In Vitro Effect of Leptin on Growth Hormone (GH)- and Insulin-Like Growth Factor-I (IGF-I)-stimulated Progesterone Secretion and Apoptosis in Developing and Mature Corpora Lutea of Pig Ovaries

Abstract

Abstract. This study was designed to determine whether leptin modulates growth hormone (GH)-and insulin like growth factor-I (IGF-I)-stimulated progesterone (P4) production by corpora lutea (CL). Luteal cells were recovered from early developing (ELP) and mature (MLP) corpora lutea and cultured in defined medium with various combinations of GH, IGF-I, and leptin (0-200 ng/ml). P4 concentrations in the media were determined after 48 h of culture. During the early luteal phase, leptin at all used doses had no effect on basal P4 secretion, but it did suppress caspase-3 activity. When added in combination with GH, it had no effect on either GH-stimulated P4 secretion or apoptosis. Concomitant treatment with IGF-I and leptin decreased P4 secretion and parallelly increased the apoptosis rate. In mature corpora lutea of full secreting capacity, leptin at all doses had no effect on basal and GH-stimulated P4 secretion and caspase-3 activity. Only at the highest dose (200 ng/ml) when leptin was added with IGF-I did P4 secretion decrease with no effect on the caspase-3 activity. We conclude that the role of leptin is to restrict the stage of CL formation. During this luteal phase, leptin acts as an antiapoptotic factor and, at the same time, reverses antiapoptotic action of IGF-I, thereby protecting cells from excessive apoptosis and supporting retention of appropriate cell numbers, which is necessary for maintenance of homeostasis in developing CL. Key words: Caspase-3 activity, Corpus luteum, Growth hormone (GH), Insulin-like growth factor-I (IGF-I), Pig, Progesterone (J. Reprod. Dev. 51: [727][728][729][730][731][732][733] 2005) eptin mediates transmission of information about nutritional status to centers that control the function of the reproductive system. The porcine leptin receptor complementary DNA has be en clo ned and se que nce d, an d th e gen e expression evaluated in the porcine ovary [1]. The authors of the related report showed the presence of leptin mRNA in porcine corpus luteum, theca, and granulosa cells. In a recent paper [2], a biphasic effect was shown for leptin. The authors of the report measured progesterone (P4) production by cultured porcine granulosa cells isolated from ovaries of prepubertal gilts and showed that leptin at 10 ng/ml increased P4 production, while a dose of 1000 ng/ml decreased it. In vivo serum leptin concentrations rise during the follicular phase and reach their peak during the luteal phase of the spontaneous cycle [3]. We previously showed a direct, maturation-dependent

Action of IGF-I on Expression of the Long Form of the Leptin Receptor (ObRb) in the Prepubertal Period and Throughout the Estrous Cycle in the Mature Pig Ovary

“…In preovulatory follicles, leptin acts synergistically with IGF-I on the luteinizition process, which starts just before ovulation [3]. During CL development, leptin given alone acts as an antiapoptotic factor, and when combined with IGF-I, a known antiapoptotic factor, it protects against excessive apoptosis and supports the appropriate cell numbers necessary for maintenance of homeostasis in the developing CL [4]. Studies performed mainly in rats and pigs have suggested that intraovarian IGF-I synthesis is of major importance in promoting follicular development, primarily by amplifying the actions of pituitary gonadotrophins and GH [18,19].…”

“…The authors thank Dr B. Szafranska (University of Warmia and Mazury, Olsztyn, Poland) for the generous gift of P 4 …”

“…During luteal phase, leptin action is restricted to the stage of corpus luteum (CL) formation. It acts as an antiapototic factor and at the same time, it reverses the antiapoptotic action of IGF-I, thereby protecting cells from excessive apoptosis and supporting retention of appropriate cell numbers, which is necessary for maintenance of homeostasis in the developing CL [4]. It has been suggested that expression of the leptin receptor gene varies throughout the estrous cycle, thereby modulating the sensitivity of the ovary to leptin.…”

Immunoassay - A Standard Method to Study the Concentration of Peptide Hormones in Reproductive Tissues in vitro

“…Furthermore, the role of leptin in CL is restricted to the period of the luteal phase. Leptin protects luteal cells from excessive apoptosis and supports an appropriate cell number, which is necessary for maintenance of homeostasis in developing CL (Gregoraszczuk & Ptak, 2005). Fig.…”

“…Schematic summarizing leptin effect on steroid secretion in porcine ovary. (─) no effect, (↑) stimulatory effect, and (↓) inhibitory effect (Gregoraszczuk et al, 2004(Gregoraszczuk et al, , 2005(Gregoraszczuk et al, , 2006 Evidence has also emerged indicating a potential direct role for leptin in the regulation of mammalian oocyte and preimplantation embryo development. Leptin and its receptor have been observed by immunoblotting and immunohistochemistry methods to be present in the secretory endometrium and preimplantation embryos.…”