Effects of various secretagogues upon 42 K and 22 Na uptake during in vitro hormone release from the rat adenohypophysis

1. The in vitro uptake of 22 Na and 42 K was measured simultaneously in rat adenohypophyses during hormone release produced by several secretagogues and during inhibition of hormone release in Ca‐free media. 2. Intracellular adenohypophysial [Na + ] and [K + ] changed only slightly when the uptake changed. This would indicate that relative permeability changes were the primary effect of the treatments. 3. The uptake of 42 K was increased by elevated external [K + ], but was unaffected by the presence or absence of Ca 2+ . Acid extracts of hypothalamus‐stalk—median eminence or cerebellum also increased the 42 K uptake. 4. The uptake of 22 Na or 24 Na was decreased by elevated [K + ]. Uptake was increased in Ca‐free Krebs—Ringer bicarbonate; but was unaltered when [K + ] was concurrently increased. 5. Neither purified growth hormone releasing hormone, synthetic lysine‐vasopressin, dibutyryl cyclic AMP nor theophylline had an effect on the uptake of either K + or Na + . 6. The rapid uptake of 22 Na and its smaller volume of distribution compared to absolute measurements of intracellular [Na + ] suggest that the plasma membrane of adenohypophysial cells is relatively impermeable to Na + . 7. We conclude that changes in the uptake of Na + and K + associated with hormone release are incidental to the release process. 8. Hormone release produced by elevated external [K + ] is most likely due to a non‐specific increase in permeability of the cell membranes, facilitating Ca 2+ entry into the cytoplasm. 9. The results suggest that the low resting transmembrane potentials of adenohypophysial cells may be due to their conjoint relatively high permeability to both K + and Ca 2+ , rather than K + and Na + .