Ghrelin enhances viability of rat spermatozoa during incubation at 37°C

Antioxidant properties of ghrelin have been demonstrated in recent studies. In the present study, the effects of chronic administration of ghrelin on the motility and plasma membrane integrity of rat spermatozoa during incubation at 37ºC were investigated. Thirty 45-day-old male Wistar rats were divided into control and treatment groups. Rats in the treatment group were daily injected subcutaneously with 1 nmol of ghrelin for 10 consecutive days and the control rats received normal saline. Sperm was collected after killing of rats on days 5, 15 and 40 after the last injection, and sperm characteristics were examined at 0, 3 and 5 h after incubation at 37ºC. Mass motility and forward progressive movement of spermatozoa were significantly higher in ghrelin-treated animals at 3 and 5 h of incubation on day 5 (P<0.05). After 3 h of incubation on day 15, only mass motility was greater than that of the control group. Plasma membrane integrity was assessed by hypoosmotic swelling (HOS) “water test”. The mean value of HOS reacted spermatozoa was higher in the treatment group on days 5 and 15 during 0, 3 and 5 h of incubation (P<0.05). However, the percentage of HOS-positive spermatozoa was not significantly different on day 40 between groups. There was a high correlation at 3 and 5 h of day 5 between the forward progressive movement (r = 0.92 and 0.94, P<0.0001) as well as overall sperm motility (r = 0.78 and 0.81, P<0.01) with HOS test in the ghrelin-treated animals. These results can be attributed to the antioxidative effects of ghrelin on the rat sperm especially on its plasma membrane which probably protects the sperm plasma membrane against oxidative damage during incubation and causes subsequent significant increase in the HOS test results. This may result in higher sperm motility index during 5 h of incubation.