Specific characteristics of sympathetic fibres innervating the heart of young rats
Vlk, J.; Volín, M.
Physiologia Bohemoslovaca 29(3): 201-208
1980
ISSN/ISBN: 0369-9463 PMID: 6447301 Document Number: 164319
The noradrenaline content of the heart of albino rats was determined spectrofluorometrically by the trihydroxyindole method after adsorption to aluminium oxide. The concentration (mg/kg tissue) changed during postnatal life: at 10 and 18 days, 0.13; 24 days, 0:18; 35 days, 0.21; 45 days, 0.34; over 3 mo., 0.68. The low transmitter concentration in the heart tissue of the young was studied to determine if it reflected in the function of the sympathetic fibers innervating the sinoatrial node. The region of the sinoatrial node was stimulated electrically in isolated atria and the positive chronotropic reaction of preparations from 15 day old young and adult rats to various forms of stimulation (bursts of 1-5 s, frequencies of 10-100 Hz, voltage 10-25 V, duration of individual pulses 0.02-0.08 ms) were compared. The reactions of young and adult rats were identical except for 2: with the shortest pulses (0.02 ms), the sympathetic innervation of the young hardly reacted, while adult animals had a marked positive chronotropic reaction; with 5 s bursts young rats reacted significantly more strongly than adult animals. The first of these differences could be related to lower excitability of infant rat nerve fibers; insufficient reuptake of noradrenaline in the heart of infant rats could have accounted for the second.