Biomedical subjects

G Almazan

Publications and source records attributed to G Almazan.

At least 37 records · Page 2Linked to original sources

PubMed1997

Key role for cyclooxygenase-2 in PGE2 and PGF2alpha receptor regulation and cerebral blood flow of the newborn.

Ibuprofen, a cyclooxygenase (COX) inhibitor nonselective for either COX-1 or COX-2 isoform, upregulates cerebrovascular prostaglandin E2 (PGE2) and PGF2alpha receptors in newborn pigs. COX-2 was shown to be the predominant form of COX and the main catalyst of prostaglandin synthesis in the newborn brain. We proceeded to establish direct evidence that COX-2-generated prostaglandins govern PGE2 and PGF2alpha receptor density and function in the cerebral vasculature of the newborn. Hence, we determined PGE2 and PGF2alpha receptor density and functions in brain vasculature by using newborn pigs treated with saline, ibuprofen, COX-1 inhibitor (valerylsalicylate), or COX-2 inhibitors (DUP-697 and NS-398). Newborn brain PGE2 and PGF2alpha concentrations were significantly reduced by ibuprofen, DUP-697, and NS-398 but not by valerylsalicylate. In newborn pigs treated with DUP-697, NS-398, and ibuprofen, PGE2 and PGF2alpha receptor densities in brain microvessels were increased to adult levels; there was also a significant increase in inositol 1,4,5-trisphosphate (IP3) production and cerebral vasoconstrictor effects of 17-phenyl trinor PGE2 (EP1 receptor agonist), M&B-28767 (EP3 receptor agonist), PGF2alpha, and fenprostalene (PGF2alpha analog). Treatment with ibuprofen or DUP-697 also increased the upper blood pressure limit of cerebral cortex and periventricular blood flow autoregulation from 85 to > or = 125 mmHg (uppermost blood pressure studied). However, valerylsalicylate treatment did not affect cerebrovascular PGE2 and PGF2alpha receptors, IP3 production, or vasoconstrictor effects in newborn animals. These in vivo and in vitro observations indicate that COX-2 is mainly responsible for the regulation of PGE2 and PGF2alpha receptors and their functions in the newborn cerebral vasculature.

Animals↗

PubMed1996

Carbachol stimulates c-fos expression and proliferation in oligodendrocyte progenitors.

To determine if muscarinic receptor-activation plays a role in oligodendrocyte development, the effect of carbachol a stable acetylcholine analog, on gene expression and proliferation was investigated. Using Northern blot analysis we showed that carbachol caused a time and concentration-dependent increase in c-fos mRNA. This effect was blocked by atropine, a non-selective muscarinic antagonist. In addition, the muscarinic-stimulated c-fos increase was inhibited by 1-(5-isoquinoline-sulfonyl)-2-methylpiperazine (H-7), a potent inhibitor of protein kinase C (PKC), but not by N-2-(p-bromocinnamylamino)-ethyl-5-isoquinoline-sulfonamide (H-89), a potent inhibitor of protein kinase A, suggesting the involvement of PKC in mediating the response. Down-regulation of PKC by overnight pre-treatment with 12-O-tetradecanoylphorbol 13-acetate (TPA) blocked only the phorbol ester-stimulated c-fos accumulation while no effect was observed in the carbachol-induced response. These results suggested that carbachol stimulated an H-7 sensitive PKC pathway which may be different than that activated by TPA. Further evidence for two separate mechanisms of proto-oncogene induction was provided by the additive effect of carbachol and TPA. Induction of c-fos mRNA by carbachol was dependent on both influx of extracellular Ca2+ and release from intracellular stores, as both EDTA and BAPTA blocked the response. Since activation of muscarinic receptors can affect cell division in other cellular systems, the effect of carbachol on [3H]thymidine and bromodeoxyuridine incorporation into oligodendrocyte DNA was measured. Carbachol stimulated DNA synthesis in oligodendrocyte progenitors. This effect was mediated by muscarinic receptors as [3H]thymidine incorporation was prevented or significantly reduced by the addition of atropine. In conclusion, the present findings suggest that, the neurotransmitter, acetylcholine may act as a trophic factor in developing oligodendrocytes, regulating their growth and development in the central nervous system.

Animals↗

PubMed1996

A p65/p95 neural surface receptor is expressed at the S-G2 phase of the cell cycle and defines distinct populations.

A surface receptor complex of Mr approximately 65 000 (p65) and approximately 95 000 (p95) is expressed in cells of the central nervous system of mice. This receptor is recognized by monoclonal antibody 87.92.6 or by reovirus type 3 haemagglutinin as unnatural ligands. The p65/p95 receptor is expressed mostly in neural embryonic precursors undergoing proliferation, especially those in the S-G2 phase of the cell cycle. Receptor expression decreases progressively throughout embryogenesis to low but detectable levels in the adult brain. Biochemical characterization revealed that the neural p65/p95 receptor complex is indistinguishable from the p65/p95 receptor expressed in T cells, where receptor ligation leads to a mitogenic block. In neural and lymphoid tissues the p65/p95 receptor (or an associated protein) possesses a tyrosine kinase enzymatic activity. Receptor ligation in neural cells resulted in the rapid tyrosine phosphorylation of cellular proteins which are different from substrates phosphorylated in T cells. Differential substrate coupling to the receptor may account for differences in signal transduction and biology between neural cells and T cells. Further study of this receptor complex may help define important features of neural proliferation, differentiation and survival.

Animals↗

PubMed1996

Ontogenic differences in the functions of myocardial alpha1 adrenoceptor subtypes in rats.

The present study was done to determine possible ontogenic differences in the functions of rat myocardial alpha1, adrenoceptor (alpha1 AR) subtypes in view of reported greater inotropic responses of myocardium of neonatal than of adult rats to alpha1, AR agonists. Methoxamine, phenylephrine and norepinephrine were used as alpha1 AR agonists. Phenylephrine and norepinephrine were used in the presence of 3 microM propranolol. It was found that the ratios of chloroethylclonidine (CEC)-insensitive alpha1 AR subtype (alpha1A AR) to CES-sensitive alpha, AR subtype (alpha1B AR) were approximately 50:50 in neonatal (1 week old) and 20:80 in adult rat ventricles. alpha1A AR selective antagonists WB 4101 and 5-methylurapidil+ (5-MU) inhibited the inotropic effects of alpha1, AR agonists both on neonatal and on adult rat ventricles; in contrast, selective inactivation of alpha1B AR by CEC inhibited the inotropic effects of alpha1 AR agonists only on ventricles from adult but not from neonatal animals. WB 4101 inhibited methoxamine-induced increases in inositol phosphates by ventricular slices from both adult and neonatal rats; in contrast, CEC inhibited these effects of methoxamine only in tissues from adult but not in tissues from neonatal animals. In conclusion, this study, to our knowledge, demonstrates for the first time that the effects of alpha AR agonists on right ventricular contractions and phosphoinositol turnover are mediated primarily by alpha 1A AR subtype in the neonatal and by both alpha1A AR and alpha1B AR subtypes in the adult rat.

Animals↗

PubMed1995

Glutamate induces c-fos proto-oncogene expression and inhibits proliferation in oligodendrocyte progenitors: receptor characterization.

The effect of glutamate on c-fos expression in oligodendrocyte progenitors was investigated by Northern blot analysis. Glutamate caused rapid and transient induction. Both 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX) and 6,7-dinitroquinoxaline-2,3-dione (DNQX), two competitive non-NMDA ionotropic receptor antagonists, reduced glutamate-induced c-fos expression, whereas the NMDA antagonist MK-801 was ineffective. In addition, the glutamate receptor agonists (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid hydrobromide (AMPA) and kainate strongly induced c-fos. However, the metabotropic receptor agonist trans-(+/-)-1-amino-(1S,3R)-cyclopentanedicarboxylic acid (trans-(+/-)-ACPD) did not increase c-fos mRNA level and the antagonist L-(+)-2-amino-3-phosphonopropionic acid did not block glutamate-induced c-fos mRNA. These findings indicate that c-fos induction in oligodendrocyte progenitors is mediated through the AMPA/kainate receptors, while NMDA and metabotropic receptor subtypes are not involved. Chelation of extracellular calcium by EDTA prevented glutamate-induced c-fos expression. Similarly, the protein kinase C inhibitor 1-(5-isoquinoline-sulphonyl)-2-methylpiperazine dihydrochloride (H7) and down-regulation of protein kinase C by prolonged exposure to phorbol-12-myristate 13-acetate blocked c-fos induction. These results suggest that induction of c-fos through AMPA/kainate receptors is dependent on extracellular calcium influx and involves downstream activation of phorbol ester-sensitive protein kinase C. The effect of glutamate on oligodendrocyte progenitor proliferation was assessed by [3H]thymidine incorporation. Glutamate and the agonists kainate and AMPA, but not trans-(+/-)-ACPD, caused a dose-dependent decrease in [3H]thymidine incorporation. All these pharmacological agents were not toxic to oligodendrocyte progenitors. CNQX reversed the inhibitory effects produced by glutamate and the various agonists. These results suggest that glutamate may modulate the growth and differentiation of oligodendrocytes in the central nervous system.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed1995

Characterization and co-culture of novel nontransformed cell lines derived from rat endometrial epithelium and stroma.

Normal and neoplastic growth of epithelial cells depends on mutual interactions between epithelial and stromal cells. As a tool for the study of the underlying molecular mechanisms, we have developed temperature-sensitive, nontransformed cell lines derived from rat uterine epithelium and stroma by transfecting primary cultures with a temperature-sensitive mutant of the SV40 large T antigen. The epithelial and stromal cell lines obtained shared relevant morphological characteristics with the primary cells from which they were derived. Immunocytochemical analysis showed that the epithelial cell lines expressed the intermediate filament cytokeratin, whereas the stromal lines expressed the intermediate filament vimentin. Alkaline phosphatase activity was present in all cell lines examined. All cell lines were anchorage dependent and did not form foci. One epithelial cell line expressed oxytocin mRNA, a gene product recently shown to be highly expressed in vivo in the uterine epithelium at term. If grown on Matrigel, this cell line formed domelike structures, a further characteristic of its differentiated phenotype. In an attempt to reconstitute an endometrium in vitro, epithelial cells were seeded on top of a layer of stromal cells. Paraffin cross sections showed that this in vitro system consisted of a bilayer structure. Four to five cuboidal epithelial cells were typically anchored atop one stromal cell, forming an endometriumlike tissue. The present in vitro system should provide a useful model for further studies on endometrial functions and epithelial/stromal cell interactions at a molecular level.

Alkaline Phosphatase↗

PubMed1995

Immortalization and characterization of rat microglial cells.

Microglial cell lines from rat brain were established by transfer of a temperature sensitive simian virus 40 large tumour antigen by means of a retrovirus. Four weeks after infection, colonies were generated in the presence of neomycin and granulocyte-macrophage colony stimulating factor (GM-CSF), and subsequently subcloned. Both bulk cell lines and clones proliferate actively at 33 degrees C, whereas the rate of division was significantly decreased at 39 degrees C when the large T antigen is non-functional. At 39 degrees C, these cells take on the microglial phenotype as demonstrated by immunoreactivity to ED-1 (an intracellular antigen), OX-42 (complement type 3 receptor), W3/25 (CD4 homologue), OX-6 (MHC class II antigen) and OX-18 (MHC class I antigen). These cells are capable of active phagocytosis and retain these properties for 10-15 passages. Long-term culture of these lines and clones, greater than 15 passages, displayed a gradual down-regulation of all cell surface specific antigens that were not rescued by lipopolysaccharide (LPS), interferon-gamma (gamma-IFN), GM-CSF or colony-stimulating factor-1 (CSF-1). The expression of the SV-40 large T antigen was unaffected. These results demonstrate the feasibility of immortalizing short-term cell lines with the SV-40 large T antigen for their use in the characterization of microglial properties.

Animals↗

PubMed1994

Identification of tyrosine 620 as the major phosphorylation site of myelin-associated glycoprotein and its implication in interacting with signaling molecules.

Myelin-associated glycoprotein (MAG) is a myelin-specific cell adhesion molecule of the immunoglobulin supergene family and is tyrosine-phosphorylated in the developing brain. To define the role of MAG in signal transduction, the tyrosine phosphorylation sites were analyzed. The major tyrosine phosphorylation residue was identified as Tyr-620, which was found to interact specifically with the SH2 domains of phospholipase C (PLC gamma). This domain may represent a novel protein binding motif that can be regulated by tyrosine phosphorylation. MAG also specifically bound the Fyn tyrosine kinase, suggesting that MAG serves as a docking protein that allows the interaction between different signaling molecules.

Animals↗

PubMed1994

Rat oligodendrocytes express muscarinic receptors coupled to phosphoinositide hydrolysis and adenylyl cyclase.

Muscarinic receptors expressed by rat oligodendrocyte primary cultures were examined by measuring changes in second messengers following exposure to carbachol, an acetylcholine analog, and by polymerase chain reaction. Inositol phosphate levels were measured in [3H]myo-inositol-labelled young oligodendrocyte cultures following stimulation with carbachol. Atropine, a specific muscarinic antagonist, prevented the carbachol-induced accumulation of inositol phosphates. The formation of inositol trisphosphate was concentration- and time-dependent, with the peak at 100 microM carbachol and 10 min. Carbachol increased intracellular calcium levels, which were dependent both on the mobilization of intracellular stores and influx of extracellular calcium. In initial experiments with more selective antagonists, the mobilization of intracellular calcium was preferentially inhibited by pirenzepine, a selective M1 antagonist, but not methoctramine, a selective M2 antagonist, suggesting M1 muscarinic receptor involvement. A role for protein kinase C in the regulation of carbachol-stimulated inositol phosphate formation and intracellular calcium mobilization was demonstrated, as acute pretreatment with phorbol-12,13-myristate acetate abolished the formation of both second messengers. Pretreatment with 100 microM carbachol abolished the 40% increase in the cyclic AMP accumulation stimulated by isoproterenol, a specific beta-adrenergic agonist. In turn, the inhibition was alleviated by pretreatment with atropine, suggesting muscarinic receptor involvement. Polymerase chain reaction carried out with specific m1 and m2 muscarinic receptor oligonucleotide primers, confirmed that these cells express, at least, the two muscarinic receptor subtypes. Without excluding the expression of other subtypes, these results suggest that developing oligodendrocytes express m1 (M1) and m2 (M2) muscarinic receptors capable of mediating phosphoinositide hydrolysis, mobilization of intracellular calcium and the attenuation of beta-adrenergic stimulation of cyclic AMP formation.

Adenylyl Cyclases↗

PubMed1994

Protein kinases mediate basic fibroblast growth factor's stimulation of proliferation and c-fos induction in oligodendrocyte progenitors.

Primary culture was used to examine the effects of basic fibroblast growth factor (bFGF) on oligodendrocyte progenitor proliferation and c-fos expression. Basic FGF induced proliferation approximately six fold. This increased DNA synthesis could be blocked both with genistein, a tyrosine kinase inhibitor, and H-7, a protein kinase C (PKC) inhibitor. These results indicate that protein tyrosine kinase activity and protein kinase C are involved in mediating oligodendrocyte progenitor proliferation. The protooncogene c-fos was investigated as a likely proliferation mediator. Firstly, optimal conditions for bFGF-induced c-fos expression were determined. The oncogene responded maximally between 30 and 60 min of bFGF stimulation. Induction in response to bFGF occurred at 1 ng/ml, increased in a concentration-dependent manner and was maximal at 50 ng/ml. H-7 (50 microM) and genistein (100 microM) blocked c-fos induction as did PKC down-regulation with chronic treatment of phorbol 12-myristate 13-acetate. These results indicate that bFGF induces c-fos expression through receptor tyrosine phosphorylation and PKC activation. Thus similar early signals lead to bFGF-driven proliferation and c-fos induction suggesting a link between these two processes.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1993

Phosphorylation and disruption of intermediate filament proteins in oligodendrocyte precursor cultures treated with calyculin A.

Treatment of primary cultures of oligodendrocyte precursors with calyculin A, a potent inhibitor of protein phosphatases 1 and 2A, caused the phosphorylation of two intermediate filament components, nestin and vimentin. Phosphoamino acid analysis demonstrated that phosphorylation took place mainly on serine and to a lesser extent on threonine residues. In addition, calyculin A treatment caused a shift in the distribution of the two proteins from the Triton-X-100 insoluble fraction to the detergent soluble fraction as demonstrated by immunoblotting. This redistribution, which was evident within 15 min after treatment and was nearly completed by 90 min, was accompanied by a disruption of the intermediate filament network. Thus, both nestin and vimentin retracted from the cytoplasmic processes to form a large perikaryal ring as shown by immunocytochemical analysis. Both morphological and biochemical changes were reversed 2-5 hr after removal of calyculin A from the culture medium.

Amino Acids↗

PubMed1993

Gene expression in the developing cerebellum during perinatal hypo- and hyperthyroidism.

The intensity of p75NGFR receptor-like immunoreactivity and the mRNAs encoding p75NGFR, T alpha 1 alpha-tubulin, GAP-43 and the myelin proteins MBP and PLP were measured in the developing cerebellum to study the effects of perinatal thyroid hormone imbalance in rats. Results compared to age-matched controls provide in vivo evidence for differential gene regulation by thyroid hormone in the developing cerebellum. We found that p75NGFR immunoreactivity was strikingly elevated in hypothyroid rats, whereas p75NGFR mRNA content remained only twice as high as that of control levels on postnatal day 15 (P15). When p75NGFR immunoreactivity was still elevated in hypothyroid rats, Purkinje cells exhibited proximal axonal varicosities, axonal twisting and differences in axonal caliber. The mRNAs encoding proteins involved with neurite growth-promoting elements, T alpha 1 alpha-tubulin and GAP-43, were also increased in hypothyroidism, possibly reflecting a neuronal response to a deficiency in, or damage to, cerebellar neurons, or a general delay in their down regulation. Similar increases were not observed for the myelin specific genes. MBP and PLP mRNAs were first detected on P2 of hyperthyroid rats, and they increased with age. Hypo- or hyperthyroidism did not affect the initial onset of MBP and PLP expression, however, hyperthyroidism increased levels of PLP and MBP mRNAs between P2 and P10. By contrast, the most consistent decrease in MBP and PLP mRNAs in rats with thyroid hormone deficiency was observed only on P10. At later times (P15 and P30), the two mRNA levels were similar to controls in all groups. These results are consistent with a role for thyroid hormone in the earlier stages of cerebellar myelination. Hypothryoidism led to specific increases in T alpha 1 alpha-tubulin and GAP-43 mRNAs, and in the immunoreactivity and mRNA levels of p75NGFR receptor--all changes that may play a role in the observed abnormal neuronal outgrowth.

Animals↗

PubMed1993

Norepinephrine-stimulated PI hydrolysis in oligodendrocytes is mediated by alpha 1A-adrenoceptors.

Oligodendrocyte progenitors were labelled with [3H]-myo-inositol in order to determine the effect of adrenergic agents on the accumulation of [3H]-inositol phosphates (InsP). Both norepinephrine and phenylephrine, a selective alpha 1-adrenoceptor agonist, increased the formation of [3H]-InsP, while isoproterenol, a beta-adrenoceptor agonist, did not. Propranolol (beta) and yohimbine (alpha 2), two adrenoceptor antagonists, had no significant effect on the NE-stimulated [3H]-InsP formation. By contrast, the response to NE was significantly blocked by phenoxybenzamine and the alpha 1-receptor antagonist, prazosin. Pretreatment with chloroethylclonidine, which selectively inactivates alpha 1B receptors, had no effect on NE-induced [3H]-InsP formation, while WB4101 had high potency in inhibiting this response. Pertussis toxin, which inactivates certain G-proteins, caused a approximately 60% reduction. NE-stimulated formation of [3H]-InsP depended on extracellular calcium influx, because it was decreased by 55% and 75% by chelation with EGTA or the addition of 1 mM CdCl2, respectively. These results suggest that oligodendrocyte progenitors express alpha 1-adrenoceptors characteristic of the alpha 1A subtype.

Adrenergic alpha-Agonists↗

PubMed1992

An oligodendrocyte precursor cell line from rat optic nerve.

We have established permanent cell lines from the optic nerve of the rat with a temperature sensitive immortalizing oncogene (Simian Virus 40 large T-antigen carrying both the tsA58 and U19 mutations). The oncogene was transduced into primary cultures via a replication deficient retrovirus, and infected cells were selected with the antibiotic G418. A clonal cell line (tsU19-5) displayed some properties of oligodendrocyte precursors: it proliferated, bound the monoclonal antibody A2B5 (which recognizes minor ganglioside species), and expressed the intermediate filament vimentin and the enzyme 2',3'-cyclic-nucleotide 3'-phosphodiesterase (CNP) at 33 degrees C (the permissive temperature for the oncogene). At 39 degrees C (the non-permissive temperature), some cells had the potential to differentiate further, and expressed several oligodendrocyte specific components: galactocerebroside, myelin basic protein, proteolipid protein and CNP. These results suggest that conditional oncogenes can establish neural precursor cell lines which are still capable of differentiation in vitro.

Animals↗

PubMed1992

Myelin associated glycoproteins confer heterophilic adhesion properties to an immortalized optic nerve derived cell line.

We have transfected an immortalized optic nerve-derived cell line with the cDNA's encoding the two isoforms of MAG. Our aim was to assess whether expression of L-MAG (72 KDa) and S-MAG (67 KDa) in these cells confer adhesion properties when a suspension of single cells is allowed to aggregate. The selected cell lines expressed MAG mRNAs and proteins of the appropriate molecular size, and the proteins were targeted correctly to the plasma membrane. Both L-MAG and S-MAG-expressing transfectants exhibited enhanced self-adhesive properties, aggregating with faster kinetics and forming larger aggregates than MAG-negative control cells. The interaction appears to be mostly heterophilic since MAG+ and MAG- cells which were labeled with a fluorescent probe bound equally well to pre-aggregated MAG+ transfectants and their interaction was blocked by monoclonal anti-MAG antibodies. A further finding which supports the role of MAG in adhesion was the observation that MAG was preferentially localized at the junctions between cells, in confluent cultures.

Animals↗

PubMed1990

Transfection of transformed shiverer mouse glial cell lines.

In the course of studies on glial cell differentiation in the mouse mutant shiverer, we have established by infection with a temperature-sensitive retrovirus encoding the SV40 T antigen a few glial cell lines that divide rapidly at 33 degrees C, the permissive temperature, and whose phenotypes at the nonpermissive temperature (39 degrees C) resemble either astrocytes or oligodendrocytes. One astrocyte-like clone (clone SF11) expresses glial fibrillary acidic protein at 33 degrees C and expresses this marker strongly at 39 degrees C as well. One oligodendrocyte-like clone (DM5) that we have succeeded in maintaining at 33 degrees C can be induced to express galactocerebroside and 2',3'-cyclic nucleotide 3'-phosphodiesterase at the elevated temperature but never expresses the more differentiated markers of the myelination state, such as the myelin proteolipid protein or the myelin-associated glycoprotein. Clone DM5, as is the case with other oligodendrocyte clones we have prepared by the method described here, is quite fragile and survives for only several (5-6) days at the higher temperature. Both clonal lines can serve as host cells for expressible cDNAs introduced by transfection, such as the neurofilament protein, NF-M, and the small myelin basic protein.

Animals↗

PubMed1989

Ontogeny of hypothalamic vasopressin, oxytocin and somatostatin gene expression.

The expression of 3 neuropeptide genes, vasopressin (AVP), oxytocin (OT) and somatostatin (SOM), was studied in the developing rat hypothalamus using Northern blot analysis combined with densitometric scanning. A unique profile of developmental expression was established for each of the 3 genes. SOM mRNA is detectable at embryonic day 14 and reaches 40% of the adult levels by embryonic day 18. By contrast, accumulation of AVP and OT mRNA is mainly a postnatal event. AVP mRNA, although detectable in the late embryo, rises gradually after birth and attains 40% of adult levels after the second postnatal week. Maturation of OT gene expression occurs even later and parallels AVP gene expression with a lag time of one week. Observed increases in mRNA levels are due to an upregulation of gene expression since they occur essentially following cessation of neuronal cell proliferation. The rise in AVP and OT mRNA accumulation coincides with the establishment of synaptic input to AVP and OT neurons. Expression of the SOM gene, by contrast, occurs prior to neuronal cell differentiation and points to a possible function of SOM in the embryonic brain.

Aging↗

PubMed1988

Regulation of poly(A) tail size of vasopressin mRNA.

Dehydration represents a strong stimulus for the secretory activity of hypothalamic vasopressinergic neurons and induces a sustained rise in hypothalamic [Arg8]vasopressin (AVP) mRNA. We now report that, in addition to the change in mRNA accumulation, this stimulus leads to an increase in the size of the mature AVP gene transcripts. Using Northern blot analysis in conjunction with internal RNA size markers, we demonstrate here that a 6-day period of salt imbibition induced a gradual size increase of AVP mRNA from 810 to a maximum of 930 bases. This change was fully reversed by day 30 following termination of the salt treatment. Any alteration of the mRNA capping or polyadenylation sites was ruled out by S1 mapping. However, poly(A) tail removal reduced AVP mRNA of all treatment groups to exactly the same size (600 bases). It is concluded that the dehydration-induced size change is due to a greater than 50% increase of the mean steady state length of the poly(A) tail. It remains to be determined to what extent the observed increase in poly(A) tail length may have an effect on AVP mRNA stability or translational efficiency.

Animals↗