A MODEL FOR THE MOVEMENT OF SALICYLATE ACROSS THE PAROTID EPITHELIUM

¹ Department of Pharmacology, Medical College of Virginia, Health Sciences Division, Virginia Commonwealth University, Richmond, Virginia

Salivary/plasma (S/P) concentration ratios of salicylate (a weak acid) were determined under conditions of variable blood pH and states of hydration. Salivary pH was also monitored and an attempt was made to correlate S/P ratios with salivary and blood pH according to Jacobs' equation (Cold Spring Harbor Symp. Quant. Biol. 8: 30-39, 1940) for the movement of weak acids across a lipid interphase. The theoretical values were not in agreement with the experimental. According to the equation, dogs infused with HCl (low blood pH) should have had higher steady-state S/P ratios than controls (normal blood pH), and controls higher steady-state S/P ratios than dogs infused with NaHCO₃ (high blood pH). Since the reverse was found experimentally, it is suggested that the apical membrane presents the major lipid barrier and therefore the primary pH-dependent process occurs here. In agreement with the findings of Burgen (J. Cell. Physiol. 48: 113-138, 1956), diffusion from the plasma into the epithelial tissue appears to occur through aqueous pores and is not pH dependent. Infusion of saline or glucose at an equivalent rate produced no effect on blood or salivary pH and, as expected, no effect on the steady-state S/P ratios. Infusion of saline, glucose, HCl or NaHCO₃, however, appeared to increase the permeability of the gland in a manner nonspecific for the composition of the infusate. This suggests that hydration of the animal may be a factor in determining the permeability of the gland to weak electrolytes.

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