Inhibition of compensatory ovarian hypertrophy in the mouse and vole: a comparison of Altschule's pineal extract, pineal indoles, vasopressin, and oxytocin

Melatonin influences on steroidogenic gene expression in the ovary of pinealectomized rats

OBJECTIVE

To analyze the expression of genes related to steroidogenesis in the ovary of pinealectomized rats.

DESIGN

Experimental research.

SETTING

University research laboratory.

ANIMAL(S)

Thirty female adult rats.

INTERVENTION(S)

Administration of vehicle (GI), pinealectomy with vehicle (GII), or pinealectomy with melatonin replacement (10 μg/night) for 60 consecutive days (GIII), then euthanasia after 2 months of treatment, ovary collection complementary DNA microarray analyses, confirmatory quantitative reverse-transcriptase polymerase chain reaction analyses, and immunohistochemical analyses for localizing steroidogenesis changes in the ovary.

MAIN OUTCOME MEASURE(S)

Biologic molecular study followed by immunohistochemical analysis.

RESULT(S)

The changes in the expression of CYP11A1, CYP17A1, and CYP19A1 after pinealectomy (GII) compared with control (GI) showed the Cyp17a1 expression level increased in the theca interna and interstitial cells in the GII rats compared with the other groups.

CONCLUSION(S)

Melatonin deprivation (pinealectomy) or administration may influence the ovarian CYP17A1 expression and steroidogenesis.

Physiological and pharmacological properties of 5-methoxytryptophol

5-methoxytryptophol (5-ML) is a pineal indoleamine derived from serotonin shown to be biologically active in a number of species. This indolamine exhibits a circadian pattern synchronized with the day-night cycle with significant increases during daylight, already recognized in vertebrates. The multiplicity of physiological and endocrine functions of 5-ML is remarkable; it is involved in circadian rhythms, reproduction and sexual processes. Furthermore, a number of pharmacological benefits of 5-ML have been reported, including immunomodulatory, antitumor and antioxidative activities. However, the molecular mechanisms of these pharmacological effects remain unclear. The purpose of this article is to provide an overview on the general properties and physiological functions of 5-ML. An attempt has been made to fully document all studies performed using 5-ML. In addition, this article aims to gain insight into the current state of knowledge regarding pharmacological and therapeutic effects of this indoleamine.

Effects of Photoperiod, Melatonin, and the Pineal Gland on Compensatory Gonadal Hypertrophy during Postnatal Development in the Marsh Rice Rat (Oryzomypalustris)

The roles of photoperiod, melatonin, and the pineal gland in regulating the magnitude of compensatory gonadal hypertrophy (CGH) and other reproductive and non-reproductive organ growth during post-weaning development were examined in the marsh rice rat Oryzomys palustris. Juvenile rice rats of both sexes were left gonadally intact (control group) or unilaterally castrated (ULC) and housed on 12L:12D, 14L:10D, or 16L:8D. Within a photoperiod (14L:10D and 16L:8D, but not 12L:12D), growth of the remaining testis, but not the remaining ovary, as well as several additional organs in both sexes were significantly affected, suggesting that the compensatory hypertrophy of the testis is photoperiod-dependent. There was no effect of testis asymmetry on CGH as ULC of either testis in rice rats housed on 14L:10D resulted in a comparable increase of CGH. Melatonin implants in rice rats maintained on 16L:8D had little to no effect (CGH included) on most parameters examined. Both melatonin implants and pinealectomy (separate experiments) in rice rats transferred to 12L:12D prevented short photoperiod-induced effects on CGH, the growth of the reproductive organs and the Harderian glands. Evening melatonin injections had a significant inhibitory effect on the growth of the remaining testis (no CGH was observed) and all other parameters measured. Lastly, ULC did not alter the percentage of males which successfully mated compared to intact animals. Taken together, these data suggest that photoperiod, melatonin, and the pineal gland can affect and regulate reproductive (e.g., CGH in some cases) and non-reproductive growth during postnatal development in the marsh rice rat.

Mode of action of inhibin-like pineal antigonadotropin is different from melatonin during compensatory ovarian hypertrophy

Both melatonin and pineal antigonadotropic peptides have the same end effect, i.e., prevention of the hypertrophic response when tested in the conventional compensatory ovarian hypertrophy (COH) model. The present work was undertaken to study the effect of melatonin and a melatonin- and steroid-free inhibin-like ovine pineal antigonadotropin (PI) on serum follicle stimulating hormone (FSH), luteinizing hormone (LH), and prolactin (PRL) following hemoiovariectomy in adult Holtzman rats and also to ascertain if any similarity exists in their mode of action during COH. While melatonin prevented the transient rise in FSH at 12 hr after unilateral ovariectomy (ULO), thus retaining the basal preoperative level, PI depressed basal levels of FSH too. In addition, melatonin suppressed PRL and LH levels at 12 hr and 120 hr after ULO, respectively. PI, on the other hand, had no effect on serum LH and PRL levels. In light of our earlier in vitro results, which showed a direct inhibitory effect of PI and not of melatonin on pituitary FSH synthesis and release, the present results indicate a dichotomy in the mode of action of PI and melatonin. PI acts directly at the level of the pituitary while melatonin may act at the level of the hypothalamus or higher brain centers to suppress the FSH surge and the ensuing compensatory response.

Effects of pinealectomy and melatonin administration on certain indices of ovarian hyperplasia and/or hypertrophy in rats with both ovaries intact or after unilateral ovariectomy

In earlier studies from other laboratories it was shown that melatonin decreased ovarian weight in rats and inhibited compensatory hypertrophy of the remaining ovary after unilateral ovariectomy. This study was designed to examine the influence of melatonin on certain indices of ovarian hyperplasia and/or hypertrophy in adult female rats with both ovaries preserved and with either an intact pineal gland or with the pineal gland removed (pinealectomy, PX) or, finally, in sham-PX animals. Similar studies were conducted on rats after unilateral ovariectomy, referring the examined parameters to the remaining intact ovary. The studies included mitotic activity of granulosa layer cells and corpus luteum cells, ovarian weight, ovarian cross-sectional area, cross-sectional area of the granulosa layer of all the Graafian follicles and the cross-sectional areas of the corpora lutea, visible on the ovarian cross-section. On the basis of results, we conclude that: 1) the effect of PX on the processes of ovarian hyperplasia and hypertrophy may vary; analogously, exogenous melatonin administration may influence ovarian hyperplasia and hypertrophy in different ways; 2) PX and exogenous melatonin may, under certain conditions, exert similar biological effects, even synergistic effects; 3) melatonin inhibits ovarian growth processes, while the effects of PX are variable; 4) the results indicate that in experiments performed on rats, with the use of two control groups, i.e., intact and sham-PX, melatonin effects on these two groups may differ.

Effect of a pineal indolamine, 5-methoxyindole-3-acetic acid, on the estrous cycle and reproductive organs of female Wistar albino rats

It has been suggested that the pineal gland has a specific role in the control of cyclic sexual activity in rats. One or more of the compounds isolated from this gland have been considered to be possible anti-fertility agents. In this study, the effect of different doses of 5-methoxyindole-3-acetic acid (5-MIAA) on the estrous cycle and the reproductive organs of female rats was studied. Daily injections of either 100 or 200 micrograms of 5-MIAA significantly prolonged the estrous cycles of mature female rats. After injections of 5-MIAA, an increase in diestrous smears was observed; in addition, the animals had estrous cycles without proestrous phase. Following the injections of 200 micrograms of 5-MIAA, a significant increase in uterine weight, plasma 17 beta-estradiol level and in the number of follicles were observed, and after injections of 5-MIAA (50, 100, 200 micrograms) a medium level of plasma progesterone was obtained. Thus it is concluded that 5-MIAA has an effect on the ovulation process of female rats.

N-acetyltransferase activity and indole contents of the male Syrian hamster Harderian gland: changes during the light:dark cycle

The activities of N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase (HIOMT) and the indole contents of the Harderian glands of male Syrian hamsters were studied throughout a 24-h period. NAT activity exhibited a sharp rise 1 h after lights on, decreasing to basal levels 1 h later. Neither a HIOMT activity nor a melatonin concentration rhythm was detected throughout the 24 h. The 5-hydroxytryptamine (serotonin) concentration was highest during the dark phase reaching a peak at 0300 h; with light onset serotonin levels exhibited a rapid short-term drop. The 5-hydroxytryptophol concentration was highest during the mid- to late photophase; the lowest values to this constituent were measured late in the dark phase and at 1 h after lights on. The 5-hydroxyindole acetic acid concentration of the Harderian glands was rather stable throughout the 24-h period but levels did show a short-lived drop 1 h after light onset. Only a few animals contained detectable amounts of N-acetyl-5-hydroxytryptamine (N-acetylserotonin) in their Harderian glands. In agreement with previous work on the Harderian glands of female Syrian hamsters, the present results in males suggest that light onset is associated with marked changes in Harderian indoleamine metabolism.

Effects of afternoon injections of O-acetyl-5-methoxytryptophol, melatonin or 5-methoxytryptophol in female Syrian hamsters

Female Syrian hamsters were maintained in a 14:10 light: dark photoperiod (lights on 6 a.m.) and injected each afternoon between 4 p.m. and 6 p.m. with diluent or with 25 micrograms melatonin, O-acetyl-5-methoxytryptophol (aML) or 5-methoxytryptophol (ML). After 7 or 12 weeks of treatment, only the melatonin-treated hamsters were acyclic. Gross inspection of their ovaries revealed that they were smooth, brown, and devoid of corpora lutea and large follicles. Progesterone levels of the acyclic animals were midway between the high levels observed during estrus and postestrus and the low levels observed on cycle days 2 and 3. Additionally, the melatonin-treated hamsters had significantly reduced uterine weights and pituitary and plasma levels of prolactin. Hamsters treated with aML had significantly lower pituitary prolactin and plasma and pituitary levels of LH only at the 7 week timepoint. ML-treated hamsters had lower pituitary prolactin levels also at 7 weeks. The endocrine changes wrought by injections of aML and ML, however, were insufficient to ultimately affect vaginal cyclicity. In conclusion, it would appear that at the dose used and the time administered melatonin is the more active of the indoles tested in the female hamster, at least in terms of alterations in reproductive physiology.

Natural and synthetic analogues of melatonin and related compounds. I. Effects on the reproductive system of the male Syrian hamster

The potential antigonadotrophic properties of a number of synthetic and natural melatonin analogues were examined. Adult male hamsters received daily subcutaneous injections (25 micrograms/animal/day) each afternoon for 7 or 10 weeks. The only analogue to possess antigonadotrophic activity similar to melatonin wa 6-chloromelatonin; melatonin and 6-chloromelatonin produced a significant reduction in both testicular and accessory sex organ weights, plasma LH and pituitary prolactin. These results suggest that, in the Syrian hamster, 6-chloromelatonin acts as a melatonin agonist and may be of use to elucidate further the physiological role of melatonin.

Influence of pinealectomy on circadian patterns of plasma luteinizing hormone, follicle-stimulating hormone, testosterone and dihydrotestosterone in the male rat

The effect of pinealectomy on the circadian periodicity in plasma gonadotropins (LH and FSH), testosterone (T) and dihydrotestosterone (DHT) was investigated in adult male rats maintained under conditions of 12 h light/12 h dark (light on 06:00-18:00 h). Animals were killed at 3 hour intervals over 24 hours by decapitation. Plasma concentrations of LH, T and DTH (but not FSH) were found to exhibit significant circadian variations as determined by analysis of variance. No distinct LH or T nadir was recorded but peaks were observed at 09:00 h. Peak DHT values were recorded near the middle of the dark period. Pinealectomy resulted in an altered daily LH and T rhythmicity, and also in an abolished DHT rhythmicity. The fact that there was no significant increase in mean gonadotropin levels at 50 days after pinealectomy suggests that the pineal regulates the timing of gonadotropin secretion rather than the quantity. Since pinealectomy was found to abolish the circadian rhythm of DHT but not of T, we deduced that the pineal may also be responsible for the rhythmic conversion of T to DHT.

A radioimmunoassay for N-acetylserotonin in biological tissues

We have developed a specific radioimmunoassay for N-acetylserotonin. Cross-reactivity of 23 related or selected compounds is less than 1 percent; sensitivity is 10 to 25 picograms per tube; within assay coefficient of variation is 7.5 to 8.4%; and between assay coefficient of variation is from 7.1 to 11.1%. Satisfactory parallelism has been demonstrated for rat, hamster and rabbit serum, rat and hamster serum extract and rat brain retina and pineal extract. An extracted sample of rat serum gave one peak on HPLC which corresponded to authentic N-acetylserotonin. Daytime levels of N-acetylserotonin have been established for each of the tissues studied. This radioimmunoassay provides a sensitive and specific method for determination of N-acetylserotonin levels in biological tissues.

Enhancement of serum FSH levels after pinealectomy

The effect of pinealectomy on the circadian periodicity in serum gonadotropins was investigated in adult male rats. Pinealectomy resulted in an elevation of the serum FSH concentration 7 days after the operation. A 4-fold increase in serum FSH over 24 h with no concommitant increase in serum LH following pinealectomy suggests that the control of FSH secretion could be mediated via the pineal gland.

Neuroendocrine function in long-term pinealectomized male rats, following visual and audiogenic stress

Intact, sham-pinealectomized and pinealectomized adult male rats were maintained for 10 weeks on a light : dark (L : D) cycle of 12 : 12,with lights on at 6 a.m. Subsequently they were acutely exposed to (1) visual or (2) audiogenic stress for periods of 2 or 30 min, immediately following which they were decapitated and serum ACTH, corticosterone, FHS, LH, PRL and TSH concentrations were determined. Serum ACTH and corticosterone levels were similar in control and operated groups following both types of stresses. Serum FSH and LH concentrations were elevated in pinealectomized animals as compared to controls, following 30 min of exposure to visual stimulation; no difference in these parameters was observed between the groups following audiogenic stress. Serum PRL levels tended to be lower in pinealectomized animals following both stresses. Serum TSH concentrations following visual stimulation were similar in all groups, but audiogenic stimulation resulted in elevated TSH levels as compared to controls. These data demonstrate that the pineal gland plays an integral role in the responses of the parvicellular neuroendocrine axes to acute neurogenic stress. Possible molecular bases for this involvement are discussed.

Location by paper chromatography of compensatory ovarian hypertrophy (COH) inhibiting activity in acetic acid extracts from bovine pineals

Acetic acid extracts of bovine pineals and cerebral cortex were separated on Sephadex G-25 columns. Subsequently two low molecular weight fractions, F2 and F3, were ultrafiltered through the membranes UM2 and UM05. The UM05 residues were gel filtered on Sephadex G-15 columns or chromatographed on Dowex W50-X4 columns. Fractions from these columns were tested and those which showed COH-inhibiting activity were separated by preparative paper chromatography in different solvents. The absorption spectra of those fractions were recorded and tested for COH-inhibiting activity were separated by preparative paper chromatography in different solvents. The absorption spectra of those fractions were recorded and tested for COH-inhibition. By these methods, a COH-inhibitor was localized in three different solvents. Some active paper chromatography fractions were studied in high pressure, reverse phase, liquid chromatography. This latter method showed that the active fractions obtained by paper chromatography contain several orthophthlaldehyde (OPT) positive compounds. Key words: acetic acid, bovine pineal extracts, compensatory ovarian hypertrophy (COH), paper chromatography, high pressure, reverse phase, liquid chromatography.

Testing the TRH hypothesis of pineal function

In the Syrian hamster gonadal involution may be induced by exposure of the animal to darkness, short photoperiod, or blindness for several weeks. These conditions also influence body metabolism by inducing a substantial decrease in thyroxin concentrations. The role of the pineal gland in these phenomena has been demonstrated by experiments showing that if pinealectomized hamsters are subjected to darkness, short photoperiod, or blindness, their gonads do not involute and plasma thyroxin levels remain normal. Since thyrotrophin releasing hormone (TRH) causes the release of both prolactin and thyrotrophin from the pituitary we can predict on theoretical grounds that TRH mediates both pineal-gonad and pineal-thyroid phenomena. Melatonin may be the pineal hormone regulating hypothalamic TRH levels.

Influence of melatonin, constant light, or blinding on reproductive system of gerbils (Meriones unguiculatus)

Male and female gerbils were implanted s.c. with a pellet containing 2 mg melatonin/23 mg beeswax every 2 weeks for a total of 3 implants. A significant depression of ovarian and uterine weight was noted in female gerbils receiving melatonin implants. In the melatonin-treated male gerbils, growth of the accessory organs was significantly inhibited although testis size was not depressed.

Estrogen and progesterone secretion in monkeys (Macaca fascicularis) following melatonin or Altschule's pineal extrac

Large doses (30MG) of melatonin given weekly to crab-eating monkeys throughout five menstrual cycles did not change the pattern of estrogen and progesterone secretion during the period of injection or in the two succeeding cycles. Altschule's pineal extract, unlike melatonin, had no effect on estrogen or progesterone secretion during the period of injection or in the two succeeding cycles, when it was given daily between days 7 and 17 of the menstrual cycle.