Am. Attia, Possible involvement of beta-adrenergic receptors in the enhancement of nocturnal pineal N-acetyltransferase activity due to parathion administration, TOXICOLOGY, 142(2), 2000, pp. 79-86
The purpose of the present study was to examine the effects of administrati
on of sublethal doses of O,O-diethyl-O-p-nitrophenyl phosphorothioate (para
thion) on serum epinephrine (EPI) and norepinephrine (NE), as well as on ni
ght-time rat pineal melatonin synthesis, both in the presence and absence o
f propranolol, a P-adrenergic receptor antagonist. In the first experiment,
two groups of adult albino rats were administered parathion orally (1.08 a
nd 2.17 mg/kg/day; the total received by each animal was 6.5 and 13.0 mg/kg
body weight over 6 days); another two groups received corn oil only. Anima
ls were killed at 23:00 and 01:00 h by decapitation. Serum EPI was augmente
d at 01:00 h, but NE was increased at 01:00 and 23:00 h due to administrati
on of the high dose of parathion (13 mg/kg). In the second experiment, two
groups of adult male albino rats were administered parathion orally (13 mg/
kg); another two groups received an intraperitoneal injection of propranolo
l (20 mg/kg body weight, 1 h before the lights were turned off). In additio
n, two groups were given a saline injection. Four hours after darkness onse
t, pineal N-acetyltransferase (NAT) activity as well as pineal and serum me
latonin levels were measured. Parathion by itself significantly augmented n
octurnal pineal NAT activity and serum melatonin levels in otherwise untrea
ted rats; the insecticide was ineffective in reference to this enzyme when
it was given in conjunction with the P-adrenergic receptor antagonist propr
anolol. The augmentation of NAT activity by parathion also caused significa
nt reduction in pineal serotonin (5-HT); again, this response was blocked b
y propranolol treatment. The results are consistent with the idea that para
thion influences pineal 5-HT metabolism either at the level of the P-adrene
rgic receptor or via the sympathetic innervation to the pineal gland. (C) 2
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