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At least 37 records · Page 2Linked to original sources
PubMed1976

Mesenteric vasodilator effect of 5-hydroxytryptamine: possible enteric neuron mediation.

The superior mesenteric blood flow response to intra-arterial injections (0.5-25 mug) and infusions (5-30 mug/min) of 5-hydroxytryptamine (5-HT, serotonin) was investigated in anesthetized cats in which nerve activity to the intestine was altered by surgical and pharmacological procedures. With the superior mesenteric periarterial nerves intact, low doses of 5-HT (less than 5 mug) produce vasodilatation, whereas higher doses produce vasoconstriction. When the periarterial nerves are cut either at the start of or during the experiments, vasodilatation is elicited over the entire dose range, and doses of 5-HT which initially produce vasoconstriction elicit vasodilatation after nerve sectioning and also after alpha-adrenergic receptor blockade. These vascular responses are not secondary to changes in arterial pressure or intestinal motility. The vasodilator response to 5-HT is unaffected by alpha- or beta-adrenergic or cholinergic receptor blockade, by ganglionic blockade, or by histamine receptor blockade, but is blocked by tetrodotoxin and also the 5-HT antagonist, dihydroergotamine.

Adrenergic alpha-Antagonists↗
PubMed1975

Interstitial fluid pressure and alkaline gastric secretion.

The interstitial fluid pressure of the submucosa of the gastric fundus was monitored by means of Guyton's capsules in dogs anesthetized with pentobarbital. The intracapsular pressure (ICP) was measured during secretion produced by: a) hypertonic solutions placed inside the stomach; b) arterial hypertension (200 mmHg) applied during intra-arterial infusion of histamine, and c) intra-arterial infusion of acetylcholine. The first procedure did not modify the ICP. On the other hand, whenever interstitial fluid appeared in the gastric lumen during hypertension plus histamine, the mean ICP increased, mostly due to augmented capillary filtration. The hydraulic coefficient measured in these experiments was at least 4 orders of magnitude larger than the respective osmotic coefficient. The action of acetylcholine was complex: large doses enlarged the net capillary filtration, but small doses increased the mean ICP by muscle stimulation only. Contraction of the muscularis mucosae might be the most important mechanism underlying bulk flow of interstitial fluid in physiological conditions. It is concluded that hydraulic gradients across the epithelium might account for the "secretion" of "alkaline" juice.

Acetylcholine↗
PubMed1979

Experimental studies on the pathogenesis of asystole after verapamil in the dog.

The effect of verapamil on automaticity and conduction in the atrioventricular (A-V) junctional region was studied in anesthetized dogs. In five normal dogs verapamil, 10 microgram/ml, was selectively perfused into the A-V nodal artery and caused first degree heart block, which progressed to second degree heart block in three of the five. Higher concentrations of verapamil, 25 microgram/ml, caused complete heart block in three of five other dogs, but no episodes of asystole (defined as a ventricular pause of 10 or more seconds). In six other dogs after beta receptor blockade with propranolol, 20 microgram/ml, perfused into the A-V nodal artery, verapamil, 10 microgram/ml, regularly caused second degree heart block; in four of the six dogs there was a transient episode of third degree A-V block, and in two of these there was a period of asystole. In each of the 10 dogs pretreated with reserpine, verapamil, 10 microgram/ml, caused third degree A-V block; in seven of these there was a period of asystole with ventricular standstill up to 30 seconds. Concentrations of verapamil that do not produce high grade heart block in the normal heart thus readily cause both high grade block and prolonged ventricular standstill after elimination of adrenergic influences in the A-V junction.

Adrenergic beta-Antagonists↗
PubMed1977

Prostaglandin release by slow reacting substance from guinea pig and human lung tissue.

Slow reacting substance (SRS) injected into the pulmonary artery released prostaglandins E (PGE) and F2alpha (PGF2alpha) and the 15-keto-13, 14-dihydro PG metabolites from non-sensitized and ovalbumin sensitized, isolated, perfused guinea pig lungs. PGs were also released from lungs incubated with SRS. Sensitized lungs released more PGs in both types of preparations. Indomethacin inhibited the effect of SRS. Passively sensitized human lung fragments, in parallel to guinea pig lung, released PGE, PGF2alpha and the metabolites when incubated with SRS or antigen. In in vivo experiments, SRS and arachidonic acid given intravenously increased the airway insufflation pressure in anesthetized quinea pigs. These effects, but not the action of injected PGF2alpha and histamine, were abolished by indomethacin. The results indicate that one of the modes of SRS action is by release of PGs, and are consistent with the hypothesis that PGs are predominantly "secondary" mediators (in the temporal sense) of the antigen-antibody reaction.

Airway Resistance↗
PubMedDate not supplied

Direct and reflex myocardial effects of intracoronary administered contrast materials in the anesthetized and conscious dog: comparison of standard and newer contrast materials.

The direct and indirect actions on left ventricular dynamics of contrast material (sodium meglumine diatrizoate) currently used for coronary arteriography, modified ionic material (sodium meglumine calcium metrizoate) and non-ionic material (metrizamide) were assessed in conscious and anesthetized dogs. In both anesthetized and conscious animals, the diatrizoate compound caused an early (3--10 sec after injection) decrease in peak dp/dt and dp/dt/LVP40, followed by late (10--20 sec after injection) increases in these variables. The predominant early and later effects of the calcium metrizoate compound were increases in parameters of LV contractile state. Metrizamide produced no significant early alterations, but later induced a small increase in these variables. The positive inotropic actions of each of the contrast materials were attenuated by beta adrenergic blockade. The early effects of the contrast materials were similar in the presence of segmental ischemia. The late positive inotropic effects in response to the diatrizoate compound and metrizamide were not observed in the ischemic state, while the positive inotropic response induced by the calcium metrizoate compound was significantly reduced. Thus intracoronary administration of sodium meglumine diatrizoate produced direct myocardial depression, followed by adrenergically mediated myocardial stimulation. Calcium metrizoate caused prominent direct and adrenergically mediated augmentation in contractile state. Metrizamide induced the least alteration in LV contractile state.

Adrenergic beta-Antagonists↗
PubMed1979

A pharmacological analysis of the contractile action of histamine upon the ileal region of the isolated, blood-perfused small intestine of the rat.

1. The mode of action of histamine was investigated on the rat isolated small intestine perfused at a fixed flow rate through the superior mesenteric artery with blood from the carotid artery of a heparinized donor rat. Compounds were closely injected into the superior mesenteric artery. 2. Increasing doses (1 to 100 micrograms) of histamine caused a monophasic fast contraction of the ileum. 3. The fast contraction was abolished by tetrodotoxin, hexamethonium, morphine or mepyramine, but was not prevented by atropine. 4. The present study indicates that histamine produces the fast contraction of the ileum by primarily acting on the myenteric nerve plexus involving cholinergic interneurones.

Animals↗
PubMed1975

Interaction of the chemoreflex and the pulmonary inflation reflex in the regulation of coronary circulation in conscious dogs.

The interaction of chemoreflex and pulmonary inflation reflex control of the coronary circulation was examined in conscious dogs by comparing the responses to chemoreflex stimulation (intracarotid injection of nicotine) when ventilation was allowed to increase with those when ventilation was controlled. The responses were also compared with those elicited by both forced mechanical and spontaneous hyperinflation. When the heart rate was constant, intracarotidly administered nicotine induced an increase in the depth of respiration followed closely by an increase in late diastolic coronary flow from 48 +/- 2 to 106 +/- 8 ml/min and a reduction in late diastolic coronary resistance from 1.62 +/- 0.08 to 0.78 +/- 0.06 mm Hg/ml min-1. After beta-receptor and cholinergic blockade, a similar coronary dilation in response to nicotine occurred only when ventilation was allowed to increase. However, when ventilation was controlled, intracarotidly administered nicotine increased coronary resistance after combined beta-receptor and cholinergic blockade. The reflex coronary dilation was not observed after carotid sinus nerve section or after alpha-receptor blockade. Thus, nicotine stimulation of the carotid chemoreflex results in a striking coronary dilation that has two components. The minor component involves a chemoreflex with its efferent pathway in tthe vagi. The major component of coronary dilation follows an increase in the depth of respiration, and its efferent component appears to involve withdrawal of alpha-adrenergic constrictor tone. An almost identical period of reflex coronary dilation followed either forced mechanical or spontaneous hyperinflation in the conscious dog.

Adrenergic alpha-Antagonists↗
PubMed1979

Improvement in arterial oxygenation by saralasin infusion in man.

Simultaneous hemodynamic and blood gas measurements were performed in 26 hypertensive adults, who were cigarette smokers, before and after a 30-minute infusion of saralasin (5 microgram/kg/min) which is a highly specific competitive antagonist of angiotensin II (AII). The arterial pressure fell in nine, rose in seven and was unchanged in ten patients. The mean cardiac index for the entire group remained unchanged. Pulmonary arterial or wedge pressure, pulmonary vascular resistance, arterial PCO2 and pH did not change. Unrelated to the hemodynamic changes, the mean arterial oxygen pressure (PaO2) increased from 68.6 +/- 2.2 mm Hg to 73.9 +/- 2.1 mm Hg (P less than 0.001). In the absence of a significant increase in alveolar ventilation as indicated by an unchanged mean PCO2 and lacking a hemodynamic explanation, the mechanism for the rise in PaO2 is speculative at this stage. The possibility of an improvement in the distribution of ventilataion by saralasin infusion is under investigation.

Adult↗
PubMedDate not supplied

Substance P-like peptides and vasopressin release from posterior pituitary lobe incubated in situ after intracarotid injections of hypertonic solution in rats.

The experiments were performed on male rats, drinking 2% NaCl solution ad libitum for 12 days instead of tap water. The pituitary gland was exposed by the transpharyngeal approach under urethane-chloralose anaesthesia. The posterior lobe remained in neural and partial vascular connection with the hypothalamus, whereas the anterior lobe was entirely removed. Samples of the outflow medium from the incubated in situ rat posterior pituitary lobe were collected during 30 min intervals. Substance P-like peptides and vasopressin activities were assayed by the biological tests. Injections of hypertonic solution into the internal carotid artery did not change vasopressin release, but induced an increase in Substance P release from the posterior pituitary lobe into the incubation medium. Under conditions of unexcitability of the osmosensitive cells, triggering vasopressin release, the injection of hypertonic solution into the internal carotid artery stimulated the Substance P-like peptides release from the posterior pituitary lobe.

Animals↗