Development of the sympathetic nervous system response to endotoxicosis in the rat: importance of non-baroreflex mechanisms in pre-weanlings and adults.
The sympathetic nervous system response to endotoxicosis was studied in the rat at ages before (11-12 days) and after (19-20 days) maturation of the baroreflex and in adults by recording preganglionic impulses during i.v. infusions of endotoxin (S. enteriditis). At all ages, the discharge rate increased before there was any decrease in arterial blood pressure. The magnitude of the increase (65%) was the same in 11-12 days-old and adult rats while 19-20 days-old rats were hyperactive (278% increase). Subsequently, in the hypotensive phase of the endotoxicosis (diastolic pressure decrease 50-60%) there was an additional increase in discharge in the 19-20 days- old rats (43% and in adults (70%) but not in 11-12 days-old rats. The hypotensive discharge rate of the 11-12 days-old rat reached only 20% of the maximum; it reached 80% in the hyperactive 19-20 days-old rat and 65% in adults. At all ages, the elevated hypotensive discharge rate persisted after steady state blood pressure was raised by infusing dextran. The discharge rate was diminished transiently during pressor responses to accelerated infusion or bolus injections of dextran. The conclusions are: (i) endotoxic stimulation of sympathetic outflow is initiated by a non-baroreflex mechanism in adult as well as in pre-weaning rats; (ii) there is added stimulation during hypotension after the baroreflex is mature, but (iii) the non-baroreflex stimulation continues to excite the preganglionic neurons and obtunds baroreflex feedback inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)
Mills
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Department of Pharmacology, Duke University Medical Center, Durham, North Carolina 27710.
D000375:Aging / Q000502:physiology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D003911:Dextrans / Q000494:pharmacology; D004731:Endotoxins / Q000494:pharmacology*; D005260:Female; D008297:Male; D011311:Pressoreceptors / Q000187:drug effects / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D012772:Shock, Septic / Q000503:physiopathology*; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology*
D003911:Dextrans; D004731:Endotoxins