Time-dependent effect of melatonin on actin mRNA levels and incorporation of 35S-methionine into actin and proteins by the rat hypothalamus.
The synthesis of the cytoskeletal protein actin exhibits, in the rat hypothalamus, a diurnal variation with maxima during morning hours. The objective of the present study was to assess whether melatonin injection could affect the in vitro incorporation of 35S-methionine into actin, as well as the levels of actin mRNA, in the hypothalamus of adult male rats treated either acutely or chronically with the hormone at 10:00 or 18:00. Injection of 100 micrograms/kg of melatonin for ten days at either time induced a significant depression in the incorporation of 35S-methionine into a 43 kDa protein with the electrophoretic mobility of actin. The specific activity of total soluble proteins after labeled methionine incubations decreased only after evening melatonin administration (100 micrograms/kg, ten days). Hypothalamic actin mRNA levels, quantitated by dot-blot analysis, decreased only after the injection of 100 micrograms/kg melatonin for ten days at 10:00. Neither a 10-micrograms/kg dose of melatonin, nor a single injection of 100 micrograms/kg melatonin, caused any significant change in the parameters examined. Melatonin (100 micrograms/kg for ten days) did not modify hypothalamic somatostatin or H-Ras mRNA concentration. These results suggest the existence of an inhibitory effect of melatonin on hypothalamic actin synthesis.
Iovanna
J
J
Departamento de Fisiología, Facultad de Medicina, Universidad de Buenos Aires, Argentina.
Dusetti
N
N
Cadenas
B
B
Cardinali
D P
DP
D000199:Actins / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002940:Circadian Rhythm; D004591:Electrophoresis, Polyacrylamide Gel; D011905:Genes, ras / Q000235:genetics; D007031:Hypothalamus / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D008550:Melatonin / Q000494:pharmacology* / Q000502:physiology; D008715:Methionine / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism; D012333:RNA, Messenger / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013004:Somatostatin / Q000235:genetics; D013997:Time Factors
D000199:Actins; D011506:Proteins; D012333:RNA, Messenger; D013004:Somatostatin; D008715:Methionine; D008550:Melatonin