Biomedical subjects

L Tapia-Arancibia

Publications and source records attributed to L Tapia-Arancibia.

At least 73 records · Page 4Linked to original sources

PubMed1986

Cyclic AMP regulates somatostatin mRNA accumulation in primary diencephalic cultures and in transfected fibroblast cells.

Although the factors controlling the secretion of the neuropeptide somatostatin have been extensively studied, little is known about the mechanisms that control somatostatin biosynthesis. Somatostatin secretion is regulated by numerous agents that increase intracellular levels of cAMP. We sought to determine whether cAMP also regulates somatostatin mRNA accumulation. We found that forskolin elicited an increase in somatostatin secretion and mRNA levels in primary cultures of rat diencephalic cells. Another secretagogue, KCl, was as effective as forskolin in causing somatostatin secretion but had no effect on mRNA accumulation. Somatostatin expression in fibroblast cells transfected with the somatostatin gene was also regulated by forskolin. These results demonstrate that somatostatin mRNA accumulation can be regulated through a cAMP-dependent pathway, that this pathway is operative in heterologous cells transfected with the somatostatin gene, and that stimulation of somatostatin secretion and mRNA accumulation can be uncoupled from one another.

Animals↗

PubMed1986

[Effect of forskolin and VIP on the release of somatostatin and the cAMP content of cultured rat diencephalon neurons].

Forskolin, a direct activator of adenylate cyclase, stimulates somatostatin release in dispersed fetal diencephalic cells in culture (10 j). It was found that concentrations ranging from 10(-8) M to 10(-4) M increase the release of somatostatin in a dose-dependent manner, as well as the formation of intracellular cyclic AMP. Furthermore, VIP (10(-6) M) which produces a significant (p less than 0.03) elevation of SRIF release at 30 min of incubation, also induces a prompt increase of intracellular cyclic AMP (10 min). These results suggest that VIP could stimulate the somatostatin release through a cyclic AMP-dependent mechanism.

Animals↗

PubMed1985

Vasoactive intestinal peptide and PHI stimulate somatostatin release from rat cerebral cortical and diencephalic cells in dispersed cell culture.

To determine the effect of vasoactive intestinal peptide (VIP) on the secretion of somatostatin by neurons, dispersed fetal cerebral cortical and diencephalic cells grown in culture were exposed on day 10 or 11 of culture to various concentrations of VIP, and for comparison to the structurally related peptides PHI (Peptide Histidine Isoleucine-27), growth hormone (GRH1-44-NH2) and secretin and to cholecystokinin. VIP elicited a dose-dependent release of somatostatin from both cortical and diencephalic cells, the lowest effective concentration being 6 X 10(-9) M. PHI also brought about release of somatostatin, but was between 0.06 and 0.1 times as potent as VIP. Placed together in a concentration of 10(-7) M, the two peptides did not have an additive effect. In this system GRH1-44-NH2, secretin and CCK octapeptide were without effect.

Animals↗

PubMed1985

Electron microscopic immunocytochemical study of somatostatin neurons in the periventricular nucleus of the rat hypothalamus with special reference to their relationships with homologous neuronal processes.

The neurons containing somatostatin in the rat periventricular nucleus were studied by using a modified electron microscopic immunocytochemical technique that improves both the penetration of immunoreagents into unembedded immunostained tissues and the preservation of ultrastructural morphology. Inside perikarya and dendrites, immunostaining was not only associated with neurosecretory granules but also with ribosomes and saccules of the cis face of the Golgi apparatus. In the axonal profiles found in this region the labeling was observed both on neurosecretory granule cores and on the limiting membrane of small synaptic-like vesicles. Throughout the periventricular nucleus, both non-synaptic and synaptic relationships were shown between labeled neurons. Non-synaptic relationships mainly consisted of direct apposition of the membranes of neighboring neurons by dendrosomatic, somasomatic or dendrodendritic contacts. These labeled perikarya and dendrites were also synaptically contacted by labeled axonal endings containing numerous aggregated synaptic-like vesicles. The physiological significance of the synaptic and non-synaptic relationships between somatostatinergic neurons is discussed in terms of possible synchronization between homologous neurons of the somatostatin neuroendocrine system and control of these neurons by a central ultra-short loop feedback mechanism.

Animals↗

PubMed1985

Evidence for alpha 1-adrenergic stimulatory control of in vitro release of immunoreactive thyrotropin-releasing hormone from rat median eminence: in vivo corroboration.

The aim of this study was to investigate whether the alpha-adrenergic stimulation of TSH secretion may occur directly at the median eminence (ME) level by modulating the release of TRH. The effects of pharmacological manipulations of the two subtypes of central alpha-adrenergic receptors, alpha 1 and alpha 2, were tested on in vitro TRH release from medial basal hypothalami containing mainly the ME. Hypothalamic fragments were superfused with a modified Locke medium, and TRH was measured by RIA in samples collected every 10 min. After a preliminary period of 40 min to test TRH release during basal conditions, drug effects were checked for 20 min. Superfusion with norepinephrine (NE) (10(-10), 10(-8), 10(-6) M) induced a rapid and dose-dependent rise of TRH release; epinephrine (10(-8) M) induced an effect similar to that of NE 10(-8) M. Phentolamine (10(-7) M), an alpha-adrenergic antagonist, completely blocked the NE (10(-8) M)-induced release of TRH, which was not modified by the beta-adrenergic antagonist propranolol (10(-7) M). Neither antagonist had an effect on basal TRH release when added alone to the medium. The NE-induced release of TRH was completely suppressed by prazosin (10(-7) M), whereas yohimbine had no effect. Superfusion with clonidine (10(-9), 10(-8), 10(-7), 10(-6) M), an alpha 2-receptor agonist, did not alter basal TRH release. In contrast, phenylephrine (10(-8) and 10(-6) M), an alpha 1-receptor agonist, induced a significant (P less than 0.01) rise in TRH release. These results were corroborated in vivo in several unanesthetized rats bearing a push-pull cannula previously and stereotaxically implanted into the ME. Perfusion with artificial cerebrospinal fluid containing NE (10(-7), 10(-6) M) or phenylephrine (10(-7) M) elicited a rapid rise in TRH release, within 15 min after the onset of drug perfusion. Clonidine (10(-5) M), similarly perfused for 15 min, had no effect. Our data suggest a direct stimulatory influence of catecholamines on TRH release at the ME level that is mediated through alpha 1-adrenergic receptors.

Animals↗

PubMed1984

K+-induced thyrotropin-releasing hormone release from superfused mediobasal hypothalami in rats. Inhibition by somatostatin.

Somatostatin (SRIF), in concentration of 10(-6) M, significantly inhibited the depolarization-induced release of immunoreactive thyrotropin-releasing hormone (IR-TRH) from superfused mediobasal hypothalami (MBH) containing mainly the median eminence (ME), without affecting the basal release of TRH. The total amount of K+-induced TRH release was 0.24 +/- 0.02 and 0.61 +/- 0.08 pg/MBH/min, respectively, in the presence and absence of SRIF in the medium. The data are consistent with a role of SRIF as a neuromodulator on TRH release from the ME. In contrast, superfusion with Locke medium containing triiodothyronine (10(-6) M) had no effect on basal and K+-induced IR-TRH release in our system.

Animals↗

PubMed1983

Opiate inhibition of K+-induced TRH release from superfused mediobasal hypothalami in rats.

The effect of morphine and leucine enkephalin on basal and K+-induced TRH release by superfused mediobasal hypothalami in rats was investigated in an oxygenated modified Locke medium at 37 degrees C during 10 min. Both opiates (morphine, 10(-6) M; leucine enkephalin, 10(-6) M) did not modify the spontaneous release of TRH, but significantly decreased the depolarization-induced TRH release. Naloxone (10(-6) M) had no effect when added alone to the medium, but reversed the opiate inhibition of TRH release. The data suggest that endogenous opiates exert a modulatory action on TRH nerve endings in the mediobasal hypothalami, probably through presynaptic specific opiate receptors.

Animals↗

PubMed1983

Direct evidence of short-term cold-induced TRH release in the median eminence of unanesthetized rats.

IR-TRH release in the median eminence was directly estimated in conscious rats during the first 130 min of exposure to cold (4 degrees C), using a push-pull cannulation. A three-fold increase in IR-TRH release was observed, with a peak of 10.00 +/- 2.19 pg/15 min occurring 40 min after exposure to cold; control rats, left at 24 degrees C, stayed at the baseline secretion rate of 3.40 pg/15 min which was the sensitivity limit of the RIA assay.

Animals↗

PubMed1982

Somatostatin connections between the hypothalamus and the limbic system of the rat brain.

Somatostatin (SRIF) content of several brain structures was evaluated by radioimmunoassay in rats bearing various types of hypothalamic transections, as well as lesions of the amygdala. Analysis of the regional changes in SRIF concentrations after surgery suggest the following conclusions: (1) hypothalamic somatostatinergic neurons project to the limbic system, with the exception of the amygdaloid nuclei; (2) the olfactory tubercle, the lateral septal nucleus, the habenula and probably the hippocampus receive somatostatin projections from periventricular SRIF-containing cells; (3) somatostatin-containing fibers take a lateral course after leaving periventricular cells and join the medial forebrain bundle; (4) somatostatin innervation of the amygdala seems to be intrinsic.

Amygdala↗

PubMed1982

Somatostatin in catecholamine-rich nuclei of the brainstem.

Somatostatin (SRIF) concentrations in catecholamine-rich nuclei of the rat brainstem were measured by radioimmunoassay. The study was performed both in control or sham operated animals and after transecting the major projections of hypothalamic SRIF-containing neurons. Concentrations of the peptide were found to be relatively high in the locus coeruleus, the parabrachial nucleus and the nucleus of the solitary tract; they were intermediate in the lateral reticular nucleus (A1 cell group) and low in the substantia nigra. Transection of hypothalamic periventricular efferents resulted in a 58% depletion of SRIF content in the locus coeruleus, while concentrations of the peptide in other areas were unaffected. Transection of the medial forebrain bundle at the level of the lateral hypothalamus decreased SRIF content by 55% in the substantia nigra, but not in the other nuclei tested. It is concluded that the hypothalamus contributes significantly to the somatostatinergic innervation of the locus coeruleus and the substantia nigra, whereas SRIF in the other nuclei is intrinsic or originates outside the hypothalamus.

Animals↗

PubMed1982

Somatostatin receptors on rat anterior pituitary membranes.

[125I]Iodo-Tyr1-somatostatin (SRIF) binds with high affinity to one class of sites in the rat anterior pituitary with a KD of 0.91 +/- 0.22 nM and a receptor concentration of 104.4 +/- 1.9 fmol/mg protein. This binding is saturable with respect to tissue concentration and is time-, temperature-, pH-, and calcium-dependent. It is also reversible as a function of time. The rates of association and dissociation were calculated to be 5.98 X 10(7) M-1 min-1 and 0.578 min-1, respectively. Binding of [125I]iodo-Tyr1-SRIF is not inhibited by morphine, beta-endorphin, [D-Ala2]Met-enkephalin, LHRH, TRH, histidylproline diketopiperazine, neurotensin, substance P, bombesin or vasoactive intestinal peptide. In contrast SRIF, [Tyr1]SRIF, and [D-Trp8,D-Cys14]SRIF displace [125I]iodo-Tyr1-SRIF binding with Ki values 0.10 +/- 0.05, 0.46 +/- 0.18, 0.05 +/- 0.01 nM, respectively. The constants of inhibition of a series of alanine monosubstituted analogs of SRIF are correlated (r = 0.89) with their biological potency on GH secretion. Furthermore, postnatal development patterns of [125I]iodo-Tyr1-SRIF binding sites follow the ability of SRIF to inhibit GH release. Thus, [125I]iodo-Tyr1-SRIF binding to adenohypophyseal membranes seems to reflect interaction with SRIF receptors on adenohypophyseal cells. Since biological effects of the peptide have been reported on GH, thyrotropin-stimulating hormone, and PRL secretion, further studies are required to determine the cell types upon which this binding occurs.

Animals↗

PubMed1982

Reciprocal interactions of somatostatin with thyrotropin-releasing hormone and vasoactive intestinal peptide on prolactin and growth hormone secretion in vitro.

Reciprocal interactions of somatostatin (SRIF) and vasoactive intestinal peptide (VIP) or TRH on in vitro PRL and GH release from male rats hemipituitaries were investigated. SRIF did not modify basal PRL release, but TRH- or VIP-induced release was inhibited by SRIF in a dose-dependent manner [effective concentration-fifty (EC50) = 1.7 +/- 0.9 nM for SRIF inhibition of TRH stimulation and EC50 = 0.8 +/- 0.5 nM for SRIF inhibition of VIP stimulation]. VIP and TRH did not affect GH release by themselves, but reduced the inhibition of GH secretion elicited by SRIF (EC50 = 7.6 +/- 3.4 nM for TRH blockade of SRIF inhibition and EC50 = 4.6 +/- 3.1 nM for VIP blockade of SRIF inhibition). Secretin, a partial structural analog of VIP, also blocked SRIF-induced inhibition of GH and stimulated PRL release. Secretin stimulation of PRL release was also prevented by SRIF. [D-Trp8,D-Cys14]SRIF, a potent analog of SRIF, antagonized VIP stimulation of PRL secretion with the same apparent affinity as the native peptide. The maximal stimulation, but not the apparent affinity of VIP action on prolactin release was reduced by SRIF, suggesting that the interaction is of a noncompetitive nature. This conclusion as further substantiated by the observation that neither TRH nor VIP were able to displace specific 125I-labeled [Tyr1] SRIF high affinity binding to pituitary membranes. The three peptides tested thus appear to exhibit reciprocal interactions mediated by independent receptor sites on GH as well as on PRL-producing cells.

Animals↗

PubMed1981

Noradrenaline stimulates somatostatin release from incubated slices of the amygdala and the hypothalamic preoptic area.

Neurotransmitter effects were studied on in vitro release of immunoreactive somatostatin (SRIF) from slices prepared from several regions of the rat brain: mediobasal hypothalamus (MBH), preoptic anterior hypothalamic area (POA) and amygdaloid complex (AMY). Potassium (K+, 56 mM) stimulated SRIF release in all structures tested in a calcium dependent manner. Morphine, dopamine, GABA and serotonin did not modify SRIF release in any structure; noradrenaline (NA) was not effective on MBH slices, but elicited a dose-dependent stimulation of SRIF release from POA and AMY (ED50 = 6.4 +/- 1.4 nM and 3.6 +/- 1.2 nM respectively). Converse orders of potency of adrenergic agonists were observed in both structures (POA, adrenaline greater than noradrenaline greater than isoproterenol; AMY, isoproterenol greater than adrenaline greater than noradrenaline). Phentolamine blocked NA-induced SRIF release in the POA while propranolol was ineffective. On the contrary, propranolol, but not phentolamine, antagonized NA stimulation in the amygdala. The data suggest that NA acting through specific receptors modulate SRIF release from POA and AMY. In POA, NA effect seems mediated through alpha adrenergic receptors while in AMY, beta receptors are involved. The possibility that these interactions of NA with SRIF release are correlated with effects of NA on growth hormone secretion or on epileptic events is discussed.

Amygdala↗

PubMed1981