The role of alpha 1- and alpha 2-adrenoceptors in canine systemic capacitance vessels--a study with measurement of mean circulatory pressure.
We investigated the presence of alpha-adrenoceptor subtypes in systemic capacitance vessels by examining the effects of alpha 1- and alpha 2-agonists or antagonists on the mean circulatory pressure (MCP). Dogs were anesthetized with pentobarbital, and after total spinal anesthesia, epinephrine was given intravenously to maintain mean blood pressure at about 80 mmHg. 1. With intravenous injection of phenylephrine (alpha 1-agonist, 10 micrograms/kg, n = 7), and of BHT 920 (alpha 2-agonist, 5 micrograms/kg, n = 7), MCP increased significantly from 9.8 +/- 0.4 (mean +/- SE) to 10.9 +/- 0.3 mmHg (+11.2%, p less than 0.01), and from 9.3 +/- 0.4 to 10.3 +/- 0.4 mmHg (+10.8%, p less than 0.05), respectively. 2. Intravenous injection of prazosin (alpha 1-antagonist, 150 micrograms/kg, n = 7) and of yohimbine (alpha 2-antagonist, 30 micrograms/kg, n = 7) decreased MCP significantly from 9.9 +/- 0.4 to 8.2 +/- 0.5 mmHg (-17.2%, p less than 0.01), and from 9.8 +/- 0.2 to 7.6 +/- 0.3 mmHg (-22.4%, p less than 0.01), respectively. 3. Intravenous injection of phenylephrine (10 micrograms/kg, n = 7) after pretreatment with prazosin (150 micrograms/kg) decreased MCP significantly from 9.5 +/- 0.3 to 7.8 +/- 0.3 mmHg (-17.9%, p less than 0.01). MCP decreased significantly from 9.9 +/- 0.3 to 8.2 +/- 0.3 mmHg (-17.2%, p less than 0.01) after intravenous injection of BHT 920 (5 micrograms/kg, n = 7) following pretreatment with yohimbine (30 micrograms/kg).(ABSTRACT TRUNCATED AT 250 WORDS)
Hirose
I
I
2nd Department of Internal Medicine, Gifu University School of Medicine, Japan.
Ito
H
H
Nagata
K
K
Sahashi
T
T
Wada
H
H
Takai
K
K
Hirakawa
S
S
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D001381:Azepines / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology*; D002302:Cardiac Output / Q000187:drug effects; D004285:Dogs; D006339:Heart Rate / Q000187:drug effects; D010656:Phenylephrine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D014655:Vascular Resistance / Q000187:drug effects / Q000502:physiology*; D015016:Yohimbine / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D001381:Azepines; D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D015016:Yohimbine; C024763:talipexole; D011224:Prazosin