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Biomedical subjects

M A Valenzuela

Publications and source records attributed to M A Valenzuela.

At least 55 records · Page 3Linked to original sources
PubMed1989

[Hypocortisolemia with neither signs nor symptoms of cortisol deficiency: research on transcortin characteristics].

Low plasma levels of cortisol, as a result of primary or secondary adrenal hypofunction, is usually associated to findings of hypocortisolism. Low plasma cortisol levels without clinical manifestations have been observed in patients in which cortisol binding capacity (CBG) is altered. In this paper we report a clinically normal patient, with very low plasma cortisol levels. We investigated a possible CBG defect or the presence of a CBG binding substance as an explanation of the clinical findings. We found a normal CBG and no competing substance. Therefore, the presence of low cortisol levels suggests the presence in this patient of a receptor with increased sensitivity to cortisol, or another molecule that can be recognized as glucocorticoid by the cortisol receptor.

Adrenal Glands↗
PubMed1977

Hydrolysis of synthetic pyrophosphoric esters by an isoenzyme of apyrase from Solanum tuberosum.

A highly purified isoenzyme of apyrase obtained from potatoes (Solanum tuberosum var. Pimpernel) exhibits a low specificity for the organic moiety of synthetic pyro- and triphosphates. Methyl di- and tri-phosphates were hydrolysed at higher rates than ADP and ATP, but their Km values were also higher. Steric hindrance at the carbon atom linked to the pyrophosphate chain decreases both binding and maximum rate, whereas length or polarity of the organic chain do not have systematic effects. t-Butyl diphosphate, inorganic pyrophosphate, adenosine 5'-[alpha,beta-methylene]triphosphate and adenosine 5'-[beta,gamma-methylene]triphosphate are competitive inhibitors of the hydrolysis of ATP and ADP.

Adenosine Triphosphatases↗
PubMed1975

Reduction of doxorubicin (adriamycin) bone marrow toxicity.

Doxorubicin (adriamycin), an antineoplastic antibiotic, is a potent suppressant of bone marrow. Previous studies on doxorubicin disposition indicated that its diversion from bone marrow in the first few minutes after administration should result in a marked decrease in total exposure to the drug (concentration X time) with a concomitant reduction in concentration-time-dependent toxicity. To test this hypothesis, the descending aorta of rabbits was occluded just proximal to the iliac bifurcation for 30 min to deprive bone marrow of blood flow. Both these rabbits and the control rabbits were given 5 mg/kg of doxorubicin intravenously, and the total white cell could in peripheral blood was monitored periodically for 15 days. The decrease in toxicity produced by the occlusion was quite evident by comparison of white cell counts and deaths in all groups. A possible mechanism of this effect was shown to be a decreased doxorubicin exposure of bone marrow tissue in the occluded animals as judged by relative doxorubicin concentration-time curves in rabbits with and without the aortic occlusion.

Animals↗