RENIN SECRETION IN CONSCIOUS LYON HYPERTENSIVE RATS

To characterize the renin secretory profile in Lyon hypertensive (LH) rats, renin responses to reductions of arterial pressure and beta-adre noceptor stimulation were assessed in conscious unrestrained LH (n = 1 3) and Lyon normotensive (LN, n = 14) rats under normal-salt diet. Mea n arterial pressure (MAP) in the infrarenal aorta was recorded beat to beat for 3 h. Then, plasma renin concentration (PRC) was measured 1) in basal conditions, 2) during 10-mmHg stepwise reductions of MAP down to 60 mmHg using a chronically implanted aortic inflatable cuff, and 3) during isoprenaline infusion (62.5, 125, and 250 ng . kg(-1). min(- 1) iv). Compared with LN, LH rats had an elevated MAP (146 +/- 3 vs. 1 11 +/- 1 mmHg, P < 0.001) and decreased PRC [4.2 +/- 0.6 vs. 8.2 +/- 0 .8 ng angiotensin (ANG) I . ml(-1). h(-1), P < 0.001] and kidney renin content (216 +/- 14 vs. 1,149 +/- 103 mu g ANG I . h(-1). g(-1), P < 0.001). Pressure-dependent renin release occurred below 90 mmHg in LN rats and below 80 mmHg in LH rats, and its sensitivity in the low-pres sure range did not differ between strains. Isoprenaline-induced increa ses in PRC were weaker (P <( 0.01) in LH than in LN rats. In additiona l LH and LN rats (n = 6-8), acute ANG II AT(1)-receptor blockade with losartan (20 mg/kg, followed by 10 mg . kg(-1). h(-1) iv for 2 h) indu ced lesser (P < 0.001) PRC increases in LH than in LN rats. Renin resp onses to isoprenaline remained blunted (P < 0.01) during losartan infu sion in LH rats. We conclude that, in LH rats, renin secretion is inde pendent of MAP in the range of its spontaneous variations and is poorl y responsive to beta-adrenoceptor stimulation, the alteration of which cannot be explained by an enhanced feedback inhibition by ANG II.