1. The mechanism of post-ischaemic ectopic impulse generation in nerve is not known, and previous measurements of excitability changes in human motor axons have appeared to conflict. We have used automatic threshold tracking and different stimulus-response combinations to follow the effects on excitability of brief (5-10 min) periods of ischaemia, too short to induce motor fasciculations. Excitability changes have been compared at different sites in axons innervating hand, arm and foot muscles. 2. Threshold was determined as the percutaneous stimulus current required to excite a single motor unit, or to evoke a constant multiunit response, after rectifying and integrating the electromyogram (EMG). Three different waveforms of stimulus current were compared: short (less than or equal to 2 ms) pulses, long (100-200 ms) pulses to measure rheobase, and 100 ms current ramps. We also measured accommodation by recording the effects of subthreshold depolarizing currents on excitability. 3. Ischaemic and post-ischaemic excitability changes were greatest in the proximal parts of the longest motor axons, and greater if the sphygmomanometer cuff was inflated over, rather than proximal to, the stimulating site. 4. Using integrated EMG responses from abductor digiti minimi, the ulnar nerve stimulated above the elbow became rapidly much less excitable after ischaemia when tested with short pulses, but more excitable when tested with current ramps. The rheobase rose briefly, but then fell, often below resting level, always staying below the pulse and ramp thresholds. 5. The latency of the response to a rheobasic stimulus altered in parallel with the threshold to short current pulses, and increased dramatically after ischaemia. This latency increase was associated with a prolonged phase of 'negative accommodation', i.e. the continued increase in excitability to a maintained subthreshold depolarizing current. 6. Changes in excitability and accommodation similar to those occurring after ischaemia were recorded following high frequency trains of stimuli. They were attributed primarily to hyperpolarization by the electrogenic sodium pump, since comparable changes could be induced by passing a steady hyperpolarizing current through the stimulating electrode. 7. Threshold and latency recordings from single motor units during and after ischaemia resembled in most respects the multiunit responses, but single unit rheobase did not show a post-ischaemic fall below the resting level. Repetitive firing contributed to the low multiunit thresholds recorded with long current pulses during the post-ischaemic period. 8. We conclude that human motor nerves become simultaneously both more and less excitable than normal after 10 min of ischaemia, depending on the choice of stimulus and response.

Current recordings from single chloride channels were obtained from excised and cell-attached patches of rat and human axons. In rat axons the channels showed an outwardly rectifying current-voltage relationship with a slope conductance of 33 pS at negative membrane potentials and 65 pS at positive potentials (symmetrical 150 mM CsCl). They were measurably for cations (PNa/PCs/PCl=0.1/0.2/1). Channel currents were independent of cytoplasmatic calcium concentration. Inactivation was not observed and gating was weakly voltage dependent. Cl− channels in human axons showed similar gating behavior but had a lower conductance.

The contrast between resistance to ischemia and ischemic lesions in peripheral nerves of diabetic patients was explored by in vitro experiments. Isolated and desheathed rat peroneal nerves were incubated in the following solutions with different glucose availability: 1) 25 mM glucose, 2) 2.5 mM glucose, and 3) 2.5 mM glucose plus 10 mM 2-deoxy-D-glucose. Additionally, the buffering power of all of these solutions was modified. Compound nerve action potential (CNAP), extracellular pH, and extracellular potassium activity (aKe) were measured simultaneously before, during, and after a period of 30 min of anoxia. An increase in glucose availability led to a slower decline in CNAP and to a smaller rise in aKe during anoxia. This resistance to anoxia was accompanied by an enhanced extracellular acidosis. Postanoxic recovery of CNAP was always complete in 25 mM HCO3(-)-buffered solutions. In 5 mM HCO3- and in HCO3(-)-free solutions, however, nerves incubated in 25 mM glucose did not recover functionally after anoxia, whereas nerves bathed in solutions 2 or 3 showed a complete restitution of CNAP. We conclude that high glucose availability and low PO2 in the combination with decreased buffering power and/or inhibition of HCO3(-)-dependent pH regulation mechanisms may damage peripheral mammalian nerves due to a pronounced intracellular acidosis.

The renal response to atrial natriuretic factor is blunted in cirrhosis with ascites. This might be due to alterations of renal receptors for atrial natriuretic factor. Therefore density and affinity of glomerular atrial natriuretic factor binding sites of bile duct-ligated rats with ascites (n = 10) and of sham-operated controls (n = 10) were determined. Glomerular atrial natriuretic factor binding sites were identified to be of the B-(biologically active) and C-(clearance) receptor type. Discrimination and quantitative determination of B and C receptors for atrial natriuretic factor were achieved by displacement experiments with atrial natriuretic factor(99-126) or des(18-22)atrial natriuretic factor(4-23), an analogue binding to C receptors only. Density of total glomerular atrial natriuretic factor binding sites was significantly increased in bile duct-ligated rats (3,518 ± 864 vs. 1,648 ± 358 fmol/mg protein; p < 0.05). This was due to a significant increase of C-receptor density (3,460 ± 866 vs. 1,486 ± 363 fmol/mg protein; p < 0.05), whereas density of B receptors was not significantly different in bile duct-ligated rats (58 ± 11 vs. 162 ± 63 fmol/mg protein). Affinity of atrial natriuretic factor to its glomerular binding sites did not differ significantly between both groups. These data suggest that an altered glomerular atrial natriuretic factor receptor density could be involved in the renal resistance to atrial natriuretic factor in cirrhosis with ascites.

Binding sites for atrial natriuretic factor (ANF) were determined on isolated rat glomeruli as well as on glomerular membranes. To define optimal conditions, binding of ANF was investigated varying incubation time, temperature and protein concentration. Binding conditions were found to be best at 4°C for 5 hours with 15 μg of glomerular protein. Saturation and affinity cross-linking experiments confirmed the presence of two distinct receptor subtypes - the B-receptor (130 kDa) and the C-receptor (65 kDa). Quantitative differentiation of both ANF binding sites was achieved by competitive displacement with two different unlabeled ANF ligands: a) rANF(99-126) (homologous displacement), b) des(18-22)rANF(4-23)NH2(heterologous displacement). Intact glomeruli and glomerular membranes did not differ significantly in receptor density for the B-receptor (71 ± 37 vs. 94 ± 53 fmol/mg protein) or the C-receptor (976 ± 282 vs. 966 ± 167 fmol/mg protein) or in affinity constants for the B-receptor (43 ± 36 vs. 52 ± 44 pM) or the C-receptor (876 ± 377 vs. 307 ± 36 pM). Glomerular membranes compared to glomeruli showed less nonspecific binding and less intra-assay variation of measuring points done in triplicates. This method of selective displacement should allow to study the influence of various physiological and pathophysiological conditions on the binding properties of B-and C-receptors for ANF.

Atrial natriuretic factor is a hormone intimately involved in water and salt homeostasis. The heart constitutes the major but not exclusive site of synthesis of this hormone. Among other functions, the gastrointestinal tract has endocrine functions, plays an important role in volume regulation of the body, and seems to be a target organ for atrial natriuretic factor. Therefore, the presence of atrial natriuretic factor was investigated in the human gut. Immunoreactive atrial natriuretic factor was found in intraoperatively obtained samples of normal human colon. Acidic extracts of human large intestine contained about 0.4 pmol/g wet wt of atrial natriuretic factor. Analysis of atrial natriuretic factor immunoreactivity by gel-filtration and reverse-phase high-performance liquid chromatography showed that about 65% of the immunoreactivity corresponded to the atrial natriuretic factor phohormone and about 35% corresponded to the C-terminal ANF99-126. Immunohistochemistry showed atrial natriuretic factor prohormone location in enterochromaffin cells of the colon mucosa. Altogether, these findings show the presence of atrial natriuretic factor prohormone in enterochromaffin cells of the human large intestine and may suggest this organ as a site of atrial natriuretic factor synthesis in humans.

The authors tried to differentiate malignancy-related from nonmalignant ascites with a sequence of sensitive followed by specific ascitic-fluid parameters. There were four results of this study. First, of nine parameters investigated in a first series of 48 patients, 28 with nonmalignant and 20 with malignancy-related ascites, ascitic-fluid cholesterol and fibronectin yielded the best negative predictive value of 92% each. Carcinoembryonic antigen (CEA) and cytologic examination both showed a positive predictive value of 100%. Second, combining cytologic examination (sensitivity, 70%) and CEA determination (sensitivity, 45%) increased the sensitivity to 80%. Third, cytologic findings were negative in all ascitic-fluid samples with a cholesterol concentration below the cutoff value of 45 mg/100 ml. Fourth, based on the results of the first series of 48 patients, the diagnostic sequence with cholesterol as a sensitive parameter, followed by the combination of cytologic examination and CEA determination as specific parameters, was tested in a second series of 71 patients, 37 with nonmalignant and 34 with malignancy-related ascites. Again cytologic examination was negative in all samples with cholesterol levels below 45 mg/100 ml. In the total of 119 patients, this diagnostic sequence did not identify 9% of patients with malignancy-related ascites, and 82% of samples classified as malignancy related by cholesterol levels above 45 mg/100 ml were confirmed by positive cytologic examination and/or CEA level above 2.5 ng/ml. Thus, a diagnostic sequence with ascitic-fluid cholesterol determination, followed by cytologic examination and CEA determination, in samples with cholesterol levels above 45 mg/100 ml should permit a cost-efficient routine differentiation of malignancy-related from nonmalignant ascites.

In 11 patients with decompensated cirrhosis and deteriorating renal function, the effect of the vasoconstrictor substance 8-ornithin vasopressin (ornipressin; POR 8; Sandoz, Basel, Switzerland) on renal function, hemodynamic parameters, and humoral mediators was studied. Ornipressin was infused at a dose of 6 IU/h over a period of 4 hours. During ornipressin infusion an improvement of renal function was achieved as indicated by significant increases in inulin clearance (+65%), paraaminohippuric acid clearance (+49%), urine volume (+45%), sodium excretion (+259%), and fractional elimination of sodium (+130%). The hyperdynamic circulation was reversed to a nearly normal circulatory state. The increase in systemic vascular resistance (+60%) coincided with a decrease of a previously elevated renal vascular resistance (-27%) and increase in renal blood flow (+44%). The renal fraction of the cardiac output increased from 2.3% to 4.7% (P less than 0.05). A decline of the elevated plasma levels of noradrenaline (2.08-1.13 ng/mL; P less than 0.01) and renin activity (27.6-14.2 ng.mL-1.h-1; P less than 0.01) was achieved. The plasma concentration of the atrial natriuretic factor increased in most of the patients, but slightly decreased in 3 patients. The decrease of renal vascular resistance and the increase of renal blood flow and of the renal fraction of cardiac output play a key role in the beneficial effect of ornipressin on renal failure. These changes develop by an increase in mean arterial pressure, the reduction of the sympathetic activity, and probably of an extenuation of the splanchnic vasodilation. A significant contribution of atrial natriuretic factor is less likely. The present findings implicate that treatment with ornipressin represents an alternative approach to the management of functional renal failure in advanced liver cirrhosis.