Effect of Food Restriction on Serum and Pineal Indoles

Abstract

<p>Food restriction has profound effects on various endocrine axes and on amine metabolism. In the present study, the effect of reduced food availability on pineal and serum indole was determined in adult male Wistar rats. Under a lighting regimen of 14 h light and 10 h dark, 3 weeks of 50% food restriction led to a reduction in 24 h mean serum tryptophan and serum serotonin levels but an increase in serum melatonin levels. The duration of the night-time melatonin rise was increased secondary to an earlier rise of both pineal and serum melatonin. Such changes in circulating melatonin may account for the gonadal regression observed in underfed animals. This pineal-gonadal interaction was further investigated after animals were subjected to shortened photoperiod or after pinealectomy. Shortened photoperiod failed to influence either the serum melatonin profile or the undernutrition-related gonadal regression. Pinealectomy, however, was able to reverse though incompletely the gonadal regression in underfed animals. When the pineal responsiveness to beta-adrenergic stimulation was determined in food restricted animals, both the time course and the dose responses were altered. The changes in pineal and serum melatonin post-stimulation, however, were atypical of either a sub- or supersensitive pineal gland.</p> <p>Based on the present study, food availability proves to be another factor that can influence pineal activity. Its effect on the pineal, however, depends on the duration of food restriction and the environmental light/dark cycle.</p>