Conjunctivitis in dupilumab clinical trials.

BACKGROUND: Dupilumab blocks the shared receptor component for interleukin (IL)-4 and IL-13. It is approved in the U.S.A. for patients aged ≥ 12 years with moderate-to-severe atopic dermatitis (AD) uncontrolled by topical prescription medicines or who cannot use topical medicines, for patients in Japan whose AD is uncontrolled with existing therapies, for patients with moderate-to-severe AD in Europe who are candidates for systemic therapy and for patients aged ≥ 12 years for maintenance treatment of moderate-to-severe asthma uncontrolled with their current medicines. AD trials have reported increased incidence of conjunctivitis for dupilumab vs. placebo. OBJECTIVES: To characterize further the occurrence and risk factors of conjunctivitis in dupilumab clinical trials. METHODS: We evaluated randomized placebo-controlled trials of dupilumab in AD (n = 2629), asthma (n = 2876), chronic rhinosinusitis with nasal polyps (CRSwNP) (n = 60) and eosinophilic oesophagitis (EoE) (n = 47). RESULTS: In most AD trials, dupilumab-treated patients had higher conjunctivitis incidence than placebo controls. Higher baseline AD severity and previous history of conjunctivitis were associated with increased conjunctivitis incidence. Conjunctivitis was mostly mild to moderate. Most cases recovered or resolved during the treatment period; two patients permanently discontinued dupilumab due to conjunctivitis or keratitis. Common treatments included ophthalmic corticosteroids, antibiotics, and antihistamines or mast cell stabilizers. Most cases were diagnosed by the investigators. In asthma and CRSwNP trials, the incidence of conjunctivitis was lower for both dupilumab and placebo than in AD trials; dupilumab did not increase the incidence compared with placebo. In the EoE trial, no patients had conjunctivitis. CONCLUSIONS: Conjunctivitis was more frequent with dupilumab treatment in most AD trials. In dupilumab trials in other type 2 diseases, incidence of conjunctivitis was overall very low, and was similar for dupilumab and placebo. In AD, the incidence of conjunctivitis was associated with AD severity and prior history of conjunctivitis. The aetiology and treatment of conjunctivitis in dupilumab-treated patients require further study. What's already known about this topic? Ocular disorders, including allergic conjunctivitis, are common in patients with atopic dermatitis (AD). In most dupilumab AD trials, dupilumab-treated patients had higher conjunctivitis incidence than those receiving placebo. Most cases were mild to moderate and recovered or were recovering during study treatment; study treatment discontinuation due to conjunctivitis was rare. Conjunctivitis incidence was very low and similar for dupilumab and placebo in clinical trials in asthma, chronic rhinosinusitis with nasal polyps and eosinophilic oesophagitis. What does this study add? This analysis confirms and extends the results of the individual clinical trials. Baseline disease-related factors, including AD severity, prior conjunctivitis history and certain biomarkers (thymus and activation-regulated chemokine, IgE, eosinophils), were associated with increased incidence of conjunctivitis. Patients who responded well to dupilumab had reduced incidence of conjunctivitis. Further study is needed to elucidate the aetiology and treatment of conjunctivitis in dupilumab-treated patients with AD.

Hypothalamic 5 alpha-reductase and 3 alpha-oxidoreductase activity in the male rat.

The aim of the present study was to assess the progesterone (Pr) transforming 5 alpha-reductase (5 alpha-R) and 3 alpha-oxidoreductase (3 alpha-OR) activities in the hypothalamus of the male rat as a function of age and following castration and/or adrenalectomy performed at the sixth day of life. The hypothalamic activity of these enzymes was estimated from the sum of the 5 alpha- or 3 alpha-reduced metabolites produced from 14C-labeled Pr incubated "in vitro" with hypothalamic tissue. Plasma levels of testosterone (T), progesterone (Pr), estrone (E1), luteinizing hormone (LH) and follicle stimulating hormone (FSH) were measured simultaneously. Special attention was paid to the GC/MS analysis of the endogenous content of the hypothalamic Pr-metabolites 3 alpha-hydroxy-pregn-4-en-20-one (3 alpha-Pr), 5 alpha-pregnane-3,20-dione (5 alpha-Pr) and 3 alpha-hydroxy-5 alpha-pregnan-20-one (5 alpha,3 alpha-Pr). The high 5 alpha-R and 3 alpha-OR activities estimated in the hypothalamus of prepubertal rats are not related to the action of gonadal or adrenal steroids. Substantial and comparable endogenous 3 alpha- and/or 5 alpha-Pr-metabolites were found in hypothalami from both prepubertal and mature rats. The results of the present study do not provide evidence for a contributory role of the 3 alpha-hydroxylated Pr derivative to the regulation of gonadotropin secretion in the male rat.

On the validity of blood flow measurement using colored microspheres.

The aim of this study was 1) to investigate the validity of repeated estimations of blood flow using colored microspheres (CMS) and 2) to develop and validate a method that permits four consecutive estimations in the same animal using nonradiolabeled microspheres (NRMS). Several mixtures of different types of microspheres were injected in dogs, with each mixture containing the radiolabeled microspheres (RMS; labeled with 113Sn) with either three CMS, four CMS, or three CMS and one type of fluorescent (crimson labeled) microsphere (FMS). The blood flows estimated with the use of any of the injected microspheres were compared with those measured using the RMS as the "gold standard." The results were analyzed by 1) regression analysis, 2) variance analysis (ANOVA I), and 3) estimation of the limits of agreement between RMS and NRMS flow rates. The results indicate that simultaneous estimations of blood flow obtained with the use of more than three CMS lack accuracy and reliability. A combination of three types of CMS with crimson-labeled FMS, however, offers the possibility to estimate consecutively four different flow rates in the same animal in an accurate way and with relatively high precision.

Progesterone-transforming enzyme activity in the hypothalamus of the male rat.

The aim of the present study was to assess the activities of the progesterone (Pr) transforming enzyme systems 3alpha-oxidoreductase (3alpha-OR), 5alpha-reductase (5alpha-R) and 20alpha-oxidoreductase (20alpha-OR) in the hypothalamus of the male rat, at different stages of sexual maturation and following castration and adrenalectomy. Special attention was paid to transformation to 3alpha-reduced compounds previously shown to inhibit FSH synthesis and secretion. Homogenates of hypothalamic tissue were incubated with 14C-progesterone. Pr-metabolites were isolated, identified by gas chromatography/mass-spectrometry (GC/MS) and measured by liquid scintillation counting (LSC). In adult rats a ratio of 6:2.5:1 for 5alpha-R:3alpha-OR:20alpha-OR enzyme- activities was found. The hypothalamic 5alpha-R and particularly 3alpha-OR activities were considerably higher before puberty (10-20 day old rats) than in adulthood. Adrenalectomy in adult rats resulted in an increased activity of the three enzyme systems. No significant changes were seen following castration. Among the isolated metabolites, 3alpha-hydroxy-pregn-4-en-20-one (3alpha-Pr) and 3alpha-hydroxy-5alpha-pregnane-20-one (5alpha,3alpha-Pr) were identified. Conversion to both these neurosteroids was considerably higher during prepuberty than in adulthood. The finding that before puberty the hypothalamus has a markedly increased capacity to convert Pr to 3alpha-reduced compounds, such as 3alpha-Pr, known to effectively inhibit FSH release, warrants further research into the mechanisms regulating the hypothalamic formation of biologically active Pr derivatives and their role in the regulation of gonadotropin secretion.

Hemodynamic and metabolic effects of flunarizine in experimental subarachnoid hemorrhage in dogs.

BACKGROUND AND PURPOSE: Cerebral blood flow and oxygen metabolism were measured and a cerebral angiography was performed in dogs with experimental subarachnoid hemorrhage to assess the relation between arterial narrowing (vasospasm) and the fall of blood flow. Cerebral blood volume and the cerebrovascular CO2 reactivity were also measured to estimate the cerebrovascular reserve. Several groups of dogs were treated with flunarizine in different regimens to assess its possible therapeutic effect. METHODS: The experiments were performed in the three-hemorrhage canine model for subarachnoid hemorrhage. Cerebral blood flow and cerebral oxygen metabolism were measured in anesthetized (nitrous oxide) dogs using positron emission tomography in combination with the 15O steady-state method. Basilar artery diameter was evaluated by digital subtraction angiography. RESULTS: In normal dogs, cerebral blood flow, oxygen consumption, and oxygen extraction ratio were 46.4 +/- 9.0 ml/100 ml per minute, 3.65 +/- 0.76 ml/100 ml per minute, and 39.9 +/- 3.4%, respectively; basilar artery diameter was 1.33 +/- 0.25 mm. Repeated subarachnoid blood injection (3 x 5 ml) reduced basilar artery diameter to < 20% of normal (p < 0.01). Cerebral blood flow was reduced by only 25% (p < 0.001); oxygen consumption was preserved at a low normal level by a 29% compensatory increase of the oxygen extraction (p < 0.001). Cerebral blood volume and cerebrovascular CO2 reactivity remained nearly normal. Early (after the first blood injection) peroral treatment with flunarizine (0.5 mg/kg daily) resulted in less severe basilar artery narrowing (56% of normal; p < 0.05 versus untreated). However, this treatment had no effect on cerebral blood flow, blood volume, oxygen consumption, and extraction. CONCLUSIONS: The observed fall of cerebral blood flow in experimental subarachnoid hemorrhage is not related to arterial narrowing but to an increased cerebrovascular resistance at the level of the small parenchymal vessels, and the latter, in contrast to arterial narrowing, is unaffected by flunarizine.

Streptokinase treatment versus calcium overload blockade in experimental thromboembolic stroke.

Thromboembolic brain ischemia was produced in dogs using an autologous blood clot model. The effect of postembolic treatment with flunarizine and streptokinase on hemispheric cerebral metabolic rate for oxygen (CMRO2), oxygen extraction ratio (OER), and cerebral blood flow (CBF) was studied by positron emission tomography (oxygen-15 technique) 24 hours after the insult. We studied five groups of experimental dogs and compared them with a control group of nonembolized dogs. Group I received no treatment, Group II was treated locally with 500,000 IU streptokinase starting 30 minutes after the insult, Group III received streptokinase locally 30 minutes after the insult and 0.1 mg/kg i.v. flunarizine immediately after the insult and 2 hours later, Group IV received flunarizine as Group III, and Group V was orally pretreated with 0.5 mg/kg/day flunarizine during 2 weeks preceding embolization. Compared with the contralateral hemisphere, in the embolized hemisphere a significant reduction of CMRO2 (-25% to -40%) and CBF in normocapnia (-35%) and hypercapnia (-50%) was observed in Groups I, II, and V. In Groups III and IV, CMRO2, OER, and CBF of the embolized hemisphere were within the normal range during normocapnia and hypercapnia; the extent of the ischemic lesions was markedly less than in the other groups of experimental dogs. We conclude that flunarizine treatment after experimental thromboembolic stroke had a favorable influence on brain tissue. Chronic preventive flunarizine treatment failed to have a beneficial effect.

[The use of radionuclides, specifically positron-emission tomography, in the determination of the blood circulation and metabolism of the brain. Application in experimental cerebral embolism]. / Gebruik van radionucliden, in het bijzonder positronenemissietomografie bij het bepalen van de doorbloeding en het metabolisme van de hersenen. Toepassing bij experimentele hersenembolie.

The introduction of positron emission tomography (PET) to study the cerebral circulation and metabolism is for the present the last step in the evolution of a technology which started 40 years ago with the gas clearance method developed by Kety and Schmidt. To study cerebral blood flow and metabolism in humans the steady state 15O method (Frackowiak et al., 1980) is widely used in different PET centers. We have used this method in experimental animals. The principles of the method and the mathematical models which are at the basis of the calculation of cerebral blood flow (CBF) and oxygen metabolism (cerebral metabolic rate for oxygen, CMRO2 and oxygen extraction ratio, OER) are relatively simple but during its application in vivo several problems arise as described. The steady state method of Frackowiak et al. allowed in our experiments the accurate measurement of cerebral blood flow and oxygen metabolism in anesthetized dogs. We have investigated the effect of experimental cerebral embolism in different series of experiments. Two different models of cerebral ischemia were assessed. In the first model focal ischemia was produced by infusing Sephadex particles (mean diameter 40 microns) into the left common carotid artery; in the second model an autologous blood clot (100 microliters) was injected into the left internal carotid artery. With both procedures the ischemia was practically limited to the ipsilateral hemisphere. Moreover in the two models the effects of ischemia were very reproducible. This is probably due to the good standardization of the embolization procedures. The results clearly indicate a differential effect of microembolization with particles and blood clot embolization, illustrating the importance of the technique used to produce cerebral embolization in experimental animals. PET offers possibilities for diagnosis of cerebral ischemia. At variance with the classical techniques for studying cerebral blood flow PET also allows simultaneous assessment of cerebral metabolism and to differentiate between brain tissue which is irreversible damaged and tissue which can be potentially salvaged. Therefore PET also offers new possibilities in clinical and experimental research. The reproducible effects obtained with the blood clot model, the metabolic cerebral effects of which are similar to those of clinical stroke, will allow to study the effect of different therapeutic approaches for stroke such as thrombolysis and calcium entry blockade.

Experimental thromboembolic stroke studied by positron emission tomography: immediate versus delayed reperfusion by fibrinolysis.

Acute obstruction of the middle cerebral artery (MCA) was obtained by injecting a single autologous blood clot into the internal carotid artery of dogs. The technique induced very reproducible unilateral ischemic lesions in the MCA territory; hemorrhagic transformation of the lesions was often seen. The hemodynamic and metabolic effects of blood clot embolism were studied in 35 dogs with positron emission tomography (PET) and the 15O steady-state technique, and compared with a control group of seven intact animals. In the acute phase, the involved brain tissue still had a nearly normal oxygen consumption (-11%) despite the lowered tissue perfusion (-20%) caused by the vascular obstruction. The lowered oxygen availability was compensated by an increased oxygen extraction ratio (+11%). Twenty-four hours after the insult, the hemodynamic situation had barely changed, and the ischemic event had evolved into a brain infarct in which oxygen consumption was clearly lowered (-25%) and accompanied by a significant lowering (-22%) of the oxygen extraction ratio compared with the acute situation. Therapeutic thrombolysis by local administration of streptokinase (500,000 IU), starting 30 min after the insult, was not able to salvage any brain tissue or to ameliorate tissue perfusion despite angiographically confirmed clot lysis. However, when fibrinolytic therapy was started within the first 5 min after the insult, hemispheric blood flow was normalized, and most of the threatened brain tissue was salvaged, as was indicated by its normalized oxygen consumption and oxygen extraction ratio. Early fibrinolysis was accompanied by definite clinical improvement and substantial reduction in the severity of the morphological lesions that were never hemorrhagic.

PET studies of changes in cerebral blood flow and oxygen metabolism after unilateral microembolization of the brain in anesthetized dogs.

Cerebral blood flow and oxygen metabolism have been measured with the steady-state oxygen-15 technique and positron emission tomography in anesthetized dogs. Regional microembolization was induced by infusing Sephadex particles (diameter, 40 micron) into one of the common carotid arteries. In the first series of experiments, 2.5 mg Sephadex was infused, and the dogs were examined within 3-4 hours after embolization. In a second series 0.55 mg Sephadex was infused, and the dogs were examined either in the first 3-4 hours or 24-48 hours after embolization. Cerebral blood flow, oxygen extraction ratio, and cerebral oxygen utilization were measured at 3 PCO2 levels. In the acute experiments, cerebral oxygen utilization in the embolized hemisphere was 6 (0.55 mg Sephadex) and 25% (2.5 mg Sephadex) lower than on the contralateral side. While cerebral blood flow was symmetrically distributed in normocapnia and hypocapnia, it was 9 (0.55 mg Sephadex) and 35% (2.5 mg Sephadex) lower in the embolized hemisphere during hypercapnia. In normocapnia and hypocapnia the lower oxygen utilization in the embolized hemisphere was characterized by a lower oxygen extraction ratio, and in hypercapnia by an unchanged (0.55 mg Sephadex) or by a higher (2.5 mg Sephadex) extraction ratio. The different effect on oxygen extraction ratio in the control and embolized hemispheres resulted in images of uncoupling between perfusion and oxygen demand that varied according to the PCO2. The experiments also showed a fall in cerebral blood flow in the embolized hemisphere after 3-4 hours, indicating delayed hypoperfusion. After 24-48 hours, blood flow was about 10% higher in the embolized hemisphere, and this was observed at the 3 PCO2 levels, while the oxygen extraction ratio was systematically lower. Oxygen utilization in the embolized hemisphere was depressed to practically the same extent as in acute experiments. It can be concluded that between 4 and 24 hours after microembolization the cerebral microcirculation shows important changes, with installation of luxury perfusion in the face of an unchanging decreased oxygen metabolism.

Local cerebral glucose utilization during intracerebral pH changes.

The effect of ventriculocisternal perfusion with mock CSF with alkaline or acidic pH on the local CMRglu (LCMRglu) in the caudatoputamen was studied in artificially ventilated and relaxed rats. In control rats both lateral cerebral ventricles were perfused with mock CSF at pH 7.4. In the experimental series one cerebral ventricle was infused with normal mock CSF while the other was infused with mock CSF in which the pH was decreased or increased by changing [HCO-3]. LCMRglu was depressed in acidotic brain tissue while it was strongly increased in alkalotic brain tissue. The importance of these alterations in brain glucose metabolism for the homeostatic regulation of brain pH is discussed.

Genetic factors in non-specific bronchial reactivity in rats.

Two bronchoconstrictory agents, serotonin (5 HT) and carbachol, were investigated in different inbred rat strains in order to delineate possible factors influencing the bronchial reactivity. The challenge was given intravenously and a single dose was given to an individual animal. Inbred strains of rats differed significantly from each other in their reactivity to 5 HT and to carbachol. IC rats were good reactors to both 5 HT and carbachol. RA rats were intermediate reactors to both agents. OM/N rats had a good reaction to 5 HT, but showed only a minor bronchoconstriction after carbachol. BN and LE rats were poor reactors to both agents. The strain reactivities to the 2 provocation agents were not related. Breeding studies, using a good reactor, IC, and a poor reactor, DA strain, showed that the bronchial reactivity to 5 HT was inherited with a pattern that fitted with the autosomal recessive way of inheritance, high reactivity being recessive.

Effect of amiloride on cisternal fluid [HCO3-] in acute respiratory acidosis.

In the present study we investigated if an amiloride inhibitable Na+ -H+ exchange mechanism may also be involved in the regulation of cisternal cerebrospinal fluid (CSF) [HCO3-] during acute respiratory acidosis (ARA). In anesthetized, paralyzed and ventilated dogs either mock CSF (group I, control) or mock CSF containing amiloride (group II) was injected into the cerebral lateral ventricles and ARA was induced by 8-10% CO2 breathing during 4 1/2 hours. During hypercapnia arterial PCO2 and plasma [HCO3-] rose respectively by about 35 mm Hg and 3 mmol/L in both groups. The rise in cisternal CSF PCO2 (about 40 mm Hg) was similar. However, changes in CSF [HCO3-] were significantly different between the two groups; in the control group, mean CSF [HCO3-] rose by 2.4, 4.1 and 4.4 mmol/L respectively, 1 1/2, 3 and 4 1/2 h after induction of ARA. In the amiloride group the respective rise was only 1.1, 2.5 and 2.5 mmol/L. The differences in CSF [HCO3-] could not be ascribed to differences in CSF lactate concentration. We conclude that an amiloride inhibitable Na+ -H+ exchange may play a role in the regulation of CSF [HCO3-] during acute respiratory acidosis in dogs.

Local cerebral glucose utilization in systemic acidosis.

Cerebral glucose metabolism (CMRglu) is decreased during acute and prolonged hypercapnic acidosis and during prolonged metabolic (HCl) acidosis; it is increased in acute (hypocapnic) metabolic acidosis and is not changed in acute isocapnic metabolic acidosis. The alteration in CMRglu can be explained by the changes occurring in intracerebral pH under these experimental conditions. In pontine gray matter, n. tractus solitarii, and n. ambiguus, three structures participating in the neuronal regulation of ventilation, local CMRglu is increased in all acidotic groups, suggesting coupling of function and metabolism at the local level during acidosis-induced hyperventilation.

Effects of 'DIDS', an anion transport blocker, on CSF [HCO3-] in respiratory acidosis.

During acute respiratory acidosis increments in cisternal cerebrospinal fluid (CSF) [HCO3-] approximate decrements in CSF [Cl-] with CSF [Na+] remaining unchanged; the mechanisms mediating this reciprocal anionic relationship are unclear. In the present study we investigated the effects of DIDS (4,4'-diisothiocyano-disulfonic stilbene), a known inorganic anion exchange blocker, on CSF ionic regulation in acute respiratory acidosis. In two groups of anesthetized paralyzed dogs we injected either mock CSF (group I, n = 8) or mock CSF containing DIDS (group II, n = 9) into the lateral cerebral ventricles. After 45 min, acute respiratory acidosis was induced for 6 h. During acute respiratory acidosis, CSF PCO2 rose in average by 38 mm Hg in both groups; increments in CSF [HCO3-], however, were significantly lower by about 2 mEq/L in DIDS-treated animals than in controls throughout the experimental period. Such differences were not due to changes in CSF lactate concentration which were similar in both groups. Furthermore, CSF [Na+] remained unchanged in both groups. Since disulfonic stilbene derivatives combine selectively with the carrier involved in anion transport and inhibit inorganic anion exchange, the data in the present study suggest that in the central nervous system a DIDS-inhibitable carrier is involved in the rise of CSF [HCO3-] observed during acute respiratory acidosis.

Effects of acetazolamide on ionic composition of cisternal fluid during acute respiratory acidosis.

We studied the effects of intravenous acetazolamide (50-200 mg/kg) on cerebrospinal fluid (CSF) electrolytes and pH regulation in 10 anesthetized and nephrectomized dogs (group II): acetazolamide was injected at -1 h, and respiratory acidosis was induced at zero time for 6 h. A control group of 10 animals (group I) was treated similarly except that an equal volume of 0.45% saline was injected intravenously instead of acetazolamide. The mean CSF PCO2 values in group I were 49.7 +/- 3.4 (SD), 50.2 +/- 3.6, 92.3 +/- 7.0, 100.3 +/- 8.1, and 97.8 +/- 7.3 Torr, respectively, at -1, 0, 3, 4.5, and 6 h; respective values in group II were 49.8 +/- 2.0, 55.2 +/- 5.2, 95.8 +/- 6.4, 103.1 +/- 16.7, and 104.9 +/- 14.1 Torr. During acute respiratory acidosis CSF [HCO3-] rose progressively with time in group I, and the mean values were 28.1 +/- 1.4 (SD), 29.2 +/- 1.7 and 30.1 +/- 1.9 mmol/l, respectively, 3, 4.5, and 6 h after induction of acidosis; respective values in group II were 28.2 +/- 1.1, 28.3 +/- 0.9, and 28.5 +/- 1.4 mmol/l. Acetazolamide at various doses administered inhibited any further rise in CSF [HCO3-] beyond the 3rd h of acidosis. The lower rise in CSF [HCO3-] in group II could not be ascribed to differences in CSF lactate concentration which changed similarly in both groups. Increments in CSF K+ and phosphate concentrations were significantly higher in the acetazolamide group than in the control group, the former presumably reflecting efflux of K+ from intracellular to extracellular fluid compartment. We conclude that in nephrectomized dogs during acute respiratory acidosis intravenously administered acetazolamide diminishes the rise in CSF [HCO3-], impairs CSF H+ regulation, and increases CSF K+ and phosphate concentrations.

Effects of SITS, an anion transport blocker, on CSF ionic composition in metabolic alkalosis.

Disulfonic stilbenes combine with the carrier protein involved in anion transport and inhibit the exchange of Cl- for HCO3- in a variety of biomembranes. Our aim was to determine whether such a mechanism is operative in the regulation of cerebrospinal fluid (CSF) [HCO3-] in metabolic alkalosis. In anesthetized, curarized, and artificially ventilated dogs either mock CSF (group I, 9 dogs) or mock CSF containing SITS, 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (group II, 7 dogs) was periodically injected into both lateral cerebral ventricles. During 6 h of isocapnic metabolic alkalosis, produced by intravenous infusion of Na2CO3 solution, plasma [HCO3-] was increased by approximately 14 meq/l in both groups. In SITS-treated animals the mean cisternal CSF [HCO3-] increased by 7.7 meq/l after 6 h, and this was significantly higher than the respective increment, 3.5 meq/l, noted in the control group. Increments in CSF [HCO3-] in both groups were reciprocated by decrements in CSF [Cl-] with CSF [Na+] remaining unchanged. Cisternal CSF PCO2 and lactate concentrations showed similar increments in both groups. It is hypothesized that in metabolic alkalosis a carrier transports HCO3- out of cerebral fluid in exchange for Cl- and that SITS inhibits this mechanism. The efflux of HCO3- out of CSF in metabolic alkalosis would minimize the rise in CSF [HCO3-] brought about by HCO3-] influx from blood into CSF and therefore contributes to the CSF [H+] homeostasis.

Response of local blood flow in the caudate nucleus of the cat to intraventricular administration of carbachol.

The effect of perfusion of the cerebral ventricles with artificial cerebrospinal fluid containing carbachol on the blood flow in the caudate nucleus of the cat and the possibility to inhibit this effect by anticholinergic drugs was studied by means of the hydrogen clearance technique. After a control period during which both lateral ventricles were perfused with artificial CSF of identical composition, the drug under study was added on one side (experimental side) while the other side continued to be perfused with the control artificial CSF (control side). The blood flow on the experimental side and on the control side were compared. A dose dependent response to carbachol was observed. Lower concentrations of carbachol (10(-6) up to 10(-4)M) caused vasodilatation whereas high concentrations (10(-3)M) caused local vasoconstriction. The increase in the local blood flow caused by the low carbachol concentrations was reduced by both atropine (10(-5)M) and hexamethonium (10(-3)M). The fall in CBF observed with the high carbachol concentration was prevented by atropine (10(-5)M). It may be concluded that low, physiologically more meaningful, carbachol concentrations cause a local vasodilatation due to interaction with both muscarinic and nicotinic receptors.

Correction of CSF HCO-3 after its experimental increase in normocapnia: inhibition by acetazolamide.

In anaesthetized normocapnic dogs CSF [HCO-3] was increased to ca 33 mmol/l by perfusing the brain ventricles for 45 min with a mock CSF containing a high [HCO-3] which in addition contained 2.5 mg/ml acetazolamide to inhibit central carbonic anhydrase. In dogs with normal plasma [HCO-3], CSF [HCO-3] fell by 5.4 mmol/l in 2 h following the end of the perfusion. Lowering plasma [HCO-3] to 11 mmol/l by infusing HCl intravenously increased the CSF [HCO-3] fall to 7.5 mmol/l. Increasing plasma [HCO-3] to 36 mmol/l completely impeded the fall in CSF [HCO-3]. It is concluded that in these experiments clearing of HCO-3 from the CSF is critically dependent on plasma [HCO-3]. When the data are compared to those of comparable experiments without intraventricular administration of acetazolamide (Weyne et al. 1982), they indicate that acetazolamide impedes clearing of HCO-3 from CSF at high and at normal plasma [HCO-3] but not at low plasma [HCO-3]. The experiments therefore suggest a dual contribution for the clearing of HCO-3 from the CSF after its experimental increase: diffusion along the CSF-plasma gradient for HCO-3 and a carbonic anhydrase dependent clearing of HCO-3.

Changes in the brain surface pH and cisternal cerebrospinal fluid acid-base variables in respiratory arrest.

Using flat-surface pH electrodes we continuously measured changes in the brain surface pH during respiratory arrest in anesthetized and paralyzed dogs which were previously ventilated with pure oxygen. Respiratory arrest was induced by halting the respirator. The mean arterial PO2 fell from 502.7 +/- 15.9 (1 SD) to 23.7 +/- 18.5, and the mean arterial PCO2 rose from 36.4 +/- 3.5 to 80.4 +/- 7.1 mm Hg, 10 min after asphyxia. The arterial blood pressure increased gradually over several minutes but fell relatively abruptly and profoundly at the end, due to circulatory failure. Initially, and as long as the arterial blood pressure and, therefore, cerebral blood flow were upheld (phase 1), changes in the brain surface pH were small (delta pH/delta t= -0.026 pH unit/min) in spite of severe hypercapnia. When cerebral perfusion pressure fell due to circulatory failure (phase 2), cerebral ischemia occurred and there was an abrupt fall in brain surface pH (delta pH/delta t= -0.067 pH unit/min). Changes in cisternal CSF [H+] grossly underestimated the magnitude of brain surface acidosis during the period of respiratory arrest; the initial difference between the mean brain surface fluid and cisternal CSF [H+] which was 8.9, rose to 15.1 and 47.4 nmol/L, respectively, 5 and 10 min after asphyxia. Changes in sagittal venous blood acid-base variables were more pronounced than those observed in the arterial blood or cisternal CSF; 5 min after respiratory arrest, arterial and sagittal venous blood and cisternal CSF and brain surface pH were 7.20, 7.09, 7.19 and 7.11, respectively. We conclude that (1) in the course of respiratory arrest cerebral outcome can potentially be determined by circulatory failure as evidenced by simultaneous changes in the arterial blood pressure and brain surface pH; (2) cisternal CSF acid-base changes lag behind those on the brain surface and CSF analyses provide unreliable information about the severity of brain acid-base changes during asphyxia; (3) changes in cerebral venous blood acid-base variables best represent the severity of metabolic aberrations in the brain during respiratory arrest.