The role of somatotropic hormone in the endocrine and local control of reproductive function in the domestic hen (Gallus domesticus L.) (review)

Pituitary somatotropic hormone (STH) has long been considered solely as a metabolic hormone that promotes the body growth and development until the puberty completion. However, studies in recent decades have shown that the area of STH action on the body is much wider (K.L. Hull et al., 2001; M. Lu et al., 2019). It has been established that, in addition to the pituitary gland, STH is produced in many cells and tissues, including nervous (C. Arámburo et al., 2014), immune (G. Mo et al., 2022) and reproductive (S. Harvey, 2010; M. Luna et al., 2014), where it plays an autocrine/paracrine role. The works of various researchers have shown that STH is involved in the regulation of a wide range of processes associated with the reproductive function in mammals and humans, such as sexual differentiation, puberty, steroidogenesis, gametogenesis and ovulation, as well as pregnancy and lactation (J.R. Silva et al., 2009; J. Devesa et al., 2019; C.W. Chang et al., 2022; X.Y. Zhou et al., 2023). On the contrary, much less is known about the participation of STH in the regulation of the reproductive system function in female birds. The present review article examines general information about the structural and functional properties of STH and its receptor (G.P. Baumann, 2009; M.J. Waters, 2016). The paper presents modern views on the mechanisms of activation of the hormone signaling pathways, key molecular mediators involved in its intracellular signal transmission, as well as the main mechanisms regulating STH synthesis/secretion (F. Dehkhoda et al., 2018; S.J. Frank, 2020; Y. Chhabra et al., 2021). Information is provided on the extrapituitary expression of STH and its receptor in the ovary and oviduct of the domestic hen (Gallus domesticus L.) which represents a convenient model for studying processes associated with reproduction in birds (M. Luna et al., 2014; A. Hrabia, 2015). The relationships of the STH concentration in the blood and the content of somatotropic receptors in reproductive tissues with the functional activity and/or the developmental stage of the latter, as well as the age and reproductive status of the birds are considered (A. Hrabia et al., 2008; A. Hrabia et al., 2013; Smekalova et al., 2019). The review systematizes accumulated data on the STH role in the endocrine and local control of the hen reproductive function, namely, on the effect on reproductive tissues when administered to birds in vivo (A. Hrabia et al., 2011; H. Mohammadi et al., 2016; A. Hrabia, 2022) and on the steroidogenic activity, proliferation and apoptosis of follicular cells in vitro (A. Hrabia et al., 2012, 2014; A. Smekalova et al., 2020; A. Smekalova et al., 2021). The STH influence on the follicular cells of the domestic hen ovary has been shown to depend on the degree of the follicle maturity, the interaction of the follicle wall layers, the stage of the ovulatory cycle and the avian age (A. Smekalova et al., 2020; O.V. Aleynikova et al., 2021). Insulin-like growth factors are also considered as possible mediators of the STH effect on the hen reproductive system (O. Onagbesan et al., 2009; S.M. Ahumada-Solórzano et al., 2016). It is concluded that STH plays a significant role in the regulation of follicles maturation, their preparation for ovulation and the formation of egg components, and it can also act as a survival factor for oviduct cells.