Effects of pre-junctional alpha-receptor blockade on vascular neuro-effector characteristics in rats on high sodium intake.
Various in-vitro studies have indicated a direct attenuating effect of sodium on the affinity of adrenergic alpha 2-receptors. It has been suggested that ingested sodium in this way might increase blood pressure by reducing the activity of central alpha 2-receptors and thereby increasing sympathetic discharge. However, such an effect of sodium would also impair the function of peripheral alpha 2-receptors. In the present study we have therefore investigated the effect of high sodium intake on the alpha 2-receptor-mediated inhibition of the vascular neurogenic response. Male Wistar rats were given 2% NaCl in their drinking water from 4 to 9 weeks of age. Another group receiving plain tap water served as controls. Segments of small branches from the mesenteric artery were mounted in a myograph. Responses to transmural nerve stimulation were determined before and after alpha 2-receptor blockade with either yohimbine or idazoxan. The response to a continuous nerve stimulation that elicited 30% of maximal contraction was increased 2-3 times after addition of either idazoxan (0.1 microM) or yohimbine (0.3 microM), with no significant difference between sodium-treated and control rats; if anything the enhancement was slightly greater in the sodium-treated group. Also, responses to intermittent burst stimulation were increased from 30 to about 80% of maximal response in both rat groups. The results thus indicate that high sodium intake does not affect the inhibitory influence of pre-junctional alpha 2-receptors on the vascular neurogenic response.
Sjöblom-Widfeldt
N
N
Department of Physiology, University of Gothenburg, Sweden.
Nilsson
H
H
Gustafsson
H
H
Ely
D L
DL
Folkow
B
B
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D004146:Dioxanes / Q000494:pharmacology; D019329:Idazoxan; D008297:Male; D008638:Mesenteric Arteries / Q000187:drug effects / Q000294:innervation; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000294:innervation; D009469:Neuromuscular Junction / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains; D012965:Sodium Chloride / Q000008:administration & dosage*; D009435:Synaptic Transmission / Q000187:drug effects; D014655:Vascular Resistance / Q000187:drug effects*; D015016:Yohimbine / Q000494:pharmacology
D000317:Adrenergic alpha-Antagonists; D004146:Dioxanes; D015016:Yohimbine; D012965:Sodium Chloride; D019329:Idazoxan