Attenuation by leptin of the effects of fasting on ovarian function in hens (Gallus domesticus)

Abstract

Thirty-four-week-old laying hens received injections of recombinant chicken leptin to assess the role of leptin in avian ovarian function. In the first experiment, the hens (n = 60) were divided into three groups: (i) fed ad libitum; (ii) fasted; and (iii) fasted + leptin. Hens were fasted for 5 days and those treated with leptin received 250 g leptin kg −1 body weight twice a day, i.p. In the second experiment, the hens (n = 72) were divided into four groups: (i) fed ad libitum; (ii) fasted; (iii) fasted + leptin given only during fasting (5 days); or (iv) fasted and leptin given during both fasting and 5 days of re-feeding (10 days). LH was measured in blood plasma, and progesterone and oestradiol were measured in blood plasma and the ovary by radioimmunoassay. Apoptosis was examined in the walls of the three largest yellow hierarchical follicles (F3-F1; F3 < F2 < F1; 25-35 mm) by the TdT-mediated dUTP nick-end labelling method. Results showed that the injections of leptin during fasting: (i) delayed cessation of egg laying; (ii) attenuated regression of yellow hierarchical follicles; (iii) altered ovarian steroidogenesis; and (iv) abolished the fasting-induced apoptosis in the wall of F3-F1 follicles during the first 2 days of fasting and partially attenuated apoptosis after 5 days of fasting. Prolongation of leptin injections into the re-feeding period considerably delayed the restoration of the ovary. Expression of leptin receptor in laying hens was determined by RT-PCR. The highest expression of leptin receptor was observed in the hypothalamus. Lower receptor mRNA expression was found in the hypophysis, whereas the lowest expression was observed in the ovary. Within the ovary, a relatively high expression of leptin receptor was found in the stroma with cortical follicles < 1 mm, the wall of white (1-8 mm) and small yellow follicles (> 8-12 mm), and the granulosa layer of F3 follicles. The expression of leptin receptor in the granulosa layer of F2 and F1 follicles was barely detectable. This was in contrast to a much higher expression of leptin receptor maintained in the theca layer of F3-F1 follicles. The present results indicate that in chickens leptin might be involved in the adaptation to starvation due to attenuation of follicular apoptosis. The presence of leptin receptors in the ovary indicates the possibility of a peripheral effect of the hormone.

Monitoring leptin activity using the chicken leptin receptor

“…Our results add an important strength to previous reports demonstrating chickens' response to exogenous administration of various leptins (Raver et al 1998, Denbow et al 2000, Paczoska-Eliasiewicz et al 2003, Lohmus et al 2004, Kuo et al 2005, by demonstrating for the first time a specific induction of signal transduction via CLEPR in response to human and frog leptins in vitro. It is possible that our inability to detect leptin activity in bird serum samples was due to below-detection threshold leptin levels, which could still be of physiological significance, rather than to a lack of natural ligand for CLEPR.…”

“…Administration of this leptin in chickens resulted in inhibition of food intake (Dridi et al 2000, Cassy et al 2004. Additional studies have demonstrated the effect of this leptin on the immune response (Lohmus et al 2004), the onset of sexual maturity (PaczoskaEliasiewicz 2006), egg production during and after fasting (Paczoska-Eliasiewicz et al 2003), and downregulation of heat shock protein-70 (Figueiredo et al 2007).…”

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

“…Ohkubo et al (2007) used a monoclonal antibody to part of ch-ObR to map it and found the short isoform in only a few tissues but the long isoform expressed more widely (mostly brain). These avian receptors use JAK-STAT (Adachi et al, 2008) and are expressed in ovary, brain and pituitary (Paczoska-Eliasiewicz et al, 2003). …”

Manipulation of primary sex-ratio: an updated review

“…It is also involved in the regulation of energy stores, food intake and satiety (Bado et al, 1998;Brann et al, 2002). Leptin plays a role as activator of hypothalamic-pituitary-gonadal axis, inducing FSH-LH release and modulating steroidogenesis (McCann et al, 2001;Paczoska-Eliasiewicz et al, 2003). Thus, high leptin levels induce the production of gonadal steroids when a certain threshold of fatness is attained, acting as a permissive factor for reproduction (Brann et al, 2002).…”

“…Thus, high leptin levels induce the production of gonadal steroids when a certain threshold of fatness is attained, acting as a permissive factor for reproduction (Brann et al, 2002). Leptin levels in ovarian tissue increases during follicular maturation and ovulation in rats (Ryan et al, 2003), and leptin receptors have also been described in avian ovary (Ohkubo et al, 2000;Paczoska-Eliasiewicz et al, 2003). Moreover, leptin attenuates follicular atresia in chickens (Paczoska-Eliasiewicz et al, 2003).…”