Increased Caloric Intake on a Fat‐Rich Diet: Role of Ovarian Steroids and Galanin in the Medial Preoptic and Paraventricular Nuclei and Anterior Pituitary of Female Rats

Abstract

Previous studies in male rats have demonstrated that the orexigenic peptide galanin (GAL), in neurones of the anterior parvocellular region of the paraventricular nucleus (aPVN) projecting to the median eminence (ME), is stimulated by consumption of a high-fat diet and may have a role in the hyperphagia induced by fat. In addition to confirming this relationship in female rats and distinguishing the aPVN-ME from other hypothalamic areas, the present study identified two additional extra-hypothalamic sites where GAL is stimulated by dietary fat in females but not males. These sites were the medial preoptic nucleus (MPN), located immediately rostral to the aPVN, and the anterior pituitary (AP). The involvement of ovarian steroids, oestradiol (E(2)) and progesterone (PROG), in this phenomenon was suggested by an observed increase in circulating levels of these hormones and GAL in MPN and AP with fat consumption and an attenuation of this effect on GAL in ovariectomised (OVX) rats. Furthermore, in the same four areas affected by dietary fat, levels of GAL mRNA and peptide immunoreactivity were stimulated by E(2) and further by PROG replacement in E(2)-primed OVX rats and were higher in females compared to males. Because both GAL and PROG stimulate feeding, their increase on a fat-rich diet may have functional consequences in females, possibly contributing to the increased caloric intake induced by dietary fat. This is supported by the findings that PROG administration in E(2)-primed OVX rats reverses the inhibitory effect of E(2) on total caloric intake while increasing voluntary fat ingestion, and that female rats with higher GAL exhibit increased preference for fat compared to males. Thus, ovarian steroids may function together with GAL in a neurocircuit, involving the MPN, aPVN, ME and AP, which coordinate feeding behaviour with reproductive function to promote consumption of a fat-rich diet at times of increased energy demand.

Adult Consequences of Post-weaning High Fat Feeding on the Limbic–HPA Axis of Female Rats

“…Estrogen is known to potentiate corticosterone levels (Kitay et al 1965) and protect against high fat diet-induced insulin resistance and glucose intolerance (Riant et al 2009). Plasma estrogen levels were not evaluated in our study, but it is known to increase proportionally with the fat content of diet in adult female rats (Leibowitz et al 2007). Consequently, an increase of estradiol levels in adolescent HF females could have facilitated the elevation of corticosterone levels observed after puberty.…”

The role of diet in the pathogenesis and management of irritable bowel syndrome (Review)

“…1) (92). This system regulates several functions of the gastrointestinal tract, such as motility, secretion, absorption, microcirculation of the gut, local immune defence and cell proliferation (96)(97)(98)(99)(100)(101)(102)(103)(104)(105). This regulatory system consists of a large number of bioactive messengers (Table I).…”

Physiology, Signaling, and Pharmacology of Galanin Peptides and Receptors: Three Decades of Emerging Diversity

“…In rats, galanin was also reported to increase preference for a high-fat diet given a choice between fat, carbohydrate, and protein (Tempel et al, 1988), although other contemporary studies observed less of a difference in macronutrient choice Crawley, 1999;see Gundlach, 2002, for review). More recent studies in female rats also documented that ovarian steroids likely function together with galanin in a neural circuit, involving the medial preoptic nucleus, the anterior PVN, and the median eminence and anterior pituitary, to coordinate feeding behavior with reproductive function to promote consumption of a fatrich diet at times of increased energy demand (Leibowitz et al, 2007). Kyrkouli and colleagues (2006) further examined the influence of PVN galanin on dark/active phase nutrient intake in rats in a self-selection feeding paradigma choice between isocaloric diets enriched in protein, carbohydrate, or fat.…”