Pharmacokinetics of cefodizime in patients with various degrees of renal failure.

The pharmacokinetics of cefodizime, a new expanded-spectrum cephalosporin for parenteral use, was studied in 45 subjects with various degrees of renal failure. Patients were divided into five groups according to the following creatinine clearances: group I >80 ml/min; group II <80-30 ml/min; group III <30-15 ml/min; group IV <15-5 ml/min and group V <5 ml/min. Cefodizime was administered as a 1 g i.v. bolus. Plasma and urinary concentrations of cefodizime were determined by high-performance liquid chromatography, using for detection UV absorbance. The following pharmacokinetic parameters were calculated: maximum plasma concentration (C5 min), area under the plasma concentration-time curve (AUC), terminal half-life (T1/2), terminal rate constant (lambda-z), total clearance (Clt), volume of distribution (Vd), mean residence time (MRT), urine data-derived terminal half-life (T1/2 r), renal clearance (Clr). The results of this study showed that renal failure induced changes in cefodizime pharmacokinetics. Our data demonstrated a close correlation between degree of renal impairment and pharmacokinetic changes. The maximum plasma concentration (C5 min) was higher in patients with renal failure; T1/2 was increased; AUC also increased from 470.40 +/- 17.80 mg.h/l in the control group to 1,562.30 +/- 170.8 mg.h/l in group V. Moreover, no side effect was observed after treatment with 1 g i.v. of cefodizime. Although renal failure induces significant changes of cefodizime pharmacokinetics, the drug was well tolerated and only in patients with severe renal insufficiency we advise to monitor the interval dose of cefodizime or adjust doses to renal function.

Physiological and pharmacological properties of an endogenous sodium pump inhibitor.

To investigate on Na+, K+-ATPase behavior in chronic uremia, pre and postdialysis serum from 10 chronic dialysis patients and 10 healthy subjects was pooled and subjected to reverse phase C-18 HPLC. Only one fraction, isolated from pre and postdialysis sera, eluting at 28 min (F1), was found to display significant effects on electrophysiological and transepithelial 22Na flux pattern of rabbit distal colon mucosa mounted in Ussing type chambers; indeed, serosal addition of uremic F1 to colonic mucosa resulted in a slow, but constant, decline in short-circuit current (Isc) (deltaIsc = 1.55+/-0.16 microEq h(-1) cm(-2), mean +/- S.E.M., n=12, p<0.01) and transepithelial conductance (G(T)) (from 4.50+/-0.23 to 3.71+/-0.33 mS cm(-2), p<0.01, n=12). Measurement of transepithelial 22Na fluxes in the presence of pre or postdialysis sera also showed a significant Na+ absorption rate decrease (from 1.3+/-0.22 to 0.48+/-0.30 microEq h(-1) cm(-2), mean +/- S.E.M., n=4, p<0.01), mainly due to a decrease in mucosal-to-serosal Na+ flux. By contrast, assays of peaks isolated from healthy sera did not inhibit Isc and transepithelial Na+ transport. The incubation of highly purified basolateral membranes with F1 for 1 min produced a approximately 26% inhibition of Na+, K+-ATPase. These findings are consistent with the presence of an endogenous inhibitor of sodium pump activity in uremic plasma; it is of pharmacological interest in that it may participate in the development of unpredictable responsiveness to digitalis therapy in pathophysiologic states.

Functional role of nitric oxide in guinea pig tracheal epithelium.

Nitric oxide (NO) may play an important regulatory role in airway function. We have, thus, investigated in vitro whether epithelium derived NO may modulate cholinergic neurotransmission, via release of NO in guinea pig trachea, by using L-arginine (L-ARG), a precursor of NO synthesis, and L-N(G)-nitro-arginine-methyl-ester (L-NAME), an inhibitor of NO synthase. Results show that L-ARG and L-NAME modify acetylcholine sensitivity in epithelium-intact smooth muscle preparations, suggesting a probable NO synthesis by tracheal guinea pig epithelium.

K+ channels and guinea-pig trachea: a possible functional modulation by GABAB receptors.

K+ channel activators represent a novel class of smooth muscle relaxant agents. There is now much evidence demonstrating that K+ channels, localized to prejunctional neurons and post-junctional smooth muscle membranes, can regulate airway smooth muscle activity, inducing smooth muscle cell membrane hyperpolarization. K+ channel activity may be influenced by some neurotransmitters, such as adenosine, serotonin and noradrenaline. More recently, it has been observed that the stimulation of GABAB receptors influences K+ channels in the hippocampus, dorsal rafe and spinal cord neurons. The aim of this study was to investigate the effects of levcromakalim in guinea-pig trachea at pre- and post-junctional sites and to evaluate whether GABAB receptors may modulate K+ channel activation. Levcromakalim (from 1 nM to 1 microM) relaxed guinea-pig trachea (IC50 10 +/- 0.9 nM) previously contracted by KCl (30 mM). This effect was reversed by a pretreatment with tetraethylammonium (10 mM) (IC50 120 +/- 0.7 nM). A 30-min pretreatment with baclofen (1 microM) or phaclofen (1 microM) failed to modify the effects of levcromakalim (IC50 18 +/- 1.0 nM and 14 +/- 0.6 nM, respectively). The contractile responses to electrical field stimulation (71.20 +/- 5.12% of acetylcholine--100 microM--contraction) was significantly (P < 0.05) reduced by a pretreatment with levcromakalim (10 nM) (54.00 +/- 6.68%). This reduction was antagonized by tetraethylammonium (10 nM) (72.20 +/- 14.27%).(ABSTRACT TRUNCATED AT 250 WORDS)

Metabotropic glutamate receptors are involved in the control of breathing at the medulla oblongata level of anaesthetized rats.

The goal of the present study was to identify sites in the medulla oblongata where metabotropic glutamate receptors are involved in regulating respiration. Unilateral microinjections (50 nl) of L-glutamate (L-glu) (10-25-50 mM) into the nucleus tractus solitarii (NTS) of anaesthetized rats elicited apnea (8.6 +/- 0.3 sec; 21.3 +/- 3.6 sec; 66.3 +/- 16.5 sec respectively; N = 6) and arterial hypotension (7.3 +/- 2.4 mmHg; 10.1 +/- 2.3 mmHg; 35.3 +/- 7.5 mmHg respectively; N = 6). Similarly, in other rats 1-aminocyclopentane-1, 3-dicarboxylic acid (ACPD) (1-5-10 mM), a selective agonist of metabotrophic glutamate receptors, also induced apnea (22.4 +/- 2.5 sec; 32.5 +/- sec; 92.5 +/- 1.4 sec respectively; N = 6) and arterial hypotension (12.7 +/- 2.2 mmHg; 19.6 +/- 4.3 mmHg; 26.5 +/- 1.5 mmHg respectively; N = 6). Paired experiments showed that unilateral microinjections of L-glu (50 mM) and ACPD (1 mM) into the nucleus retroambigualis (NRA) of anaesthetized rats elicited apnea (20.2 +/- 2.6 sec and 33.8 +/- 3.2 sec respectively; N = 6) and arterial hypotension (15.7 +/- 3.7 mmHg and 22.5 +/- 4.5 mmHg respectively; N = 6). The ACPD effects on apnea and hypotension in NTS and NRA were not prevented by a 3 min pretreatment with L-AP3 (30 mM), a putative antagonist of metabotropic glutamate receptors (19.5 +/- 1.4 sec; 12.3 +/- 3.2 mmHg and 30.6 +/- 2.9 sec; 23.4 +/- 3.8 mmHg respectively; N = 6). These data suggest that metabotropic glutamate receptors are involved in NTS and NRA regulation of cardiorespiratory functions.(ABSTRACT TRUNCATED AT 250 WORDS)

Docosahexaenoic acid and signaling pathways in rabbit colon.

The effects of one of the main components of fish oil, docosahexaenoic acid (DHA), on prostaglandin (PG) and Ca2+ signaling pathways were examined in intact mucosa and freshly isolated crypt cells of rabbit descending colon. Preincubation of serosal mucosa for 20 min with 1 microM DHA fully suppressed the short-circuit and transepithelial conductance increase induced by serosal addition of 10 microM arachidonic acid (AA). DHA at 1 microM also prevented the Cl- secretion promoted by 10 microM AA, as estimated by unidirectional 36Cl flux measurements (net flux = 0.68 +/- 0.30 versus -1.91 +/- 0.20 microEq/hr/cm2, four experiments, p < 0.001), whereas it did not affect the electrophysiological and ion flux responses to PGE2. Addition of 1 microM DHA to the serosal side of the mucosa also inhibited the PG cascade activation elicited by AA (PG synthesis and second messenger cAMP increase). In vitro assays of colonic cyclooxygenase activity showed that 1 microM DHA inhibited (with a 20-min lag) cyclooxygenase activity to the same extent as 5 microM indomethacin (approximately 82% and 80%, respectively). DHA also affected the Ca2+ signaling pathway; in isolated crypt cells, the cytosolic free Ca2+ concentration ([Ca2+]i) dropped by 49 +/- 7.6% (mean +/- standard error, six experiments) after incubation with 1 microM DHA. The sustained phase of the [Ca2+]i response to 500 nM concentrations of the intracellular Ca(2+)-ATPase inhibitor thapsigargin was also inhibited within 150 sec upon 1 microM DHA addition (141 +/- 5.8 versus 243 +/- 8.2 nM [Ca2+]i mean +/- standard error, eight experiments, p < 0.01). The [Ca2+]i-lowering effect of DHA, which was not achieved by incubation with other free fatty acids, was not prevented by removal of Na+ from the incubation medium (-46 +/- 4.3% versus -47 +/- 3.8%, mean +/- standard error, four experiments), nor it was mediated by cAMP-, protein kinase C-, or calmodulin-dependent mechanisms. The incubation of highly purified basolateral membranes of crypt cells with 1 microM DHA for 1 min produced a 5-fold increase (IC50 = 0.25 microM) in the plasma membrane Ca(2+)-ATPase activity (34.3 +/- 2.73 versus 6.02 +/- 0.50 nmol/mg of protein/min, mean +/- standard error, four experiments, p < 0.0001), thus indicating that the DHA effects on the Ca2+ pathway were mediated mainly by an increase in plasma membrane Ca2+ pump activity. These findings suggest that DHA is a powerful modulator of the cellular response to activation of PG and Ca2+ signaling pathways.

Role of calcium in chloride secretion mediated by cAMP pathway activation in rabbit distal colon mucosa.

Effects of Ca2+ on adenosine 3',5'-cyclic monophosphate (cAMP)-mediated Cl- secretion were investigated in intact mucosa and isolated crypt cells of rabbit descending colon. Addition of 10 microM prostaglandin (PG)E2 or forskolin to tissues incubated in Ca(2+)-free medium increased the size of short-circuit current (Isc) and Cl- secretion as estimated by unidirectional 36Cl flux measurements (net flux = -2.31 +/- 0.24 vs. -1.22 +/- 0.10 mueq.h-1.cm-2, n = 4, P < 0.001). Addition of 10 microM PGE2 to tissues incubated in 1.2 mM Ca2+ Ringer induced a 7-fold increase in mean cAMP level, whereas it produced an 11-fold increase in tissues exposed to Ca(2+)-free medium. Membrane preparations from whole mucosa incubated in Ca(2+)-free medium displayed a cyclic nucleotide phosphodiesterase activity significantly lower than controls (18.76 +/- 0.54 vs. 31.20 +/- 0.39 pmol cAMP. mg protein-1.min-1, means +/- SE, n = 4, P < 0.001). Ca2+ removal also affected adenylate cyclase (AC) responsiveness to agonists; AC activity increased in controls by 54 and 226% after stimulation with 10 microM PGE2 and forskolin, respectively, but it increased more (77 and 325%, respectively) after incubation in Ca(2+)-free solutions.(ABSTRACT TRUNCATED AT 250 WORDS)

Antiflammins suppress the A23187- and arachidonic acid-dependent chloride secretion in rabbit distal colonic mucosa.

Antiflammins are synthetic peptides with sequence homology to proteins inhibitory for phospholipase A2. The effects of antiflammins on chloride secretion induced by the calcium ionophore A23187, arachidonic acid (AA) and prostaglandin E2 (PGE2) were investigated in distal rabbit colonic mucosa mounted in Ussing-type chambers. 100 nM AF-2 (antiflammin 2, peptide HDMNKVLDL) fully prevented the increase in Isc, net chloride secretion, tissue PGE2 and second messenger cAMP induced by 5 microM A23187. AF-1 (antiflammin 1, peptide MQMKKVLDS) also inhibited, although to a lesser extent, the A23187-mediated increase in Isc. AF-2 inhibition began at doses of 100 nM (delta Isc -0.20 +/- 0.08, microEq h-1 cm-2, mean +/- S.E.M., N = 3) and was maximal at doses comprised between 200 and 250 nM (delta Isc -0.51 +/- 0.12, microEq h-1 cm-2, mean +/- S.E.M., N = 3). AF-2 also inhibited the increase in Isc and chloride secretion induced by the incubation with 10 microM AA and bradykinin but it was ineffective when tissues were stimulated with 10 microM PGE2. 100 nM AF-2 brought about an inhibition of the increase in AA-mediated increases in PGs and cAMP comparable to that of 10 microM of the cyclooxygenase inhibitor indomethacin. In vitro assay of colonic cyclooxygenase activity showed that 100 nM AF-2 and AF-1 inhibited cyclooxygenase activity (73 and approximately 30%, respectively), but they did not modify the in vitro activity of porcine phospholipase A2.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanism of arachidonic acid transport across rabbit distal colonic mucosa.

The initial rate of [1-14C]arachidonic acid (AA) entry in the serosal side of rabbit distal colonic mucosa mounted in Ussing-type chambers is linear and independent of intracellular metabolism. When the maximal AA uptake was plotted as a function of medium AA concentration in ranges between 50 and 500 nM, saturation of the AA uptake with increasing concentrations was observed. The time course of the uptake of oleic acid and palmitic acid was similar to that observed with AA, and their separate addition to incubation medium strongly reduced the AA uptake. The influx of arachidonate was largely inhibited by ouabain and by incubation with mucosal sodium-free solution and amiloride, while it was increased when colonic mucosa was exposed to luminal amphotericin B. However, voltage-clamp studies showed that the AA entry rate appeared to be linearly related (r = 0.99) to transepithelial potential difference (PD) and suggested that the sodium dependence of AA translocation is an indirect effect of the changes in transepithelial PD induced by sodium transport shifts. These features provide evidence that there is a common entry pathway for AA and other long-chain free fatty acids mediated by a mechanism of facilitated diffusion driven by transmembrane PD.

Arachidonic acid metabolites and chloride secretion in rabbit distal colonic mucosa.

The relationships between arachidonic acid (AA) metabolism and chloride secretion were investigated in mucosal preparations of rabbit distal colon. Tissues displayed a significant cyclooxygenase activity already in nonstimulated conditions and incubation with exogenous AA and calcium ionophore A23187 produced a predominant prostaglandin F2 alpha (PGF2 alpha) profile [PGF2 alpha greater than PGE2 greater than thromboxane B2 (TxB2) greater than 6-keto-PGF1 alpha] as assessed by HPLC of tissue homogenates, whereas 5-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE) was not detected in AA- or A23187-stimulated tissues. Radioimmunological assays showed that PGE2 synthesis was time dependent, plateaued at 10 min, and proceeded at rates 15-20 times over TxB2 and 6-keto-PGF1 alpha. Among the PGs produced by colonic mucosa, only PGE2 and, to a lower extent, PGF2 alpha were found to stimulate chloride secretion and cAMP synthesis. Pretreatment with 10 microM 5,8,11,14-eicosatetraynoic acid, a cyclo- and lipoxygenase inhibitor, prevented AA-induced chloride secretion and PG and cAMP synthesis with the same strength as the cyclooxygenase inhibitor indomethacin. No effects were found after preincubation with nordihydroguaiaretic acid, a lipoxygenase blocker with moderate cyclooxygenase inhibitory properties, and caffeic acid, a lipoxygenase inhibitor. 5-HETE (5 microM) had no effect on short-circuit currents (Isc) and chloride transport, but it significantly reduced the increase in Isc, chloride secretion, and PGE2 synthesis elicited by AA or A23187. Platelet-activating factor, reported to stimulate rabbit colon Isc through an indomethacin-sensitive pathway, was not detected at concentrations as low as 10(-10) M.

[Histo-radiologic correlations in patients with primary hyperoxaluria]. / Correlazioni isto-radiologiche nei pazienti con iperossaluria primitiva.

The use of new dialythic technics has increased the survival times for patients with primary hyperoxaluria. From here the possibility of visualizing X-rays signs specific of oxalosis besides the typical bone lesions of hyperparathyroidism secondary to chronic renal failure. Recent hysto-pathological studies allowed to correlate such radiological findings to a new pathogenetical mechanism that would be responsible of the bone lesion specific for oxalosis and that might be caused by the presence of reabsorption cavities made up by macrophagic cells fagocyting cristals.

Concentration polarization phenomenon in new and re-used RP610 hemofilters during post-dilutional hemofiltration.

RP610 hemofilters have been used up to five times in post-dilutional hemofiltration. Clearance studies were performed "in vivo" (creatinine and phosphate) and "in vitro" (Cr51 EDTA, I131 Hypaque, Co57 vitamin B12, H3 Inulin, C14 Dextran, I125 Albumin,) in new hemofilters and in those re-used once and five times. Hydraulic permeability and rejection coefficients, for the six markers different molecular weight, were also measured. Our preliminary results show that repeated cleansing with Amuchina does not alter the characteristics of RP610 hemofilters. A scintigraphic method is suggested for visualizing possible changes in polarized areas between new and re-used hemofilters.

Bone oxalosis and renal osteodystrophy.

Bone biopsy specimens from four patients with hyperoxaluria who underwent hemodialysis were studied. Calcium oxalate crystals are laid down in marrow spaces and sometimes inside the bone matrix and uncalcified osteoid tissue. They are clearly visible by polarizing microscope and are stained grayish-brown by Pizzolato's method. Most are surrounded by basophilic, amorphous material. By electron microscope they appear as elongated, empty spaces and after hydrogen peroxide treatment appear as fragmented, slightly electron-dense, needle-like structures. In marrow spaces, oxalate crystals aggregate in round clusters surrounded by a granulomatous reaction. This, however, cannot remove the oxalate crystals. Bone histology shows advanced renal osteodystrophy, ie, severe osteomalacia and hyperparathyroidism. The granulomatous reaction induced by the oxalate crystals probably contributes to and worsens the changes from hyperparathyroidism.

The evolution of renal osteodystrophy in patients undergoing continuous ambulatory peritoneal dialysis (CAPD).

Since the introduction of continuous ambulatory peritoneal dialysis by Popovich et al [1] and the subsequent modification of the technique by Oreopoulos et al [2], an increasing number of patients with end-stage renal disease are maintained on this new treatment modality. To date, there has not been any report of the effect of CAPD on the evolution of renal osteodystrophy which is one of the major complications of chronic renal failure. In this report we will present the results of our radiological and biochemical studies of renal osteodystrophy in 28 patients who have been on CAPD from 6 to 23 months.

A new semiautomated apparatus for hemofiltration.

A new semiautomated apparatus for hemofiltration has been described. It is a postdilutional hemofiltration system that utilizes the RP-610 dialyzer and is made of standard lines used for hemodialysis, a blood pump and two precise volumetric pumps, Logeais-TEC model, for the ultrafiltrate and for the substitution fluid. The ultrafiltrate compartment of the hemofilter is connected to a manometer for detecting positive or negative pressure. The transmembrane pressure TmP is given only by the pressure on the blood side that is regulated by the screw clamp in the venous line. Once started the whole system may be regulated by this screw clamp in order to maintain zero pressure in the ultrafiltrate compartment, provided that ultrafiltration rate does not exceed 65 ml/min. This system is sufficiently accurate to replace bed scales or any other gravimetric device.