Insulin stimulates volume absorption in the rabbit proximal convoluted tubule

The present in vitro microperfusion study examined whether insulin affects volume absorption (J(v)) in the proximal convoluted tubule (PCT). PCT were perfused with an ultrafiltrate-like solution and were bathed in a serum-like albumin solution. Addition of a physiologic concentration of 10^-10 M insulin to the bathing solution resulted in a stimulation of J(v) and a more negative transepithelial potential difference (PD). There was a progressive stimulation of the lumen negative PD and J(v) with higher insulin concentrations. Maximal stimulation occurred at 10^-8 M bath insulin. The insulin-induced stimulation of volume reabsorption was also observed when glucose and amino acids were removed from the luminal perfusate. Direct examination of the effect of insulin on glucose, chloride, and bicarbonate absorption demonstrated that the transport of all these solutes was stimulated by insulin. Addition of insulin to the luminal perfusate had no affect on J(v). These data show that insulin has a direct effect to stimulate J(v) in the proximal tubule.