Endocrine and lipid effects of oral L-arginine treatment in healthy postmenopausal women

As a substrate for nitric oxide synthesis, L-arginine may give the same pro tection as estrogen, but its other biologic effects may adversely affect at herogenesis. Therefore, possible endocrine and lipid effects of L-arginine were investigated in a double-blind, placebo-controlled, single crossover s tudy. After randomization, oral L-arginine (9 g) or placebo was given daily for 1 month, with crossover to the alternate therapy after a 1-month washo ut period, to 10 postmenopausal women receiving no estrogen. Compared with placebo, L-arginine increased growth hormone (1.5 +/- 1.8 mg/L vs 0.6 +/- 0 .6 mg/L, P = .04) but had no effect on insulin and catecholamines. Total ch olesterol, triglyceride, apolipoprotein E, and low-, very-low-, and high-de nsity lipoprotein cholesterol levels were also unaffected. Lipoprotein(a) m easured by an immunoturbidimetric method was increased by L-arginine in 9 o f 10 women relative to placebo (0.46 +/- 0.35 g/L vs 0.38 +/- 0.30 g/L, P = .053), and the changes in lipoprotein(a) levels significantly correlated w ith the relative increase in growth hormone (r = 0.85, P = .03). However, l ipoprotein(a) measured by an enzyme-linked immunosorbent assay failed to de monstrate significant changes. Lack of an increase by L-arginine in lipopro tein(a) with a verifiable apolipoprotein(a) isoform-independent method, des pite an increase in growth hormone, questions the validity of previous obse rvations for growth hormone-induced increases in lipoprotein(a). The observ ed lack of effect on major endocrine hormones and lipid profile support the safety of oral L-arginine administration.