Mpr = 1(β-mercapto-β,β-cyclopentamethylene)-propionic acid Pen = Penicillamine. Appropriate references are quoted in the review sections. L-368,899, epelsiban (GSK 557296), and glicosiban are nonpeptide oxytocin receptor antagonists. The two cysteins in position 1 and 6 are linked by a disulfide bridge shown with a continuous line.
Pyridinyl)-2-(4-morpholinyl)-2-oxoethyl]-6-2,5-piperazinedioneĥ-2-methoxypyridineĭifferent amino acid residues are written in italics. M pr-Tyr(Me) -Ile-Gln-Asn-Cys-Pro- Arg-GlyNH 2ġ-((7,7-dimethyl-2(S)-(2(S)-amino-4-(methylsulfonyl) butyramido)bicyclo-heptan-1(S)-yl)methyl) sulfonyl)-4-(2-methylphenyl)piperazine
Pen -Phe(Me) -Ile- Tyr-Asn-Cys-Pro- Orn-GlyNH 2 M pr-Tyr(Me) -Ile-Gln-Asn-Cys-Pro- Orn-GlyNH 2 H-C ys-Tyr- Phe-Gln-Asn-Cys-Pro- Arg-GlyNH 2 H-C ys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-GlyNH 2 Įffect on Erectile Function/Sexual Activity Although caution is always required when such a large amount of findings appear suddenly (see ) these studies have allowed the suggestion that oxytocin may have a role in the treatment of mental diseases such as schizophrenia, autism, drug addiction, eating disorders, fibromyalgia, and other neuropsychological disturbances, often with contradictory and negative results. Nonetheless, these reports further stressed the involvement of oxytocin in the functions recalled above in human beings, i.e., trust, empathy, facial expression recognition, decision making, and so on (see and references therein). However, some skepticism for the blood–brain barrier crossing and survival abilities of the peptide in blood circulation is still present among researchers in this field (see and Section 8). In the last fifteen years, there have been many reports that have appeared and that are still appearing that have reported the effects of intranasal oxytocin, a delivery route believed to allow the crossing of the blood–brain barrier by the peptide, which can then reach and act at the level of the central nervous system (see ). Since their discovery in the 1980s (see ), these central oxytocinergic neurons have been involved in numerous central functions, i.e., memory learning affiliative and socio-sexual behaviors, from erectile function to copulatory behavior yawning, and many others, from the control of pain and feeding behavior to drug dependence (see ). The PVN and surrounding periventricular structures also contain the cell bodies of parvocellular oxytocinergic neurons that project to extra-hypothalamic brain areas (i.e., medial preoptic area, ventral tegmental area, hippocampus, amygdala, septum, bed nucleus of the stria terminalis, medulla oblongata, and spinal cord) (see ). These neurons project to the neurohypophysis, from which the peptide is released through blood circulation. Oxytocin is found in the same amount in female and male mammals in the magnocellular and parvocellular neurons, whose cell bodies are in the paraventricular (PVN) and supraoptic (SO) nuclei of the hypothalamus. Oxytocin is the neurohypophyseal peptide that is well known for its hormonal role in lactation and parturition and was discovered and synthesized together with the other neurohypophyseal peptide arginine-vasopressin in the 1950s by the Nobel Price Du Vigneaud and coworkers (see Table 1 for the amino acid sequence of neurohypophyseal peptides and a few of their peptidic and non-peptidic analogues). Possible explanations for the failure of oxytocin to improve sexual behavior in men and women and strategies to attempt to overcome this impasse are considered. Unexpectedly, the results of these studies do not appear to confirm the facilitatory role of oxytocin found in male and female sexual behavior in animals, both in men and women. The second part summarizes the results of studies done mainly with intranasal oxytocin in men and women with the aim to translate the results found in laboratory animals to humans. The first part of this review summarizes the results of studies done in laboratory animals that support a facilitatory role of oxytocin in male and female sexual behavior and reveal mechanisms through which this ancient neuropeptide participates in concert with other neurotransmitters and neuropeptides in this complex function, which is fundamental for the species reproduction. Among the functions in which oxytocin is thought to be involved are those that play a role in social and sexual behaviors, and the involvement of central oxytocin in erectile function and sexual behavior was indeed one of the first to be discovered in laboratory animals in the 1980s. A continuously increasing amount of research shows that oxytocin is involved in numerous central functions.
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