Apelin is a novel bioactive peptide as the endogenous ligand for APJ. Apelin and 
APJ have also been identified in the testis, hypothalamic nuclei such as 
arcuate, supraoptic and paraventricular nuclei, implicating roles in the control 
of reproduction. Therefore, the present study was designed to investigate the 
effects of chronic central infusion of apelin-13 on LH, FSH and testosterone 
levels and testis morphology. 21 Wistar-Albino male rats received continuous 
intracerebroventricular infusion via Alzet osmotic mini pumps filled artificial 
cerebrospinal fluid (vehicle) or apelin-13 at concentrations of 1 or 10 nmol (10 
μl/h) for seven days. At the last 90 min of the infusion period, the blood 
samples were collected at 15 min intervals (0-90 min) for LH and FSH analyses. 
At the last sampling point, the blood samples were analyzed for testosterone 
levels. Infusion of high dose apelin-13 significantly suppressed LH release 
compared with the vehicle values at 30, 60 and 75 min (p<0.05). However, FSH 
levels did not significantly differ among the groups. Serum testosterone levels 
in high dose apelin-13 group were statistically lower than the control group 
(p<0.05). In addition, histological examination showed that infusion of high 
dose apelin-13 significantly decreased the number of Leydig cells compared with 
the control and lower dose apelin-13 groups (p<0.05, p<0.01). Our results 
suggest that apelin-13 may play a role in the central regulation and decreases 
testosterone release by suppressing LH secretion. Thus, antagonists of the 
apelin receptor may, therefore, be useful for pharmaceuticals in the treatment 
of infertility.