Investigations on the effects of long-term administration of a methionine-enkephalin analogue on the adrenal zona fasciculata of rats treated with dexamethasone or dexamethasone and ACTH

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.

The influence of prolonged dexamethasone treatment of pregnant rats on the perinatal development of the adrenal gland of their offspring

The effects of prolonged dexamethasone (Dx) administration to pregnant rats on the structure and function of the adrenal glands of fetal and neonatal offspring have been investigated by combined stereological and ultrastructural methods, as well as by metaphase index determination. Pregnant rats were injected subcutaneously with Dx (0.3 mg/kg body weight/day) during 5 days, starting from day 16 of gestation. The dams and their fetuses were killed 24 hr after the last injection. The neonatal offspring were killed in the same way on the 3rd and 14th day of life. Because in fetal and 3-day-old neonatal rats zona reticularis (ZR) was poorly defined and could not be clearly seen as a separate zone, zona fasciculata (ZF) and ZR were analyzed as one, inner zone (IZ). In 14-day-old rats ZF and ZR were analyzed separately. Proliferative activity of adrenocortical cells was estimated following the application of Vincristine sulphate. Dx treatment of pregnant rats induced a marked decrease of fetal adrenal gland volume and the volumes of zona glomerulosa + capsula (ZG + C) and IZ as the consequence of atrophic changes in the gland and reduction of the average volume and total number of adrenocortical cells. Similar morphometric changes were found in 3- and 14-day-old pups. However, in 3-day-old animals the number of cortical cells in the ZG was increased, whereas on the 14th postnatal day cortical cell number remained decreased only in the ZF. The multinuclear giant cells, numerous lymphocytes, and the resorption zones, present in the adrenal cortex of fetuses and 3-day-old pups of both experimental and control dams, were not seen in 14-day-old offspring. These results demonstrate that prolonged treatment of pregnant rats with Dx in the period when intensive differentiation of the fetal hypothalamo-hypophyseal system takes place inhibits proliferative activity of adrenocortical cells and evokes considerable atrophic changes in the adrenal glands of offspring from 20 days gestation to 14 days after birth. The histological appearance of the adrenal cortex and the ultrastructure of adrenocortical cells suggest that cortical cell function was inhibited.

Neuropeptides in the adrenal gland: distribution, localization of receptors, and effects on steroid hormone synthesis

In this review we defined and classified the neuropeptides (NPs) related to the adrenal gland, according to Palkovits (Frontiers Neuroendocrinol 10:1 1988). The concentration (RIA) and distribution (immunohistochemistry) of NPs, as well as the localization of the receptors (radioligand studies) were summarized. Direct effects of NPs on aldosterone and corticosterone synthesis obtained by in vivo, in situ perfusion, and in vitro experimental approaches were reviewed. Data (from different rat strains and genders) for 35 NPs are presented.

Effects of neuropeptide-Y and substance-P on the secretory activity of dispersed zona-glomerulosa cells of rat adrenal gland

Neuropeptide-Y (NPY) and substance-P (SP), two peptides contained in the chromaffin granules of adrenal medullary cells, were found to partially inhibit both basal ACTH-stimulated release of aldosterone and 18-hydroxy-corticosterone by isolated rat zone-glomerulosa cells, without affecting the overall post-pregnenolone yield or basal progesterone output. Conversely, the exposure to both peptides increased 11-deoxy-corticosterone and corticosterone secretion. These data indicate that NPY and SP are able to exert a direct suppression of 18-hydroxylase activity in rat zona-glomerulosa cells, without conceivably altering the earlier steps of aldosterone synthesis. The possible physiological implications of these findings are discussed in light of previous studies suggesting a net adrenoglomerulotrophic effect of NPY and SP in vivo.

Evidence that long-term administration of a methionine-enkephalin analogue stimulates the growth and steroidogenic capacity of rat inner adrenocortical cells

A prolonged infusion with D-ala2-met-enkephalinamide (DALA) caused a significant increase in both basal and ACTH-stimulated corticosterone secretion by dispersed inner adrenocortical cells of rats whose hypothalamo-hypophyseal axis was pharmacologically interrupted. This effect of DALA was associated with a notable hypertrophy of isolated cells. These findings suggest that enkephalins are involved in the stimulation of the growth and steroidogenic capacity of the cells of the inner layers of rat adrenal cortex.

Effects of substance P on the rat adrenal zona glomerulosa in vivo

Substance P (SP) acutely enhanced the plasma concentration of aldosterone in rats whose hypothalamo-hypophyseal-adrenal axis and renin-angiotensin system were pharmacologically interrupted. The maximal response was obtained with a dose of 100 micrograms/kg. A prolonged (7 days) subcutaneous infusion with SP (50 micrograms/kg/hr) caused a notable hypertrophy of zona glomerulosa cells associated with significant rises in both basal and angiotensin-stimulated plasma levels of aldosterone. Zona fasciculata and the blood concentration of corticosterone were not affected. These findings suggest that SP is specifically involved in the stimulation of the growth and secretory activity of the rat zona glomerulosa.