Regional sampling and the effects of experimental heart failure in sheep: differential responses in A, B and C-type natriuretic peptides

While regional plasma concentrations of the endocrine hormones atrial and brain natriuretic peptide (ANP and BNP) have been studied, there are few reports of regional changes in the largely paracrine C-type natriuretic peptide (CNP) and its amino terminal fragment NT-CNP. Accordingly, we have performed trans-organ arteriovenous sampling for measurement of plasma ANP, BNP, CNP and NT-CNP in anesthetized sheep before and after induction of experimental heart failure. ANP and BNP plasma concentrations are sourced from a single organ (the heart) and are subject to substantial extraction across most tissue beds. In contrast, our data demonstrate that multiple tissues including liver, heart, hind limb and kidney contribute to circulating CNP. Given that arteriovenous gradients for NT-CNP were similar, this is likely to represent de novo secretion. Circulating levels of CNP and NT-CNP were raised in heart failure but to a much lesser degree than ANP and BNP. There was no evidence of net extraction of CNP or NT-CNP across any tissue bed.     

Urotensin II: evidence for cardiac, hepatic and renal production

Although urotensin II (UII) has been reported to circulate in human plasma and be raised in cardiovascular disorders, little, if any, information is available regarding the source of plasma UII. Accordingly, we have performed trans-organ arteriovenous sampling for measurement of UII concentration in anesthetized sheep. Plasma UII levels were measured in the low picomolar range in normal sheep and arterial plasma levels rose steadily with increasing time of anesthesia. Significant arteriovenous gradients were observed across the heart (36%), liver (40%) and kidney (44%). This is the first report to identify the heart, liver and kidney as sources of UII in the circulation.     

Increased cardiac sympathetic nerve activity in heart failure is not due to desensitization of the arterial baroreflex

Increased sympathetic drive to the heart worsens prognosis in heart failure, but the level of cardiac sympathetic nerve activity (CSNA) has been assessed only by indirect methods, which do not permit testing of whether its control by arterial baroreceptors is defective. To do this, CSNA was measured directly in 16 female sheep, 8 of which had been ventricularly paced at 200-220 beats/min for 4-6 wk, until their ejection fraction fell to between 35 and 40%. Recording electrodes were surgically implanted in the cardiac sympathetic nerves, and after 3 days' recovery the responses to intravenous phenylephrine and nitroprusside infusions were measured in conscious sheep. Electrophysiological recordings showed that resting CSNA (bursts/100 heartbeats) was significantly elevated in heart-failure sheep (89 +/- 3) compared with normal animals (46 +/- 6; P < 0.001). This increased CSNA was not accompanied by any increase in the low-frequency power of heart-rate variability. The baroreceptor-heart rate reflex was significantly depressed in heart failure (maximum gain -3.29 +/- 0.56 vs. -5.34 +/- 0.66 beats.min(-1).mmHg(-1) in normal animals), confirming published findings. In contrast, the baroreflex control of CSNA was undiminished (maximum gain in heart failure -6.33 +/- 1.06 vs. -6.03 +/- 0.95%max/mmHg in normal sheep). Direct recordings in a sheep model of heart failure thus show that resting CSNA is strikingly increased, but this is not due to defective control by arterial baroreceptors.     

Identification of amino-terminal pro-C-type natriuretic peptide in human plasma

We report the first identification of a circulating peptide from the amino-terminal end of proCNP. A specific radioimmunoassay was established based on antisera to the synthetic peptide proCNP(1-15). Extracts of plasma, drawn from patients with congestive heart failure or from sheep with experimental heart failure, were subjected to size exclusion and reverse-phase high-pressure liquid chromatography (HPLC) coupled to radioimmunoassay (RIA). These studies revealed the presence of an immunoreactive peptide with a molecular weight (M(r) approximately 5 kDa) similar to that expected for NT-proCNP(1-50), a potential fragment released during processing of pro(CNP). The same material was isolated from extracts of homogenized ovine pituitary, a tissue known to be a relatively enriched source of CNP. Plasma NT-proCNP levels in 22 patients with congestive heart failure (9.7 +/- 0.5 pmol/L, mean +/- SEM, range 5.4-13.7 pmol/L) were raised (P = 0.003) compared to those in 16 healthy volunteers (7.4 +/- 0.3 pmol/L, range 5.7-10.7 pmol/L) and were higher than levels reported for CNP in similar subjects. This first identification of circulating NT-proCNP opens the possibility of studying the factors regulating CNP production and metabolism in vivo.     

Non-esterified long-chain fatty acid metabolism in fed sheep at rest and during exercise

The role of circulating, non-esterified, long-chain fatty acids (NEFA) as a source of energy for the whole animal and skeletal muscle was investigated in fed non-pregnant sheep at rest and during exercise. Infusion of tracer quantities of [1-14C]oleic or [1-14C]stearic acid was combined with the use of arteriovenous difference studies on fed sheep at rest or during a 2 h period of exercise on a belt treadmill moving at 4.5 km h-1. At rest all parameters of NEFA metabolism indicated a minimal role for oxidation. Thus the concentration in plasma (0.07 +/- 0.01 mmol l-1), entry rate (0.08 +/- 0.02 mmol h-1 kg-1 body wt), contribution to whole animal oxidation (1.2 +/- 0.3%) and utilization of NEFA by skeletal muscle (0.046 +/- 0.008 mmol h-1 kg-1 muscle) were all low. Exercise prompted a shift to lipolysis and accordingly the above parameters increased markedly some 13-24-fold. The circulating concentration of ketone bodies showed only a small increase during exercise and consequently the role of ketone bodies as an energy source during exercise was minimal. Glucose utilization by skeletal muscle was considerable in animals at rest and it represented the most significant potential fuel of skeletal muscle. Exercise resulted in a sustained increase of 3-4-fold in the utilization of glucose by skeletal muscle. Thus the traditional view that NEFA and not glucose is a predominant fuel of skeletal muscle of fed sheep should be appraised.     

Responses of cardiac sympathetic nerve activity to changes in circulating volume differ in normal and heart failure sheep

Factors controlling cardiac sympathetic nerve activity (CSNA) in the normal state and those causing the large increase in activity in heart failure (HF) remain unclear. We hypothesized from previous clinical findings that activation of cardiac mechanoreceptors by the increased blood volume in HF may stimulate sympathetic nerve activity (SNA), particularly to the heart via cardiocardiac reflexes. To investigate the effect of volume expansion and depletion on CSNA we have made multiunit recordings of CSNA in conscious normal sheep and sheep paced into HF. In HF sheep (n = 9) compared with normal sheep (n = 9), resting levels of CSNA were significantly higher (34 +/- 5 vs. 93 +/- 2 bursts/100 heart beats, P < 0.05), mean arterial pressure was lower (76 +/- 3 vs. 87 +/- 2 mmHg; P < 0.05), and central venous pressure (CVP) was greater (3.0 +/- 1.0 vs. 0.0 +/- 1.0 mmHg; P < 0.05). In normal sheep (n = 6), hemorrhage (400 ml over 30 min) was associated with a significant increase in CSNA (179 +/- 16%) with a decrease in CVP (2.7 +/- 0.7 mmHg). Volume expansion (400 ml Gelofusine over 30 min) significantly decreased CSNA (35 +/- 12%) and increased CVP (4.7 +/- 1.0 mmHg). In HF sheep (n = 6) the responses of CSNA to both volume expansion and hemorrhage were severely blunted with no significant changes in CSNA or heart rate with either stimulus. In summary, these studies in a large conscious mammal demonstrate that in the normal state directly recorded CSNA increased with volume depletion and decreased with volume loading. In contrast, both of these responses were severely blunted in HF with no significant changes in CSNA during either hemorrhage or volume expansion.     

Ovine atrial natriuretic factor: sequence of circulating forms and metabolism in plasma.

The sequence of ovine ANF is not known, yet sheep have been used extensively for ANF studies. We sequenced the circulating form of ovine ANF from coronary sinus plasma of sheep in paced heart failure. The main circulating form was identical to human ANF(99-126). Small amounts of ANF identical to human ANF(103-126) and ANF(101-126) peptides were also found. Incubation of labeled ANF in ovine serum suggested ANF(103-126) could be a degradation product of ANF(99-126). The endopeptidase-24.11 degradation product ANF(99-105/106-126) was not found in ovine plasma, in contrast to human plasma where it was a minor component. These results show that while the main circulating forms are similar in sheep and humans, there are differences in the minor peptides.     

Cytokines are not a requisite part of the pathophysiology leading to cardiac decompensation

An increase in circulating levels of proinflammatory cytokines has been proposed as an important pathogenic factor contributing to cardiac injury during chronic heart failure. To determine whether plasma levels of the cytokines tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) increase during pacing-induced heart failure, we paced the hearts of seven dogs at 210 beats/min for 3 weeks and at 240 beats/min for an additional week to induce severe clinical signs of cardiac decompensation. Hemodynamic measurements and blood samples from the aorta and coronary sinus (CS) were taken at control, at 3 weeks, and in end-stage failure. Decompensated heart failure occurred at 29 +/- 1.8 days, when left ventricular (LV) end-diastolic pressure was 25 +/- 1.3 mmHg, LV systolic pressure was 92 +/- 4 mmHg, mean arterial pressure was 77 +/- 3 mmHg, and dP/dtmax was 1219 +/- 73 (all P < 0.05 vs control). Arterial concentration of IL-6 was 12 +/- 4.0 U/ml at control, 11 +/- 2.7 U/ml at 3 weeks, and 10 +/- 1.7 U/ml in end-stage failure (NS). At the same time points, IL-6 in CS plasma was 12 +/- 3.5, 13 +/- 2.8 and 11 +/- 2.4 U/ml, respectively (NS vs control and vs arterial concentrations). TNF-alpha did not reach detectable concentrations in arterial or CS blood at any time. TNF-alpha and IL-6 concentrations did not increase in arterial blood, were not released in the CS from the heart during the development of pacing-induced heart failure, and can not universally be implicated in the pathogenesis of all forms of cardiac dysfunction. Our findings are consistent with other data from patients in which severe heart failure was not associated with increased levels of circulating cytokines.     

Changes in arterial blood pressure, heart rate and haematocrit during acute hyperkalaemia in conscious sheep.

The systolic, diastolic and mean arterial blood pressures, heart rate and haematocrit were measured at 15 minute intervals before, during and after 2 hour infusions of 0-4 mol.l-1 NaCl at 2-2 ml min-1 into conscious intact sheep and 0-4 mol. l-1 KCl at 2-2 ml. min-1 into conscious sheep which were either intact or adrenalectomized. The haemotocrit was also measured in splenectomized sheep receiving 0-4 mol. l-1 KCl. The NaCl infusion had no significant effect on blood pressure(BP), heart rate and haematocrit. Both intact and adrenalectomized sheep were able to withstand an increase in plasma potassium concentration in excess of 50% of the preinfusion concentration before any substantial fall in BP occurred. In intact and adrenalectomized sheep, heart rate and haematocrit increased rapidly and progressively throughout the potassium infusions and at maximum plasma potassium concentration the mean increments in these parameters for both groups of sheep were 21-6+/-2-69 beats/min and 7-5+/-0-47% respectively. Heart rate and haematocrit were more closely correlated with the plasma potassium concentration than with any other variable measured in these experiments. Adrenalectomy did not reduce the ability of the sheep to maintain their BP or to increase their heart rate and haematocrit. As the mean increase in haematocrit during potassium infusion into splenectomized sheep was 1-3+/-0-45% most of the increase in haematocrit observed in the potassium-infused intact and adrenalectomized sheep was caused by ejection of red cells from the spleen into the circulation.     

Pro-atrial natriuretic peptide (1-98): the circulating cardiodilatin in man

The nature of plasma cardiodilatin, the amino-terminal product of the human pro-atrial natriuretic peptide, was investigated by two separate radioimmunoassays directed against the N-terminal and the putative C-terminal of the cardiodilatin molecule: ANP-[Asn1-Lys16] and ANP-[Lys87-Arg98], respectively. Serial dilutions of normal and cardiac failure plasma exhibited parallelism with the synthetic peptide standard curves in both assays. The concentrations of N- and C-terminal cardiodilatin-immunoreactivity equivalents (-IE) were significantly higher in cardiac failure patients. N-terminal-IE: 912 +/- 87, normal subjects 129 +/- 13 (mean +/- SEM); C-terminal-IE: 7979 +/- 1784, normal subjects 895 +/- 213 (both p less than 0.001). Although the concentrations determined by the two assays were not identical, significant correlations were found between them in both normal subjects (r = .69, p less than 0.001) and cardiac failure patients (r = .72, p less than 0.01). Characterisation by gel permeation and fast protein liquid chromatography demonstrated coelution of the N- and C-terminal cardiodilatin immunoreactivities in a single chromatographic peak. These results suggest that the circulating cardiodilatin in normal subjects and patients with cardiac failure contains the entire prohormone amino-terminal sequence ANP-[Asn1-Arg98].     

Plasma levels and cardiovascular gene expression of urotensin-II in human heart failure

The peptide urotensin-II (U-II) has been described as most potent vasoconstrictor identified so far, but plasma values in humans and its role in cardiovascular pathophysiology are unknown. We investigated circulating urotensin-II and its potential role in human congestive heart failure (CHF). We enrolled control individuals (n=13; cardiac index [CI], 3.5+/-0.1 l/min/m2; pulmonary wedge pressure [PCWP], 10+/-1 mm Hg), patients with moderate (n=10; CI, 2.9+/-0.3 l/min/m2; PCWP, 14+/-2 mm Hg) and severe CHF (n=11; CI, 1.8+/-0.2 l/min/m2; PCWP, 33+/-2 mm Hg). Plasma levels of urotensin-II differed neither between controls, patients with moderate and severe CHF nor between different sites of measurement (pulmonary artery, left ventricle, coronary sinus, antecubital vein) within the single groups. Hemodynamic improvement by vasodilator therapy in severe CHF (CI, +78+/-3%; PCWP, -55+/-3%) did not affect circulating U-II over 24 h. Preprourotensin-II mRNA expression in right atria, left ventricles, mammary arteries and saphenous veins did not differ between controls with normal heart function and patients with end-stage CHF. In conclusion, urotensin-II plasma levels and its myocardial and vascular gene expression are unchanged in human CHF. Circulating urotensin-II does not respond to acute hemodynamic improvement. These findings suggest that urotensin-II does not play a major role in human CHF.     

Plasma and urinary clearance rates of atrial natriuretic factor during ontogeny in sheep

The present study was designed to determine the plasma clearance rate of atrial natriuretic factor (ANF) during development in chronically-instrumented fetal, newborn and adult non-pregnant sheep. To determine the contribution of the kidney in the metabolism of ANF, urinary clearance of ANF was also measured. Intravenous infusion of ANF (0.025 and 0.1 microgram.min-1.kg-1) produced a significant decrease in mean arterial blood pressure in newborn lambs and in adult non-pregnant sheep. Estimated plasma ANF clearance rate for the 0.025 and 0.1 microgram.min-1.kg-1 ANF infusion rate were respectively 177 +/- 55 and 155 +/- 34 ml.min-1.kg-1 in fetuses, 138 +/- 26 and 97 +/- 13 ml.min-1.kg-1 in newborn lambs and, 148 +/- 33 and 103 +/- 25 ml.min-1.kg-1 in adult nonpregnant ewes. Fetal, newborn and adult ANF plasma clearance rates during high ANF infusion rate (0.1 microgram.min-1.kg-1) were not significantly different. Low or high ANF infusion rate was not associated with significant changes in urinary ANF concentration or urinary ANF excretion rate. Taken together, the present study demonstrates that ANF plasma clearance rate is similar in fetal, newborn and adult non-pregnant sheep and that the excretory function of the kidney contributes only minimally to ANF plasma clearance rate.     

Plasma nitrate accumulation during the development of pacing-induced dilated cardiac myopathy in conscious dogs is due to renal impairment.

Heart failure is associated with an increase in plasma nitrate and nitrite (NOx). To date there is still some controversy regarding the causes of nitrate accumulation during the development of heart failure. The goal of this study was to analyze the underlying mechanisms that cause accumulation of plasma nitrates during the development of heart failure in dogs. Dogs were chronically instrumented for measurement of hemodynamics and renal function. Hearts were paced initially at 210 bpm for 3 weeks and then at 240 until the development of heart failure. Hemodynamics, renal function, renal blood flow, arterial blood gases, hemoglobin, plasma and urine NOx levels, and creatinine levels were measured weekly. Heart failure was assessed by hemodynamic alterations, physical signs such as lethargy, ascites, cachexia, and postmortem evidence of cardiac hypertrophy. LVSP (from 127 +/- 3 to 106 +/- 3 mmHg), LV dP/dt (from 2658 +/- 173 to 1439 +/- 217 mmHg/s), MAP (from 101 +/- 1.9 to 83 +/- 1.8 mmHg) fell, whereas LVEDP tripled (from 6.4 +/- 0.9 to 20 +/- 2.6 mmHg), and heart rate rose (from 101 +/- 4.2 to 117 +/- 6.3 bpm), all changes P < 0.05. RBF (from 146 +/- 10 to 96 +/- 9.9 ml/min), urine output (V) (from 0.26 +/- 0.02 to 0.16 +/- 0.02 ml/min), GFR (from 63 +/- 1.8 to 49 +/- 2 ml/min), and Na excretion (from 45 +/- 4.5 to 14 +/- 4.6 microEq/min) all decreased (P < 0.05), whereas RVR increased (from 0.68 +/- 0.05 to 0.94 +/- 0.1 mmHg/ml/min). These changes took place during a rise in plasma NOx (from 3.7 +/- 0.5 to 16+/-3.3 microM), a decrease in urine NOx (from 33 +/- 9.9 to 8.1 +/- 4.9 microM), and a concurrent increase in NOx reabsorption (from 221 +/- 31 to 818 +/- 166 nmol/min). There was a direct correlation between the increase in plasma NOx levels and an increase in filtered load (r(2) = 0.97, P = 0.02), a negative correlation between NOx levels and NOx excretion (r(2) = 0.65 P < 0.09), and a direct correlation between plasma NOx levels and NOx reabsorption (r(2) = 0.97, P = 0.02). These results indicate that elevated plasma NOx during heart failure are most likely the result of an impairment of the renal function and not increased NOx production. Furthermore, without knowing changes in renal function the measurement of plasma NOx in and of itself is a meaningless index of NO formation.     

Immunoreactive endothelin in human plasma: marked elevations in patients in cardiogenic shock

Endothelin (ET) is a recently discovered, endothelium-derived peptide that may be the most potent vasoconstrictor yet identified. Although there is much interest in the possible systemic actions of circulating ET in vivo, there is no data on ET levels under physiological conditions, or in cardiovascular disease. We used a radioimmunoassay that was sufficiently sensitive to detect ET immunoreactivity (irET) in the SepPak-extracted plasma from 14 healthy volunteers in a range from 0.03 to 0.69 pg/ml (mean 0.26 +/- 0.236 pg/ml). ET levels were not significantly different from normal in 5 patients with stable congestive heart failure (0.46 +/- 0.36 pg/ml). However, irET was increased markedly in 6 patients in cardiogenic shock (3.65 +/- 1.14 pg/ml), and (less so) in 6 patients on chronic dialysis (1.05 +/- 0.41) and in 4 with pulmonary hypertension (1.52 +/- 0.45) (p less than 0.001). The present results suggest that circulating irET concentration is responsive to altered cardiovascular conditions, and therefore support a potential role for ET as a vasoactive hormone.     

Radioimmunoassay of 5-methoxy tryptophol in sheep plasma and pineal glands

No 5-methoxytryptophol (ML) could be detected in sheep plasma using a specific, sensitive radioimmunoassay developed for the purpose. Blood samples were collected from sheep during darkness and daylight and during various stages of the estrous cycle, but in no sample was the ML content above the detection limit of the method. Addition of 1 mM pargyline and neostigmine to blood immediately after collection to block metabolism did not result in a detectable ML concentration. The failure to detect ML was not due to degradation since added ML was not degraded by blood enzymes even after 16 hours incubation at 37 degrees C. Injection of 100 microgram and 1 mg ML sc in sheep resulted in a rapid rise of ML to 95-130pg/ml and 560-1000pg/ml respectively and disappearing with a half life of approximately 15-20 minutes. Sheep pineal glands collected during the light phase contained ML (51 +/- 5pg/mg tissue. X +/- SE, n = 7) which represents less than 6% of the melatonin content. It is concluded that if ML is present in sheep blood it is present at very low levels. It is thus unlikely to be a major circulating pineal hormone in this species, however, its role within the CNS as a local hormone cannot be excluded.     

Lung fluid balance during acute renal failure in sheep

To determine whether uremia changes lung vascular permeability, we measured the flow of lymph and proteins from the lungs of acutely uremic sheep. Acute renal failure was induced by either bilateral nephrectomy or by reinfusing urine. Both models of renal failure increased the plasma creatinine from 0.8 +/- 0.3 to 11 +/- 1 mg/dl in 3 days but caused no significant change in the flow of lymph from the lungs. To determine whether uremia increased the protein clearance response to elevated pulmonary microvascular pressures, we inflated a balloon in the left atrium for 2 h before and 3 days after inducing acute renal failure. In seven sheep, before removing the kidneys, the 20 cmH2O elevation of left atrial pressure increased the protein clearance 3.9 +/- 3.0 ml/h (from 9.5 +/- 4.9 to 13.4 +/- 5.4 ml/h). Three days after the bilateral nephrectomy the same increase in left atrial pressure increased the protein clearance 6.4 +/- 3.6 ml/h (from 6.1 +/- 2.1 to 12.5 +/- 5.2 ml/h), which was a significantly larger increase than that measured before the nephrectomy (P less than 0.05). Sham nephrectomy in seven sheep caused the protein clearance response to the elevated left atrial pressure to fall from 4.7 +/- 1.9 ml/h before the sham nephrectomy to 2.6 +/- 1.4 ml/h 3 days later (P less than 0.05). Uremia due to reinfusion of urine in five sheep did not affect the protein clearance response to elevations in left atrial pressure. Neither model of acute uremia increased the postmortem extravascular lung water volume.(ABSTRACT TRUNCATED AT 250 WORDS)     

Correlation between pentosidine and endothelin-1 in subjects undergoing chronic hemodialysis.

Advanced glycation end-products (AGEs), which accumulate in the blood and tissues of patients with chronic renal failure (CRF) undergoing chronic hemodialysis, play an important role in the pathogenesis of uremic complications. Endothelin 1 (ET1), a 21-amino acid peptide with vasoconstricting and mitogenic properties, is an important factor in the endothelial dysfunction occurring in uremia. The circulating levels of both AGEs and ET1 have been reported to be increased in chronic renal failure. In the present study we evaluated the possible relationship between pentosidine and ET1 plasma levels in CRF patients undergoing chronic hemodialysis treatment. The plasma concentrations of "free" and bound pentosidine (HPLC methods) and endothelin-1 (RIA method) were measured before the hemodialysis session in 40 nondiabetic CRF patients (22 males and 18 females; 54+/-3 years) on chronic hemodialysis for at least 1 year. Forty age- and sex-matched normal subjects served as a control group. In hemodialyzed patients, the overall pentosidine residues and pentosidine-free adduct plus pentosidine-free adduct bound reversibly to protein levels (24.9+/-2.04 pmol/mg protein and 110.5+/-5.9 pmol/ml, respectively) were significantly higher than those recorded in normal subjects (2.0+/-0.2 pmol/mg protein and 0.7+/-0.2 pmol/ml, respectively ). Endothelin-1 was also significantly (p<0.01) increased in CRF patients (10.6+/-0.4 pmol/ml in CRF patients and 2.7+/-0.3 pmol/ml in normal subjects). A significant positive correlation (p<0.01) was seen between "total" pentosidine (pentosidine residues and pentosidine-free adduct plus pentosidine-free adduct bound reversibly to protein) levels and endothelin-1 plasma values. The correlation between pentosidine and endothelin-1 provides further evidence that some AGEs exert a detrimental effect on the vascular endothelium, thereby contributing to the hypertension and other cardiovascular damage seen in CRF patients.     

Effect of myiasis and acute restraint stress on plasma levels of immunoreactive beta-endorphin, adrenocorticotrophin (ACTH) and cortisol in the sheep

Cutaneous myiasis in sheep arising from the activity of Lucilia cuprina larvae can result in significant physiological changes in susceptible animals. The stress imposed on the pituitary-adrenal axis of the sheep in response to myiasis and acute restraint is the subject of this investigation. Merino wethers were exposed to handling restraint, and blood sampling, during examination for blowfly strike; where necessary, they were treated for cutaneous myiasis. Significant changes in the plasma concentrations of immunoreactive beta-endorphin (beta-EP), ACTH and cortisol were found in sheep with extensive myiasis, as compared with unstruck sheep or those with only localized myiasis. In five susceptible sheep with extensive cutaneous myiasis, mean plasma levels of beta-EP, ACTH and cortisol were 307 +/- 71 pg ml-1, 953 +/- 58 pg ml-1 and 232 +/- 46 nmol l-1 respectively, compared with 818 +/- 89 pg ml-1, 641 +/- 41 pg ml-1 and 107 +/- 17 nmol l-1 in six unstruck sheep handled similarly. Whereas significant increases in plasma ACTH and cortisol can result from pituitary-adrenal responses to acute emotional or surgical stress, and are usually accompanied by a concomitant release of beta-EP from the pituitary, the present findings indicate a marked reduction in beta-EP levels and a significant increase in ACTH and cortisol in sheep following blowfly strike and acute handling restraint. This result suggests that cutaneous myiasis in susceptible sheep can alter the pituitary-adrenal response to acute restraint stress, and this could occur either by an alteration of precursor processing in the pituitary or by the selective release of ACTH.     

Endotoxemia produces an increase in arterial but not venous lipid peroxides in sheep

Our purpose was to determine the effect of an endotoxin-induced lung injury on circulating lipid peroxides. We measured both malondialdehyde (MDA) and conjugated dienes (as optical density at 233 nm) in aortic and venous plasma and lung lymph in 10 unanesthetized sheep given 1 microgram/kg of Escherichia coli endotoxin. Total lipids and prostanoids 6-ketoprostaglandin F1 alpha and thromboxane B2 were also measured. Six control sheep were also studied. Animals were monitored for a 12-h period and then killed, and lung tissue MDA was determined. A two-phase endotoxin response was noted with an initial pulmonary hypertension followed by a steady-state increase in protein-rich lung lymph flow (QL) between a 3- and 6-h period. Aortic plasma MDA was significantly increased from a base line of 4.8 +/- 1.4 to 8.9 +/- 1.6 and 7.5 +/- 1.3 nmol/ml at 1 and 4 h post-endotoxin. Aortic plasma conjugated dienes increased in all 10 sheep post-endotoxin. Venous levels of both MDA and conjugated dienes were not significantly increased. Lung QL increased two- to three-fold. Lung lymph MDA increased significantly at 1 h post-endotoxin. Lymph conjugated dienes decreased. Plasma and lymph lipid peroxide levels returned to base line by 12 h in most animals. However, tissue MDA remained significantly increased in all sheep from base line of 45 +/- 9 to 85 +/- 14 nmol/g tissue. We conclude that both MDA and conjugated dienes are transiently released into aortic plasma during endotoxin-induced oxidant lung injury.(ABSTRACT TRUNCATED AT 250 WORDS)