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Biomedical subjects

A Rivera

Publications and source records attributed to A Rivera.

At least 19 recordsLinked to original sources
PubMed1992

A phase II study of 5-fluorouracil and high-dose folinic acid in combination with cyclophosphamide and mitoxantrone for advanced breast cancer.

38 patients with advanced breast adenocarcinoma were treated in a phase II study with 5-fluorouracil and high-dose folinic acid combined with cyclophosphamide and mitoxantrone. 6 patients had received prior chemotherapy for advanced disease, all with an anthracycline-containing regimen. Treatment was generally well tolerated. The most common side-effect was myelosuppression, with 1 toxic death due to leukopenia-related sepsis. 1 patient developed severe congestive heart failure 12 months from the end of therapy. 36 patients were evaluable for response. The overall response rate was 55%. Median duration of response was 8 months and median survival time was 16 months. This regimen warrants further investigations.

Adult↗
PubMed1992

Effects of in utero phrenic nerve section on the development of collagen and elastin in lamb lungs.

Interference with fetal breathing movements is known to retard morphologic development of the lung and to reduce compliance. We hypothesized that the lower compliance might be in part due to effects on lung structural proteins. We studied the effects of phrenic nerve section in utero on lung compliance and on the lung contents of collagen, elastin, and DNA. At 110 to 112 days of gestation, one fetal lamb in each of 12 twin pregnancies had either both phrenic nerves cut (PX) or a sham operation (S). The other twin was left unoperated (Upx, Us) as a control. They were killed 14 to 22 days later, and the concentrations in lung parenchyma of collagen (as hydroxyproline HPro), elastin, and DNA were measured, together with lung compliance and dry and wet weight. Paired comparisons were made (PX versus Upx and S versus Us). Both operated groups (PX, S) had smaller lungs with lower water content than did their unoperated twins. Absolute static compliance in PX was reduced, but compliance relative to lung weight was unchanged, and there was no significant difference between S and Us. There were no significant effects of PX on the concentrations of HPro, elastin, and DNA, or on the elastin/collagen ratio. Compliance was not correlated with either HPro or elastin content. HPro content increased significantly with gestational age in all groups. It is concluded that phrenic nerve section retards the increase of lung compliance and possibly air space, but it does not affect the overall rate of lung cell proliferation or of deposition of elastin or collagen.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Hepatic function during short-term total parenteral nutrition: effect of exposure of parenteral nutrients to light.

Total parenteral nutrition (TPN) solutions either exposed to light (+L) or protected from light (-L) were infused for 5 days through jugular cannulas in freely moving rats placed in metabolic cages. At the end of the 5 day period, bile flow, biliary inorganic phosphate and biliary gamma-glutamyl transferase activity, as well as biliary concentrations of several essential and branch chain amino acids were significantly lower in the -L animals compared to +L animals. In addition, biliary glutathione was significantly lower in the +L animals. In both groups of animals, plasma tyrosine decreased significantly from pre-TPN values despite a doubling of plasma phenylalanine concentrations suggesting that tyrosine may become a conditionally essential amino acid in rats provided TPN. Our findings indicate that short-term parenteral infusion of light exposed TPN solutions alters hepatobiliary function as well as amino acid homeostasis and that the changes are minimized by light protection of the infusates. The exact mechanisms of the contribution of light exposure in the induction of hepatic dysfunction remain to elucidated.

Amino Acids↗
PubMed1991

Condom knowledge, history of use, and attitudes among chemically addicted populations.

The need for behavioral change of risky sexual practices has been of the highest priority since the onset of the AIDS epidemic. The major focus of education for safe sex has been emphasis on condom use. We surveyed 124 individuals applying to treatment for various chemical dependencies and 60 individuals applying for non-chemical-dependency medical treatment on various aspects of condom knowledge, history of use, and attitudes. Respondents reported that AIDS has motivated them to increase their use of condoms, however, only 13.9% always use them. Education is needed in the areas of increasing protection. Along with the use of a condom, the need for a reservoir tip and the risks associated with multiple sex partners should be stressed.

Adult↗
PubMed1991

Humoral factors reduce gap junction sensitivity to cytoplasmic pH. II. In vitro manipulations.

Our previous studies demonstrated a diurnal rhythm in the response of gap junctions between crayfish giant axons to acidification and that the response was reduced after eyestalk ablation, sinus gland removal, or visual stress. In this paper we describe experiments to test whether compounds in the circulating hemolymph were responsible for modulation of the responsiveness gap junction channels to intracellular pH. In axons from destalked animals in which the hemolymph had been replaced with normal saline, the maximal junctional resistance after acidification (Rjmax) reached control values. In contrast, Rjmax reached only 30% of control after acidification in axons from animals that had been destalked but not perfused. Hemolymph drawn after eyestalk ablation was tested on axons from control animals. Treatment with hemolymph drawn 1 day after destalking resulted in control Rjmax values, while treatment with hemolymph drawn 7 days after destalking resulted in Rjmax values of only 5-40%. Similarly, pretreatment for 1 h with 100 microM ecdysterone resulted in low Rjmax values. These experimental results suggest that a circulating compound, most likely ecdysterone or a related molecule, regulates the physiological properties of gap junctions from crayfish lateral axons.

Animals↗
PubMed1991

[Functional significance of the serum/saliva testosterone ratio in various diseases].

Serum/salivary testosterone ratio (ST/SlvT) expresses the relationship in absolute values between bound and unbound testosterone. This ST/SlvT ratio in supposedly healthy men (n = 25) and women (n = 72) and in patients with several disorders, prostatic carcinoma (n = 19), varicocele (n = 9) and hirsute women (n = 16), has been studied. Both serum and salivary testosterone were measured by an RIA method. ST/SlvT ratio values found in healthy men (78.4 +/- 30.9) did not differ significantly from values found in the varicocele group (111.1 +/- 49.3), but a significant difference (p less than 0.001) from those found in men with prostatic carcinoma (12.3 +/- 7.2) was observed. When the ST/SlvT ratio values obtained in healthy women (18.1 +/- 7.3) were compared with those obtained in hirsute women (1.56 +/- 5.7) no significant differences were observed. The results obtained may indicate the dissociation among the hormone transport, testosterone metabolic clearance and hormone secretion by the salivary glands.

Adult↗
PubMed1990

Protein phosphorylation and hydrogen ions modulate calcium-induced closure of gap junction channels.

The regulation of the cell-to-cell pathway formed by gap junctions seems to involve the interaction of the junctional channels with either calcium or hydrogen ions, as well as protein phosphorylation and calmodulin. These mechanisms of junctional regulation have been considered to act independently on specific sites of the gap junction protein; however, the possibility that they may be interrelated has not been adequately explored mainly due to the difficulties involved in simultaneous measurement of intracellular cations and protein phosphorylation. To further understanding of mechanisms regulating gap junctions, we have internally perfused coupled lateral axons from crayfish with solutions containing different calcium and hydrogen concentrations under conditions favoring phosphorylation, while monitoring the junctional conductance. We found that calcium ions regulate cell communication probably through a direct interaction with the channel protein. Phosphorylation and low pH do not alter junctional conductance themselves, but appear only to modulate the effects of calcium, possibly by altering the affinity of the channel for calcium. We propose that a combination of free intracellular calcium and protein phosphorylation form an important physiological mechanism regulating intercellular communication.

Animals↗
PubMed1990

Cord blood gamma glutamyl transferase activity: effect of gestational age, gender, and perinatal events.

Gamma glutamyl transferase (GGT) activity was measured in cord blood of 125 preterm and term neonates ranging from 26 to 42 weeks of gestation. The enzyme activity was higher in cord blood of infants from 33 to 37 weeks' gestation than in those of younger or older gestation. Furthermore, GGT activity in infants of greater than 37 weeks' gestation was significantly higher in male than in female infants. There were no significant correlations between GGT and Apgar scores, regardless of gestational age. However, GGT activity in term infants with a history of perinatal events suggestive of stress (meconium passage in utero, fetal decelerations, tight nuchal cord, or difficult delivery) was significantly higher than in term infants without such perinatal history. No such association existed in infants of less than 38 weeks' gestation. Infants of 33 to 37 weeks' gestation delivered vaginally had significantly higher cord GGT activity than those delivered by cesarean section. This difference was not apparent in younger or older infants. These data suggest that GGT activity reflects gender, gestational age, route of delivery, and perinatal stress. Further investigation is required to establish the reasons for these differences and to determine the usefulness of such enzyme activity in the delineation of liver dysfunction during postnatal development.

Birth Weight↗
PubMed1990

Toxicity studies of intravenous vitamin E in newborn rabbits.

This study was designed to investigate the toxicity of intravenously administered alpha-tocopherol, alpha-tocopheryl acetate, and a polysorbate vehicle similar to that used in a commercial preparation of alpha-tocopheryl acetate intended for intravenous administration. Cesarean-delivered newborn rabbits fed intravenously were administered 100 mg of either alpha-tocopherol or alpha-tocopheryl acetate in a polysorbate vehicle, or the vehicle only, or no treatment for 6 or 7 days. Two intravenous diets were employed which differed in nutritional content and were termed low energy (LE) and high energy (HE). High concentrations of alpha-tocopherol were present in the tissues of all pups that received either treatment with alpha-tocopherol or alpha-tocopheryl acetate in the polysorbate vehicle, irrespective of the nutritional regimen. Pups in all treatment and control groups which received the LE diet had hepatic centrilobular degeneration, necrosis and pigment accumulation, which was attributed to malnutrition. No additional toxicities could be attributed to the vitamin E or polysorbate treatments. Administration of the HE diet eliminated the nutrition-related centrilobular degeneration, and revealed treatment-related liver changes. HE pups treated with alpha-tocopheryl acetate in the polysorbate vehicle had microscopic evidence of mild bile stasis and had elevated serum bilirubin. Minimal lipidosis or fatty change in the liver was observed only in alpha-tocopherol and alpha-tocopheryl acetate-treated pups. Lipidosis in the spleen was moderate in the alpha-tocopherol group and minimal in the alpha-tocopheryl acetate group. Lipidosis also occurred in the adrenal gland primarily in the alpha-tocopheryl acetate group.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Childhood separation anxiety and panic disorder: a comparative study.

1. The relationship between childhood separation anxiety and panic disorder in adults is analyzed using data from a multicenter trial in 107 patients. 2. The patients included in this study presented anxiety disorder with or without agoraphobia, diagnosed according to DSM-III criteria. 3. The percentage of patients with antecedents of separation anxiety was 17.8% in patients without agoraphobia and 21.7% in patients with agoraphobia. These rates are significantly higher than those encountered in a group of normal controls (4%). 4. The existence of separation anxiety in childhood does not seem to significantly modify the clinical manifestations or severity of panic disorder in the adult.

Adult↗
PubMed1989

Some aspects of the neuromuscular system of Ascaris.

1. The structure and physiological properties of the somatic neuromuscular system of the nematode Ascaris lumbricoides var. suum are discussed taking into account early work from this laboratory, the results of other workers, and experiments in progress. 2. Anatomically, the central feature of the somatic musculature is the presence of a specialized muscular, but not contractile, structure: the syncytium or sarcopile, formed by the terminal processes of the muscle cell arms that contact the nerve cord. In this region, they are electrically coupled to one another and form chemical synapses with the nerve fibres. 3. The syncytium serves, primarily, as a nerve-muscle manifold, or device which allows the neural control of the muscle fields with great economy in the amount of nervous tissue, numbers of chemical junctions and quantities of synaptic transmitters. 4. The structure of the syncytium is being studied with the scanning electron microscope. The results reveal the convergence of the arms on discrete sites as they approach the cords, as well as a longitudinal arrangement of the terminal processes as they course over the cords, at least in the posterior region of the animal. 5. The characteristics of the electrical coupling between the muscle cells are being investigated. A pattern has been observed that is dependent on the position of the cell pairs with respect to the longitudinal axis of the animal. 6. A study of signal propagation in the arms has revealed that the morphology of the muscle cells contributes to the extent and preferential direction of propagation.

Animals↗
PubMed1989

[Internal pancreatic fistula. Presentation of a new case].

Internal pancreatic fistulas are a well-known complication of chronic pancreatitis and should be added to the classic complications of malabsorption, diabetes, pain and pseudocyst. The fact that it is an infrequent complication (Bradley compiled about 200 reported cases in 1982) motivated us to make this clinical report. The importance of total parenteral nutrition (NPT), which leads to cure in 50% of these patients, and the usefulness of endoscopic retrograde cholangiopancreatography (ERCP) are evaluated in the cases in which surgery is contemplated.

Adult↗
PubMed1988

Calmodulin acts as an intermediary for the effects of calcium on gap junctions from crayfish lateral axons.

Lateral axons from the abdominal nerve cord of crayfish were internally perfused with the calcium receptor calmodulin (CaM) in solutions with low (pCa greater than 7.0) or high (pCa 5.5) calcium concentrations and studied electrophysiologically and morphologically. Results from these experiments show that when the internal solution contains calcium-activated calmodulin (Ca2+-CaM) the junctional resistance between the axons increases from control values of about 60 to 500-600 k omega in 60 min. In contrast, axons perfused with calmodulin in low calcium solutions maintain their junctional resistance at control levels during the 60-min perfusion. Similar results are obtained when only one or both coupled axons are perfused. The morphological study shows that in the perfused axons the axoplasmic organelles are replaced or grossly perturbed by the perfusion solution up to the region of the synapses. Additionally, in axons perfused with Ca2+-CaM there are regions where the synaptic gap between the membranes decreases from a control 4-6 to 2-3 nm. Both electrophysiological and morphological results can be interpreted as indicating that calcium-activated calmodulin acts directly on the junctional channels to induce their closure.

Animals↗
PubMed1988

How many channels should there be in a gap junction?

The junctional resistance of the gap junctions between the lateral giant axons of the crayfish has been measured in coupled and uncoupled conditions and the number of gap junction particles has been counted under the same conditions. From these two sets of data it can be concluded that the plaque-forming particles observed in freeze fracture replicas of the synaptic area are all gap junctional particles and that their channels are open. Based on this and published results from other isolated pairs of coupled cells, an inverse relationship has been found between the input resistance of the cells and the calculated number of open gap junctional channels between them. The relationship applies to both excitable and nonexcitable cells.

Animals↗