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Biomedical subjects

R Calvo

Publications and source records attributed to R Calvo.

At least 37 records · Page 2Linked to original sources
PubMed1990

Electron paramagnetic resonance investigation of photosynthetic reaction centers from Rhodobacter sphaeroides R-26 in which Fe2+ was replaced by Cu2+. Determination of hyperfine interactions and exchange and dipole-dipole interactions between Cu2+ and QA-.

We report electron paramagnetic resonance (EPR) experiments in frozen solutions of unreduced and reduced photosynthetic reaction centers (RCs) from Rhodobacter sphaeroides R-26 in which Fe2+ has been chemically replaced by the isotope 65Cu2+. Samples in which the primary quinone acceptor QA is unreduced (Cu2+QA:RCs) give a powder EPR spectrum typical for Cu2+ having axial symmetry, corresponding to a d(x2 - y2) ground state orbital, with g values g parallel = 2.314 +/- 0.001 and g perpendicular = 2.060 +/- 0.003. The spectrum shows a hyperfine structure for the nuclear spin of copper (65I = 3/2) with A parallel = (-167 +/- 1) x 10(-4) cm-1 and /A perpendicular/ = (16 +/- 2) x 10(-4) cm-1, and hyperfine couplings with three nitrogen ligands. This has been verified in samples containing the naturally occurring 14N isotope (l = 1), and in samples where the nitrogen ligands to copper were replaced by the isotope 15N (l = 1/2). We introduce a model for the electronic structure at the position of the metal ion which reflects the recently determined three-dimensional structure of the RCs of Rb. sphaeroides (Allen, J. P., G. Feher, T. O. Yeates, H. Komiya, and D. C. Rees. 1987. Proc. Natl. Acad. Sci. USA. 84:5730: Allen, J. P., G. Feher, T. O. Yeates, H. Komiya, and D. C. Rees. 1988. Proc. Natl. Acad. Sci. USA, 85:8487) as well as our EPR results. In this model the copper ion is octahedrally coordinated to three nitrogens from histidine residues and to one carboxylate oxygen from a glutamic acid, forming a distorted square in the plane of the d(x2 = y2) ground state orbital. It is also bound to a nitrogen of another histidine and to the other carboxylate oxygen of the same glutamic acid residue, in a direction approximately normal to this plane. The EPR spectrum changes drastically when the quinone acceptor QA is chemically reduced (Cu2+QA-:RCs); the change is due to the exchange and dipole-dipole interactions between the Cu2+ and QA- spins. A model spin Hamiltonian proposed for this exchange coupled cooper-quinone spin dimer accounts well for the observed spectra. From a comparison of the EPR spectra of the Cu2+QA:RC and CU2+QA-:RC complexes we obtain the values /J0/ = (0.30 +/- 0.02) K for the isotropic exchange coupling, and /d/ = (0.010 +/- 0.002) K for the projection of the dipole-dipole interaction tensor on the symmetry axis of the copper spin. From the EPR experiments only the relative signs of J0 and d can be deduced; it was determined that they have the same sign. The magnitude of the exchange coupling calculated for Cu2+QA-:RC is similar to that observed for the Fe2+QA-:RC complex (J0 = -0.43K). The exchange coupling is discussed in terms of the superexchange paths connecting the Cu2+ ion and the quinone radical using the structural data for the RCs of Rb. sphaeroides. From the value of the dipole-dipole interaction, d, we determined R approximately 8.4 A for the weighted distance between the metal ion and the quinone in reduced RCs, which is to be compared with 10 A obtained from x-ray analysis of unreduced RCs. This points to a shortening of the Cu2+ -QA- distance upon reduction of the quinone, as has been proposed by Allen et al. (1988).

Amino Acid Sequence↗
PubMed1990

Decrease in penbutolol central response as a cause of changes in its serum protein binding.

Penbutolol is a beta-adrenoceptor antagonist that is extensively bound to alpha 1-acid glycoprotein (alpha 1-AGP), a protein that increases in inflammatory diseases thereby binding more drug in such conditions. Changes in serum binding can lead to modifications in the pharmacokinetics and pharmacodynamics of a drug, therefore, the central effect (as the anticonvulsant response) and brain uptake of penbutolol given intravenously to mice with experimental inflammation have been measured. A significant decrease of the central effect of penbutolol and its brain uptake was seen in diseased when compared with control animals (P less than 0.01). A parallel decrease in free fraction of penbutolol in diseased vs normal animals was detected. These results suggest that there is an increase in serum binding of basic drugs related to increments in alpha 1-AGP concentration, which reduces their central pharmacological effect.

Animals↗
PubMed1990

Congenital hypothyroidism, as studied in rats. Crucial role of maternal thyroxine but not of 3,5,3'-triiodothyronine in the protection of the fetal brain.

To study the protective effects of maternal thyroxine (T4) and 3,5,3'-triiodothyronine (T3) in congenital hypothyroidism, we gave pregnant rats methimazole (MMI), an antithyroid drug that crosses the placenta, and infused them with three different doses of T4 or T3. The concentrations of both T4 and T3 were determined in maternal and fetal plasma and tissues (obtained near term) by specific RIAs. Several thyroid hormone-dependent biological end-points were also measured. MMI treatment resulted in marked fetal T4 and T3 deficiency. Infusion of T4 into the mothers increased both these pools in a dose-dependent fashion. There was a preferential increase of T3 in the fetal brain. Thus, with a T4 dose maintaining maternal euthyroidism, fetal brain T3 reached normal values, although fetal plasma T4 was 40% of normal and plasma TSH was high. The infusion of T3 pool into the mothers increased the total fetal extrathyroidal T3 pool in a dose-dependent fashion. The fetal T4 pools were not increased, however, and this deprived the fetal brain (and possibly the pituitary) of local generation of T3 from T4. As a consequence, fetal brain T3 deficiency was not mitigated even when dams were infused with a toxic dose of T3. The results show that (a) there is a preferential protection of the brain of the hypothyroid fetus from T3 deficiency; (b) maternal T4, but not T3, plays a crucial role in this protection, and (c) any condition which lowers maternal T4 (including treatment with T3) is potentially harmful for the brain of a hypothyroid fetus. Recent confirmation of transplacental passage of T4 in women at term suggests that present results are relevant for human fetuses with impairment of thyroid function. Finding signs of hypothyroidism at birth does not necessarily mean that the brain was unprotected in utero, provided maternal T4 is normal. It is crucial to realize that maintainance of maternal "euthyroidism" is not sufficient, as despite hypothyroxinemia, the mothers may be clinically euthyroid if their T3 levels are normal.

Animals↗
PubMed1990

Contribution of maternal thyroxine to fetal thyroxine pools in normal rats near term.

Normal dams were equilibrated isotopically with [125I]T4 infused from 11 to 21 days of gestation, at which time maternal and fetal extrathyroidal tissues were obtained to determine their [125I]T4 and T4 contents. The specific activity of the [125I]T4 in the fetal tissues was lower than in maternal T4 pools. The extent of this change allows evaluation of the net contribution of maternal T4 to the fetal extrathyroidal T4 pools. At 21 days of gestation, near term, this represents 17.5 +/- 0.9% of the T4 in fetal tissues, a value considerably higher than previously calculated. The methodological approach was validated in dams given a goitrogen to block fetal thyroid function. The specific activities of the [125I]T4 in maternal and fetal T4 pools were then similar, confirming that in cases of fetal thyroid impairment the T4 in fetal tissues is determined by the maternal contribution. Thus, previous statements that in normal conditions fetal thyroid economy near term is totally independent of maternal thyroid status ought to be reconsidered.

Analysis of Variance↗
PubMed1990

Thyroid hormone economy in pregnant rats near term: a "physiological" animal model of nonthyroidal illness?

We have studied the changes in thyroid hormone economy that occur in normal pregnant rats between 17-22 days of gestation. T4 and T3 decreased in all extrathyroidal tissues studied, namely plasma, liver, kidney, lung, heart, and skeletal muscle. The exception is the concentration of T3 in cerebral cortex, which remains unchanged, possibly as a consequence of an increase in type II 5'-iodothyronine deiodinase activity. The marked decrease observed in most T4 and T3 pools was not accompanied by a commensurate increase in circulating TSH levels, which at 21 days gestation were either unchanged or actually decreased. The TSH response to TRH appeared to be prolonged. alpha-Glycerophosphate dehydrogenase activity was decreased in the liver, in accordance with its thyroid hormone deficiency. Hepatic type I 5'-iodothyronine deiodinase activity, however, did not decrease, but was slightly increased. Thus, thyroid hormone economy in the pregnant rat near term shows striking similarities with several (but not all) of the changes described in patients with nonthyroidal illness and in several animal models used to study this condition. It is suggested that attenuation of the negative feedback response to the decrease in thyroid hormone pools, leading to low levels of thyroid hormones in most tissues, is the normal physiological response to situations where preservation of energy (and protein) represents a distinct adaptive advantage, as in the case of the pregnant rat and her conceptus.

Animals↗
PubMed1990

Serum binding of ketoconazole in health and disease.

The plasma protein binding of ketoconazole, an oral antifungal agent of a weak basic nature, was measured after the addition of the drug (10 micrograms.ml-1) to serum from 35 healthy individuals, ten patients with chronic renal disease and seven patients with hepatic cirrhosis. The percentage of free ketoconazole was markedly increased in patients with chronic renal disease and in patients with hepatic cirrhosis, when it was compared with the group of healthy volunteers (7.33 +/- 0.11 in renal patients; 6.12 +/- 1.43 in hepatic patients compared with 2.93 +/- 0.12 in healthy individuals). The binding ratio of ketoconazole in health and disease was significantly related to plasma albumin concentration, but not to plasma alpha 1-acid glycoprotein (AAG) concentration. Moreover, ketoconazole binds to isolated human serum albumin in a greater proportion but does not bind to isolated AAG indicating that human serum albumin is the major binding protein for this drug in plasma.

Adult↗
PubMed1989

Displacement of warfarin from human serum proteins by halothane anaesthesia.

The in vitro effects of the halothane metabolite, trifluoroacetic acid, on the binding of warfarin to human serum proteins have been investigated. An increase in the percentage of free warfarin following incubation with different concentrations of trifluoroacetic acid (1 and 4 mmol/l) was observed. In addition, protein binding of warfarin was studied in serum from patients undergoing halothane anaesthesia (1-2.5%; 2.5 h). After 24 h from the end of the halothane anaesthesia, an increase in the percentage of free warfarin was also detected (0.92 +/- 0.06% at 24 h vs 0.60 +/- 0.02% before halothane administration; P less than 0.005). We conclude that halothane anaesthesia may temporarily potentiate the pharmacological effect of warfarin in the postoperative period following anaesthetic procedures.

Adult↗
PubMed1989

Thyroid hormones and 5'-deiodinase in rat brown adipose tissue during fetal life.

Brown adipose tissue (BAT) iodothyronine 5'-deiodinase (5'D) activities are very high during fetal life but decrease 10-fold a few hours before birth. Accordingly, BAT 3,5,3'-triiodothyronine (T3) concentrations are also very high. The temporal patterns of changes in BAT 5'-D and fetal plasma insulin are similar (and differ from the pattern for catecholamines) but are not superimposable. A causal role for insulin in the activation of fetal BAT 5'-D is therefore not supported by the data. Maternal thyroidectomy leads to a decrease in the total and relative weight of fetal BAT and to a 30-50% increase in BAT 5'-D activities; BAT thyroid hormone concentrations are essentially unchanged. Fetal hypothyroidism was induced by giving methimazole and resulted in a marked decrease of BAT thyroxine (T4) and T3 concentrations. This treatment increased BAT 5'-D activity only on day 21 of gestation, but no effect was observed on day 20. The fetal 5'-D response to thyroid hormones infused into the methimazole-treated dams was studied at 21 days of gestation. The increase in BAT 5'-D induced by methimazole treatment was prevented by T4 infused into control dams but not by T3. In fetuses from thyroidectomized dams, the pattern of 5'-D regulation by thyroid hormones was impaired. It is suggested that the high concentrations of thyroid hormones present in fetal BAT might participate in the general maturation and development of fetal BAT.

Adipose Tissue, Brown↗
PubMed1989

Effect of heparin administration on flunitrazepam protein binding.

Non-esterified fatty acids have been shown to displace diazepam from its plasma binding sites both in vitro and in vivo. However, the binding of other benzodiazepines such as lorazepam is not affected in similar situations. Flunitrazepam exhibits a substantial degree of binding to plasma proteins, therefore it was deemed interesting to investigate the role of free fatty acids on flunitrazepam binding to human plasma proteins. Incubation of plasma with sodium oleate (1.5 and 3.0 microEq per ml) produced a decrease in the binding of flunitrazepam. The free fraction increased from 4.20 +/- 0.34 to 6.30 +/- 0.53 and to 22.18 +/- 1.28% respectively). Sodium heparin administration (10IU/kg, intravenously) increased free fatty acids levels and produced similar changes in the binding of flunitrazepam. After ten minutes of heparin administration free fatty acids increased from 0.16 +/- 0.03 mEq/l to 0.34 +/- 0.01 mEq/l and the free fraction of flunitrazepam in plasma increased from 3.70 +/- 0.22% to 6.20 +/- 1.24%. These binding data further support a relationship between increases in the concentrations of free fatty acids and decreases in the fraction of flunitrazepam bound to plasma proteins.

Adult↗
PubMed1988

Effect of sodium valproate on midazolam distribution.

The displacement of midazolam, a new water-soluble, short acting benzodiazepine, from its plasma binding sites by sodium valproate, has been studied in man. An increase of its free fraction (ranging from 2.71 to 5.35%) in plasma from epileptic patients receiving sodium valproate was observed. A similar situation was created in rabbits by pretreatment with sodium valproate (600 mg kg-1 day-1) and posterior hypnosis with midazolam. Due to the interaction, sodium valproate-pretreated rabbits showed an increase in midazolam brain levels (130.91 micrograms g-1 in cortex vs 84.55 micrograms g-1 in control animals). Therefore, it seems likely that displacement of midazolam by sodium valproate in epileptic patients could lead to an increase of the midazolam response.

Adult↗
PubMed1988

Serum protein binding of penbutolol in patients with hepatic cirrhosis.

Serum protein binding of penbutolol, a non-cardioselective beta-blocker agent of basic nature, has been studied in healthy subjects and in patients with hepatic cirrhosis. The percentage of free penbutolol in serum containing 200 ng/ml was markedly increased in patients with hepatic cirrhosis, when compared with the group of healthy volunteers (8.17 +/- 1.13% in patients vs 3.41 +/- 0.19 in control). No significant differences in the levels of serum alpha-acid-glycoprotein (the major protein implicated in the serum binding of penbutolol) were detected. Differences in the overall affinity constant for the binding were apparent between both groups (nKa = 5.28 X 10(5) M-1 in patients vs 12.03 X 10(5) M-1 in healthy volunteers). These results suggest a qualitative change in alpha-acid-glycoprotein molecule, from hepatic patients, but further studies are needed to clarify this point.

Adult↗
PubMed1987

A special outpatient clinic for following patients with implanted tachyarrhythmia devices.

Implantable anti-tachycardia devices have become an additional therapeutic option for those patients afflicted with life-threatening tachyarrhythmias. Follow-up of these complex devices are time-consuming and, if mismanaged, may be dangerous to the patient. For these reasons, a special anti-tachycardia device clinic was started at Newark Beth Israel Medical Center in July 1984. From the inception of the clinic to September 1985, 24 patients were followed. Seventy-five percent had antitachycardia devices (ATDs) implanted for treatment of ventricular tachyarrhythmias (VT/VF) with the remaining 25% for supraventricular tachycardias. All patients were seen every 3 months or more often if clinically required. Of 112 clinic examinations, 102 (91%) were scheduled appointments (group I) while the remaining 10 visits (group II) were unscheduled and preceded by symptomatic episodes. The problems detected in clinic (groups I and II) ranged from sudden failure of an AICD to apprehension. Appropriate nonoperative treatment was given during clinic evaluation for 60% of the problems detected in group II, while the remaining 40% required eventual surgical intervention. Compliance throughout the 15-month follow-up period was 100%. Major benefits of the clinic cited by patients and their families were continuity of care, the time allotted to meet the individual needs, and management of most problems on an out-patient basis.

Electrocardiography↗
PubMed1986

Interaction between thiopentone and sodium valproate. An in vitro and in vivo study.

The effect of sodium valproate on the binding of thiopentone to serum protein was studied in vitro. In the absence of valproate the unbound fraction of thiopentone was 15.2 +/- 0.64%, but with concentrations of valproic acid in excess of the therapeutic range, it increased to 22.42 +/- 1.65%. Scatchard plots for thiopentone in the absence and presence of valproate were investigated also. The barbiturate was bound by one group of binding sites with the association constant, Ka = 2.81 X 10(3) litre mol-1 and the number of binding sites (n) = 2.3. There was a marked decrease in this association constant in the presence of valproic acid (Ka = 1.82 X 10(3) litre mol-1), but without significant change in the number of binding sites (n = 2.13). Additionally, the effect of administration of sodium valproate i.v. on thiopentone anaesthesia was examined in rabbits. The recovery time from thiopentone was markedly longer in the presence of the anticonvulsant drug (17.0 min v. 37.1 min).

Anesthesia Recovery Period↗
PubMed1986

Differential effects of valproic acid on the serum protein binding of lorazepam and diazepam.

Valproic acid and free fatty acids have been shown to displace diazepam from its plasma binding sites both in vitro and in vivo. Since lorazepam exhibits a substantial degree of binding, but differs from other benzodiazepines in that no increase in its free fraction in serum is observed when free fatty acids are raised, the effect of valproate on the serum protein binding of diazepam and lorazepam was assessed. Sodium valproate produced a marked increase in the free fraction of diazepam, but practically no effect on the percentage of free lorazepam.

Blood Proteins↗
PubMed1985

Underestimation of albumin content by bromocresol green, induced by drug displacers and uremia.

Phenylbutazone and clofibric acid, two drugs strongly bound to human albumin, produce low readings of albumin content in serum when the bromocresol green immediate reaction is used. This abnormality is observed at drug concentrations within the range obtained during therapeutic use, and tends to be more marked in diluted samples of serum. Abnormally low values of albumin content are also obtained when the bromocresol green method is used in uremic sera, and the disparity seems related to the degree of carbamylation of these samples. The reported interferences are great enough in some cases as to suggest that the use of the immediate reaction between bromocresol green and serum should not be considered a valid measure of albumin content when these factors cannot be totally excluded.

Adult↗