title: Effects of various secretagogues upon 42K and 22NA uptake during in vitro hormone release from the rat adenohypophysis.
abstract: 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(+).
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology; D002463:Cell Membrane Permeability; D000242:Cyclic AMP / Q000494:pharmacology; D013006:Growth Hormone / Q000494:pharmacology; D007031:Hypothalamus; D066298:In Vitro Techniques; D008239:Lysine / Q000494:pharmacology; D008564:Membrane Potentials; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D010906:Pituitary Hormone-Releasing Hormones / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism* / Q000502:physiology; D011194:Potassium Isotopes; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D012975:Sodium Isotopes; D014667:Vasopressins / Q000494:pharmacology
chemical_list: D010906:Pituitary Hormone-Releasing Hormones; D011194:Potassium Isotopes; D012975:Sodium Isotopes; D014667:Vasopressins; D013006:Growth Hormone; D012964:Sodium; D000242:Cyclic AMP; D008239:Lysine; D011188:Potassium; D002118:Calcium