In an animal experiment the levels of various endogenous compounds are measured in the spinal fluid after application of noxious stimuli. One of the compounds that increase as a result of the experiment is a pentapeptide with a strong affinity to delta- and mu-receptors. Which of the following substances is most likely to have a common molecular origin with the pentapeptide described above?

Question

In an animal experiment the levels of various endogenous compounds are measured in the spinal fluid after application of noxious stimuli.  One of the compounds that increase as a result of the experiment is a pentapeptide with a strong affinity to delta- and mu-receptors.  Which of the following substances is most likely to have a common molecular origin with the pentapeptide described above?

Quizplus · Accepted Answer

Enkephalins, endorphins, and dynorphins are endogenous opioid peptides that are part of the body's naturally occurring opioid system. These endogenous peptides are released in response to noxious stimuli and bind to different opioid receptors to allow physiologic modulation of pain. Several different types of opioid receptors have been identified and include mu, delta, kappa, and N/OFQ receptors. Available narcotics like morphine and hydromorphone produce therapeutic analgesic effects by binding to mu receptors and modulating pain perception. Endogenous opioid peptides also play a significant role in gastrointestinal, endocrine, autonomic, and emotional function. Beta-endorphin is one endogenous opioid peptide that is derived from proopiomelanocortin (POMC). POMC is a polypeptide precursor that goes through enzymatic cleavage and modification to produce not only beta-endorphins, but also ACTH and MSH. The fact that beta-endorphin and ACTH are derived from the same precursor suggests that there may be a close physiological relationship between the stress axis and the opioid system. (Choice A) Prolactin is a somatotropic hormone synthesized in the anterior pituitary and is responsible for breast development and milk production. It is structurally similar to growth hormone. (Choice B) TSH is a glycoprotein hormone synthesized in the anterior pituitary and is responsible for stimulating the secretion of thyroid hormone. It is also responsible for growth of the thyroid gland. (Choice D) Growth hormone belongs to the family of somatotropic hormones. It is synthesized in the anterior pituitary and is responsible for overall body growth. (Choice E) Vasopressin, also known as antidiuretic hormone (ADH), is a hormone synthesized in the hypothalamus and released from the posterior pituitary. It primarily functions to regulate fluid retention in the kidneys, but also causes arteriolar contraction of smooth muscle resulting in a pressor effect. (Choice F) Somatomedin C is a peptide that is structurally similar to insulin. Also referred to as insulin like growth factor, somatomedin C is released in response to growth hormone and stimulates growth in target cells. Educational Objective: Beta-endorphin is one endogenous opioid peptide that is derived from proopiomelanocortin (POMC). POMC is a polypeptide precursor that goes through enzymatic cleavage and modification to produce not only beta-endorphins, but also ACTH and MSH. The fact that beta-endorphin and ACTH are derived from the same precursor suggests that there may be a close physiological relationship between the stress axis and the opioid system.

In an Animal Experiment the Levels of Various Endogenous Compounds