N. Hirschmann

Diurnal Rhythms of Pineal Nucleic Acids and Protein

A diurnal rhythm in pineal protein was found to occur in mature rats. In the male, a peak level is reached about 4 p.m., preceded by a gradual increase during the period of light and followed by a dec

The effect of heat on rat pineal hydroxyindole-O-methyl transferase activity

Exposure of adult male rats to continuously elevated temperature of 32–34°C caused a significant decrease of HIOMT activity involved in the specific metabolic process of production of melatonin, considered an active pineal hormone. The effect was already evident after 24 h exposure and increased further during the next 48 h. The results obtained substantiate previous data that the pineal gland may be involved in the system regulating adaptation to extreme temperature changes.

The effect of 17 β-estradiol on pineal metabolism

Abstract A single injection of 10 μg 17β-estradiol was administered subcutaneously to immature female rats aged 21 and 31 days and the pineal RNA, DNA and protein levels were measured 15, 18 and 24 hours after injection. An increase in the protein content of the pineal occurred 24 hours after injection, accompanied by a prior elevation in pineal RNA and DNA, indicating accelerated protein metabolism. No change were found in either the pineal nucleic acids or protein of immature female rats that received seven daily injections of 5μg 17β-estradiol/rat. The suggestion is put forward that the intensified pineal protein synthesis is caused by increased LH secretion.

The effect of light and darkness on nucleic acids and proteiin metabolism of the pineal gland

Abstract Exposure of female rats to continuous light from the day of weaning — 21st day of age — for ten, twenty and thirty days caused a significant inhibition in their pineal RNA and protein synthesis, amounting to 20 per cent compared with control animals kept in conditions of alternating light and darkness. The main inhibition occurred within the first ten days of exposure, coinciding with the period of most active physiological production of nucleotides and proteins. No change was found in the pineal DNA levels of the rats exposed to continuous light, indicating that the reduced RNA and protein results from a decreased cellular metabolism unrelated to physiological cell multiplication. This would imply an inhibition of parenchymal hypertrophy of the pineal under conditions of continuous light. The three parameters tested were the same in rats exposed to continuous darkness and animals kept under an alternating diurnal light-dark cycle.

The effect of pinealectomy on rat plasma corticosterone levels under various conditions of light

Abstract The interrelationship between the pineal gland and adrenal cortex and possible role light may be playing in this connection has been studied by subjecting pinealectomized and control maturing female rats to constant light, constant darkness or an alternate light-dark schedule and then measuring their blood corticosterone levels. Elevated plasma corticosterone levels could be seen in pinealectomized animals maintained for 10 days in alternating light and constant darkness. However, only in the light-deprived rats did the increase reach significant proportions. Thirty days after pinealectomy no disparity existed between the various groups. These data indicate that the pineal gland exerts an inhibitory effect on adrenocortical function especially in rats kept in darkness. Light was found to affect the pituitary-adrenal axis by stimulating corticosterone secretion, but this was not dependent upon presence of the pineal. Pinealectomy combined with continuous light had no additive effect, the same degree of increase in plasma corticosterone being produced by each factor alone or the two together.

Pineal N-acetyltransferase depression in rats exposed to heat.

Exposure of adult male rats to increased temperature of 33±1°C for 3 and 10 days brought about decreases in pineal N-acetyltransferase activity. These and previous findings of pineal HIOMT inhibition under similar conditions support the postulation of a possible thermoregulatory role for the pineal gland.

Pineal gland changes of rats exposed to heat

Ratten, die 20 oder mehr Tage bei 33°C gehalten werden, weisen — absolut gemessen — erniedrigten RNS- und Gesamtprotein-Gehalt der Pineals auf, während DNS und Drüsengewicht konstant bleiben. Da die Tiere durch die Hitzeexplosion an Gewicht verlieren, wird der RNS- und Proteingehalt-Abfall pro Körpergewicht nicht wahrnehmbar.

Pinealectomy-Induced Changes in Blood and Pituitary Luteinizing Hormone and Prolactin Levels During the Last Phase of Pregnancy in Rats

Serum LH levels were higher in pinealectomized than in sham-operated control rats during all 4 of the last days of pregnancy studied, although reaching significance only during the final 2 days, 21 and 22. Prolactin (Prl) levels in the serum on the final day of pregnancy, and its contents in the pituitary throughout the entire study period, were significantly lower in pinealectomized rats. Pituitary weights were lower in pinealectomized than in control animals during days 21 and 22 of pregnancy, but no differences were found between the 2 groups in the average number of living foetuses and resorptions. The results presented would seem to indicate that during the last phase of pregnancy the pineal gland plays a role in the modification of gonadotropin synthesis and release. It appears that with LH the release, and with Prl mainly the synthesis, is being affected by the pineal, although the release of Prl may be influenced as well.

Inversion of Pineal N-Acetyltransferase Rhythm by Reversed Environmental Lighting

By reversing the regimen of environmental lighting a complete inversion of the diurnal rhythm of pineal N-acetyltransferase was brought about. The nocturnal rise of N-acetyltransferase was rapidly reversed by light, yet the diurnal fall of the enzyme was not affected by darkness. Three days’ exposure of the rats to the reversed light regimen was necessary before a 180° inversion was achieved, producing a 10- to 12-fold increase in day-time (dark period) levels of the enzyme. However, after two days a 3-fold increase in the enzyme was already evident in relation to values of control rats kept on a normal lighting regimen. It is concluded that N-acetyltransferase activity and consequently serotonin and melatonin levels of the pineal, although regulated by an endogenous mechanism in the central nervous system, can be shifted by changes in environmental light which may be synchronizing the endogenous rhythms.

A thin-layer chromatographic assay for measuring pineal hydroxyindole-O-methyltransferase activity.

A thin-layer chromatographic procedure for measuring pineal HIOMT activity is described, based on the methylation of NAS to melationin. The method enalbes simple and accurate determination in small alipuots from a single pineal organ homogenate.