The Effect of Melatonin Treatment and Exposure to Continuous Darkness on the Reactivity of Smooth Muscles to Drugs in Rats

Abstract

Melatonin is the major secretory product of the pineal gland, playing an integral role in numerous metabolic, physiological and behavioral processes.
This study represents an attempt to understand the effect of environmental changes on the responses of a selected isolated tissue to pharmacologically
active substances in certain species which may lead to important experimental and clinical implications in future. Twenty male albino wistar rats were divided
into three experimental groups:
Group 1: Control animals, comprising 6 rats were exposed to 12:12 hour light: dark cycle for 4 weeks.
Group 2: Composed of 8 rats, was kept in a dark environment for 4 weeks.
Group 3: Consisted of 6 rats aged 6-7 weeks, subjected to continuous darkness for 2 weeks, at the end of the first week the rats treated daily with s.c melatonin injection at 1.00 p.m. for 7 consecutive days. The result of this study showed that the vas deferens preparation from the third group reacted with significant increase in reactivity to nor-adrenaline and 5-HT than that of control and continuous dark animals.
The limitation of time and shortage of materials may be blamed for the kind and quantity of results obtained and the conclusions made. Therefore, further studies with regard to the exposure period have to be undertaken in future to extensively elaborate on this point.