Plasma oxytocin concentration during intravenous infusion at 2 ml/hr of hypertonic saline in virgin (A) (2 m NaCl) or pregnant (B) (2.6 m NaCl) rats pretreated withl-NNA or vehicle. Oxytocin secretion was enhanced by pretreatment with l-NNA in virgin rats but not in pregnant rats. Changes in plasma sodium concentrations (insets) were not different between the groups. Data are means ± SEM; *p < 0.05 compared with basal; #p < 0.05 compared with controls.