Plasma melatonin levels in patients suffering from colorectal carcinoma.

Plasma melatonin was determined in samples of patients with colorectal carcinoma and in controls using an iodinated radioimmunoassay. Both groups showed large individual variability in absolute melatonin levels. However, during the night, melatonin concentration in cancer patients was significantly lower than in controls.

Compensation of the natural magnetic field does not alter N-acetyltransferase activity and melatonin content of rat pineal gland.

The aim of this study was to investigate if compensation of the natural magnetic field (NMF) influences pineal melatonin production. Rats were exposed to an artificial magnetic field (AMF) that compensated the NMF during the night for 30 min. In another experiment rats were treated with the beta-adrenergic agonist isoproterenol prior to treatment with the same AMF during the day.

Inhibition of day time, but not isoproterenol-stimulated pineal N-acetyltransferase activity by an unidentified pineal compound.

Day time rat pineal N-acetyltransferase (P-NAT) activity is higher when homogenate used for incubation is diluted. Samples containing homogenate equivalent to 1/80 pineal gland had highest enzyme activity when compared with samples that contained homogenate equivalent to 1/40 and 1/20 pineal gland, respectively. Thus P-NAT activity is inhibited by a compound present in the pineal gland of the rat.

N-acetyltransferase of rat pineal gland acetylates isoniazid.

The tuberculostatic drug isoniazid is acetylated by pineal N-acetyl transferase (P-NAT) of the rat. Kinetics of isoniazid acetylation are different compared to that of serotonin acetylation. Apparent enzyme kinetic parameters for the unstimulated type of P-NAT were: Km: 4.