GENDER-DIFFERENTIAL LIVER PLASMA-MEMBRANE AFFINITIES IN HEPATIC TETRABROMOSULFONEPHTHALEIN (TBS) UPTAKE

The sex difference in the hepatic uptake of tetrabromosulfonephthalein (TBS) was investigated in male and female rats in two different exper imental models. In the intact animal, the initial plasma disappearance constant rate, the initial velocity of uptake, and the plasma clearan ce of TBS were significantly higher in females than in males. In sinus oidal liver plasma membrane vesicles, kinetic parameters of TBS uptake were investigated in both sexes. The IC, was lower in females than in males (5.5 +/- 0.4 vs 17 +/- 4 mu M, P < 0.05), whereas V-max shelved comparable values (544 +/- 15 vs 581 +/- 60 nmol TBS/min/mg protein, mean +/- SD, NS, females and males, respectively). Collectively, these data indicate that the sex difference in hepatic uptake of TBS is loc ated at the sinusoidal liver plasma membrane and is due to a greater a ffinity of the electrogenic transport system(s) in females.