Hypophysis Vasopressin

Vasopressin Hypophysis Isolated posterior lobe (rat P2Y) Sperlagh et al. 1999... 

The posterior pituitary gland is the source of circulating oxytocin and vasopressin (iantidiuretic hormone, ADH). These hormones are actually produced in specific nerve cells in the hypothalamus and travel down the axons into the neuro-hypophysis. The structures of oxytocin and vasopressin are shown in Chapter 4. It may be seen that both are nanopeptides with disulfide bonds and that they differ by two amino acids only. Both hormones originate from larger proteins vasopressin from prepressophysin and oxytocin from pro-oxyphysin. These are converted to pressophysin and oxyphysin, respectively (collectively,... 

The hydrolysis of triacylglycerol to monoacylglycerol and fatty acids by hormone-sensitive lipase can be stimulated by epinephrine, norepinephrine, adrenal steroids, glucagon, and the hypophysial hormones, luteotropin (prolactin or luteinizing hormone), )3- and a-lipotropins, somatotropin, thyrotropin, and vasopressin. 

Oxytocin and vasopressin cannot easily be separated from the common aliphatic amino acids on Sephadex G-25 in spite of a considerable difference in molecular size. In a solvent consisting of acetic acid, pyridine, and water (60 15 25 parts by volume) the separation is an easy matter. The explanation is very simple. The gel is not capable of extensive swelling in this solvent and consequently the pores are smaller and the peptides are therefore excluded. This technique has also been used to separate a- and /3-meIanophore-stimulating hormones of the hypophysis (Porath and Schally, 1962). Gel filtration in mixed volatile solvents provides a convenient way to desalt peptide mixtures a problem often difficult to resolve. 

Two neuropeptides, corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP) are released from parvoceUular neurons in the hypothalamic PVN to initiate a stress response. The terminal endings of these neurons, located in the median eminence of the hypothalamus, release CRH and AVP into the hypothalamic-hypophysial portal vessel system, where they travel to the anterior pituitary. The two neuropeptides act syn-ergistically on pituitary corticotrophs to activate the synthesis of pro-opiomelanocortin (POMC). This peptide, discussed in detail below, is processed to produce several peptides including adrenocorticotrophic hormone (ACTH), or corticotropin. ACTH released from corticotrophs travels via the bloodstream to act on cells in the zona fasciculata layer of the adrenal cortex, stimulating the synthesis and release of the glucocorticoids, cortisol (in humans) or corticosterone (in rodents). 

Engler D, Pham T, Fullerton MJ, Ooi G, Funder JW, Clarke IJ (1989) Studies of the secretion of corticotropin-releasing factor and arginine vasopressin into the hypophysial-portal circulation of the conscious sheep. I. Effect of an audiovisual stimulus and insulin-induced hypoglycemia. Neuroendocrinology 49 367-381. 

Pituitary, Posterior, Pituamin Di-Sipidin Pitni-trin. Desiccated hypophysis. The cleaned, dried, and powdered posterior lobe of pituitary body of domesticated animals used for food by man. Contains both oxytocin and vasopressin, q.q.v. 

Kadowaki, K., Kishimoto, J., Leng, G., and Emson, P. C. (1994). Up-regulation of nitric oxide synthase (NOS) gene expression together with NOS activity in the rat hypothalmo-hypophysial system after chronic salt loading—Arginine vasopressin and oxytocin secretion. Endocrinology (Baltimore) 134, 1011-1017. 

Neurohypophysial hormones a group of hormones produced in the hypothalamus (not, as the name suggests, in the neurohypophysis see Hypophysis). The action spectrum of these phylogenetically ancient hormones, Oxytocin (see) and Vasopressin (see), extends from an effect on the smooth muscle of the uterus, mammary gland and blood vessels, to an alteration of the permeability of the skin, urinary bladder and kidney tubules. The carrier protein of N.h. is Neurophysin (see). N.h. are small molecules (nonapeptides) and they represent an ideal model for the study of the mechanism of hormone action at a molecular biological level. 

Control of ACTH Secretion. While the neurohypophysis is technically part of the brain, the anterior lobe of the hypophysis is disconnected from the central nervous system except for the existence of a common circulatory system, the portal system of the hypophysis. These differences between the anatomical structures of the anterior and posterior lobes are at the origin of the differences between the mechanisms controlling ACTH secretion. The secretion of ACTH is probably not triggered by any neurosecretory mechanism, like that triggering vasopressin secretion. 

The peptide type of structure is frequently employed for the chemical transmission of messages by means of hormones. An example is provided by the two hormones of the posterior hypophysis of vertebrates, oxytocin and vasopressin. These two polypeptides have been extracted from the gland itself, by rather a drastic treatment such that it still remains debatable... 

In order to ascertain the site and mode of action of vasopressin in man with hypophysial-adrenal axis blocked by corticosteroids, it is necessary to recall that morphine is always effective for the prevention of ACTE release after vasopressin (14,15) therefore it is conceivable that the site of corticosteroid inhibition is proximal to the site of vasopressin stimulation, whereas the morj ine acts distally to or at the site of vasopressin stimulation (6,7,13). 

Neurosecretion. The posterior lobe of the hypophysis contains two hormones, ocytocin and vasopressin, but both are formed actually in the hypothalamus and not in the posterior lobe. It has been demonstrated that the two hormones are synthesized in neurosecretory cells and transported through the axon of the connecting nemon. The whole process is termed neurosecretion. The transported prod-... 

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