Role of nitric oxide in the systemic and pulmonary circulation of anesthetized turtles (Trachemys scripta)

In reptiles the influence of local vascular factors on blood flow regulatio n is vaguely understood. The aim of this study was to investigate the role of nitric oxide (NO) on vascular function in anesthetized Trachemys scripta . The experimental protocol consisted of serial injections of sodium nitrop russide (SNP; 25 mu g . kg(-1)), L-arginine (185 mg . kg(-1)) and L-NAME (5 0 mg . kg(-1)). SNP induced a systemic vasodilation (0.05 to 0.02 kPa . min . kg . mL(-1), P = 0.015), with no change in pulmonary vascular resistance (0.07 versus 0.08 kPa . min . kg . mL(-1), P > 0.05). L-Arg had no effect on resistances but increased cardiac output by 17%. L-NAME increased system ic resistance (33% increase; P = 0.01) while pulmonary resistance was uncha nged. These effects are consistent with in vivo and in vitro studies on the systemic vasculature of different reptilian species, suggesting that NO ha s an important role in maintaining systemic vascular tone. The pulmonary va sculature did not respond to NO due to either a lack of an endogenous NO to ne or a relaxed state of the pulmonary vasculature. The importance of NO-ba sed mechanisms versus other neuro-humoral modulators in the reptilian circu lation remains uncertain. However, as established in prior studies, choline rgic control of the proximal pulmonary artery is the main regulator of pulm onary resistance while systemic resistance depends on a more complex suite of neural, humoral and local effecters that include NO. J. Exp. Zool. 286:6 83-689, 2000. (C) 2000 Wiley-Liss, Inc.