Verónica Piñeiro

Leptin, reproduction and sex steroids.

Leptin is a hormone secreted mainly by the adipose cells with a primary role in the regulation of body weight by establishing a feedback loop between the energy reserves and the hypothalamic centers that control food intake. Recent data suggest that, in addition, leptin interacts with other endocrine systems to provide critical information about the size of the fat stores, acting as a permissive factor that allows the triggering of energy-demanding situations, as the onset of puberty and the reproduction, only when the size of the fuel reserve is large enough to guarantee its success. In addition, leptin appears to play a role during pregnancy and lactation, as it is produced by the placenta and is present in maternal milk. The fact that leptin levels are always higher in females, even after correcting for body fat content, suggests that the interaction between the adipose tissue and the reproductive system is modulated in a different way in males and females by androgenic and estrogenic hormones. In fact, adipose tissue samples taken from male donors are completely refractory in vitro to the action of both estrogens and androgens. On the contrary, dihydrotestosterone, androstenedione and dehydroepiandrosterone-S are potent inhibitors of leptin secretion, while estradiol induces a strong stimulation in adipose tissue taken from women. Testosterone is devoid of activity in either gender.

Effect of milk minerals on calf gains and sex differences in mineral composition of milk from Iberian red deer (Cervus elaphus hispanicus)

Milk mineral content has received little attention in studies focusing on milk nutrient effects on offspring growth. This study examines calf growth in Iberian deer and compares the influence of milk minerals, other nutrients, and lactation variables relevant for growth to discern the relative weight of each factor. In addition, because Iberian deer hinds are the first mammal found to produce different milk for sons and daughters, the present study examines whether there are also sex differences in milk mineral composition. Concentrations and yields of Ca, P, Mg, Na, K, Fe, and Zn in milk of 46 red deer hinds were monitored through 18 weeks of lactation. Calf growth was influenced by Ca and P percent, and total Fe production. Milk for males had a lower content in Ca and P, a greater content of K, and Mg, whereas no sex effects were found in Na, Fe, or Zn percentages. Higher percentages in Ca and P for daughters might constitute a compensatory response, as daily production was not biased towards females in Ca or P, whereas in the latter and all the other minerals daily production was greater for heavier calves, which are usually males. In conclusion, milk mineral content and production influence calf growth even after controlling for other important lactation variables and nutrients, and they show effects and interactions more complicated than expected.