Biomedical subjects

S B Jones

Publications and source records attributed to S B Jones.

At least 127 records · Page 7Linked to original sources

PubMed1984

Local epicardial chemical ablation of vagal input to sino-trial and atrioventricular regions of the canine heart.

In open-chest, pentobarbitalized dogs, right and left cervical vagi were electrically stimulated (20 Hz, 5.0 ms, 4-6 volts) before and after carefully painting phenol (90%) over each of 6-8 narrow strips (2-3 mm width) and over restricted portions of the superior and inferior right atrium. Successive phenol strips were applied until the sino-atrial nodal (SAN) region had been completely surrounded, and also applied over a triangular fat pad at the junction of the inferior vena cava (IVC) and inferior left atrium (ILA). Electrical excitation of the autonomic trunks following each sequential epicardial phenol blockade resulted in successive deletion of cardio-inhibitory responses, a majority of sympathetic excitatory responses remaining intact. We conclude that most vagal fibers reach the SAN region via the superior-posterior right atrium (SVC and superior pulmonary veins) and these can be ablated leaving most vagal fibers to the atrioventricular nodal AVN region unimpaired. Phenol painting at the junction of IVC and ILA abolished vagal inhibition of conduction across the A-V junction. These studies illustrate distinct vagal distributions to the SAN and AVN regions of the canine heart. After all responses to vagal stimulation have been abolished, sympathetic alterations in heart rate and A-V conduction remain, thus revealing important differentiation in sympathetic fiber distribution to these key regions of automaticity and conduction.

Animals↗

PubMed1984

Alterations in subsidiary pacemaker function after prolonged subsidiary pacemaker dominance in the canine right atrium.

In vivo and in vitro techniques were used to study the functional characteristics of subsidiary atrial pacemaker activity 4 to 11 months after surgical excision of the sinoatrial node region of the dog heart. Characteristics of this long-term subsidiary atrial pacemaker activity were compared with those of sinoatrial node and short-term subsidiary atrial pacemaker activities. Extracellular bipolar electrodes were used to estimate the site of earliest activation and monitor spontaneous rate. Under both in vivo and in vitro conditions, long-term pacemaker activity was located in the same region of the inferior right atrium as was short-term pacemaker activity. Under in vitro conditions, long-term activity was characterized by a reduced sensitivity to acetylcholine and overdrive pacing and by a lack of dependence on beta-adrenergic stimulation compared with short-term activity. Furthermore, long-term pacemaker activity was more sensitive to acetylcholine and less sensitive to norepinephrine (greater than 10(-7) M) compared with sinoatrial node activity. It is concluded that the subsidiary atrial pacemakers that emerge soon after removal of the sinoatrial node are the same as those pacemakers that ultimately assume long-term control of the heart. In addition, after subsidiary atrial pacemakers assume dominant pacemaker function, their dependence on norepinephrine and their response to acetylcholine and overdrive pacing are reduced. These changes facilitate a more stable regulation of atrial pacemaker rhythm and, thereby, make subsidiary atrial pacemaker function more like that of the sinoatrial node.

Acetylcholine↗

PubMed1984

Influence of cardiac denervation on subsidiary atrial pacemaker stabilization.

Overdrive suppression was determined by measuring cardiac cycle lengths after rapid atrial pacing in nine alert conscious dogs sustaining total intrapericardial denervation. Rapid atrial pacing was performed at 125-400% of spontaneous heart rate for 30 s and at 200% spontaneous rate for 30, 60, 120, and 180 s, with and without cholinergic (atropine 0.2 mg/kg iv) or adrenergic blockade (propranolol 0.5 mg/kg iv). Corrected recovery time (CRT) was defined as the first recovery cycle length minus average control cycle length. To compare responses of the intact sinoatrial node (SAN) and subsidiary atrial pacemakers, CRT was measured in the conscious animal before and after SAN excision. Immediately after SAN excision, a junctional rhythm was frequently observed, but within a short time (min-h), subsidiary atrial pacemaker dominance was established with well-formed P waves and P-R interval averaging 85.3 +/- 3.4 ms. CRT before SAN excision ranged from 100 to 300 ms. Following pacing at 125-400% of spontaneous heart rate soon after SAN excision, CRT was markedly prolonged, ranging up to 6,000 ms. Atropine and propranolol did not influence CRT in the denervated preparation. CRT of subsidiary atrial pacemakers in the normally innervated dog heart returned to control pre-SAN excision values in 1-2 wk. In the denervated heart complete autonomic denervation exaggerated time required for return to control CRT values to 5-8 wk.

Animals↗

PubMed1984

Plasma catecholamines in rats during rewarming from induced hypothermia.

The present study sought to quantitate the levels of plasma catecholamines [norepinephrine (NE), epinephrine (E), and dopamine (DA)] during induction and rewarming from hypothermia. Male rats (317 +/- 8 g) were made hypothermic by exposure to 0.9% halothane at -10 to -15 degrees C while blood pressure (carotid artery), heart rate, and colonic temperature (Tc) were monitored. Anesthesia was discontinued when Tc reached 28 degrees C. Tc continued to fall but was held at 20-20.5 degrees C for 30 min. Rewarming was then initiated by raising ambient temperature to 22 degrees C. Arterial blood samples were taken 1) before cooling, 2) just before rewarming, 3) when Tc reached 22 degrees C during rewarming, and 4) when Tc reached 27 degrees C during rewarming. Plasma was assayed radioenzymatically for catecholamines using both phenylethanolamine-N-methyltransferase and catechol-O-methyltransferase procedures, and hypothermic induction resulted in significant increases in NE, E, and DA above control levels (P less than 0.01). With rewarming to Tc = 22 degrees C, all catecholamines increased above the level observed during hypothermia (P less than 0.01), and NE and DA increased still further (P less than 0.01) when Tc reached 27 degrees C. The levels of plasma catecholamines observed during hypothermia and during the rewarming phase indicate a role of the sympathoadrenal medullary system in the metabolic adjustments associated with hypothermia and recovery. During rewarming, the levels of E and NE attained exceed those at which both substances may be expected to act as circulating hormones.

Adaptation, Physiological↗

PubMed1984

Plasma catecholamines in the conscious rat during endotoxicosis.

Blood pressure, heart rate, and plasma catecholamines were determined in conscious unanesthetized rats given intravenous saline or endotoxin (LPS from S. enteritidis). Rats were monitored for 6 hr and survival determined at 24 hr. Blood pressure and heart rate measurements were determined using implanted arterial cannulae. The first of two protocols involved surgical implantation of cannulae 24 hr prior to the administration of endotoxin (2.0 mg/kg) or saline. Significant hypotension during the first hour following endotoxin was observed but significant increases in heart rate were not observed until 3 hr. Plasma norepinephrine (NE) and epinephrine (E) were significantly elevated at 30 min. Norepinephrine remained elevated (6 times control) during 6 hr, whereas E was elevated (60 times control) at 30 min but was less elevated at 6 hr. The second protocol involved endotoxin or saline administration immediately following implantation of cannulae. In this group, 16.7 mg/kg of endotoxin or saline was given. All animals died and plasma catecholamines were elevated at higher levels than those of the first group. Results suggest marked elevations in plasma catecholamines during endotoxicosis. Additional data analysis suggests that plasma NE and E may provide an early index of impending circulatory shock.

Animals↗

PubMed1983

alpha 2-Adrenergic receptor binding in human platelets: alterations during the menstrual cycle.

We studied the effect of several clinically important variables on the characteristics of alpha 2-adrenergic receptors in human platelet membranes. The number and affinity of the receptor binding sites were determined from radioligand binding experiments, with [3H]yohimbine being the radioligand of choice. Platelets from female subjects had a cyclic variation in the number of alpha 2-adrenergic receptors that coincided with their menstrual cycles. The number of alpha 2-receptors was highest at the onset of menses and dropped to 74% to 79% of that value during the middle of the cycle. In concurrent experiments we did not observe comparable cyclic changes in receptor binding sites in platelets from male subjects. There was no age-dependent alteration in receptor number in a sample of 39 subjects ranging in age from 8 to 80 yr, but the number of alpha 2-receptors in platelets from male and female subjects differed. We also tested the possibility of a circadian rhythm in alpha 2-receptor number but found no cyclic changes as a function of time of day. There was no alteration in alpha 2-adrenergic receptor binding in the platelets from five subjects with Parkinson's disease. Finally, there was no change in receptor affinity as a function of any of the variables tested. These data should apply to the design of further studies on the clinical importance of platelet alpha 2-adrenergic receptors.

Adolescent↗

PubMed1983

Caffeine inhibition of aflatoxin production: mode of action.

Evaluation of caffeine and a number of related methylxanthines indicated that the ability of the compound to inhibit growth and aflatoxin production by Aspergillus parasiticus is highly specific and does not involve an inhibition of cyclic AMP phosphodiesterase. Supplementation of the culture medium with purine bases, nucleosides, and nucleotides suggested that the inhibition of fungal growth could be partially overcome by adenine or guanine but that the purines had little effect on the inhibition of aflatoxin production. Likewise, increasing the levels of trace minerals did not overcome the inhibition of toxin production. Electron microscopic evaluation of caffeine-treated and -untreated cultures indicated that the compound produced observable changes in the ultrastructure of the fungus.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed1983

Cardiac and splenic norepinephrine turnovers in endotoxic rats.

Although sympathetic hyperactivity has been implicated in the pathogenesis of endotoxin shock, methodologies employed to assess the activity have been indirect in nature and results have been equivocal. The present experiments quantitated postganglionic sympathetic activity by measuring norepinephrine (NE) turnovers in hearts and spleens of fasted male Holtzman rats injected intravenously with Salmonella enteritidis lipopolysaccharide (2 mg/300 g rat; 5.7-6.7 mg/kg). NE turnovers were measured over 12 h by the [3H]NE decay method. Cardiac NE turnovers were increased in endotoxic rats (0.075 micrograms X g-1 X h-1) compared with controls (0.009). Similarly, NE turnovers in spleens of endotoxic rats (0.099 micrograms X g-1 X h-1) were increased compared with control rats (0.033). Because NE reuptake is depressed in spleens of severely shocked endotoxic rats, the singular effect of reduced reuptake (desmethylimipramine treatment, 20 mg/kg) on NE turnovers was evaluated in spleens of a separate group of control rats. Desmethylimipramine had no effect on the slopes of the NE decay lines compared with untreated rats (-0.015 +/- 0.008 vs. -0.015 +/- 0.029, respectively). Thus these experiments support the concept of heightened sympathetic activation during endotoxicosis as assessed quantitatively in a noninvasive, unanesthetized rat model.

Animals↗

PubMed1982