Changes of plasma L-arginine levels in spontaneously hypertensive rats under induced hypotension

Nicardipine, a dihydropyridine type calcium channel blocker, was infused at two flow-rates into spontaneously hypertensive (SH) and control normotensi ve Wistar-Kyoto (WKY) rats (young, 6-week-old and adult, 23-week-old, n = 5 ) under pentobarbital anesthesia, to cause hypotension. Mean arterial blood pressure and the concentrations of plasma amino acids and norepinephrine ( NE) were measured before infusion and at each step of the infusion. The red uction in blood pressure caused by nicardipine induced a decrease in plasma L-arginine concentration in both young and adult SH rats, this effect bein g larger in adult rats. There was no significant change in plasma levels of L-arginine in age-matched WKY rats. The concentration of other amino acids did not change in both rat strains. On the contrary, there was an increase in plasma NE concentration in both SH and WKY rats after infusion with nic ardipine. Plasma L-arginine concentration showed a good inverse correlation with the logarithm of plasma NE concentration in SH and WKY rats and the c orrelation was expressed as Y = -alpha log(X) + m (Y, plasma L-arginine con centration (nmol/mL); X, plasma NE concentration (pmol/mL); alpha, a slope; and m, an intercept). alpha, 43.0 and 4.35 for 23-week-old SH and WKY rats , respectively, and 17.0 and 4.0 for 6-week-old SH and WKY rats, respective ly. The present data together with previous data suggest a direct noradrene rgic stimulation of the synthesis of nitric oxide (NO) from L-arginine. The findings also indicate an impairment of the L-arginine metabolism or pools in SH rats compared with WKY rats. The deficiency of L-arginine increases with the age of SH rats and could be related to the development and mainten ance of hypertension due to inefficient production of NO. Copyright (C) 199 9 John Wiley & Sons, Ltd.