Effects of clonidine, dihydralazine and splanchnic nerve stimulation on the release of neuropeptide Y, MET-enkephalin and catecholamines from dog adrenal medulla.
Various neuropeptides are costored together with catecholamines in the adrenal medulla. The concurrent release (evaluated by adrenal vein plasma levels) of these neuropeptides [neuropeptide Y (NPY), met-enkephaline (ME)] and catecholamines [adrenaline (A) and noradrenaline (NA)] from the adrenal gland was examined in chloralose-anesthetized dogs after intravenous administration of clonidine (10 micrograms/kg) and dihydralazine (1 mg/kg). These results were compared to those obtained after the stimulation of the right splanchnic nerve at 1, 5 and 10 Hz frequencies. The increment in the release of catecholamines and neuropeptides was evaluated for dihydralazine and splanchnic nerve stimulation. Dihydralazine (at its maximal effect) induced a significant preferential increase 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. However, 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 frequency 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 resulted in similar elevations of NA, ME, and NPY-LI adrenal plasma levels (about 4 times) whereas A only increased twice. Clonidine decreased catecholamine and ME adrenal plasma levels (the maximal percent decrease when compared with control values was about 75%) whereas NPY adrenal plasma levels remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)
Damase-Michel
C
C
Laboratoire de Pharmacologie Médicale et Clinique, INSERM U317, Faculté de Médecine, Toulouse, France.
Tavernier
G
G
Giraud
P
P
Montastruc
J L
JL
Montastruc
P
P
Tran
M A
MA
D000313:Adrenal Medulla / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D000818:Animals; D002395:Catecholamines / Q000097:blood / Q000378:metabolism; D002838:Chromaffin System / Q000187:drug effects / Q000502:physiology; D003000:Clonidine / Q000494:pharmacology*; D004078:Dihydralazine / Q000494:pharmacology*; D004285:Dogs; D004558:Electric Stimulation; D004744:Enkephalin, Methionine / Q000378:metabolism; D005260:Female; D008297:Male; D009478:Neuropeptide Y / Q000378:metabolism; D018377:Neurotransmitter Agents / Q000378:metabolism*; D013153:Splanchnic Nerves / Q000502:physiology*
D002395:Catecholamines; D009478:Neuropeptide Y; D018377:Neurotransmitter Agents; D004744:Enkephalin, Methionine; D003000:Clonidine; D004078:Dihydralazine