Cardiac effects of injections of epinephrine into the spinal intermediolateral column.
Small doses of epinephrine (0.008, 0.05, and 0.1 pmol, i.e., 20-nl volumes of 0.40, 2.5, and 5 microM solutions) produced a dose-dependent increase in heart rate when micro-injected into the right intermediolateral column (IML) at T2 spinal level. These effects were mediated via alpha 1-adrenergic receptors because prazosin blocked them. The presence of alpha 1-adrenergic receptors at this site was confirmed by microinjections of phenylephrine (a specific agonist for these receptors); phenylephrine elicited tachycardia. Larger doses of epinephrine (320, 2,000, and 3,200 pmol, i.e., 20-nl volumes of 16, 100, and 160 mM solutions) caused bradycardia when microinjected into the IML. These effects were mediated via alpha 2-adrenergic receptors because idazoxan blocked them. The presence of alpha 2-adrenergic receptors at this site was confirmed by microinjections of clonidine (a specific agonist for these receptors); clonidine elicited bradycardia. Injections of the vehicle (20 nl of normal saline containing 0.3% ascorbic acid, pH 7.4) did not evoke a response. Epinephrine, prazosin, or idazoxan did not alter the responses to L-glutamate. None of the doses of epinephrine elicited any response when injected intravenously. The aforementioned results provide pharmacological evidence for the presence of alpha 1- and alpha 2-adrenergic receptors in the IML at T2. Thus a basis is provided for investigating the role, if any, of alpha-adrenergic receptors in the IML in mediating cardiovascular responses elicited by the stimulation of different brain stem areas.
Malhotra
V K
VK
Section of Neurosurgery, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark 07103.
Kachroo
A
A
Sapru
H N
HN
D000818:Animals; D001919:Bradycardia / Q000139:chemically induced; D003000:Clonidine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004837:Epinephrine / Q000008:administration & dosage*; D006321:Heart / Q000187:drug effects*; D006339:Heart Rate / Q000187:drug effects; D007278:Injections, Spinal; D008297:Male; D008845:Microinjections; D010656:Phenylephrine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013116:Spinal Cord / Q000502:physiology*; D013610:Tachycardia / Q000139:chemically induced
D010656:Phenylephrine; D003000:Clonidine; D004837:Epinephrine