STUDIES ON THE MECHANISM OF SALT AND WATER SECRETION FROM THE LACRIMAL GLAND

Abstract

By stimulating the lacrimal gland of rabbits with pilocarpine, the tears were collected through the fistula inserted into the nasolacrimal duct, and the ionic composition was analysed with special reference to the rate of lacrimal flow, and ionic concentrations in serum. The secretion potential was also measured with reference to the secretion of ions in tears. The osmolarity of tears is mainly produced by salts which are chiefly composed of Na+ and Cl-and partly of K+ and HC3 - and is kept almost constant at a slightly higher level than that of serum, irrespective of the rate of tear flow. The concentrations of Na+, HCO3 - and Cl- in tears are all kept constant, irrespective of the rate of tear flow, while the K+ concentration changes parallel to changes of the rate of tear flow. The concentrations of Na+ and HCO3 - in tears are approximately the same as that of the respective ion in serum even when the concentration in serum is changed by salt infusion, while K+ and Cl- concentrations are always higher in tears than in serum. The Cl- concentration in tears bears a linear relation with that in serum of which the regression coefficient is 1 and the intercept constant is about 25 mEq. The pH of tears is approximately the same as the serum pH and is determined by HCO3 - concentration and CO2 partial pressure which equilibrate with those in serum. The potential being measured by external leading from the luminal side and the outside of the lacrimal gland, a resting potential of about 4-27 mV was detected. The negative side of the potential is in the lumen of gland. The negativity of the potential in the luminal side increases as the rate of tear flow is increased by stimulation of lacrimal gland, and thus the secretion potential of about 7-22 mV appears. The secretion potential runs parallel to the time course of the rate of tear flow, though the peak of the former somewhat lags behind that of the latter. The increase of the resting potential as well as the secretion potential was provoked by raising the Cl- concentration in serum by NaCl infusion. The changes of potential may be due to the acceleration of Cl- secretion. On the other hand, the potential was reduced after KC1 infusion, probably owing to the promotion of K+ secretion by a rise of serum K+ concentration. From the above results and analysis of the interrelation between the rate of tear flow and the rate of ionic secretion as well as the secretion potential, it was deduced that the secretion potential as well as the water secretion (tear flow) of the lacrimal gland is associated with the active secretion of Cl- through the lacrimal gland cells, while Na+, HCO3 - are all transported passively in equilibration with those in serum. The K+ secretion is also an active process and results in decreasing secretion potential.