Biomedical subjects

M M Valença

Publications and source records attributed to M M Valença.

At least 19 recordsLinked to original sources

PubMed2006

Adenosine A1 receptor-mediated inhibition of in vitro prolactin secretion from the rat anterior pituitary.

In previous studies, we demonstrated biphasic purinergic effects on prolactin (PRL) secretion stimulated by an adenosine A2 agonist. In the present study, we investigated the role of the activation of adenosine A1 receptors by (R)-N6-(2-phenylisopropyl)adenosine (R-PIA) at the pituitary level in in vitro PRL secretion. Hemipituitaries (one per cuvette in five replicates) from adult male rats were incubated. Administration of R-PIA (0.001, 0.01, 0.1, 1, and 10 microM) induced a reduction of PRL secretion into the medium in a U-shaped dose-response curve. The maximal reduction was obtained with 0.1 microM R-PIA (mean +/- SEM, 36.01 +/- 5.53 ng/mg tissue weight (t.w.)) treatment compared to control (264.56 +/- 15.46 ng/mg t.w.). R-PIA inhibition (0.01 microM = 141.97 +/- 15.79 vs control = 244.77 +/- 13.79 ng/mg t.w.) of PRL release was blocked by 1 microM cyclopentyltheophylline, a specific A1 receptor antagonist (1 microM = 212.360 +/- 26.560 ng/mg t.w.), whereas cyclopentyltheophylline alone (0.01, 0.1, 1 microM) had no effect. R-PIA (0.001, 0.01, 0.1, 1 microM) produced inhibition of PRL secretion stimulated by both phospholipase C (0.5 IU/mL; 977.44 +/- 76.17 ng/mg t.w.) and dibutyryl cAMP (1 mM; 415.93 +/- 37.66 ng/mg t.w.) with nadir established at the dose of 0.1 microM (225.55 +/- 71.42 and 201.9 +/- 19.08 ng/mg t.w., respectively). Similarly, R-PIA (0.01 microM) decreased (242.00 +/- 24.00 ng/mg t.w.) the PRL secretion stimulated by cholera toxin (0.5 mg/mL; 1050.00 +/- 70.00 ng/mg t.w.). In contrast, R-PIA had no effect (468.00 +/- 34.00 ng/mg t.w.) on PRL secretion stimulation by pertussis toxin (0.5 mg/mL; 430.00 +/- 26.00 ng/mg t.w.). These results suggest that inhibition of PRL secretion after A1 receptor activation by R-PIA is mediated by a Gi protein-dependent mechanism.

Adenosine↗

PubMed2005

Yet another application of the Monte Carlo method for modeling in the field of biomedicine.

By means of Monte Carlo simulations performed in the C programming language, an example of scientific programming for the generation of pseudorandom numbers relevant to both teaching and research in the field of biomedicine is presented. The relatively simple algorithm proposed makes possible the statistical analysis of sequences of random numbers. The following three generators of pseudorandom numbers were used: the rand function contained in the stdlib.h library of the C programming language, Marsaglia's generator, and a chaotic function. The statistical properties of the sequences generated were compared, identical parameter values being adopted for this purpose. The properties of two estimators in finite samples of the pseudorandom numbers were also evaluated and, under suitable conditions, both the maximum-likelihood and method of moments proved to be good estimators. The findings demonstrated that the proposed algorithm appears to be suitable for the analysis of data from random experiments, indicating that it has a large variety of possible applications in the clinical practice.

Algorithms↗

PubMed2003

Lateral femoral cutaneous neuralgia: an anatomical insight.

A detailed anatomic study was carried out on the lateral femoral cutaneous nerve to better understand the etiology and treatment of lateral femoral cutaneous neuralgia. As it passed from the pelvis into the thigh, the lateral femoral cutaneous nerve ran through an "aponeuroticofascial tunnel," beginning at the iliopubic tract and ending at the inguinal ligament; as it passed through the tunnel, an enlargement in its side-to-side diameter was observed, suggesting that the fascial structures proximal to the inguinal ligament may be implicated in the genesis of lateral femoral cutaneous neuralgia. The finding of pseudoneuromas at this location, distant from the inguinal ligament, supports this hypothesis. The anterior superior iliac spine is located approximately 0.7 cm from the lateral femoral cutaneous nerve and serves as the bony landmark for nerve localization. Within the first 3 cm of leaving the pelvis, the lateral femoral cutaneous nerve was observed deep to the fascia lata; therefore, surgical dissection within the subcutaneous fascia may be conducted with relative impunity near the anterior superior iliac spine just inferior to the inguinal ligament. In 36% of cases there was no posterior branch of the nerve, which is correlated to lateral femoral cutaneous neuralgia symptoms often being limited to the anterior branch region. An accessory nerve was found in 30% of cases.

Adult↗

PubMed2003

Parkia pendula lectin as histochemistry marker for meningothelial tumour.

Lectins have been intensively used in histochemical techniques for cell surface characterization. These proteins are involved in several biological processes and their use as histochemical markers have been evaluated since they can indicate differences in cell surfaces. Parkia pendula lectin (PpeL) was evaluated as histochemical marker for meningothelial meningioma biopsies. Tissue slices were incubated with PpeL conjugated to horseradish peroxidase (PpeL-HRP) and Concanavalin A-HRP (ConA-HPR) and the binding visualized with diaminobenzidine and hydrogen peroxide. The lectin-tissue binding was inhibited with D-glucose. PpeL showed to be a useful tool for the characterization of meningothelial tumour and clinico-pathological diagnosis.

Adult↗

PubMed2002

Nitrergic modulation of vasopressin, oxytocin and atrial natriuretic peptide secretion in response to sodium intake and hypertonic blood volume expansion.

The central nervous system plays an important role in the control of renal sodium excretion. We present here a brief review of physiologic regulation of hydromineral balance and discuss recent results from our laboratory that focus on the participation of nitrergic, vasopressinergic, and oxytocinergic systems in the regulation of water and sodium excretion under different salt intake and hypertonic blood volume expansion (BVE) conditions. High sodium intake induced a significant increase in nitric oxide synthase (NOS) activity in the medial basal hypothalamus and neural lobe, while a low sodium diet decreased NOS activity in the neural lobe, suggesting that central NOS is involved in the control of sodium balance. An increase in plasma concentrations in vasopressin (AVP), oxytocin (OT), atrial natriuretic peptide (ANP), and nitrate after hypertonic BVE was also demonstrated. The central inhibition of NOS by L-NAME caused a decrease in plasma AVP and no change in plasma OT or ANP levels after BVE. These data indicate that the increase in AVP release after hypertonic BVE depends on nitric oxide production. In contrast, the pattern of OT secretion was similar to that of ANP secretion, supporting the view that OT is a neuromodulator of ANP secretion during hypertonic BVE. Thus, neurohypophyseal hormones and ANP are secreted under hypertonic BVE in order to correct the changes induced in blood volume and osmolality, and the secretion of AVP in this particular situation depends on NOS activity.

Animals↗

PubMed2001

[Idiopathic facial paralysis (Bell's palsy): a study of 180 patients].

The objective of this study was to analyze some clinical and epidemiologic aspects, as well as the follow up of 180 patients with Bell's palsy. In the study population there was a predominance of female (66.7%). Two peaks of incidence in the age distribution were identified: third-fourth and sixth decades of life. In the group of 180 patients there were 198 events of facial paralysis, 17 recurrences and in one patient the paralysis was bilateral at the onset. In 15 patients (8.3%) there were recurrences of the facial paralysis, in 12 cases (70.6%) the recurrences were ipsilateral. The left side of the face was involved in 55.6% of the cases. In eight patients the paralysis occurred during pregnancy (n=5) or puerperium (n=3). As associated conditions we found: arterial hypertension (11.7%), diabetes mellitus (11.1%), pregnancy or puerperium (4.4%; 6.7% in the women), and neurocysticercosis (1.1%). In 72.8% of the cases no association with such conditions was found. In 22.8% of the patients some kind of sequelae were identified: hemifacial spasm (12.8%), partial recovery of the motor deficit (10.6%), syndrome of the crocodile tears (3.3%), sincinetic contraction (2.8%), and the Marcus Gunn inverse phenomenon (1.1%). In conclusion, this study shows that the idiopathic facial paralysis may lead to important sequelae in more than 20% of the patients.

Adolescent↗

PubMed2000

[Etiology of the epileptic seizures in Recife city, Brazil: study of 249 patients].

The etiological causes of the epileptic seizures presenting by 249 patients were studied, in a neurological clinic in Recife City, Brazil. The cause of the seizure was not identified in 43.0% of the patients. As suspected causal factors we found: ischemic cerebrovascular disease (ICVD, 17.3%), cysticercosis (8.8%), head trauma (HT, 6.8%), brain tumors (6.8%), hemorrhagic cerebrovascular disease (HCVD, 4.8%), vascular malformation (3.6%), other causes (8. 4%). In the patients with age less than 15-year-old, the most frequent cause was cysticercosis (10.3%), following vascular malformation (5.1%), and ICVD (5.1%). In the group between 15 and 45 years of age the major cause of seizure was cysticercosis (11.6%), following HT (10.7%), ICVD (4.5%), and brain tumors (3.6%). On the other hand, in the patients with more than 45-year-old the main cause was ICVD (36.7%), following brain tumors (12.3%), HCVD (11.2%), and cysticercosis (5.1%). Im conclusion, cerebrovascular disease was the most prevalent cause of epileptic seizures, considering all groups of patients. Although, cysticercosis was main cause found in the patients with less than 45 years of age.

Adolescent↗

PubMed1994

Experimental murine schistosomiasis and thyroid function.

In humans the hepatosplenic form of schistosomiasis may be associated with some degree of somatosexual underdevelopment. In the present study we induced an experimental hepatosplenic form of schistosomiasis by infecting 21-day-old mice with the São Lourenço da Mata-PE strain of Schistosoma mansoni and evaluated thyroid function and its relationship with somatosexual development. Plasma levels of T3 and T4 were determined in 115-day old male albino Swiss mice by radioimmunoassay as a measure of thyroid function. Prepuberal infection with S. mansoni resulted in significant increases in liver (74%) and spleen (138%) weights, although there were no changes in animal growth or plasma T3 and T4 concentrations under the experimental conditions used. The present study demonstrates that prepuberal infection of mice with S. mansoni induces the development of a hepatosplenic form of schistosomiasis during adult life with apparently normal thyroid function.

Animals↗

PubMed1992

Intrinsic pulsatile secretory activity of immortalized luteinizing hormone-releasing hormone-secreting neurons.

Mammalian reproduction is dependent upon intermittent delivery of luteinizing hormone-releasing hormone (LHRH) to the anterior pituitary. This mode of secretion is required to sensitize maximally the gonadotrophs to LHRH stimulation and to regulate gonadotropin gene expression. While LHRH secretion is pulsatile in nature, the origin of the pulse generator is unknown. In this report, we show that this oscillator could be located within the LHRH neuronal network. When immortalized LHRH neurons are placed into a perifusion system, LHRH is secreted into the medium in a pulsatile fashion under basal conditions. LHRH secretion and the number of LHRH pulses are reduced when calcium is removed from the medium. Perifusion also influences pro-LHRH processing, since the molar ratio of its processed products varies dramatically when the cells are transferred from a static system. Several different cellular mechanisms may underlie these changes in secretion and processing. Lucifer yellow experiments reveal that some cells are dye-coupled. Hence, these cells could be electrically coupled through gap junctions such that secretion from individual cells could be coordinated. Secretion could also be synchronized through the observed synapse-like contacts. These contacts could perform a negative-feedback role to regulate not only the amount of LHRH released but also the molecular forms secreted. The organization of LHRH neurons into interconnected clusters could serve to coordinate LHRH secretion from individual cells and, thereby, orchestrate functions in vivo as diverse as the onset of puberty, the timing of ovulation, and the duration of lactational infertility.

Calcium↗

PubMed1992

Immortalized hypothalamic gonadotropin-releasing hormone neurons.

The neuroendocrine hypothalamus has been intensively studied using whole animals and tissue slices. However, it has been difficult to approach questions at the molecular and cellular level. By targeting expression of the oncogene product, simian virus 40 T antigen, in transgenic mice using the regulatory domain of the rat gonadotropin-releasing hormone (GnRH) gene, we have produced specific hypothalamic tumours. These tumours have been cultured to produce clonal cell lines (GT-1 cells) that express T antigen, GnRH and many other neuronal markers, but do not express other hypothalamic hormones. These immortal cell lines have a distinctive neuronal phenotype, process the GnRH peptide accurately and secrete GnRH in a pulsatile pattern. Thus, by targeting oncogenesis to a defined population of neurons using the regulatory region of a gene that is expressed late in differentiation of that cell lineage, we have succeeded in immortalizing hypothalamic GnRH neurons. The GT-1 cell lines are an excellent model for future molecular, cell biological, physiological and biochemical investigations into the mechanisms involved in regulation of GnRH and the characteristics of an isolated central nervous system neuron. Their derivation demonstrates the utility of targeting tumorigenesis to specific differentiated neurons of the central nervous system in transgenic mice.

Animals↗

PubMed1990

Role of substance P in the medial preoptic area in the regulation of gonadotropin and prolactin secretion in normal or orchidectomized rats.

The present studies were designed to evaluate the role of substance P (SP) in the control of the release of luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin (PRL). SP was microinjected into the medial preoptic area (MPOA) of conscious, freely moving intact or orchidectomized (ORCX; 21 days post-ORCX) adult male rats. Microinjection of SP into the MPOA induced a significant decrease in plasma LH and FSH concentrations, effects which were accompanied by an elevation in plasma PRL concentration. To examine the participation of endogenously secreted SP in the activity of the MPOA neurons controlling release of these cited pituitary hormones, another study was performed in which either a potent and specific antagonist to SP (D-Pro2, D-Trip7,9-SP; SP-ANT) or an antibody against SP (SP-AB), was injected into the MPOA. SP-ANT and SP-AB both elevated plasma LH, FSH and decreased plasma PRL concentration. These data suggest that endogenous SP within the MPOA exerts an important inhibitory tonus over LH and FSH release and an excitatory tonus over PRL release. In conclusion, SP seems to participate as a neurotransmitter or neuromodulater in the control of LH, FSH and PRL secretion, at least in part, by acting at the level of MPOA, a region in which the neuronal cell bodies that produce LH-releasing hormone and the associated gonadotropin-releasing hormone-associated peptide are located.

Animals↗

PubMed1989

Effect of adenosine on gonadotropin and prolactin secretion by hemipituitaries in vitro.

Incubation of hemipituitaries from male rats (200-220 g) with 10 nM to 1 microM adenosine induced a dose-dependent decrease of the release of luteinizing hormone (LH) and follicle stimulating hormone (FSH) into the medium, and increased prolactin (PRL) secretion. The effects of 10 nM adenosine were blocked by 100 nM caffeine, whereas 100 nM caffeine alone had no effect on the release of the hormones. Preincubation of hemipituitaries with 1 microM adenosine also inhibited 10 nM luteinizing hormone-releasing hormone (LHRH)-induced LH and FSH release by greater than 90%. These data indicate a regulatory role for adenosine in pituitary LH, FSH and PRL release, and also a possible modulatory effect of adenosine on the LHRH-LH and FSH system.

Adenosine↗

PubMed1989

Testes alterations in pubertal benznidazole-treated rats.

To determine the side effects of benznidazole, an antiparasitic chemotherapeutic agent against chagasic infection, rats were treated with 80 mg benznidazole kg-1 day-1, p.o., for 30 days, while controls received the vehicle. Treated animals developed severe testicular atrophy (0.25 +/- 0.02 g/100 g vs 0.44 +/- 0.02 g/100 g for the controls), though plasma testosterone level, relative weight of seminal vesicles and prostate were similar to those of the controls. Histological examination of the testes revealed a statistically significant alteration in the spermatogenic process with a marked decrease in the frequency of meiosis, number of tubular sections with mature spermatids and depletion of germinal epithelium.

Animals↗

PubMed1989

Ether and immobilization stress effects on pituitary adrenal function in hemidecorticate rats.

Hemidecortication (HD) (left cerebral hemisphere) was performed in rats with the aim of analyzing the modulating effect of the cerebral cortex on the hypothalamic-pituitary-adrenal axis. Corticosterone release induced either by ether or immobilization stress was evaluated in control (C) and HD rats. The percentage increase in corticosterone was greater in HD than in C rats after 15 min of ether stress (HD = 142%, C = 50%) and after 60 min of immobilization stress (HD = 197%, C = 126%). An in vitro test showed that the release of ACTH induced by corticotropin releasing hormone (CRH) from hemipituitary fragments from HD rats was not different from that in control rats. These results suggest an inhibitory effect of the cerebral cortex on the hypothalamus which may modulate the secretion of corticotropin releasing peptides.

Animals↗

PubMed1989

Modulatory effects of adrenergic agonists on testosterone secretion from rat dispersed testicular cells or Percoll-purified Leydig cells.

1. Freshly dispersed testicular interstitial cells as well as Percoll-purified Leydig cells were studied in vitro in order to evaluate the effect of adrenergic agonists on testosterone (T) secretion. 2. Epinephrine and phenylephrine did not change the rate of T release under basal conditions in freshly dispersed interstitial cells, but enhanced it during human chorionic gonadotropin (hCG) stimulation. Norepinephrine and clonidine had no effect on T secretion. 3. In contrast, in Percoll-purified Leydig cells epinephrine increased T release both under basal and hCG-stimulated conditions. 4. These data demonstrate that neurotransmitters may participate in T secretion from isolated Leydig cells.

Animals↗

PubMed1988

Characterization of adrenergic control of the Leydig cell steroidogenesis: identification of both stimulatory and inhibitory components.

Percoll-purified Leydig cells were studied in vitro in order to evaluate the effect of adrenaline on testosterone (T) secretion. Adrenaline enhanced the basal and potentiated the hCG-induced T release. A similar effect was also obtained with the beta 2-agonist, salbutamol. Although phenylephrine, an alpha 1-agonist, did not alter the basal T secretion, it enhanced hCG-mediated T secretion. Para-aminoclonidine, an alpha 2-agonist, decreased the basal T release without altering the hCG-stimulated T release. These data demonstrate that either inhibitory or stimulatory effects on T release can be obtained and that they depend on the adrenoreceptor subtype involved.

Animals↗

PubMed1988

Role of opiates in the regulation of water and salt metabolism: effects of the FK 33-824 injection into the subfornical organ of both normal and hypophysectomized rats.

The present study was performed to evaluate the participation of the subfornical organ (SFO) in the opioid modulation of urinary volume (Uv), and of sodium and potassium excretion. Intact and hypophysectomized (HYPOX) adult male rats were implanted with a cannula into the SFO, and injected with the opiate agonist FK 33-824 (FK). FK induced a significant decrease in Uv and in Na+ and K+ excretion in both intact and HYPOX rats. The data show that opioids play an important role in the regulation of hydromineral metabolism by the SFO.

Animals↗

PubMed1987

Evidence for a negative ultrashort loop feedback mechanism operating on the luteinizing hormone-releasing hormone neuronal system.

The present studies were designed to determine whether an ultrashort loop feedback mechanism is involved in the regulation of LHRH secretion. Daily administration of a highly potent LHRH agonist (LHRH-AGO; [D-Ala6,Des-Gly10] LHRH ethylamide) immediately after orchidectomy (ORDX) significantly attenuated the rise of plasma LH from days 2 through 10 after ORDX. Concomitantly with the diminished LH rise after ORDX, a significant increase in LHRH content in the arcuate nucleus was observed in LHRH-AGO-treated rats. Measurement of LHRH levels in hypophyseal portal blood in rats 10 days after ORDX combined with daily agonist treatment revealed a significant decrease in LHRH values in portal plasma compared with those in orchidectomized controls. Arcuate nuclei-median eminence (ME) fragments obtained from ORDX rats treated in vivo with LHRH-AGO for 5 days showed a decreased basal secretion of LHRH and a diminished response to K+ stimulation compared with the release from fragments obtained from ORDX saline-treated controls. To evaluate whether a tonic LHRH inhibitory activity operates within the ME, additional experiments were performed in which ME fragments were incubated in vitro in the presence of a potent LHRH antagonist [( D-pGlu1,D-Phe2,D-Trp3,6]LHRH). The antagonist significantly enhanced the basal secretion of LHRH in a dose-dependent manner. The latter results suggest that LHRH antagonists may enhance LHRH release, perhaps by interacting with LHRH receptors playing an inhibitory role on the endogenous secretion of the decapeptide. These observations strongly suggest a tonic inhibitory or modulatory role of LHRH neurons in the regulation of their own function.

Animals↗