EFFECTS OF CLONIDINE, DIHYDRALAZINE AND SPLANCHNIC NERVE-STIMULATION ON THE RELEASE OF NEUROPEPTIDE-Y, MET-ENKEPHALIN AND CATECHOLAMINES FROM DOG ADRENAL-MEDULLA
C. Damasemichel et al., EFFECTS OF CLONIDINE, DIHYDRALAZINE AND SPLANCHNIC NERVE-STIMULATION ON THE RELEASE OF NEUROPEPTIDE-Y, MET-ENKEPHALIN AND CATECHOLAMINES FROM DOG ADRENAL-MEDULLA, Naunyn-Schmiedeberg's archives of pharmacology, 348(4), 1993, pp. 379-384
Various neuropeptides are costored together with catecholamines in the
adrenal medulla. The concurrent release (evaluated by adrenal vein pl
asma levels) of these neuropeptides [neuropeptide Y (NPY), met-enkepha
line (ME)] and catecholamines [adrenaline (A) and noradrenaline (NA)]
from the adrenal gland was examined in chloralose-anesthetized dogs af
ter intravenous administration of clonidine (10 mug/kg) and dihydralaz
ine (1 mg/kg). These results were compared to those obtained after the
stimulation of the right splanchnic nerve at 1, 5 and 10 Hz frequenci
es. The increment in the release of catecholamines and neuropeptides w
as evaluated for dihydralazine and splanchnic nerve stimulation. Dihyd
ralazine (at its maximal effect) induced a significant preferential in
crease in catecholamines (expressed as mean (SEM): NA: 17.3 (5.4) fold
, A: 13.1 (2.6) fold) and ME (16.0 (7.1) fold) versus basal values. Ho
wever, the significant increase in NPY-LI was only 2.0 (0.4) times the
baseline. Splanchnic nerve stimulation induced a frequency-dependent
increase in catecholamines and neuropeptides. When the stimulation fre
quency was increased from 1 Hz to 5 Hz, NA and A levels increased 17.9
(4.3) and 14.0 (2.2) fold, respectively and ME levels 14.1 (3.0) fold
. By contrast, NPY-LI was increased only 2.3 (0.3) fold under the same
conditions. Increasing the stimulation frequency from 5 Hz to 10 Hz r
esulted in similar elevations of NA, ME, and NPY-LI adrenal plasma lev
els (about 4 times) whereas A only increased twice. Clonidine decrease
d catecholamine and ME adrenal plasma levels (the maximal percent decr
ease when compared with control values was about 75%) whereas NPY adre
nal plasma levels remained unchanged. In conclusion, the present data
indicate that i) both adrenal ME and NA always exhibit corelease in a
parallel fashion which is not the case for NPY and ii) different popul
ations of chromaffin vesicles could be preferentially mobilized accord
ing to different physiological and pharmacological patterns.