Darkness-Elicited Changes in Rat Reproduction Not Mediated by Pineal Gland

Nir, I.; Hirschmann, N.

doi:10.1159/000179529

Cited by 3 publications

(2 citation statements)

References 7 publications

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“…Under normal conditions, birth is rarely observed during darkness (Bosc, 1981) when melatonin is secreted (Ozaki et ai, 1976;Wilkinsons ai, 1977;Adler et ai, 1979;Illnerova& Vanêcék, 1980;Ho et ai, 1984). In our experiments, no toxic effects have been noted for the dams and their litters as has been reported for melatonin implants in rats (Tigghelaar & Nalbandov, 1975;Nir & Hirschmann, 1982). With melatonin implants, which gave a constant release of the hormone (Murakami et ai, 1983), a significant reduction in length of gestation has been observed (Nir & Hirschmann, 1980), as found here but to a lesser extent in rats in Groups M and FM compared with those in Groups V and FV.…”

Section: Discussionsupporting

confidence: 81%

Time of parturition in rats after melatonin administration or change of photoperiod

Mj¹

1987

Reproduction

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Two experiments were carried out with rats isolated at mating (Day 1 of gestation) and kept in a standard light regimen of 14 h light (14L:10D). All treatments started on Day 8 of gestation; periodicities of 23:45 h, 24:00 h and 24:15 h were applied to the light phase (14L) in Exp. I and to daily treatment with melatonin (0.3 mg/rat) or its vehicle in Exp. II. In Exp. II, the animals were placed in a continuous dim light regimen and injections were given at a time corresponding to lights off. In all groups, rats delivered on the afternoon of Day 22 and on the morning of Day 23 after a cessation of parturitions. The rates of births during these two times depended on the periodicities of the light phase or those of melatonin administration. With a periodicity of 24:15 h, 85.7% of rats in Exp. I and 85.7% of rats in Exp. II delivered on Day 22. With a periodicity of 23:45 h, 83.0% of births occurred on Day 23 in Exp. I and 57.7% in Exp. II with melatonin instead of 25.9% in the corresponding vehicle controls. These results suggest that melatonin secretion may be a mechanism whereby photoperiod regulates the time of parturition in the rat.

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Section: Discussionsupporting

confidence: 81%

Time of parturition in rats after melatonin administration or change of photoperiod

Mj¹

1987

Reproduction

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“…By contrast, under an increased level of estrogen and a decreased level of progesterone on the 22nd day of pregnancy the serum PRL level must be decreased by pinealectomy, since pineal removal eliminates the PRL releasing mechanism activated by increased estrogen. Indeed, Nir and Hirschmann (1982) have indicated that pinealectomy significantly decreased serum PRL levels on the 22nd day of rat pregnancy but had an insignificant effect on the 21st day. These changes of the estrogen and progesterone concentrations during this period seem to adequately explain the different influences of pinealectomy on PRL secretion.…”

Section: Discussionmentioning

confidence: 99%

Possible role of the pineal gland in pituitary prolactin secretion in female rats.

Minato¹,

Takahashi

Ikeno

et al. 1984

Tohoku J. Exp. Med.

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Wistar female rats housed under conditions of 12 hr dark/12 hr light were pinealectomized (PX) or underwent sham-operation (SO) 21 days after ovariectomy, on the 7th or on the 15-17 th day of pregnancy. Serum and pituitary prolactin (PRL) levels in ovariectomized (OVX) rats were determined 9 days after pinealectomy. In the case of OVX rats receiving estrogen and progesterone injections (OVX-EP), PRL levels were determined 48 hr after injection administered 7 day after pinealectomy. PRL levels in pregnant rats were determined on the 20th day of pregnancy and in postpartum rats, on the 3rd day following parturition. As compared with the SO control, pinealectomy resulted in a significant decrease in the serum PRL level in the OVX-EP rats but in a significant increase in that level in the OVX, pregnant and postpartum rats. In OVX-EP rats, exogenous estrogen raised the serum PRL level less in PX than in SO rats, probably because the pineal gland is closely related to the facilitation of PRL secretion by estrogen. The high estrogen level in OVX-EP rats seemed to trigger pineal stimulation of PRL release, but low estrogen levels in OVX and postpartum rats or markedly high levels of progesterone in pregnant rats on the 20th day are thought to cause pineal inhibition.prolactin ; pineal gland ; estrogen ; progesterone There have been no uniform conclusions about the role of the pineal gland in pituitary prolactin (PRL) secretion in the rat, because different experimental conditions have resulted in either inhibition or facilitation of PRL release by the pineal gland. We have previously studied the change in PRL secretion after pineal removal and administration of pineal bioactive substances, such as melatonin, serotonin and arginine vasotocin (AVT) and have demonstrated that antagonistic mechanisms of the pineal gland which affect pituitary PRL secretion

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Morphological and biochemical changes in the pineal gland in pregnancy

Lew¹

1987

Life Sciences

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Darkness-Elicited Changes in Rat Reproduction Not Mediated by Pineal Gland

Cited by 3 publications

References 7 publications

Time of parturition in rats after melatonin administration or change of photoperiod

Time of parturition in rats after melatonin administration or change of photoperiod

Possible role of the pineal gland in pituitary prolactin secretion in female rats.

Morphological and biochemical changes in the pineal gland in pregnancy

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