Biomedical subjects

H Jarry

Publications and source records attributed to H Jarry.

At least 73 records · Page 4Linked to original sources

PubMed1995

Effect of GABAergic compounds on gonadotropin-releasing hormone receptor gene expression in the rat.

Using a competitive reverse transcription-polymerase chain reaction (RT-PCR), the amounts of GnRH receptor (GnRHR) transcript in a discrete nucleus micropunched from rat brain slices were determined. GnRHR transcript was highly expressed in anterior pituitary >> median eminence > posterior mediobasal hypothalamus (pMBH) > preoptic area (POA) but not in cortex and posterior pituitary, which were used as control tissues. To examine the effect of GABA on GnRHR transcript level, 10 nmol of muscimol, a GABA-A receptor agonist, or baclofen, a GABA-B receptor agonist, was microinjected into the lateral ventricle of ovariectomized rats. Two hours after an intraventricular injection, rats were decapitated. Blood was collected 1 h before and after drug administration and used for LH determination. Serum LH levels were significantly reduced by muscimol but not by baclofen within 2 h. The activation of GABA-A receptors with muscimol resulted in a significant inhibition in GnRHR transcript level in both the pMBH and POA but not in the pituitary. The activation of GABA-B receptors with baclofen, however, did not produce any effect on GnRHR transcript level in the pMBH and POA, as well as the pituitary. This experiment demonstrates for the first time that GABAergic neurotransmission, through GABA-A receptors, is involved in the regulation of GnRHR transcript level in the rat hypothalamus. This suggests that GABAergic neurotransmission regulates GnRHR gene expression in a coordinated, yet complex, fashion in the control of the neuroendocrine function of GnRH-LH axis.

Animals↗

PubMed1995

Luteotropic and luteolytic effects of oxytocin in the porcine corpus luteum.

The presence and the release of oxytocin (OT) by corpora lutea (CL) of a number of species (Wathes et al. 1986, Watkins and Choy 1988) including ruminants (Ivell and Richter 1984, Hirst et al. 1986, Rodgers et al. 1983, Sawyer et al. 1986), primates (Dawood and Khan-Dawood 1986, Khan-Dawood 1987, Maas et al. 1992, Khan-Dawood et al. 1993), and the pig (Pitzel et al. 1984, Einspanier et al. 1991, Jarry et al. 1992) have been amply verified. Conflicting results concerning the effects of OT on steroidogenesis have been published; the peptide has been shown to be luteotrophic (Sawyer et al. 1986, Maas et al. 1992, Jarry et al. 1990), to have no effects (Rodgers et al. 1985) or to be luteolytic (Auletta et al. 1984, Auletta et al. 1988, Pitzel et al. 1988) and it appears that this confusion is only in part due to species differences but also the age of the luteal tissue seems to be of crucial importance for the understanding of the effects of OT (Schams et al. 1983, Wuttke et al. 1993, 1994). In the present contribution we will focus largely on our results obtained in the pig and where applicable, compare them with those obtained in other species. We will thus demonstrate that OT is released by luteal cells (Jarry et al. 1990, Einspanier et al. 1991, Jarry et al. 1992) and that luteal cells have OT receptors (Sernia et al. 1989, Pitzel et al. 1993a) which mediate the effects of the peptide on steroidogenesis. Finally, we will address the question whether OT is inhibitory or stimulatory to progesterone (P) and estradiol (E2) release, and we will come to the conclusion that OT is both luteotropic and luteolytic (Wuttke et al. 1993, 1994). The CL of all species investigated so far consists of two steroidogenic cell types. The so-called large luteal cells stem from follicular granulosa cells and they appear to be barely responsive to luteinizing hormone (LH)/human chorionic gonadotrophin (hCG) but they are highly receptive to prostaglandin F2 alpha (PGF2 alpha) (Hansel and Dowd 1986, Pitzel et al. 1990). Furthermore, they appear to produce OT (Rodgers et al. 1983, Theodosis et al. 1986). The small luteal cells are believed to derive from the follicular theca cells (Hansel and Dowd 1986, Pitzel et al. 1990). They are LH-receptive but synthesize few, if any, regulatory peptides. In the last few years it has become increasingly evident that cells deriving from the white blood cell line are involved in processes such as ovulation and luteolysis. Of crucial importance for the understanding of luteolysis is the morphological observation that macrophages invade the CL at the time of luteal regression (Adashi 1990, Paavola 1977, Kirsch et al. 1981).

Animals↗

PubMed1994

Effects of taurine on basal and stimulated luteinizing hormone (LH) and LH-releasing hormone secretion in ovariectomized rats: in vitro studies.

Taurine (Tau), a putative inhibitory amino acid neurotransmitter, has been shown to inhibit luteinizing hormone (LH) release in vivo. We investigated the effect of this amino acid on LH secretion by cultured anterior pituitary cells. A 5-h incubation with Tau (10(-3)-10(-8) M) did not affect basal or LH-releasing hormone (LHRH)-stimulated LH release. Basal LHRH release from superfused mediobasal hypothalamic fragments was not affected by Tau (10(-3) M). However, this substance clearly diminished LHRH release after stimulation with KCl (50 mM) or N-methyl-D-aspartate (10(-4) M). It is concluded that Tau may exert an inhibitory effect on LH secretion acting at the hypothalamic level.

Animals↗

PubMed1994

In vivo-effect of intraadrenal nicotine and substance P application on rat adrenal medullary catecholamine secretion.

The present study was conducted to characterize in vivo the intraadrenal catecholamine (CA) secretion in rats. This was possible by using a microdialysis system (MDS) which mimics some properties of an artificial capillary. One end of this system was connected to a peristaltic pump, from the other end fractions were sampled at 5 min intervals. Concentrations of epinephrine (E) and norepinephrine (NE) in adrenal dialysate fractions were determined by HPLC electrochemical detection. Through this MDS nicotine was administered directly into the adrenal medulla of freely moving rats and the response of catecholamine release was determined. In the second part of the study the effect of exogenous substance P (SP) on spontaneous as well as on nicotine-stimulated CA release was investigated. Like nicotine, SP was administered directly into the adrenal medulla. At a flow rate of 25 microliter/min the transfer rates of CA and nicotine were approximately 1% whereas SP passed at a rate of 01.-0.2%. Under resting conditions CA release remained constant. In response to 2 x 10(-7) M nicotine (which resulted in local concentration of 2 x 10(-7) M), E and NE secretion increased 2.9 and 5.4-fold, respectively. However, due to an increased E response this difference attenuated with a later onset of the first stimulus. The higher concentrations of 10(-4) M resulted in 8.1 and 10.8-fold increases for E and NE. This latter response is clearly supraphysiologic and therefore the 2 x 10(-5) M concentration was used for further experimentation. CA secretion was stimulated with nicotine four times at 30 min intervals.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Glands↗

PubMed1994

In vitro prolactin but not LH and FSH release is inhibited by compounds in extracts of Agnus castus: direct evidence for a dopaminergic principle by the dopamine receptor assay.

Women suffering from premenstrual mastodynia often respond to stimuli of prolactin (Prl) release with a hypersecretion of this hormone. Pharmacological reduction of Prl release by dopamine agonists or treatment with extracts of Agnus castus (AC) improve the clinical situation of patients with such premenstrual symptoms. Extracts of AC contain compounds which inhibit in vivo Prl release in women as well as in vitro from dispersed rat pituitary cells. It is yet unknown whether this inhibitory action of AC is only exerted on Prl release or whether release of other pituitary hormones like LH and FSH is also affected. The effects of AC on LH and FSH release were examined in vitro using rat pituitary cell cultures. To rule out that the Prl-inhibiting properties of AC are at least in part due to a cytotoxic component, pituitary cell cultures were subjected to the MTT test. To assess whether the Prl inhibitory effect of AC preparations is due to compounds acting as dopamine (DA) agonists, we used the corpus striatum membrane DA receptor binding assay. Our results demonstrate for the first time that AC extract contains an active principle that binds to the D2 receptor. Thus, it is very likely that it is this dopaminergic principle which inhibits Prl release in vitro from rat pituitary cells. Furthermore we give evidence for the specificity of action of AC on hormone release, since gonadotropin secretion remained unaffected. The findings of the present study support the therapeutical usefulness of AC extracts for treatment of premenstrual mastodynia which is associated with hypersecretion of Prl. Furthermore, the beneficial effects of AC appear to be due to the inhibition of pituitary Prl release.

Animals↗

PubMed1993

Competitive PCR for quantitation of gonadotropin-releasing hormone mRNA level in a single micropunch of the rat preoptic area.

A competitive polymerase chain reaction (PCR) for quantitating gonadotropin-releasing hormone (GnRH) mRNA level in a single micropunch of the rat preoptic area (POA) is described. The POA (600 microns in depth) was micropunched from frozen rat brain slices and used for mRNA isolation using Dynabeads-oligo(dT) magnetic separation technique. The target RNA combined with a synthetic, deletion mutant GnRH cRNA as an internal standard, is co-reverse transcribed, and their cDNAs are subsequently co-amplified by Taq DNA polymerase in the same tube in which the same GnRH primers are used. This PCR protocol is sensitive enough to detect GnRH mRNA level in a single POA micropunch derived from an individual rat. There is a linear increase of the amount of GnRH PCR products as a function of input RNA and of the number of PCR cycles. Addition of mutant GnRH cRNA as an internal standard allows us to quantitate GnRH mRNA level in biological samples and to compensate variations of PCR reaction between samples. Following preoptic treatment with 5'-ADMP, which depletes selectively norepinephrine (NE), GnRH mRNA level was significantly reduced. This simple, yet highly sensitive PCR method appears to be a valuable tool for the study of the cellular and molecular regulation of GnRH gene expression in a variety of experimental models.

Animals↗

PubMed1993

Different steroidogenic response of young and aged porcine small and large luteal cells to prostaglandin F2 alpha, oxytocin and estradiol.

The role of oxytocin (OXT) and prostaglandin F2 alpha (PGF2 alpha) in the process of luteal regulation, particularly their function in the early luteal phase is poorly understood. Therefore the effects of both compounds on in vitro steroid release of porcine luteal cells harvested from young/middle-aged (day 4-6, day 0 = 1st estrous day) or old (day 12-14) corpora lutea were tested. As corpora lutea (CL) contain at least two different steroidogenic cell populations, fractions of the so called small (SLC) and large (LLC) luteal cells were prepared and tested in separate experiments. In SLC as well as LLC from young CL OXT and PGF2 alpha inhibited progesterone (P) production but induced a strong increase of estradiol (E2) release. In old SLC and LLC OXT and PGF2 alpha were still inhibitory to P release but OXT was ineffective and PGF2 alpha had a moderate stimulatory effect on luteal E2 secretion. In SLC cultures from young but not from old CL E2 exerted a powerful stimulatory effect on progesterone (P) secretion, i.e. E2 has strong luteotrophic effects in the early luteal phase. Indeed, the pronounced inhibitory effect of OXT and PGF2 alpha on P release from SLC could be counteracted by the addition of exogenous E2 to the culture media. Therefore, we suggest that in the early luteal phase OXT as well as PGF2 alpha have an indirect, E2-mediated luteotrophic effect on P release which is stronger than the direct inhibitory action on P secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

The stimulatory effect of pituitary adenylate cyclase activating polypeptide (PACAP) on LH release from rat pituitary cells in vitro does not involve calcium mobilization.

The hypothalamic peptide "pituitary adenylate cyclase activating polypeptide (PACAP)" stimulates cAMP production in cultured rat pituitary cells and enhances LH release. It has been suggested that the stimulation of LH release by PACAP comprises two distinct mechanisms: a direct stimulatory action on LH secretion and a potentiation of the response of the gonadotrophes to LHRH. Thus the possibility exists that PACAP may enhance LH secretion not only by increased cAMP production but also by increasing cytosolic Ca2+ concentrations ([Ca2+]). In the present study we examined whether PACAP affects cytosolic [Ca2+] in identified rat gonadotrophes (as determined by the fura-method) and whether the suggested potentiating effect of PACAP on LHRH induced LH release is dependent on Ca2+. PACAP (1 nM) and 0.1 nM LHRH significantly increased LH concentrations in the culture medium after 5 hrs of incubation. Coincubation of cells with both peptides resulted in an additive increase of LH release. While the stimulatory effect LHRH was blunted in Ca(2+)-free medium, PACAP remained stimulatory to LH release. PACAP stimulated cAMP formation regardless whether the culture medium contained Ca2+ or not. Gonadotrophes were selected by their response to LHRH (1 microM) and were subsequently challenged with PACAP (1 microM). About 75% of gonadotrophes responded also to PACAP with an increase of cytosolic [Ca2+] which was blunted by removal of extracellular Ca2+. We suggest that in the rat pituitary the majority of the gonadotrophes are PACAP responsive as determined by an increase of cytosolic [Ca2+].(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Effects of angiotensin II and atrial natriuretic peptide on LH release are exerted in the preoptic area: possible involvement of gamma-aminobutyric acid (GABA).

The preoptic/anterior hypothalamic area (PO/AH) contains the majority of LHRH neurons of which the function is regulated by a variety of neurotransmitters and peptides. In this area, numerous estrogen-receptive neurons utilize gammaaminobutyric acid (GABA) as neurotransmitter and these neurons communicate directly with LHRH neurons. Angiotensin II (AII) and atrial natriuretic peptide (ANP) are known to be involved in the regulation of LH secretion. The site of action of these peptides and the mechanisms by which they influence LHRH neurons, are largely unknown. Therefore the effects of intrapreoptic application of AII and ANP on serum LH levels of ovariectomized (ovx) and of ovx estrogen-primed rats were investigated. The peptides were applied into the PO/AH by means of push-pull cannula and in the effluent fractions GABA was measured. In the ovx estrogen-primed rat, prominent LH and prolactin surges were observed. At the time of increased LH levels preoptic GABA release was significantly reduced. At this time application of AII or ANP into the PO/AH was without effect on either LH or prolactin levels in the serum or on preoptic GABA release rates. In ovx, not steroid-primed rats intrapreoptic AII application suppressed serum LH levels significantly and this treatment had a slight stimulatory effect on preoptic GABA release rates. This effect of AII could be antagonized by prior preoptic treatment with saralasin, a specific AII receptor blocking peptide. Preoptic treatment with ANP resulted in a slight increase in serum LH levels which was accompanied by a slight, but significant reduction of preoptic GABA release rates.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II↗

PubMed1993

Luteotrophic and luteolytic actions of ovarian peptides.

Corpora lutea of all species investigated so far, including the human, produce oxytocin and a variety of other regulatory peptides. The role of these peptides is largely unknown. The subtypes of large luteal cells are able to produce tumour necrosis factor (TNF) and at the end of the luteal phase TNF-producing macrophages invade the aged corpus luteum, indicating that this cytokine may be involved in the process of luteolysis. The present contribution reviews briefly the known functions of oxytocin and substance P in the corpus luteum and then elaborates the possible involvement of luteal and macrophage TNF during luteolysis. Oxytocin applied to intact corpus luteum stimulates the secretion of progesterone and oestradiol. The stimulation of progesterone secretion by oxytocin is due to the stimulated oestrogen production. TNF, when tested in vitro, inhibits both luteal cell progesterone and oestradiol production. The TNF-mediated inhibition of aromatase activity therefore prevents the luteotrophic effects of a variety of peptides including oxytocin. This appears to be the mechanism by which TNF induces luteolysis.

Animals↗

PubMed1993

Laterality of the gonadotrophin releasing hormone pulse generator in the rat: interaction of neurons located in both preoptic areas as a basic feature.

Though the pivotal importance of pulsatile gonadotrophin releasing hormone (GnRH) release from the hypothalamus for sufficient luteinizing hormone (LH) secretion is well recognized, the mechanisms causing GnRH pulses are still largely unknown. In the rat, the GnRH neurons are concentrated in the preoptic area, which is a bilateral structure of the anterior hypothalamus. This distribution into two distinct brain areas raises the question of whether the GnRH neurons in both preoptic areas are simultaneously or alternatively active and whether an interaction between both areas is required to generate GnRH pulses. We addressed these questions by unilateral manipulations of the activity of GnRH neurons using either electrical lesion or local infusion of gamma-aminobutyric acid (GABA), a neurotransmitter known to inhibit LH release via a hypothalamic action. Acute lesion of one preoptic area caused complete cessation of pulsatile LH release which was restored after 48 h. An acute inhibition of LH release was also observed after unilateral preoptic application of GABA. It is concluded that an interaction of both preoptic areas is mandatory for GnRH pulse generation. However, we suggest that the pacemaker function is not intrinsic to GnRH nor GABA neurons but the cross-talk between these neurons within and between both preoptic areas results in episodic GnRH release.

Animals↗

PubMed1993

Demonstration of oxytocin receptors in porcine corpora lutea: effects of the cycle stage and the distribution on small and large luteal cells.

Recent investigations have demonstrated an inhibitory effect of oxytocin (OXT) on luteal cell progesterone (P) release under in vitro conditions. This inhibitory effect was counteracted by an OXT antagonist, indicating that it was receptor-mediated. In the present investigation, we demonstrated the presence of OXT binding sites in porcine luteal tissue using a radioiodinated OXT antagonist, [1-(beta mercapto-beta,beta-cyclopentamethylene propionic acid),2-(ortho-methyl)-Tyr2-Thr4-Orn8-Tyr-NH2] vasotocin (OTA), as ligand. For membrane fractions of porcine luteal tissue, Kd values of 0.7-0.8 nM were obtained; these are comparable to those of porcine myometrial fractions, measured under the same experimental conditions. Competition studies with luteal membrane fractions yielded a Ki(OXT) of 10(-9) M. This is a dose of OXT that exerts inhibitory effects on P release under both in vitro and in vivo conditions. To evaluate putative variations of luteal OXT receptor concentrations during the estrous cycle, membrane fractions prepared from corpora lutea (CL) of the early or midluteal (Days 2-6) and late luteal phase (Days 9-11) were used. While no differences in Kd values were observed, OXT binding capacities were significantly (p < 0.05) higher in CL from the early/midluteal phase (Bmax(E/M) = 116 +/- 12 fmol/mg protein) compared to CL from the late luteal phase (Bmax(L) = 65 +/- 10 fmol/mg protein). OXT binding sites were present in both small (SLC) and large luteal cells (LLC). SLC but not LLC responded to hCG with a significant increase of OXT binding sites, whereas E2 augmented OXT receptor binding in SLC as well as in LLC.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Estradiol modulates the LH release response to N-methyl-D-aspartate in adult female rats: studies on hypothalamic luteinizing hormone-releasing hormone and neurotransmitter release.

We investigated the effect of ovariectomy (OVX) and subsequent estradiol benzoate (EB) treatment upon the N-methyl-D-aspartate (NMDA)-induced LH secretion in adult female rats. Furthermore, the release of LHRH, norepinephrine (NE), dopamine (DA), 5-hydroxyindoleacetic acid (5-HIAA) and gamma-aminobutyric acid (GABA) from superfused hypothalamic fragments explanted from OVX and OVX-EB rats was determined. Two weeks after OVX, animals received EB (100 mg/kg) s.c., or oil vehicle (OVX-EB or OVX groups, respectively). Two days thereafter, at 09.00 h, NMDA (15 or 30 mg/kg) was given as an i.v. bolus; blood samples were drawn before and 10 min after drug administration. In OVX rats, NMDA had no significant effect on LH levels, whereas it stimulated LH release in OVX-EB animals at both doses tested (315 and 362% from basal values, p < 0.001). For hypothalamic superfusion studies OVX and OVX-EB animals were decapitated at 09.00 h, and the mediobasal hypothalami (MBH) dissected on ice. NMDA (10(-4) M) was added to the superfusion medium for a 10 min period. Basal LHRH release (OVX: 1.41 +/- 0.18; OVX-EB: 1.59 +/- 0.28 pg/10 min/MBH) was significantly (p < 0.05) enhanced by NMDA (OVX: 2.97 +/- 0.95; OVX-EB: 2.80 +/- 0.61 pg/10 min/MBH). EB treatment had no significant effect on basal or NMDA-induced LHRH output.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Effects and interactions of prostaglandin F2 alpha, oxytocin, and cytokines on steroidogenesis of porcine luteal cells.

In the porcine corpora lutea (CL), prostaglandin F2 alpha (PGF2 alpha) and oxytocin (OXT) inhibit progesterone (P) but stimulate estradiol (E2) secretion from luteal cells kept under primary culture conditions. In vivo, both compounds are reported to have luteolytic properties when administered during the late luteal phase; in young CL, however, both substances stimulate P secretion, an effect which is E2-mediated. During the late luteal phase luteal cells appear to produce cytokines, and in addition, cytokine-producing macrophages invade the CL. We tested therefore whether cytokines, particularly tumor necrosis factor-alpha (TNF), have effects on basal or human CG-stimulated steroidogenesis. Furthermore, the interactions of cytokines with PGF2 alpha and/or OXT were investigated. TNF, and less potently interleukin (IL)-1 and IL-2 but not IL-6, inhibited basal as well as human CG-stimulated release of P and E2 in both small and large luteal cells. The inhibiting effect of PGF2 alpha and OXT on P secretion was augmented by these active cytokines. The stimulatory effect of PGF2 alpha and OXT on small and large luteal cell E2 production was completely inhibited. A profound stimulatory effect of E2 and small luteal cell P secretion was completely prevented by the cytokines, with TNF being more potent than IL-1 or -2. We conclude that the cytokines, particularly TNF, have luteolytic functions by their direct inhibiting effects on luteal cell P production. In addition, the cytokines inhibit synthesis and action of PGF2 alpha- and OXT-stimulated E2 secretion. Since E2 is a potent stimulator of luteal cell P production, this luteotropic signal is eliminated by cytokines, which add to the process of luteolysis.

Androstenedione↗

PubMed1993

In vivo measurement of rat ovarian collagenolytic activities.

Ovarian collagenases are necessary for the process of ovulation, and they are believed to be activated by the preovulatory LH surge. This information is largely based on in vitro investigations in which the balance between inhibitory and stimulatory principles involved in the activation of collagenase are largely disrupted. Therefore, we developed a simple and reliable method to measure collagenolytic activity in vivo in freely moving rats. By the use of a microdialysis system, a peptide coupled with methyl-coumarin is perfused into the bursa of the ovary. Collagenolytic enzymes cleave this peptide, and the cleaved fragments rediffuse into the microdialysis system. The effluent is collected in fractions, and the peptide-methyl-coumarin complex is cleaved, which results in liberation of fluorescent methyl-coumarin. This assay is linear over a wide range of collagenolytic activity, and other proteases, such as trypsin or plasmin, do not give any fluorescent signal. In proestrous rats, collagenolytic activity increases after the onset of the preovulatory LH surge. In animals in which the LH surge was disrupted by the surgical procedure but had a normal proestrous PRL surge, neither progesterone nor collagenolytic activity increased in the perfusate fluid. This indicates that it is only LH, not PRL, that activates follicular collagenolytic enzymes. Similar results were obtained in immature PMSG/hCG-treated animals. Using a well established zymographic assay, these results were confirmed, and it was further demonstrated that type I and type IV collagenase are active in the rat ovary.

Amino Acid Sequence↗

PubMed1992

Contrasting effects of pituitary adenylate cyclase activating polypeptide (PACAP) on in vivo and in vitro prolactin and growth hormone release in male rats.

Pituitary adenylate cyclase activating polypeptide (PACAP) is produced by hypothalamic neurons which terminate within the median eminence suggesting that it may be a hypophysiotropic hormone. However, little endocrine activity has been ascribed to the peptide. Therefore we studied the effects of PACAP on prolactin (Prl) release from dispersed cultivated rat pituitary cells in vitro using conventional cultures as well as the reverse hemolytic plaque assay (RHPA). Furthermore the effects of the peptide on in vitro GH release were assessed. In addition, the activity of the peptide on in vivo release of Prl and GH was studied in hypothalamus-lesioned animals. PACAP dose dependently inhibited Prl release form dispersed pituitary cells in both, monolayer cell cultures and the RHPA, whereas GH secretion was not affected. In hypothalamus-lesioned rats which have high Prl levels due to the absence of hypothalamic dopamine, PACAP further stimulated Prl release. Serum GH increased more than 20 fold in response to the intravenous PACAP infusion. Thus in vitro (inhibition of Prl release, no effect on GH release) and in vivo (stimulation of both hormones) experiments yielded contradicting effects of PACAP on pituitary hormone release. We suggest that PACAP may stimulate the release of a paracrine, yet unknown factor which in the intact pituitary overrides the direct inhibitory action of PACAP on the lactotropes. The same or another paracrine factor may also enhance in vivo GH release. In cell culture the paracrine factor is diluted by the medium. Therefore the peptide never reaches effective concentrations which are present within the intact pituitary tissue.

Animals↗

PubMed1992

Demonstration of oxytocin release by bovine luteal cells utilizing the reverse hemolytic plaque assay.

Corpora lutea (CL) of a number of species produce oxytocin (OXT). In the present experiments we studied basal, prostaglandin (PG) F2 alpha-stimulated and ascorbate-stimulated OXT release from individual bovine luteal cells utilizing the reverse hemolytic plaque assay (RHPA). Using a mixture of C- and N-terminus-specific antisera against OXT, we were able to demonstrate OXT plaque formation by individual luteal cells. CL consist of two steroidogenic cell types: large luteal cells (LLC), believed to derive from granulosa cells and to produce and secrete OXT, and small luteal cells (SLC), thought to derive from theca cells. To distinguish between these two cell types, we designated cells greater than 20 microns as LLC and those less than 20 microns as SLC. On the basis of this morphological parameter, OXT release from both LLC and SLC was demonstrable. After an incubation period of 15 h, 7% of both cell types formed OXT plaques. PGF 2 alpha and ascorbate increased the size of plaques surrounding both LLC and SLC to more than 200% and 240%, respectively (basal plaque size = 100%). The number of plaque-forming cells increased only slightly in the presence of either PGF 2 alpha or ascorbate in comparison to basal conditions. We suggest that the RHPA can be used to demonstrate peptide release from luteal cells. It is concluded that LLC may be subdivided into functional subclasses because less than 10% of bovine luteal cells release OXT. Known OXT secretagogues increased the amount of OXT released. It appears that not only LLC but also SLC secrete this peptide.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Amino acid neurotransmitter release in the preoptic area of rats during the positive feedback actions of estradiol on LH release.

To investigate the role of amino acid neurotransmitters in the regulation of LH secretion in ovariectomized (ovx) rats with or without estrogen substitution, we measured the release rates of gamma-aminobutyric acid (GABA), taurine, glycine, aspartate, glutamate, homocysteic acid, and also of the neurally inactive amino acids serine and glutamine in push-pull perfusate samples of the preoptic/anterior hypothalamic area (PO/AH) collected at 30-min intervals. To achieve this we had to develop a highly sensitive assay utilizing phenylisothiocyanate prederivatization which was followed by HPLC chromatography. In confirmation of our earlier results we observed again a conspicuous drop of preoptic GABA release prior to and during the time of estrogen-induced LH surge. In addition, the release rates of the excitatory amino acid neurotransmitters aspartate and glutamate in the PO/AH increased during this time. Interestingly, also secretion of taurine and glycine was increased during the LH surge, whereas preoptic release rates of serine and glutamine and of homocysteic acid, the putative endogenous ligand of the so-called N-methyl-D-aspartate receptor, remained unchanged. No such changes of amino acid neurotransmitters release rates were observed in ovx rats. This finding underlines that the changes of amino acid secretion in ovx estrogen-primed rats are likely due to the influence of the steroid rather than due to a diurnal rhythm. We conclude that GnRH neurons are under a tonic inhibitory tone exerted by GABA which is relieved during the time of the estrogen-induced LH surge. During this time, aspartate and glutamate may have additional stimulatory effects on GnRH neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗