The effect of continuous darkness and continuous light on the reactivity of smooth muscles to drugs in the rat vas deferens

Abstract EN

Background : The vasoconstricting agents: nor-adrenaline and 5- hydroxytryptamine (5-HT) have a stimulant action on smooth muscle contractility of the rat vas deferens. Objective : This study aimed to investigate the effect of exposure to continuous darkness and continuous light on the contractility of the vasa deferntia smooth muscles from rats to applied nor-adrenaline and 5-HT. Method : Male albino wistar rats were divided into 3 experimental groups.

Group 1 : Control animals, were exposed to the ordinary photoperiod each day.

Group 2 : Rats were kept in a dark room.

Group 3: In a room under a bright artificial light.

All animals were killed after 4 weeks. Results : Vasa deferentia preparations from continuous dark group of rats exhibited a reduced reactivity with a significant lower maximal response to 5-HT than those from control rats.

The maximal response in the control vasa deferentia preparations were nearly doubled compared with that of the continuous dark preparation where as they responded to exogenous nor-adrenaline with no significant difference from those of continuous dark animals.

Vasa deferentia of continuous light animals responded with decreased reactivity and a smaller maximal response to both vasoconstrictors compared with that of control animals. Conclusion : It is concluded that changes in the rhythm of the photoperiod have considerable effects on the reactivity of the vasa deferentia smooth muscle from rats to applied nor-adrenaline and 5-HT.