Effects of adrenergic agonists and antagonists on the numbers of synaptic ribbons in the rat pineal gland
Seidel, A.; Sousa Neto, J.A.; Klauke, N.; Huesgen, A.; Manz, B.; Vollrath, L.
European Journal of Cell Biology 52(1): 163-168
1990
ISSN/ISBN: 0171-9335 PMID: 2167223 Document Number: 359810
In the pineal gland numbers of synaptic ribbons (SR) undergo day/night changes which parallel the rhythm of melatonin synthesis. Since pineal biosynthetic activity is controlled by activation of adrenoreceptors, we investigated the effects of adrenergic agonists and antagonists on pineal synaptic ribbon numbers and N-acetyltransferase (NAT) activity, the key enzyme of melatonin synthesis in rats. In vivo application of the .beta.-adrenergic antagonist propranolol decreased melatonin synthesis when given during the dark phase but did not affect SR numbers. Treatment during daytime with the .beta.-adrenergic agonist isoproterenol increased pineal NAT activity whereas SR numbers did not change. Norepinephrine stimulated NAT activity in vitro in a dose-dependent manner, but did not elevate SR numbers. Incubation with an analog of the second messenger cyclic adenosine monophosphate increased both NAT activity and SR numbers. These results suggest that the .beta.-adrenergic system does not play a decisive role in the regulation of the nocturnal increase in SR numbers observed in the rat pineal gland.