Chronic administration of recombinant ovine leptin in growing beef heifers: Effects on secretion of LH, metabolic hormones, and timing of puberty1

Abstract

Serum concentrations of leptin increase linearly from approximately 16 wk before until the week of pubertal ovulation in beef heifers. To test the hypothesis that exogenous leptin can hasten the onset of puberty in heifers, we examined the effects of chronic administration of recombinant ovine leptin (oleptin) on timing of puberty, pulsatile and GnRH-mediated release of LH, and plasma concentrations of GH, IGF-I, and insulin. Fourteen fall-born, prepubertal heifers (Brahman x Hereford, 12 to 13 mo; 304.7+/-4.12 kg) were used. Heifers were stratified by age and BW and assigned randomly to one of two groups (seven animals per group): 1) Control; heifers received s.c. injections of saline twice daily (0700 and 1900) for 40 d; and 2) Leptin; heifers received s.c. injections of oleptin (19.2 microg/kg) twice daily at 0700 and 1900 for 40 d. Blood samples were collected at 10-min intervals for 5 h on. d 0, 5, 10, 20, 30, and 40, and twice daily, just before each treatment injection, throughout the study. On d 41, heifers received i.v. injections of GnRH at 0 (0.0011 microg/kg) and 90 min (0.22 microg/kg), with additional sampling for 5.5 h to examine releasable pools of LH. Diets promoted a gain of 0.32+/-0.09 kg/d, which did not differ between groups. Plasma concentrations of leptin increased markedly in leptin-treated heifers and were greater (P < 0.001) than controls throughout (27.8+/-0.8 vs. 4.9+/-0.12 ng/mL). None of the heifers reached puberty during the experiment, but did so within 45 d of its termination. Mean concentrations of plasma LH, GH, IGF-I, and insulin were not affected by treatment, nor was there an overall effect on the frequency of LH pulses. However, a treatment x day interaction (P = 0.02) revealed that the frequency of LH pulses (pulses/ 5 h) was greater (P = 0.03) in controls (3.6+/-0.36) than in leptin-treated heifers (1.7+/- 0.28) on d 10. Characteristics of GnRH-induced release of LH were not affected by treatment. In summary, chronically administered leptin failed to induce puberty or alter endocrine characteristics in beef heifers nearing the time of expected puberty.

Leptin in farm animals: where are we and where can we go?

“…infusion into ewes restricted for 6 months (23 kg below controls) restored LH (Henry et al, 2001). Yet Maciel et al (2004) infused ovine leptin into prepubertal heifers for 40 days and raised plasma leptin by 7 times but did not affect LH pulses, or mean LH, or induce puberty. Morrison et al (2001) found lower LH pulse frequency in restricted lambs than fed lambs and this did not change with i.c.v.…”

Effect of chronic infusion of leptin and nutrition on sexual maturation of zebu heifers1

“…The dose of leptin used in the current study (4.8 μg/kg BW twice daily or 9.6 μg/kg BW per day) was chosen based on a previous study by Maciel et al (2004a), in which chronic administration of oLeptin at 38.4 μg/kg BW per day for 40 d generated a linear increase in leptin concentrations of treated animals, reaching plasma concentrations values 35-fold greater in treated than nontreated animals. Therefore, we chose for the current study the lowest dose of oLeptin able to signifi cantly increase leptin concentrations above the nontreated group (9.6 μg/kg BW per day).…”

“…The dose of leptin adopted in this study was based on previous studies with prepubertal heifers (Garcia et al, 2002;Maciel et al, 2004a). The aim was to raise serum leptin concentration to 5 to 10 ng/mL for a period of 8 to 12 h after a single injection.…”

Controle sobre GnRH durante o anestro pós-parto em bovinos

“…Isso pode ser evidenciado em novilhas de corte submetidas a jejum, nas quais esse hormônio foi capaz de prevenir a redução na frequência de pulsos de LH e também aumentar a responsividade da hipófise anterior ao GnRH (MACIEL et al, 2004). Já em vacas de corte adultas em jejum, a leptina altera a secreção de GnRH e de LH (AMSTALDEN et al, 2002).…”

“…Já em vacas de corte adultas em jejum, a leptina altera a secreção de GnRH e de LH (AMSTALDEN et al, 2002). Porém, esses efeitos não são observados quando os animais têm suas necessidades nutricionais supridas (MACIEL et al, 2004;AMSTALDEN et al, 2005). Ao contrário do LH, o padrão de secreção de FSH parece não ser afetado pela subnutrição e pela consequente diminuição na leptinemia, possivelmente devido a uma menor influência do GnRH sobre a produção desse hormônio (PADMANABHAN & MCNEILLY, 2001).…”