Pineal N-acetyltransferase Research Articles

Regulation of sensitivity to beta-adrenergic stimulation in induction of pineal N-acetyltransferase.

Stimulation by isoproterenol causes large increases in the activity of rat pineal N-acetyltransferase (arylamine acetyltransferase or acetyl-CoA:arylamine N-acetyltransferase, EC 2.3.1.5) after a variable lag period. Lengthening periods of exposure to light cause rapid increases in the sensitivity of pineal N-acetyltransferase to induction by isoproterenol. This supersensitivity, which develops gradually over a 12 hr period, is correlated with increasingly longer lag periods in the induction of the enzyme, and with progressively greater maximal response. Repeated administration of isoproterenol to supersensitive animals rapidly reverses the above changes and causes relative subsensitivity. The sensitivity of N-acetyltransferase to induction by dibutyryl-cyclic tamp added to pineals in organ culture was found to change in parallel with the sensitivity to isoproterenol. Stimulation of cyclic AMP levels in the pineal by isoproterenol was also greater in supersensitive rats than in the subsensitive animals, whether the supersensitivity had been caused by denervation or by exposure to light for 12 hr. The above experiments suggest that there are two sites for the regulation of the sensitivity of N-acetyltransferase to induction by catecholamines. The first site regulates the capacity of intracellular processes (i.e., induction of tn-acetyltransferase) to respond to cyclic AMP as a second messenger.

Regulation of pineal rhythms in chickens: refractory period and nonvisual light perception.

Pineal serotonin N-acetyltransferase activity and melatonin content exhibit marked daily rhythms in chickens; peak values occur during the period of low locomotor activity which coincides with dark in a 24-h light-dark regime. We studied the regulation of these daily rhythms by measuring pineal serotonin N-acetyltransferase activity, hydroxyindole-O-methyltransferase (HIOMT) activity, and melatonin content in experiments in which birds were exposed to light-to-dark and dark-to-light transitions at atypical times. We observed that there is a refractory period for dark-initiation of the increase in pineal N-acetyltransferase activity and melatonin content. We also learned that a dark-to-light transition causes a rapid decrease in dark-elevated pineal N-acetyltransferase activity and melatonin content. The rapid decrease occurs in blinded chickens as well as sighted ones. HIOMT activity did not change consistently in any of the experimental treatments.

Pineal N-acetyltransferase in chickens: Rhythm persists in constant darkness

The daily rhythm in an enzyme, pineal serotonin N-acetyltransferase activity was studied in chickens kept in conditions of constant dark. The rhythm persisted and had a period length of approximately 24 hours which are characteristics of truly circadian rhythms. The detailed documentation of the rhythm (Fig. 1) shows the shape of the oscillation and clear anticipation of the time of lights on. Both the rise and fall of the rhythm occur without stimulation by light or dark.

Isoprotenerol induction of pineal serotonin N-acetyltransferase in normotensive and spontaneously hypertensive rats.

Verabreichung von Isoprotenerol, eines β-adrenergen Agonisten, induziert einen signifikant hoheren Anstieg der Aktivitat der Serotonin-N-Acetyltransferase in der Epiphyse von spontan hypertensiven, im Vergleich mit normotensiven, Rattenmannchen. Derselbe Unterschied wurde auch bei Weibchen beobachtet, jedoch liegen die Aktivitatswerte bei spontan hypertensiven Mannchen allgemein hoher. Die durch Isoprotenerol erhohte Induktion der Serotonin-N-Acetyltransferase erzeugt hinsichtlich der Catecholamine in den Pinealozyten von spontan hypertensiven Ratten eine veranderte Reaktivitat der Achse β-Rezeptor-Adenylzyklasesystem-Serotonin-N-Acetyl transferase.

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.

Dark induced increase in pineal serotonin N-acetyltransferase activity: a refractory period.

Nachweis, dass Ratten, aus normaler Lichtperiode abrupt in Dunkelheit versetzt, keine Zunahme der NATase-Aktivitat im Pinealorgan zeigen und dass Isoproterenol-Injektion die Zunahme der NATase auslost.

Effects of light and temperature on the pineal gland in suckling rats.

Enucleated and enucleated+Harderianectomized (E+H) 12-day-old rats were exposed to an additional 5 h of light or placed in the dark at 17.00. Body temperatures were lower in both groups in the dark in comparison to rats with comparable treatments in the light. These results suggest that removal of the Harderian gland does not alter the animal’s response to environmental temperature. Intact, suckling animals were placed in the dark at 7, 22, and 34°C for 4 h or left with their mother. Pineal N-acetyltransferase was significantly higher in the group at 22 °C than in any other group, suggesting that the activity of this enzyme is influenced by environmental temperature in suckling rats. Pineal serotonin (5-HT) shows little change under these conditions. However, if rats at these temperatures also are exposed to overhead lighting, dramatic increases occur in pineal 5-HT at both 22 and 34 °C. N-acetyltransferase levels are significantly lowered at 34°C only; pineal HIOMT does not change. These findings are compatible with the hypothesis that light and temperature both regulate pineal function in the suckling rat, probably by different mechanisms. The diurnal variation in pineal 5-HT in 12-day-old E+H rats is abolished by constant light for 3 days but not by constant dark. This pattern is similar to that found in intact adults in constant light or constant dark.

Pineal N-acetyltransferase activity in blinded and anosmic male rats.

The pineal N-acetyltransferase activity in normal, blinded, anosmic, and anosmicblinded male rats has been examined 10 weeks after surgery at 4 times of the day. In normal animals, the values are about 2700 during the night and 100 during the day. Anosmia does not alter this rhythm. In blinded and blinded-anosmic animals, enzyme activity is not synchronized with time of day. During the 24-hr sampling period, 40% of the blinded and blinded-anosmic animals have enzyme values greater than 2000 units, and 45% have values less than 100 units. Blinded animals are known to have a synchronized diurnal rhythm in N-acetyltransferase 6 days after blinding. Thus it appears quite possible that, 10 weeks after surgery, the rhythm in blinded individual animals has become asynchronous relative to the rhythm in other blinded animals. (Endocrinology89: 1020, 1971)

Observations on the pineal gland, the Harderian glands, the retina, and the reproductive organs of adult female rats exposed to continuous light.

SUMMARY Harderian gland removal caused enlargement of the uteri of adult female albino rats which were maintained in 14 h light and 10 h darkness/day. Constant light exposure led to regression of the ovaries, adrenal glands and Harderian glands while the uteri exhibited a significant hypertrophic response. None of these changes were affected by surgical removal of the Harderian glands. The eyes and the retinas of albino rats maintained under continuous illumination underwent atrophic changes with the receptor cell elements of the retinas completely disappearing within 9½ weeks. Constant light obliterated the diurnal rhythm in the pineal enzyme, N-acetyltransferase. Neither the activity of pineal hydroxyindole-O-methyl-transferase nor the activity of pineal N-acetyltransferase were influenced by removal of the Harderian glands.

Pineal N-acetyltransferase activity: effect of sympathetic stimulation.

Stimulation of preganglionic sympathetic fibers to the superior cervical ganglia elevates the activity of pineal N-acetyltransferase. After the stimulation-induced rise in enzyme activity, a return toward baseline levels occurs whether or not nerve stimulation is continued. The ability of pineal N-acetyltransferase activity to fall in the presence of stimulation may account for the persistence of its rhythm in blinded animals.