Hormone oxytocin and

The posterior pituitary is innervated by direct nervous stimulation from the hypothalamus, resulting in the release of specific hormones. The hypothalamus synthesizes two hormones, oxytocin and vasopressin. These hormones are stored in and released from the posterior pituitary lobe. Oxytocin exerts two actions (1) it promotes uterine contractions during labor, and (2) it contracts the smooth muscles in the breast to stimulate the release of milk from the mammary gland during lactation. Vasopressin is an antidiuretic hormone (ADH) essential for proper fluid and electrolyte balance in the body. Specifically, vasopressin increases the permeability of the distal convoluted tubules and collecting ducts of the nephrons to water. This causes the kidney to excrete less water in the urine. Consequently, the urine becomes more concentrated as water is conserved. 

The hypothalamic releasing factors regulate release of the anterior pituitary trophic hormones. As summarized in Figure 52-1, the releasing factors are produced in various neuronal groups within the hypothalamus and are transported to the median eminence for release into the portal circulation to the anterior pituitary. Neurons in the hypothalamus also produce the hormones oxytocin and vasopressin, which are released by the posterior pituitary into the blood. Therefore, it is not surprising that behavior and experience, which influence the hypothalamus, sometimes alter the secretion of these hypothalamic releasing factors and hormones. 

Plasma prolactin levels are reduced with acute treatment and remain suppressed after 28 days of chronic treatment (Murphy et al. 1998). With acute treatment, no effects are seen on plasma luteinizing hormone or testosterone levels. However, chronic dietary 5% ginseng increases testosterone levels in male rats (Fahim et al. 1982). Chronic ginsenosides do not alter posterior pituitary hormones oxytocin and vasopressin (Zierer 1991). Similarly, human males administered ginseng extract showed an increase in plasma testosterone, dihydrotestosterone, follicle-stimulating hormone, and luteinizing hormone, but a decrease in prolactin (Salvati et al. 1996). 

The posterior pituitary gland secretes two major hormones, oxytocin and vasopressin (antidiuretic hormone) (Table 75-1). Oxytocin... 

Plain preparations of oxytocin and derivatives are classified in HOIB Posterior pituitary lobe hormones. Oxytocin and derivatives. 

The posterior pituitary releases two hormones, oxytocin and vasopressin. Oxytocin induces contractions in the gravid uterus and is therefore used when labor acceleration is desired. Because it is chemically similar to vasopressin, oxytocin has antidiuretic effects and can cause fluid retention. Oxytocin and other uterine contractants and relaxants are listed in Table 10.3. 

Recall What are the structural differences between the peptide hormones oxytocin and vasopressin How do they differ in function ... 

The neurohypophyseal hormones oxytocin and vasopressin are involved in autism. Elevated levels of blood serotonin occur in one third to two thirds of persons with autism. Parents of autistic children often have elevated blood serotonin levels, as well as an increased incidence of depression, obsessions, and compulsions. 

Proton magnetic resonance spectroscopy was used to monitor individual amino acid residues in bovine neurophysin, in the nonapeptide hormone oxytocin, and in the complex formed between them. For neurophysin I alone, a normal titration curve... 

Any chemist knows that the more steps there are in a chemical synthesis, the lower the final yield. For example, if each step in a 10-step synthesis furnishes a 90 percent yield of product, the yield of the final product will be only about 35 percent. That is why it is not possible to extend Du Vigneaud s masterful syntheses (see chapter 6) of the hormones oxytocin and vasopressin (9 amino acid residues each) to proteins, even small ones such as ribonuclease A (124 amino acid residues). In order to pursue this daunting challenge Robert Bruce Merrifield (1921-2006), at Rockefeller University, devised a new concept solid-phase synthesis. The idea is disarmingly simple covalently attach an amino acid to a macroscopic particle that can be exposed to the reaction, washed, and then separated by simple filtration. Each reaction step requires no chromatography and no crystallization, just washing and filtering. At the end, completed peptide chains are chemically released from the particles. 

After the war du Vigneaud returned to the endeavor interrupted by the penicillin problem, to the isolation of the pituitary hormones oxytocin and... 

D. W. Urry, M. Danishi, R. Walter, Secondary structure of the cyclic moiety of the peptide hormone oxytocin and its deamino analog. Proc. Natl. Acad. Sci. US 66 111-116 (1970) also D.W. Urry, R. Walter, Proposed conformation of oxytocin in solution, ibid. 68 956-958 (1971)... 

Deslauriers, R., 1. C. P. Smith, and R. Walter Conformational flexibility of the Neurohypophyseal Hormones oxytocin and Lysine-Vasopressin. A Carbon-13-Spin-Lattice Relaxation Study of back-bone and side chain. J. Amer. Chem. Soc. 96, 2289 (1974). 

Neurophysins small proteins associated with the hormones oxytocin and vasopressin. In bovines, oxytocin-like arginine vasopressin and N.n are synthesized from a single polypeptide precursor, as are oxytocin and N. I. Most species have more than two N., but usually there are two major N.The middle sequence of N. is conserved, and the N. differ in their terminal sequences. The N. bind to the neurohormones with which they are synthesized and are secreted with them into the blood. The biological function, if any, of the N. is not known. [H. Land et al. Nature 302 (1983) 342-344 A. G. Robinson in D.T. Krieger J.C Hughes (eds.) Neuroendocrinology (Sinauer Assoc., Sunderland, Mass., 1980)]... 

Visneaud, Vincent du (1901-78) American biochemist whose principal contribution was in the field of amino acids. He showed how a series of these important protein constituents were synthesized in the body. He also achieved the laboratory synthesis of thiamine and penicillin, and the hormones oxytocin and vasopressin. He was awarded the 1955 Nobel Prize in chemistry. 

However, insulin is not a very typical protein because of the shortness of its polypeptide chains and the -S-S- bridge which links residues 6 and 11 of the A chain. Similar loops containing six residues are found in the posterior pituitary hormones oxytocin and vasopressin, while one containing seven residues is found in calcitonin. Their special significance, if any, is not known. 

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