Stress- and age-related serum glucose changes in Spontaneously Hypertensive and Sprague-Dawley rats

Abstract

The serum glucose levels of90·day-old and l-year-old male Spontaneously Hypertensive (SHR) and Sprague-Dawley (SD) rats were examined in two experiments. Half of each strain and age group were exposed to 51-min daily sessions of unpredictable, uncontrollable grid shocks during a 30-day period prior to sampling via decapitation. The other half remained undisturbed in their cages. Dietary intake was equated across all groups within each strain. Stress-induced increases were observed in both age groups, in both strains (ps < .05). The SHRs showed an age x stress interaction with old, stressed animals having the highest levels (ps < .05). Both younger SD groups had higher levels than corresponding older SD groups (ps < .05).Stress has been shown to increase serum glucose levels in rats (e.g., Balkin, 1981; Ehrentheil, Reyna, Adams, Giovanniello, & Chen, 1967). The Spontaneously Hypertensive Rat (SHR) has been characterized by Kopin and his coworkers as hyperreactive physiologically to stressful stimulation, showing relatively higher levels of circulating catecholamines than age-matched Wistar Kyoto rats that are normotensive (see McCarty, Chiueh, & Kopin, 1978; and McCarty, Kvetnansky, Lake, Thoa, & Kopin, 1978).Although basal serum glucose levels tend to remain constant with age, Reaven and his associates (BrachoRomero & Reaven, 1977; Nariyima et al., 1984;Reaven et al ., 1983) and others have reported glucose intolerance and insulin resistance in older rats. reported that SHRs become progressively hyperglycemic and hyperlipidemic with increasing age. They also develop increased ACTH synthesis and secretion, increased adrenocortical responsiveness, and increased plasma corticosterone levels with aging.The aim of the present study was to investigate the combined effects of stress and aging on the serum glucose response of SHRs. The SHRs were maintained on a highlipid diet as part of our work on the effects of psychological stress on cholesterol metabolism. Therefore, relatively higher glucose levels were expected because of the synergistic action of the diet and stress (Yamaguchi, Takashima, Masuyama, & Matsuoka, 1978). It was expected that stress would result in elevated serum glucose, and that the old, stressed SHRs would have the highest levels. But first we examined the effects of all these conWe thank Katherine Cranker, Joseph Miano, Patrick Graham, Jay Watsky, and Kathleen Clancy for their assistance during various phases of the study . Requests for reprints should be sent to J. Starzec, Psychology Department, State University College at Cortland, P.O. Box 2000, Cortland, NY 13045. ditions on the normotensive rats that we have studied most often, Sprague-Dawley (SO) rats . EXPERIMENT 1 MethodSUbjects. The subjects were 24 SO male rats obtained from Taconic Farms, Germantown, New York. Half were 90 days old (young), and the rest were 1 year old (old) at the beginning of the stress procedure. All were maintained on a diet consisting of 10% butter, 4% cholesterol, I % cholic acid, and 85 % powdered Purina Rode...