Effect of constant light on nychthemeral variations in serum testosterone in male Macaca radiata

Abstract

Circardian and seasonal variations in reproductive functions of mammals have been investigated extensively. Serum testosterone exhibits a nychthemeral variation in man and the rhesus monkey. Exposure of laboratory rodents which are nocturnal in habit to continuous illumination causes precocious puberty in immature rats and hamsters, and constant oestrus in cycling rats due to elevated gonadotropins. Conversely, prolonged exposure to darkness causes atrophy of testes in the hamster due to suppression of circulating FSH and LH. Relatively less information is available on the effects of light on reproduction in the human and non-human primates. From a study of the effects of constant light on serum testosterone in the male bonnet monkey (Macaca radiata), we have found that M. radiata shows a nychthemeral variation in serum testosterone.