Late-Pregnancy Changes in Peripheral Plasma Beta-Endorphin in Rhesus Monkeys(Macaca mulatto)

Abstract

Peripheral plasma beta-endorphin (BEP) was measured in 10 pregnant monkeys during the third trimester (14–21 weeks gestation, term = 23.5 weeks). The study was intended to identify a late-pregnancy rise in BEP that has been reported in women. Levels rose in late pregnancy only in animals that delivered within a few days of the final sample. When both BEP and beta-lipoprotein (BLP) were measured in a further group of 10 animals, the late-pregnancy BEP rise was not accompanied by a rise in BLP. Multiple regression indicated that plasma BEP was correlated with plasma cortisol but that an independent influence of gestational age could be detected. We conclude that monkeys exhibit a rise in BEP just prior to parturition that is not accompanied by increases in cortisol and BLP that would indicate general maternal pituitary activation

A Theory of Natural Addiction

“…44 The most powerfully addictive drugs, however, differ from natural rewards in that their effects on dopamine transmission are not diminished by repeated administration. 45 This would seem to suggest that if dopamine in the limbic system does in fact represent a physical substrate of learning, then the sort of learning that takes place in the presence of drugs of addiction is properly viewed as pathological.…”

“…The prospect of such an undertaking for all behavior-altering substances is daunting, given the unfortunate fact that-for most drugs-our understanding of the 44 ∆ 9 -tetrahydrocannabinol, or THC, is the pharmacologically active constituent of marijuana. 45 The difference presumably stems from the fact that the endogenous neurochemical signals generated by natural rewards are subject to adaptive regulation; exogenous ligands (i.e., drugs) are not subject to such limitations. It is important to note that the distinction is not absolute: drugs of addiction are subject to habituation, but to a much lesser degree than natural rewards.…”

“…Subsequent studies have successfully used morphine and other opiates to induce place preference in a variety of species, as well as place aversion when-in place of opiates-the opioid antagonist naloxone is used [78], [77]. 21 For example, endogenous opioid levels are known to rise during pregnancy in rats, monkeys, and humans, and all three classes of endogenous opioids (i.e., endorphins, enkephalins, and dynorphins) have been shown to vary dramatically during pregnancy [44], [45], [90], [116].…”