Instructed by chemical messengers from the brain, the pituitary produces thyroid stimulating hormone (TSH) and adrenal corticotropic hormone (ACTH). The brain also instructs the pituitary seasonally to produce and release follicle stimulating hormone (FSH) and luteinising hormone (LH) in females. FSH does as its name indicates while LH triggers the release of follicles from the ovaries, ovulation. In males, LH stimulates male sex hormone (testosterone) production. For example, after a successful fight with another pet over the right to mate with a female, the hypothalamus signals the pituitary to increase LH production. Increased LH is the brain's reward to the testes, pumping up circulating testosterone. Clinical conditions involving FSH and LH production are very rare. In addition to these hormones, the pituitary produces two others of clinical significance. Antidiuretic hormone (ADH) helps the kidneys concentrate urine. Growth hormone (GH) influences the activity of most cells and organs in the body.
Lack of pituitary antidiuretic hormone (ADH) causes 'diabetes insipidus' characterised by copious drinking and urinating. This is a rare condition. In young pets this is a functional problem in the pituitary. In middle-aged and older pets the condition is most likely caused by a pituitary tumour. Affected pets drink and urinate incessantly. The specific gravity of urine is 1.010 or less. Disease is confirmed by a monitored water deprivation test and treated with synthetic ADH called DDAVP, given as eye drops twice daily. DDAVP is also available in tablet form. The prognosis in young pets is excellent, much less so in older individuals when a pituitary tumour is the cause.