Arterial baroreceptors and brain histamine contribute to bradycardia to peripheral hyperosmolality.
The purpose of this study was to determine whether the bradycardic response to peripheral hyperosmolality in conscious rats is dependent on afferent baroreceptor mechanisms and whether central histamine H2 receptors play a role in baroreflex-mediated changes in heart rate (HR). Mean arterial pressure (MAP) and HR were recorded continuously during a 30-min infusion of 2.5 M NaCl (10 microliters.100 g-1.min-1) hypertonic saline (HTS). HTS infusion significantly increased MAP (21 +/- 4 mmHg) and reduced HR (-62 +/- 10 beats/min) in rats with intact arterial baroreceptors. In sinoaortic-denervated rats, HR remained unchanged from control despite a significant increase in MAP. After intracerebroventricular (lateral ventricle) administration of cimetidine or ranitidine (H2-receptor antagonists) in intact rats, HTS infusion significantly increased MAP (19 +/- 2 and 17 +/- 2 mmHg, respectively) but the bradycardia was abolished (-12 +/- 10 and -10 +/- 10 beats/min, respectively). In contrast, central H2-receptor blockade did not alter reflex HR responses to the intravenous administration of phenylephrine and nitroprusside or to the central administration of histamine or angiotensin II. These results indicate that the bradycardic response to HTS infusion is mediated through the arterial baroreceptor reflex and involves in part a selective histaminergic pathway.
Kenney
M J
MJ
Department of Biology, Rhodes College, Memphis, Tennessee.
Bealer
S L
SL
D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D001158:Arteries / Q000502:physiology*; D001921:Brain / Q000378:metabolism*; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D006632:Histamine / Q000378:metabolism* / Q000494:pharmacology; D006635:Histamine H2 Antagonists / Q000494:pharmacology; D008297:Male; D009599:Nitroprusside / Q000494:pharmacology; D009994:Osmolar Concentration; D010656:Phenylephrine / Q000494:pharmacology; D011311:Pressoreceptors / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012462:Saline Solution, Hypertonic / Q000494:pharmacology
D006635:Histamine H2 Antagonists; D012462:Saline Solution, Hypertonic; D000804:Angiotensin II; D009599:Nitroprusside; D010656:Phenylephrine; D006632:Histamine