Exp. Geront. Vol. 13. pp. 213-225.

0531-5565/78/0801-0213502.00/0

© Pergamon Press Ltd 1978. Printed in Great Britain.

INFLUENCE OF AGE ON STRESS-INDUCED HEPATIC ULTRASTRUCTURAL ALTERATIONS IN THE RAT MILAGROS SALAS* and BEATRIZ TUCHWEBER'~ *lnstitut de M6decine et de Chirurgie Exp6rimentales and tD6partement de Nutrition, Universit6 de Montr6al, Montr6al, Canada H3C 3J7 (Received for publication 2 December 1977)

INTRODUCTION THE RESPONSE of animals to stressors is considerably influenced by many exogenous and endogenous factors, particularly age (Selye, 1976). Although many investigators have studied the general response of animals, from fetal life to senility, few reports have dealt with the stress-induced hepatic ultrastructural changes in relation to age. In earlier experiments (Salas and Tuchweber, 1975) we found that the ultrastructural response of the liver of young rats to a series of acute stressors is characterized by rough endoplasmic reticulum (RER) fragmentation and dilation, glycogen depletion and mitochondrial enlargement. The most striking change, however, is an increase in the number and size of autophagic vacuoles. These alterations appear to be directly correlated to the hypothermia elicited by the stressors (Salas et al., 1976; 1977). For instance, it was demonstrated that the usual hepatic ultrastructural changes in restrained rats were prevented if the animals were kept at an elevated ambient temperature of 32-34°C instead of the usual room temperature of 24-26°C, and it is possible that this protection may be acquired through inhibition of restraint-induced hypothermia (Salas et al., 1977). In these experiments, we will compare the stress response of the liver of weanling rats with that of young and mature animals of the same species. METHODS AND PROCEDURES Twenty-two-day-oldweanlings (35-50 g), 1-month-oldyoung adults (95-105 g), 3- to 4-month-old and 8- to 9-month-oldmature (300-400 g) female Charles River CD ® rats (Canadian Breeding Farms and Laboratories Ltd, St. Constant, Quebec) were divided into groups, each containing 6 animals. They were housed one per cage in a room at a temperature of 24+2°C. Absolute controls were maintained at/libitum on laboratory chow and tap water. Fasted controls received no food or water for 48 h, except in the case of weanlings which were exposed to inanition for 43 h. Restrained animals were immobilized by taping their limbs to metal plates either for 48 h or, in the case of weanlings, for 43 h. (Immobilization of the latter group for 48 h resulted in a high mortality rate). Restrained rats received no food or water. Autopsy Rectal temperature was monitored with a YS-1 Tdethermometer® (Yellow Springs Instrument Co.) before autopsy, which was performed between 9 and 10 a.m. (43 or 48 h after the beginning of restraint and/or withdrawal of food and water).

* Recipient of a fellowship from the Conseil de la Recherche en Sant6 du Qu6bec. t To whom reprint requests should be addressed. 213

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MILAGROS SALAS AND BEATRIZ TUCHWEBER

Morphological methods For light microscopy, liver tissue was fixed in alcohol formol and embedded in paraffin. Sections (4-8 ta thick) were cut and stained with hematoxylin-phloxine for examination of general structure, or with periodic acid Schiff (PAS) for the demonstration of glycogen. Frozen sections were also cut and stained with Oil red O for the detection of lipids. For electron microscopy, immediately after decapitation, a small portion of tissue was excised from the left lateral lobe of the liver arid placed in Millonig's osmium fixative, where it was minced into tiny cubes and kept for I h at 4°C. The tissue specimens were then dehltdrated in graded ethanol and embedded in epon resin. Sections (0"5 ta thick) were cut on a Porter-Blum MT-2 microtome, stained with toluidine blue, and examined with a light microscope. Ultra thin sections (approximately 50 mla) were stained with uranyl acetate and Reynold's lead citrate, and examined with a Carl Zeiss EM 9A electron microscope. Sections were cut from selected midzonal areas. RESULTS.

Body temperature T h e r e was a significant decrease in b o d y t e m p e r a t u r e after restraint in a l l g r o u p s o f rats. H o w e v e r , the weanlings were the oltly animals t h a t s h o w e d a m a r k e d fall in b o d y t e m p e r a ture a f t e r fasting a l o n e (Table 1). TABLE 1.

Stressor"

EFFECTO.F FASTING

OR RESTRAINT ON THE BODY TEMPERATURE OF WEANLINGS, YOUNG AND MATURE RATS

Weanling rats I

1-month-old rats t

3- to 4-month-old 8- to 9-month-old rats~ rats 1 None 36.8 4-0.1 36.8 4-0-4 36:7 4-0.4 35"5 4-0.2 (5) (6) (4) (8) Fasting2 31.04-1.5"* 35.8 +0.8NS 37.0±0.3NS 35.1 4-0.2NS (4) (6) (5) (8) Restraint2 26-4-I-0.3'** 26;1 4-0.3*** 26-2 4-1.2*** 29.74-1.1 *** (6) (**) (6) (***) (7) (***) (10) (*+*) 1 All animals were restrained for 48 h. except the weanlings which were restrained for 43 h. 2 The fasted or restrained animals did not have access to food or water for either 43 or 48 h. NS = p >0.05; * = p

Influence of age on stress-induced hepatic ultrastructural alterations in the rat.

Exp. Geront. Vol. 13. pp. 213-225. 0531-5565/78/0801-0213502.00/0 © Pergamon Press Ltd 1978. Printed in Great Britain. INFLUENCE OF AGE ON STRESS-I...
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