The primary site of action of parathyroid hormone

1951 ◽  
Vol 26 (6) ◽  
pp. 252-264
Author(s):  
D. K. O’Donovan
Keyword(s):  
Parathyroid Hormone ◽  
Primary Site ◽  
Site Of Action

THE EFFECT OF ULTRAVIOLET RADIATION UPON ENZYMATIC ACTIVITY AND VIABILITY OF THE YEAST CELL

1952 ◽  
Vol 30 (6) ◽  
pp. 561-570
Author(s):  
J. G. Aldous ◽  
D. K. R. Stewart
Keyword(s):  
Alcohol Dehydrogenase ◽  
Ultraviolet Radiation ◽  
Lactic Dehydrogenase ◽  
Population Viability ◽  
Primary Site ◽  
Hexokinase Activity ◽  
Viable Cells ◽  
Site Of Action ◽  
Survival Level ◽  
Nuclear Damage

Suspensions of the cells of baker’s yeast were irradiated with ultraviolet light for sufficient times to produce populations of 75, 50, 30, and 5% viable cells. After washing and drying, various enzyme solutions were prepared from these cells. Enzymatic activities, on a nitrogen basis, were compared to those of solutions prepared from a nonirradiated population. At the 50% survival level, hexokinase, carboxylase, and zymase were inhibited to a degree roughly proportional to the viability. Carboxylase, and to a certain extent, hexokinase activity varied directly as the population viability. Catalase, alcohol dehydrogenase, and lactic dehydrogenase showed no diminution in activity even at the 5% survival level. These results suggest that although ultraviolet radiation may produce nuclear damage, the primary site of action may be certain enzymes of the cytoplasm.

scholarly journals Effects of an azasterol inhibitor of sterol 24-transmethylation on sterol biosynthesis and growth of Leishmania donovani promastigotes

1995 ◽  
Vol 308 (1) ◽  
pp. 31-38 ◽  
Author(s):  
P A Haughan ◽  
M L Chance ◽  
L J Goad
Keyword(s):  
Cell Proliferation ◽  
Leishmania Donovani ◽  
Primary Site ◽  
Sterol Biosynthesis ◽  
Proliferation Inhibition ◽  
Complete Replacement ◽  
Inhibition Of Growth ◽  
Absolute Requirement ◽  
Cell Proliferation Inhibition ◽  
Site Of Action

Leishmania donovani promastigotes were cultured in the presence of an azasterol (20-piperidin-2-yl-5 alpha-pregnane-3 beta,20-diol) to determine the effects on sterol biosynthesis and cell proliferation. Inhibition of growth increased gradually with azasterol concentrations up to 5 micrograms/ml; concentrations of azasterol exceeding 5 micrograms/ml were lethal. Sterol biosynthesis was affected by the azasterol when administered at concentrations as low as 100 pg/ml. The primary site of action was the alkylation at C-24 of a delta 24-sterol precursor. The 24-alkylated sterols [ergosta-5,7,24(24(1))-trien-3 beta-ol and ergosta-5,7,22-trien-3 beta-ol] of the protozoan were replaced by delta 24-cholesta-type sterols which then accumulated in the cells. Administration of the azasterol together with a bis-triazole inhibitor of the 14 alpha-methylsterol 14-demethylase reaction, which operates in sterol biosynthesis, resulted in depletion of 24-alkylsterols and their replacement with predominantly 14 alpha-methylsterols lacking a 24-alkyl group. Continuous subculture of promastigotes in the presence of the azasterol resulted in gradual depletion of 24-alkylsterols and their complete replacement by delta 24-cholesta-type sterols. Transfer of the azasterol-treated cells to medium lacking azasterol resulted in a gradual restoration, after several subcultures, of the normal 24-alkylsterol pattern. The results indicate that, although 24-alkylsterols are normally produced by the protozoan, it can nevertheless survive with sterols possessing only the cholestane skeleton. Thus there is no absolute requirement for 24-alkylsterols to fulfil some essential ‘sparking’ role associated with cell growth in promastigotes.

Carbonic anhydrase distribution in rodent embryos and its relationship to acetazolamide teratogenesis.

1981 ◽  
Vol 29 (10) ◽  
pp. 1213-1218 ◽  
Author(s):  
C M Schreiner ◽  
K S Hirsch ◽  
W J Scott
Keyword(s):  
Enzyme Activity ◽  
Carbonic Anhydrase ◽  
Staining Pattern ◽  
Carbonic Anhydrase Activity ◽  
Primary Site ◽  
Mouse Embryos ◽  
Histochemical Method ◽  
Site Of Action ◽  
Activity Form ◽  
Low Activity

The carbonic anhydrase inhibitor, acetazolamide, leads to a unique distal postaxial right forelimb deformity in rats and CBA/J mice, but SWV mice are completely resistant. Using Hansson's histochemical method, the distribution of carbonic anhydrase and its inhibition by acetazolamide in rat, CBA/J mouse, and SWV mouse embryos were compared. Carbonic anhydrase activity was demonstrable in many tissues of sensitive rat and CBA/J mouse embryos and in resistant SWV mouse embryos. The forelimb buds of resistant and sensitive embryos possess carbonic anhydrase activity in the area between the ectoderm and adjacent mesenchyma with no localization of enzyme activity corresponding to the malformation seen in acetazolamide teratogenesis. This suggests that carbonic anhydrase in the forelimbs is not the primary site of action for acetazolamide. A distinctive staining pattern of nucleated erythrocytes in resistant embryos indicated the presence of a low activity form of carbonic anhydrase in nearly half of the erythrocytes. A five-to tenfold greater amount of acetazolamide was needed to completely inhibit carbonic anhydrase activity in nucleated erythrocytes from resistant embryos than in those from sensitive embryos. The existence of a low activity form of carbonic anhydrase in SWV embryo erythrocytes may be the basis of resistance to acetazolamide teratogenesis.

Site of action of endotoxin in evoking bradycardia

1969 ◽  
Vol 47 (12) ◽  
pp. 999-1008
Author(s):  
B. Blattberg ◽  
M. N. Levy
Keyword(s):  
Heart Rate ◽  
Portal Vein ◽  
Femoral Artery ◽  
Primary Site ◽  
Cardiac Response ◽  
Renal Vasculature ◽  
Site Of Action ◽  
Small Doses ◽  
Anesthetized Dogs ◽  
The Individual

Previous investigation of the mechanism responsible for the bradycardia evoked by the intravenous injection of bacterial endotoxin revealed that the primary site of action of the endotoxin must be some subdiaphragmatic structure. The present study was undertaken to localize more precisely this site of action. In anesthetized dogs, the renal pedicles or the intestinal arteries were ligated before endotoxin was administered. It was found that exclusion of the intestinal vascular bed prevented the fall in heart rate, whereas occlusion of the renal vasculature did not alter the cardiac response. To localize the mesenteric site of action of endotoxin more precisely, small doses of endotoxin were injected into each of the individual intestinal arteries and into the splenic artery and the portal vein. The response was compared with that evoked by the injection of an equivalent amount of endotoxin into a femoral artery. It was observed that when endotoxin was injected into the intestinal arteries, bradycardia resulted. However, when endotoxin was injected into the femoral artery or the portal vein, no significant change in heart rate was detected, indicating that the intestines probably are the site of action for evoking bradycardia.

The Benzodiazepine Receptor and its Role in Anxiety

1988 ◽  
Vol 152 (5) ◽  
pp. 599-600 ◽  
Author(s):  
Sandra E. File
Keyword(s):  
Binding Sites ◽  
Gaba Receptors ◽  
Benzodiazepine Receptor ◽  
Primary Site ◽  
Affinity Binding ◽  
High Affinity Binding ◽  
Inhibitory Neurotransmitter ◽  
High Affinity ◽  
Site Of Action ◽  
The Brain

Ten years ago, specific high-affinity binding sites for benzodiazepines (BDZs) were found in the brain (Mohler & Okada, 1977; Squires & Braestrup, 1977). These binding sites are believed to be the primary site of action of BDZs and are found on the same protein as GABA receptors. GABA is the main inhibitory neurotransmitter in the brain.

Distal site of action of parathyroid hormone on phosphate reabsorption

1975 ◽  
Vol 229 (6) ◽  
pp. 1556-1560 ◽  
Author(s):  
FG Knox ◽  
C Lechene
Keyword(s):  
Parathyroid Hormone ◽  
Proximal Tubule ◽  
Phosphate Transport ◽  
Distal Nephron ◽  
Phosphate Reabsorption ◽  
Site Of Action ◽  
Flow Experiments ◽  
Filtered Load ◽  
Stop Flow ◽  
Distal Site

The sites of inhibited phosphate transport following administration of bovine parathyroid hormone (bPTH) to thyroparathyroidectomized (TPTX) dogs were investigated. Phosphate reabsorption by the proximal and distal nephron was studied using recollection micropuncture, stop-flow methodology, and electron-probe microanalysis. Following bPTH, delivery of phosphate from the proximal tubule increased from 26 to 37% of the filtered load, P less than .01. Fractional phosphate excretion increased from 2.3 +/- 1.5 to 21.4 +/- 2.3%, P less than .001. The increased delivery of phosphate at the point of micropuncture in the proximal tubule accounted for approximately half of the phosphaturia. In six TPTX dogs, which were saline loaded, similiar increases in phosphate delivery from the proximal tubule from 27 +/- 1 to 36 +/- 2% of the filtered load resulted in a strikingly smaller phosphaturia, 5.1 +/- 1 to 9.8 +/- 2.4%, NS. In stop-flow experiments, phosphate concentratin ratios were slightly increased in the proximal nephron and markedly increased in the distal nephron following bPTH. It is concluded that parathyroid hormone markedly decreases phosphate transport in the distal nephron.

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