Ventilatory long-term facilitation in unanesthetized rats

Wetested the hypothesis that unanesthetized rats exhibit ventilatorylong-term facilitation (LTF) after intermittent, but not continuous,hypoxia. Minute ventilation (E) and carbon dioxide production (CO₂) were measured inunanesthetized, unrestrained male Sprague-Dawley rats via barometricplethysmography before, during, and after exposure to continuous orintermittent hypoxia. Hypoxia was either isocapnic [inspiredO₂ fraction (FI_O2) = 0.08-0.09 and inspired CO₂ fraction(FI_CO2) = 0.04] or poikilocapnic(FI_O2 = 0.11 andFI_CO2 = 0.00). Sixty minutes afterintermittent hypoxia, E orE/CO₂ wassignificantly greater than baseline in both isocapnic and poikilocapnicconditions. In contrast, 60 min after continuous hypoxia,E andE/CO₂ were notsignificantly different from baseline values. These data demonstrateventilatory LTF after intermittent hypoxia in unanesthetized rats.Ventilatory LTF appeared similar in its magnitude (after accounting forCO₂ feedback), time course, and dependence on intermittenthypoxia to phrenic LTF previously observed in anesthetized,vagotomized, paralyzed rats.

     

Ventilatory response to hypoxia in unanesthetized newborn kittens

We studied the ventilatory response to hypoxia in 11 unanesthetized newborn kittens (n = 54) between 2 and 36 days of age by use of a flow-through system. During quiet sleep, with a decrease in inspired O2 fraction from 21 to 10%, minute ventilation increased from 0.828 +/- 0.029 to 1.166 +/- 0.047 l.min-1.kg-1 (P less than 0.001) and then decreased to 0.929 +/- 0.043 by 10 min of hypoxia. The late decrease in ventilation during hypoxia was related to a decrease in tidal volume (P less than 0.001). Respiratory frequency increased from 47 +/- 1 to 56 +/- 2 breaths/min, and integrated diaphragmatic activity increased from 14.9 +/- 0.9 to 20.2 +/- 1.4 arbitrary units; both remained elevated during hypoxia (P less than 0.001). Younger kittens (less than 10 days) had a greater decrease in ventilation than older kittens. These results suggest that the late decrease in ventilation during hypoxia in the newborn kitten is not central but is due to a peripheral mechanism located in the lungs or respiratory pump and affecting tidal volume primarily. We speculate that either pulmonary bronchoconstriction or mechanical uncoupling of diaphragm and chest wall may be involved.     

Indomethacin does not potentiate renovascular constriction during hypercapnia in unanesthetized rabbits

The role of prostanoids in regulation of the renal circulation during hypercapnia was examined in unanesthetized rabbits. Renal blood flow (RBF) was determined with 15 μm radioactive microspheres during normocapnia (PaCO₂ 30 mmHg) and hypercapnia (PaCO₂ 60 mmHg), before and after intravenous administration of indomethacin (10 mg/kg) or vehicle (n=6 for each group). Arterial blood pressure was not different among the 4 conditions in each group. RBF was 438±61 and 326 ± 69 (P<0.05) ml/min per 100 g during normocapnia and hypercapnia, respectively, before indomethacin, and following administration of indomethacin, RBF was 426 ± 59 ml/min per 100 g during normocapnia and 295 ± 60 ml/min per 100 g during hypercapnia (P<0.05). In the vehicle group, RBF was 409±74 and 226±45(P<0.05) ml/min per 100 g during normocapnia and hypercapnia, respectively, before vehicle; and following administration of vehicle, RBF was 371±46 ml/min per 100 g during normocapnia and 219 ± 50 (P<0.05) per 100 g during hypercapnia. RBF during normocapnia was not affected by administration of indomethacin or vehicle. The successive responses to hypercapnia were not different within the indomethacin and vehicle groups, and the second responses to hypercapnia were not different between the two groups. These findings suggest that prostanoids do not contribute significantly to regulation of the renal circulation during normocapnia and hypercapnia in unanesthetized rabbits.     

Indomethacin does not potentiate renovascular constriction during hypercapnia in unanesthetized rabbits

The role of prostanoids in regulation of the renal circulation during hypercapnia was examined in unanesthetized rabbits. Renal blood flow (RBF) was determined with 15 micron radioactive microspheres during normocapnia (PaCO2 congruent to 30 mmHg) and hypercapnia (PaCO2 congruent to 60 mmHg), before and after intravenous administration of indomethacin (10 mg/kg) or vehicle (n = 6 for each group). Arterial blood pressure was not different among the 4 conditions in each group. RBF was 438 +/- 61 and 326 +/- 69 (P less than 0.05) ml/min per 100 g during normocapnia and hypercapnia, respectively, before indomethacin, and following administration of indomethacin, RBF was 426 +/- 59 ml/min per 100 g during normocapnia and 295 +/- 60 ml/min per 100 g during hypercapnia (P less than 0.05). In the vehicle group, RBF was 409 +/- 74 and 226 +/- 45 (P less than 0.05) ml/min per 100 g during normocapnia and hypercapnia, respectively, before vehicle; and following administration of vehicle, RBF was 371 +/- 46 ml/min per 100 g during normocapnia and 219 +/- 50 (P less than 0.05) ml/min per 100 g during hypercapnia. RBF during normocapnia was not affected by administration of indomethacin or vehicle. The successive responses to hypercapnia were not different within the indomethacin and vehicle groups, and the second responses to hypercapnia were not different between the two groups. These findings suggest that prostanoids do not contribute significantly to regulation of the renal circulation during normocapnia and hypercapnia in unanesthetized rabbits.     

Unit activity of the posterior hypothalamus during brain and skin temperature changes in unanesthetized rabbits

Changes in the firing rate of posterior hypothalmic neurons in response to local elevation of the brain temperature by 0.6–1.5°C and to a rise and fall (separately and simultaneously) of the skin temperature by 3–5°C were investigated in unanesthetized rabbits. Neurons responding selectively to changes in brain temperature and skin temperature and neurons responding to both temperature stimuli were found in the posterior hypothalamus. During combined stimulation the unit activity was changed much more than in response stimulus. It is concluded that the region of the posterior hypothalamus participates in the integration of impulses from central and peripheral temperature receptors.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 490–496, September–October, 1973.     

Effects of almitrine on respiration in unanesthetized newborn rabbits

We previously demonstrated that almitrine, a peripheral chemoreceptor stimulant, increased tidal volume (VT), expired minute ventilation (VE), and respiratory frequency (f) and decreased inspiratory (TI) and expiratory time (TE) in sleeping adult cats. We now hypothesized that almitrine would induce an increase in ventilation in a young animal model. Respiration was studied by the barometric method in 11 unanesthetized New Zealand White rabbit pups between 3 and 6 days of age. Recordings were made in 0.21 FIO2 at base line and after cumulative intraperitoneal infusions of almitrine (2.5, 5.0, and 7.5 mg/kg). The chamber pressure deflection (proportional to VT after appropriate calculation) was computer sampled at 200 Hz. At least 100 breaths for each dose in each animal were analyzed. We found that a 7.5-mg/kg intraperitoneal dose of almitrine increased f to 135 +/- 9% (SE) of base line and decreased TE and TI to 72 +/- 8% and 79 +/- 8% of base line, respectively. Changes in VE, VT/TI, and VT were not significant. Recognizing that apnea is associated with inadequate ventilation and a prolonged TE (failure of the "inspiratory on-switch"), these results, particularly the increase in f and decrease in TE, suggest that almitrine might be useful in treating apnea in preterm infants.     

Hyaluronan affects extravascular water in lungs of unanesthetized rabbits

We have determined whether changes in lung hyaluronan content affect extravascular water in lungs of unanesthetized rabbits. Three groups of experiments were performed. In group 1 (n = 12), no infusions were given; in group 2, nine pairs of rabbits received either intravenous hyaluronidase (750 U.kg-1.min-1) or an equivalent volume of saline; in group 3, nine pairs of rabbits received either hyaluronidase or saline, followed by intravenous saline infusion amounting to 24% of body weight. At the end of each experiment, one lung was analyzed for extravascular lung water by the wet-dry method. Except for group 3, in all animals the other lung was analyzed for hyaluronan content by a method that involved hydrolyzing lung hyaluronan with fungal hyaluronidase to release reducing N-acetyl glucosamine groups, which were quantified. In group 1, lung hyaluronan, which varied from 50 to 159 micrograms/g dry wt (mean 106 +/- 35 micrograms/g dry wt), significantly correlated with variation in extravascular lung water (mean 4.2 +/- 0.3 g/g dry wt). In group 2 rabbits given hyaluronidase, lung hyaluronan was 40% lower and extravascular lung water was 14.6% lower than in paired controls (P less than 0.01). In group 3, volume expansion did not affect lung water, except after hyaluronidase when lung water was 47% higher than paired controls. We conclude that in the lung the content of hyaluronan is one of the determinants of extravascular water content.     

Effects of an adenosine analogue administration on the striatal NMDA receptors in an experimental model of epilepsy

Specific [3H]-MK801 binding to rat NMDA receptors following the administration of the convulsant drug 3-mercaptopropionic acid (MP) and the adenosine analogue cyclopentyladenosine (CPA) was studied in striatal membrane fractions. MP administration (150 mg/kg, i.p.) caused an increase of 53% and 82% in [3H]-MK801 binding during seizure and the postseizure period respectively. Administration of CPA (2 mg/kg, i.p.) raised [3H]-MK801 binding by 72%. When CPA was administered 30 min before MP and rats sacrificed at seizure (CPA + MPc), an increase of 64%, was observed. Saturation results indicate that receptor sites increased their maximal binding capacity (Bmax) in all treatments while the apparent dissociation constant (Kd) remained unchanged. MP administration brought about an increase of 52% and 42% in [3H]-MK801 binding sites during seizure and postseizure respectively. Administration of CPA raised receptor density by 75%. When CPA was administered 30 min before MP and rats sacrificed at seizure (CPA + MPc), an increase of 62%, was observed. These results show that striatal NMDA receptors have a selective role in seizure activity in the basal ganglia and that the adenosine analogue administration may modify [3H]-MK801 binding in a way similar to that of the convulsant drug.     

Inhibitory effect of an in vivo activated soft analogue of A-phenyl-B-triazolium metyrapone during pupariation in Sarcophaga bullata

Experiments with the ovoviviparous fleshfly Sarcophaga bullata (Parker) (Dipt., Sarcophagidae), showed that the compound 4-(dodecanoyloxymethyl)-1-(2-methyl-1-oxo-1-phenyl-2-propyl)-(1,2,4-triazolium) chloride (NKI-42002) was an in vivo inhibitor of the cytochrome P-450-dependent monooxygenase system (MFO) during pupariation. The hard analogue of A-phenyl-B-triazolium metyrapone and the soft analogue of A-phenyl-B-imidazolium metyrapone showed no specific activity. Our results suggest that the soft quaternary group may help the transport of A-phenyl-B-triazolium metyrapone to the MFO system.A dose of 0.8 nmole/spec. of NKI-42002 had both a specific (delay in pupariation:1.64 ratio) and toxic (perc. of mortality:56) effect. The effects of the 0.4 nmole/spec. NKI-42002 can be eliminated by the simultaneous injection of 0.4 pmole/spec. of 20-OH ecdysone. These reversal studies support the hypothesis that NKI-42002 interferes with the biosynthesis of 20-OH ecdysone.

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Résumé Au cours d'études sur la mouche ovovivipare Sarcophaga bullata, on a constaté que le composé 4-(dodécanoyloxyméthyl)-1-(2-méthyl-1-oxo-1-phenyl-2-propyl)-(1,2,4-triazolium) chlorure (NKI-42002) était un inhibiteur in vivo du système cyt. P-450 dépendant mono-oxygénase (MFO) lors de la formation des pupes. Les analogues, solide du A-phényl-B-triazolium métyrapone et fluide du A-phényl-B-imidazolium métyrapone, n'ont présenté aucune activité spéciale. Ces résultats suggèrent que le groupe quaternaire fluide peut faciliter le transfert du A-phényl-B-triazolium métyrapone au système MFO.La dose de 0,8 nmole/ind. de NKI-42002 a présenté une action tant spécifique (retard à la pupaison; ratio 1,64), que toxique (mortalité 56%). On peut éliminer l'influence d'une dose de 0,4 nmole/ind. de NKI-42002 par injection simultanée d'une dose de 0,4 pmole/ind. de 20-OH ecdysone. Ces résultats confortent l'hypothèse suivant laquelle le NKI-42002 interfère avec la biosynthèse de la 20-OH ecdysone.

     

An arsenical analogue of adenosine diphosphate.

An analogue of ADP was made in which the terminal phosphono-oxy group, -O-PO(OH)2, has been replaced by the arsonomethyl group, -CH2-AsO(OH)2. This compound cannot form a stable analogue of ATP because anhydrides of arsonic acids are rapidly hydrolysed, so that any enzyme that phosphorylates ADP and accepts this analogue as a substrate should release orthophosphate in its presence. The analogue proves to be a poor substrate for 3-phosphoglycerate kinase (V/Km is diminished by a factor of 10(2)-10(3)) and a very poor substrate for pyruvate kinase (V/Km is diminished by a factor of 10(5)-10(6)). No substrate action was detected with adenyl kinase and creatine kinase.