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INVOLVEMENT OF α 1 ‐ADRENOCEPTORS IN CHRONOTROPIC RESPONSES TO ENDOGENOUSLY RELEASED AMINES IN THE PITHED RAT
Author(s) -
Luca A. De,
Rand M. J.
Publication year - 1988
Publication title -
clinical and experimental pharmacology and physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 103
eISSN - 1440-1681
pISSN - 0305-1870
DOI - 10.1111/j.1440-1681.1988.tb01006.x
Subject(s) - chronotropic , prazosin , propranolol , yohimbine , medicine , diltiazem , stimulation , endocrinology , chemistry , tyramine , heart rate , antagonist , blood pressure , receptor , calcium
SUMMARY 1. In pithed rats, yohimbine (1 mg/kg i.v.) enhanced the positive chronotropic responses to spinal stimulation of cardiac sympathetic nerves with eight pulses delivered at 2 or 4 Hz, indicating that auto‐inhibition was operating, but did not increase responses to shorter lengths of trains of 8 pulses at 8, 16 or 32 Hz which did not allow sufficient time for auto‐inhibition to come into effect. 2. The positive chronotropic response to cardiac sympathetic nerve stimulation with eight pulses at 8 Hz of about 60 beats/min was not affected by prazosin (1 mg/kg) or diltiazem (0.2 mg/kg), but was reduced to about 20% of the control value by propranolol (1 mg/kg). 3. In the presence of propranolol, the residual positive chronotropic responses to cardiac sympathetic nerve stimulation were virtually abolished by prazosin (1 mg/kg) or diltiazem (0.2 mg/kg). 4. The positive chronotropic response to tyramine (0.1 mg/kg i.v.) was reduced from 100 to 12 beats/min by propranolol (1 mg/kg), and the residual response was abolished by prazosin. 5. The findings indicate that noradrenaline released from cardiac sympathetic terminals by nerve stimulation or by tyramine acts on α 1 ‐adrenoceptors to produce a positive chronotropic response that is revealed when β‐adrenoceptors are blocked.