Increased hypoxic stress decreases AMP hydrolysis in rabbit heart.

OBJECTIVE: AMP conversion to adenosine by cytosolic 5'nucleotidase (5NT) or to IMP by AMP deaminase determines the degree of nucleotide degradation, and thus ATP resynthesis, during reoxygenation. To elucidate the regulation of AMP hydrolysis during ischemia, data from 31P NMR spectroscopy and biochemical analyses were integrated via a mathematical model. Since 5NT is downregulated during severe underperfusion (5% flow), we tested 5NT regulation during less severe underperfusion (10% flow) and then made the perfusate hypoxic to see if the greater stress reactivated 5NT. METHODS: 31P NMR spectra and coronary venous effluents were obtained from Langendorff-perfused rabbit hearts subjected to two 30-min periods of underperfusion (10% flow); the second period with or without additional hypoxia (30% O2). Data were analyzed with a mathematical model describing the kinetics of myocardial energetics and metabolism. RESULTS: A single 30-min period of 10% flow causes downregulation of AMP hydrolysis and the data from the second period of underperfusion are best described by lower 5NT activity, even in the presence of extra hypoxia. Thirty percent less purines appear in the venous effluent than predicted by the phosphoenergetics (PCr and ATP) when IMP is not allowed to accumulate by the model, however the model indicates that a constant accumulation of IMP via AMP deaminase could explain the discrepancy between expected and measured purines in the venous effluent. CONCLUSIONS: While AMP hydrolysis to adenosine is prominent in early ischemia and acts to preserve cellular energy potential, during a second ischemic period, nucleotides are conserved by the stable inhibition of AMP hydrolysis. Furthermore, during 10% flow conditions, nucleotides are conserved, possibly via an IMP-accumulatory pathway.

Synovial perfusion in the human knee: a methodologic analysis.

Synovial perfusion was quantified in milliliters per minute per knee by two quite different clearance methods based on (1) counting tritiated water in serial aspirates of intraarticular saline, and (2) external counting of joints injected with free radioiodide. In each case, the serial counting data determine a rate constant that is multiplied by a distribution volume to provide the clearance in flow terms of milliliters per minute. This report updates and summarizes these data and compares the two methods to each other and to alternative assessments of synovial blood flow. Available methods such as laser Doppler flowmetry (with data output measured in volts) and solute clearance constant determinations (in min-1) are useful for selected purposes but cannot be used to quantify the articular flux (in milligrams per minute) of any solute. Radiolabeled microspheres provide data (in milliliters per minute per g of tissue) but are unsuitable for human use. The two clearance methods provide comparable results, but the free iodide technique seems most suitable for physiologic investigations. The latter potentially includes critical evaluations of synovial blood flow in relation to issues such as palpable warmth, visible erythema, articular ischemia, the permeability of synovial vessels, the genesis of effusions, the delivery and removal of therapeutic agents, and the concentration of every synovial fluid solute from micronutrients through cytokines, plasma proteins, and molecular markers of cartilagenous injury.

Cartilage matrix molecules in serum and synovial fluid.

The search continues for constituents of articular cartilage in the serum and synovial fluid of patients with arthritis. This work is driven by the hope that such "markers" will be useful in the diagnosis and management of rheumatic diseases. Absent information about the kinetics of these molecules continues to hinder interpretation of their concentration. Recent progress includes recognition of markers that appear to be specific for diseased cartilage and identification of factors that may distinguish between reversible and irreversible disease.

Not water, but formalin, dissolves urate crystals in tophaceous tissue samples.

OBJECTIVE: To examine the relative solubility of urate crystals in water, formalin, and ethanol. METHODS: Weighed aliquots of synthetic crystals were incubated in each solvent for 72 h at 4 degrees C and were then examined by polarized microscopy. RESULTS: urate crystals were insoluble in alcohol, sparingly soluble in water, and markedly soluble in formalin. CONCLUSION: The marked solubility of urate in formalin is consistent with formation of urate:formaldehyde addition products.

Avoidance of endotoxin-induced inflammation during studies of albumin clearance from caprine joints.

Intra-articular injection of radiolabelled, commercial goat serum albumin (GSA) produces acute arthritis in caprine joints. This inflammation distorts clearance values and vitiates studies of normal lymphatic function. Endotoxin, routinely found in commercial albumin preparations, appears to cause this local reaction. We describe a simple method for the preparation of low-endotoxin, radioiodinated serum albumin from aseptically collected serum. We have used this technique to prepare GSA for use as a tracer molecule in clearance studies of synovial joint lymphatic function. The isolated protein exhibits antigenic and chemical characteristics indistinguishable from those of commercial GSA but contains at least 1000-fold less endotoxin. In contrast to commercial GSA preparations, this albumin does not produce local inflammation when injected into synovial joints and is cleared from caprine joints in the normal monoexponential manner. Low levels of endotoxin seriously distort studies of articular albumin kinetics and may induce comparable artifacts when commercial protein preparations are used to study other physiological systems.

Effects of steps in cardiac output and arterial pressure in awake dogs with AV block.

In awake dogs with atrioventricular block, we examined the responses in total peripheral resistance and atrial rate to square-wave changes in mean arterial pressure or cardiac output. We compared the responses 2-3 min after a step change with the responses 19-20 min after a step. With resetting of arterial pressure control, the compensatory responses should decrease as the baroreceptors reset to the prevailing pressure. With step changes in mean arterial pressure or cardiac output, the responses in both peripheral resistance and atrial rate increased from minutes 2-3 to minutes 19-20. The responses in peripheral resistance also increased in animals studied after bilateral vagal block. All of the above changes were significant in the majority of cases. In another experiment, the animals were "conditioned" by 20 min at imposed high or low pressure. When control was returned to the animal after conditioning at high pressure, arterial pressure was not significantly different (P greater than 0.05) from the initial control levels. When control was returned after conditioning at low pressure, arterial pressure was significantly greater (P less than 0.05) than during the initial control period. These results indicate an absence of resetting of the entire arterial pressure control system.

Effects of calcium antagonists on intracerebral penetrating arterioles in rats.

There is no direct information on the effect of calcium antagonists on intracerebral penetrating arterioles, which are responsible for a significant part of total cerebrovascular resistance. In a study on rats, the effects of four calcium antagonists (diltiazem, verapamil, nifedipine, and nimodipine) on isolated intracerebral penetrating arterioles with mean resting diameters (+/- standard error of the mean) of 52.3 +/- 3.0 micron were investigated. Vessel diameters were monitored in vitro by means of a video microscope dimensional analyzer under constant transmural pressure (60 mm Hg) after cannulation. Each calcium antagonist produced maximal dilation of about 50% (diltiazem 46.4% +/- 5.6%, verapamil 53.1% +/- 6.0%, nifedipine 46.9% +/- 6.1%, and nimodipine 47.1% +/- 5.4%) with varied sensitivity (median effective dose (ED50): diltiazem 1.52 X 10(-6) M, verapamil 1.08 X 10(-7) M, nifedipine 8.65 X 10(-9) M, and nimodipine 1.62 X 10(-9) M). Dilation effects persisted for a significantly longer time after washout with calcium antagonists such as diltiazem (15.5 +/- 1.8 minutes), nifedipine (19.0 +/- 3.9 minutes), and nimodipine (30.0 +/- 1.6 minutes) than after washout with adenosine (8.5 +/- 1.0 minutes). It appeared that the magnitude of vasodilation was greater and the duration of dilation after washout longer in intracerebral penetrating arterioles than that reported for pial arterioles, although sensitivity to each calcium antagonist was quite similar to that reported for larger cerebral arteries. These data provide a possible explanation for the apparent disparity between clinical efficacy and angiographically determined vessel diameter when patients with cerebral vasospasm are treated with calcium antagonists. These agents may have a greater effect on intracerebral penetrating arterioles than on angiographically visible larger arteries.

Vasomotor responses of rat intracerebral arterioles to vasoactive intestinal peptide, substance P, neuropeptide Y, and bradykinin.

The effect of vasoactive peptides on vascular smooth muscle in the cerebral microcirculation was examined using an isolated intracerebral arteriole preparation. Extraluminally applied vasoactive intestinal peptide (VIP) dilated the spontaneous tone of intracerebral arterioles to 118.9 +/- 3.1% of control diameter at pH 7.30, with an EC50 of 7.27 X 10(-8) M. Similar degrees of dilation to VIP were seen in vessels preconstricted by changing bath solution to pH 7.60. Substance P had no effect on vessel diameter at pH 7.30. However, in vessels precontracted by pH 7.60, significant dose-dependent dilation was observed with an EC50 of 2.55 x 10(-10) M. Neuropeptide Y constricted intracerebral arterioles to 81.22 +/- 2.7% of control diameter, with an EC50 of 6.23 x 10(-10) M. Bradykinin dilated intracerebral arterioles at pH 7.30 and pH 7.60 to 130 +/- 3.0% of control diameter. VIP and bradykinin are potent vasodilators of intracerebral arterioles. Neuropeptide Y is a vasoconstrictor. The effect of substance P appeared to be either pH-dependent or dependent on some degree of precontraction by another agonist, but no effect on vessel diameter was seen at pH 7.30.

Cholinergic vasodilation of intracerebral arterioles in rats.

Much morphological and physiological evidence indicates that cholinergic mechanisms play a significant role in the control of cerebral blood flow. Despite in situ data suggesting that an intrinsic cholinergic mechanism produces vasodilation in the intracerebral microcirculation, there is no direct information on the effect of acetylcholine (ACh) on intracerebral arterioles. We investigated cholinergic mechanisms in isolated perfused intracerebral arterioles from pentobarbital sodium-anesthetized Sprague-Dawley rats. In arterioles with resting diameters of 46.8 +/- 6.6 microns (mean +/- SE) ACh produced no significant dilation at pH 7.30. At pH 7.60, however, a significant dose-dependent dilation to a maximum of 119.0 +/- 1.0% of control diameter was observed. Carbachol, a long-acting cholinergic agonist, similarly failed to dilate vessels at pH 7.30 but significantly dilated vessels at pH 7.60. Prostaglandin F2 alpha produced a maximum contraction to 68.3 +/- 2.7% of control diameter (n = 8). ACh at concentrations of 10(-4) and 2 X 10(-4) M induced a significant dilation of this prostaglandin-induced contraction. In vessels similarly preconstricted with serotonin, 10(-4) M ACh produced significant dilation. Atropine, having no effect on vessel diameter when administered alone, blocked cholinergic vasodilation of intracerebral arterioles at pH 7.60. Attempts at endothelial removal, although successful in eliminating endothelial cells from the preparation, significantly impaired smooth muscle contractility. ACh has no significant effect on the spontaneous cerebrovascular tone in this preparation, but in vessels preconstricted by a variety of means it produced vasodilation mediated by atropine sensitive receptors.

Histaminergic vasodilation of intracerebral arterioles in the rat.

Histamine from various sources is found in significant amounts around cerebral vessels and may play a significant role in controlling CBF. The effect of histamine on the intracerebral microcirculation has not been examined. We have used an in vitro technique for the isolation and cannulation of intracerebral arterioles from the rat to study the effect of histamine on the spontaneous tone developed by these vessels. Extraluminally administered histamine caused dose-dependent vasodilation of isolated intracerebral arterioles with a maximal dilation of 139 +/- 2.4% of control diameter. The dilation was blocked by the H2 receptor antagonist cimetidine, but was only incompletely attenuated by the H1 receptor blocker chlorpheniramine. Histamine effects a dilation of the spontaneous tone of intracerebral resistance vessels, which is mediated by H2 receptors.

Habitat aridity and urine concentrating ability of nearctic, insectivorous bats.

Urine concentrating ability of nearctic, insectivorous bats determined from renal anatomy was significantly correlated to total annual precipitation and potential evapotranspiration to precipitation ratio of the habitat where the animal was collected. Habitat aridity measured by water input accounted for as much variation in urine concentrating ability as habitat aridity measured by both water and energy input. Habitat aridity, regardless of how it was measured, explained only 25% of the among-species variation in urine concentrating ability. Factors other than habitat aridity significantly affect the urine concentrating ability of insectivorous bats.

Interspecific comparison of subcutaneous tissue fluid pressure in the bat wing.

Tissue fluid pressures were recorded from subcutaneous tissues of three bat species by means of an improved servo-micropipet pressure recording system. Experimental animals were restrained but unanesthetized during the procedure by methods which avoided vascular occlusion. Tissue fluid pressures averaged +0.46 +/- 2.08 mm Hg (n = 12) in the Mexican free-tailed bat, +0.21 +/- 0.63 mm Hg (n = 14) in the pallid bat, and -0.31 +/- 1.01 mm Hg (n = 12) in the little brown bat. None of the average values differed significantly (P greater than 0.25) from the others or from atmospheric pressure (P greater than 0.20). Tissue fluid pressures in the subcutis of the bat were near atmospheric in agreement with the results obtained in the bat and other species by earlier investigators using both hypodermic needles and micropipets.

Postnatal changes in hematology of the bat Antrozous pallidus.

Blood oxygen capacity increases with growth as the result of increasing hemoglobin concentration, which is accompanied by increasing red blood cell count and hematocrit. Hematological profile of the postnatal bat approaches that of the adult by 42 days of age when the animal begins to fly. Hematological development in the bat is similar to that in other altricial small mammals.