Insulin-like growth factor 1 stimulates renal epithelial Na+ transport

Insulin-like growth factor 1 (IGF1) stimulates vectorial Na+ transport in a classical model of the mammalian distal nephron, the toad urinary bladder. Net mucosal to serosal Na+ flux is stimulated by concentrations of IGF1 as low as 0.1 nM, and the response is maximal at 10 nM. Na+ transport increases within minutes of the serosal addition of IGF1, reaches a maximum in 2-3 h, and is sustained for at least 5 h. Neither the initial nor the sustained response to IGF1 is dependent on a new protein synthesis. The IGF1 response is inhibited by a concentration of amiloride (10(-5) M) that is known to specifically block the conductive apical Na+ channel but that has little effect on the Na+-H+ antiporter. Further studies will be necessary to establish a role for this growth factor in normal renal epithelial function, but it is possible that the natriferic and growth-stimulatory effects of IGF1 are intimately related.