摘要:

Benzodiazepine binding to brain membrane preparations obtained from epileptic and nonepileptic carrier fowl was compared. [3H]Flunitrazepam binding to whole brain homogenates from 2-day-old chicks and [3H]diazepam binding to synaptosomal membranes and homogenates from adult chickens were determined. Scatchard analysis revealed no differences in either the number of receptors or their affinity for the ligands when the epileptics were sacrificed in the interictal state. Evoked seizures in adult epileptics had no effect on the number or affinity of binding sites using [3H]diazepam as the ligand. Moreover, the ability of gamma-aminobutyric acid to facilitate benzodiazepine binding was not different in epileptic fowl when compared with carriers.

ISSN:0008-4212    

DOI:10.1139/y85-016

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The purpose of the present studies was to examine, by micropuncture, the effect of salmon calcitonin on fractional sodium and solutes deliveries to the juxtamedullary end-descending limb of the rat. All animals were postprandial and thyro-parathyroidectomized Munich-Wistar rats. Group 1 (N = 8) consisted of time control water-diuretic rats; group 2 (N = 8) received synthetic salmon calcitonin (10 mU/min) intravenously while undergoing water diuresis; group 3 (N = 8) was treated as group 2 but also received calcium intravenously to prevent the calcitonin-induced fall in plasma calcium. Calcitonin, alone and with calcium, produced a marked fall in urine flow rate and a marked increase in urinary osmolality. Concomitant fractional water delivery to the end-descending limb fell significantly (28 ± 0.8 to 21 ± 1.0%,p < 0.05), while fractional solute and sodium deliveries increased significantly (36 ± 1.3 to 55 ± 2.6%,p < 0.05; 34 ± 2.0 to 48 ± 3.5%,p < 0.05, respectively). The three groups did not significantly differ in fractional water and sodium deliveries to the superficial end-accessible proximal tubule. We conclude that salmon calcitonin is antidiuretic in the rat and that it also produces an increase in fractional sodium and total solute deliveries to the end-descending limb, which we suggest is due to transepithelial sodium addition. The physiological significance of these observations to water homeostasis in vivo remains to be determined.

ISSN:0008-4212    

DOI:10.1139/y85-017

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

In the present study, we tested the hemodynamic and renal response of 15 sham-operated dogs and 15 dogs with subacute (5–9 days) biliary obstruction to either acute or more chronic hemorrhage. All studies were conducted on sedated but unanaesthetized animals. Both groups were comparable before blood withdrawal with respect to central hemodynamics and renal perfusion. Serum bilirubin was 0.70 ± 0.09 mg/dL for control dogs and 8.25 ± 0.14 for experimental dogs (P < 0.05). In the acute protocol, nine control and seven jaundiced dogs were bled over a period of 30–40 min to lower blood pressure by 19.1 and 19.5%, respectively. Blood volumes required to achieve this drop were 21.3 and 20.05 mL/kg, respectively (P > 0.05). Cardiac output declined by an equivalent value for each group and glomerular filtration rate and clearance ofp-arninohippurate remained unchanged from control values. In six control and eight experimental dogs, 500 mL of blood was withdrawn over 5 days. Although blood pressure and cardiac output declined for each group by an equivalent amount, renal perfusion remained unchanged for each group from control values. We conclude that acute or chronic hemorrhage of modest degree does not predispose to acute renal insufficiency in dogs with subacute biliary obstruction.

ISSN:0008-4212    

DOI:10.1139/y85-018

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Estimates of Na+pumping capacity were made using Na+-loaded canine iliac arteries. Ouabain-sensitive uptake of204Tl or86Rb was used to measure near-maximal pump rates and [3H]ouabain binding to measure the number of pump sites. Compared with Rb+, Tl+had the higher affinity for the pump and showed better signal-to-noise characteristics. Maximal uptakes were 0.545 μmol∙g−1∙min−1for Rb+and 0.40 μmol∙g−1∙min−1for Tl+Specific ouabain binding (Kd: 28.62 ± 0.58 nM) was inhibited by external K+, Tl+, and Rb+and a maximal binding of 51.6 pmol/g wet weight translated into 3.2 × 1013sites per gram wet weight. Using these values, the maximal values of K+transported per pump site per minute lie between 7752 and 10562. If each activation of the pump moves 2K+, the turnover rates could lie between 3876 and 5281 per

ISSN:0008-4212    

DOI:10.1139/y85-019

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Field stimulation of the circular muscle of the opossum esophagus produces a transient hyperpolarization (inhibitory junction potential, IJP) followed by an "off" depolarization. A similar nonadrenergic, noncholinergic (NANC) response in guinea pig taenia caecum has been shown to be due to an increase in the potassium ion permeability of the smooth muscle cell membrane. Double sucrose gap studies showed a decrease in resistance during the IJP, and a reversal at an estimated membrane potential of about −90 mV (4 mMK+). The reversal potential was dependent on the extracellular potassium concentration, shifting to −75 mV when the potassium in the superfusion medium was increased to 10 mM. The IJP in the opossum esophageal circular smooth muscle is therefore like the IJP of the guinea pig taenia caecum in that it is probably due to a selective increase in potassium ion permeability. Potassium conductance blocking agents, tetraethylammonium chloride (TEA, 20 mM) and 4-aminopyridine (4-AP, 5 mM) both caused a depolarization of the smooth muscle cell membrane, but TEA increased the membrane resistance, whereas 4-AP did not affect the membrane conductance in a consistent way. A decrease in IJP amplitude owing to these agents was not apparent. Apamin (10 μM) did not affect the membrane potential, the membrane resistance, or the IJP. Quinine (0.1 mM) produced effects quantitatively similar to those of TEA. Quinine (1 mM) did abolish the IJP, however, this was likely due to a blockade of impulse transmission of the intramural nerves. These results suggest that the receptor-operated channels opened by the NANC-nerve mediator in this tissue are unusual in that they are different from those functioning to maintain the resting membrane potential and they differ from those involved in the IJP in the guinea pig taenia caecum.

ISSN:0008-4212    

DOI:10.1139/y85-020

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The influence of pacemaker shifts on sinoatrial conduction time (SACT) was studied by investigating the effects of vagal stimulation on SACT and atrial conduction in anesthetized open-chest dogs. Isochronal maps were drawn from unipolar electrograms simultaneously recorded at 60 epicardial sites on the right atrial free wall and the inferior and superior vena cava. Vagal stimulation caused atrial conduction velocity to increase from 0.99 ± 0.10 m/s (mean ± SD) to 1.23 ± 0.23 m/s (p < 0.01), and the pacemaker to shift to lower positions along the superior vena cava – right atrial junction. As a result of the changes, the distances and the atrial conduction times from the stimulating and recording electrodes to the pacemaker site varied, and hence, the SACT values obtained indirectly by premature atrial stimulation varied. The isochronal maps were used to measure the atrial conduction times from stimulating to recording electrodes (a), from stimulating electrode to pacemaker site (b), and from pacemaker site to recording electrode (c). Indirect SACT was lengthened by vagal stimulation from 43 ± 16 to 64 ± 22 ms (p < 0.02). After correcting by subtracting the atrial conduction time (b+c−a), these values became 26 ± 6 ms (control) and 40 ± 11 ms (vagal stimulation) (p < 0.01). SACT values measured directly from the electrograms were 27 ± 7 ms (control) and 42 ± 10 ms (vagal stimulation) (p < 0.01). Corrected indirect SACTs were closer to direct SACTs than were the uncorrected indirect SACTs. It was concluded that (i) vagal stimulation induced pacemaker shift, increased atrial conduction velocity, and prolonged SACT; (ii) constant atrial pacing induced a pacemaker shift toward the stimulating electrode; and (iii) atrial conduction time must be taken into account to correctly estimate SACT.

ISSN:0008-4212    

DOI:10.1139/y85-021

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Studies were performed on five cats to assess the role of extrinsic vagal innervation in the control of peristalsis in the smooth muscle oesophagus. Transient vagal nerve blockade was accomplished by cooling the cervical vagosympathetic nerve trunks previously isolated in skin loops on each side of the neck. Peristalsis throughout the body of the oesophagus was monitored using a continuously perfused multilumen manometry tube. Striated and smooth muscle portions of the esophagus were delineated by abolishing smooth muscle activity with atropine. Secondary peristalsis was assessed by intra-oesophageal balloon distension studies. The threshold volume for balloon-induced secondary peristalsis was lower in the smooth muscle oesophagus. Unilateral vagal blockade reduced the incidence of primary and secondary peristalsis in the striated muscle oesophagus but not in the smooth muscle oesophagus. Bilateral vagal nerve blockade abolished primary swallow-induced peristalsis and secondary peristalsis in both the smooth and striated muscle cat oesophagus. Administration of cholinergic agents or adrenergic blocking agents failed to restore secondary peristalsis in the smooth muscle oesophagus during vagal cooling. We conclude that connections to the central nervous system via the vagal nerve trunks are required for normal secondary as well as primary peristalsis in both the smooth and striated muscle portions of the cat oesophagus.

ISSN:0008-4212    

DOI:10.1139/y85-022

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The pulmonary vascular responses to acute hypoxia and to infusions of histamine and 5-hydroxytryptamine (5-HT) were recorded in unanesthetized standing bull calves under neutral (16–18 °C) and cold (3−5 °C) temperature conditions. Cold exposure alone resulted in a significant increase in pulmonary arterial wedge pressure from 10.2 ± 3.5 to 15.9 ± 4.9 Torr (1 Torr = 133.322 Pa). Resistance to blood flow between the pulmonary wedge and the left atrium significantly increased from 0.50 ± 0.51 to 1.21 ± 0.78 mmHg∙L−1∙min−1(1 mmHg = 133.322 Pa) with cold exposure. This apparent pulmonary venoconstrictor response to cold exposure was further evaluated to determine if hypoxia, histamine, or 5-HT responsiveness was altered by cold exposure. Twelve minutes of hypoxia increased pulmonary arterial and systemic arterial pressures, heart rate, and respiratory rate similarly in cold and neutral temperatures. Cold exposure did not alter the dose-related reductions of systemic arterial and pulmonary arterial pressures in response to histamine. Similarly, the decreases in systemic arterial pressure and heart rate and increases in pulmonary arterial and left atrial pressures in response to 5-HT were not significantly different in cold and neutral conditions. It was concluded that acute, mild cold exposure results in an increase in resistance to blood flow in the pulmonary venous circulation without a general increase in pulmonary vascular reactivity, as measured by responses to hypoxia, histamine, and 5

ISSN:0008-4212    

DOI:10.1139/y85-023

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The role of progesterone in the initiation of parturition in the sheep is unclear. Whether a decrease in plasma progesterone is the essential prerequisite for the initiation of parturition or whether other factors also maintain uterine quiescence until delivery is not known. The effect of withdrawal of progesterone on the initiation of parturition has been investigated by intravenous administration of trilostane, a 3β-hydroxysteroid dehydrogenase Δ5−4isomerase inhibitor, to late pregnant sheep. Twenty-five or 100 mg trilostane caused a precipitous decrease in plasma progesterone to about 30% of preinjection levels. Progesterone remained depressed for up to 7 days after treatment. 13,14-Dihydro-15-keto-prostaglandin F2α(PGFM) became elevated between 7 and 36 h after trilostane injection but gradually returned to preinjection levels during the subsequent 36 h, at a time when plasma progesterone was still depressed. Four of 11 animals treated with 100 or 200 mg trilostane aborted prematurely at a time when plasma PGFM was maximal and plasma progesterone minimal. There were no consistent changes in plasma estradiol-17β or ovine placental lactogen concentrations after treatment with trilostane. It is suggested that a decrease in plasma progesterone will cause a transient increase in plasma PGFM concentrations which can lead to the premature initiation of parturition. In some instances the myometrium does not appear to respond to the elevated PGFM concentrations even when the estrogen:progesterone ratio is elevated by a decrease in plasma progesterone.

ISSN:0008-4212    

DOI:10.1139/y85-024

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The effects of weaning on the level of glycogen and the activities of glycogen synthase and phosphorylase were determined in rat liver. Glycogen levels in rat liver increased at the start of the weaning period and reached a plateau on postnatal day 20. The active form of glycogen synthase increased until postnatal day 19 and then declined. Total glycogen synthase (active + inactive) remained high during the suckling period and declined to a new low level during the weaning period. The activity ratio (active/total) increased from day 16 to days 18 – 22 and then decreased to the same level as found during the suckling period. At the onset of weaning the active form of phosphorylase decreased, whereas total phosphorylase initially increased and then decreased after postnatal day 20. Both forms of phosphorylase increased again at the end of the weaning period. The activity ratio decreased at the start of weaning and remained low throughout the rest of the weaning period. The effects of premature weaning were similar to those observed in normally weaned animals, but the changes occurred sooner and were more pronounced.

ISSN:0008-4212    

DOI:10.1139/y85-025

出版商:NRC Research Press    

年代:1985

数据来源: NRC