AJP - Regulatory, Integrative and Comparative Physiology, Vol 252, Issue 5 842-R847, Copyright © 1987 by American Physiological Society
Homeostatic control of manganese excretion in the neonatal rat
N. Ballatori, E. Miles and T. W. Clarkson
Previous studies in neonatal and suckling animals showed that immature
animals have a greatly diminished capacity to excrete manganese and
therefore were considered to be unable to regulate tissue manganese
concentrations. In contrast, the present studies indicate that suckling
rats have the capacity to excrete excess manganese at rates nearly
comparable to those of adults. Eight- to 10-day-old rats given a tracer
dose of 54MnCl2 (essentially carrier free), either via gavage or by
intraperitoneal injection showed little elimination of the 54Mn until the
18-19th day of life, when there was an abrupt increase in the rate of the
metal's excretion. However, when manganese was given in doses of 1 and 10
mg/kg, the young animals excreted from 30-70% of the dose in only 4 days,
at which time a new rate of excretion was achieved. This enhanced rate of
excretion remained constant until the 18-19th day of life, when it was
again accelerated. Biliary excretion of manganese, the primary route for
the elimination of the metal, was only 30-60% lower in 14-day-old rats
compared with adults at doses ranging from tracer to 10 mg 54Mn/kg. For
both the 14-day-old and adult rats, an apparent biliary transport maximum
was reached at a dose of 10 mg Mn/kg. These studies indicate that the
excretory pathways for manganese are well developed in the neonatal rat.
The avid retention of tracer quantities of manganese by the neonate may be
a consequence of the scarcity of this essential trace metal in its diet.
