PII S0361-9230(98)00050-1 Zucker obese rats are insensitive to the CRH-increasing effect of oleoyl-estrone Cristina Cabot, 1,2 Maria del Mar Grasa, 1,2 Jordi Estruch, 2 Jose ´ -Antonio Ferna ´ ndez-Lo ´ pez, 1 Xavier Remesar 1 and Maria ` Alemany 1 * 1 Departament de Bioquı ´mica i Biologia Molecular, Facultat de Biologia, Universitat de Barcelona, Barcelona, Spain; 2 Laboratoris SALVAT, SA, Esplugues de Llobregat, Barcelona, Spain [Received 3 April 1998; Accepted 8 April 1998] ABSTRACT: Adult female Zucker lean and obese rats were treated for 14 days with 3.5 nm/kg oleoyl-estrone (OE) in lipo- somes (Merlin-2) through continuous i.v. injection with osmotic minipumps. Rat wt. and food intake were measured daily. On days 0, 3, 6, 10, and 14, groups of rats were killed and their hypothalamic nuclei [lateral preoptic (LPO), median preoptic (MPO), paraventricular (PVN), ventromedial (VMH), and arcuate (ARC)] were dissected, homogenized, and used for the mea- surement of corticosterone-releasing hormone (CRH) by radio- immunoassay. The OE treatment decreased food intake by 67.4% in lean and 62.6% in obese rats (means for 14 days). Body wt. decreased steadily in lean and obese rats, the gap between controls and treated rats becoming 11.5% of initial body wt. in the lean and 12.4% in the obese. The levels of CRH in the ARC nucleus were at least 10-fold higher than in the other nuclei. No changes in CRH were observed in any of the nuclei of obese rats, with levels up to day 6 similar to those of lean rats. In the lean rats, the LPO and ARC nuclei showed peaks on day 10, while the MPO showed no changes and the PVN and VMH nuclei showed a progressive increase, to a maximum at the end of the study (day 14). This contrasted with the peak of plasma adrenocorticotropic hormone (ACTH) and corticosterone (day 6 in lean and day 14 in obese rats). There was a definite lack of correlation between the plasma levels of these two hormones and the levels of CRH in the hypothalamic nuclei, and between the latter and the decreases in appetite in the rats. The loss of appetite induced by OE is not necessarily mediated by CRH, because the obese rats show an intense decrease in voluntary food intake but their hypothalamic nuclei CRH levels do not change at all. Hypothalamic nuclei CRH does not, necessarily, mediate the rise in glucocorticoids induced by OE treatment, because this is observed in lean and obese rats, lean rats increases being mismatched with those of hypothalamic CRH. The OE induced changes in hypothalamic CRH require a fully functional leptinergic pathway, because it is not observed in Zucker fa/fa rats lacking a working leptin receptor. This—indi- rectly—shows that leptin is needed for its synthesis or modu- lation. © 1998 Elsevier Science Inc. KEY WORDS: CRH, Oleoyl-estrone, Appetite, Hypothalamus, Energy expenditure, Obesity, Zucker obese rat. INTRODUCTION Corticotropin-releasing hormone (CRH) is a peptide produced in the hypothalamus [1] and controls the secretion of adrenocortico- tropic hormone (ACTH) by the hypophysis [2]. The CRH also participates in the regulation of autonomic responses, essentially those related to stress [3,4], and intervenes in the control of brown adipose tissue thermogenesis [5,6]. The CRH plays a key role in the control of food intake [7], and its low concentration in the hypothalamus of Zucker obese rats has been postulated as a possible cause of their obesity [8]. The administration of CRH induces powerful anorectic effects [9,10], but also prevents the anorectic effects of other agents such as estradiol [11]. Estrogens also modulate the transcription of the CRH gene in the hypothalamus [12,13]. The effects of CRH depend on the sex of the subject, and may be involved in sexual metabolic response dimorphism [14]. Zucker obese rats show no changes in the paraventricular (PVN) nucleus CRH, and their hypothalamus contains less CRH than that of lean rats [8]. The ob/ob mice are fully responsive to CRH [15]. Oleoyl-estrone (OE) is carried by lipoproteins, its administra- tion in liposomes induces rapid and significant losses in the fat stores of rats [16]; this effect is also observed in Zucker obese rats [17] and in rats receiving a cafeteria diet [18]. The loss of fat reserves is mainly the consequence of lowered food intake com- bined with a maintained energy expenditure [16]. Modification of the fatty acid or the steroid nucleus results in the loss of its slimming activity [19]. The administration of OE involves a de- crease in the synthesis and release of leptin, as well as increased circulating levels of ACTH and glucocorticoids [20]. However, in the Zucker obese rats, leptin is not affected [21], suggesting that the effect of OE on the fat mass is independent of leptin. In Zucker fa/fa rats, ACTH and corticosterone increase during treatment with OE, but the pattern of change is fairly different from lean rats [21]. Nevertheless, Zucker obese rats lose wt. during treatment with OE, as a consequence of lower food intake in spite of a decrease in energy expenditure [17]. Because CRH is involved both in the control of appetite and of energy expenditure, we * Address for correspondence: Prof. Dr. Maria ` Alemany, Departament de Bioquı ´mica i Biologia Molecular, Facultat de Biologia, Universitat de Barcelona, Av. Diagonal, 645, 08028 Barcelona, Spain; Fax: 34-93-4021559; E-mail: alemany@porthos.bio.ub.es Brain Research Bulletin, Vol. 46, No. 6, pp. 529 –534, 1998 Copyright © 1998 Elsevier Science Inc. Printed in the USA. All rights reserved 0361-9230/98 $19.00 + .00 529