A pH-stat technique was used to study the mechanisms underlying the intestinal alkalinization evoked by the heat-stable enterotoxin of Escherichia coli (STa) in the rat denervated jejunum in vivo. In addition, concomitant changes of transepithelial potential difference and fluid transport were also investigated. To test the possible involvement of the enteric nervous system in the STa-stimulated alkaline secretion and potential difference, the mesenteric nerves were electrically stimulated or neuropeptide Y or methionine-enkephalin was infused intravenously. None of these interventions inhibited to any large extent the STa-stimulated alkaline secretion, whereas a greater suppression was noted on the concomitantly increased potential difference. Furthermore, neuropeptide Y but not methionine-enkephalin significantly inhibited STa-induced jejunal fluid secretion although neuropeptide Y was without effect on basal fluid transport. It is concluded that the enteric nervous reflex(es) which are of significant importance in explaining STa-evoked fluid secretion plays a minor role in controlling alkaline secretion. Furthermore, alkaline secretion may not contribute to the increase in potential difference caused by STa Amiloride (10(-4) or 10(-3) M) had no effect on the STa-stimulated alkaline secretion, implying that some cellular mechanism other than an inhibition of Na+/H+ exchanger explains the observed response. Similarly, acetazolamide had no effect on the STa-stimulated alkaline secretion or potential difference, suggesting that the secreted alkaline is of extracellular origin rather than from the cellular metabolism in the enterocytes.