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Biomedical subjects

J D Méndez

Publications and source records attributed to J D Méndez.

At least 19 recordsLinked to original sources
PubMed2001

Regulation of hyperglycemia and dyslipidemia by exogenous L-arginine in diabetic rats.

The effect of L-arginine on the pattern of lipids and lipoproteins in normal and diabetic rats was studied. Three groups of 48 rats were studied during 12 days and compared with a control group (Group I, n = 5). Group I consisted of normal rats not treated with L-arginine. Group II. Normal rats treated with 10 mM L-arginine (i.p.). Group III. Diabetic rats (alloxan 120 mg/kg, i.p.) not treated (diabetic control). Group IV. Diabetic rats treated with 10 mM L-arginine (i.p.). The rats of each group were divided in subgroups of four each. Rats were anesthetized and blood was taken from aorta to determine glucose, triglycerides, cholesterol, total lipids, and low (LDL) and high density lipoproteins (HDL) and their corresponding apoproteins (Apo A-I and Apo B-100). We observed that the alloxan concentration used in this study reproduces the clinical manifestations of disease including hyperglycemia (from 132.5 +/- 7.6 to 544.3 +/- 16.9 mg/dL) in 96 h. As a consequence the levels of triglycerides, cholesterol, total lipids, and LDL and its apoprotein Apo B-100 were increased, whereas HDL and its apoprotein Apo A-I were diminished. The L-arginine injection tends to normalize the glycemia from 24 h; similarly, hyperlipidemia (triglycerides from 924.7 +/- 220.1 to 68.5 +/- 8.4 mg/dL, cholesterol from 107.7 +/- 0.6 to 64.5 +/- 4.2 mg/dL, LDL from 24.2 +/- 2.5 to 8.0 +/- 2.9 mg/dL) was also diminished. These results suggest that the beneficial effect of L-arginine administration on serum glucose values and lipid levels in diabetic rats can be mediated by polyamine formation, although the effect of L-arginine on insulin release as observed by other authors is not discarded.

Animals↗
PubMed2001

[Changes in pancreatic arginase activity in pubertal and adult rats induced by castration].

Arginase activity in kidney, and small intestine in several mammalian species is sensitive to castration, a finding that could suggest their dependence on testosterone. However, as far as we know, information on regulation of pancreatic arginase activity is scarce. In this paper, the effect of orchidectomy on pancreatic arginase activity in pubescent and adult rats was studied. Male pubescent and adult rats, 21 days old and 4 months old, respectively, were orquidectomizades and sacrificed at various times post-surgery. Groups of intact rats served as controls. Arginase activity and proteins were measured in pancreatic tissue. The activity of this enzyme was measured in serum in addition to glucose, triglycerides and total proteins. In pubescent rats pancreatic and serum arginase activities peaked at day 5 post-surgery, increased arginase activity in adult rats was seen at day 20. Changes in serum and pancreatic proteins in pubescent, but not in adult, castrated rats were observed. Taken together, these results suggest that pancreatic arginase activity is androgen-dependent and that there is age-difference, probably due lo distinct patterns of hormone secretion in pubescent and adult rats.

Age Factors↗
PubMed1999

Rapid determination of dry weight in human dental pulp by a colorimetric reaction.

This study was designed to assess total carbohydrate (TC) concentration, as well as the noncollagenous protein content, in human dental pulp. Pulps were obtained from eight premolars (13.10 +/- 4.33 mg weight, mean +/- SD) and homogenized in saline solution. TC content was as follows: 16.68 +/- 9.49 micrograms/mg of tissue (mean +/- SD); 3.22 +/- 1.69 ng of TC/mg protein (mean +/- SD); and 16.23 +/- 6.80 micrograms of TC/mg total organic material (mean +/- SD). The high concentration of carbohydrates observed in the pulp is a result of the presence of glycoproteins, glycosaminoglycans (chondroitin-6-sulfate, heparan sulfate, hyaluronic acid, and dermatan sulfate), and proteoglycans, whose structural, biochemical, and physiological functions have been well documented. Dry weight determination using dichromate solution was used because it shows less dispersion than when the data on carbohydrates and proteins are expressed as wet weight.

Adolescent↗
PubMed1999

[Hypoglycemia as a risk factor in embryonic development in maternal diabetes mellitus. Review of the literature].

Hypoglucemia, or decrease in normal blood glucose concentration, is an important sequel of tight control of type 1 diabetic patients. In pregnant diabetic women, hypoclycemia does not appears affect the embryo or fetal development; while in rodent, it is an important cause of teratogenesis and/or embryotoxicity, when it is presented during organogenesis. Despite metabolic, endocrine and temporal differences between human and rodent pregnancy, a possible damage to the product, caused by hypoblycemia during pregnancy in human, must be considered.

Animals↗
PubMed1997

Inhibition of platelet aggregation by L-arginine and polyamines in alloxan treated rats.

The antiaggregating effect of L-arginine and polyamines (putrescine, spermidine and spermine) was studied in platelets of normal and diabetic rats (120 mg/Kg alloxan, i.p.). This effect was compared with insulin. The assays of platelet aggregation were carried out using platelet-rich plasma (PRP) obtained from both groups of animals. The platelet aggregation test were first standardized by using PRP obtained from human health donors. 2.5 mumoles/ml ADP, 250 mumoles/ml epinephrine and 0.4 U/ml of thrombin were used as inductors of platelet aggregation. 60% of inhibition was observed with 10 microM of L-arginine or polyamines in PRP of normal rats, and 50% with PRP of diabetic rats when thrombin was used as an agonist. These results show that L-arginine and the polyamines putrescine, spermidine and spermine have an antagonist action in platelet aggregation. In addition, we demonstrated the platelet arginase activity not only in rat platelets but also in human, was less under hyperglycaemia. The activity of this enzyme has been associated with polyamine synthesis, required to regulate platelet function.

Animals↗
PubMed1993

[Effect of L-arginine and polyamines on sperm motility].

The biochemical and physiological relevance of L-arginine is described in the male reproductive system. This amino acid has been used successfully in the treatment of some reproductive diseases. L-arginine is the precursor in the synthesis of putrescine, spermidine and spermine. It has been suggested that these polyamines have important role as initiators in the spermatic motility processes. Some practical uses for L-arginine are proposed.

Arginine↗
PubMed1992

Effect of L-arginine on pancreatic arginase activity and polyamines in alloxan treated rats.

The effect of L-arginine on the arginase activity and polyamine levels was studied in the pancreas of normal and diabetic rats (120 mg/kg alloxan, i.v.). Four groups were formed (10 male adults per group). I-Control-0.154 M NaCl. II-Diabetic-0.154 M NaCl (96 h after alloxan). III-Control plus 10 mM L-arginine IV-Diabetics plus 10 mM L-arginine. Rats were sacrificed 20 min after L-arginine injection. Glucose in serum and dry weight, proteins, arginase activity and polyamines (HPLC) in pancreas were measured. Higher ratio mg protein/mg dry weight and arginase induction was observed for groups III and IV. Putrescine was low as a consequence of diabetes but restored with L-arginine. The concentrations of spermidine and spermine were lower. These results may suggest that arginine is metabolized to putrescine in the pancreas and that polyamines may be utilized in regenerating processes or for recovering the endocrine pancreatic function.

Animals↗
PubMed1991

[Experimental models for study of fluorosis].

In most animal species, acute fluorosis is triggered by the accidental consumption of substances with a high content of fluorine, widely used in pest control. Fluorine normally concentrates in bones and teeth, and forms nearly 0.05% of these structures in mature animals, positively contributing to increase resistance of enamel to caries and favoring mineralization after eruption, a process which increases with age. The present article submits a form of study of fluorosis, stressing due warning as to its harmful effects.

Animals↗
PubMed1991

[Current concepts of odontogenesis].

Tooth growth and development involve complex biochemical and physiological processes. Some vitamins are required as coenzymes, but these molecules are also needed to synthesize specific proteins with structural or transport functions. Collagen synthesis is carried out by ascorbic acid interaction. Vitamin A induces calbindin synthesis. Collagen and calbindins are both involved in the mineralization and development of hard tissues. The formation, eruption and growth of teeth are also mediated by the interaction of several hormones.

Animals↗
PubMed1986

Uterine arginase inhibition affect the rat embryonic development.

The presence of polyamines (putrescine, spermidine and spermine) and the enzymatic activity of extrahepatic arginase (E.C. 3.5.3.1) which catalizes the hydrolysis of L-arginine into L-ornithine and urea have been related with cellular growth and development in several tissues. The enzymatic activity of arginase in rat implantation sites and its participation in reproductive process is demonstrated. Long-Evans adult rats during the 4th or 5th days of pregnancy were utilized. Arginase activity is higher in non-decidualized tissue (86.1 +/- 33 nmoles of urea/mg protein/min-1) when was compared with implantation sites (61.7 +/- 17). Intrauterine administration of several concentrations of a new synthetic L-ornithine analogue, AIAVA (2-amine-5-iodoacetamide valeric acid), produced embryonic growth arrest concomitant with arginase inhibition but not ornithine decarboxylase. From our results it is possible to stress the metabolic importance of uterine arginase in reproductive process.

Animals↗
PubMed1983

Inhibition of rat embryonic development by the intrauterine administration of alpha-difluoromethylornithine.

Decarboxylation of L-ornithine by L-ornithine decarboxylase (ODC; E.C.4.1.1.17.) is the initial step in the biosynthesis of putrescine, ODC activity is generally low in most tissues, marked increases are associated with rapid tissue growth and particularly with mammalian embryogenesis. 0.5 mg/kg of DL-alpha-difluoromethylornithine (DFMO) (irreversible inhibitor of ODC) was administered to uterine horns of Long-Evans adult rats during the 4th day of pregnancy. As control material, saline (0.15 M) was administered to contralateral uterine horn. The animals were sacrificed on different days, the uterine horns were removed and the number of implant of implanted embryos were counted. DNA, RNA, protein and dry weight content in implantation sites (5th day of pregnancy) indicated that decidualization following DFMO took place normally but that embryonic growth was arrested in the treated horn. When 100 micrograms of putrescine were added together with DFMO, the embryotoxic effect was absent.

Animals↗
PubMed1981

A rapid colorimetric assay for dry weight.

A rapid, precise colorimetric method for the determination of dry weight in the range 100 1,000 micro grams is reported. The method involves reacting biological materials with an acid solution of dichromate for 20 min at 92 degrees C followed by determination of the optical density at 630 nm of the product formed. The principal advantage of the dichromate method over the standard weight method are: 1) The shorter time required for determination, 2) its greater sensitivity, exactitude and precision using standard laboratory equipment, 3) the method is insensitive to inorganic compounds and therefore can be applied to tissue homogenates prepared in inorganic solutions. The only disadvantage of the method seems to be that dichromate will react specifically with carbon containing groups and therefore the participation of nitrogen, or other elements, in the composition of the biological material, will give proportionately lower absorbances.

Animals↗
PubMed1975

Effect of intrauterine copper on the nucleic acids, polysome pattern, and glycoprotein composition of the human endometrium.

The modifications induced by the intrauterine release of copper in the macromolecular and glycoprotein composition of the proliferative and secretory human endometrium were studied. In addition, the endometrial changes produced in women users of copper-T intrauterine devices in the polysome pattern and in the content of ribonucleoprotein particles were determined during the secretory phase. A group of ten untreated normal women (control group) and 15 users of 200 mm.-2 copper-T intrauterine device were selected for this study from the outpatient clinic of the Hospital de Ginecologia y Obstetricia No. 2 del Instituto Mexicano del Seguro Social. The main changes observed in the copper-T users were: a significant decrease in the endometrial content of RNA in both phases of the menstrual cycle, a significant decrease in protein in the secretory phase, and drastic changes in the fucose-sialic acid ratios, which decreased during the proliferative and increased during the secretory phases. Normal human secretory endometrium contained 4.89 plus os minus 0.28 (mean plus or minus standard error (S. E.) mg. ribonucleoprotein particle per gram wet weight, while the endometrium of the Cu-T users showed a significant decrease to 2.52 plus or minus 0.17 (mean plus or minus S. E.). In addition, the Cu-T induced a decrease in the heavy components of the polysome pattern with a concomitant increase in the lighter components.

Adult↗
PubMedDate not supplied

Inhibition of platelet aggregation by putrescine, spermidine, and spermine in hypercholesterolemic rabbits.

BACKGROUND: Hypercholesterolemia causes alterations in platelet function. Platelet hyperaggregation is considered a predisposing factor for atherosclerosis. In this paper, the antiaggregating effect of the polyamines putrescine, spermidine, and spermine was studied on platelets of normal and hypercholesterolemic rabbits. METHODS: New Zealand rabbits were fed with a cholesterol-enriched diet for 10 weeks. Lipids and glucose were determined in serum. The assays of platelet aggregation were carried out using platelet-rich plasma (PRP) obtained from both control and cholesterol-fed rabbits. We used 2.5 micromol /mL ADP and 2 microg/mL collagen as inductors of platelet aggregation. In addition, arginase activity and L-arginine content were determined in PRP. RESULTS: Serum total cholesterol and LDL-cholesterol concentrations were increased from 26.3 +/- 8.1 to 1,485.0 +/- 26.8 mg/dL and from 15.9 +/- 5.9 to 1,383.8 +/- 58.9 mg/dL, respectively, whereas triglyceride concentration increased from 88.3 +/- 35.6 to 411.0 +/- 154.5 mg/dL upon cholesterol feeding. Seventy-five percent of platelet aggregation inhibition was observed with 10 microM of polyamines in PRP of normal rabbits. Spermine inhibited platelet aggregation by 54% in PRP of hypercholesterolemic rabbits when ADP was used as agonist. The order of polyamine action was spermine > spermidine > putrescine. In addition, we found that platelet arginase activity and L-arginine content were unaltered upon hypercholesterolemia. CONCLUSIONS: These results show that the polyamines putrescine, spermidine, and spermine have antagonist action in platelet aggregation and suggest a key role of polyamines in platelet aggregation under normal and hypercholesterolemic conditions.

Animals↗
PubMedDate not supplied

Fetal development in alloxan-treated rats.

The effect of alloxan on embryo and fetal development in rats was evaluated. Alloxan was injected intraperitoneally (ip) in pregnant rats at doses of 80 to 150 mg/kg at Day 0 (day of fertilization), and 110 mg/kg at Day 4 of pregnancy. Hyperglycemia was rarely produced at alloxan doses from 80 to 100 mg/kg, and the frequency of malformations observed was low. Higher doses (110 to 150 mg/kg) caused severe hyperglycemia, and maternal or embryonic death. When 110 mg/kg was administered on Day 4 of gestation (the day before embryo implantation), all rats had resorption nodules and litters with embryos with delayed growth. We recommend the induction of diabetes mellitus on Day 4 of pregnancy for studies of diabetes-gestation interaction.

Alloxan↗