We investigated the effect of platelet-activating factor (PAF) on basal and insulin-stimulated sodium-dependent neutral amino acid transport by system A in rat soleus muscle. Fasted male Sprague-Dawley rats (75-100 g) were given an intravenous injection of saline or PAF (4 micrograms/kg) and killed 1 hr later. Isolated soleus muscles were incubated in media containing 1-14C-alpha-aminoisobutyric acid (AIB; system A amino acid analog), 3H-inulin, and 0 (basal) or 100 mU/ml insulin. Na(+)-free media were assessed by Na(+)-independent AIB uptake. The rate of AIB uptake by muscle was corrected for uptake into extracellular (inulin) space. Basal cellular AIB uptake by soleus muscles from PAF-treated rats was 30.2% lower than in controls. Insulin increased the absolute rate of cellular AIB uptake above basal levels to the same extent in muscles of control and PAF-treated rats, although the rate of maximal insulin-stimulated AIB uptake was 20% lower in muscles of PAF-treated rats. Na(+)-independent AIB uptake (measured in Na(+)-free media) was the same in muscles of control and PAF-treated rats. The fact that AIB uptake in Na(+)-free media was the same in muscles of control and PAF-treated rats indicates that the reduction in basal and insulin-stimulated AIB uptake in muscles of PAF-treated rats was due to an alteration of system A Na(+)-dependent amino acid transport.