Biology Reference
In-Depth Information
Reproductive Function
Puberty
Energy Homeostasis
Food Intake
Energy Homeostasis
Food Intake
Leptin
Sex Steroids
Insulin
Ghrelin
GI Tract
Gonads
Adipose
Pancreas
Fig. 17.1
Schematic diagram of various hormonal signals, originated from various peripheral tissues,
involved in the integral control of food intake, energy balance, and reproductive function (including
puberty). Paradigmatic examples of hormones with proven roles in the integral control of food intake
and the reproductive axis are presented, including factors from adipose tissue (leptin: inhibitory signal
for food intake; stimulatory/permissive signal for puberty and reproduction), pancreas (insulin; same
profi le as leptin in terms of actions on food intake and reproduction), gastrointestinal tract (ghrelin:
stimulatory signal for food intake; inhibitory signal for the reproductive axis), and the gonads (sex ste-
roids, such as estrogens, which are food-intake suppressing signals and conduct both negative and posi-
tive feedback effects on the gonadotropic axis). The central mechanisms whereby these peripheral
metabolic signals affect reproductive function remain to be fully characterized
additional call of caution, it is possible that the set of metabolic signals, and their
physiological relevance, in the regulation of puberty (the period of full activation
of the HPG axis) vs. fertility (maintenance of the capacity to reproduce during
adulthood) might be different.
Compelling evidence suggests that the metabolic control of the HPG axis, and
specifi cally leptin-mediated actions, are conducted mainly at central levels, where
leptin is thought to modulate the activity of hypothalamic gonadotropin-releasing
hormone (GnRH) neurons [
14
]. The effects of leptin, however, seem to be conducted
indirectly, as GnRH neurons do not physiologically express leptin receptors [
15
],
suggesting the participation of intermediate pathways that would convey the modula-
tory actions of the adipocyte hormone. As summarized in the following sections,
strong evidence points out that
Kiss1
neurons are sensitive to changes in body energy
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