6533b829fe1ef96bd1289b5a

RESEARCH PRODUCT

Acetylcholine overflow from isolated perfused hearts of various species in the absence of cholinesterase inhibition

subject

description

1. The content of acetylcholine in the tissue and effluent of isolated hearts of various birds and mammals was determined in the absence of inhibition of cholinesterase. 2. Stimulation of both vagus nerves for 15 min at 20 Hz caused marked negative chronotropic effects in all species. Spontaneous or stimulation-induced overflow of acetylcholine into the effluents was not detected in mammals. In the avian heart, the order of spontaneous overflow was: duck = chicken > pigeon, whereas the order of evoked overflow was: chicken > pigeon > duck. The acetylcholine overflow from the cat heart was below the limit of estimation (3 pmol g−1 min−1). In the chicken heart, the evoked overflow per min (284 pmol) was at least 95 times the overflow from the cat heart. 3. The average content of acetylcholine in the avian hearts was of the same order of magnitude (8.3–11.5 nmol/g) while the overflows ranged from 97 to 1615 pmol g−1 15 min−1. The acetylcholine content of cat and guinea-pig hearts was similar to that of avian hearts. 4. It is concluded that neither the spontaneous nor the stimulation-induced overflows of acetylcholine were correlated with the acetylcholine content in the tissue. The stimulation-induced overflow of acetylcholine into the effluent is much higher in avian than in mammalian hearts which, presumably, is due to differences in the amount of acetylcholine released from the terminal nerves.