THE ROLE AND MECHANISM OF ACTION OF MELATONIN ON REPRODUCTION PROCESSES IN TROPICALISED RODENTS

Abstract

The primary aim of this study is to obtain a better understanding of the role and mechanism of light on the pineal gland-melatonin axis and reproductive functions in tropical rats. This was achieved by exposing two strains of rats to selected wavelengths of light namely, white, blue, green or yellow during the photophase of 121:12D periodicity starting on day 18 of age until the end of experimentation. Pineal-reproductive interactions were examined by measuring night-time concentration of pineal and serum melatonin as well as serum levels of follicular stimulating hormone (FSH), luteinising hormone (LH), progesterone (P4) and testosterone (T) in adult rats. Various reproductive parameters including sexual maturation, adult mating behaviour, fertility status and female oestrous cyclicity were also monitored under different coloured lighting conditions. Findings of this study highlighted the importance of wavelength as determinant of effects of light on reproductive functions. Comparison made between the albino and pigmented rat strains revealed differences in the sensitivity of the photoreception-pineal gland axis to different spectra of light. Diversity in reproductive responses to different spectra of light was also noted to be strain- as well as sex-dependent. Correlation between the pineal gland melatonin content, serum melatonin levels and reproductive responses to the different coloured lights was not consistently clear. Results indicated that both pineal melatonin-dependent and independent pathways involved in relaying lighting information to the neuroendocrine-reproductive axis possibly exist in rats. The photoreception and transduction systems in albino Wistar rats are clearly different from those in pigmented DA rats.