Uptake of dehydroascorbic acid and ascorbic acid to isolated nerve terminals and secretory granules from ox neurohypophyses

TY - JOUR

T1 - Uptake of dehydroascorbic acid and ascorbic acid to isolated nerve terminals and secretory granules from ox neurohypophyses

AU - Thorn, N A

AU - Nielsen, F S

AU - Jeppesen, C K

AU - Christensen, B L

AU - Farver, O

PY - 1986/12

Y1 - 1986/12

N2 - When uptake of L-[14C]ascorbic acid ([14C]AA) to various organs in guinea-pigs was studied after intracardiac injection, the adenohypophysis, pars intermedia, and the neurohypophysis had an uptake per milligramme protein which was about half of the uptake to the adrenals. Adrenal uptake was 20 +/- 2.8 pmol mg-1 protein microCi-1 injected. The uptake to the different parts of the hypophysis was considerably higher than the uptake to pancreas, liver, kidney, spleen and other organs. When isolated nerve endings (neurosecretosomes) from ox neurohypophyses were incubated with a medium containing labelled dehydroascorbic acid ([14C]DHA), the uptake was much slower than when the medium contained labelled ascorbic acid. The uptake of [14C]DHA showed a linear dependence on concentration, and was not influenced by addition of Mg2+ and ATP. Addition of Mg2+ + ATP, omission of Ca2+ and Mg2+ or exchange of Na+ in the medium with K+ had no effect on the uptake of ascorbic acid. When isolated secretory granules from ox neurohypophyses were incubated with a medium containing [14C]DHA, uptake was considerably faster than the uptake when they were incubated in a medium containing [14C]AA. The uptake of dehydroascorbic acid was linear with the concentration in the medium and was not changed by addition of Mg2+ ATP. Addition of 10 mM NH4Cl or exchange of 120 mM K+ in the incubation medium with Na+ did not change the uptake of dehydroascorbic acid. The contents of copper, zinc, iron and cobalt were determined in isolated nerve endings (A) and membranes (B) as well as in lysate (C) from isolated neurosecretory granules. The results (in nmol mg-1 protein) were for Cu: (A): 0.25 +/- 0.01 (SEM), (B): 0.67 +/- 0.16, (C): 0.22 +/- 0.06; for Zn: (A): 0.53 +/- 0.13, (B): 6.97 +/- 0.75, (C): 1.8 +/- 0.53; and for Fe: (A): 15.6 +/- 1.9, (B): 6.92 +/- 0.32, (C): 3.15 +/- 0.43. In all preparations the cobalt content was below the detection limit (less than 5 pmol mg-1 protein).

AB - When uptake of L-[14C]ascorbic acid ([14C]AA) to various organs in guinea-pigs was studied after intracardiac injection, the adenohypophysis, pars intermedia, and the neurohypophysis had an uptake per milligramme protein which was about half of the uptake to the adrenals. Adrenal uptake was 20 +/- 2.8 pmol mg-1 protein microCi-1 injected. The uptake to the different parts of the hypophysis was considerably higher than the uptake to pancreas, liver, kidney, spleen and other organs. When isolated nerve endings (neurosecretosomes) from ox neurohypophyses were incubated with a medium containing labelled dehydroascorbic acid ([14C]DHA), the uptake was much slower than when the medium contained labelled ascorbic acid. The uptake of [14C]DHA showed a linear dependence on concentration, and was not influenced by addition of Mg2+ and ATP. Addition of Mg2+ + ATP, omission of Ca2+ and Mg2+ or exchange of Na+ in the medium with K+ had no effect on the uptake of ascorbic acid. When isolated secretory granules from ox neurohypophyses were incubated with a medium containing [14C]DHA, uptake was considerably faster than the uptake when they were incubated in a medium containing [14C]AA. The uptake of dehydroascorbic acid was linear with the concentration in the medium and was not changed by addition of Mg2+ ATP. Addition of 10 mM NH4Cl or exchange of 120 mM K+ in the incubation medium with Na+ did not change the uptake of dehydroascorbic acid. The contents of copper, zinc, iron and cobalt were determined in isolated nerve endings (A) and membranes (B) as well as in lysate (C) from isolated neurosecretory granules. The results (in nmol mg-1 protein) were for Cu: (A): 0.25 +/- 0.01 (SEM), (B): 0.67 +/- 0.16, (C): 0.22 +/- 0.06; for Zn: (A): 0.53 +/- 0.13, (B): 6.97 +/- 0.75, (C): 1.8 +/- 0.53; and for Fe: (A): 15.6 +/- 1.9, (B): 6.92 +/- 0.32, (C): 3.15 +/- 0.43. In all preparations the cobalt content was below the detection limit (less than 5 pmol mg-1 protein).

KW - Animals

KW - Ascorbic Acid

KW - Cattle

KW - Cobalt

KW - Copper

KW - Cytoplasmic Granules

KW - Dehydroascorbic Acid

KW - Female

KW - Guinea Pigs

KW - Nerve Endings

KW - Pituitary Gland, Posterior

KW - Tissue Distribution

KW - Zinc

U2 - 10.1111/j.1748-1716.1986.tb08021.x

DO - 10.1111/j.1748-1716.1986.tb08021.x

M3 - Journal article

C2 - 3811987

SN - 0302-2994

VL - 128

SP - 629

EP - 638

JO - Acta Physiologica Scandinavica, Supplement

JF - Acta Physiologica Scandinavica, Supplement

IS - 4

ER -