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Biomedical subjects

R F Lowe

Publications and source records attributed to R F Lowe.

102 records · Page 6Linked to original sources
PubMedDate not supplied

The effects of barbiturates upon the hemodynamic responses to intravenous methionine-enkephalin in dogs: modulation by the GABA complex.

In conscious animals, the intravenous administration of enkephalins increases heart rate (HR) and mean systemic arterial blood pressure (MAP); however, when given during barbiturate anesthesia, enkephalins reduce HR and MAP. We have investigated the potential role of the gamma-aminobutyric acid (GABA) complex (consisting of chloride-ion channel and binding sites for GABA, benzodiazepine, and barbiturate/picrotoxin) as the site of modulation of enkephalin responses by certain anesthetic agents in our chronically instrumented dog model. In our model, methionine-enkephalin (Met5-ENK) (35 micrograms/kg intravenously) increased HR and MAP, but following induction of general anesthesia with barbiturate (pentobarbital) or of sedation with benzodiazepine (diazepam), Met5-ENK produced vasodepressor responses despite differing levels of consciousness in the treated animals. Subsequent administration of picrotoxin restored pressor responses to Met5-ENK in the barbiturate-treated dogs, but not in those treated with benzodiazepine; picrotoxin did not alter the level of consciousness. Picrotoxin had no effect upon Met5-ENK responses in the conscious state. In contrast, alpha-chloralose, a convulsive anesthetic agent which does not appear to alter GABA complex activity, blunted but did not reverse pressor responses to Met5-ENK, despite causing a level of anesthesia similar to that produced by barbiturate. The observed pressor response to Met5-ENK during alpha-chloralose anesthesia was totally inhibited by naloxone, indicating that this response was still mediated by opiate receptors. Our data are compatible with modulation of enkephalin responses by GABA complex activity. Systemic enkephalins may generate afferent signals which may subsequently undergo GABA complex processing; the state of activation of the GABA complex may then determine whether systemic enkephalin signals are translated as vasopressor or vasodepressor responses.

Animals↗
PubMedDate not supplied

Hemodynamic actions of endothelin in conscious and anesthetized dogs.

The newly described endogenous peptide, endothelin, was administered to five chronically instrumented conditioned dogs. Endothelin produced significant and simultaneous increases in both heart rate (HR) and mean arterial pressure (MAP) in conscious dogs. Endothelin also produced significant increases in MAP in anesthetized animals. Ganglionic suppression induced by hexamethonium (10 mg/kg) and atropine (0.1 mg/kg) blocked HR responses and markedly inhibited the pressor responses to endothelin in conscious animals. These results suggest that endothelin in part acts to elevate blood pressure and heart rate through modification of autonomic nervous system tone. When endothelin and angiotensin II were administered in mole equivalent doses, angiotensin II produced a pressor response of greater magnitude than did endothelin in conscious animals.

Anesthesia, General↗
PubMedDate not supplied

Endothelin produces systemic vasodilation independent of the state of consciousness.

The effects of endothelin, ET-1, on pulmonary and systemic hemodynamics were studied in the open chest dog and changes in systemic arterial pressure in dogs under conscious and anesthetized states were compared. Rapid intravenous (IV) bolus injections of ET-1, 100-1,000 nanograms/kg, significantly decreased systemic arterial pressure, and significantly decreased systemic vascular resistance whereas left atrial pressure and pulmonary vascular resistance were not altered. Reductions in systemic arterial pressure in response to bolus injection of ET-1, 100 and 300 nanograms/kg IV, during conscious state and during anesthesia were similar, respectively. The present data suggest that ET-1 dilates the systemic vascular bed independent of the animal's state of consciousness. The present data also suggest that when compared to the systemic vascular bed, the pulmonary vascular bed is less responsive to bolus administration of ET-1.

Anesthesia, General↗
PubMedDate not supplied

Acute hypotension alters hemodynamic response to methionine-enkephalin in conscious dogs.

In the conscious dog, intravenous administration of methionine-enkephalin produces simultaneous increases in both heart rate (HR) and mean arterial blood pressure (MAP). This report describes both depressor and cardioaccelerator responses to methionine-enkephalin (10 micrograms/kg IV) in conscious dogs following acute hypotension induced by either bolus injection of isoproterenol (0.1-5.0 micrograms/kg IV) or infusion of sodium nitroprusside (SNP, 3-8 micrograms/kg/min). Cardiovascular responses to methionine-enkephalin were blocked by naloxone. Pretreatment of the dogs with the beta-adrenergic receptor antagonist propranolol failed to prevent the hypotensive response to methionine-enkephalin following SNP infusion. The results indicate that the hemodynamic responses to methionine-enkephalin can be altered by acute manipulation of blood pressure. These results may have implications relative to the role of endogenous opiates in regulation of blood pressure, especially in acute hypotensive states.

Animals↗
PubMedDate not supplied

A history of primary angle closure glaucoma.

The satisfactory control and cure of attacks of primary angle closure glaucoma spans one hundred years following von Graefe's iridectomy in 1856. Gonioscopy was required to validate the theories of shallow anterior chamber and pupillary obstruction, but the gonioscopists looked for the causes of angle closure in their own territory at the angle in the periphery of the anterior chamber and disregarded the center. General agreement of the importance of pupil block was thereby delayed for over ten years. Advances in pharmacology and the invention of laser surgery gave opthalmologists a comfortable control of a formerly distressing, blinding disease.

Glaucoma, Angle-Closure↗
PubMedDate not supplied

Severe hemolytic disease of the newborn associated with anti-JSb.

The red blood cells of the group A infant of a group O central African Negro woman of the Zezuru tribe with anti-Lea and anti-JSb in her serum were found to be strongly agglutinated by a commerical antiglobulin reagent six days after birth. The high concentration of bilirubin in the infant's serum gradually decreased but he became profoundly anemic and, in the absence of a suitable donor, was successfully transfused with blood from his mother. Subsequent tests using the maternal anti-JSb diluted one in ten to avoid agglutination by the anti-Lea showed that the frequency of the JS(b-) phenotype in group O Zezuru is approximately one per cent.

ABO Blood-Group System↗