Some Aspects of Renal Energy and Lipid Metabolism in Newborn Rats

Abstract

Some aspects of renal energy and lipid metabolism were studied in the postnatal period of rats. Oxygen consumption, RQ values, stimulation of oxygen consumption by exogenous substrates (8 mM glucose, 8 mM acetate, 1 mM palmitate), and conversion of acetate or palmitate to CO₂ were measured in slices of cortex and inner medulla. The results obtained in 5-day-old rats are not essentially different from those observed in adults. On the other hand, the phenomenon of triacylglycerol storage in kidney cortex during starvation (well known in adult animals) is absent in the newborn rat. It can be demonstrated first in 30-day-old rats. At the same age renal arteriovenous concentration differences for total glycerol indicate a significant uptake during starvation and a release in the fed state.

Lipolytic Activity of Renal Cortex during Ontogenetic Development in Rats

“…In kidney cortex of starved 5-day-old rats alka line lipolysis is very low. At this age no uptake of total glycerol (= free and esterified) can be detected [12]. During maturation, en hanced uptake of fatty acids and TG storage in kidney cortex is observed for the first time in starved 30-day-old rats.…”

“…According to our previous measurements of oxygen con sumption and RQ [12] endogenous TG is an important fuel of kidney cortex in adult and 5-day-old rats, irrespective of the nutritional state. A lipase-promoting intracellular TG breakdown to supply fatty acids as a meta bolic fuel has, therefore, to be postulated in adult and newborn animals.…”

“…An alkaline lipolysis has to be expected because the kidney of adult rats takes up great amounts of free and esterified fatty acids (more than can be oxidized) during the state of starvation [12]. A considerable enzyme activity of this type could be demonstrated not only in starved but also in fed rats.…”

“…TG storage in kidney cortex during starvation, due to excessive uptake of free and esterified fatty acids, occurs in adult rats only. This phenomenon is absent in the newborn rat kidney [11,12]. The utilization of endogenous TG as a metabolic fuel re quires the previous hydrolysis of TG into glycerol and fatty acids.…”

“…Exogenous labelled acetate and palmitate ac-count for only 10-50% of total oxygen con sumption of rat kidney cortex slices or dog kidney in vivo [1,7,[9][10][11]18], This can be demonstrated already on slices from 5-dayold rats [12]. TG storage in kidney cortex during starvation, due to excessive uptake of free and esterified fatty acids, occurs in adult rats only.…”