Opiate receptor subtypes in the regulation of thyrotropin and prolactin secretion in the rat

Opioid-induced endocrinopathy in cancer patients: an underestimated clinical problem

The impact of both endogenous and exogenous opioids on the endocrine system has been known for many years. With the increased use of opioids in chronic pain treatment, the research focuses mainly on their effects on the endocrine system in patients with chronic non-malignant pain. Despite the wide dissemination of cancer, there has been little research on the possible effects of opioids on the endocrine system in cancer patients. For the growing number of cancer survivors and patients in long-term remission who take opioids, other aspects of endocrine disorders caused or exacerbated by opioids will have practical and clinical importance. Conversely, this problem may be less relevant for patients in active cancer treatment or in the advanced stage of disease. This article presents the available research on the effects of opioids on the endocrine system and the clinical consequences resulting from opioid use in cancer patients. Clinicians who use opioids in clinical practice should be aware of the existence of the endocrine symptoms of opioid therapy. There is still a need for more research in this area to maintain the best possible quality of life for cancer patients treated with opioid analgesics.

The effects of opioids and opioid analogs on animal and human endocrine systems

Opioid abuse has increased in the last decade, primarily as a result of increased access to prescription opioids. Physicians are also increasingly administering opioid analgesics for noncancer chronic pain. Thus, knowledge of the long-term consequences of opioid use/abuse has important implications for fully evaluating the clinical usefulness of opioid medications. Many studies have examined the effect of opioids on the endocrine system; however, a systematic review of the endocrine actions of opioids in both humans and animals has, to our knowledge, not been published since 1984. Thus, we reviewed the literature on the effect of opioids on the endocrine system. We included both acute and chronic effects of opioids, with the majority of the studies done on the acute effects although chronic effects are more physiologically relevant. In humans and laboratory animals, opioids generally increase GH and prolactin and decrease LH, testosterone, estradiol, and oxytocin. In humans, opioids increase TSH, whereas in rodents, TSH is decreased. In both rodents and humans, the reports of effects of opioids on arginine vasopressin and ACTH are conflicting. Opioids act preferentially at different receptor sites leading to stimulatory or inhibitory effects on hormone release. Increasing opioid abuse primarily leads to hypogonadism but may also affect the secretion of other pituitary hormones. The potential consequences of hypogonadism include decreased libido and erectile dysfunction in men, oligomenorrhea or amenorrhea in women, and bone loss or infertility in both sexes. Opioids may increase or decrease food intake, depending on the type of opioid and the duration of action. Additionally, opioids may act through the sympathetic nervous system to cause hyperglycemia and impaired insulin secretion. In this review, recent information regarding endocrine disorders among opioid abusers is presented.

Activation of mu opioid receptors in the pre-optic-anterior hypothalamus releases prolactin in the conscious male rat

Microinjection of opioid agonists into the pre-optic-anterior hypothalamus (PO/AHA) was used to determine the identity of the opioid receptor subtype(s) involved in the stimulation of prolactin release. The mu agonist DAGO [(D-Ala2, NMe-Phe4, Gly-o15)-enkephalin] was the only opioid agonist to show dose-dependent release of prolactin, the lowest significant dose being 0.001 nmoles. Neither the specific delta agonist DPDPE [(D-Pen2, D-Pen5)-enkephalin] nor the specific kappa agonist U50,488H [(trans-3,4-dichloro-N-methyl-N-(2-(1-pyrrodinyl)-cyclohexyl)-benz ene acetamide] showed dose-dependent increase of prolactin secretion, or indeed any significant increase in prolactin secretion in the dose range 0.01-1 nmoles and 0.01-10 nmoles respectively. We suggest that mu (and not kappa or delta) opioid receptors in the PO/AHA are involved in the opioid stimulated release of prolactin in the conscious male rat.

Blockade of opioid receptors with naltrexone inhibits thyrotropin increase after noise stress but does not prevent the decrease caused by immobilization

The influence of naltrexone-induced opioid receptor blockade on the response of thyrotropin to two different acute stressors was studied in adult male rats. Naltrexone slightly but significantly reduced basal thyrotropin levels and abolished the increase in serum thyrotropin caused by acute noise stress. In contrast, the opioid antagonist did not prevent the decrease in serum thyrotropin caused by another much more severe stressor such as immobilization. The present data offer the first evidence that endogenous opioids could play a stimulatory role in the control of thyrotropin secretion in a presumably physiological condition such as the response to a mild stressor. In addition, factors other than opioids could be involved in the inhibition of thyrotropin secretion under severe stress.