The secretion of catecholamines, chromogranin A and neuropeptide Y from the adrenal medulla of the cat via the adrenolumbar vein and thoracic duct: different anatomic routes based on size.
Secretion of the adrenal medulla was stimulated in nine cats by insulin-induced hypoglycemia. Levels of catecholamines (mol. wt 153-183), neuropeptide Y (mol. wt 4254) and chromogranin A (mol. wt 48,000) were measured in concurrently collected samples of adrenolumbar venous blood and thoracic duct lymph for up to 4 h following insulin administration. Insulin-induced hypoglycemia elicited an increase in the secretion of catecholamines, which reached peak levels in the adrenolumbar venous plasma at 1.5-2 h and in the lymph at 2.5 h. Although catecholamines were the most numerous measured molecules in the lymph, levels of norepinephrine and epinephrine were 75-250-fold less than those found in the adrenolumbar venous plasma. Neuropeptide Y in the adrenolumbar venous plasma reached peak levels between 1 and 1.5 h; at this time approximately 20% of the peak venous amount was detected in the lymph. Chromogranin A was found in approximately equal amounts in both plasma and lymph; the peak level in the plasma occurred at 1.5-2 h, while that in the lymph was reached at 2-3 h. We suggest that the size of a molecule influences the route it takes following exocytosis from the chromaffin vesicle. Smaller molecules such as catecholamines may pass directly into the circulation, while larger molecules such as chromogranin A may be temporarily sequestered in the interstitial space before passing into the lymph, and hence into the circulation.
Carmichael
S W
SW
Department of Anatomy, Mayo Clinic/Foundation, Rochester, MN 55905.
Stoddard
S L
SL
O'Connor
D T
DT
Yaksh
T L
TL
Tyce
G M
GM
D000313:Adrenal Medulla / Q000098:blood supply / Q000378:metabolism*; D000818:Animals; D002395:Catecholamines / Q000097:blood*; D002415:Cats; D053379:Chromogranin A; D002864:Chromogranins / Q000097:blood*; D007003:Hypoglycemia / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000097:blood*; D009478:Neuropeptide Y / Q000097:blood*; D013897:Thoracic Duct / Q000502:physiology*
D002395:Catecholamines; D053379:Chromogranin A; D002864:Chromogranins; D009419:Nerve Tissue Proteins; D009478:Neuropeptide Y