Effects of aging on renal response to parathyroid hormone in vitro.
Renal cortex homogenates from aged (greater than 5 y) rabbits showed decreased specific activities of brush border membrane enzymes compared to those from control young (6 m) rabbits but the specific enzyme activities of basolateral membrane, endoplasmic reticulum and mitochondria did not differ between the two groups. The stimulatory effects of parathyroid hormone (PTH) on the Ca(2+)-pump enzyme [(Ca(2+)+Mg2+)-ATPase] activity in kidney cortex homogenates were markedly less in aged rabbits, but the effect of cAMP on this enzyme activity was similar. Moreover, the production of cAMP induced by PTH was markedly less in the renal cortex homogenates from aged rabbits. From these results, we have proposed the following mechanism; aging--decrease in the response of cAMP to PTH in renal cortex--decrease in the stimulatory effect of PTH via cAMP on the Ca(2+)-pump enzyme--decreased reabsorption of Ca2+ from ureter--increased urinary Ca2+ secretion. This pathway may contribute to the worsening of senile osteoporosis.
Department of Molecular Cardiology, Center for Adult Diseases, Osaka, Japan.
K
K
Itoh
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T
Hara
D000375:Aging / Q000378:metabolism*; D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism*; D003576:Electron Transport Complex IV / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000201:enzymology; D005260:Female; D066298:In Vitro Techniques; D007672:Kidney Cortex / Q000187:drug effects* / Q000201:enzymology; D008871:Microvilli / Q000187:drug effects / Q000201:enzymology; D008928:Mitochondria / Q000201:enzymology; D009245:NADH Dehydrogenase / Q000378:metabolism; D010281:Parathyroid Hormone / Q000494:pharmacology*; D011817:Rabbits; D005723:gamma-Glutamyltransferase / Q000378:metabolism
D010281:Parathyroid Hormone; D000242:Cyclic AMP; D009245:NADH Dehydrogenase; D003576:Electron Transport Complex IV; D005723:gamma-Glutamyltransferase; D000469:Alkaline Phosphatase; D017301:Ca(2+) Mg(2+)-ATPase; D002118:Calcium