vasopressin(redirected from Pitressin)
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a hormone secreted by the posterior lobe of the hypophysis; causes constriction of vessels (acting on the smooth muscles of their walls) and increased blood pressure (pressor effect); also maintains at a proper level the reverse absorption of water in the straight tubules of the kidneys, that is, decreases the quantity of urine discharged (antidiuretic effect). Vasopressin is formed in the neurosecretory cells of the anterior nuclei of the hypothalmus, from which it enters the hypophysis along the nerve fibers. The antidiuretic action of the hormone is one of the factors that maintain the relative constancy of the water-salt metabolism in the bodies of vertebrate animals and man. A deficiency of vasopressin may lead to diabetes insipidus, in which discharge of urine is sharply increased. Vasopressin is contained in preparations obtained from the posterior hypophysis—Pituitrin and adiurekrin. Chemically, vasopressin is an octapeptide constructed of eight amino acids (in the majority of animals and in humans vasopressin consists of cysteine, tyrosine, phenylalanine, glutamine, asparagin, proline, arginine, and glycine; in pigs lysine is found instead of arginine). In structure and effect vasopressin is similar to another hormone of the hypophysis—oxytocin.
G. N. KASSIL’