Intrarenal infusions of endothelin in conscious dogs: interactions with prostanoids and angiotensin II

Endothelin (2, 5, and 10 pmol/kg/min) was infused into the renal artery of conscious dogs, producing graded and progressive reductions in renal blood flow (RBF) without initial vasodilatation, parallel reductions in glomerular filtration rate (GFR), and reduced Na+ excretion, but little change in urine flow. Pretreatment of the dogs with either ibuprofen (20 mg/kg orally) or aspirin (30 mg/kg p.o.) did not significantly alter the effects of endothelin (5 pmol/kg/min) on RBF, GFR, or Na+ excretion. However, endothelin caused antidiuresis in these cyclooxygenase-inhibited dogs, indicating that the effects of endothelin on water reabsorption were prostanoid mediated. Treatment with captopril (1.5 mg/kg + 0.5 mg/kg/h) did not significantly alter any of the responses to endothelin. The local effects of endothelin in the kidneys of conscious dogs were vasoconstriction and reduced Na+ excretion which were not mediated or modified by either angiotensin II or prostanoids.

Regional systemic ANP differences in fetal lambs: role of coronary sinus outflow distribution

Although it is known that the atrial natriuretic peptide (ANP) level in right ventricular (RV) blood supplying the caudal part of the fetus is greater than in left ventricular blood perfusing the cephalic part of the fetus, the extent to which any preferential passage of coronary sinus blood into the right ventricle contributes to regional differences between ANP levels in fetal cephalic and caudal arteries is unknown. To address this question, experiments were performed in eight late-gestation fetal lambs, 3-7 days after catheters were inserted into the left atrium, major arteries and veins, and coronary sinus (via the left hemiazygous vein). The plasma ANP level in the abdominal aorta (171 +/- 33 pg/ml) was higher than in the carotid artery (103 +/- 15 pg/ml; P < 0.05), and both were lower than in the coronary sinus (736 +/- 89 pg/ml; P < 0.005). The coronary sinus outflow, measured with radioactive microspheres injected into the hemiazygous vein, was preferentially distributed to the right ventricle (94.7 +/- 1.3%) and thence to the abdominal aorta (89.5 +/- 1.6%). This streaming of the coronary sinus outflow contributed 13.3 +/- 0.9 and 1.4 +/- 0.4 pg/ml to ANP levels in the abdominal aorta and carotid artery, respectively, and thereby accounted for 11.9 +/- 0.9 pg/ml of the abdominal aorta-carotid artery ANP difference of 68 +/- 25 pg/ml.(ABSTRACT TRUNCATED AT 250 WORDS)

Nitric oxide inhibition does not prevent the hypotensive response to increased renal perfusion in rabbits

1. The involvement of nitric oxide (NO) and platelet activating factor (PAF) in the systemic depressor responses to increased renal perfusion pressure (RPP) were investigated. 2. In anaesthetized rabbits, the left kidney was perfused via an extracorporeal circuit which allowed RPP to be increased from 65 mmHg to 125 mmHg. The response of systemic blood pressure (SBP) to increasing RPP was measured in the same rabbits. 3. One group of rabbits (n = 5) was treated with NG-nitro-L-arginine (NOLA) to inhibit NO synthase activity (20 mg/kg i.v. bolus). Another group (n = 5), received 250 mmol/L NaHCO3 (4 mL/kg bolus) as vehicle treatment. 4. Following an increase in RPP to 125 mmHg, SBP fell at a rate of 0.43 +/- 0.06 mmHg/min in the vehicle treated rabbits. After NO synthase inhibition the rate of fall in SBP of 0.34 +/- 0.07 mmHg/min was not significantly different from that in the vehicle group (P = 0.3). 5. Blockade of NO synthesis did not alter the renal blood flow, renal vascular resistance changes and pressure-related natriuresis and diuresis responses to increased RPP to 125 mmHg. 6. PAF receptor blockade, using WEB 2086 (0.5 mg/kg plus 0.5 mg/kg/h), did not alter the systemic, renal haemodynamic or urinary responses to increasing renal perfusion pressure to 125 mmHg. 7. These findings indicate that neither NO nor PAF play an important role in the blood pressure lowering activity, intrarenal haemodynamics and urinary excretory responses observed when RPP was increased to a level within the physiological range.

Effects of exercise on aspects of visual function

Strenuous exercise has been reported to affect various aspects of visual and ocular function. In the first of two experiments, the effects of cycling, jogging and stair running on a range of visual functions were examined. None of these forms of exercise was found to have any significant effect on visual acuity, refractive error, dark focus, amplitude of accommodation or pupil size. Contrast sensitivity (CS), measured by an ascending method of limits (AML), was found to improve significantly after cycling and jogging but not after stair running. To investigate if the apparent improvement in CS was related to a change in 'sensitivity' or a change in decision criteria, CS was re-measured before and after cycling using both the AML and a 'criterion-free' method of constant stimuli (MOCS) procedure. Results obtained using the AML, confirmed the findings of the first experiment. However, results obtained using the MOCS procedure showed no significant change with exercise. This suggests that the improvement in CS found using the AML was due to a shift in subjects' decision criteria rather than a physiological change in 'sensitivity'. It is argued that this change in decision criteria may be related to the positive mood changes which have been found to occur after exercise. This study demonstrates the importance of differentiating between changes in 'sensitivity' and changes in decision criteria especially where mood or motivation (and hence decision criteria) may be confounded with the independent variable. This is particularly important when evaluating the effects of exercise on visual function or evaluating the efficacy of vision training.

Exercise does not increase visual field sensitivity

The effect of exercise on visual field sensitivity was investigated for both static and kinetic visual fields using the Humphrey Field Analyser (HFA). The visual fields of 20 young visually normal subjects were measured before and after a 10-min controlled period of exercise. Ten of these 20 subjects then formed a control group, where the same experimental regime was followed without the exercise period. A significant increase in mean static sensitivity in the superior field was found as a result of exercise; however, this is likely to be a learning effect as a similar increase was also found for the control condition. Exercise had no other effect on either the kinetic or static visual fields.

Nonuniform enhancement of baroreflex sensitivity by atrial natriuretic peptide in conscious rats and dogs

The influence of atrial natriuretic peptide (ANP) on the blood pressure (BP)-heart rate (HR) baroreflex was studied in conscious chronically instrumented dogs and rats. In both species, sigmoid steady-state baroreflex curves were constructed from the baroreflex changes in HR to alternating slow injections of vasopressor and vasodepressor drugs. When this method was used in dogs, ANP caused a small but significant (P < 0.05) enhancement of the sensitivity (22 +/- 10%) and curvature (26 +/- 10%) of the baroreflex, which was without a change in HR range. In rats, ANP had no significant effect on any baroreflex parameter derived from steady-state curves. By contrast, in the same rats, fast reflex HR responses to rapid increases in BP (ramp) exposed a substantial (81 +/- 21%) ANP-induced enhancement of baroreflex sensitivity. Contribution from arterial vs. nonarterial afferents to the baroreflex is not uniform between these two techniques (steady state reflects largely arterial baroreceptor input, ramp evokes a greater proportion of cardiopulmonary afferent activation). The present study demonstrated that baroreceptor HR reflex responses to ANP depend on the baroreflex techniques employed and probably exposed a selectivity by ANP for nonarterial baroreflex pathways.

Pressure range for release of renomedullary depressor substance in rabbits

We investigated the relation between renal perfusion pressure and the release of a renal vasodepressor substance in vivo to determine whether this substance was released at physiological pressures. We perfused the left kidneys of anesthetized rabbits using an extracorporeal circuit that allowed renal perfusion pressures to be set at 65 mm Hg (control) and increased to 95, 125, 155, or 185 mm Hg for 30-minute experimental periods. Systemic blood pressure did not change significantly when renal perfusion pressure was maintained at 65 mm Hg throughout. When renal perfusion pressure was increased to 95, 125, 155, or 185 mm Hg, systemic blood pressure fell significantly at rates of 0.17 +/- 0.04, 0.79 +/- 0.31, 0.60 +/- 0.11, and 2.18 +/- 0.79 mm Hg/min, respectively (P < .05). Restoration of renal perfusion pressure to 65 mm Hg abruptly reversed the falls in systemic blood pressure in each group. There was a natriuresis and diuresis that were both pressure related and progressive in the face of each constant level of increased renal perfusion pressure. In summary, there was a continuum of arterial vasodepressor responses across a renal perfusion pressure range from resting pressure to 185 mm Hg. We suggest that the threshold level for the release of significant amounts of a renal medullary depressor substance, probably medullipin, is just above normal arterial blood pressure and that the rate of release increases with increasing arterial pressure.

Reliability of visual performance measurement under optical degradation

Small groups of experienced subjects wore three types of bifocal contact lens which were shown to reduce visual performance at distance and near conditions. Monitor-based contrast sensitivity, Pelli-Robson contrast threshold, and high- and low-contrast visual acuity were each measured on two separate occasions. For each bifocal contact lens type the test-retest difference did not increase significantly with reduction in visual performance. Despite this the reliability of the visual performance measures was shown to be reduced compared to previous reports with normal well-corrected subjects and the test-retest repeatability coefficients (95% confidence limits) increased as the average visual performance declined. The poor reliability is of interest to the practitioner fitting bifocal contact lenses, and confirms previous suggestions that reliability may be related to visual degradation (e.g. ocular disease). In addition Pelli-Robson contrast thresholds were shown to be correlated with the spatial frequency represented by the presumed fundamental frequency of the component letters.

Optical performance of decentered bifocal contact lenses

Contact lenses frequently do not center over the pupil. The potential changes in optical performance introduced by poor centration of bifocal contact lenses have only been described previously from theoretical considerations. The present study measured the modulation transfer function (MTF) of rigid concentric-design refractive and rigid diffractive bifocal contact lenses with varying apertures and amounts of decentration. Decentration was shown to have a greater effect on the MTF of the refractive than on the MTF of the diffractive bifocals. The MTF of the refractive bifocals was related to the proportion of the aperture covered by the central optic zone (COZ). Unexpectedly, the MTF of the distance focus of the diffractive bifocal contact lenses was reduced at moderately high spatial frequencies. The practitioner should be aware of the effects of decentration of bifocal contact lenses.

Mediators of the hypotensive response to increased renal perfusion in rabbits

We have previously shown that increasing the renal perfusion pressure by using an extracorporeal circuit in anesthetized rabbits resulted in a progressive fall in systemic arterial pressure. Prior ablation of the renal medulla with 2-bromoethylamine abolished the hypotensive response. In the present study, we investigated whether vasodilator prostanoids or platelet activating factor (PAF), both known to be produced in the renal medulla, were responsible for the hypotensive response to increased renal perfusion pressure. Anesthetized animals were treated with indomethacin (5 mg/kg + 0.5 mg/kg per hour), the PAF antagonist WEB 2086 (0.5 mg/kg + 0.5 mg/kg per hour), enalaprilat (2 mg/kg + 10 micrograms/kg per hour), or all three agents. In response to acute elevation of renal artery pressure to 170 mm Hg, systemic mean arterial pressure fell at 0.76 +/- 0.17, 0.59 +/- 0.08, and 0.76 +/- 0.17 mm Hg/min in the indomethacin, WEB 2086, and enalapril groups, respectively. These responses were not significantly different from the rate of 1.00 +/- 0.21 mm Hg/min in a control group that received vehicle infusion alone. Renal blood flow and the diuretic and natriuretic responses were also similar in all groups. Thus, increased renal perfusion pressure resulted in a progressive fall in systemic arterial pressure that was not mediated by PAF, prostaglandins, or suppression of renin release and angiotensin II production.

Afferent control of vasopressin and renin release during haemorrhage in normal and autonomically blocked rabbits

1. The role of the arterial and cardiac baroreceptors on the arginine vasopressin (AVP) and plasma renin activity (PRA) responses to haemorrhage was studied in conscious rabbits. They were bled at a rate of approximately 3% of their blood volume (BV)/min, both when the autonomic nervous system (ANS) was intact and during ANS blockade, which markedly enhances the AVP response due to the much greater haemodynamic disturbance. Under each condition of ANS function 2 x 2 factorial analysis was performed, each with four groups of rabbits, including animals with both sets of baroreceptors working, one or other set working and neither set working. 2. With intact ANS, haemorrhage had to be terminated at different times in the four groups. This presents problems for factorial analysis due to differences in the relationship between plasma AVP (or PRA) and release rate. A method for overcoming this was developed by extrapolating the BV-log AVP curves to a common time from the start of bleeding. 3. Under both conditions of ANS function the arterial and cardiac baroreceptors together accounted for 90-95% of the rise in AVP during haemorrhage. With normal ANS function, the rise in AVP was about 70% through cardiac (probably ventricular) baroreceptors (P = 0.01) and about 30% through arterial baroreceptors (P = 0.08). This compares with an earlier study at a rate of bleeding of 1.8% BV/min, where the entire drive came from the cardiac receptors. During ANS blockade, plasma AVP was enhanced approximately five-fold, which was mostly mediated through the arterial baroreceptors, but the cardiac baroreceptor component was also greater; arterial/cardiac baroreceptor drive was 2/1. 4. Baroreflexes played no role in renin release during haemorrhage, but the experiments with ANS blockade suggest that a hormonal factor, which was related to the cardiac innervation, may limit the rise in PRA in the latter part of haemorrhage.

Regional blood flow effects of ANP in conscious dogs: preferential gastrointestinal vasoconstriction

We studied total and regional blood flow responses to human atrial natriuretic peptide (alpha-hANP) using radioactive microspheres in six conscious dogs. Hemodynamic responses to infusions of alpha-hANP at 75 ng.kg-1.min-1 were determined in each dog in the presence and absence of autonomic reflexes using the ganglion blocking agent pentolinium. When autonomic reflexes were blocked, alpha-hANP caused a substantial reduction in gastrointestinal (GI) vascular conductance (35%) but had no significant effects in brain, kidneys, liver, skeletal muscle, or skin. This alpha-hANP-induced fall in GI conductance contributed more than 40% to the fall in total peripheral conductance (TPC) of 24% occurring after autonomic blockade. A fall in myocardial vascular conductance, most prominent in the left ventricle, contributed a further 40% to the fall in TPC. When autonomic reflexes were intact, alpha-hANP caused vasoconstriction in the GI region (29% fall in vascular conductance), had no significant effects on myocardial vascular conductance but significantly increased splenic vascular conductance. In addition to these systemic responses, alpha-hANP infusion also significantly reduced pulmonary vascular conductance, independent of autonomic reflex activity or changes in pulmonary artery pressure. Thus our results in conscious dogs demonstrate that alpha-hANP causes a systemic vasoconstriction, most pronounced in the GI region.

Evidence for a renomedullary vasodepressor system in rabbits and dogs

Renal perfusion was increased in anesthetized rabbits and dogs by using an extracorporeal circuit. When left kidney perfusion pressure was raised in rabbits (145-240 mm Hg), arterial pressure fell by 1.34 +/- 0.20 mm Hg/min. Pretreatment of the rabbits with 2-bromoethylamine hydrobromide, which destroyed the renal medulla, abolished the fall in arterial pressure (-0.08 +/- 0.08 mm Hg/min) in response to increased renal perfusion pressure. In dogs (with blockade of autonomic ganglia by pentolinium, converting enzyme inhibition [captopril/enalaprilat], and surgical renal denervation), increasing renal perfusion pressure to 170-220 mm Hg resulted in a fall in arterial pressure by 0.32 +/- 0.03 mm Hg/min (or by 28.9 +/- 3.1 mm Hg over a 90-minute period). Mean arterial pressure did not change significantly in identically prepared dogs not subjected to increased renal perfusion pressure, whereas pretreatment of dogs with bromoethylamine abolished the hypotensive response to increased renal perfusion pressure. Thus, the hypotensive response to increased renal perfusion was dependent on the presence of an intact renal medulla, but hypotension still occurred in the presence of converting enzyme inhibition, autonomic ganglion blockade, and renal denervation. The results provide in vivo evidence in two species that a vasodepressor factor from the renal medulla is released in response to increased renal perfusion.

Afferent vascular resistance control during hemorrhage in normal and autonomically blocked rabbits

We examined the role of the arterial and cardiac baroreceptors on the hindquarter conductance and heart rate responses of conscious rabbits bled at approximately 3% blood volume (BV)/min to 80% BV (i.e., 20% BV removed). We used rabbits with both sets of baroreceptors working and when only one or neither sets was working. Each animal was studied with normal effector function and during autonomic blockade (hormonal + local effectors), where release of arginine vasopressin (AVP) and renin (angiotensin II, ANG II) were enhanced. The local response (LR) to hemorrhage was determined in a separate group of neurohumorally blocked rabbits. The estimated constrictor response (ECR) was the difference between the LR and net conductance response. In normal rabbits, the ECR was 49 units, with the estimated arterial-to-cardiac barorecptor drive ratio approximately 2.8:1 and with the two receptor groups acting by simple addition. Both barorecptors contributed to the rise in heart rate, with the relative arterial-to-cardiac baroreceptor drive ratio approximately 4:1. When hemorrhage was performed during autonomic blockade, ECR was 84 units (compared with normal rabbits, P less than 0.01), but blood pressure was poorly maintained and the constrictor effect was not under baroreceptor control. Although the baroreceptors were critical for AVP release during autonomic blockade, they played no role in renin release (ANG II production); the latter was released in large amounts, producing near-maximum constriction, which was unrelated to the afferent input. Thus neurally mediated regulation during hemorrhage has substantial advantages over that mediated primarily through the pressor hormones.

Influence of higher brain centres and vasopressin on the haemodynamic response to acute central hypovolaemia in rabbits

We tested whether suprapontine brain centres contribute to the sudden failure of vasoconstriction that occurs in unanaesthetized rabbits during acute reduction in central blood volume. Haemorrhage was simulated by gradually inflating a cuff around the thoracic inferior vena cava so that cardiac output fell by about 8% per min. In intact rabbits, and in rabbits that had undergone craniectomy but not decerebration, the haemodynamic response to simulated haemorrhage was always biphasic. During the first, compensatory phase, systemic vascular conductance fell almost in proportion to the fall in cardiac output so that arterial pressure fell by only about 10 mmHg. When cardiac output had fallen by about 50%, a decompensatory phase supervened in which systemic vascular conductance rose abruptly, arterial pressure fell steeply to less than 40 mmHg, and the plasma arginine vasopressin (AVP) level rose. High mesencephalic decerebration did not affect the compensatory phase, but it abolished the decompensatory phase and there was no rise in the plasma AVP level. The decompensatory phase was not restored by intravenous administration of AVP. We came to two conclusions as a result of this study. Suprapontine brain centres do not influence the arterial baroreflex-mediated vasoconstriction that occurs during the first phase of acute central hypovolaemia. However, the sudden failure of vasoconstriction that occurs during the second phase of acute central hypovolaemia, attributable to a signal from the heart and mediated by a delta-opioid receptor mechanism in the brainstem, does depend on the integrity of suprapontine brain centres, though not on neurohypophysial AVP release.

Oxyhaemoglobin increases the production of endothelin-1 by endothelial cells in culture

Cultured endothelial cells from bovine thoracic aortas conditioned with serum-free culture media released an endothelin-1 (ET)-1-like substance. Concentrations of ET-1-like material were determined by bioassay as contractions of isolated ring segments of dog internal mammary vein and by radioimmunoassay. ET-1-like immunoreactivity (ET-1-IR) increased progressively over a 24 h conditioning period and correlated with the bioassay for the first 12 h. Oxyhaemoglobin (1-3 microM) caused a significant two-fold increase in the concentration of ET-1-IR in the medium at 6, 8 and 12 h incubation. Methaemoglobin also caused an approximate doubling of the amount of ET-1-IR at eight h of incubation. NG-Monomethyl-L-arginine (L-NMMA), a blocker of the production of endothelium-derived relaxing factor (EDRF), had no effect on the time-dependent increase in ET-1-IR in the conditioned medium. These results may have important implications for the mechanisms underlying vascular smooth muscle hyperreactivity such as cerebral spasm following subarachnoid haemorrhage.

Renovascular hypertension: information from experiments using conscious dogs

1. Evidence from experiments in conscious, instrumented dogs shows that hypertension from renal artery stenosis is due to: (i) the stimulus, the mechanical resistance of the stenosis; and (ii) the secondary responses to this, especially angiotensin II (initially) and cardiovascular hypertrophy. 2. The hydraulic resistance of the stenosis is responsible for about 20-25% of the rise in blood pressure. 3. Angiotensin II is initially the most important secondary response to the stenosis. Within days, however, other as yet undetermined factors become dominant in the maintenance of the hypertension. The most important of these factors is probably cardiovascular hypertrophy. 4. These secondary factors are homeostatic, in that they mitigate the effects of stenosis on renal function.

Angiotensin II and the maintenance of GFR and renal blood flow during renal artery narrowing

The time course of the renal blood flow and GFR responses to narrowing of the renal artery in conscious dogs is reviewed. The initial response to this threat to renal perfusion is renal vasodilatation, but within minutes a secondary vasoconstriction mediated by angiotensin II begins to develop. Angiotensin II-mediated contraction of mesangial cells is also demonstrable, but this does not apparently reduce the filtration surface area of the glomerular capillaries. The intrarenal effects of angiotensin II restore GFR back to normal within one to two weeks, by which time circulating plasma angiotensin II levels are no longer elevated. In contrast to its effects on GFR, angiotensin II has minimal effects on renal blood flow after stenosis. This may be because, (i) blood flow is mainly determined by the hydraulic resistance of the stenosis; (ii) renal vasoconstriction has relatively little effect on flow due to the particular hemodynamic properties of the stenoses, and (iii) a major site of action of angiotensin II may be within the glomerulus. Thus angiotensin II has a homeostatic role in the maintenance of GFR during renal artery narrowing and one component of this role may involve mesangial contraction.

Atrial natriuretic peptide infusion causes vasoconstriction after autonomic blockade in conscious dogs

Many studies have shown that atrial natriuretic peptide (ANP) reduces mean arterial pressure (MAP) in conscious animals by lowering cardiac output (CO) with no change or even increased total peripheral resistance (TPR). Because ANP is thought to be a vasodilator, the lack of fall in TPR in conscious animals is generally considered to be due to autonomic reflex increases in vascular resistance. In the present study in conscious, trained, chronically instrumented dogs (n = 7), we measured hemodynamic and renal excretory responses to 30-min infusions of alpha-human ANP (alpha hANP; 25, 50, and 100 ng.kg-1.min-1) in the presence and absence of autonomic nervous system blockade using the ganglion blocking agent pentolinium. In the absence of blockade, MAP and CO fell, whereas TPR rose with alpha hANP infusions, but these changes did not reach significance. There were significant increases in renal vascular resistance (RVR; 16-25%) and mesenteric vascular resistance (MVR; 14-40%). During autonomic nervous system blockade, alpha hANP caused dose-related reductions in MAP (7-12%), due to falls in CO (13-34%). Remarkably, the absence of autonomic reflex responses exposed substantial dose-related increases in TPR (5-33%). Autonomic blockade did not alter the ANP-induced increases in MVR but did abolish the rises in RVR. In summary, ANP caused vasoconstriction in mesenteric vasculature and substantial vasoconstriction in other nonrenal areas, independent of autonomic reflexes.

A randomised trial of cisplatin and vindesine versus supportive care only in advanced non-small cell lung cancer

The value of chemotherapy in advanced non-small cell lung cancer (NSCLC) remains contentious. Because of this two separate but very similar trials were set up in Australia and Southampton (UK). Two hundred and one patients with stage IIIb or IV NSCLC were randomly assigned to cisplatin 120 mg m-2 on days 1 and 29 and vindesine 3 mg m-2 weekly x 6 or to no chemotherapy. Both groups were eligible to receive radiotherapy or other palliative treatment as required. Of 188 evaluable patients, 97 received chemotherapy and 91 were in the control arm. Response was assessed between days 42 and 49. Responders continued chemotherapy at the same doses though cisplatin being given 6 weekly x 4 and the vindesine 2 weekly x 12. The overall response rate to chemotherapy was 28%; there were no significant differences according to major prognostic criteria. Although the overall survival of the chemotherapy group (median 27 weeks) was longer than that of the no chemotherapy group (median 17 weeks) this was not statistically significant (log rank P = 0.33). For patients without dissemination (IIIb), median survival was 45 weeks in the chemotherapy arm and 26 weeks in the non-chemotherapy (log rank P = 0.075). Toxicity was universal and frequently severe: of 17 patients discontinuing chemotherapy after one cycle, 13 did so because of unacceptable toxicity. This chemotherapy cannot be recommended as routine treatment. Further phase III studies of chemotherapy in advanced NSCLC should continue to use a no chemotherapy control and should also attempt to measure quality of life, an issue not addressed effectively in this or other recent trials.

A phase II study of mitoxantrone in advanced squamous cell cancer of the head and neck

Twenty patients with advanced squamous cell carcinomas (SCC) of the head and neck were entered into a phase II study of mitoxantrone at a dosage of either 12 mg/m2 or 14 mg/m2 given at 3 weekly intervals. None of the patients had received prior chemotherapy. One patient had a partial remission. Two patients died from unrelated causes. One patient withdrew from the trial prior to receiving any chemotherapy. Sixteen patients either failed to respond or progressed during the course of the treatment. Side effects included nausea and vomiting in 6 patients and neutropenia in 6 patients. This study failed to detect a significant response of squamous cell carcinomas of the head and neck to mitoxantrone therapy at the described doses.

Reflex release of vasopressin and renin in hemorrhage is enhanced by autonomic blockade

We determined the relationships during hemorrhage between nominal blood volume (BV) and 1) plasma arginine vasopressin (AVP), 2) plasma renin activity (PRA), and 3) mean arterial pressure (MAP). Conscious rabbits were studied under normal conditions and during total autonomic blockade (TAB) at bleeding rates of 2 and 4 ml/min. Normally, MAP was well maintained until BV had been reduced to approximately 65% of control (termed 65% BV) after which it fell abruptly. The threshold for a rise in AVP was 80-75% BV, followed by exponential rises to levels of 14 and 24 times control at the slow and fast rate of bleeding. PRA rose earlier in hemorrhage, but this rise was more gradual, to values at 60% BV of 5.5 and 7 times control at the two rates of bleeding. During TAB, MAP fell rapidly and both BV concentration curves were shifted to the left with the rises in AVP and PRA/unit delta BV greater than normal; at 75% BV at each rate of hemorrhage, AVP and PRA had risen, respectively, to approximately 40 and 8 times control. Normally, the rises in the AVP and PRA (i.e., angiotensin II) concentrations were modest during the nonhypotensive phase, consistent with their minimal constrictor action observed in a parallel study. During the hypotensive phase, both reached high levels in the constrictor range. During TAB, high concentrations were reached with small BV loss, representing a model of near-maximum release of PRA and AVP.

Effect of endurance exercise on cardiac secretion and renal clearance of atrial natriuretic peptide in normal humans

Previous work from our laboratory has shown that (i) regular endurance exercise lowers blood pressure (BP), and (ii) acute exercise increases circulating levels of atrial natriuretic peptide (ANP). We hypothesised that increased ANP release may contribute to the antihypertensive effect of regular exercise. Using arterial and selective venous (coronary sinus and renal vein) catheterization and sampling, we measured cardiac secretion and renal clearance of ANP at rest in 7 normal healthy males (mean age 36 years), before and after 4 weeks of training. Body weight and haematocrit remained unchanged. Systolic BP fell by 10 mmHg with training (p = 0.008), diastolic BP fell by 6 mmHg (p = 0.006) and heart rate decreased by 9 beats/minute (p = 0.002), but central venous pressure remained unchanged. Arterial, coronary sinus and renal vein ANP concentrations did not change with training. There was no significant rise in cardiac secretion of ANP with training (sedentary: 42.6 +/- 13.2 ng/ml, trained: 47.4 +/- 17.9 ng/ml, p n.s.). Renal extraction of ANP was 72 +/- 4% before training, and unchanged (66 +/- 5%) after the exercise period. Renal clearance of ANP was also unaltered by training (514.2 +/- 48.4 ml/min before, and 508.9 +/- 74.8 ml/min after training, p n.s.). We conclude that as ANP release is not increased by training, the peptide does not account for the anti-hypertensive effect of endurance exercise. Other humoral and/or neural mechanisms possibly mediate the beneficial haemodynamic effects of training.

Cardiac secretion and renal clearance of atrial natriuretic peptide in normal man: effect of salt restriction

1. Previous studies of endogenous atrial natriuretic peptide (ANP) in humans have examined changes in plasma levels, rather than regional secretion and clearance of the peptide. Using arterial and selective venous catheterization and sampling, and measurement of regional organ flow, we measured haemodynamics, cardiac secretion of ANP and renal clearance of ANP in six healthy volunteers at rest, on a normal sodium diet. 2. Salt restriction decreases plasma concentrations of ANP. We assessed the contribution of the heart and kidney to this decrease, by measuring cardiac secretion and renal clearance of ANP at the termination of a low salt diet. 3. Twenty-four hour urinary sodium excretion fell on the low salt diet from 163 to 29 mmol/day [standard error of the difference (SED)+/- 14, P less than 0.001]. Body weight decreased on salt restriction from 76.4 to 75.4 kg (SED +/- 0.33, P less than 0.05). Brachial mean arterial pressure fell by 6% (P less than 0.05), but right atrial pressure was unchanged. Renal vein plasma renin activity increased by 56% with sodium restriction (P less than 0.01), whereas arterial ANP concentrations fell by 39% (P less than 0.05). 4. Coronary sinus ANP levels fell from 417 to 268 pg/ml (SED +/- 74, P less than 0.05), whereas renal vein concentrations were unaltered. There was a 47% decrease in cardiac secretion of ANP in the low salt state (P less than 0.05). Net extraction of ANP across the kidney (about two-thirds) and renal clearance of ANP were unchanged on the low salt diet. Thus decreased plasma ANP with sodium restriction is due to reduced cardiac secretion.

Direct and neurohumoral cardiovascular effects of atrial natriuretic peptide

We studied the hemodynamic changes produced in conscious, chronically instrumented rabbits during steady-state administration of atrial natriuretic peptide (ANP). We administered synthetic alpha-human ANP intravenously (i.v.) at progressively increasing doses of 1, 2, and 4 micrograms/min, each for 30 min. In different experiments in each rabbit, we determined the effects of the peptide under closed-loop conditions in the intact animal and the "direct" circulatory effects of the peptide after "total" blockade of the autonomic nervous system (TAB) and after combined neurohumoral blockade (NHB), where in addition the vascular effects of vasopressin and angiotensin II were also prevented. In intact rabbits, ANP produced a dose-related reduction in mean arterial pressure (MAP, -3 to -14%), which was entirely due to a fall in cardiac output (CO, -14 to -20%), and there was a small rise in total peripheral resistance (TPR 5-12%). Heart rate remained unchanged. In rabbits subjected to TAB and NHB, all hemodynamic effects of ANP were attenuated. There were dose-related falls in left and right atrial pressures which reached maxima of -3.3 +/- 0.9 and -1.8 +/- 0.2 mm Hg, respectively. There was a reversible rise in hematocrit, probably owing to a shift of approximately 8% in blood volume. These effects occurred mainly through direct actions of the peptide, and there was no evidence of systemic vasodilatation. The magnitude of reflex autonomic effects appeared to be less than expected for the observed fall in MAP, suggesting that ANP also inhibited cardiovascular reflexes.