24-Hour Changes in Catecholamine Synthesis in Rat and Hamster Pineal Glands

Abstract

The purpose of this study was to examine the 24-hour variation in endogenous tyrosine hydroxylase (TH) activity and thus catecholamine (CA) synthesis in the hamster and rat pineal gland. To determine CA synthesis a time course of the accumulation of dihydroxyphenylalanine (DOPA) after DOPA decarboxylase inhibition with m-hydroxybenzylhydrazine (NSD-1015) was measured at 0, 15 and 30 min by liquid chromatography with electrochemical detection. Animals were under long photoperiods (LD 14:10; lights on at 06.00 h). In the hamster pineal gland, CA synthesis was greater in the dark (24.00 h) (0.017 ng/pineal/min) than in the light (12.00 h) (0.008 ng/pineal/min). Similarly, CA synthesis in the rat pineal was 0.037 ng/pineal/min (dark) and 0.005 ng/pineal/min (light). In a 24-hour study, animals were injected with NSD-1015,30 min prior to killing to determine if 24-hour changes were present in CA synthesis. In the hamster, DOPA in the dark (p < 0.001) was significantly greater than in the light (1.33 ± 0.42 ng/pineal at 06.00 h; 0.33 ± 0.07 at 13.00 h) in this study. No significant difference was measured in norepinephrine (NE) concentration during this 24-hour period. In the rat, DOPA accumulation was significantly different (p < 0.001) in the dark as compared to the light (0.86 ± 0.09 ng/pineal at 03.00 h; 0.21 ± 0.08 at 12.30 h). Within this 24-hour period, NE concentration fluctuated significantly between 2.28 ± 0.33 ng/pineal (15.30 h) to 4.65 ± 0.59 (05.30 h). These results indicate for the first time a definite 24-hour rhythm in endogenous TH activity and NE synthesis in the hamster pineal gland even though NE content does not change. In addition, a 24-hour change in CA synthesis and content is present in the rat pineal gland.

Norepinephrine or Isoproterenol Stimulation of Pineal N-Acetyltransferase Activity and Melatonin Content in the Syrian Hamster Is Restricted to the Second Half of the Daily Dark Phase

“…In summary, it appears likely that the nighttime rise in pineal melatonin, at least in the Syrian hamster, may be de termined not only by the synthesis and release o f N E from the sympathetic neurons at this time [4], but also by the in creased sensitivity of the [l-receptors on the pinealocyte membrane. Previously, it was generally felt that the release o f N E was the primary feature determining the nocturnal rise in pineal melatonin.…”

“…However, between 02.00 and 06.00 h there is a sharp rise in pineal melatonin content with the peak usually occurring at 04.00-05.00 h. It appears then, that the night time rise in melatonin in the hamster pineal gland could be controlled by the sensitivity o f the membrane receptors to the neurotransmitter N E . Interestingly, it has been shown that catecholamine production in the postganglionic neu rons in the Syrian hamster pineal gland also increases at night, suggesting maximal release at or just prior to the time the catecholamine receptors increase their sensitivity to the neurotransmitter [3,4], Studies in rats have shown that the number o f |)-receptors on pinealocyte membrane actually increases during the dark period [17]; whether this is also true for the Syrian hamster is not known, although the pres ent findings would suggest it is.…”

Generation of the Melatonin Endocrine Message in Mammals: A Review of the Complex Regulation of Melatonin Synthesis by Norepinephrine, Peptides, and Other Pineal Transmitters

“…The pivotal role of NE in the control of rat pineal metabolic activity has been supported by several experiments: 1) intraperitoneal injections of an NAergic agonist during the day stimulate MEL synthesis with a comparable amplitude to that of the endogenous nocturnal increase (see King and Steinlechner, 1985 for review); 2) SCGx abolishes the nocturnal increase in Aanat mRNA, AA-NAT activity, and MEL synthesis (Deguchi and Axelrod, 1972b;Roseboom et al, 1996;Garidou et al, 2001); 3) electrical SCG stimulation during the day provokes an increase in MEL synthesis in the pineal gland (Bowers and Zigmond, 1980); 4) exogenous NAergic stimulation of the pineal gland in organ cultures or in perifusion (Simonneaux et al, 1989) or of pinealocytes in primary culture Simonneaux et al, 1994b) induces a large increase in AA-NAT activity and MEL release; 5) the synthetic rate and renewal of NE in the pineal gland are higher at night than during the day (Brownstein and Axelrod, 1974;Craft et al, 1984); and 6) the use of pineal microdialysis to study the in situ regulation of MEL synthesis has demonstrated the positive coupling between the nighttime release of NE and stimulation of MEL synthesis (Drijfhout et al, 1993(Drijfhout et al, , 1996c.…”

Circadian Variation of β-Adrenoceptor Binding Sites in the Pineal Gland of the Syrian Hamster and Prevention of the Nocturnal Reduction by Light Exposure or Propranolol Treatment

“…Agonists typically downregulate (i-adrenoceptors in cell membranes [9,23]. Although the norepinephrine (NE) con tent of the hamster pineal exhibits no circadian rhythm, the catecholamine synthesis is significantly higher at night than during the day [4] and it is very likely that NE release also increases at night. The low receptor numbers at 04:00 h may therefore be explained as a downregulation of the receptors by the agonist NE.…”