Evidence for the participation of opioids in the regulation of carbohydrate metabolism in rat mammary glands.

The possible involvement of opioids in carbohydrate metabolism in rat mammary glands was investigated by studying the effects of administration of morphine and naloxone on six enzymes. Morphine inhibited phosphofructokinase (PFK) and stimulated phosphohexose isomerase (PHI) activities. Nalozone treatment alone, to both intact and ovariectomized/adrenalectomized animals, resulted in stimulation of PFK and inhibition of PHI activities. A combined dose of morphine and naloxone to intact animals showed that the opiate antagonist was able to reverse the morphine-induced changes. Evidence is presented to show that the changes observed in PHI activity may be the result of the indirect action of opioids on luteinizing hormone releasing hormone. However, the changes observed in PFK activity might be the result of direct action of opioids. Failure to observe changes in enzyme acstivities after naloxone treatment of hypophysectomized animals suggests the opiate antagonist might be acting on the pituitary gland to block the release of endorphins.