Growth Hormone Association With Testicular Recrudescence in a Free‐Living Passerine, <i>Amandava amandava</i>

Emerging evidence confirms the expression of functional growth hormone (GH) receptors in the male and female reproductive systems, and suggests that the GH signaling might influence gonadal function by acting at different levels of the hypothalamic-pituitary-gonadal (HPG) axis in animals and mammals. Despite this, the role of GH in the modulation of the gonadal cycle in seasonal breeders has been less explored. This study focused on a free-living passerine, Amandava amandava (Red Munia), a distinct seasonal breeder. It aimed at elucidating the plasticity in pituitary expression of the GH, and alteration in the plasma hormone profile across life-history stages parallel to the testicular cycle (histomorphometry and plasma levels of testosterone). The pituitary expression and plasma GH levels remained elevated during the breeding cycle, where the energy-demanding process of testicular recrudescence occurs. The study correlated the plasma GH level with various parameters of the testis and suggests that physiological GH, in association with pituitary gonadotropins, may facilitate the growth and functionality of the testis. The extrapituitary localization of GH in the hypothalamus, optic chiasma, and cerebral cortex during the breeding cycle suggests its paracrine role in the modulation of the gonadotropin-releasing hormone secretion. GH may help meet energy requirements and achieve reproductive status during the transition from the non-breeding to breeding life-history stage, interacting with hormones from other endocrine axes related to reproduction.