Endogenous opioid peptides in the control of the normal menstrual cycle and their possible role in athletic XXXX .

@entity1 @entity4545 @entity935 @entity134 @entity1866 @entity2761
The remarkable morphinic capacities of endogenous opioid peptides give these agents particular and interesting properties. They can be found on different locations throughout the @entity1 body, where they bind to specific receptors. By means of various agonists and antagonists it was shown that endogenous opioids possibly play a prominent role in the control of hypophyseal secretions. The menstrual cycle is thought to represent one of the most important phenomena in which these agents are involved. In the presence of a @entity134 -sufficient environment (that is to say, in the luteal phase) @entity4545 exerts a tonic inhibition on the secretion of GnRH and thereby on the LH-release. Moreover, the regulation of prolactin is probably under the control of endorphins interfering via @entity935 ( @entity2761 ). It becomes possible to explain a number of @entity1866 in this manner. The increased plasma concentrations of @entity4545 , which are found after physical exercise, give rise to speculations as to their involvement in the frequently appearing @entity1866 in @entity1 athletes. The hypothesis proposing prolactin as being entirely responsible for these phenomena is unconvincing. We believe that endogenous opioid peptides could have a possible inhibitory effect on the GnRH-LH-axis. At this moment, methodological inaccuracies and differences of various studies make it very difficult to arrive at any firm conclusion.
