Melatonin's inhibition of pituitary, adrenal, testicular and accessory gland growth in male golden hamsters: pineal dependence and organ differences with shielding and intracranial surgery

Effects of intracranial surgery on pineal lipid droplets, on other structures, and on melatonin secretion

Unique effects of sham-pinealectomy [intracranial surgery (IS)] which include reduced functional activity of the adrenal gland and suppressed circadian rhythms of the adrenal medulla, and which are reversed by pinealectomy, have been reported in rodents. To clarify the mechanisms, we investigated whether or what changes occur in pineal functional activity after IS. Sixty-six male rats of normal and IS groups were used at 50 days of age. The pineal gland was first examined by quantitative electron microscopy. The Sudan III-stained lipid droplet content of the pinealocytes and plasma melatonin level were then investigated using the same animals. In IS rats, the lipid droplet content of the pinealocytes decreased in both the dark and light phases 14 days after surgery. Mean volumetric ratio of nucleus, nucleolus, and mitochondria tended to increase in IS rats. The mean plasma concentration of melatonin showed apparent day-night changes, but no significant changes because of IS, 36 h and 14 days after surgery. But in the dark phase 14 days after surgery, plasma melatonin levels showed increased dispersion of values (P < 0.04). Thus, after IS the lipid content of pinealocytes showed changes not closely related to those of plasma melatonin level. From these and other results it is speculated that IS effects are dissimilar to usual stress responses, that day-night rhythms of functional activities of the pineal and adrenal medulla are differently controlled, and that pineal gland-dependent IS effects are most probably induced by changed sensitivity/states of target mechanisms to the pineal hormone melatonin.

Diurnal variations in melatonin binding sites in the hamster brain: impact of melatonin

The distribution of 125I-melatonin binding sites in the male Syrian hamster brain was recorded at 3 times over a 24 h period. The binding in the hypothalamus, hippocampus, medulla-pons and midbrain of the hamsters varied significantly over the 24 h period with different patterns and phases. No such variations were observed in the parietal cortex. Daily morning (10.00 h) or late afternoon (18.00 h) injections of melatonin for 28 days markedly increased the serum concentrations of melatonin at all times recorded. Serum concentrations of testosterone were significantly lower in animals injected with melatonin in the late afternoon than in the untreated controls; no such decrease was observed in animals injected in the morning despite the continuously elevated levels of circulating melatonin. The daily melatonin injections did not significantly affect 125I-melatonin binding in the hypothalamus, parietal cortex and medulla-pons. In the midbrain, 125I-melatonin binding decreased regardless of the time of injection. In the hippocampus, morning melatonin injections caused a marked decrease in 125I-melatonin binding at all times recorded whereas melatonin injected in the late afternoon led to a decrease in 125I-melatonin binding at 10.00 h only. These results indicate diurnal variations in 125I-melatonin binding sites in discrete brain areas of the golden hamster, persisting despite prolonged duration of elevated levels of circulating melatonin. The differential effects of timed melatonin injections on the hippocampal 125I-melatonin binding sites are positively correlated with the counter-antigonadal response produced by morning melatonin injections.

Melatonin inhibits mitotic activity of adrenocortical cells in vivo and in organ culture

The goal of this study was to examine the effects of melatonin, as well as those of melatonin and corticotropin (1-24 adrenocorticotrophic hormone (ACTH); Synacthen Depot) administered together, on the mitotic activity of adrenocortical cells in male and female mice. Melatonin was given subcutaneously once daily, in late-afternoon injections (between 16:00 and 18:00) in doses of 1 microgram, 10 micrograms, and 100 micrograms, and ACTH in a dose of 0.1 mg (10 U) daily for 10 days. Additionally, the highest dose of melatonin (100 micrograms daily) was administered together with ACTH. The metaphase-arrest technique using colchicine as a stathmokinetic agent was employed in the study. Melatonin, in all the examined doses, significantly decreased mean mitotic activity rate (MMAR) of the adrenal cortex in both male and female mice. Moreover, in a dose of 100 micrograms, melatonin suppressed the mitogenic effect of ACTH on the adrenal cortex. Furthermore, the present study investigated the effects of melatonin (5 x 10(-7)M), N-acetylserotonin (NAc-5HT) (5 x 10(-7)M), and ACTH (250 mU/ml or 1,000 mU/ml) alone as well as the effect of ACTH (250 mU/ml) applied jointly with melatonin on the mitotic activity of adrenocortical cells in rat adrenal explants incubated in vitro. Both pineal indoleamines (melatonin and NAc-5HT) significantly decreased the MMARs of adrenocortical cells. Corticotropin, as well as ACTH and melatonin applied together, also reduced the MMAR of adrenocortical cells. The present data suggest that melatonin may be directly involved in the inhibitory control of adrenocortical cell proliferation.

Effects of melatonin on the growth of MtT/F4 anterior pituitary tumor: evidence for inhibition of tumor growth dependent upon the time of administration

In the present report, we have examined the anti-tumor potential of melatonin by utilizing the MtT/F4 anterior pituitary transplantable tumor. The tumor was obtained (Bogden Labs.) in cryopreserved condition and transplanted (in the left rear thigh), and allowed to grow for 8 weeks in adult Fischer 344 rats, maintained under uniform laboratory conditions of light (LD 14:10; lights on at 06:00 h), and temperature (21-23 degrees C). Subsequently, the tumor was dissected out, minced, and washed in Medium 199, and similarly transplanted into groups of adult Fischer 344 rats representing the final tumor recipient groups utilized for the evaluation of melatonin's anti-tumor effects. Melatonin (50 micrograms/0.1 ml/animal) was administered subcutaneously either early in the morning (at 08:00 h), or late in the afternoon (at 18:00 h), for 6 weeks, beginning the day after tumor transplantation. The matched controls were given equal volumes of physiological saline. A careful record of the appearance and growth of the tumor was maintained by examining the animals every morning. At the termination of the experimental schedule, the tumor masses were carefully dissected out, rinsed with normal saline, dried, and weighted on a sensitive Mettler balance. Our results showed that melatonin significantly increased the latency period of the tumor, irrespective of the time of drug administration. Analysis of the final tumor weights showed that afternoon, but not morning, injections of melatonin significantly reduced both the absolute (P less than 0.025) and relative (P less than 0.05) tumor weights in comparison to the saline-injected matched control. These results suggest that a) melatonin exhibits its anti-tumor efficacy on MtT/F4 tumor, by delaying the appearance of the tumor, and b) the anti-tumor potential of melatonin is greatly dependent on the time of administration of the drug within the daily light-dark cycle.

Effects of melatonin on adrenomedullary dopamine-beta-hydroxylase activity in golden hamsters: evidence for pineal and dose dependencies

Pineal influence in the control of adrenomedullary function in golden hamsters was investigated by examining changes in adrenal dopamine-beta-hydroxylase (DBH) activity following pinealectomy, either alone or in combination with melatonin administration. Adult males acclimated to an LD 14:10 photoperiod were distributed in five experimental groups: intact controls (NO), sham-pinealectomized (S), sham-pinealectomized with black plastic shielding of the pineal region, pinealectomized (PX), and pinealectomized with the operated region shielded. Animals representing all of these groups were injected (between L11 and L11.75) with either vehicle, or a low dose (25 micrograms) or a high dose (2,500 micrograms) of melatonin daily for 28 days, after which they were killed, and the adrenals were collected for assay of DBH activity by means of a sensitive radioenzymatic method. We found that PX + vehicle led to increased (P less than .05) adrenal DBH activity in comparison with either NO or S groups; daily 25 micrograms of melatonin resulted in lowered DBH activity in the NO group when compared with NO + vehicle (P less than .001) or S + vehicle (P less than .001) groups; PX + 25 micrograms melatonin reversed the action of 25 micrograms melatonin in the NO + 25 micrograms group; 2,500 micrograms melatonin was without effect on adrenal DBH in any of the injected surgical groups. These results show an inhibitory pineal influence on adrenal DBH activity, and that this was dose dependent.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of tumor cell growth by protein factors derived from the developing mouse brain

It was recently reported (Endoh et al. 1981, Exp Cell Biol 49:272-277) that conditioned medium of neonatal mouse brain (CM-NB) inhibited the growth of mouse neuroblastoma cells. In this work we fractionated CM-NB by size exclusion high performance liquid chromatography, and separated two active principles (28,000 and 62,000 daltons) Each or a combination of the 28,000 and 62,000 dalton fractions showed a differential inhibitory effect on DNA synthesis or clonal growth of the three human lung cell lines: the normal diploid fibroblast WI38 cells were less susceptible than their simian virus 40-transformed VA13 cells and carcinoma A549 cells. This preferential growth-inhibition of malignant cells was also observed for rat fibroblast 3Y1 and its simian virus 40-transformed W3Y cells, and for two other normal and five other malignant cell lines. The growth-inhibitory activity of CM-NB or the 28,000 and 62,000 dalton fractions was lost by pronase, trypsin, tetrahydrofuran, acetonitrile, or dithiothreitol in the presence of guanidine, and also labile to heat, vigorous agitation, or freeze-thawing. The activity was also found in the conditioned medium of prenatal mouse brain, but not in either the conditioned medium of the adult brain and of the secondary culture of the neonatal brain, or in the homogenate and rinsing fluid of the neonatal brain. Thus the mouse brain at the terminal stage of ontogenesis liberates proteinaceous factors, which exhibit a preferential growth-inhibition of tumor or transformed cells and act on malignant cells of human and rodent origin.

Increases in volume, fluid content, and lens weight of eyes following systemic administration of melatonin

Melatonin's effects were studied in male golden hamsters (Mesocricetus auratus) distributed among five surgical groups (nonoperated, sham-pinealectomized, sham-pinealectomized plus black plastic shielding of the pineal region, pinealectomized, and pinealectomized plus black plastic shielding of the pineal region) and three injection groups (vehicle only, 25 micrograms melatonin, and 2,500 micrograms melatonin). Injections (s.c.) were daily for 28 d at L11 to L11.75 in a (light:dark) L:D 14:10 artificial photoperiod. Animals (N = 112) were killed and dissected on the day after the last injection (at 55-65 d of age). None of the surgical procedures affected weights of eyes or their parts, nor did they influence the effects of administered melatonin on the eyes. Melatonin caused an increase in absolute and relative eye weight and an increase in fluid content of intraocular space. The magnitudes of these effects were positively related to melatonin dose. These same eyes had a progressively lower weight of nonlenticular tissues with low to high doses of melatonin, probably in relation to greater fluid content, and suspected increase in intraocular pressure. Lens wet and dry weights were significantly greater in animals receiving melatonin, but only at the high dose. These actions of melatonin are likely to be direct and are shown to not require the presence of the pineal. Experiments of other designs are suggested in order to determine whether the effects of the low, near physiological, dose of melatonin represent physiological actions of endogenous melatonin, synthesized and released within the eye. However, effects of large doses of melatonin on the eye are still noteworthy in relation to interpretation of experiments employing such dosages, and of disease states involving changes in intraocular pressure.

Effects of melatonin and control injections on pineal serotonin and norepinephrine: afternoon injections lower serotonin levels thirty-six percent at light-dark transition

Pineal weight and serotonin (5-HT) and norepinephrine (NE) contents were studied in male Sprague-Dawley rats that were maintained under controlled light:dark conditions (LD 14:10; lights on 0700-2100) and that received daily subcutaneous injections of either melatonin (20 micrograms in 0.1 ml per animal) or the same volume (0.1 ml) of vehicle alone, at one of two times (0800-0900 or 1800-1900). Animals were sacrificied at four times (1000, 1400, 2000, or 2300) on the day after the last of the 7 consecutive d of injection. Pineal glands were quickly weighed and then frozen for 5-HT and NE assay by the Maickel and Miller extraction and fluorescence methods. Pineal NE content showed differences related to time of day, in confirmation of early work. But no effects attributable specifically to melatonin were found. Melatonin also failed to affect pineal 5-HT content significantly. But injection of either melatonin or vehicle at 1800-1900 led to a reduction in 5-HT content averaging 36% when sampled at either 2000 or 2300, and in comparison with animals injected at 0800-0900. It is suggested that a stresslike or zeitgeberlike effect of injections within a critical period at the end of the daily light phase can cause an earlier-than-normal daily fall in pineal 5-HT content.

Stimulatory effects of melatonin on ependymal epithelium of choroid plexuses in golden hamsters

Ependymal epithelial cells from the choroid plexuses (CPs) separately of lateral (I + II), IIIrd and IVth ventricles of male Golden Hamsters were studied by electron microscopy and morphometry. The 16 hamsters were distributed between three injections groups: vehicle only, 25 micrograms and 2500 micrograms melatonin (M) by subcutaneous injection daily at L11 to L11.75 in a LD 14:10 daily photoperiod. After 28 consecutive daily injections, animals were killed and the CPs were dissected, fixed and prepared for electronmicroscopy. Thirteen measures of the CP ependymal cells were made, by planimetry, morphometry or direct counting or linear measurement on the EM prints. Effects of melatonin occurred only on the cells from the lateral ventricles. Here M at high dosage caused cell swelling (averaging 50% increase in area), and other cellular changes were graded in relation to M dosage. These were increased (to 26%) in mitochondrial area per cell, and increased (to 50%) in length of apical microvilli. Since in other work the latter form a major locus of ouabain-sensitive Na+, K+-ATPase, it is suggested that M may possibly have a stimulatory effects on transport and related CSF secretory activities by these cells.