Biomedical subjects

L Cacicedo

Publications and source records attributed to L Cacicedo.

At least 55 records · Page 3Linked to original sources

PubMed1991

Influence of hypothyroidism duration on developmental changes in the hypothalamic factors implicated in growth hormone secretion in the male rat.

The effects of hypothyroidism duration on several factors implicated in GH secretion control were studied in the male rat at different maturity stages, ranging from the peripuberal period to adulthood. Thyroid ablation was performed on 22-day-old Wistar male rats maintained on a low iodine diet (T group). Age-paired controls (C group) were fed with the same diet, supplemented with potassium iodide. Subgroups of T and C animals (aged 32, 42, 52, 82 and 112 days) were studied 10, 20, 30, 60 and 90 days after surgery. After pentobarbital anesthesia, jugular blood was withdrawn before and 5 min after an intravenous TRH stimulus, for GH assay. Hypothalamic and pituitary tissues were obtained in order to measure GH, immunoreactive somatostatin (IR-SRIF) and growth hormone-releasing factor (IR-GRF). Growth rate and serum testosterone confirmed that C rats reached sexual maturity by day 30 of the study. Mean +/- SE serum GH (ng/ml) increased (p less than 0.05) in C animals from day 10 (38.5 +/- 5) to day 30 (67.4 +/- 7.3), with no significant variations thereafter. The same time sequence pattern was observed in pituitary GH concentrations. In T rats, both serum and pituitary GH decreased progressively from day 10 to 90, being significantly lower than in C at all times of the study. No GH response to TRH could be found in C groups. In contrast, GH increased significantly (p less than 0.05) in T animals after TRH at days 20 and 30.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Secretions of somatostatin and VIP in cultures of fetal rat neuroblasts increased by amino acids.

Neuroblasts obtained from 17 day old rat embryos were incubated for 8 days, after which half of them were treated with 10(-6) M FACE (a mixture of amino acids high in glycine, alanine and aspartic acid), and the other half were left as controls. At the end of 20 days, levels of somatostatin (SRIF) were over 6,000 pg/plate in neuroblasts treated with FACE, versus 500 pg/plate in controls. At this time vasoactive intestinal peptide (VIP) levels were over 230 pg/plate in the FACE treated cultures, while their controls contained less than 150 pp/plate. Protein totals were similar (about 1,000 micrograms/plate) in all FACE treated cultures and controls, indicating that increases in SRIF and VIP were not determined by changes in cell population, but by their synthetic and/or secretory activities triggered by minute amounts of FACE. These results may be of interest in the understanding of Alzheimer's disease.

Amino Acids↗

PubMed1990

Influence of thyroid hormones on somatostatin processing in cultured cerebro-cortical cells.

Previous data from our laboratory showed that prolonged exposure of cultural cerebral cortical cells to high potassium concentrations and veratridine resulted in the stimulation of immunoreactive somatostatin (IR-SRIF) synthesis and caused a major increase in its high molecular weight forms. Somatostatin (SRIF) synthesis by cortical and hypothalamic cells was also affected by thyroid hormone (TH). In the present work we have examined to what extent TH might also affect SRIF processing. Cerebral cortical cells maintained as monolayer culture for 7-10 days received triiodothyronine (T3) in concentrations of 10(-11) M and 10(-7) M for 48 h. We found that the total amount of IR-SRIF was increased by high T3 concentrations as reported previously. When the IR-SRIF was characterized by high pressure liquid chromatography (HPLC) or gel filtration, it was evident that thyroid hormone treatment modified the elution profile of IR-SRIF in cells and medium on Bio-Gel P-10 and HPLC, increasing somatostatin 28 (S-28) and decreasing somatostatin 14 (S-14). The results indicate that thyroid hormones affect SRIF processing, leading to a major increase in the synthesis of its high molecular weight forms.

Animals↗

PubMed1990

Depolarizing influences regulate somatostatin synthesis and processing in cultured cerebral cortical cells.

There is increasing evidence that persistent depolarization plays a critical role not only in excitation-secretion coupling, but also in the mechanisms linking excitation of neuronal cells to long-term adaptative changes in biosynthesis of neuropeptides. Somatostatin (SRIF) release and synthesis are affected by numerous agents, such as high concentrations of potassium that cause depolarization of cellular membrane. In the present work, we tried to determine whether prolonged exposure to veratridine (VTD) regulates SRIF synthesis. We found that exposure to VTD (100 microM) resulted in the stimulation of total (cell content + media) immunoreactive SRIF (IR-SRIF). This effect was calcium- and sodium-dependent, since it was prevented when verapamil (VPM) 20 microM or tetrodotoxin (TTX) 1 microM were added simultaneously with VTD. Cerebral cortical cells were exposed to high potassium concentrations, and the nature of the IR-SRIF was characterized by high-pressure liquid chromatography (HPLC) or gel filtration. It was evident that chronic exposure to high potassium concentrations modified the elution profile of medium IR-SRIF on HPLC and gel filtration, causing an increase in somatostatin-28 (S-28) and a decrease in somatostatin-14 (S-14). The results indicate that chronic exposure to VTD or high potassium concentration increases immunoreactive somatostatin and augments synthesis of its high-molecular-weight forms. This suggests that chronic membrane depolarization activating sodium and calcium channels initiates the entry of calcium ions, which triggers somatostatin release and causes a depletion of its intracellular stores. The stimulation of somatostatin secretion could be coupled to synthesis of the peptide.

Animals↗

PubMed1990

Neurosecretory and trophic action on fetal rat neuroblasts induced by an amino acid mixture.

The effects of a synthetically obtained mixture of amino acids (FACE) were investigated on the trophic and neurosecretory activity of in vitro cultures of fetal rat neuronal cells. The addition of 10(-6) M FACE to the culture medium significantly increased cell DNA content. Secretions of IR-SRIF, IR-VIP, and IR-GRF were also augmented in different proportions by the presence of FACE. Time studies demonstrated that IR-SRIF was significantly increased after 48 (P less than 0.05) and 72 (P less than 0.01) hr of exposure to FACE, and IR-VIP secretion was potentiated after only 24 hr of culture. Dose-response experiments with 10(-7) to 10(-4) M FACE indicated that concentrations of 10(-5) and 10(-4) M significantly increased both somatostatin released to the medium and cell content of IR-SRIF. FACE concentrations as low as 10(-10) M augmented the secretion of IR-GRF, and there was a dose-response correlation between 10(-10) and 10(-5) M FACE. The release and cell content of IR-VIP were also increased by FACE, with a dose-response relation at concentrations of 10(-9) to 10(-6) M. It can thus be concluded that FACE has a powerful effect on the multiplication and survival of fetal cerebrocortical cells and is also an important potentiator of IR-SRIF, IR-VIP, and IR-GRF secretion.

Amino Acids↗

PubMed1990

Demonstration of immunoreactive vasoactive intestinal peptide (IR-VIP) and somatostatin (IR-SOM) in rat thymus.

In the present work we demonstrate immunohistochemically the presence of both immunoreactive vasoactive intestinal peptide (IR-VIP) and immunoreactive somatostatin (IR-SOM) cells in the thymus of neonatal and adult rats. IR-VIP and IR-SOM from thymic tissue extracts were identified by gel chromatography, HPLC as VIP standard, and somatostatin S-28, respectively. IR-VIP (352.7 pg/thymus) amounts greater than those of IR-SOM (38.7 pg/thymus) detected by radioimmunoassay in the thymus of 3-month-old rats reflected the abundance of IR-VIP positive cells demonstrated by immunohistochemistry. Somatostatin-like immunoreactive cells were identified as epithelial or neuroendocrine-like cells arranged in the thymic cortico-medullary border, whereas IR-VIP positive cells appeared to be large lymphoid cells distributed along the connective tissue trabeculae. Furthermore, IR-VIP lymphoid cells occurred in the periarteriolar lymphoid tissue of the splenic white pulp where lymphoblasts accumulate. The results are discussed with respect to the mutual interactions between the neuroendocrine and immune systems and the possible role played by neuropeptides in these interactions.

Animals↗

PubMed1990

Immunoreactive levels of pineal arginine vasopressin change during the rat estrous cycle.

It has been reported that mammalian pineal activity is influenced by reproductive hormones. However, even though a relationship between serum estrogen levels and pineal indole metabolism is well documented, little is known about other pineal components. Among peptides, arginine vasopressin (AVP) has been identified in the pineal gland of several species. In the present work, variations of immunoreactive (IR)-AVP in the rat pineal during the estrous cycle were studied by radioimmunoassay. Pineal IR-AVP levels increased significantly at the proestrus afternoon, and returned to basal levels by the end of estrus. These variations were partially related to those of serum estradiol concentration. Although the functional role of AVP in the rat pineal has not been clearly elucidated, these findings provide an additional indication that it might be involved in the reproductive function of the female rat.

Analysis of Variance↗

PubMed1989

Thyroid hormone action on ACTH secretion.

Thyroid hormone effects on pituitary ACTH have not been well established. Adult male Sprague-Dawley rats were rendered hypo- and hyperthyroid while undergoing treatment with 6-Propylthiouracil (PTU) and L-Thyroxine (T4). At the time of decapitation, plasma values for T4 (micrograms/100 ml) were 3.9 +/- 0.4 in the control, 17.3 +/- 2.2 in the T4 and less than 2 in the PTU treated group; plasma T3 and TSH confirmed hyper- and hypothyroidism in the T4 and PTU treated groups respectively. Plasma immunoassayable ACTH and corticosterone were significantly increased in hyperthyroid and decreased in the PTU treated animals. Pituitaries were removed and incubated in DMEM. After 3 h incubation, ACTH content and secretion to the medium were significantly lower in the PTU group. As expected, pituitary TSH content and secretion were decreased in the T4 treated animals. These data indicate that thyroid hormones influence pituitary-adrenal function by increasing ACTH secretion and consequently corticosterone production.

Adrenocorticotropic Hormone↗

PubMed1989

Divergent effects of acute depolarization on somatostatin release and protein synthesis in cultured fetal and neonatal rat brain cells.

The influence of membrane depolarization on somatostatin secretion and protein synthesis by fetal and neonatal cerebrocortical neurons was studied. Cortical cells obtained by mechanical dispersion were maintained as monolayer cultures for 8 days. The ability of fetal cerebrocortical and hypothalamic cells to release immunoreactive somatostatin (IR-SRIF) was confirmed. Total protein synthesis was determined by the incorporation of [3H]phenylalanine into trichloroacetic acid-precipitable proteins. To study the effect of acute depolarization on protein synthesis, cells were incubated for 30 min with [3H]phenylalanine or [3H]leucine and the depolarizing agent. In fetal cerebrocortical cells, potassium (30 and 56 mM) decreased protein synthesis and RNA levels and increased IR-SRIF release. Depolarization by veratridine, a sodium channel activator, induced a similar effect. The effect of veratridine on IR-SRIF and protein synthesis was reversed by tetrodotoxin, a sodium channel blocker, or verapamil, a calcium channel blocker. These findings suggest that protein synthesis by cerebrocortical cells is decreased in fetal brain cells by membrane depolarization and is dependent on Na+ and Ca2+ entry into cells. In postnatal (day 7) cerebrocortical cells, depolarization induced by high potassium concentrations led to a concomitant increase in protein synthesis, RNA content, and somatostatin release. These findings indicate that depolarization of the cellular membrane is coupled to an increase in protein synthesis in neonatal, but not in fetal, dispersed brain cells.

Animals↗

PubMed1989

Synthesis and secretion of vasoactive intestinal peptide by rat fetal cerebral cortical and hypothalamic cells in culture.

To establish the neurosecretory activity of brain vasoactive intestinal peptide (VIP)ergic neurons and to characterize the molecular forms of secretion of these cells, fetal cerebrocortical and hypothalamic cells were grown in primary cultures for periods up to 4 weeks, their regulation by depolarization and calcium and sodium channel active agents was studied, and the chromatographic patterns of cell and medium VIP were determined. Mechanically dispersed cultured fetal telencephalic and diencephalic cells showed a progressive increase in immunoreactive VIP in both cells and media, reaching maximum values between 110-290 pg/mg protein.culture plate on days 15-20. Immunoreactive VIP in both cells and media corresponded almost exclusively to VIP-28 on exclusion chromatography and HPLC, and was identical to the form extracted from whole fetal brain. This indicates that both the stored and secreted forms of VIP are the mature 28-amino acid-containing peptide. To determine the influence of membrane depolarization on VIP release, the potassium concentration in the medium was increased to 30 and 56 mM, inducing a marked increase in medium VIP concentrations. The effects of K+ were dependent on Ca2+ transport, since release was blocked by the addition of verapamil, a Ca2+ channel blocker (20 microM). VIP release was stimulated by Na+ channel activation using the drug veratridine (100 microM); this effect was blocked by tetrodoxin. The influence of GH-releasing factor (GRF) on VIP release was studied by adding GRF (10(-9)-10(-7) M), alone or in the presence of anti-rGRF immunoglobulins (antirat GRF immunoglobulin G) to the incubation medium. Rat GRF stimulated VIP release and the simultaneous addition of antirat GRF immunoglobulin G blocked this effect. These findings confirm that VIP regulation by brain cells corresponds to the well defined patterns of membrane activation observed in other neuronal systems. They, furthermore, demonstrate that VIP release is under GRF influence.

Animals↗

PubMed1989

Growth hormone-releasing factor production by fetal rat cerebrocortical and hypothalamic cells in primary culture.

Recent data from our laboratory and others have shown radioimmunoassayable GRF (IR-GRF) in the rat brain cortex. In the present study the ontogenesis of immunoreactive rat(r) GRF (IR-GRF) in long term dissociated fetal rat cerebrocortical and hypothalamic cell cultures and the regulation of its secretion by potassium depolarization and calcium channel-blocking agents were investigated. The chromatographic profiles of IR-rGRF from cell extracts were determined and compared with those from in vivo cerebrocortical and hypothalamic tissues. Mechanically dispersed cultured telencephalic and diencephalic cells from 17- to 21-day-old fetal rats showed a progressive increase in IR-rGRF, reaching maximum values (media plus cells) between 775-1020 (pg/mg protein) in hypothalamic cells on days 10-20 and between 450 and 950 pg/mg protein in cortical cells on days 25-30. IR-rGRF from acidic extracts of cells and adult cortical and hypothalamic tissues adsorbed onto octadecylsilyl-silica columns corresponds primarily to rGRF-(1-43)OH on HPLC. In gel filtration chromatography, almost all IR-rGRF from cultured cerebrocortical cells and fetal and adult cortical tissues coeluted with rGRF-(1-43)OH. IR-rGRF from cultured hypothalamic cells showed an additional component with a higher mol wt eluting in the void volume. To determine the influence of membrane depolarization of rGRF release, potassium (K+) concentrations in the medium were increased to 30 and 56 mM, inducing a marked increase in medium rGRF concentrations. Verapamil, a Ca2+ channel blocker (20 microns) reverses the effect of 56 mM potassium depolarization, suggesting that it is at least partially dependent upon Ca2+ transport. These data indicate that fetal rat cerebrocortical and hypothalamic cells in culture produce and release rGRF in response to depolarizing agents. The presence of rGRF in cortical tissue suggests that there are other physiological roles besides those implicated in the stimulation of GH secretion.

Animals↗

PubMed1989

Thyroid hormone regulates vasoactive intestinal peptide (VIP) mRNA levels in the rat anterior pituitary gland.

Vasoactive intestinal peptide (VIP) is a secretagogue for pituitary prolactin, but the importance of this peptide in the normal control of prolactin secretion is unclear. Recent studies suggest VIP synthesis within the rat anterior pituitary. We have shown (Endocrinology 124:1077) that the content of rat pituitary VIP increases in hypothyroidism. To confirm in situ pituitary synthesis of VIP and determine whether thyroid hormone effects on pituitary VIP relate to changes in VIP mRNA, Northern and in situ hybridization analyses of VIP mRNA in rat pituitaries were performed. Northern hybridization demonstrated an RNA species from rat pituitary consistent with rat VIP mRNA. Hypothyroidism increased the content of pituitary VIP mRNA, and replacement with 1-thyroxine prevented this increase. In situ hybridization showed multiple, widely-distributed hybridizing cells in pituitaries from hypothyroid animals. A distinct population of VIP-producing pituitary cells exists which may serve to modulate prolactin secretion in a paracrine or autocrine fashion.

Animals↗

PubMed1988

Thyroid hormone action on biosynthesis of somatostatin by fetal rat brain cells in culture.

Thyroid hormone (TH) action on somatostatin (SRIF) secretion and synthesis by fetal rat brain cells in culture was studied. Cortical and hypothalamic brain cells were maintained as monolayer cultures for 7-10 days. T3, T4, and [3H] phenylalanine [( 3H]Phe) (40 microCi/plate) were added simultaneously for 48 h. Alternately, cultures were pulse labeled with [3H] Phe for only the last 3 h, after being exposed to TH for 45 h. 3H-Labeled SRIF-like material [( 3H]IR-SRIF) was purified by immunoaffinity chromatography and further characterized by gel filtration in Bio-Gel P-10. Total protein synthesis was determined by the incorporation of [3H]Phe into trichloroacetic acid precipitable proteins. Forty eight-hour T3 treatment had a biphasic effect on secretion of IR-SRIF by both cortical and hypothalamic cells. In cortical cells, low doses of T3 (10(-11) M) significantly increased (P less than 0.01) and high T3 doses (10(-7) M) significantly decreased (P less than 0.05) total IR-SRIF (nanograms per plate); control: 2 +/- 0.25; T3 (10(-11) M): 3 +/- 0.3; T3 (10(-7) M): 1.3 +/- 0.1. Similarly, T4 had a significant stimulatory action at 10(-9) M, being inhibitory at 10(-7) M (picograms/plate); control: 290 +/- 20 T4 (10(-9) M): 510 +/- 40; T4 (10(-7) M): 201 +/- 10. When [3H]Phe was added during the 48 h of the experiment, [3H]IR-SRIF synthesis in response to T3 by cortical cells significantly increased after exposure to 10(-11) M (P less than 0.05) and decreased with 10(-7) M (P less than 0.05). When [3H]Phe was added for only the last 3 h or incubation with T3, the action was inhibitory at both 10(-11) M and 10(-7) M. Trichloroacetic acid precipitable material decreased in a dose response manner between T3, 10(-11) M and 10(-7) M. These findings suggest that at this time of brain development, SRIF synthesis by cortical and hypothalamic cells is affected by TH.

Animals↗

PubMed1987

Effect of gastroduodenostomy on intestinal vasoactive intestinal peptide (VIP) levels, and VIP binding and VIP stimulation of cyclic AMP in intestinal epithelial cells from rat.

The concentration of VIP in duodenum and jejunum as well as the interaction of VIP (binding and stimulation of cyclic AMP accumulation) with epithelial cells from both gut segments were studied in rats after surgical bypass of the pylorus by gastroduodenostomy. Duodenal VIP concentration increased in rats with gastroduodenostomy as compared to sham-operated animals. The binding capacity (but not the affinity) of VIP binding sites and the efficiency (but not the potency) of VIP on cyclic AMP accumulation decreased in the condition of gastroduodenostomy. However, no modifications in either VIP concentration and interaction could be seen at the jejunal level.

1-Methyl-3-isobutylxanthine↗

PubMed1986

Direct action of opioid peptides and naloxone on gonadotropin secretion by cultured rat anterior pituitary cells.

Most current evidence indicates that opiates act via the hypothalamus to influence pituitary function. There are no detailed studies concerning pituitary site of action. Direct action of opioids on gonadotropin secretion was studied using enzymatically dispersed rat pituitary cells maintained in a monolayer culture. A time course study demonstrated that pretreatment with beta h-endorphin (beta h-End) (10(-7) M) initiated an inhibitory effect on LH release at 24 h, and was more evident at 48 h. A dose dependent decrease in LH release by beta h-End in concentrations of 10(-9) M to 10(-7) M was shown, whereas FSH was unchanged. Equimolar concentrations (10(-7)M ) of methionine enkephaline (Met-Enk) and D-ala2-met-enkephalinamide (DALA) produced a significant decrease in LH. Naloxone (NAL) (10(-5)) enhanced the release of both LH and FSH, and also blocked the inhibitory effect of beta h-End on LH release. These results indicated that opioid peptides act directly on anterior pituitary cells, decreasing the release of LH, but not of FSH. NAL also had a direct effect increasing the release of LH and FSH, and blocking the inhibitory action of beta h-End.

Animals↗

PubMed1986

Arginine-vasopressin immunoreactive material in the gastrointestinal tract.

Like many other neuropeptides, vasopressin is not confined to the hypothalamic neurohypophysial system. Furthermore, vasopressin was found to be a potent vasoconstrictor in the rat jejunum, reducing myenteric artery flow. These associations were the basis of this investigation on the presence of vasopressin in the gastrointestinal (GI) tract by both RIA and immunohistochemistry. Portions of the gastrointestinal tract and pancreatic islets of the rat were extracted with 0.1 N HCl for RIA measurements of AVP content. Similar portions from the male cat GI tract were used for immunohistochemistry studies. Acid extracts of the GI tract were found to contain immunoreactive AVP with the highest concentration (pg/mg protein) in the fundus portion of the stomach (15.0 +/- 1.6) and slightly lower values down along the antrum-pylorus portion (6.7 +/- 0.6), proximal jejunum (8.6 +/- 0.2), distal ileum (9.7 +/- 0.3) and colon (11.9 +/- 0.5). In the pancreatic islets the concentration was much higher (72.0 pg/mg protein). The extract inhibition curves showed parallelism with the appropriate standard preparation of AVP in the specific RIA. Immunohistochemical localization showed IR-AVP in the nerve fibers around the myenteric plexus of the second portion of the duodenum. It was also found in fibers starting from where the myenteric plexus goes through the layer of muscle fibers, penetrating the submucosa and duodenal mucosa, ending near the capillaries situated along the basal side of the villous epithelium cells. Similar IR-AVP activity was found in cells located in the mucosal epithelium of the duodenum, jejunum, ileum, colon and rectum.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1986

Interaction of thyrotrophin releasing hormone and the enkephalin analogue DAMME on pituitary hormone secretion.

Because TRH counteracts the inhibitory effect of opiate peptides on LH secretion in cultured cells from normal pituitaries, six normal postmenopausal women were studied to determine whether TRH interacts in vivo with opioid peptides in the regulation of pituitary hormone secretion. At two different times a constant 3 h infusion of either saline or TRH (5 micrograms/min) was initiated. At 60 min a 250 micrograms bolus of the opiate agonist peptide D-Ala2-MePhe4-met-enkephalin-0-ol (DAMME) was injected in one of the two saline and TRH infusion tests. The four treatments, i.e. saline infusion alone, saline infusion with a DAMME bolus, TRH infusion alone; and TRH infusion with DAMME bolus were given at random with an interval of at least 7 d. Blood samples were taken every 15 min during the 3 h study. DAMME induced a significant fall (P less than 0.05) in serum LH (from 35 +/- 8.5 to 18.3 +/- 5.1 mIU/ml) (mean +/- SEM) without significantly affecting FSH levels (from 29 +/- 11.2 to 26.9 +/- 12.4 mIU/ml). These changes were not antagonized by the continuous infusion of TRH. PRL had a monophasic response pattern to continuous isolated TRH infusion; the basal levels increased from 4.2 +/- 1.2 to 24.5 +/- 6.8 ng/ml at 30 min and then slowly decreased with a plateau from 90 min until the end of the study. DAMME administration at 60 min induced a significant second peak of PRL secretion (44 +/- 6.5 ng/ml) 30 min later (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed1986

The functional value of collateral testicular vascularisation. An experimental study.

The functional value of the collateral testicular vascularisation has been studied in the rat. In some cases the spermatic artery was sectioned at different levels and in others the vasal artery was sectioned. Hormonal, pathological and anatomical parameters were investigated. The results support the concept that the vasal artery is the most important collateral artery and that the cremasteric artery plays little, if any, part. They also support the view that following proximal section of the testicular artery, the collateral testicular blood supply is variable and the effects of this division are unpredictable and inconsistent.

Animals↗