Effect of osmotic pressure on spontaneous afferent discharge in the nerves of the perfused rabbit liver.

Rabbit livers were perfused with Krebs solution via the portal vein and small bundles of the hepatic nerve were monitored for spontaneous afferent impulses arising in the liver. The concentration of the Krebs solution was varied by altering the amount of water in which the salts were dissolved. An alteration from 5% more concentrated to 5% more dilute and vice versa did not affect this spontantous discharge. Addition to the Krebs solution of up to 60 mM sucrose, of up to 22 mM mannitol or of 0.8 mM polyethylenglycol 6000 mol. wt. did not alter the frequency of impulses. Perfusion with bovine serum, or Krebs solution containing approx. 0.6 mM polyvinylpyrrolidone, mol. wt. 44000, or dextran mol. wt. 110000 increased the frequency of discharge in some nerve bundles. An alteration of 0.06 mM in the concentration of dextran produced a significant change of frequency. It is concluded that spontaneous discharge in some afferent hepatic nerves is influenced by colloidal osmotic pressure but not by changes of ionic osmotic pressure. The nerves affected differ from 'sodium-sensitive' nerves and from the 'osmoreceptors' of Niijima.