PARTIAL RESTORATION OF IMPAIRED ALPHA(1)-ADRENERGIC RESPONSIVENESS INPAROTID CELLS OF AGED RATS BY S-ADENOSYLMETHIONINE TREATMENT

The age related decrease in alpha(1)-adrenergic stimulated inositol 1, 4, 5 trisphosphate (IP3) production in parotid cells of aged rats can be partially restored by treatment with S-adenosylmethionine (SAM). T his effect is completely blocked by S-adenosyl homocysteine (SAH) and occurs in association with an increase in the conversion of phosphatid ylethanolamine to phosphatidylcholine and a decrease in membrane visco sity. In contrast, SAM treatment actually inhibits stimulated IP3 prod uction in cells of young rats. The membrane viscosity of these cells i s lower than that of those from aged rats. Although conversion of phos phatidylethanolamine to phosphatidylcholine is enhanced, no further de crease in membrane viscosity is elicited in young cell preparations. T hese findings suggest that age changes in the membrane environment may result in impaired alpha,-adrenergic signal transduction and that suc h alterations may be at least partially reversible by SAM treatment.