Reply to Letter to the editor * Georg

To the Editor: excluding any unspecific effect of anaesthesia. This was not the case in the studies cited by Dr. Pagliaro. Therefore, We thank Dr. Pagliaro for his comments. In his letter Dr. we believe that the references cited in our review are Pagliaro focused on two points of the discussion of appropriate and that these investigations have considerable chronotropic effects of endogenous nitric oxide (NO) in methodological advantages to demonstrate a negative v our review [1]: (1) the use of N -nitro-L-arginine-methychronotropic effect of endogenous NO. lester (L-NAME) and (2) a possible involvement of autonomic reflexes due to increases in blood pressure. L-NAME is a widely used prodrug to inhibit NO-synthReferences ase (NOS) because of its convenient water solubility. To effectively inhibit NOS, L-NAME has to be deesterified to v [1] Kojda G, Kottenberg K. Regulation of basal myocardial function by N -nitro-L-arginine, and in whole blood its halflife is 29 NO. Cardiovasc Res 1999;41:514–523. min [2]. Thus, it is unlikely that the intact ester has any [2] Pfeiffer S, Leopold E, Schmidt K, Brunner F, Mayer B. Inhibition of considerable effect in-vivo. It is known that high conG nitric oxide synthesis by N -nitro-L-arginine methyl ester (LG centrations of L-NAME can block muscarinergic receptors NAME): Requirement for bioactivation to the free acid. N -nitro-Lin-vitro [3]. In-vivo this blockade would result in an arginine Br J Pharmacol 1996;118:1433–1440. [3] Buxton ILO, Cheek DJ, Eckman D, Westfall DP, Sanders KM, Keef atropine like tachycardia, but there is no evidence of an G KD. N -nitro L-arginine methyl ester and other alkyl esters of antimuscarinergic effect of orally applied L-NAME. arginine are muscarinic receptor antagonists. Circ Res 1993;72:387– The baroreceptor reflex balances sudden but not sus395. tained changes in blood pressure. In hypertension there is a [4] Chapleau MW, Cunningham JT, Sullivan MJ, Wachtel RE, Abboud resetting of baroreceptors resulting in diminished baroFM. Structural versus functional modulation of the arterial baroreflex. Hypertension 1995;26:341–347. receptor induced pulse frequency (relatively diminished [5] Merrill DC, Thompson MW, Carney CL, Granwehr BP, Schlager G, parasympathetic nerve activity) at any given blood presRobillard JE, Sigmund CD. Chronic hypertension and altered sure [4]. This was also observed in a chronically hypertenbaroreflex responses in transgenic mice containing the human renin sive transgenic mouse strain [5]. Thus, the bradycardia and human angiotensinogen genes. J Clin Invest 1996;97:1047– observed in normal mice treated for 3 weeks with L1055. [6] Kojda G, Laursen JB, Ramasamy S, Kent JD, Kurz S, Burchfield J, NAME and in mice lacking the eNOS gene is most likely Shesely EG, Harrison DG. Protein expression, vascular reactivity not a consequence of the concommitant mild increase in and soluble guanylate cyclase activity in mice lacking the endotheliblood pressure. This interpretation is consistant with our al nitric oxide synthase: contributions of NOS isoforms to blood observation that treatment of mice lacking the eNOS gene pressure and heart rate control. Cardiovasc Res 1999;42:206–213. with L-NAME resulted in further bradycardia in the [7] Vandecasteele G, Eschenhagen T, Scholz H, Stein B, Verde I, absence of any change of blood pressure [6]. It is also Fischmeister R. Muscarinic and beta-adrenergic regulation of heart rate, force of contraction and calcium current is preserved in mice consistant with a recently published study demonstrating lacking endothelial nitric oxide synthase. Nat Med 1999;5:331–334. that isolated atria of mice lacking the eNOS gene have a [8] Shesely EG, Maeda N, Kim HS, Desai KM, Krege JH, Laubach VE, normal response to muscarinergic stimulation [7]. Sherman PA, Sessa WC, Smithies O. Elevated blood pressures in Finally, measurements of blood pressure and heart rate mice lacking endothelial nitric oxide synthase. Proc Natl Acad Sci were obtained from conscious and trained animals [6,8] USA 1996;93:13176–13181.