Opioids in the milk.
In various studies, the milk has been screened for the presence of free or precursor-bound opioids. In fact, various opioid receptor ligands with agonistic or even antagonistic activity were found. Besides the alkaloid morphine, peptides derived from alpha-casein (alpha-casein exorphins), beta-casein (beta-casomorphins; beta-casorphin), alpha-lactalbumin (alpha-lactorphins) and beta-lactoglobulin (beta-lactorphin) were among the agonists. In addition, certain peptides derived from k-casein (casoxins) or from lactoferrin (lactoferroxins) were found to behave like opioid antagonists. Although a functional role in the mammalian organism for all of these compounds appears to be well possible, evidence has only been presented for the functional significance of beta-casomorphins, so far. These peptides might play a role in reproduction or nutrition in the female, in the newborn's or in a milk consumer's organism, respectively. Thus, opioids related to milk might represent essential exogenous extensions of the endogenous opiodergic systems.
Teschemacher
H
H
Rudolf-Buchheim-Institut für Pharmakologie, Justus-Liebig-Universität Giessen, Germany.
Koch
G
G
D000595:Amino Acid Sequence; D000818:Animals; D004723:Endorphins / Q000032:analysis* / Q000737:chemistry; D006801:Humans; D008892:Milk / Q000032:analysis*; D008895:Milk, Human / Q000737:chemistry; D008969:Molecular Sequence Data
D004723:Endorphins