Hypothalamic–pituitary–somatotropic axis with growth hormone deficiency or Laron syndrome ( insensitivity) show symptoms like short stature, dwarfism and obesity, but are also protected from some forms of cancer. Conversely, acromegaly and gigantism are conditions of GH and IGF-1 excess usually due to a pituitary tumor, and are characterized by overgrowth and tall stature. Hypothalamic–pituitary–somatotropic axis The hypothalamic–pituitary–somatotropic axis (HPS axis), or hypothalamic–pituitary–somatic axis, also known as the hypothalamic–pituitary–growth axis, is a hypothalamic–pituitary axis which includes the secretion of growth hormone (GH; somatotropin) from the somatotropes of the pituitary gland into the circulation and the subsequent stimulation of insulin-like growth factor 1 (IGF-1;
Pituitary pars intermedia dysfunction by corticotropes in the pars distalis of the equine pituitary. In a normal horse, this accounts for the majority of ACTH production. ACTH produced by the pars distalis is subject to negative feedback in a normal horse, so high cortisol levels reduce ACTH production by the pituitary, subsequently reducing cortisol levels. In a horse with PPID, ACTH levels are high as a result of pars intermedia production, but it is not subject to negative feedback regulation. Despite the high levels of ACTH, cortisol levels vary, and are sometimes lower than normal. Additionally, hyperplasia of the adrenal cortex is infrequent. The