The period centralized the pituitary as a master regulator of peripheral physiology, linking neuroendocrine signals to metabolism and reproduction. Methodological advances produced practical ACTH assays and stimulation tests, enabling reliable measurement of ACTH activity and distinguishing adrenal from pituitary sources of dysfunction. Early demonstrations showed that anterior pituitary output controls systemic protein metabolism and influences energy balance, while studies of ovarian hormone synergy and adrenal-controlled adiposity extended endocrine control to reproduction and metabolism.