Atrial natriuretic peptide-induced secretory responses in rabbit vs rat ileum

The aim of this study was to characterize and compare the effect of atrial natriuretic peptide (ANP) on ileal transport function in two common laboratory animals, the Hooded-Lister rat and the New Zealand White rabbit. ANP 1 microM produced a maximal increase in short circuit current (Isc) that was Cl- dependent in both rat and rabbit. The maximal response in rat tissue was twice the magnitude of that seen in the rabbit. Furthermore, the rabbit Isc response was rapid and transient compared with that of the rat. In both rats and rabbits, the ANP response was dependent on extracellular Ca++. Neural blockade had no effect on the rat ANP response but significantly inhibited the ANP response in rabbits. In the rat, the effect of ANP is mediated by seratonin (5-HT) acting through 5-HT2 receptors. In contrast, no role for 5-HT could be seen in the rabbit ileal ANP response. In intact tissue in both rat and rabbit, ANP stimulated a significant rise in cGMP levels. ANP had no effect on cAMP levels in either species. The findings suggest a separate and distinct mechanism for ANP-mediated intestinal Cl- secretion in the rat ileum compared with the rabbit.