these cases, however, the dissociation constant (Kd) failed to show any significant daily variation.(ABSTRACT TRUNCATED AT 250 WORDS)

Luteinizing hormone content of the pars tuberalis of the hypophysis of neonatally androgenized female rats.

The immunoreactive LH content of the pars tuberalis of neonatally androgenized female rats was studied and found to be significantly lower than that of control females at oestrus or of control males. It is concluded that the rat pars tuberalis does secrete LH and that this secretory activity is diminished by neonatal androgenization in a manner that differs from that reported for the LH secretion in the pars distalis.