ABSTRACT
The release of adenosine from cardiac tissue was simulated by use of a model equation which consists of a saturable transfer term for both unidirectional influx and efflux, representing a symmetrical facilitated diffusion mechanism. This proposed model can account for positive and negative changes in adenosine release from cardiac tissue brought about by competitive transport inhibitors.
Subject(s)
Adenosine/metabolism , Models, Biological , Myocardium/metabolism , Biological Transport/drug effects , Biomechanical PhenomenaABSTRACT
Isolated epithelium of guinea pig jejunum secretes hypoxanthine and xanthine by a transport process that is capable of uphill transport and dependent on metabolic energy supply. Unidirectional influx of hypoxanthine across both the luminal and the contraluminal cell membrane appears to be saturable; influx across the contraluminal membrane is inhibited by 2,4-dinitrophenol (DNP). Efflux across the luminal membrane is diminished by DNP; efflux across the contraluminal membrane is increased by DNP. This evidence suggests the existence of a mediated transport system both in the luminal and the contraluminal cell membrane. Additionally, intracellular metabolism of hypoxanthine seems to regulate transepithelial permeation: increased hypoxanthine salvage by the phosphoribosyltransferase reduces the rate of secretion. However, the incorporation of hypoxanthine into the nucleotides is limited when the hypoxanthine is added to the luminal side of the epithelium, and the permeation rate in the absorptive direction is not markedly influenced by the rate of hypoxanthine salvage. These findings are a further example of the functional orientation of the jejunal epithelial cells with respect to enzymic activity and transepithelial transport properties.
Subject(s)
Hypoxanthines/metabolism , Jejunum/metabolism , Xanthines/metabolism , Animals , Biological Transport, Active/drug effects , Dinitrophenols/pharmacology , Guinea Pigs , In Vitro TechniquesABSTRACT
Midodrine, i.v. or orally administered, causes a prolonged elevation of blood pressure and a reduction in heart rate. These cardiovascular changes are not correlated to the plasma levels of the intact drug. On administration of either midodrine or its metabolite, ST-1059, formed by cleavage of the glycine residue, the elevation of blood pressure and the reduction in heart rate were significantly correlated to the plasma level of ST-1059. The results are in agreement with the assumption that the pressor activity of midodrine is mainly exerted by its metabolite ST-1059.
Subject(s)
Adrenergic alpha-Agonists , Ethanolamines/pharmacology , Midodrine/pharmacology , Animals , Blood Pressure/drug effects , Dogs , Heart Rate/drug effects , Hemodynamics/drug effects , Male , Midodrine/blood , Midodrine/metabolism , Time FactorsABSTRACT
2-[Bicyclo(2,2,1)heptane-2-endo-3-endo-dicarboximido]-glutarimide (taglutimide, K-2004) proved to be a new sedative-hypnotic drug which did not produce any toxic effects when administered orally to mice even at a very high dosage. Central-nervous depression was demonstrated by a reduction in spontaneous motor activity, potentiation of the central-depressant effect of pentobarbital, antagonism of the central-stimulant effect of amphetamine after oral administration and by narcotic activity after i.v. administration of the drug. Furthermore, oral administration of taglutimide potentiated the analgesic action of morphine without being effective on its own. Only weak potentiation of chlorpromazine-induced catalepsy, but not of reserpine-induced catalepsy was observed after taglutimide pretreatment. The drug influenced neither motor co-ordination nor the toxicity of ethanol. Taglutimide exhibited no anticonvulsant activity with respect to maximum electroshock or strychnine-induced seizures. No effect on heart rate or blood pressure was demonstrable after taglutimide treatment in conscious dogs.
