Showing papers by "Shiu-Fun Pang published in 1990"

Fluctuation of blood melatonin concentrations with age: result of changes in pineal melatonin secretion, body growth, and aging

Abstract: Melatonin in the systemic circulation of rats fluctuates with age, and the causes for such changes were investigated. Male rats (aged 7 days, 16 days, 18 days, 20 days, 30 days, 48 days, 60 days, and greater than 17 months) were adapted under a lighting regime of 12L:12D for at least 7 days. Pineals and blood samples from the trunk or confluens sinuum were collected in the dark period. Melatonin in tissues was extracted, identified, and determined by gas chromatography-mass spectrometry (GC-MS) and/or radioimmunoassay. Tissue melatonin levels obtained by radioimmunoassay correlated closely with those quantified by GC-MS. Thus, the melatonin radioimmunoassay used is a reliable assay method for melatonin in the plasma and pineal of the rat. Plasma melatonin in the confluens sinuum of rats exhibited episodic release superimposed on a basal release pattern. It was suggested that there are two pools of melatonin in the pineal gland, a readily releasable pool and a bound pool. The mean plasma levels of melatonin in the confluens sinuum of rats increased with age with the highest level recorded at 60 days old and declined to a lower level at greater than 17 months old. The above age-related changes, being similar to the alterations in pineal melatonin levels with growth and aging, suggest that, under our experimental conditions, levels of pineal melatonin increase or decrease with its secretory rate. In developing rats, the age-related increase in the rate of secretion of pineal melatonin as reflected by increases in melatonin levels in the confluens sinuum or pineal melatonin content before adulthood is different from the changes in melatonin levels in the systemic circulation which showed an early developmental rise, followed by an active period and then a prepubertal decline. However, when the body weight was taken into consideration, changes in the levels of pineal melatonin content per 100 gm body weight or the calculated blood melatonin levels (plasma melatonin in the confluens sinuum/body:head ratio) correlated well with the fluctuation of serum melatonin in the systemic circulation. Thus, the developmental changes in the concentrations of melatonin in the general circulation are the result of 1) changes in the rate of pineal melatonin secretion and 2) increase in the dilution factor because of increase in body size. In old rats, levels of plasma melatonin in the confluens sinuum and pineal melatonin content decreased indicating a decline in the rate of pineal melatonin secretion.(ABSTRACT TRUNCATED AT 400 WORDS)

Patterns of Pineal Melatonin Secretion in Rabbits: Diurnal Variation of Basal and Pulsatile Release

Abstract: The level and release pattern of plasma melatonin in the confluens sinuum of 28 sighted and 18 blinded (i.e. acute bilateral orbital enucleation) rabbits anesthetized with pentobarbital were studied. The animals had been adapted to a 12:12 h light-dark regime. Blood samples were collected from the cannulated confluens sinuum and/or the femoral artery at either 2- or 4-min intervals in both the light and dark phases. Plasma melatonin was determined by radioimmunoassay. In all rabbits studied, plasma melatonin in the confluens sinuum exhibited an episodic release pattern, with pulses superimposed on a basal level. At 4-min sampling intervals, the pulsatile release of melatonin in sighted rabbits were 3.8 peaks/h in the light phase; shorter sampling interval (2-min) revealed more frequent pulsatile release of melatonin (5.1 peaks/h). In sighted animals in the light phase, the level of melatonin in the plasma of confluens sinuum was 7–15 times higher than that obtained from the plasma collected at the same time from the peripheral artery where the level of melatonin also exhibited pulsatile pattern. In blinded animals, melatonin levels in terms of mean concentration, mean maximum level and mean minimum (or baseline) level obtained in the dark phase were 12–14 times higher than those obtained in the light phase. These results suggest that the level of melatonin exhibits a diurnal rhythm in the confluens sinuum of rabbits.