Nupafant, a PAF-antagonist prototype for suppression of ventricular fibrillation without liability for QT prolongation?

BACKGROUND AND PURPOSE: PAF antagonists inhibit ischaemia-induced ventricular fibrillation (VF) in animals. However, unfavourable ancillary actions (on QT interval and coronary flow) have been reported with the PAF antagonist, BN-50739. If these are class actions, they would preclude development of PAF antagonists as novel anti-VF drugs. Our purpose was to examine this proposition using the hitherto untested PAF antagonist, nupafant. EXPERIMENTAL APPROACH: Two rat heart preparations (Langendorff and 'dual coronary' perfusion) were used to assay nupafant's effects on ischaemia-induced VF, coronary flow and QT interval, and to test for the site-selectivity necessary if any effects on VF are caused by PAF antagonism. KEY RESULTS: Global (whole-heart) delivery of 10 microM nupafant, reduced the incidence of ischaemia-induced VF and widened QT interval without affecting coronary flow. Importantly, lower concentrations (0.1 and 1 microM) had no effect on VF, yet widened QT almost identically to 10 microM nupafant. When nupafant was delivered selectively to (and entrapped within) the involved region it partially protected against VF (P<0.05). This occurred without change in QT interval. Selective nupafant delivery to the uninvolved region was without effect. CONCLUSIONS AND IMPLICATIONS: Nupafant protects against ischaemia-induced VF primarily by site-selective actions in the ischaemic region but, unlike BN-50739, the effect is unrelated to its QT widening action, and is not compromised by any effect on coronary flow. This establishes proof of concept that VF suppression by PAF antagonism need not invariably be associated with QT prolongation or vasodilatation, justifying further development of this drug class.

Thrombolytic activity of BB-10153, a thrombin-activatable plasminogen.

BACKGROUND: BB-10153 is an engineered variant of human plasminogen, modified to be activated to plasmin by thrombin. Thrombin-activatable plasminogen was designed as a novel thrombolytic agent which would persist in the blood as a prodrug and be activated to plasmin only at fresh or forming thrombi by the thrombin that is tightly localized there. We previously described the construction of several thrombin-activatable plasminogens and their in vitro clot lysis activity. OBJECTIVES AND METHODS: The current study was an examination of the thrombolytic properties of BB-10153 in vivo; comparison was made with tissue-type plasminogen activator (t-PA) in a femoral artery copper coil thrombosis model in the anesthetized dog and rabbit. Heparin was not coadministered so that the fundamental activity of the agents could be compared. RESULTS: BB-10153, administered as an intravenous bolus of 5 mg kg(-1) in the dog and 10 mg kg(-1) in the rabbit, produced a comparable incidence of reperfusion to 3 mg kg(-1) t-PA. Reocclusion at these doses occurred in 4/4 dogs and 5/7 rabbits treated with t-PA and in 2/6 dogs and 0/10 rabbits treated with BB-10153. There was no reocclusion in three dogs dosed with 10 mg kg(-1) BB-10153. BB-10153 did not affect plasma alpha2-antiplasmin levels or the bleeding time, whereas 3 mg kg(-1) t-PA caused marked depletion of alpha2-antiplasmin and fibrinogen and increased the bleeding time. The plasma half-life of BB-10153 was 3-4 h. CONCLUSIONS: The long half-life and thrombus-selective thrombolytic activity of BB-10153 might allow it to overcome the bleeding and reocclusion shortfalls in the performance of current thrombolytics.

The role of nursing unit managers in educating nurses.

This paper presents the findings of a work sampling study undertaken in New South Wales (Australia) to ascertain the amount of time spent by nursing unit managers directly educating nurses. The results indicate that they spend very little time in teaching, traditionally one of their role tasks. It is argued that their teaching at unit level should focus on their role as leader, mentor, preceptor and coach. This role shift needs to be articulated to managers and nurses to minimise confusion over the role and to ensure that direct teaching is placed into the hands of expert clinicians.

Cardiovascular responses to carotid chemoreceptor stimulation in the dog: their modulation by urinary bladder distension.

Respiratory, heart rate and hindlimb vascular responses were studied in response to increasing levels of stimulation of the carotid body chemoreceptors, together with an examination of the modulation of their effects by distension of the urinary bladder in the dog anaesthetized with a mixture of chloralose and urethane. The vascularly isolated carotid bifurcation regions were perfused with blood, stimulation of the carotid bodies being carried out by three different levels of hypoxic isocapnic blood (PO2 approximately 58, 40 and 22 mmHg) obtained from a donor animal. A vascularly isolated hindlimb was autoperfused at constant blood flow through its femoral artery. In spontaneously breathing animals, increasingly intense hypoxic stimulation of the carotid bodies caused a progressive augmentation of respiratory minute volume. Superimposition of distension of the bladder increased ventilation further, by the same amount during hypoxic as during normoxic blood perfusion of the chemoreceptors. Prevention of the effects of lung stretch afferent stimulation by artificial ventilation modified the heart rate and hindlimb vascular responses to excitation of the carotid bodies by revealing or accentuating the primary cardiovascular responses, bradycardia and vasoconstriction. In contrast, no such respiratory modulation was apparent in the cardiovascular responses to bladder distension. When, under conditions of artificial ventilation and in the absence of changes in the arterial baroreceptor input, the primary cardio-inhibitory and vasoconstrictor responses to carotid chemoreceptor stimulation predominated, the heart slowed progressively as the stimulus was increased. At the same time the cardio-accelerator effects of bladder distension progressively diminished, indicating an interaction between the cardiac reflex responses evoked by the two inputs. In contrast, the reflex vascular responses resulting from stimulation of the two inputs were additive, at least for PO2 levels of carotid body perfusate down to approximately 40 mmHg. In conclusion these experiments demonstrate the differential nature of the integration of respiratory and cardiovascular responses evoked by stimulation of the carotid chemoreceptors and bladder distension.

Design and construction of a light-delivery system for photodynamic therapy.

We have developed a device to divide the output from a dye laser into as many as eight beams of equal power with negligible total power loss. In this system, 630-nm s-plane polarized laser light was split by a series of highly polarization-sensitive plate beamsplitters. Each of the beams was coupled to a 200, 400, or 600 microm diameter optical fiber. Brewster-window-type attenuators allowed the power of each beam to be individually set. It was possible to reconfigure the device to produce four, two, or one output(s). We discuss the design requirements of the beamsplitter device and describe its construction from mostly commercially available components. An apparatus for positioning and stabilizing each optical fiber relative to the skin surface of a patient is also described. The illumination from the fiberoptic supported by such an apparatus strikes a defined surface area and is independent of patient movement. Both the beamsplitter device and the optical fiber positioner are used routinely in photodynamic therapy (PDT) of malignant tumors in the clinic and in the laboratory.

Preclinical and clinical studies of MMP inhibitors in cancer.

The role of matrix metalloproteinases in tumor angiogenesis and growth is now well recognized for models of both human and animal cancer. Clinical studies currently under way with the prototype matrix metalloproteinase inhibitor, marimastat, will establish whether inhibitors of these enzymes are of benefit in the treatment of different types of human cancer. On chronic therapy in humans, marimastat induces a reversible tendinitis that can also be detected in certain animal species. This paper compares the ability of broad-spectrum and various types of selective matrix metalloproteinase inhibitors to induce tendinitis and to exhibit anticancer effects in an animal cancer model. Under conditions in which both systemic exposure and inhibitor potency are controlled, selective inhibitors are less pro-tendinitic, but are weaker anticancer agents than broad-spectrum agents such as marimastat. The clinical relevance of these findings is discussed.

Clinical and cost effectiveness of post-acute neurobehavioural rehabilitation.

The value of post-acute, community based social and behavioural rehabilitation for people with serious neurobehavioural disability has been the subject of a dispute for a number of years. Some authorities doubt that major changes in social adaptability and independence is possible several years post-injury. This paper attempts to assess both the clinical and cost effectiveness of such rehabilitation on a group who have suffered serious brain injury and display behaviour problems and cognitive deficits which prevent them living as independent members of the community. The discharge and follow-up data on 76 people who have received rehabilitation indicates that, with a minimum of 6 months rehabilitation, many severely damaged individuals can progress to less dependent placements in the community, and maintain higher levels of social activity (independence) with fewer hours of care support. This can amount to a per capita lifetime reduction of over 1 million pounds per annum in the cost of supporting such people in the community. Time between injury and the beginning of rehabilitation is a factor influencing outcome but longer periods of rehabilitation (beyond 12 months for the most seriously disabled) is not associated with a better outcome, measured by a reduction in care hours. The cost effectiveness of rehabilitation is greater for those who receive treatment within 2 years of injury. However, those who received rehabilitation at later stages also achieved significant social outcomes and savings on care hours.

Clinical effects of human macrophage inflammatory protein-1 alpha MIP-1 alpha (LD78) administration to humans: a phase I study in cancer patients and normal healthy volunteers with the genetically engineered variant, BB-10010.

BB-10010 is a genetically engineered variant of human macrophage inflammatory protein-1 alpha (hMIP-1 alpha) with improved pharmaceutical formulation properties. Although initially described as a pro-inflammatory cytokine, it is now recognised that hMIP-1 alpha has additional effects on haemopoietic stem cell cycling and on human immunodeficiency virus uptake by macrophages. In view of the potential clinical utility of the molecule, we have embarked on a clinical trials programme to evaluate the safety, tolerability and haematological effects of BB-10010. We now report the results of two phase I clinical studies in which 49 subjects (9 patients with advanced breast carcinoma and 40 normal healthy volunteers) received escalating doses of BB-10010, from 0.1 to 300 micrograms/kg using the subcutaneous (s.c.) or intravenous route (i.v.) of administration. Treatment was associated with a dose-related increase in monocyte count which peaked at 200% of steady-state levels and was preceded by an acute, short-lived, monocytopenia, 50-100% of baseline. no measurable effects were noted on other leucocyte subsets or on circulating progenitor cell numbers. In all cases, BB-10010 was extremely well tolerated with no significant toxicity observed at any dose level and a maximum tolerated dose was not defined. Pharmacokinetic analysis revealed that serum concentrations of BB-10010 were detectable using doses of > or = 10 micrograms/kg i.v. or > or = 30 micrograms/kg s.c., and that a single s.c. injection resulted in sustained plasma levels over a 24 h period. These preliminary studies have confirmed the safety and tolerability of BB-10010 using a dose range up to 300 micrograms/kg. Further clinical studies are ongoing to determine the biological effects and to investigate the potential myeloprotective properties using a variable dose range and schedule of BB-10010 in combination with cytotoxic chemotherapy.

A randomized phase-II study of BB-10010 (macrophage inflammatory protein- 1alpha) in patients with advanced breast cancer receiving 5-fluorouracil, adriamycin, and cyclophosphamide chemotherapy.

BB-10010 is a variant of the human form of macrophage inflammatory protein-1alpha (MIP-1alpha), which has been shown in mice to block the entry of hematopoietic stem cells into S-phase and to increase their self-renewal capacity during recovery from cytotoxic damage. Its use may constitute a novel approach for protecting the quality of the stem cell population and its capacity to regenerate after periods of cytotoxic treatment. Thirty patients with locally advanced or metastatic breast cancer were entered into the first randomized, parallel group controlled phase II study. This was designed to evaluate the potential myeloprotective effects of a 7-day regimen of BB-10010 administered to patients receiving six cycles of 5-fluorouracil (5-FU), adriamycin, and cyclophosphamide (FAC) chemotherapy. Patients were randomized, 10 receiving 100 microgram/kg BB-10010, 11 receiving 30 microgram/kg BB-10010, and nine control patients receiving no BB-10010. BB-10010 was well-tolerated in all patients with no severe adverse events related to the drug. Episodes of febrile neutropenia complicated only 4% of the treatment cycles and there was no difference in incidence between the treated and nontreated groups. Studies to assess the generation of progenitor cells in long-term bone marrow cultures were performed immediately preceding chemotherapy and at the end of six dosing cycles in 18 patients. Circulating neutrophils, platelets, CD 34(+) cells, and granulocyte/macrophage colony-forming cell (GM-CFC) levels were determined at serial time points in cycles 1, 3, and 6. The results showed similar hemoglobin and platelet kinetics in all three groups. On completion of the six treatment cycles, the average pretreatment neutrophil levels were reduced from 5.3 to 1.7 x 10(9)/L in the control patients and from 4.3 to 1.9 and 4.5 to 2.5 x 10(9)/L in the 30/100 microgram/kg BB-10010 groups, respectively. Relative to their pretreatment values, 50% of the patients receiving BB-10010 completed the treatment with neutrophil values significantly higher than any of the controls (P = .02). Mobilization of GM-CFC was enhanced by BB-10010 with an additional fivefold increase over that generated by chemotherapy alone, giving a maximal 25-fold increase over pretreatment values. Bone marrow progenitor assays before and after this standard regimen of chemotherapy indicated little long-term cumulative impairment to recovery from chemotherapy. Despite the limited cumulative damage to the bone marrow, which may have minimized the protective value of BB-10010 during this regimen of chemotherapy, better recovery of neutrophils in the later treatment cycles with BB-10010 was indicated in a number of patients.

Matrix metalloproteinase expression during experimental autoimmune encephalomyelitis and effects of a combined matrix metalloproteinase and tumour necrosis factor-alpha inhibitor.

Matrix metalloproteinases (MMPs) are a large family of Zn2+ endopeptidases that are expressed in inflammatory conditions and are capable of degrading connective tissue macromolecules. MMP-like enzymes are also involved in the processing of a variety of cell surface molecules including the pro-inflammatory cytokine TNF-alpha. MMPs and TNF-alpha have both been implicated in the pathology associated with neuro-inflammatory diseases (NIDs), particularly multiple sclerosis (MS) and its animal model experimental autoimmune encephalomyelitis (EAE). We have shown that BB-1101, a broad spectrum hydroxamic acid-based combined inhibitor of MMP activity and TNF processing, reduces the clinical signs and weight loss in an acute EAE model in Lewis rats. However, little is known about which MMPs are involved in the neuroinflammatory process. In order to determine the optimum inhibitory profile for an MMP inhibitor in the treatment of NID, we investigated the profile of MMP expression and activity during EAE. The development of disease symptoms was associated with a 3-fold increase in MMP activity in the cerebrospinal fluid (CSF), which could be inhibited by treatment with BB-1101, and an increase in 92 kDa gelatinase activity detected by gelatin substrate zymography. Quantitative PCR analysis of normal and EAE spinal cord revealed the expression of at least seven MMPs. Of these, matrilysin showed the most significant change, being elevated over 500 fold with onset of clinical symptoms and peaking at maximum disease severity. Of the other six MMPs detected, 92 kDa gelatinase showed a modest 5 fold increase which peaked at the onset of clinical signs and then declined during the most severe phase of the disease. Matrilysin was localised by immunohistochemistry to the invading macrophages within the inflammatory lesions of the spinal cord. Matrilysin's potent broad spectrum proteolytic activity and its localisation to inflammatory lesions in the CNS suggest this enzyme could be particularly involved in the pathological processes associated with neuro-inflammatory disease.

Sensitivity and specificity of QEEG in children with attention deficit or specific developmental learning disorders.

The sensitivity and specificity of QEEG-based discriminant functions were evaluated in populations of children diagnosed with specific developmental learning disorders and those with attention deficit disorders. Both populations of children could be distinguished from each other, and from the normal population, with high levels of accuracy. Pretreatment QEEG could be utilized to distinguish ADD/ADHD children who responded to dextroamphetamine from those who responded to methylphenidate, again with high levels of accuracy. This paper provides a replication of all presented discriminant functions, and should provide the research basis for the generalized utilization of QEEG in the initial evaluation of children with learning and/or attention disorders.

BB-10010: an active variant of human macrophage inflammatory protein-1 alpha with improved pharmaceutical properties.

The stem cell inhibitor, macrophage inflammatory protein-1 alpha (MIP-1 alpha) or LD78, protects multipotent hematopoietic progenitors in murine models from the cytotoxic effects of chemotherapy. Clinical use of human MIP-1 alpha during chemotherapy could therefore lead to faster hematologic recovery and may allow dose intensification. We have also shown that human MIP-1 alpha causes the rapid mobilization of hematopoietic cells, suggesting an additional clinical use in peripheral blood stem cell transplantation. However, the clinical evaluation of human MIP-1 alpha is complicated by its tendency to associate and form high molecular weight polymers. We have produced a variant of rhMIP-1 alpha, BB-10010, carrying a single amino acid substitution of Asp26 > Ala, with a reduced tendency to form large polymers at physiologic pH and ionic strength. This greatly increases its solubility, facilitating its production and clinical formulation. We confirmed the potency of BB-10010 as a human MIP-1 alpha-like agonist in receptor binding, calcium mobilization, inhibition of colony formation, and thymidine suicide assays. The myeloprotective activity of BB-10010 was shown in a murine model of repeated chemotherapy using hydroxyurea. BB-10010 is therefore an ideal variant with which to evaluate the therapeutic potential of recombinant human MIP-1 alpha.

Urinary bladder distension: its effects on carotid baroreceptor reflex left ventricular inotropic response in the dog.

1. The effects of distension of the urinary bladder on heart rate, maximum rate of change of left ventricular pressure (dP/dt max) and hindlimb vascular resistance together with their modulation at different carotid sinus pressures were studied in dogs anaesthetized with a mixture of chloralose and urethane and artificially ventilated. 2. When the carotid sinus mean perfusion pressure was raised in randomly selected steps from 60 to 210 mmHg, it caused a progressive bradycardia, and a reduction in left ventricular dP/dt max and in arterial blood pressure, together with vasodilatation in the perfused hindlimb. Distension of the bladder at each level of carotid sinus pressure resulted in tachycardia, a small but significant increase in left ventricular dP/dt max (160 +/- 30 mmHg s-1) and hindlimb vasoconstriction. 3. When heart rate and arterial blood pressure were held constant to exclude these secondary effects on left ventricular dP/dt max, raising the carotid sinus pressure caused a progressive reduction in left ventricular dP/dt max and hindlimb vasodilatation. Superimposition of tests of bladder distension at each level of sinus pressure resulted in variable responses, but overall there was a significant increase in left ventricular dP/dt max of 190 +/- 54 mmHg s-1. Hindlimb vasocontriction, however, was a consistent finding. 4. The gain of the relationship between the carotid sinus perfusion pressure and left ventricular dP/dt max was unaffected by distension of the bladder. 5. It is concluded that, when changes secondary to increases in heart rate and blood pressure are prevented, distension of the bladder causes a small but significant reflex increase in left ventricular dP/dt max. The responses, however, are variable and the possible reasons for this are discussed.

Mobilization of early hematopoietic progenitor cells with BB-10010: a genetically engineered variant of human macrophage inflammatory protein-1 alpha.

BB-10010 is a genetically engineered variant of human macrophage inflammatory protein-1 alpha with improved solution properties. We show here that it mobilizes stem cells into the peripheral blood. We investigated the mobilizing effects of BB-10010 on the numbers of circulating 8-day spleen colony-forming units (CFU-S8), CFU-S12, and progenitors with marrow repopulating ability (MRA). A single subcutaneous dose of BB-10010 caused a twofold increase in circulating numbers of CFU-S8, CFU-S12, and MRA 30 minutes after dosing. We also investigated the effects of granulocyte colony-stimulating factor (G-CSF) and the combination of G-CSF with BB-10010 on progenitor mobilization. Two days of G-CSF treatment increased circulating CFU-S8, CFU-S12, and MRA progenitors by 25.7-, 19.8-, and 27.7-fold. A single administration of BB-10010 after 2 days of G-CSF treatment increased circulating CFU-S8, CFU-S12, and MRA even further to 38-, 33-, and 100-fold. Splenectomy resulted in increased circulating progenitor numbers but did not change the pattern of mobilization. Two days of treatment with G-CSF then increased circulating CFU-S8, CFU-S12, and MRA by 64-, 69-, and 32-fold. A single BB-10010 administration after G-CSF treatment further increased them to 85-, 117-, and 140-fold, respectively, compared with control. We conclude that BB-10010 causes a rapid increase in the number of circulating hematopoietic progenitors and further enhances the numbers induced by pretreatment with G-CSF. BB-10010 preferentially mobilized the more primitive progenitors with marrow repopulating activity, releasing four times the number achieved with G-CSF alone. Translated into a clinical setting, this improvement in progenitor cell mobilization may enhance the efficiency of harvest and the quality of grafts for peripheral blood stem cell transplantation.

Amelioration of experimental acute pancreatitis with a potent platelet-activating factor antagonist.

The effect of a potent platelet-activating factor (PAF) antagonist, BB-882, on an experimental model of acute pancreatitis induced in male Wistar rats by a technique of microvascular ischaemia was studied. A single intraperitoneal injection of BB-882 (5 mg/kg) 30 min after induction of the disease in 12 animals significantly reduced (P < 0.001) the rise in the level of serum amylase (mean 2477 (range 2100-3280) units/l) compared with that in 12 control animals (mean 3928 (range 2800-5900) units/l) and significantly improved (P < 0.001) the mean pancreatic histology score (5.0 (range 3-10) versus 12.3 (range 8-18) in controls). PAF is a biologically active ether phosphorylcholine synthesized in cell membranes and a potent inflammatory mediator. Pancreatic tissue levels of this compound are increased in experimental acute pancreatitis and pretreatment with PAF receptor antagonists can ameliorate the progression of this disease. BB-882 alters the early course of experimental pancreatitis and may have a clinical therapeutic role.

Effects of distension of the urinary bladder on the cardiovascular reflexes from the carotid baroreceptors in the dog.

1. The hindlimb vasoconstrictor effects of distension of the urinary bladder were studied at different levels of input from the carotid sinus baroreceptors in the dog anaesthetized with a mixture of chloralose and urethane. 2. The vascularly isolated hindlimb was perfused at constant blood flow through its femoral artery, so that a change in pressure gradient (mean femoral arterial perfusion pressure minus mean inferior vena caval pressure) indicated a similar directional change in vascular resistance. The vascularly isolated carotid sinus regions were perfused with blood at a constant pulsatile flow. 3. Raising the carotid sinus mean perfusion pressure in randomly selected steps of 30 mmHg from 60 to 210 mmHg had little effect on heart rate unless the blood pressure was controlled, when a progressive bradycardia occurred, but caused a progressive reduction in arterial blood pressure and vasodilatation in the perfused hindlimb. Distension of the bladder at each level of carotid sinus pressure resulted in tachycardia, hypertension and hindlimb vasoconstriction. 4. The cardiac responses to bladder distension were the same at all carotid sinus pressures. When the blood pressure was controlled, however, the response was reduced at high and low sinus pressures. 5. The relationship between the carotid sinus perfusion pressure and hindlimb perfusion pressure (i.e. vascular resistance) was affected by distension of the bladder in two ways. In the one, hindlimb perfusion pressure increased by approximately the same amount at all levels of carotid sinus pressure indicating resetting of the carotid sinus baroreceptor reflex control of hindlimb vascular resistance towards vasoconstriction without change in gain of the reflex. In the other, the pressure increases were diminished at the higher levels of carotid sinus pressure indicating both resetting and an increase in gain of the reflex. 6. Both types of response occurred in the spontaneously breathing animal, in animals artificially ventilated, while pacing the heart, with the arterial blood pressure maintained constant at about 100 mmHg, and after division of the cervical vagosympathetic nerves. The frequency of occurrence of each type of response, however, varied under the different conditions. 7. The possible reasons for the two types of vascular response are discussed.

Reliability of labial closure force measurements in normal subjects and patients with CNS disorders.

This study determined the reliability of maximal upper and lower lip closing forces measured using a strain-gauged cantilever beam assembly. An intraclass correlation approach was used to explicitly partition the "error free" between-subject variance and measurement error variance across repeated days (2) and across repeated trials (5). Ten healthy adults served as controls and 30 patients with diagnoses of multiple sclerosis, cerebrovascular accident, or Parkinson's disease served as subjects. The intraclass correlation analyses revealed generally high reliability (R greater than .90) for upper and lower lip force measurements, for various combinations of control and/or patient groups, and within each individual patient group. There was moderate correspondence between the quantitative measures of lip force and the clinical assessment of combined upper (r = .67) and lower lip closure force (r = .62) but low correspondence between the quantitative measures of lip force and the presence of motor speech deficit. The lower lip force of patients with Parkinson's disease (M = 3.1 N) on Day 1 was markedly reduced from that of all other patient groups and controls (M = 10.1 N). These results yield helpful information for the design of investigations of oral-motor weakness and for the quantitative assessment of an individual's clinical status.

A comparison of vasodilator activity of agents activating cyclic nucleotides with those inhibiting their metabolism in rabbit isolated ear artery.

1. The effects of forskolin, a direct activator of adenylate cyclase and sodium nitroprusside, a direct activator of guanylate cyclase, were studied on rabbit isolated ear arteries preconstricted with 80 mM potassium. 2. Bolus injection of these two compounds resulted in vasodilatation. They had similar potencies in this tissue but forskolin had a significantly longer duration of action than sodium nitroprusside. 3. In the same tissue, perfusion with isobutylmethylxanthine (IBMX), a non-selective phosphodiesterase (PDE) inhibitor, or zaprinast, selective for the PDE primarily responsible for the metabolism of guanosine 3':5'-cyclic monophosphate (cyclic GMP), resulted in vasodilatation. However, SK&F 94120 selective for cyclic AMP-PDE (PDE III), primarily responsible for the metabolism of adenosine 3':5'-cyclic monophosphate (cyclic AMP), resulted in vasodilatation only at very high concentrations. The rank order of potency for the compounds was IBMX greater than zaprinast greater than SK&F 94120. 4. The effects of these three PDE inhibitors were studied on the vasoconstriction produced by perivascular sympathetic nerve stimulation in the absence of raised potassium. IBMX and zaprinast, caused a reduction in the response at 50 Hz stimulation frequency and a shift in the frequency-response curve to the right. SK&F 94120 did not displace the frequency-response curve but did reduce the response at 50 Hz. The same order of potency for the inhibition of the vasoconstrictor responses to perivascular sympathetic nerve stimulation was found as for vasodilatation i.e. IBMX greater than zaprinast greater than SK&F 94120. 5. These results indicate that in the same tissue direct activation of adenylate and guanylate cyclase results in vasodilatation. Non-specific PDE and cyclic GMP-PDE inhibition also resulted in vasodilatation and inhibition of vasoconstrictor responses to sympathetic nerve stimulation. However a selective cyclic AMP-PDE (PDE III) inhibitor did not result in vasodilatation, except at very high concentrations, or inhibit sympathetic vasoconstrictor responses except to reduce the response at 50Hz stimulation. These findings provide further support for the ability of PDE inhibitors to be tissue selective.

Cardiovascular responses to stimulation of cardiac receptors in the cat and their modification by changes in respiration.

1. In cats anaesthetized with a mixture of chloralose and urethane, stimulation of cardiac receptors by left atrial injections of veratridine had little or no effect on pulmonary ventilation but caused bradycardia, systemic hypotension and hindlimb vasodilation with a latency of 3.3 s. 2. The hindlimb vasodilatation was due largely, if not entirely, to a reduction in sympathetic vasoconstrictor activity. 3. Similar cardiovascular responses occurred when the arterial blood pressure was maintained constant and also in artificially ventilated animals. 4. When the cardiac receptors were excited during a period of apnoea which was induced reflexly by electrical stimulation of the central cut end of a superior laryngeal nerve, the cardio-inhibitory response to left atrial injections of veratridine was enhanced but the size of the vasodilator response was unaffected. 5. In contrast, the cardiovascular effects of stimulation of the carotid body chemoreceptors, bradycardia and hindlimb vasoconstriction were enhanced by the laryngeal input. 6. The possible central mechanism responsible for the differential modulation of cardiac receptor and carotid chemoreceptor reflexes by respiration are discussed.

Synaptic rhythm of caudal medullary expiratory neurones during stimulation of the hypothalamic defence area of the cat.

1. Intracellular recordings were made from caudal medullary expiratory neurones in anaesthetized, paralysed, artificially ventilated and vagotomized cats before during and after the tachypnoeic response evoked by stimulation of the perifornical region of the hypothalamus. 2. The tachypnoeic response was evoked in seven of ten cats tested, and was represented in the phrenic nerve by a rapid two- to threefold increase in the frequency of the respiratory rhythm. The shortened duration of inspiratory discharge in the phrenic nerve was accompanied by an increase in its rate of development. If initially present, post-inspiratory phrenic discharge was intensified and extended throughout the shortened expiratory interval. 3. Intracellular recordings were obtained from twenty-one expiratory neurones during intermittent hypothalamic stimulation with short trains of pulses. Eighteen neurones showed a regular, short-latency sequence of synaptic events which consisted of an initial depolarizing potential (presumed EPSP) and a following hyperpolarizing potential (Cl--mediated IPSP) of long duration (50-150 ms when measured in expiration). The IPSP was accompanied by a phasic cessation of phrenic nerve discharge of comparable duration which was succeeded by intensified discharge. In three neurones (one experiment) the IPSP response was absent. 4. Sixteen neurones showing the EPSP-IPSP sequence were held for sufficiently long to record changes in the respiratory-related membrane potential pattern accompanying stimulation. The reduced expiratory time accompanying the response resulted in a shortened expiratory burst. In four neurones showing evidence of IPSPs in early expiration (post-inspiratory IPSPs), stimulation resulted in a phasic weakening of this inhibition which resulted in a more rapid approach to threshold and a steady rather than delayed increase in discharge. A low level of post-inspiratory IPSPs extended throughout most of the shortened expiration, resulting in an alternating rhythm of inspiratory and post-inspiratory inhibition. In the twelve neurones lacking such post-inspiratory IPSPs stimulation had no obvious effect on the shape of the expiratory trajectory. 5. In neurones which received an IPSP from hypothalamic stimulation, the overall response was associated with reduced amplitude and increased rate of decline of inspiratory inhibition of expiratory neurones. Three neurones showed high-frequency (70-80 Hz) oscillation of the membrane potential during inspiration (Mitchell & Herbert, 1974b). Hypothalamic stimulation resulted in a transient suppression of this oscillation. 6. We conclude that the short-latency inhibitory component of the response to hypothalamic stimulation is widely distributed, including expiratory neurones, some fraction of the inspiratory population and the neurones responsible for inspiratory and post-inspiratory inhibition.