Primary Care Physician and Urologist Perspectives on Optimizing Active Surveillance for Low-Risk Prostate Cancer

PURPOSE

We conducted a study to understand primary care physician (PCP) and urologist perspectives on determinants of active surveillance care delivery for men with low-risk prostate cancer.

METHODS

We conducted in-depth, semistructured, virtual interviews with a purposive sample of 19 PCPs and 15 urologists between June 2020 and March 2021. We used the behavioral theory-informed Theoretical Domains Framework to understand barriers to and facilitators of active surveillance care delivery. Interviews were recorded, transcribed, and deductively coded into framework domains and constructs by 3 independent coders. Participant recruitment continued until data saturation by group.

RESULTS

Our study included 19 PCPs (9 female; 4 in community practices, 15 in academic medical centers) and 15 urologists (3 female; 5 in private practice, 3 in academic medical centers). The most commonly reported Theoretical Domains Framework domains affecting active surveillance care were (1) knowledge and (2) environmental context and resources. Although urologists were knowledgeable about active surveillance, PCPs mentioned limitations in their understanding of active surveillance (eg, what follow-up entails). Both groups noted the importance of an informed patient, especially how a patient's understanding of active surveillance facilitates their receipt of recommended follow-up. Physicians viewed patient loss to follow-up as a barrier, but identified a favorable organizational culture/climate (eg, good communication between physicians) as a facilitator.

CONCLUSIONS

With patients increasingly involving their PCPs in their cancer care, our study presents factors both PCPs and urologists perceive (or identify) as affecting optimal active surveillance care delivery. We provide insights that can help inform multilevel supportive interventions for patients, physicians, and organizations to ensure the success of active surveillance as a management strategy for low-risk prostate cancer.

Effect of High-Dose Intravenous Eletriptan on Coronary Artery Diameter

The goal of this study was to evaluate the coronary vasoconstrictive effects of high doses of eletriptan compared with a standard dose of sumatriptan. Patients with no clinically significant coronary artery disease were randomized to receive high-dose intravenous eletriptan ( n = 24) vs a standard dose of sumatriptan ( n = 18; 6 mg subcutaneously) vs placebo ( n = 18). Serial angiograms were obtained. The primary non-inferiority analysis found equivalence between the mean maximum change in left anterior descending coronary artery diameter for eletriptan, -22% [95% confidence interval (CI) -26, -19], and sumatriptan, -19% (95% CI -22, -16). The change due to placebo was -16% (95% CI -20, -12). No individual cases of clinically significant vasoconstriction were observed. The results confirm that eletriptan has a broad cardiovascular safety margin, with plasma concentrations comparable to three to five times the Cmax of an oral 80-mg dose associated with modest vasoconstriction equivalent to standard therapeutic doses of sumatriptan.

Management of metastatic phaeochromocytoma and paraganglioma: use of iodine-131-meta-iodobenzylguanidine therapy in a tertiary referral centre

BACKGROUND

Phaeochromocytoma (phaeo) and paraganglioma (PGL) are rare conditions, which are malignant in up to 30%. Optimal treatment is controversial, but in patients with metastatic iodine-131-meta-iodobenzylguanidine ((123)I-MIBG) avid tumours, we offer (131)I-MIBG therapy. We summarize response rates, survival and safety in a cohort of such patients treated with (131)I-MIBG in our centre from 1986 to 2012.

DESIGN/METHODS

Retrospective analysis of the case notes of patients with metastatic phaeo/PGL who received (131)I-MIBG was undertaken; patients underwent clinical, biochemical and radiological evaluation within 6 months of each course of (131)I-MIBG therapy.

RESULTS

Twenty-two patients (9 males) were identified, 12 with metastatic PGL and 10 with phaeo. Overall median follow-up time after first dose of (131)I-MIBG was 53 months. In total, 68 doses of (131)I-MIBG were administered; average dose was 9967 MBq (269.4 mCi). After the first dose, >50% of patients demonstrated disease stability or partial response; progressive disease was seen in 9%. A subset of patients underwent repeated treatment with the majority demonstrating partial response or stable disease. No life-threatening adverse events were reported, but three patients developed hypothyroidism and two developed ovarian failure after repeated dosing. Five-year survival after original diagnosis was 68% and median (+inter quartile range) survival from date of diagnosis was 17 years (7.6-26.4) with no difference in survival according to diagnosis (P < 0.1).

CONCLUSIONS

(131)I-MIBG is well tolerated and associates with disease stabilization or improvement in the majority of patients with metastatic phaeo/PGL. However, stronger conclusions on treatment effectiveness are limited by lack of a directly comparable 'control group' as well as an alternative 'gold standard' treatment.

Clinically important atrial arrhythmia and stroke risk: a UK-wide online survey among stroke physicians and cardiologists

BACKGROUND

A recording of ≥30 s is required for diagnosis of paroxysmal atrial fibrillation (AF) when using ambulatory electrocardiography (ECG) monitoring. It is unclear if shorter runs of atrial arrhythmia are relevant with regard to stroke risk.

AIM

To assess current management of patients with atrial arrhythmia of <30 s duration detected on ambulatory ECG.

DESIGN

Online survey.

METHODS

An online survey was sent to cardiologists and stroke physicians in the UK, via their national societies.

RESULTS

A total of 205 clinicians responded to the survey (130 stroke physicians, 64 cardiologists, 11 other). Regarding diagnosis of AF, 87% of responders would accept a single 12-lead ECG. In contrast, only 45% would accept a single episode lasting <30 s detected on ambulatory monitoring. There was more agreement with regard to the decision to anticoagulate. When asked whether they would anticoagulate eight hypothetical patients with non-diagnostic paroxysms of AF, there was a mean agreement of responses of 78.6%, with up to 94.1% agreement for high-risk patients. There was a trend suggesting that stroke physicians were more likely to accept an atrial arrhythmia of <30 s as 'AF' than cardiology specialists [OR 1.63 (95% CI 0.88-3.01), P = 0.12].

CONCLUSIONS

There is a lack of consensus on the diagnosis and management of patients with brief runs of atrial arrhythmia detected on ambulatory ECG. Further research is needed to clarify the risk of stroke in this unique population of patients.

Walk or run? is high-intensity exercise more effective than moderate-intensity exercise at reducing cardiovascular risk?

The benefits of exercise in the prevention of cardiovascular disease are irrefutable. However, the optimum ‘dose’ of exercise in order to derive the maximum cardiovascular benefit is not certain. Current national and international guidelines advocate the benefits of moderate-intensity exercise. The relative benefits of vigorous versus moderate-intensity exercise have been studied in large epidemiological studies, addressing coronary heart disease and mortality, as well as smaller randomized clinical trials which assessed effects on cardiovascular risk factors. There is evidence that exercise intensity, rather than duration or frequency, is the most important variable in determining cardioprotection. Applying this evidence into practice must take into account the impact of baseline fitness, compliance and the independent risk associated with a sedentary lifestyle. This review aims to evaluate the role of exercise intensity in the reduction of cardiovascular risk, and answer the question: should you be advising your patients to walk or run?

ANP enhances bradycardic reflexes in normotensive but not spontaneously hypertensive rats

Baroreflex control of heart rate in spontaneously hypertensive rats (SHR) is defective, largely because of a poor vagal contribution to the reflex. We have demonstrated previously that atrial natriuretic peptide (ANP) enhances reflex bradycardia in normotensive rats through an action on nonarterial vagal afferent pathways. In the present study, we investigated whether ANP could reverse the baroreflex abnormality in SHR. Heart rate reflexes were activated by three different methods in conscious, instrumented SHR and Wistar-Kyoto rats (WKY) in the presence of intravenous infusions of vehicle (saline) or rat ANP (150 ng/kg per minute). Heart rate responses were measured by (1) the steady-state changes in blood pressure after alternating slow infusions (over approximately 15 to 30 seconds) of a pressor (methoxamine) and depressor (nitroprusside) drug (stimulating predominantly arterial baroreceptors), (2) the ramp method of rapid infusion of methoxamine (over < 10 seconds; stimulating arterial and cardiopulmonary baroreceptors), and (3) the von Bezold-Jarisch method of activating chemically sensitive cardiac receptors through serotonin injections. ANP enhanced the heart rate range of the arterial baroreflex (steady-state method) by 13 +/- 3% in WKY but had no significant effect on the sensitivity or any other parameter of the steady-state baroreflex. When a very rapid rise in blood pressure was elicited by the ramp method in WKY, ANP significantly enhanced baroreflex bradycardia (sensitivity increased by 29 +/- 9%, P < .05). ANP also enhanced the bradycardia of the von Bezold-Jarisch reflex (by 33 +/- 16%, P < .05) in WKY. By contrast, ANP did not influence baroreceptor or chemoreceptor heart rate reflex responses in SHR. We conclude that in normotensive rats, ANP facilitates cardiopulmonary bradycardic reflexes. The lack of effect of ANP in SHR may be related to an underlying structural or genetic alteration in their cardiac sensors, perhaps associated with cardiac hypertrophy, that prevents the ANP-induced activation of cardiac sensory afferents, resulting in cardioinhibition.

Interactions of blockade of nitric oxide synthase and angiotensin-converting enzyme on renal function in conscious rabbits

We tested the effects and interactions of blockade of nitric oxide (NO) synthase and angiotensin-converting enzyme (ACE) on renal function. Six rabbits were studied four times, each at 14-day intervals. The treatments were intravenous (i.v.) vehicle, NG-nitro-L-arginine (L-NNA) 5 mg/kg, captopril 500 micrograms plus 3.3 micrograms/kg/min, or L-NNA plus captopril. The studies were performed in random order. Arterial blood pressure (BP), heart rate (HR), and clearance of H2O, Na+, Li+, [3H]inulin [glomerular filtration rate (GRF)], and paraaminohippuric acid (PAH, renal plasma flow) were measured for the hour before treatment and for 3 h after treatment. Renal blood flow (RBF), renal vascular conductance, and GFR were reduced by 36 +/- 4, 41 +/- 4, and 17 +/- 5%, respectively, after L-NNA treatment. Although captopril did not affect these variables significantly when given alone, it completely abolished the effects of L-NNA. After L-NNA administration, sodium excretion decreased by 41 +/- 11%, chiefly attributable to reduced GFR, although increased reabsorption of sodium also contributed. The site of this increased reabsorption was probably the proximal nephron, since Li+ reabsorption (a marker of proximal tubular sodium reabsorption) tended to increase by 8.4 +/- 4.8%. Captopril had a natriuretic effect chiefly attributable to reduced sodium reabsorption in the proximal nephron. When these agents were coadministered, proximal tubular sodium reabsorption did not change significantly. Our data suggest the existence of a functional interaction between ACE and NO synthase in control of RBF and GFR.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial and arterial baroreceptor influences on the circulatory response to acute changes in renal perfusion

We have recently reported a neurally mediated reflex increase in hindlimb vascular resistance associated with an acute decrease in renal perfusion pressure in the chloralose-urethane-anesthetized rabbit. The present study was designed to investigate the influence of this reflex in the body's integrated response to circulatory disturbances by investigating the influence of carotid baroreceptor and left atrial receptors on this reflex and assessing the effect of acute changes in renal perfusion on the heart. Interaction of the renal-generated reflex with carotid baroreceptors was investigated by independent perfusion of the carotid sinus region. Responses in hindlimb perfusion pressure, at constant flow, to changes in renal perfusion were greatest with the carotid sinus perfusion pressure (CSP) low (27 +/- 4 mmHg (1 mmHg = 133.3 Pa) increase in hindlimb pressure at low CSP vs. 19 +/- 3 mmHg increase at normal CSP) and were inhibited with maximum carotid stimulation. Partial mitral obstruction, resulting in left atrial distension and atrial receptor stimulation, attenuated the hindlimb vascular response. The increase in hindlimb pressure under control conditions was 34 +/- 10 mmHg compared with 20 +/- 5 mmHg during atrial receptor stimulation. However, acute reduction of renal perfusion pressure did not result in any changes in heart rate, cardiac output, or inotropic state. It appears that both atrial and arterial baroreflexes modify the reflex change in hindlimb vascular resistance associated with acute alterations of renal perfusion.

The reflex effect of changes in renal perfusion on hindlimb vascular resistance in anaesthetized rabbits

This study was designed to characterise the response of the hindlimb vasculature to reduced renal perfusion in the anaesthetized rabbit and to elucidate whether the stimulus was dependent upon reduced renal perfusion pressure (RPP) or blood flow (RBF). Acute decreases in renal perfusion resulted in rapid and reversible increases in femoral perfusion (FPP). This vascular response was completely abolished following renal denervation indicating that the afferent components of the reflex is neurally mediated. Acute hindlimb responses to changes in renal perfusion pressure were present whether the limb was perfused with homologous blood or cross-perfused with blood from a donor rabbit, demonstrating that the efferent component of the response is also neurally mediated. There was a 28-s latency for initiation of the hindlimb vasoconstriction, which is consistent with recent evidence for renal autocoid stimulation of the afferent renal nerve receptors. Decreasing RPP indirectly, by altering flow, resulted in a hindlimb vasoconstriction below approximately 55 mm Hg (7.3 kPa) RPP or 15 ml/min RBF. However, decreasing RPP by directly reducing pressure in graded steps resulted in increases in FPP, which reflected the changes in renal flow; thus during the autoregulatory phase, where flow did not change as pressure fell, FPP also remained stable. The results of these protocols suggest that a neurally mediated hindlimb vascular reflex is stimulated by decreased renal flow rather than pressure.

The effect of chronic and acute administration of deuterium oxide (D2O) on vascular smooth muscle contraction in spontaneously hypertensive and Wistar-Kyoto rats

1. Oral administration of 25% D2O for 12 days reduced blood pressure of spontaneously hypertensive rats (SHR) to the level of Wistar-Kyoto (WKY) controls. 2. However, the chronic D2O treatment appeared to have little effect on the phenylephrine and potassium chloride induced dose-response curves of SHR and WKY rats, producing a decreased maximal contraction of the potassium chloride dose-response curve of SHR only. 3. Further acute studies revealed that desensitization results from chronic exposure to D2O such that 60% D2O produces a significant depression of contraction only in aortic rings obtained from SHR and WKY which had not been chronically treated with 25% D2O.

Problems associated with the measurement of mean circulatory filling pressure by the atrial balloon technique in anaesthetized rats

To examine the existence of pressure equilibrium between tributary veins and the central vena cava during the mean circulatory filling pressure manoeuvre, pressures in the hepatic portal vein, renal vein, and inferior vena cava were determined at 4-s intervals over a 20-s period of circulatory arrest induced by inflating a right atrial balloon in normal blood volume, 10% volume depletion, and 10% volume expansion states in urethane-anaesthetized rats. Portal vein pressure determined 8 s after arrest during volume depletion and expansion was significantly higher than vena caval pressure (6.2 ± 0.8 vs. 3.4 ± 0.2 and 7.7 ± 0.5 vs. 6.2 ± 0.4 mmHg (1 mmHg = 133.32 Pa), respectively; p < 0.01): this pressure disequilibrium continued for 16 s during volume expansion and for the entire 20 s during volume depletion. Renal vein pressure was equal to vena caval pressure during this manoeuvre. Portal vein pressure at normal blood volume was not significantly different from vena caval pressure following circulatory arrest (4.6 ± 0.3 vs. 3.8 ± 0.4 mmHg, respectively). Following ganglionic blockade, portal vein pressure was still significantly higher than vena caval pressure for 12 s during volume alterations. At the 8th s of the arrest the portal pressure determined in volume depletion was 3.6 ± 0.3 mmHg and the inferior vena caval pressure was 2.6 ± 0.4 mmHg (p < 0.05). Under the volume expansion condition, the respective values were 6.5 ± 0.3 and 5.3 ± 0.4 mmHg (p < 0.05). We conclude that, under conditions of blood volume alterations, there is no pressure equilibrium between the portal vein and the inferior vena cava when mean circulatory filling pressure is measured by this technique; a transhepatic barrier independent of reflex control during the measurement of mean circulatory filling pressure appears to play a role in obstructing the establishment of pressure equilibrium within the venous system.Key words: mean circulatory filling pressure, vascular capacitance, hepatic portal vein pressure, unstressed volume.

The inotropic effect of atrial natriuretic factor in the anesthetized rabbit

This study was designed to investigate whether atrial natriuretic factor (ANF) administered over the physiological, pathological and pharmacological range has a negative inotropic action on the heart. Anesthetized rabbits were infused with increasing doses of ANF (0.05, 0.25 and 0.5 micrograms kg-1 min-1), while measuring hemodynamic variables including the maximum rate of change of left ventricular pressure (dP/dtmax) as an index of inotropic state. Plasma levels of immunoreactive ANF (iANF) were measured to relate the hemodynamic changes to actual plasma levels of the peptide. Administration of ANF was associated with decreases in blood pressure, left ventricular pressure and dP/dtmax so that after 0.5 micrograms kg-1 min-1 infusion, these variables had decreased by 21 +/- 2 mmHg, 21 +/- 5.3 mmHg and 925 +/- 175 mmHg/s, respectively (P less than 0.01). There were no significant changes in right atrial pressure, left ventricular end-diastolic pressure or heart rate. Since dP/dtmax can be influenced by changing hemodynamic variables and baroreflex changes, a second group of rabbits was studied in which afterload and heart rate were held artificially constant. Again, in this group of rabbits, infusions of AFN led to decreasing inotropic state, so that at the highest infusion rate, a 14% decrease in dP/dtmax was observed (P less than 0.05). By comparison, hydralazine, a drug which causes active vasodilatation but no direct inotropic action, significantly (P less than 0.01) decreased blood pressure, left ventricular pressure and dP/dtmax when infused at a rate of 10 micrograms kg-1 min-1. However, in animals in which afterload was controlled, hydralazine did not affect any of the variables measured.(ABSTRACT TRUNCATED AT 250 WORDS)

Deuterium oxide reduces agonist and depolarization-induced contraction of rat aortic rings

The influence of deuterium oxide (D2O) on calcium-dependent vascular smooth muscle contraction was investigated. The effect of D2O on receptor-operated calcium channels was investigated with phenylephrine-induced contraction in the rat aortic ring preparation. D2O depressed the contraction response in a dose-dependent manner with 50% inhibition of maximum contraction observed with 60% D2O. The effect of 60% D2O on phenylephrine-induced contraction was reversible and not dependent on an intact endothelium. Sixty percent D2O also reduced potassium chloride induced contractions by 50%, indicating an effect on voltage-operated calcium channels. Studies with Bay K 8644, and L-type calcium channel activator, confirm an effect on utilization of extracellular calcium sources and on the voltage-operated calcium channel. Sixty percent D2O also depressed a calcium contraction dose-response curve by approximately 25%. Likewise, a change in the pD2' for nifedipine in the presence of D2O may indicate an effect on the nifedipine binding site and (or) the voltage-dependent calcium channel. Further studies were performed to determine whether the D2O effects were nonspecific or selective effects on the receptor- and voltage-operated calcium channels. Sucrose-induced contaction in the presence of 60% D2O was found to be inhibited by approximately 50%. D2O similarly affected isoprenaline relaxation, which would suggest a nonspecific D2O effect on the vascular smooth muscle contractile process.

Capsaicin-sensitive nerves influence the release of atrial natriuretic factor by atrial stretch in the rat

Although many factors may modulate the release of atrial natriuretic factor (ANF), the primary mechanism has been demonstrated to be atrial stretch. Recent studies have led to the suggestion that the peptidergic innervation of the heart, through the release of peptides, may be involved in the control of ANF secretion. We have examined the influence of chronic capsaicin treatment on three models of atrial stretch that release ANF. This treatment inhibited ANF released through in vivo blood volume expansion and through balloon inflation in the right atrium of in vitro isolated perfused hearts. Immunohistochemical and electron microscopical analysis confirmed the absence of innervation of the heart by calcitonin gene related peptide and substance P immunoreactive nerve fibres and apparent lack of effect on atrial granules in capsaicin treated rats. We conclude that capsaicin-sensitive cardiac innervation is a component modulating the release of ANF, stimulated by atrial stretch in the rat.

Studies of the desensitization of atrial natriuretic factor and nitroglycerin in rat aortic rings

1. Atrial natriuretic factor (ANF) relaxes vascular smooth muscle through activation of particulate guanylate cyclase and generation of cyclic GMP. 2. From other laboratories, there is some evidence from cultured vascular smooth muscle cell studies for homologous desensitization of ANF-induced cGMP production and down-regulation of ANF receptors. 3. This series of studies demonstrates that homologous desensitization of ANF-induced relaxation of rat aortic ring preparations also occurs. 4. Heterologous desensitization could not be demonstrated to the vasoactive peptides angiotensin II or vasopressin, nor to nitroglycerin which has previously been shown to exhibit heterologous desensitization with other nitrovasodilators and shares some common elements in the pathway to vascular smooth muscle relaxation with ANF.

Carotid sinus pressure and plasma vasopressin in anesthetized rabbits

The arterial baroreceptors are known to influence the release of vasopressin, but the quantitative relationship between baroreceptor stimulation and plasma vasopressin concentration has not been defined. These experiments examine the effect of stepwise changes in carotid sinus pressure (40-160 mmHg) on the plasma concentration of vasopressin in chloralose-urethan anesthetized rabbits. Plasma vasopressin concentration (9.2 +/- 1.2 pg/ml, n = 27) did not change in response to changes in carotid sinus pressure when the aortic depressor nerves were intact. These results were unaltered by bilateral cervical vagotomy. However, after aortic depressor nerve section, decreases in carotid sinus pressure were associated with increases in plasma vasopressin concentration. There appeared to be a greater redundancy in the baroreceptor control of plasma vasopressin than in the baroreceptor control of arterial pressure or heart rate. The results provided no evidence that receptors with vagal afferents have a tonic influence on the baroreceptor control of vasopressin release in the anesthetized rabbit.

Extracted and nonextracted atrial natriuretic peptide in rabbits during tachycardia

The time course of changes in the plasma concentration of immunoreactive atrial natriuretic peptide (iANP) accompanying tachycardia was measured in anesthetized rabbits. In contrast to the hemodynamic changes, which occurred within the 1st min of tachycardia, the plasma iANP increased gradually and did not reach significantly elevated levels until 10 min into the stimulation period. After 20 min of tachycardia iANP was almost 200 pg/ml. Immunoreactive ANP was measured prior to and following extraction. Although the basal levels of iANP were higher in the unextracted than in extracted plasma (62 vs. 22 pg/ml), the time course of changes in iANP was identical in both. The gradual increase in iANP suggests that the release of iANP in this model may not simply be a consequence of the increase in atrial pressure.

Mechanisms for the release of atrial natriuretic peptide

In assessing the role that atrial natriuretic peptide (ANP) might have in the homeostasis of fluid volume and blood pressure, it is important to define the physiological and pathophysiological conditions that determine its release into the circulation. There is substantial evidence that ANP is released through atrial distension under a variety of conditions. There are also some indications that ANP may be released through humoral factors, although it is not clear whether this is a result of direct action on the myocytes or simply a result of ensuing haemodynamic changes. There is no evidence to suggest that ANP can be released through stimulation of efferent fibres innervating the atria, but it may be released as a result of changes in myocardial work and oxygen consumption. Plasma levels of ANP are elevated in several disease states and that release appears to be a result of the haemodynamic disturbances in those conditions.

Effects of autonomic stimulation on plasma immunoreactive atrial natriuretic peptide in the anesthetized rabbit

Infusions of norepinephrine led to a significant sevenfold increase in plasma immunoreactive atrial natriuretic peptide, while infusions of acetylcholine caused no significant change in the level of the peptide. Efferent stimulation of the right vagus nerve or right inferior cervical ganglion in anesthetized, vagotomized rabbits produced no significant changes in the immunoreactive atrial natriuretic peptide. The findings suggest that the mechanism by which norepinephrine releases immunoreactive atrial natriuretic peptide is not the result of a direct action on the cardiac myocytes.

Influence of isoproterenol on plasma immunoreactive atrial natriuretic peptide and plasma vasopressin in the anesthetized rabbit

Changes in levels of plasma immunoreactive atrial natriuretic peptide (IR-ANP) were measured in response to administration of isoproterenol in the anesthetized, vagotomized rabbit. A dose-dependent increase in plasma IR-ANP was seen in response to 10 min isoproterenol infusions between 0.1 and 10.0 micrograms/kg/min. The time course of these responses showed the maximum levels of IR-ANP to be attained 10 min after the cessation of infusion. In rabbits in which plasma vasopressin (AVP) levels were also measured, the maximum levels of AVP were attained during the infusion period. There was no correlation between levels of AVP and IR-ANP suggesting that AVP released into the plasma did not affect directly the release of IR-ANP. The changes in IR-ANP in response to isoproterenol were significantly reduced in rabbits which had been administered the beta-1-adrenoceptor blocking agent, atenolol. In six rabbits in which the vagi remained intact, the increases in IR-ANP were reduced and became significant only with 10 micrograms/kg/min isoproterenol infusion. The results demonstrate that isoproterenol infusion increases the level of plasma IR-ANP in the anesthetized rabbit and suggest that this is through an effect on the heart rather than on peripheral vessels.

Plasma vasopressin response to haemorrhage in the anaesthetized rabbit

In chloralose-urethane anaesthetized rabbits the acute circulatory and plasma vasopressin (pAVP) responses to moderate haemorrhage of 6 mL/kg body weight (10% blood volume) were followed after serial section of the aortic, vagus, and carotid sinus nerves. With all nerves intact, haemorrhage resulted in significant increases in pAVP, accompanied by decreases in systemic arterial pressure and right atrial pressure. With subsequent section of each afferent nerve, pAVP still increased in response to haemorrhage regardless of the order of nerve section. These results suggest that, in the anaesthetized rabbit, there is a further component of the pAVP response to haemorrhage, in addition to those carried in the aortic, vagus, and carotid sinus nerves.

Time course of release of atrial natriuretic peptide in the anaesthetized dog

In 12 chloralose anaesthetized dogs plasma concentration of immunoreactive atrial natriuretic peptide (IR-ANP) was measured using a radioimmunoassay. Plasma IR-ANP was 74 +/- 4.8 pg/mL (mean +/- SE) and increased by 39 +/- 4.1 pg/mL when left atrial pressure was increased by 10 cm H2O during partial mitral obstruction. Observation of the time course of the changes in IR-ANP during atrial distension showed that IR-ANP was increased within 2 min of atrial distension and declined after atrial distension, with a half-time of 4.5 min. The time course of the changes in IR-ANP was unaffected by vagotomy or administration of atenolol. Maximum electrical stimulation of the right ansa subclavia failed to produce any change in IR-ANP. IR-ANP was higher in coronary sinus plasma than in femoral arterial plasma confirming that the heart was the source of the IR-ANP. The results support the hypothesis that IR-ANP is released from the heart by a direct effect of stretch of the atrial wall rather than by a neural or humoral mechanism involving a reflex from atrial receptors.

Tachycardia releases atrial natriuretic peptide in the anesthetized rabbit

In anesthetized, vagotomized rabbits the plasma concentration of immunoreactive atrial natriuretic peptide (IR-ANP) was found to be 58.5 +/- 3.4 pg/mL (n = 18) when measured using a radio-immunoassay. Tachycardia, induced by electrical pacing of the right atrium, resulted in increased plasma levels of IR-ANP. The size of the increase in IR-ANP appeared to be related to the degree of tachycardia induced. The release of IR-ANP with tachycardia was unaffected by beta-adrenergic blockade with atenolol (2 mg/kg), muscarinic blockade with atropine (2 mg/kg) or ganglionic blockade with hexamethonium (10 mg/kg). The results show that IR-ANP is released in response to tachycardia and that this does not involve a neuronal reflex.

Heterologous radioimmunoassay of atrial natriuretic polypeptide in dog and rabbit plasma

Atrial natriuretic peptide (ANP) was measured in plasma of dogs and rabbits by radioimmunoassay (RIA) using a commercially available anti alpha-ANP serum and compared to our measurements of ANP in rats and humans. Plasma concentration of ANP in dog coronary sinus (234.9 +/- 41.0 pg/ml) was significantly greater than in systemic arterial blood (81.2 +/- 8.4 pg/ml). Gel filtration of dog coronary sinus plasma resulted in an ANP peak with the elution volume (Ve) of synthetic atriopeptin III (AIII) and a minor peak eluting with the void volume (Vo). Rabbit systemic arterial plasma ANP was 53.3 +/- 4.3 pg/ml and yielded one peak, with a Ve of AIII. Ion exchange chromatography of dog and rabbit atrial extracts (AE) resulted in a major ANP region which resembled AIII. Gel filtration of AE showed larger molecular species as well as AIII. Dilutions of dog and rabbit plasma and AE were parallel with the AIII standard in radioimmunoassay.

Influence of carbon dioxide tension in the cephalic circulation on hind-limb vascular resistance in anaesthetized dogs

In dogs anaesthetized with chloralose, the effects were determined of changes in cephalic blood PCO2 on vascular resistance and on the reflex vascular responses to stimulation of baroreceptors and chemoreceptors. Both vagus nerves were cut above the nodose ganglia, both carotid sinus regions were perfused with blood at controlled pressures and the cephalic circulation was perfused with blood, equilibrated with various levels of CO2, through the brachiocephalic and left subclavian arteries. Increases in cephalic blood PCO2 between 4 and 6 kPa resulted in increases in arterial perfusion pressure in a vascularly isolated hind limb. These responses were inhibited at high carotid sinus pressures and the responses to changes in carotid pressure were enhanced at high levels of cephalic PCO2. The reflex increase in vascular resistance resulting from stimulation of carotid chemoreceptors, however, was unaffected by the level of cephalic blood CO2. These results indicate that the carbon dioxide tension in the cephalic circulation is of importance in the control of vascular resistance in the hind limb.

Release of atrial natriuretic peptide by atrial distension

A heterologous radioimmunoassay was used to measure the concentration of immunoreactive atrial natriuretic peptide (iANP) in plasma from the femoral artery of eight chloralose anaesthetized dogs. Mitral obstruction which increased left atrial pressure by 11 cmH2O increased plasma iANP from 97 +/- 10.3 (mean +/- SE) to 135 +/- 14.3 pg/mL. Pulmonary vein distension increased heart rate but did not increase plasma iANP. Bilateral cervical vagotomy and administration of atenolol (2 mg/kg) did not prevent the increase in iANP with mitral obstruction. Samples of blood from the coronary sinus had plasma iANP significantly higher than simultaneous samples from the femoral artery confirming the cardiac origin of the iANP. Release of iANP depends on direct stretch of the atrium rather than on a reflex involving left atrial receptors.

Abdominal vascular responses to changes in carbon dioxide tension in the cephalic circulation of anaesthetized dogs

Dogs were anaesthetized with chloralose, the regions of both carotid sinuses were vascularly isolated and perfused with arterial blood and both cervical vagosympathetic trunks were cut above the nodose ganglia. The cephalic circulation was perfused through the brachiocephalic and left subclavian arteries with blood which was equilibrated with various levels of CO2. The abdomen was vascularly isolated, perfused through the aorta at constant flow and drained through the inferior vena cava at constant pressure. Changes in vascular resistance were determined from changes in abdominal aortic perfusion pressure and changes in capacitance from the integral of the changes in venous outflow. An increase in PCO2 in the cephalic perfusate resulted in an increase in abdominal vascular resistance and a decrease in capacitance. However, when carotid sinus pressure was high, the response of resistance to an increase in cephalic PCO2 was abolished and that of capacitance was significantly reduced. The reflex responses of both vascular resistance and capacitance to a change in carotid sinus pressure were enhanced when the cephalic PCO2 was raised. However, the effect on the reflex capacitance response from stimulation of baroreceptors was obtained only when PCO2 was changed below 5 kPa whereas the effect on resistance occurred at higher values of PCO2. The interaction between the effects of changes in cephalic PCO2 and the carotid sinus reflex and the differential effect on resistance and capacitance vessels have been explained in terms of the known difference in the sensitivities of these vessels to sympathetic nerve activity.

Effect of cephalic carbon dioxide tension on the cardiac inotropic response to carotid chemoreceptor stimulation in dogs

Dogs were anaesthetized with chloralose and the cephalic circulation was perfused, through the brachiocephalic and left subclavian arteries, with blood equilibrated with various tensions of CO2. The vascularly isolated carotid bifurcations were perfused at a constant pressure with either arterial or venous blood. Inotropic responses were assessed by measuring the maximum rate of change of left ventricular pressure (dP/dt max) with heart rate and aortic pressure held constant. Stimulation of carotid chemoreceptors with venous blood, at all values of cephalic PCO2, always resulted in a decrease in dP/dt max. An increase in cephalic PCO2, during arterial perfusion of chemoreceptors, resulted in an increase in dP/dt max and the response to chemoreceptor stimulation was enhanced. Graded changes in cephalic PCO2 resulted in graded changes in dP/dt max during arterial perfusion of chemoreceptors. However, the value of dP/dt max during venous perfusion was not significantly affected by increases in cephalic PCO2 above normal but it did decrease significantly during cephalic hypocapnia. These results confirm that an increase in cephalic PCO2 and stimulation of carotid chemoreceptors result in opposite responses of the cardiac inotropic state. The responses to chemoreceptor stimulation were enhanced by cephalic hypercapnia but the responses to cephalic hypercapnia, although not to hypocapnia, were suppressed by chemoreceptor stimulation.

Cardiac inotropic responses from changes in carbon dioxide tension in the cephalic circulation of anaesthetized dogs

Experiments were performed on anaesthetized dogs to determine the effects of moderate changes in PCO2 in the cephalic circulation on the inotropic state of the heart and on the reflex inotropic responses from changes in carotid sinus pressure. The cephalic circulation was perfused, through the brachiocephalic and left subclavian arteries, with blood taken from the superior vena cava and equilibrated with various gas mixtures in a gas exchange unit. The carotid sinus regions were vascularly isolated and perfused with arterial blood at controlled pressures. Cardiac inotropic responses were assessed from the maximum rate of change of left ventricular pressure (dP/dtmax) with heart rate and mean aortic pressure held constant. An increase in cephalic blood PCO2 resulted in an increase in dP/dtmax and an increase in the unpaced heart rate. Small, graded changes in cephalic PCO2 resulted in graded responses of dP/dtmax. A change in carotid sinus pressure resulted in a significantly greater response of dP/dtmax when cephalic PCO2 was high. After interruption of the left cardiac sympathetic nerves, the responses of dP/dtmax to changes in cephalic PCO2 and carotid sinus pressure were nearly abolished. These results indicate that the tension of carbon dioxide in the cephalic circulation is likely to be of importance in the control of the inotropic state of the heart. They also imply that, in studies of cardiovascular reflex responses, it is important to control the carbon dioxide tension in the arterial blood.

Effects of stimulation of aortic chemoreceptors on abdominal vascular resistance and capacitance in anaesthetized dogs

1. Dogs were anaesthetized with chloralose, ventilated artificially, and the regions of the aortic arch and carotid sinuses were isolated vascularly and perfused with blood. The abdominal circulation was isolated vascularly, perfused at constant flow and drained from the inferior vena cava at constant venous pressure. Changes in vascular resistance were determined by calculating changes in abdominal aortic perfusion pressure, and changes in capacitance by integrating the changes in venous outflow. 2. Stimulation of aortic body chemoreceptors, either by changing the aortic arch perfusate from arterial to venous blood at constant perfusion pressure or by injection of sodium cyanide into the aortic arch, resulted in an increase in abdominal vascular resistance and a decrease in abdominal vascular capacitance. 3. After both cervical vagosympathetic trunks had been cut, stimulation of aortic chemoreceptors no longer resulted in resistance or capacitance responses. 4. These results indicate that stimulation of aortic chemoreceptors, like carotid chemoreceptors, results in reflex constriction of both resistance and capacitance vessels in the abdominal circulation.