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Query: UNIPROT:P01178 (oxytocin)
 15,767 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The data highlighted here suggest that the CRH effects of vasopressin and oxytocin are mediated by one and the same hypophysial receptor which has unique pharmacological specificity. The nomenclature for this receptor type is not established; both V3(53) and V1 beta 39 have been proposed. The former proposal is logical if the pharmacology of ligand recognition is emphasized, whereas the latter designation takes into account that transmembrane signalling from V1 receptors occurs via coupling proteins Go and Gi but not Gs. Such issues are best resolved after cDNA cloning of the genes for the receptors: in the meanwhile the working definition V3 seems more convenient. Several studies show that pituitary V3 receptors are regulated by the concentration of vasopressin in hypophysial portal blood and the amount of glucocorticoid hormones in the circulation (see Ref. 9 for review). Work in this area should clarify further the intracellular mechanism of the CRH action of vasopressin, as well as the factors that determine the responsiveness of corticotrophs to various secretagogues. Most recently, it has been shown that vasopressin is a potent thyrotropin-releasing hormone. This finding extends further the growing concept that there is considerable "cross-talk" between the classical neuroendocrine axes. These were previously thought to be separated by the hypothalamic organization of "final common pathways" of neuroendocrine motoneurons in the hypothalamus, each producing a unique neurohormone to regulate a single type of adenohypophysial cell. It seems that the days of the validity of this hypothesis are numbered, and an important task will be to determine the possible physiological significance of the "cross-talk" within the hypothalamo-pituitary unit in the regulation adrenocortical function.
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PMID:Receptors mediating the CRH effects of vasopressin and oxytocin. 283 75

The anteroventral periventricular nucleus (AVPv), which lies in the periventricular zone of the preoptic region, is critical for normal phasic gonadotropin secretion since lesions of this nucleus abolish the progesterone-induced surge of luteinizing hormone secretion from the anterior pituitary, block ovulation, and induce persistent vaginal estrus in female rats. However, very little is known about the neurotransmitter-specific pathways associated with this nucleus. In the present study we evaluated the distribution of biochemically specific cells and fibers within the AVPv and adjacent regions by using an indirect immunohistochemical method with antisera to serotonin (5-HT), dopamine beta-hydroxylase (DBH), tyrosine hydroxylase (TH), neuropeptide Y (NPY), cholecystokinin-8 (CCK), vasoactive intestinal polypeptide (VIP), substance P (SP), neurotensin (NT), corticotropin-releasing factor (CRF), luteotropin-releasing hormone (LRH), somatostatin (SS), thyrotropin-releasing hormone (TRH), oxytocin (OXY), vasopressin (VAS), adrenocorticotropic hormone (ACTH1-24), alpha-melanocyte-stimulating hormone (alpha-MSH), leucine-enkephalin (L-ENK), and calcitonin gene-related peptide (CGRP). Our findings indicate that both cells and fibers containing these putative neurotransmitters are differentially distributed in and around the AVPv in accordance with the cytoarchitectonic organization of this part of the preoptic region. The AVPv itself appears to receive strong inputs from SP-, VAS-, CCK-, and SS-containing pathways, whereas the highest densities of L-ENK-, NT-, 5-HT-, NPY-, and DBH-immunoreactive fibers were found in the cell-sparse zone just lateral to the AVPv. The suprachiasmatic preoptic nucleus (PSCh), a small group of cells located ventral to the AVPv just dorsal to the optic chiasm, contained high densities of alpha-MSH- and ACTH-immunoreactive fibers, as well as substantial numbers of fibers containing catecholamines or NPY. In contrast, a dense plexus of VAS-stained fibers was distributed fairly evenly throughout the AVPv and PSCh. Numerous L-ENK-immunoreactive cell bodies, and moderate numbers of CCK-, NT-, and CRF-stained cell bodies were found in the AVPv. The PSCh contained many TH-stained cells (presumably dopaminergic), in addition to a moderate number of CCK-containing cell bodies, while a high density of NT- and CRF-stained cells were found in the cell-sparse zone lateral to the AVPv, in addition to several CCK-, SP-, VIP-, and TH-containing cells.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:The distribution of neurotransmitter-specific cells and fibers in the anteroventral periventricular nucleus: implications for the control of gonadotropin secretion in the rat. 288 Jun 34

Carboxypeptidase H is one of several enzymes required for the processing of peptide hormone precursors. In this study, inhibition of carboxypeptidase H by its peptide products was investigated. Carboxypeptidase H activity in bovine adrenal medulla chromaffin granules and rat adrenal medulla homogenate was inhibited by the peptides Met- and Leu-enkephalin, vasopressin, oxytocin, luteinizing hormone-releasing hormone, substance P, and thyrotropin-releasing hormone, with oxytocin and ACTH 1-14 having the least effect, at concentrations of 2-20 mM. Inhibition by amidated peptide products (vasopressin, oxytocin, luteinizing hormone-releasing hormone, substance P, and thyrotropin-releasing hormone) show that the final products of the precursor processing pathway can regulate carboxypeptidase H. These levels of peptides are similar to known intragranular peptide concentrations indicating that product and feedback inhibition of carboxypeptidase H may play a role in the control of neuropeptide synthesis. The proenkephalin-derived peptides Met-enkephalin, Leu-enkephalin, Met-enkephalin-Arg6-Gly7-Leu8, and Met-enkephalin-Arg6-Phe7 competitively inhibited bovine and rat carboxypeptidase H with Ki values of 12.0, 6.5, 7.0, and 5.5 mM, respectively. The significantly greater Ki for Met-enkephalin may reflect the effects of higher intragranular concentration of Met-enkephalin, since one proenkephalin molecule contains four copies of Met-enkephalin and only one copy of each of the other enkephalin peptides. Thus, the products from one multivalent precursor molecule may equivalently inhibit carboxypeptidase H activity. Product inhibition of carboxypeptidase H and perhaps other processing enzymes may serve to limit the maximum peptide concentration within the secretory vesicle.
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PMID:Product inhibition of carboxypeptidase H. 288 69

1. We have reviewed recent studies in which in situ hybridization histochemistry (ISHH) was used to investigate the regulation of expression of neurohypophysial peptides and hypothalamic releasing hormones. 2. ISHH is a technique in which the presence and quantity of a specific mRNA can be determined in tissue sections with a high degree of resolution and sensitivity. 3. ISHH has been used to measure changes in cellular levels of mRNAs encoding vasopressin, oxytocin, corticotropin-releasing factor, gonadotropin-releasing hormone, thyrotropin-releasing hormone and somatostatin in response to various physiological challenges. 4. A theme emerging from these studies is that changes in levels of mRNA encoding neuroendocrine peptides reflect changes in biosynthesis and secretion.
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PMID:Neuroendocrine gene expression in the hypothalamus: in situ hybridization histochemical studies. 289 79

Neuropeptides and biogenic amines known to be present in neurons or afferent terminals in the paraventricular nucleus (PVH), supraoptic nucleus (SON) and/or lateral hypothalamus (LH) were added to small areas of these structures obtained by micropuncture and cyclic adenosine monophosphate (cAMP) levels were measured. cAMP accumulation occurred in PVH, SON and LH in response to neuropeptides of the secretin family, such as vasoactive intestinal peptide (VIP) and in response to catecholamines. Bradykinin, alpha-melanocyte-stimulating (alpha-MSH), luteinizing hormone-releasing hormone (LH-RH), oxytocin and carbamylcholine stimulated cAMP accumulation selectively in one or two of the above structures. Glucagon, cholecystokinin (CCK), somatostatin (SRIF), corticotropin-releasing factor (CRF), thyrotropin-releasing hormone (TRH), adrenocorticotropin (ACTH), melanocyte-stimulating hormone (MSH), methionine enkephalin (Met-Enk), beta-endorphin, neurotensin, bombesin and angiotensin II did not effect cAMP levels while leucine enkephalin (Leu-Enk), arginine vasopressin and gamma-aminobutyric acid (GABA) elicited regionally selective decreases in basal levels of cAMP. When interactions between some of these compounds were measured, VIP and norepinephrine exerted a more than additive effect on cAMP elevation in the PVH, while the effect on cAMP of the SON and LH was additive.
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PMID:Interaction of neuropeptides and biogenic amines on cyclic adenosine monophosphate accumulation in hypothalamic nuclei. 300 57

The effects of oxytocin (OT) on basal thyrotropin-releasing hormone (TRH)-stimulated thyrotropin (TSH) and prolactin (PRL) secretion were evaluated in normal menstruating women during follicular, periovulatory, and luteal phases. Two different studies were performed. In one study, 15 subjects were treated with OT or saline; in the other study, 20 women were tested with TRH alone or in combination with OT. Results during follicular, periovulatory, and luteal phases were similar. OT did not produce any effect on basal serum TSH and PRL levels and on the TRH-stimulated TSH secretion, whereas it significantly enhanced the PRL response to TRH. At all examined phases during the menstrual cycle, the mean peak PRL response was reached within 20 minutes after TRH injection, and the peak was about three times higher than basal value when TRH was given alone and about four times when OT was present. These data suggest that in normal women OT is not involved in the control of basal and TRH-stimulated TSH secretion and of basal PRL release. In contrast, the enhancement of the TRH-induced PRL release suggests that OT plays a role in the control of the acutely stimulated PRL secretion. Because results were similar regardless of the phase of the menstrual cycle, estrogen and/or progesterone do not appear to be involved in the effect of OT on the TRH-induced PRL release.
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PMID:Oxytocin enhances thyrotropin-releasing hormone-induced prolactin release in normal menstruating women. 310 95

Brain and spinal sites of action of the stable thyrotropin-releasing hormone (TRH) analogue, RX 77368 [pGlu-His-(3,3'-dimethyl)-Pro-NH2], for stimulation of gastric acid secretion have been investigated in urethane-anesthetized rats with gastric fistula. RX 77368 microinjected at a 7.7-pmol dose into the dorsal vagal complex or nucleus ambiguus stimulated gastric acid secretion to 62.2 +/- 15.9 and 45.3 +/- 14.3 mumol/h, respectively, whereas in the vehicle-treated group acid secretion was 0.5 +/- 1.0 mumol/h. A 10-fold higher dose of RX 77368 was inefficient when microinjected into the medial septum, central amygdala, or lateral hypothalamus. The gastric secretory response to microinjection of RX 77368 into the nucleus ambiguus was dose related (0.7-77 pmol), long-lasting (greater than 90 min), and blocked by vagotomy. TRH (144 pmol) injected into the nucleus ambiguus also stimulated gastric acid secretion but was less potent than the stable TRH analogue, whereas the unrelated peptide, oxytocin, was inactive. Intrathecal injection of RX 77368 at doses up to 2500 pmol did not modify gastric acid secretion. These results demonstrate that the dorsal vagal complex and nucleus ambiguus are TRH sites of action for stimulation of gastric acid secretion through vagal dependent pathways. These findings, added to the high concentrations of TRH-like immunoreactivity and receptors present in these nuclei, suggest a possible role of medullary TRH in the vagal regulation of gastric acid secretion.
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PMID:Medullary sites of action of the TRH analogue, RX 77368, for stimulation of gastric acid secretion in the rat. 314 Dec 37

Colocalization of thyrotropin-releasing hormone-like immunoreactivity with other neuroactive substances was examined immunohistochemically in colchicine-treated rat brains using double-staining or elution-restaining methods. Thyrotropin-releasing hormone-like immunoreactivity was shown to be located in the same neurons as: 1. enkephalin-, gamma-amino butyric acid- and tyrosine hydroxylase-, but not somatostatin-like immunoreactivity in the glomerular layer of the olfactory bulb 2. oxytocin- and cholecystokinin-, but not vasopressin-like immunoreactivity in the supraoptic nucleus 3. cholecystokinin-like immunoreactivity in posterior pituitary 4. enkephalin-like immunoreactivity in the perifornical area of the hypothalamus and 5. neuropeptide Y- and neurotensin-like immunoreactivity in the periaqueductal central grey. These findings provide further examples of coexistence of thyrotropin-releasing hormone with classical neurotransmitters and/or peptides in the rat central nervous system.
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PMID:Coexistence of TRH with other neuroactive substances in the rat central nervous system. 315 46

The binding sites for [125I]LHRH were characterized in membranes from the hypthalamus and the effect of estrogen on the binding characteristics was studied in ovariectomized female rats. The radioligand, [125I]LHRH, was found to bind specifically to membranes from the hypothalamus at a maximal level, with an optimal temperature of 0 degrees C and a pH between 7 and 8. The binding was enhanced by NaCl at a concentration of 0.1-0.2 M. The specifically bound [125I]LHRH was only displaced by LHRH, but not by sodium iodide (NaI), bovine serum albumin and other hormones, such as thyrotropin-releasing hormone, bradykinin, oxytocin, prolactin, luteinizing hormone and growth hormone. The divalent metal ions, copper (Cu2+) and mercury (Hg2+), inhibited the specific binding of [125I]LHRH completely, whereas magnesium (Mg2+) and calcium (Ca2+) caused a decrease in binding. As revealed from Scatchard plot analysis, the binding sites for [125I]LHRH in the hypothalamus had a dissociation constant of 0.40 +/- 0.03 microM and the maximum number of binding sites was 98.55 +/- 4.34 pmol/mg protein. Treatment of female rates (ovariectomized for 3 weeks) with 4 micrograms of estradiol benzoate caused a statistically significant decrease in the maximal number of binding sites without any significant effect on the dissociation constant. However, the direct addition of estradiol hemisuccinate to the membrane preparations had no statistically significant effect on the specific binding of [125I]LHRH. The present study provides the evidence that estrogen decreases the density of binding sites for [125I]LHRH in the hypothalamus in vivo.
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PMID:The effect of estrogen on luteinizing hormone-releasing hormone binding sites in hypothalamic membranes. 331 92

Somatostatin receptors in the rat pituitary gland were characterized by binding analysis with a radioiodinated high affinity somatostatin analogue, 125I-Tyr1[D-Trp8]somatostatin. Receptor binding of this derivative reached equilibrium at 30 min and was maintained at a plateau for at least 60 min. Two L-Trp8- labeled somatostatin analogues. 125I-Tyr1- and [125I-Tyr11]somatostatin, displayed less stable and lower specific uptake and higher nonspecific binding. In contrast to the rapid degradation of the L-Trp8 ligands during binding assay, 125I-Tyr1]D-Trp8]somatostatin retained more than 80% of its binding activity after 90 min of incubation with pituitary particles. Pituitary particles bound 125I-Tyr1]D-Tyr8]somatostatin with high affinity (Ka = 8.6 +/- 1.2 X 10(9) M-1) and capacity of 54.4 +/- 2.6 fmol/mg. These binding sites showed specificity for the native peptide and its active analogues, and other peptide hormones, including angiotensin II, thyrotropin-releasing hormone, vasopressin, oxytocin, substance P, and gonadotropin-releasing hormone, did not inhibit tracer binding. A good correlation was observed between the binding affinities of several somatostatin analogues and their potencies as inhibitors of growth hormone release in rat pituitary cells. These findings emphasize the physiological importance of the pituitary somatostatin receptor in mediating the inhibitory action of the peptide on growth hormone release. The use of Tyr1[d-Trp8]somatostatin as a labeled ligand permits accurate determinations of the binding affinity and concentration of receptors for somatostatin in the normal pituitary gland and provides a basis for further studies of somatostatin receptor regulation and receptor-mediated cellular effects of the tetradecapeptide.
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PMID:Pituitary somatostatin receptors. Characterization by binding with a nondegradable peptide analogue. 612 Jan 62


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