The effects of fasting on plasma corticosterone kinetics in rats

Abstract

Plasma corticosterone clearance in anaesthetized rats was measured from the disappearance of radioactivity after a bolus injection of [3~corticosterone. Mean fractional clearance rates were significantly (P < 0.05) reduced after a 48 h fast, by 32 and 22% for males and females respectively.Plasma corticosterone concentrations were increased by fasting in both sexes. Corticosterone secretion rates, calculated as the product of fractional clearance and plasma corticosterone concentration, did not differ between fed and fasted groups in either sex. The mean activity (U/liver) of the rate-limiting enzyme for corticosterone degradation, hepatic 4,5-dihydrocorticosterone :NADP+ A4-oxidoreductase, was significantly reduced by 51 and 78 % after fasting in males and females respectively. This was due to changes in both the soluble and microsomal forms of the enzyme. The binding capacity of corticosterone-binding globulin in plasma was significantly reduced by fasting in females (P < 0.001), but was not altered in males. The results suggest that reduced hormone clearance is the dominant cause of fasting hypercorticosteronaemia in the rat. Fasting: Corticosterone metabolism: RatCorticosteroids play a major role in the metabolic response to undernutrition, by causing increased release of amino acids from skeletal muscle, and their subsequent conversion to glucose in the liver (Waterlow et al. 1978;Munck et al. 1984;Tischler et al. 1988). Plasma corticosteroid concentration is generally assumed to be controlled by pituitary release of adrenocorticotrophin, which increases adrenal steroid secretion. Thus, increased levels of plasma adrenocorticotrophin and corticosteroids have been found in fasted humans (Beer et a/. 1989) and in cockerels given a diet deficient in protein (Carsia et al. 1988).The capacity of the liver to catabolize corticosterone is, however, highly dependent on the level of food consumption (Herbst et al. 1960). Since this organ is the major site of corticosteroid metabolism (Norman & Litwack, 1987), a decreased ability to catabolize corticosterone might increase plasma steroid levels independently of changes in adrenal secretion. The aim of the present investigation was to measure the turnover rate of plasma corticosterone, in order to assess the relative contributions of reduced clearance and increased secretion to the raised corticosterone levels found during fasting. In addition, measurements have been made of the binding capacity of plasma corticosterone-binding globulin (CBG), and of the activity of hepatic 4,5-dihydrocorticosterone : NADP+ A4-oxidoreductase (corticosterone reductase), the rate-limiting enzyme for corticosterone degradation. A preliminary report of this work has already been given (Woodward et al. 1990). M A T E R I A L S A N D M E T H O D S AnimalsThe rats were F1 hybrids obtained from our breeding colonies by crossing PVG/C Lister Hooded males with WAG/C Wistar Albino females. Three experiments were carried out.https://www.cambridge.org/core/terms. https://doi

Dietary Vitamin E Deficiency Increases Anxiety-Like Behavior in Juvenile and Adult Rats

“…In the case of protein or calorie malnutrition, fasting, food restriction, and protein restriction increased corticosterone levels. [32][33][34][35] Food restriction increased anxiety behavior at the same time. 36) In order to determine whether upregulation of corticosterone and increases in anxiety are specific to vitamin-E deficiency or are general in malnutrition, further investigation is necessary.…”

Plasma binding proteins as mediators of corticosteroid action in vertebrates

“…Food restriction and food deprivation activate the HPA axis, increasing circulating glucocorticoid levels over hours to days (Woodward et al 1991). The increase in CORT is thought to increase food searching behavior and foraging rates, until conditions deteriorate to the point where abandonment of the home range is necessary .…”

“…The increase in CORT is thought to increase food searching behavior and foraging rates, until conditions deteriorate to the point where abandonment of the home range is necessary . But food availability and energetic state have been shown to influence CBG capacity as well (Woodward et al 1991, Tinnikov 1993, which could alter the amount of CORT available to enter tissues. Lynn et al (In Press) measured both CORT and CBG responses to food deprivation in wild-caught, captive white-crowned sparrows (Zonotrichia leucophrys gambelii).…”

Frequent serial fecal corticoid measures from rats reflect circadian and ovarian corticosterone rhythms

“…Males and females differ in liver function, produce a different array of fecal corticosterone metabolites, maintain different levels of corticosterone and corticosteroid-binding globulin in circulation, have differential plasma corticosterone-binding capacity, and metabolize corticosterone at different rates (Gala & Westphal 1965, Eriksson & Gustafsson 1970, Ottenweller et al 1979, Woodward et al 1991. Given these large sex differences, we expected sex differences in corticoid metabolite excretion based on HPLC co-chromatography and liquid chromatography-mass spectrometry (LC-MS) analyses.…”