Accelerated purine nucleotide degradation by anaerobic but not by aerobic ergometer muscle exercise.

The exact conditions under which exercise causes purine nucleotide degradation are not well understood. We determined plasma hypoxanthine and uric acid levels serially in eight individuals during ergometer muscle exercise. When the load was increased gradually by 15 W/min, plasma hypoxanthine was elevated only after the status exceeded the anaerobic threshold (AT), as determined by analysis of expired gas. Nonstrenuous ergometer exercise, which kept the status continuously below the AT, induced neither blood lactic acid nor plasma hypoxanthine elevation. These results suggest that the AT is also the threshold for the acceleration of purine nucleotide degradation. Muscle exercise to a degree that does not exceed the AT does not cause major purine nucleotide degradation, and, therefore, is expected to be beneficial for patients with gout and/or hyperuricemia.     

Urinary calculi in hypercalcemic states

In this brief review of various hypercalcemic disorders and the likelihood of renal calculus formation, it is clearly evident that renal calculi occur much more often in hyperparathyroidism than in the other hypercalcemic states. Dystrophic calcification and nephrocalcinosis are common to all of the hypercalcemic disorders, including hyperparathyroidism, when the hypercalcemia is marked and the limit of solubility of calcium and phosphate in serum is approached. Interestingly, in sarcoidosis there are calcium oxalate crystals in variously distributed sarcoid granuloma, and the renal calculi are composed of calcium oxalate. By contrast, in hyperparathyroidism, the calculi composed of calcium phosphate predominate. This indicates a subtle and as yet undefined alteration in oxalate metabolism in sarcoidosis. An increase in urine pH occurs in hyperparathyroidism, and this enhances formation of crystalline calcium phosphate. However, the striking disparity between the frequency of calculus formation in hyperparathyroidism and that in other hypercalcemic disorders, several of which may be of relatively long duration, suggests that there indeed may be increased promoters of crystal formation in the urine of hyperparathyroid patients.     

Altered purine nucleotide degradation during exercise in patients with essential hypertension

Purine degradation occurs during strenuous muscle exercise and plasma levels of hypoxanthine (HX), purine degradation intermediate, increase. Purine nucleotide degradation has not been investigated in patients with essential hypertension (HTN). The present study determined whether purine nucleotide degradation is altered in patients with HTN. Cardiopulmonary exercise test was performed with serial measurements in blood lactate and plasma HX in 24 patients (14 men and 10 women) with essential HTN (World Health Organization [WHO] class I to II; mean age, 57.7 +/- 2.1 years) and 24 age-, sex-matched normal subjects. Exercise was terminated either by severe fatigue or excess blood pressure increase. Peak work rate (WR) (normal v HTN, 151 +/- 10 v 135 +/- 8 W, not significant [NS]) was not different, but peak oxygen uptake (peak Vo(2), 26.3 +/- 1.5 v 22.2 +/- 0.9 mL/min/kg, P <.05) and anaerobic threshold were lower in patients with HTN. Resting levels of blood lactate and plasma HX were similar, but the increment from rest to peak exercise (Delta) for lactate (Delta lactate: 4.4 +/- 0.4 v 3.4 +/- 0.4 mmol/L, P <.05) and for HX (Delta HX, 15.9 +/- 2.2 v 9.1 +/- 1.1 micromol/L, P <.05) were significantly smaller in patients with HTN. When normalized by the peak WR, Delta HX/peak WR (0.105 +/- 0.013 v 0.069 +/- 0.007 micromol/L/W, P <.05) was significantly lower in patients with HTN. Patients with HTN exhibited reduced HX response to exercise with impaired exercise capacity. The exercise-induced changes in plasma HX were smaller in patients with HT when normalized with peak WR. These results suggest that the purine nucleotide degradation is reduced in patients with HTN.     

Stimulation of human purine synthesis de novo by fructose infusion.

In order to clarify the mechanism of hyperuricemia and hyperuricosuria resulting from rapid infusion of fructose in man, the effects of an intravenous infusion of 125-200 g of fructose given over 3-4 hr on the rate of purine synthesis de novo was measured in one individual with osteoarthritis and four patients with gout. The incorporation of 1-minus 14C glycine into urinary uric acid was measured, and the pool size and turnover of urate were assessed by renal excretion of simultaneously administered 15-N urate. Fructose caused an expansion of body urate pool in all subjects, while urate turnover was increased in four. The rate of incorporation of 14-C glycine into urinary uric acid corrected for extrarenal disposal was increased in all cases (21%-430%). In two patients, rates of incorporation of 14-C glycine into urinary creatinine were increased by 10% and 11%, while rates of incorporation into uric acid were increased 84% and 159%, respectively, as a result of fructose infusion. Specific enhancement of the rate of purine synthesis de novo was suggested by these findings. The rate of infusion appeared more important than total dose in determining the magnitude of this effect. Whether the increased rate of purine synthesis was a result of direct stimulation by a fructose metabolite or was secondary to fructose-induced purine nucleotide depletion is uncertain, since the kinetics of glycine incorporation were consistent with either mechanism. Erythrocyte PP-ribose-P concentrations, however, were diminished during infusion rather than increased as might be expected if fructose infusion stimulated purine synthesis by increasing availability of this regulatory substrate.     

Mutations in the Gs alpha gene causing hormone resistance

G-protein-coupled receptors (GPCRs) and G proteins mediate the effects of a number of hormones of relevance to endocrinology. Genes encoding these molecules may be targets of loss- or gain-of-function mutations, resulting in endocrine disorders. The only mutational change of G proteins so far unequivocally associated with endocrine disorders occurs in the Gsalpha gene (GNAS1, guanine nucleotide binding protein alpha stimulating activity polypeptide 1), which activates cyclic AMP (cAMP)-dependent pathways. Heterozygous loss-of-function mutations of GNAS1 in the active maternal allele cause resistance to hormones acting through Gsalpha-coupled GPCRs, whereas somatic gain-of-function mutations cause proliferation of endocrine cells recognizing cAMP as mitogen. This review will focus on inactivating mutations leading to hormone resistance syndromes, i.e., pseudohypoparathyroidism types Ia and Ib.     

Effect of long-term thiazide therapy on intestinal calcium absorption in patients with recurrent renal calculi

Recurrent calcium-containing renal calculi are a common and poorly understood problem. Thiazide diuretics decrease urinary calcium excretion but their effect on other parameters of calcium metabolism is not established. The purpose of this study was to determine the effect of chronic administration of thiazide diuretics on intestinal calcium absorption, skeletal calcium turnover, and urinary calcium excretion, and to use this information to attempt to clarify the pathogenesis of idiopathic hypercalciuria. Forty-one patients with recurrent calcium-containing renal calculi were studied; 73% had hypercalciuria, 44% had increased intestinal absorption, and 7% had increased bone turnover. Thiazide diuretics given to 22 patients for 3–16 mo resulted in a consistent reduction in urinary calcium excretion, while calcium absorption was unchanged (< 6%) in 12 patients and significantly decreased (by 20%) in ten patients. Decreased intestinal absorption appeared to be a secondary effect of thiazides, presumably due to reduced urinary calcium losses. Bone turnover was significantly decreased by thiazides in each case in which it had been elevated and was unchanged in patients with initially normal values. These results indicate that increased bone turnover is probably not the primary defect in idiopathic hypercalciuria. The effects of long-term thiazide diuretic therapy on intestinal calcium absorption suggest that there may be two different subpopulations of patients with hypercalciuria, one with primary intestinal hyperabsorption which persists despite correction of urinary losses, and one with primary renal loss of calcium.     

Endocrine role of the lung in disease

The lung may be an important endocrine organ in disease. Endocrine dysfunction of the lung may be manifested by (1) syndromes due to ectopic secretion of hormones, usually from bronchogenic tumors; (2) other systemic syndromes, possibly attributable to humoral factors from the lung; and (3) pulmonary and systemic disorders mediated by the release from the lung of biologically active substances. The latter category includes anaphylaxis, and some reactions to pulmonary embolism, hypoxia, pulmonary edema and respiratory alkalosis.     

Overview on visceral manifestations of mitochondrial disorders

Mitochondriopathies (MCPs) that reach adult age not only manifest in the central and peripheral nervous systems, eyes, ears, and dermis, but also in visceral organs, such as endocrine organs, heart, liver, guts, kidneys and blood. Visceral manifestations occur as part of a multisystem involvement or rarely as single organ affection. Endocrinological abnormalities are found in the MELAS, MERRF , KSS , MID and DID MOAD syndromes. Cardiac involvement occurs in the MELAS, MERRF , KSS , CPEO, LHO N, NARP, and Leigh syndromes. Gastrointestinal manifestations are common in the MERRF , MNGI E, DID MOAD, and Leigh syndromes. Mitochondrial syndromes with renal manifestations are the KSS , Pearson, DID MOAD, and Leigh syndromes. The haematopoetic system is affected in the KSS , MERRF , and Leigh syndromes. In addition, visceral manifestations are found in many nonsyndromic MCPs. Although there is no causal therapy for MCPs, adequate symptomatic therapy, particularly of visceral manifestations, markedly improves quality of life and prognosis of these still often neglected or overlooked disorders.     

Disorders of distal nephron function

In this review, the distal nephron is considered to be that portion of the renal tubule commencing with the thick ascending limb of the loop of Henle and ending with the papillary collecting duct. The collecting duct, including its subdivisions in the cortex and medulla, originates from a different embryologic anlage than more proximal nephron segments, which may explain its morphologic and functional dissimilarities from the thick ascending limb and the distal convoluted tubule. This review summarizes selected aspects of the physiology of the distal nephron, with particular emphasis on the physiology of distal nephron transport of sodium, potassium, chloride and hydrogen ion. The pathophysiologic features of the following disorders of distal nephron function are reviewed: (1) pseudohypoaldosteronism, a heterogenous group of disorders in which the signs and symptoms are suggestive of aldosterone deficiency, but in which aldosterone levels are supernormal and administration of exogenous mineralocorticoid is not ameliorative; (2) pseudohyperaldosteronism (Liddle syndrome), a familial disorder in which the clinical manifestations closely resemble those resulting from an aldosterone-producing adenoma of the adrenal gland (primary aldosteronism), but in which the measured rate of aldosterone secretion and excretion is greatly subnormal; (3) Bartter syndrome and related syndromes of renal potassium wasting; (4) type 1 renal tubular acidosis (classic, distal); (5) type 4 renal tubular acidosis (hyperkalemic). Reference citations are generally to articles reporting recent advances in these areas and to review articles that contain comprehensive bibliographies.     

Hyperuricemia in acute illness: a poor prognostic sign

To clarify the role of the serum urate level and its change as a potential marker for severe tissue hypoxia, we have measured serum urate levels and urine uric acid excretion in 16 patients with acute cardiovascular disease. The six patients who died had a baseline mean serum urate level of 11.1 mg/dl (range, 6.6 to 15.5 mg/dl) and reached a peak mean value of 20.7 mg/dl (range, 13.6 to 33.0 mg/dl). Five of these patients had findings to suggest increased production of uric acid, in addition to decreased excretion of uric acid from impaired renal function. The 10 survivors had a baseline mean serum urate level of 6.8 mg/dl (range, 1.3 to 14.0 mg/dl) and a maximal mean peak value of 7.1 mg/dl (range, 3.9 to 14.0 mg/dl). There was no consistent evidence for increased production or decreased excretion of uric acid. Patients who died had a lower systolic blood pressure, arterial pH and plasma bicarbonate level and a higher heart rate and serum creatinine level compared with the patients who survived. The observations suggest that marked hyperuricemia at the height of an illness may predict a fatal outcome. Tissue hypoxia may contribute to this sequence of events by leading to the depletion of adenosine triphosphate (ATP) and activation of purine nucleotide degradation to uric acid.     

Removal of oxygen free-radical-induced 5',8-purine cyclodeoxynucleosides from DNA by the nucleotide excision-repair pathway in human cells

Exposure of cellular DNA to reactive oxygen species generates several classes of base lesions, many of which are removed by the base excision-repair pathway. However, the lesions include purine cyclodeoxynucleoside formation by intramolecular crosslinking between the C-8 position of adenine or guanine and the 5' position of 2-deoxyribose. This distorting form of DNA damage, in which the purine is attached by two covalent bonds to the sugar-phosphate backbone, occurs as distinct diastereoisomers. It was observed here that both diastereoisomers block primer extension by mammalian and microbial replicative DNA polymerases, using DNA with a site-specific purine cyclodeoxynucleoside residue as template, and consequently appear to be cytotoxic lesions. Plasmid DNA containing either the 5'R or 5'S form of 5',8-cyclo-2-deoxyadenosine was a substrate for the human nucleotide excision-repair enzyme complex. The R diastereoisomer was more efficiently repaired than the S isomer. No correction of the lesion by direct damage reversal or base excision repair was detected. Dual incision around the lesion depended on the core nucleotide excision-repair protein XPA. In contrast to several other types of oxidative DNA damage, purine cyclodeoxynucleosides are chemically stable and would be expected to accumulate at a slow rate over many years in the DNA of nonregenerating cells from xeroderma pigmentosum patients. High levels of this form of DNA damage might explain the progressive neurodegeneration seen in XPA individuals.     

When to investigate for purine and pyrimidine disorders. Introduction and review of clinical and laboratory indications

When to suspect and thus investigate for inborn errors of purine and pyrimidine metabolism is a dilemma for even the most observant investigator. Often parents of affected children, or a history involving siblings, can provide valuable clues. The recognition of new purine and pyrimidine disorders requires skill and serendipity. But even identifying known disorders can prove difficult, since they cover a broad spectrum of illnesses, can have more than one symptom, or lead to early death. This problem is compounded by the fact that they are relatively recently described and therefore often little known, either in the clinic or laboratory. The considerable heterogeneity in clinical expression within families as well as between families means that asymptomatic homozygotes may not be recognized or can present at any time from early childhood through adolescence up to their eighth decade. Consequently, all siblings should be screened. These disorders should be suspected in any case of unexplained anaemia, failure to thrive, susceptibility to recurrent infection, or neurological deficits with no current diagnosis, including autism, cerebral palsy, delayed development, deafness, epilepsy, self-mutilation, muscle weakness, the inability to walk or talk, and - unusual in children and adolescents - gout, sometimes with renal disease. Some disorders present with radiolucent kidney stones, in acute or chronic renal failure, alone or with any of the above, or as an intolerance/sensitivity to therapy (e.g. 5-fluorouracil in malignancies or azathioprine immunosuppression in organ transplantation), often with life-threatening consequences. Several parameters need to be evaluated to ensure correct diagnosis. Pitfalls which can mask diagnosis using only a single test are renal failure, blood transfusion, diet or drugs.     

Current therapeutic strategies in cardiorenal syndrome

Cardiorenal syndromes (CRS) are disorders of the heart and kidneys in which an acute or chronic dysfunction in one organ may induce acute or chronic dysfunction of the other. Primary disorders of one of these two organs often result in secondary dysfunction or injury of the other. The lack of specific trials in this field highlights the need for further studies aimed to assess titration and appropriate dosages of drugs, according to both the etiology of chronic heart failure (CHF) and also the severity of underlying renal dysfunction. Moreover, the most recent clinical trials evaluating clinical and renal outcome in acute heart failure syndromes (AHFS), failed to demonstrate an improvement in renal function and perfusion. Therefore, Current American and European Guidelines for AHFS does not provide specific recommendation for patients with renal impairment. In this scenario several questions regarding the drugs, their recommended dosage and potential adverse effects on cardiac and renal outcome need to be addressed. Subsequently, therapy inducing an improvement in the renal function, a reduction of neurohormonal activation and an improvement of renal blood flow, could lead to a reduction in mortality and hospitalization in patients with CRS.     

Metabolic defects of primary hyperuricemia and gout

Gout is a syndrome of multiple pathogeneses rather than a single disease entity. Reviewed here are the metabolic defects of primary gout, with major emphasis upon two well characterized, although uncommon, variants due to specific enzyme abnormalities: (1) structural mutants of phosphoribosylpyrophosphate (PP-ribose-P) synthetase with increased activities, resulting in increased rates of synthesis of PP-ribose-P, a key substrate of purine biosynthesis, and (2) structural mutants of hypoxanthineguanine phosphoribosyltransferase (HGPRT) with reduced activities, resulting in reduced consumption of PP-ribose-P and therefore a surplus in the amount available for purine biosynthesis de novo. The present state of our limited knowledge of control of purine biosynthesis is also reviewed briefly, and the potential mechanisms of excessive uric acid production in idiopathic gout are discussed in terms of possible excesses of substrates (PP-ribose-P or L-glutamine) of the first specific reaction of purine biosynthesis, possible defects of control of the enzyme catalyzing this reaction, or defects in maintenance of optimal concentrations of nucleotide regulators of this reaction. It is likely that the rate of production of uric acid in man is influenced by availability of substrates, cofactors and regulatory compounds, and activities of enzymes at many reaction sites other than the first specific reaction of the purine sequence, but their influences upon the rate of purine production can be conveniently analyzed in terms of their indirect effects upon this reaction. Examples cited include glucose-6-phosphatase deficiency glycogen storage disease, in which marked hyperuricemia and purine overproduction are present, and elevated activities of hepatic xanthine oxidase in gouty patients with increased uricaciduria, perhaps occurring secondary to other factors but nevertheless contributing to the excessive purine production. The basic lesions of the more than 95 per cent of patients with primary gout who do not have abnormalities of either PP-ribose-P synthetase or HGPRT remain to be defined, but will almost certainly turn out to be multiple, complex and, in many cases, subtle deviations of metabolic control.     

Adenine nucleotide changes in kidney, liver, and small intestine during different forms of ischemic injury

The purpose of this study was to better characterize renal adenine nucleotide pool responses to different forms of shock, contrast the changes to those found in other intra-abdominal organs (the liver and small intestine), and assess whether these changes are closely mimicked by those produced by renal arterial occlusion, the usual method used to study ischemic acute renal failure. Rats were subjected to hemorrhagic shock, septic shock, or cardiopulmonary shock of varying severities and durations. The liver consistently had the greatest energy depletion, followed by the kidney, and then the small intestine. However, only the kidney developed clear morphological damage (S3 brush border sloughing). Kidney adenylate pools were better preserved during septic shock and cardiopulmonary shock than during hemorrhagic shock despite comparable blood pressures. Only profound hemorrhagic shock (35-40 mm Hg for 25 minutes) decreased total adenylate pools (ATP + ADP + AMP). However, the degree of renal catabolite (nucleosides plus purine base) accumulation did not correlate with the amount of renal total adenine nucleotide depletion, partially because circulating catabolites contributed to intrarenal catabolite pools. Purine base/uric acid ratios differed among shocked organs, consistent with different degrees of xanthine oxidase activity (small intestine greater than liver greater than kidney). Renal morphological damage decreased during the immediate (0-30 minutes) postshock period, and the extent of this improvement was not altered by xanthine oxidase inhibition (oxypurinol), suggesting that the immediate postshock period is not one of serious oxidative injury. Shock, in comparison with renal arterial occlusion, caused only modest ATP loss/catabolite accumulation, very low purine base/uric acid ratios, and no immediate-reperfusion (0-30 minutes) resynthesis of the total adenylate pool. Thus, ischemia-induced renal adenylate changes may differ considerably, depending on the nature of the ischemic event.     

Miscellaneous Stone Types

Drug-induced calculi and other rare stone types, such as ammonium acid urate or protein matrix stones, represent only about 2% of all renal calculi. However, the chance to easily reverse stone formation risk by discontinuing the offending drug makes identification of these entities important for clinicians. Additionally, study of these rare stone types contributes to understanding the biochemistry of stone formation. Drug-induced calculi may be classified into two groups based on the mechanism of stone formation. The first group includes drugs that provoke calculi composed of principally the drug and its metabolites. These medications tend to be poorly soluble, highly excreted in urine, and required at high dosages for long durations of therapy. Historically, sulfonamides, triamterene, and the HIV protease inhibitor indinavir were leading causes of drug-induced calculi. Uses of novel agents within these drug classes or alternative therapies have reduced the incidence attributed to these drugs, although risk from newer, commonly used medications?Cnotably ciprofloxacin, aminopenicillins, ceftriaxone, ephedrine, and guaifenesin?C are increasingly being recognized. Microscopic analysis for crystalluria or infrared spectroscopy of collected stones aid in recognition of calculi composed primarily of a drug and its metabolites. Understanding of drug metabolism and pharmacokinetics, particularly related to effects of urine pH on drug solubility and excretion, provides a rational basis for both prevention and treatment recommendations. When possible, clinicians should avoid or exercise great caution when prescribing these medications to patients with a prior history of stones. The second group of drug-induced calculi includes drugs that cause stones due to their metabolic effects, primarily on calcium or purine metabolism. Because these calculi are identical in physical composition to the more common nephrolithiasis types, careful medication history and high clinical suspicion are required for diagnosis of these drug-induced ??metabolic?? calculi. Most drugs in this class are readily expected based on their effects on urinary calcium excretion such as calcium/Vitamin D supplements and loop diuretics. Carbonic anhydrase inhibitors, including the antiepileptics topiramate and zonisamide, are also included in this group. Ammonium acid urate stones are endemic in developing countries due to dietary limitations and recurrent diarrheal illness, but rarely occur in developed countries. Identification of these stones should raise clinical suspicion of epidemiologic risk factors including recurrent urinary tract infections with urea-splitting organisms, inflammatory bowel disease, and laxative abuse. Interestingly, these unusual clinical scenarios can recapitulate a common biochemical pathway to stone formation. Protein matrix stones are another unusual stone type associated with specific epidemiologic factors, namely recurrent urinary infections and proteinuric end-stage renal disease. Although distinctly rare, protein matrix stones provide opportunity to investigate basic biochemical mechanisms underlying stone formation.     

Acquired increases of human erythrocyte purine enzymes.

The alterations of three erythrocyte purine enzymes were studied in 12 patients with diseases associated with reticulocytosis, two patients with a partial deficiency of hypoxanthine-guanine phosphoribosyltransferase, seven patients with severe megaloblastic anemia, and 14 normal subjects. The specific activity of adenine phosphoribosyltransferase was positively correlated (r = 0.81) with the reticulocyte percentate in ten patients with a normal hypoxanthine-guanine phosphoribosyltransferase. Two apparent types of alterations of this enzyme were distinguished: (1) increased specific activity with a normal half life as in megaloblastic anemia, and (2) a prolonged half life with or without an elevation of specific activity as in the deficiency of hypoxanthine-guanine phosphoribosyltransferase. Hypoxanthine-guanine phosphoribosyltransferase and phosphoribosylpyrophosphate synthetase were increased in megaloblastic anemia, but were not correlated with the reticulocyte percentage and did not have a consistent change in the half life in the other disorders studied. The data show that acquired disorders associated with reticulocytosis may cause an elevation of the specific activity of purine enzymes in peripheral circulating erythrocytes. Therefore, these factors must be carefully considered in the interpretation of an elevated level of enzyme activity.     

Selected rare, noninfectious syndromes associated with HIV infection

Infrequent and sometimes treatable noninfectious syndromes associated with HIV disease include tenofovir-associated Fanconi syndrome, a proximal renal tubular disorder; pulmonary hypertension that appears to be due to HIV-driven inflammation resulting in endothelial proliferation; thrombotic thrombocytopenic purpura, characterized by intravascular coagulopathy; diffuse infiltrative lymphocytosis syndrome, which can affect multiple organs; and Castleman's disease, a lymphoproliferative disorder that usually occurs in a multicentric form with poor prognosis in HIV-infected patients. This article summarizes a presentation on the characteristics, diagnosis, treatment, and prognosis of these disorders by Molly E. Eaton, MD, at the International AIDS Society-USA course in Atlanta in March 2005.     

Intestinal anisakiasis. First case report from North America.

The first case of intestinal anisakiasis in North America is described. This parasitic disease is recognized as a public health hazard in Japan and Europe. Man becomes infected with a larval form of the nematode Anisakis by consuming raw or undercooked fish containing the parasite. Typically, patients present with acute abdominal syndromes. Clinical and reontgenographic features may cause confusion with regional enteritis. Histologically, a striking oesinophilic granulomatous reaction occurs. Anisakiasis is most effectively prevented by discouraging the consumption of raw fish.     

Energy metabolism in myocardial stunning.

We investigated the effect of reversible ischemia, leading to persistent contractile dysfunction (stunning), on myocardial energy metabolism. The balance of energy metabolism is expressed by the phosphorylation state of cytosolic nucleotides. This variable cannot be measured directly because of nucleotide compartmentation, but in the isolated heart it can be estimated by the release of purine catabolites. We have previously shown that increased energy consumption or impaired energy production cause purine release to increase, while primary reduction in energy consumption has the opposite effect. Isolated working rat hearts were reperfused after 10 min of global ischemia, measuring hemodynamic variables, tissue high energy phosphate compounds and purine release. In post-ischemic recovery, aortic flow and minute work decreased to 82 +/- 3% and 77 +/- 4% of control, adenine nucleotide pool was reduced by 4.6 mumol/g dry wt, phosphocreatine to creatine ratio increased significantly and purine release decreased to 42 +/- 6% (P < 0.01). The rate of purine salvage, as evaluated by the incorporation of exogenous 3H-adenosine and 14C-hypoxanthine into tissue nucleotides, was much lower than net purine release, and was unchanged after ischemia and reperfusion. The adenine nucleotide pool could be depleted to the same extent as in the stunned myocardium by prolonged (60 min) aerobic perfusion. In this group the hemodynamic variables were unchanged and purine release averaged 87 +/- 9% of control (P = NS). In other experiments prolonged perfusion was combined with preload reduction in order to decrease energy demand. This protocol reproduced the effects of ischemia-reperfusion: aortic flow and minute work averaged 79 +/- 4% and 73 +/- 9% of control, adenine nucleotide depletion was 4.4 mumol/g dry wt and purine release decreased to 38 +/- 5% (P < 0.01). Our findings support the view that stunning is not due to adenine nucleotide depletion or to impairment in energy production, which would cause purine release to increase, but rather to primary reduction in energy utilization.