Can the pineal gland modulate the effects of kisspeptin on the puberty onset in female rats?
Haluk Kelestimur1, Bayram Yilmaz2, Ahmet Ayar1, Ertugrul Kilic2, Mete Ozcan1, Ulkan Kilic2 & Ergul Alcin1
Chronic central administration of KiSS-1 peptide to immature female rats induces pubertal maturation, characterized by advanced vaginal opening, increased uterine and ovarian weights, elevated levels of luteinizing hormone (LH) and estrogen. There is evidence that the pineal gland may be also involved in puberty onset because melatonin secretion declines near puberty. We have investigated whether there is an interaction between kisspeptin and melatonin in timing of puberty onset. Wistar female rats (n=24) were weaned on day 21 and used. Twelve animals were pinealectomized (PNX), and the other half was exposed to sham operation (SHAM). Both SHAM and PNX rats received intraperitoneally either 100 nmol KiSS-1 per day or vehicle only. The animals were individually caged with free access to food and water. Vaginal opening was daily monitored starting from day 25, and the animals were decapitated when the first diestrus observed. Upon decapitation, trunk blood was collected for LH and estrogen, and the hypothalami were obtained for kisspeptin expression. Uterus and ovaries were dissected and weighed out. All animals presented vaginal opening at the age of 38 days except one rat from SHAM plus KiSS-1 and one from PNX plus vehicle groups. Peripheral administration of KiSS-1 increased uterine weight in both SHAM and PNX groups. PNX rats receiving KiSS-1 had higher (P<0.05) ovarian weight (44.84±3.6 mg) compared to PNX rats injected with vehicle (36.85±07.06 mg). The present results show that peripheral administration of KiSS-1 does not induce vaginal opening at least in the dose of 100 nmol, which was used in our study, unlike the effect of central administration. However, KiSS-1 caused an increase in ovarian weight in PNX group, which is another sign of pubertal maturation. The present findings suggest that the pineal gland may modulate the effect of kisspeptin on reproductive functions.