Action of pineal indoleamines on the reproductive systems of the male C57 mouse and golden hamster

Effects of melatonin on Leydig cells in pinealectomized rat: an immunohistochemical study

We have investigated immunohistochemically the effects of melatonin on Leydig cells in rat. Three groups of Wistar rats were used. Rats in group I and II were sham-pinealectomized (control) and pinealectomized, respectively, whereas rats in group III were pinealectomized and injected daily with melatonin for 2 months. At the end of the experiment, all animals were killed by decapitation and blood samples were obtained. Serum testosterone levels were determined with the use of a chemiluminescent enzyme immunoassay. Testicular tissue was collected and processed for semiquantitative evaluation of immunohistochemical testosterone staining. Intensity of immunostaining was determined on a scale between 0 (no staining) and 5 (heavy staining). In pinealectomized rats, serum testosterone levels were significantly increased as compared to sham-pinealectomized rats. Daily administration of melatonin after pinealectomy resulted in significant decreased serum testosterone levels as compared to levels in control and pinealectomized rats. Immunostaining of testosterone was moderate (3+) in sham-pinealectomized rats, heavy (5+) in pinealectomized rats and low (1+) in pinealectomized rats that were treated with melatonin, respectively. The results of our study indicate that pinealectomy induces increased testosterone secretion in Leydig cells and this increased secretion can be prevented by administration of melatonin.

Effects of cycloheximide and aminophylline on 5-methoxytryptophol and melatonin contents in the chick pineal gland

The chick pineal gland rhythmically synthesizes two 5-methoxyindoles, melatonin and 5-methoxytryptophol. These rhythms are circadian in nature and have opposite phases. The aim of this study was to determine the effects of cycloheximide, a protein synthesis inhibitor, and aminophylline, an inhibitor of phosphodiesterase, on 5-methoxytryptophol content in the chick pineal gland and to compare this with the drugs' action on pineal melatonin production. Inhibition of melatonin biosynthesis by cycloheximide (1 mg/kg, i.p. ), revealed by a marked reduction in the nighttime activity of serotonin N-acetyltransferase (AA-NAT; a key regulatory enzyme in melatonin synthesis) and melatonin concentrations, was accompanied by a significant increase in 5-methoxytryptophol content. In contrast, administration of aminophylline (100 mg/kg, i.p.) to light-exposed chicks significantly increased pineal AA-NAT activity and melatonin levels and decreased 5-methoxytryptophol concentrations. It is concluded that in the chick the production of pineal 5-methoxytryptophol and melatonin is inversely correlated.

Effect of pineal indoles on the chick embryo

In a study on the embryotoxicity of pineal indoles on developing chick embryos in vivo, the pineal indoles--namely, melatonin (MEL), methoxytryptamine (MTA) and methoxytryptophol (MTP)--were injected into the yolk sacs of the chick embryos through the air chambers of the eggs on the 4th day of incubation. The eggs were opened and the embryos examined after 6, 10 or 14/15 days of incubation. Abnormalities were found to occur mainly in the 6- and 10-day-old embryos, which exhibited external malformations such as twisted vertebral column, abdominal hernia, exteriorization of heart and viscera, defects of eye, beak and limb. From the results obtained from embryos on the 14th or 15th day of incubation, MEL was found to be the most toxic indole in regard to the mortality induced, whereas MTA had the highest teratogenicity because of the frequent incidence of abnormal embryos. Effect of MTP treatment on the development of chick embryos varied greatly between doses, and there were no abnormal embryos found on the 14th or 15th day of incubation.

Effects of pineal indoles on ovarian response to gonadotropin-induced ovulation in mice

Ovulation was induced in immature mice by injections of pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (HCG) spaced 48 hours apart. The mice were divided into six groups: one group received intraperitoneal injections of normal saline, another group received alcoholic saline which was used as the vehicle of pineal indoles, and the remaining groups received respectively hydroxyindoleacetic acid (HIAA), melatonin (MEL), methoxytryptamine (MTA) and methoxytryptophol (MTP). The pineal indoles were administered 24 hours before, on the same day as, 24 hours after and 48 hours after the PMSG injection. The mice were sacrificed 24 hours after the HCG injection. The numbers of growing primary follicles, multilaminar primary follicles, Graafian follicles, preovulatory follicles and corpora lutea in the ovary were not altered by treatment with pineal indoles. However, there was an increased incidence of follicular atresia in the groups treated with MEL, MTA and MTP. The pineal indoles did not affect the number of ovulated oocytes, but there was a large number of degenerated and fragmented ovulated oocytes in the MTA- and MTP-treated groups. Treatment with MEL, MTA and MTP also resulted in lower plasma levels of estradiol-17 beta and progesterone.

Changes induced by pineal indoles in post-implantation mouse embryos

1. A subcutaneous injection of hydroxyindoleacetic acid (HIAA), melatonin (MEL), methoxytryptophol (MTP) or methoxytryptamine (MTA) (1 mg/25 g body wt/injection) at 8.5 days post-coitum (p.c.) did not produce any effect on the development of embryos in utero at 10.5 days p.c. 2. Two subcutaneous injections (3 mg/25 g body wt/injection) of MTP, but not HIAA, MEL nor MTP, at 7.5 and 8.5 days p.c. brought about a decrease in gravid uterine weight and number of live fetuses and an increased incidence of early resorptions at 17.5 days p.c. 3. MEL at doses 100 and 200 micrograms/ml, MTP at doses 50 and 100 micrograms/ml and MTA at 25, 50 and 100 micrograms/ ml brought about an increase in the number of abnormal embryos cultured in vitro and an increased incidence of abnormal yolk sac circulation, body axis, optic and otic placodes, branchial apparatus, forelimb buds and cranial neural tube. 4. The findings show than melatonin, methoxytryptamine and methoxytryptophol produced an embryotoxic effect on embryos at the early somite stage in vitro while only methoxytryptamine had an adverse effect on embryonic development in vivo.

Actions of selected proteins, peptides and amino acid derivatives on mouse embryonic development in vitro

1. The actions of various compounds with antiproliferative and/or immunomodulatory activities including the ribosome-inactivating protein gelonin, the tetrapeptide tuftsin, the opioid peptide leucine-enkephalin, the antireproductive tripeptide Thr-Ser-Lys, the melatonin analog 6-methoxy-2-benzoxazolinone, and the amino acid derivatives 5-hydroxytryptamine and oxalysine on mouse embryonic development and organogenesis in vitro were investigated. 2. The various compounds were tested up to a concentration of 300 micrograms/ml. It was found that only 6-methoxy-2-benzoxazolinone, a derivative of tryptophan, produced an increase in the number of abnormal embryos and reductions in the final somite numbers and axial lengths of embryos. 3. 6-Methoxy-2-benzoxazolinone treatment also resulted in an increased incidence of abnormal morphogenesis of various organ primordia, including abnormal yolk sac circulation, twisting of body axis, absence of forelimb bud and opening of cranial neural tube.

Development of pre-implantation mouse embryos under the influence of pineal indoles

The developmental toxicity of pineal hormones on mouse embryos was examined both in vitro and in vivo. Pregnant ICR mice were divided into groups which received at 1.5 days post-coitum (p.c.) and again at 2.5 days p.c. a subcutaneous injection of one of the following pineal indoles: hydroxyindoleacetic acid (HIAA), melatonin (MEL), methoxytryptophol (MTP) or methoxytryptamine (MTA). Mice treated with the injection vehicle served as the control. The animals were sacrificed at 17.5 days p.c. The pineal indole treatment did not cause changes in the gravid uterine weight, numbers of implants, early resorption, late resorption, dead fetuses and live fetuses, fetal weight or fetal crown-rump length, and did not produce embryos with external or visceral defects. However, some mice treated with MTP or MTA produced litters in which all embryos underwent resorption. Cultured embryos at the 4-cell stage were treated with the aforementioned pineal indoles and examined after 24, 48, 72 and 96 hours. It was found that MTA retarded embryonic development at all time points studied. HIAA also produced a slight inhibitory effect on embryonic development. Some embryos underwent degeneration in response to the MTA and HIAA treatments. However, MEL- and MTP-treated embryos were in general developmentally similar to control embryos. When cultured embryos were treated at the 8-cell to compacting stage, it was found that MTA exerted only a slight retarding effect on embryonic development, while other indoles were devoid of any conspicuous effects.