DECREASED RATES OF RELEASE OF ATRIAL-NATRIURETIC-PEPTIDE FROM ISOLATED HEARTS FROM AGING HYPERTENSIVE RATS

We tested the hypothesis that in genetically hypertensive New Zealand rats left ventricular hypertrophy predisposes to left atrial disease and should be associated with a decreased release of atrial natriuretic peptide (ANP) in response to acute left atrial stretch. Abrupt distention of the left atrium was achieved by the acute onset of left atrial distention in Langendorff-perfused isolated rat hearts, which resulted in a rapid release of ANP in all groups of hearts. Comparisons were made between normotensive and hypertensive hearts using rats 2 months, 8 months, 12 months, and 16 months. Rates of release of ANP from normotensive and hypertensive hearts were similar at 2 months. Thereafter, there was a progressive impairment of ANP release, until in rats aged 16 months, rates of release achieved in hypertensive hearts 2 min after the onset of left atrial distention were only about half of those of normotensive hearts 55%, P < .005). At all ages above 2 months, hypertensive hearts failed to increase the concentration of ANP in the coronary effluent at the onset of increased heart work. Therefore, in rats with genetic hypertension, there is an impairment of release of ANP from the isolated heart in response to left atrial distention.