Bernard Kerdelhué

Inhibitory Actions of Acute Estradiol Treatment on the Activity and Quantity of Tyrosine Hydroxylase in the Median Eminence of Ovariectomized Rats

The effects of acute estradiol (E2) treatment on both the activity of tyrosine hydroxylase (TH) in the median eminence and the serum level of prolactin (PRL) were investigated. Twelve‐day‐ovariectomized rats were injected with 17β‐E2 (25μg sc) at 1100 h and sacrificed hourly from 1200 to 2300 h. TH activity was quantified by measuring the amount of exogenous tyrosine converted to L‐DOPA in vitro by aliquots of median eminence homogenates. Serum PRL levels were evaluated by radioimmunoassay. A biphasic response of TH activity to treatment was observed: an immediate decrease occurred—preceding and accompanying a rise in serum PRL—followed by an increase beyond control levels 2 h after the maximal release of PRL. The increase in TH activity could be prevented by the pretreatment of rats with a specific rat PRL antiserum, suggesting it was not due to E2 per se but rather mediated by the E2‐induced PRL elevation. To pin‐point the process underlying the E2‐induced decrease in TH activity, we evaluated the kinetic parameters of TH in the median eminence as well as its quantity (by Western blot analysis) in the median eminence and arcuate nucleus. Finally, we used a sensitive dot‐blot assay to quantify specific TH messenger ribonucleic acid in the arcuate nucleus. The decrease in TH activity after E2 treatment paralleled an immediate decrease in the affinity of TH for its pterin cofactor (6‐MPH4), while Vmax remained unchanged. A decrease in the amount of TH protein in the arcuate nucleus and median eminence as well as in the TH messenger ribonucleic acid level in the arcuate nucleus was also observed, but the latency of these effects precluded a major involvement in the immediate decline of TH activity. Therefore, when observed separately from those of PRL, E2 effects on TH in tuberoinfundibular dopaminergic neurons are clearly inhibitory consisting of a ‘deactivation’ of the enzyme together with a reduction of its synthesis.

β-Endorphin concentrations in serum, hypothalamus and central gray of hypophysectomized and mediobasal hypothalamus lesioned rats

The serum and brain concentrations of beta-endorphin immunoreactivity have been studied in intact, mediobasal hypothalamus (MBH) lesioned and hypophysectomized male rats. After hypophysectomy there is a major reduction (90%) of beta-endorphin concentration in the serum but only a partial reduction (20%) in the mediobasal hypothalamus. However, MBH lesions enhance beta-endorphin serum values in previously hypophysectomized rats. Long-term MBH lesions alone lead to an almost complete disappearance of beta-endorphin in the central gray matter with a slight decrease in the serum. These data clearly show that: (1) the pituitary is the major source of beta-endorphin in the serum; (2) the hypothalamus is the major source of beta-endorphin in the central gray matter; and (3) there is clear influence of the pituitary on hypothalamic beta-endorphin.

Preventive and curative effect of melatonin on mammary carcinogenesis induced by dimethylbenz[a]anthracene in the female Sprague–Dawley rat

IntroductionIt has been well documented that the pineal hormone, melatonin, which plays a major role in the control of reproduction in mammals, also plays a role in the incidence and growth of breast and mammary cancer. The curative effect of melatonin on the growth of dimethylbenz [a]anthracene-induced (DMBA-induced) mammary adenocarcinoma (ADK) has been previously well documented in the female Sprague–Dawley rat. However, the preventive effect of melatonin in limiting the frequency of cancer initiation has not been well documented.MethodsThe aim of this study was to compare the potency of melatonin to limit the frequency of mammary cancer initiation with its potency to inhibit tumor progression once initiation, at 55 days of age, was achieved. The present study compared the effect of preventive treatment with melatonin (10 mg/kg daily) administered for only 15 days before the administration of DMBA with the effect of long-term (6-month) curative treatment with the same dose of melatonin starting the day after DMBA administration. The rats were followed up for a year after the administration of the DMBA.ResultsThe results clearly showed almost identical preventive and curative effects of melatonin on the growth of DMBA-induced mammary ADK. Many hypotheses have been proposed to explain the inhibitory effects of melatonin. However, the mechanisms responsible for its strong preventive effect are still a matter of debate. At least, it can be envisaged that the artificial amplification of the intensity of the circadian rhythm of melatonin could markedly reduce the DNA damage provoked by DMBA and therefore the frequency of cancer initiation.ConclusionIn view of the present results, obtained in the female Sprague–Dawley rat, it can be envisaged that the long-term inhibition of mammary ADK promotion by a brief, preventive treatment with melatonin could also reduce the risk of breast cancer induced in women by unidentified environmental factors.

Interactions between 17β-estradiol and the hypothalamo-pituitary β-endorphin system in the regulation of the cyclic LH secretion

Abstract This paper further substantiates the physiological role of β-endorphin (β-END) in the control of the cyclic LH secretion and provides new data on the interactions between 17β-estradiol (17β-E2) and β-END at both the hypothalmic and pituitary levels. At the hypothalamic level, during the estrous cycle in rats, β-END concentrations were highest on diestrus I in the arcuate nucleus, median preoptic area and median eminence and lowest at the time of the preovulatory 17β-E2 surge on proestrus, before the subsequent preovulatory hypothalamic GnRH and plasma LH surges. Data obtained in ovariectomized 17β-E2-treated ewes support the direct involvement of 17β-E2 in changes in β-END and GnRH concentrations in these hypothalamic areas. At the anterior pituitary level, in vitro results obtained using anterior pituitaries from the proestrus morning cycling female rat have shown that 17β-E2 strongly suppresses β-END secretion and that GnRH stimulates the release of β-END. Furthermore, marked fluctuations were observed for plasma β-END throughout the menstrual cycle in the woman. Low β-END concentrations were observed in the period preceding the LH preovulatory surge. Taken together, these results show that: (1) decreases in hypothalamic β-END concentrations, which are controlled at least by circulating levels of 17β-E2, modulate GnRH synthesis and/or release and contribute to the mechanisms which initiate the LH surge; (2) anterior pituitary β-END might be involved in the mechanisms which terminate the LH surge.

A substance P-containing hypothalamic neuronal system projects to the median eminence

Immunoreactive substance P (SPi) was measured in the various hypothalamic structures and amygdala one week after placing a cut around the medial basal hypothalamus (MBH). SPi content decreased in the stalk-median eminence (SME), anterior and posterior parts of the arcuate nucleus (inside the isolated region) as well as in the paraventricular nucleus (outside the cut), while there was no change in the posteromedial amygdaloid nucleus. We suggest that there is a tuberoinfundibular neuronal system containing SPi with cell bodies in the MBH and terminals in the SME. In addition, nerve fibers containing SPi from outside the MBH may reach both the SME and the arcuate nucleus and might influence neuroendocrine regulation.

β-Endorphin plasma levels during neuromuscular blockade in unanesthetized cat

Plasma concentrations of beta-endorphin were measured by radioimmunoassay in cats prepared chronically for sleep-waking polygraphic recordings and blood collection. beta-Endorphin (beta-END) levels were found to be stable in baseline conditions and were used as an index of stress. After habituation of each cat to experimental conditions in a veterinary pouch with head restraint, this partial restraint (45 min) or a short-lasting paralysis (30 min) induced by gallamine triethiodide did not significantly elevate plasma concentrations of beta-END. In contrast, hypoxia, ether-induced stress or tight immobilization of the limbs promoted a 7--8-fold increase in beta-END plasma levels. Sleep-waking patterns were not significantly different in restrained and paralyzed conditions. It is concluded that short-lasting paralysis induced in habituated animals by curarizing agents is not accompanied by a significant neuroendocrine response if all possible sources of pain are carefully avoided.

Stimulatory effect of a specific substance P antagonist (RPR 100893) of the human NK1 receptor on the estradiol‐induced LH and FSH surges in the ovariectomized cynomolgus monkey

Utilizing a human NK1 receptor antagonist (RPR 100893), the present in vivo study was designed to test the hypothesis that endogenous substance P (SP) modulates the action of 17β‐estradiol in inducing luteinizing hormone (LH) and follicle stimulating hormone (FSH) surges in ovariectomized cynomolgus monkey. Plasma concentrations of LH and FSH as well as NK1 receptor antagonist and SP were measured during the development of the negative and positive feedback phases which follow a single administration of estradiol benzoate (50 μg/kg) to long‐term ovariectomized monkeys. Daily administration by gastric intubation of 1 mg/kg or 10 mg/kg of the NK1 receptor antagonist (RPR 100893) leads to detectable levels of the antagonist in the blood of treated animals for at least 6 hr after its administration. These levels are in agreement with the experimentally determined IC50 value of the antagonist.

Variations in Plasma Levels of Substance P and Effects of a Specific Substance P Antagonist of the NK1 Receptor on Preovulatory LH and FSH Surges and Progesterone Secretion in the Cycling Cynomolgus Monkey

These studies investigated the role of substance P (SP) in the regulation of the hypothalamic-pituitary-ovarian axis in cynomolgus monkeys with normal menstrual cycles. Plasma concentrations of SP were determined in blood samples taken every morning in normally menstruating cynomolgus monkeys throughout the menstrual cycle. There was a significant decreasing linear trend of SP during the follicular phase (cycle day –13 to day 0) and a significant inverse relationship between SP plasma values and plasma 17β-estradiol (E2) values from day –13 to day 0 of the adjusted cycle. Correspondingly, SP area under the curve was significantly greater during the follicular phase than the luteal phase. In a second experiment, plasma concentrations of E2, luteinizing hormone (LH), follicle-stimulating hormone (FSH) and progesterone and length of cycles were measured after five daily intragastric administrations (10 mg/kg) of an NK1 receptor (SP receptor) antagonist (RPR 100893; 10 mg/kg) initiated after serum E2 concentrations had exceeded 125 pg/ml. There was a statistically significant reduction in the amplitude (41% of control) and the area under the curve (37% of control) of the preovulatory LH surge. In addition, there was a reduction of the duration of the LH surge (3 ± 0.1 days in controls vs. 2.1 ± 0.2 days in treated animals). The present results show for the first time that there are significant variations in plasma levels of SP, with a strong negative correlation with serum levels of E2 during the follicular phase of the cynomolgus monkey, and that endogenous SP has a potentiating role in the interactive hypothalamo-anterior-pituitary mechanisms which lead to the preovulatory LH and FSH surges during the menstrual cycle in the monkey.

Short communicationNeuro-endocrine interaction on lymphocytes: Testosterone-induced modulation of the lymphocyte substance P receptor

Human IM-9 B-lymphoblasts have been shown to express the receptor for the neuropeptide substance P (SP). The present study was undertaken to evaluate the effect of sex hormones on this receptor. Testosterone inhibited [125I]SP binding in a dose-dependent manner with an IC50 of approximately 100 nM, while both estradiol and progesterone failed to inhibit SP binding even at concentrations as high as 1 microM. Furthermore, Scatchard analysis indicated that the dissociation constant (Kd) of the SP receptor was markedly increased from 0.25 nM to 2.2 nM when cells were incubated with testosterone. These data indicate a unique neuro-endocrine interaction on lymphocytes involving the substance P receptor.

TACHYKININ RECEPTOR CROSS-TALK : IMMUNOLOGICAL CROSS-REACTIVITY BETWEEN THE EXTERNAL DOMAINS OF THE SUBSTANCE K AND SUBSTANCE P RECEPTORS

In the present study, we have chemically synthesized peptides which correspond to the four putative extracellular domains of the predicted substance K (SK) receptor protein and raised specific polyclonal antibodies against these peptides. These antibodies were then tested for both structural and functional recognition of epitopes on the substance P (SP) receptor on rat AR42J pancreatic cells and human IM9 lymphoblasts, which express the SP receptor, but not the SK receptor. Antibodies directed against the first, second, and fourth external domains of the predicted SK receptor recognized a 58-kDa protein on AR42J cells. This protein has a molecular weight similar to the previously demonstrated SP receptor on both AR42J cells and IM9 cells. Furthermore, antibodies against the second and fourth extracellular domains significantly inhibited specific 125I-SP binding on both AR42J and IM9 cells, and also significantly inhibited SP-induced mobilization of [Ca2+]i on AR42J cells. These data suggest that the second and fourth extracellular domains of the SK and SP receptors may share common structural motifs for ligand binding and signaling mechanism.