Immunoreactive beta-endorphin and pro-gamma-melanotropin in the peripheral circulation during the menstrual cycle.

Abstract

AbstractThe ovary contains β‐endorphin but it is not clear whether it secretes this opioid peptide in amounts sufficient to increase β‐endorphin concentrations in the peripheral circulation, and hence effect β‐endorphin‐sensitive mechanisms controlling hypo‐thalamic secretion of gonadotropin‐releasing hormone and pituitary secretion of gonadotrophins. To examine the possible ovarian contribution to the circulating pool of β‐endorphin and related peptides we measured the plasma concentrations of immunoreactive β‐endorphin and the cosynthesized glycopeptide, pro‐γ‐melanotropin, in different phases of a normal menstrual cycle. Ovarian steroids and pituitary gonadotrophins showed the expected cyclical changes. Plasma cortisol, immunoreactive β‐endorphin and immunoreactive pro‐γ‐melanotropin concentrations were not significantly different in different phases of the cycle. There was no discernible relationship between plasma concentrations of either immunoreactive β‐endorphin or pro‐γ‐melanotropin and any of oestradiol, progesterone, luteinising hormone and follicle‐stimulating hormone overall or during any phase of the menstrual cycle. The results suggest that the ovary does not contribute significantly to the pool of β‐endorphin and related peptides in circulating blood.