Pineal Arginine Vasotocin Research Articles

Effects of sex and gonadal steroids on arginine vasotocin and mesotocin in the pineal gland and neurohypophysis of white leghorn fowls

1. Pineal and neurohypophysial arginine vasotocin (AVT) and mesotocin (MT) were measured in White Leghorn hens, cockerels and castrated males treated with either testosterone propionate (TP) or oestradiol benzoate (EB) (n = 10/group). The lighting regimen was 14 h light: 10 h dark, supplied by natural diffused sunlight and incandescent bulbs. 2. Both AVT and MT were detected in the pineal gland of all the chickens. 3. There was no significant effect of either sex or treatments on pineal MT. 4. Females had about 4 times more pineal AVT than males, regardless of their treatment. There was no effect of the treatments on pineal AVT in the males. 5. No sexual difference in neurohypophysial AVT was detected, but the neurohypophysis of the castrated males treated with EB contained less AVT than the neurohypophysis of the intact males. 6. Intact males had about twice as much MT in the neurohypophysis as females. Castrated males treated with either TP or EB had similar concentrations of neurohypophysial MT, which were lower than that of the intact males, but higher than that of the females.

Isolation and structure elucidation of bovine pineal arginine vasopressin: arginine vasotocin not identified

A large number of reports have demonstrated the presence of neurohypophysial hormone-like peptides in mammalian pineal glands and an antigonadotropic function has been ascribed to pineal arginine vasotocin (AVT). We have undertaken large scale purification of bovine pineal neurohypophysial hormone-like substances which demonstrate mouse mammary milk-ejection activity (ME-activity) in vitro. Peptides with ME-activity were extracted from more than 5 kg of bovine pineal glands. ME-activity containing peptides were found in both high (Mr approximately 10,000-15,000) and low (Mr approximately 500-1000) Mr species from Sephadex G-25 chromatography of 0.2 N acetic acid extracts. After ultrafiltration in 5% formic acid, the neurohypophysial hormone-like peptides were localized to an ultrafiltration Mr 500-1000 retentate. A homogeneous peptide, which shared an identical retention time (RT) and amino acid sequence with synthetic 8-arginine vasopressin (AVP), was isolated by serial semipreparative high performance liquid chromatography. On the other hand, the non-mammalian nonapeptide AVT was not identified.

Influence of Age on August Levels of Pineal Immunoreactive Arginine Vasotocin in Rats

The present study was undertaken to evaluate carefully the influence of age on physiological levels of arginine vasotocin-like peptide in rat pineal glands. Glands were collected from male and female rats aged 13, 33, 53, and 73 days on August 4, 12, and 19, 1984. Individual extracts were assayed for arginine vasotocin (AVT) by radioimmunoassay. The results confirm our previous observation that rat pineal AVT immunoactivity (iAVT) increases significantly during August each year; and in this study, each group of rats reached the same peak level of iAVT (700-750 pg/gland) regardless of age or gender. Thus we do not confirm a previously reported decrease in AVT activity with age. In our studies thus far, season of the year is the physiological variable with the most significant influence on pineal AVT activity levels.

A seasonal pineal peptide rhythm persists in superior cervical ganglionectomized rats

Neurohypophyseal peptide hormone activity is present in the pineal gland of mammals, and varies over a seasonal cycle. Pineal peptide levels, measured by arginine vasotocin (AVT) radioimmunoassay, increase dramatically for a brief time during August each year. The manner in which this cycle is regulated is as yet unknown. Input to the pineal from sympathetic axons arising in the superior cervical ganglia (SCG) is essential for the generation and regulation of the circadian rhythm in melatonin synthesis, and is the only pathway known to regulate pineal biochemical processes. It was of interest then to determine the impact of the SCG on the seasonal peptide cycle. Levels of pineal arginine vasotocin immunoactivity (iAVT) were monitored during August, 1984, in rats which had been superior cervical ganglionectomized (SCGX), in sham-operated and intact controls (L:D 12:12), and in rats subjected to L:D 22:2. The results indicate that SCGX does not abolish the seasonal cycle, but may influence the timing of the iAVT peak. Inhibition of pineal melatonin synthesis by exposure of rats to L:D 22:2 did not mimic the phase delay seen with SCGX, but did cause a significant increase in the amplitude of the August iAVT activity peak.

Pineal Ultrastructure and Indole Profiles Spanning the Summer Rise in Arginine Vasotocin Immunoactivity*

A correlative radioimmunological-biochemical-ultrastructural study of the rat pineal gland was undertaken during the summer months when pineal arginine vasotocin (AVT) immunoactivity increases up to 200-fold. RIA confirmed a rapid rise in AVT activity during mid-August regardless of the time of day sampled. Pineal indoles were separated by HPLC and measured using electrochemical detection. Serotonin (5-HT) and 5-hydroxyindoleacetic acid levels were consistently elevated in daytime samples, and there was a significant trend for increased day and nighttime levels of 5-HT from July to September. Mid-dark levels of melatonin also exhibited a significant increase over the sample period. Nighttime levels of N-acetylserotonin mirrored fluctuations in 5-HT in the preceding photoperiod. Ultrastructural components implicated in peptide/protein and/or indole biosynthesis were quantified by stereological morphometry. The greatest amounts of rough endoplasmic reticulum stacks, lipid droplets, and annulate lamellae-like bodies coincided with peak AVT activity. Dense-cored vesicles and synaptic ribbons were consistently more frequent during the dark period. The number of dense-cored vesicles and nucleolar size tended to be greatest before and after the peak in AVT immunoactivity. These observations are consistent with the hypotheses that endoplasmic reticulum and lipid are functionally related to the synthesis and/or storage of peptide/protein factors and that numerical changes in synaptic ribbons and dense-cored vesicles are more closely related to day/night differences in indole metabolism.

A Seasonal Variation in Arginine Vasotocin Immunoactivity in Rat Pineal Glands*

Groups of male and female laboratory rats, 28-30 days of age, were killed each week from July 1980 to September 1981. Pineal glands were collected, pooled, and extracted. Arginine vasotocin (AVT) activity in the extracts was measured by RIA. For most of the calendar year, pineal AVT immunoactivity ranged between 1.8-7.7 pg/gland. The average (+/- SE) basal AVT activity level was 4.1 +/- 0.3 pg/gland (n = 48). Both years in early August, pineal AVT activity increased several hundred fold. Values of 1720 and 1170 pg/gland were measured in mid-August of 2 successive years. The signal for this dramatic yearly rhythm, and its physiological consequences, are as yet unknown.

REM sleep suppression in cats by melatonin

The pineal indole melatonin, injected into the third ventricle of unanesthetized cats, induced NREM sleep within 11–15 min and suppressed REM sleep for about 3 hr. A dose-related effect could be established between 1, 10 and 100 ng melatonin. The reappearance of REM sleep at about 3 hr following melatonin administration occurred with a marked rebound. The present results further support the hypothesis that melatonin represents the releasing hormone for pineal arginine vasotocin.

Narcoleptic-like alterations of the sleep cycle in cats induced by a specific vasotocin antiserum

A specific arginine vasotocin (AVT) antiserum (10 μl) injected undiluted into the lateral ventricle of unanesthetized cats, induced sleep onset REM periods, markedly increased the number of REM periods, and dramatically decreased REM sleep latency. The amount of total REM sleep significantly increased and the amount of total NREM sleep significantly decreased. Neither a specific arginine vasopressin or oxytocin antiserum nor a normal rabbit serum injected undiluted into the lateral ventricle in the same volume (10 μl) was able to reproduce the effects of the AVT antiserum. It is concluded that pineal AVT is physiologically involved in the induction and/or circadian organization of REM sleep.

The pineal does not concentrate arginine vasotocin from biological fluids in vivo.

The ability of the pineal gland to concentrate circulating arginine vasotocin (AVT) from biological fluids in vivo was examined in rats. Intraventricular and intracisternal injections of AVT failed to elevate net pineal AVT content, even though CSF AVT levels were greatly increased by these treatments. Intravenous injection of AVT did elicit a light increase in pineal AVT, but plasma peptide levels wee elevated enormously. Thus, it seems unlikely that an active uptake process for AVT functions in this gland.

FURTHER EVIDENCE THAT MELATONIN REPRESENTS THE RELEASING HORMONE FOR PINEAL VASOTOCIN

SUMMARY As deduced from the antidiuretic and hydro-osmotic activities, intracarotid injection of 10 μg melatonin into urethane-anaesthetized cats significantly decreased the pineal argininevasotocin (AVT) content and increased its level in cerebrospinal fluid (CSF) between 5 and 60 min after the injection. No AVT was detectable in the plasma of cats between 5 and 60 min after the intracarotid injection of melatonin. However, between 60 and 90 min, when AVT disappeared from the CSF, a significant amount of AVT was detectable in plasma. The intracarotid injection of 10 μg serotonin was unable to induce the release of AVT into CSF or plasma, or to affect the pineal AVT content. Although intracarotid injection of 10 ng melatonin was unable to induce the release of AVT during the daylight hours, the same amount of melatonin was highly potent in inducing the release of AVT into the CSF during the night in the dark. The sensitivity of AVT to melatonin appears to be induced by darkness because the same amount (10 ng) of melatonin was ineffective when injected into animals maintained with the light on during the night. Since it was necessary to administer 5 μg melatonin during the hours of daylight to match the effects of 10 ng melatonin given at night, it appears that melatonin is about 500 times more potent in inducing AVT release during the night in the dark. The present results further consolidate the concept that melatonin represents the releasing hormone for pineal AVT and at the same time strongly suggest that AVT is first released into the CSF and reaches the blood only secondarily after its absorption from the CSF.

Pineal vasotocin: release into cat cerebrospinal fluid by melanocyte-stimulating hormone release-inhibiting factor.

The intracarotid injection of both synthetic melanocyte-stimulating hormone release-inhibiting factor (MIF) and purified MIF prepared from bovine hypothalami induces arginine vasotocin release into cerebrospinal fluid of cats and significantly decreases the pineal arginine vasotocin content at 5 minutes after the injection. The present results demonstrate an extrapituitary endocrine effect of synthetic and purified bovine MIF.

Pineal Vasotocin: Release into Cat Cerebrospinal Fluid by Melanocyte-Stimulating Hormone Release-Inhibiting Factor

The intracarotid injection of both synthetic melanocyte-stimulating hormone release-inhibiting factor (MIF) and purified MIF prepared from bovine hypothalami induces arginine vasotocin release into cerebrospinal fluid of cats and significantly decreases the pineal arginine vasotocin content at 5 minutes after the injection. The present results demonstrate an extrapituitary endocrine effect of synthetic and purified bovine MIF.

Slow-wave sleep induced in cats by extremely small amounts of synthetic and pineal vasotocin injected into the third ventricle of the brain

A single injection of 10 −6 pg synthetic arginine vasotocin (AVT), corresponding to about 600 molecules AVT, into the third ventricle of unanesthetized cats, induced slow-wave sleep 5 min after the injection. An equivalent amount, of a partially purified pineal AVT injected into the third ventricle, produced the same effects. After incubation with trypsin, pineal AVT completely lost its ability to induce slow-wave sleep. The slow-wave sleep induced by 10 −6 pg synthetic AVT injected intraventricularly could be matched by lμg synthetic AVT injected intraperitoneally. Neither synthetic arginine vasopressin, nor synthetic oxytocin, injected intraventricularly in the amount of 10 −6 pg, was able to induce slow-wave sleep. Whereas in the control animals injected with pineal AVT after incubation with trypsin, or in the control animals injected with vasopressin or oxytocin, the paradoxical sleep averaged 21.9–22.8% of the sleep time, during a total recording time of 5 hr, in the cats injected with synthetic or pineal AVT, the paradoxical sleep was completely suppressed.

Vasotocin content in the pineal gland of foetal, newborn and adult male rats.

Institute of Endocrinology, Bucharest, Rumania (Received 6 January 1975) We have reported (Pavel, 1971) that the foetal bovine pineal contains about 27 times more arginine-vasotocin (AVT) than adult pineals, as deduced from its hydro-osmotic activities, and we have suggested that pineal AVT is elaborated by secretory ependymal cells. More recently, Pavel, Dorcescu, Petrescu-Holban & Ghinea (1973) have demonstrated that pineal ependymal cells from human foetuses can synthesize an AVT-like peptide when cultured in vitro. Since it has been shown that pineal secretory ependymal cells markedly regress after birth (Palkovits, Gábor & Lukács, 1962; Anderson, 1965), we have investigated whether this regression is accompanied by a corresponding reduction in the pineal AVT content. Foetal (17–19 days post coitum), newborn (1–5 days post partum) and adult, male Wistar rats (each group comprised 30 animals) were used. The pineals, removed within 30 s of decapitation, were defatted in acetone for 24 h, homogenized