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I Ramírez

Publications and source records attributed to I Ramírez.

51 records · Page 3Linked to original sources
PubMed1987

Triacylglycerol lipase activities in isolated myocardial cells from chronically diabetic rat hearts.

Diabetes was induced by the administration of streptozotocin (55 mg/kg or 70 mg/kg) to rats. After 21-25 days, myocardial cells (myocytes) were isolated from control and diabetic rat hearts. Rates of endogenous lipolysis, measured as the output of glycerol, were elevated in the chronically diabetic myocytes. Lipoprotein lipase activity was reduced in homogenates of diabetic myocytes. Neutral triacylglycerol lipase activity was increased in myocytes from rats made diabetic with the lower dose of streptozotocin, but not in myocytes from diabetic rats given the higher dose. Diabetes had no effect on acid lysosomal lipase activity.

Animals↗
PubMed1987

Methylamine does not inhibit rates of endogenous lipolysis in isolated myocardial cells from rat heart.

Triacylglycerol lipase activity with a pH optimum of 5 was present in homogenates of myocardial cells from rat heart. Acid lipase activity was inhibited by serum, heparin, and increased ionic strength. Methylamine, a lysosomotropic agent, did not inhibit the basal or isoproterenol-stimulated rate of endogenous lipolysis as measured by glycerol output from control myocytes. Similarly, accelerated rates of glycerol output that are a consequence of an elevation in the intracellular stores of triacylglycerols in myocytes from diabetic rat hearts and from myocytes prepared with free fatty acids in the isolation solutions were not reduced by methylamine. Therefore, the acid lysosomal triacylglycerol lipase must not be involved in the mobilization of endogenous triacylglycerols in myocardial cells from rat heart.

Animals↗
PubMed1987

Characterization of lipoprotein lipase activity in the newborn rat liver.

Acetone ether powders of livers from starved newborn rats were applied to heparin-Sepharose affinity columns. The so-called hepatic triacylglycerol lipase was eluted with 0.9 M NaCl and a second lipolytic activity peak was eluted with 1.5 M NaCl. The behaviour of this 1.5 M NaCl-eluted fraction against increasing concentrations of serum, NaCl, protamine sulfate and heparin in the assay mixture was almost identical to that shown by partially purified lipoprotein lipase from adult rat adipose tissue, and clearly different from that shown by partially purified hepatic triacylglycerol lipase from the adult rat liver. We conclude that the newborn rat liver contains a lipoprotein lipase activity with similar properties to those found in adult adipose tissue lipoprotein lipase activity. It is suggested that this enzyme enables the neonatal liver to take up circulating triacylglycerols directly.

Adipose Tissue↗
PubMed1986

Effect of diabetes on acid and neutral triacylglycerol lipase and on lipoprotein lipase activities in isolated myocardial cells from rat heart.

A neutral triacylglycerol lipase activity that is separate and distinct from lipoprotein lipase (LPL) could be measured in homogenates of myocardial cells if protamine sulphate and high concentrations of albumin were included in the assay. This neutral lipase was predominantly particulate, with the highest relative specific activity in microsomal subcellular fractions. The induction of diabetes by the administration of streptozotocin to rats resulted in a decrease in LPL activity in myocyte homogenates and in particulate subcellular fractions, but the percentage of cellular LPL activity that was released during incubation of myocytes with heparin was normal. In contrast, neutral lipase activity was increased in diabetic myocyte homogenates and microsomal fractions. Acid triacylglycerol lipase activity was not changed in diabetic myocytes. The decrease in LPL in myocytes owing to diabetes may result in the decreased functional LPL activity at the capillary endothelium of the diabetic heart.

Animals↗
PubMed1986

Intralipid administration induces a lipoprotein lipase-like activity in the livers of starved adult rats.

The administration of Intralipid to starved adult rats induces the appearance of lipoprotein lipase (LPL)-like activity in the liver, whereas the so-called hepatic triacylglycerol lipase is unaffected. This LPL-like activity is eluted by 1.5 M-NaCl from heparin-Sepharose columns. This partially purified fraction is inhibited by 1.0 M-NaCl (91%) and by 1.0 mg of protamine sulphate/ml (79%), whereas it is stimulated 69-fold by the presence of 8.0 micrograms of apolipoprotein C-II/ml and inhibited by anti-LPL antibodies. We conclude that Intralipid administration induces the appearance of LPL activity in livers of starved adult rats. Its possible origin is discussed.

Animals↗
PubMed1985

Characterization of triacylglycerol hydrolase activities in isolated myocardial cells from rat heart.

Triacylglycerol (TG) hydrolase activities were characterized in myocytes isolated from rat hearts. Acid hydrolase activity with a pH optimum of 5 could be measured in myocyte homogenates, and the subcellular distribution suggested that this activity originated in lysosomes. Lipoprotein lipase (LPL) was also present in myocyte homogenates, as evidenced by TG hydrolase activity that was stimulated by serum and apolipoprotein CII, and inhibited by apolipoprotein CIII2, high ionic strength (NaCl and MgCl2, I = 1 M) and antibodies to LPL. Serum-independent neutral (pH 7.5) TG hydrolase activity was less sensitive to inhibition by 1 M-NaCl, by antibodies to LPL and by preincubation at 40 degrees C than was serum-stimulated hydrolase activity. Furthermore, there were modest but significant differences in the subcellular distribution of the serum-independent and serum-stimulated hydrolase activities. Hydrolase activities in myocyte homogenates could be solubilized by 7.2 mM-deoxycholate. Acid hydrolase activity was recovered in the unbound fraction after heparin-Sepharose chromatography, whereas LPL was bound to the affinity column and was eluted by 0.9-1.2 M-NaCl. Approximately one-third of the serum-independent TG hydrolase activity was not bound to the heparin-Sepharose affinity column. This unbound TG hydrolase activity had a pH optimum of 7 and was stimulated by 50 mM-MgCl2, but not by serum and was resistant to inhibition by high ionic strength (1 M-NaCl), to preincubation at 40 degrees C for 2 h, and by antibodies to LPL. It is concluded that, in addition to an acid lysosomal TG hydrolase and LPL, myocytes from rat heart contain a serum-independent TG hydrolase with unique characteristics.

Animals↗
PubMed1985

Starvation enhances lipoprotein lipase activity in the liver of the newborn rat.

To determine to what extent lipoprotein lipase activity in the liver of the newborn rat depends on milk ingestion, its changes were studied during different nutritional conditions. Newborns were placed with nurse rats with or without ligated nipples and they were killed at 0,8 or 24 h of life. Lipoprotein lipase in newborns liver was characterized by its inhibition in the presence of 1.0 M NaCl, its specific elution at 1.5 M NaCl on heparin-Sepharose 4B column and its requirement for serum in the assay mixture to manifest its activity. In fed animals lipoprotein lipase activity and triacylglycerol content in liver as well as circulating triacylglycerols and ketone bodies increased progressively after birth. When newborns were kept starved the change in enzyme activity was significantly enhanced, whereas the increase found after birth in the other parameters disappeared. Starvation produced reduction in circulating RIA-insulin levels in the newborn rats. Results show that liver lipoprotein lipase activity in the newborn rat is controlled by a mechanism which resembles that of the enzyme in the adult heart and indicate that its presence facilitates the uptake by the liver of fatty acids from circulating triacylglycerols for their oxidation rather than deposit.

Animals↗
PubMed1983

Circulating triacylglycerols, lipoproteins, and tissue lipoprotein lipase activities in rat mothers and offspring during the perinatal period: effect of postmaturity.

Mammary gland and adipose tissue lipoprotein lipase activities have been implicated in the changes of circulating triacylglycerol levels which occur in the mother at late gestation. In the newborn the temporal accumulation of triacylglycerols in the liver coincides with the appearance of a lipoprotein lipase peak. The relationships of these changes with the rise in circulating prolactin in the mother before parturition and the extrauterine nutritional status in the offspring were studied in a postmaturity model produced in the rat by subcutaneous injection of 7 mg progesterone/day to pregnant animals from the 20th day of gestation. Pregnant controls received the medium. Parturition occurred at day 21.5 of gestation in pregnant controls while it did not occur before the 23rd day in those receiving progesterone. At the 20th day of gestation, plasma triacylglycerol concentrations and all lipoprotein fractions (especially VLDL) were much higher in mothers not receiving progesterone than in age-matched virgins, and these differences disappeared at the 21st day of gestation. Lipoprotein lipase activity was maintained low in control mothers' adipose tissue until the 23rd postfecundation day while it greatly increased in mammary gland from parturition time. In progesterone treated mothers, both triacylglycerol and lipoprotein fractions (especially VLDL) in plasma were maintained elevated until the 23rd postfecundation day and adipose tissue and mammary gland lipoprotein lipase activities were maintained low until this time.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

[Free amino acids in plasma and milk of mexican rural lactating women].

OBJECTIVE: To determine the free amino acid pool in plasma and milk in Mexican rural lactating women. METHODS: Twenty-eight women with an age 24 +/- 5.0 (+/- SD) years, weight 50 +/- 4.9 kg and height 148 +/- 4.8 cm were studied under metabolic balance conditions. Subjects were divided into five groups (three groups of lactation at 1st, 3rd and 6th month, one post-weaning group and a control group of non pregnant, non lactating women). Amino acid analyses of the diet and of plasma and milk samples were performed using an automated amino acid analyzer. RESULTS: Differences were observed between the lactation groups and the other groups: aspartate increased at the 6th month (p < 0.05) while leucine, valine and isoleucine declined in the 3rd month (p < 0.05). In milk, valine, proline and taurine decreased at 6 months (p < 0.05), while serine and threonine raised at 3 months. Plasma levels were > 4 fold greater than milk levels for branched chain amino acids and for the basic, aromatic and neutral amino acids. In contrast, glutamate was 40 fold higher in milk than plasma and it was the predominant amino acid in the free pool of milk. CONCLUSIONS: Our results suggest that the metabolic use of amino acids and the presence of specific amino acid transport systems during lactation, contribute to specific concentrations of free amino acids in milk that were not associated with the pool of free amino acids in plasma.

Adult↗