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Biomedical subjects

J A Fischer

Publications and source records attributed to J A Fischer.

At least 217 records · Page 12Linked to original sources
PubMed1973

Acute parathyroid hormone response to epinephrine in vivo.

The acute effects of epinephrine, norepinephrine, and isoproterenol on the plasma immunoreactive parathyroid hormone (iPTH) response were studied in 13 550-600 kg cows. Catecholamines were infused for 7.0 min. During epinephrine infusions at 0.08 mumol/min iPTH increased from 0.48+/-0.12 (mean+/-SE, ng/ml) to 1.09+/-0.18 ng/ml (P < 0.02). Small increases in plasma free fatty acids and glucose could be detected with 0.08 mumol/min epinephrine; the iPTH response to epinephrine was as sensitive as the free fatty acid and glucose responses and possibly of physiological importance. Plasma calcium (total and ionized) and magnesium did not change. The responses were more pronounced at 0.8 mumol/min epinephrine with a mean iPTH increase from 0.49+/-0.16 ng/ml to 1.74+/-0.35 ng/ml (P < 0.01). Small decreases in plasma calcium occurred at 0.8 mumol/min epinephrine, but the plasma magnesium remained unchanged. However, when the plasma calcium was lowered with ethylene glycol bis(beta-aminoethyl ether)-N, N'-tetraacetic acid (EGTA), a much more pronounced lowering of the plasma calcium was required to produce comparable increases of the plasma iPTH concentrations than when epinephrine was infused. It appears that epinephrine has a direct effect on the release of iPTH from the parathyroid glands. Simultaneous infusions of calcium and epinephrine suppressed the stimulation by epinephrine. This points towards a common mechanism of the regulation of parathyroid hormone secretion caused by decreases in the extracellular calcium concentration and/or alterations in the distribution of calcium within parathyroid cells following the administration of epinephrine. The iPTH response to epinephrine was suppressed in the presence of propranolol. Isoproterenol was less active in raising iPTH than epinephrine, and norepinephrine was the least active. The stimulation by isoproterenol and the suppression by propranolol suggest beta adrenergic receptor sites within the parathyroid glands.

Animals↗
PubMed1972

Calcium-regulated parathyroid hormone peptidase.

An enzymatic activity that catalyzes the conversion of glandular parathyroid hormone to a smaller-molecular-weight, biologically and immunologically active form of this hormone has been extracted from normal parathyroid and other porcine tissues. The product of the conversion has the immunologic characteristics of the hormone that occurs in peripheral serum and in tissue culture medium from parathyroid explants. The enzyme is activated by chelating agents and is inhibited by high calcium concentrations, suggesting that this enzyme may be important in the regulation of secretion or metabolism of the hormone.

Animals↗