Intermediate pituitary

FIGURE 1 8-5 Tissue-specific processing of the pro-opiomelanocortin (POMC) precursor yields a wide array of bioactive peptide products. Processing of the POMC precursor varies in various tissues. In anterior pituitary, adrenocorticotropic hormone (ACTH (1-39)) and P-1 ipo tropin (P-LPH) are the primary products of post-translational processing. Arcuate neurons produce the potent opiate P-endorphin (P-endo (1-31)) as well as ACTIK1 -13) NIT,. Intermediate pituitary produces a-melanocyte-stimulating hormone (aMSH), acetylated P endof 1 31) and P-endo(l-27). NTS, nucleus tractus solitarius. 

THE HYPOTHALAMUS-PITUITARY SYSTEM 16.2.1 Anterior and Intermediate Pituitary... 

Endorphins are peptides produced by the intermediate pituitary that react with the brain s opioid receptors and presumably act as endogenous analgesics. The two best known endorphins from bovine brain are the pentapeptides, met-enkephalin and leu-enkephalin, whose structures are Tyr-Gly-Gly-Phe-Met and Tyr-Gly-Gly-Phe-Leu, respectively. There is evidence that the enkephalins, MSH, and ACTH are produced from the same precursor protein, pro-opiomelanocortin, molecular weight (MW) 31,000. This protein is present in both the anterior and intermediate pituitary glands. In the anterior pituitary area, this protein loses the element of ACTH (39 amino acids). In the intermediate pituitary, this protein... 

Figure 16.1 Hypothalamic-pituitary system. The hypothalamus receives various types of impulses and responds by secreting appropriate release and release-inhibiting factors. These migrate to the anterior or intermediate pituitary via the hypophyseal portal vein system and elicit the secretion of various tropic or non tropic hormones. For instance, when the organism is exposed to cold, blood TSH levels increase when under stress, blood ACTH levels rise. In some animals, the absence of light causes the release of a-MSH.

Table 16.1 Hormones of the Anterior and Intermediate Pituitary Gland and Their Hypothalamic Release and Release-Inhibiting Factors... 

MacVicar BA, Pittman QP (1986) Novel synaptic responses mediated by dopamine and gamma-aminobutyric acid in neuroendocrine cells of the intermediate pituitary. Neurosci Letts 64 35-40. 

Millington WR, O Donohue TL, Mueller GP (1987) Dopaminergic agents selectively alter the post-translational processing of P-endorphin in the intermediate pituitary of the rat. J Pharmacol Exp Ther 242 160-170. 

Millington WR, Chronwall BM (1989) Dopaminergic regulation of the intermediate pituitary. In Muller EE, MacLeod RM (eds), Neuroendocrine Perspectives, Vol. 7, pp. 1—48. Springer Verlag, New York. 

Glemboiski, C. C. (1986), The characterization of the ascorbic acid-mediated a-amidation of a-melanottopin in cultuiod intermediate pituitary lobe cells. Endocrihaldgy US, 1461-1468. 

Under separate positive control by norepinephrine, the intermediate pituitary converts ACTH to melanocyte-stimulating hormone, which accounts for the well tanned appearance. 

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