higher levels of thyroid hormone suppress gnih expression, and lower levels of thyroid hormone are associated with higher gnih levels. the inactivation of gnih expression prevents delayed puberty caused by hypothyroidism, demonstrating that gnih mediates interactions between the hpg and hpt (hypothalamic-pituitary-thyroid) axes. furthermore, thyroid hormone may function in a pathway for photoperiodic regulation of reproduction involving gnih and energy status. melatonin modulates thyroid-stimulating hormone (tsh) production in the anterior pituitary, and tsh promotes thyroid hormone production. thyroid hormone production influences metabolism and gnih production, both of which impact reproduction.