Effect of naloxone and beta-casomorphin on the hypothalamic-pituitary-luteinizing hormone axis in vitro

Interactions of morphine and Peptide 234 on mean plasma testosterone concentration

BACKGROUND

Kisspeptin-GPR54 system stimulates the hypothalamus-pituitary-gonadal (HPG) axis; dysfunction of the gene encoding the GPR54 receptor causes hypogonadism and infertility. Opioid peptides inhibit the reproductive axis. Peptide 234 is a GPR54 receptor antagonist and blocks the stimulatory effects of kisspeptin on HPG axis.

OBJECTIVES

Interactions of morphine, kisspeptin and peptide 234 on mean plasma testosterone concentration was investigated in rats. .

MATERIALS AND METHODS

In the present experimental study, seventy male Wistar rats in 14 groups (n = 5 in each group) received saline, different doses of kisspeptin (100 pmol, 1 or 3 nmol, Intracerebroventricular (ICV)), P234 (1 or 2.5 nmol) or Co- administration of kisspeptin, P234, morphine and naloxone at 09:00 - 09:30 am. In the co-administrated groups, kisspeptin was injected at 15 min following P234, morphine or naloxone injections. Blood samples were collected 60 min following injections. Plasma testosterone concentration was measured using the rat testosterone ELISA kit.

RESULTS

Injections of kisspeptin (1 or 3 nmol) significantly increased the mean testosterone concentration compared to saline. Injection of different doses of P234 (1 or 2.5nmol) did not significantly decrease mean testosterone compared to saline. Co-administration of kisspeptin and different doses of P234 significantly decreased mean testosterone concentration compared to the kisspeptin group. Co-administration of P234/morphine or P234/naloxone significantly decreased mean testosterone concentration compared to kisspeptin/saline, kisspeptin/morphine or kisspeptin/ naloxone groups.

CONCLUSIONS

Morphine and kisspeptin/GPR54 signaling pathway may interact with each other to control the hypothalamic-pituitary-gonadal axis.

Prolactin and growth hormone response to intracerebroventricular administration of the food opioid peptide gluten exorphin B5 in rats

Although it has long been known that opioid peptides cause marked changes of pituitary hormone secretion in both animals and humans, little is known about the possible effect(s) of food-derived opioids (exorphins) on pituitary function. In order to investigate the possible role of exorphins derived from wheat gluten on pituitary function, we gave the following treatments to four groups of male rats: intracerebroventricular (ICV) vehicle, Gluten Exorphin B5 (GE-B5) 200 microg ICV, naloxone intraperitoneally (IP) followed by vehicle ICV, naloxone IP followed by GE-B5 ICV. Blood samples for Prolactin (PRL) and Growth Hormone (GH) were taken at intervals for 90 minutes after vehicle or GE-B5 administration. GE-B5 strongly stimulated PRL secretion; its effect was completely abolished by naloxone administration. GH secretion was unaffected by GE-B5 under these experimental conditions. The present study shows for the first time that an opioid peptide derived from wheat gluten, GE-B5, has an effect on pituitary function when administered ICV; its mechanism of action appears to be mediated via classical opioid receptors.

Milk protein-derived opioid receptor ligands

Milk is mammalian characteristic and is of particular importance for humans: Mother's milk or its substitutes from cows' milk are absolutely essential nutriments for the neonate and cows' milk also represents a basic foodstuff for adults. However, in addition to their well-known nutritive role, milk constituents apparently are also able to carry specific information from the milk producer's to the milk receiver's organism: Thus, a number of milk protein fragments has been shown to behave like opioid receptor ligands able to address opioidergic systems in the adult's or in the neonate's organism. With respect to the proteins, which they are derived off these peptides have been named alpha-casein exorphins or casoxin D (alpha-casein), beta-casomorphins or beta-casorphin (beta-casein), casoxin or casoxin A, B, or C (k-casein), alpha-lactorphins (alpha-lactalbumin), beta-lactorphin (beta-lactoglobulin) or lactoferroxins (lactoferrin). Only casoxins and lactoferroxins display antagonistic properties; the other peptides behave like opioid receptor agonists. Most of the information available so far has been collected about beta-casomorphins. These peptides obviously can be released from beta-casein in the adult's or in the neonate's organism, where they might elicit opioid effects in the frame of a regulatory role as "food hormones". Several synthetic beta-casomorphin derivatives have been shown to be highly specific and potent mu-type opioid receptor ligands which frequently have been used as standard tools in opioid research.

Three dimensional culture of pineal cell aggregates: a model of cell-cell co-operation

Three dimensional (3-D) cultures of pineal cell aggregates were obtained by constant gyratory shaking the heterogenous cell populations, obtained from the rat pineals, in the DMEM (Dulbecco's modified Eagle's medium). Within 4 days, the pineal cells became organized into a tissue like configuration appearing as a compact ball, evidenced by the scanning electron microscopy. The 3-D aggregates seemed to be mainly composed of pinealocytes (round-oval cells), glial (elongated cells) and other unknown cells. The heterogenous cells were separated by intercellular spaces. The ultrastructural characteristics revealed by transmission electron microscopy exhibited the presence of granular lysosomes, typical of pinealocytes actively involved in the secretion. These pineal cell aggregates secreted melatonin and other indole amines i.e. 5-methoxytryptamine (5-MT), indole acetic acid (IAA), 5-methoxy-3-indole acetic acid (5-MIAA), tryptophol (TOL) and 5-methoxytryptophol (5-MTL) in the culture medium, indicating the functional aspect of pinealocytes. The 3-D aggregates cultures had advantages over the pineal monolayer cultures as, after 4 days of culture, the amounts of indole amines secreted by 3-D aggregates were higher than those secreted by monolayer cultures. Besides, the 3-D aggregates remained functional till 24 days in the gyratory culture conditions. In the continuous perifusion system, the 3-D aggregates secreted melatonin while challanged with isoproterenol. This 3-D model of pineal cell aggregates might be useful, in future, to perform other kinetic studies of the release of indole amines in perifusion experiments as this system allows the maintenance of pineal cells for a long period of time.

Rat pineal cell aggregates: ultrastructural and functional characteristics

The aggregates were obtained by constant gyratory shaking of suspension cells freshly isolated from adult rat pineal glands. Their sizes ranged from 60 to 120 microns. Within 4-5 days, the aggregates formed by pinealocytes, astrocytes, and other unidentified cells became organized in a tissue-like configuration. There was no proliferation of the fibroblast cells. Ultrastructural characteristics of the aggregates were revealed by the presence of granular lysosomes, which are typical of pinealocytes, and are actively involved in the secretion. Functional characteristics were studied in static incubation. The aggregates secreted melatonin and other indole amines in culture medium. Basal melatonin release was detected until Day 24 of culture. This secretion was stimulated 230% with Isoproterenol (beta-adrenergic agonist), 725% with Epinephrine (alpha- and beta-adrenergic agonists), and 140% with Vasoactive Intestinal Peptide after 5 days in culture, then > 1200% with Forskolin 9 days later (14-day-old aggregates). The results indicate that three-dimensional aggregates obtained from isolated pineal gland cells were the functional multicellular structures with in vivo characteristics.