The influence of light of different wavelengths on the methylating capacity of the pineal gland of male golden hamsters in relation to reproduction.

In the present experiments the influence of light of different wavelengths on pineal indole metabolism in relation to reproduction was studied. Therefore, during autumn and winter male golden hamsters were kept under natural conditions but for the sunlight which was filtered exposing the hamsters to either normal (control), red or blue light. During the gradually shortening photoperiod at the start of the experiments under normal light conditions, a marked decrease of FSH and LH plasma content as well as testicular weight was found, indicating the onset of gonadal atrophy. During this period a high synthesis of 5-methoxytryptophan (MW) and 5-methoxytryptamine (MT) was determined. The synthesis of other 5-methoxyindoles (MI) was low, while O-acetyl-5-methoxytryptophol (aML) synthesis even markedly decreased. Red and blue light did not cause significant changes in MI synthesis. As long as MT synthesis is high (under blue light), there is no increase in FSH content and testes weight is still decreasing. This influence of blue light confirms the putative antigonadotropic properties of MT. The increase of FSH content at week 9 was the first indication that recrudescence had started. At week 19, this recrudescence was also manifested in the increasing testes weight. The synthesis of melatonin (aMT), 5-methoxytryptophol (ML), 5-methoxyindole-3-acetic acid (MA) and aML increased whereas the production of MT decreased. Blue light exposure caused a significantly higher increase of synthesis of ML, MA, aML and, not-significantly, of aMT, whereas red light caused a significantly lower synthesis of MA. It was concluded that MT, a putative antigonadotropic, and aML, a putative counter-antigonadotropic, are probably important pineal compounds that transduce the photoperiodic messages, which cause either gonadal atrophy or recrudescence. The effect of blue light on indole metabolism and the reproductive cycle was more clear than that of red light. From the present results of blue light on indole metabolism, it was suggested that blue light delayed gonadal atrophy and stimulated gonadal growth, compared to red light. An opposite effect of red light was less obvious.