Anterior pituitary the secretion of thyroid-stimulating hormone (TSH). Prostaglandins are now known to inhibit adrenocorticotropic hormone (ACTH) and also to stimulate TSH, GH and LH release. GABA, through action with the hypothalamus, has been shown experimentally to influence the level of GH secretion. Clinical evidence supports the experimental findings of the excitatory and inhibitory effects GABA has on GH secretion, dependent on GABA’s site of action within the hypothalamic-pituitary unit. The homeostatic maintenance of the anterior pituitary is crucial to our physiological well being. Increased plasma levels of TSH induce hyperthermia through a mechanism involving increased metabolism and cutaneous vasodilation. Increased levels
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