Bovine pineal tripeptide threonylseryllysine retards puberty in female rats.

When injected into rodents, the bovine pineal tripeptide threonylseryllysine (TSL) elicits diverse antireproductive effects in a number of animal models. Extensive studies of its effects on pubertal development have not been carried out, however. In the present study, 1.0 microgram of T-S-L was administered daily to female Charles River CD rats throughout the peripubertal period, and effects on vaginal opening time, ovarian histology, and serum luteinizing hormone (LH) levels were observed. Since TSL is known to alter the action of luteinizing hormone releasing hormone (LHRH), it was postulated that this antireproductive tripeptide would delay the time of vaginal opening associated with first ovulation. Two hundred eighty-seven weanling females were housed at 22 degrees C under a 14L:10D photoperiod. They were divided into three groups for daily intraperitonal injections of either saline (SAL), 1.0 micrograms TSL, or 5.0 micrograms melatonin (aMT) beginning on the 23rd day of life. Subgroups of nine to ten rats from each treatment group were sacrificed on days 28, 30, 32, 33, 34, 35, 36, 37, 38, and 40. Although the body weights of all animals increased significantly during the course of the study, no significant differences were observed in this parameter among rats treated with saline, aMT, or TSL. Vaginal opening time was significantly delayed by TSL between days 32 and 40, and uterine weights were significantly lower in this group. Prepubertal increases in serum levels of LH were also significantly reduced. At the dose utilized, aMT was without significant effects on these parameters.(ABSTRACT TRUNCATED AT 250 WORDS)