Minor involvement of somatic growth in the onset of puberty of Hatano high- and low-avoidance rats

Abstract

The present study was planned to examine the effects of somatic growth on the determination of timing of puberty using Hatano high-and low-avoidance rats (HAAs and LAAs); the rats were genetically selected from Sprague-Dawley (SD) rats for good or poor performance in a two-way active avoidance-learning test. Since these two lines were found to have different characteristics, such as body weight at birth, maternal care and timing of male puberty, the present study characterized female puberty in Hatano rats and then compared postnatal growth and timing of puberty between the two lines of rats when they were nursed by foster SD dams. When nursed under biological dams, HAAs became heavier, exhibited vaginal opening at a younger age and first ovulation was accompanied by more oocytes than LAAs. In all of the HAAs, but none of the LAAs, ovulation was induced by a single s.c. injection of 5 IU equine chorionic gonadotropin (eCG) on day 22 after birth. An additional treatment with 10 IU human CG revealed that, in the ovaries of LAAs, a small number of follicles had developed to an ovulable stage as a result of the treatment. The fostering improved somatic growth, and weights of LAAs were sustained at a heavier level than those of fostered HAAs. The fostering, however, did not eliminate the line difference in the timing of puberty of both sexes; it did accelerate the vaginal opening of LAAs but not the balanopreputial separation. Thus, there is a phenotypic difference in the timing of female puberty in Hatano rats exhibiting a different timing of ovarian development in response to gonadotropin. The present study indicates that postnatal somatic growth is not the predominant determinant in the onset of puberty in Hatano rats.

Effects of Vertically Transferred 3,3',4,4',5-Pentachlorobiphenyl (PCB-126) on the Reproductive Development of Female Rats

“…PCB-126, however, did not affect the timing of puberty at a dose level of 1 µg/kg/day, which reduced the body weights of offspring on PND24. In addition, it has been shown that compensation of somatic growth does not always advance puberty in the rat [17]. Other factors, such as those exerting antiestrogenic effects, may also be involved in the delay of puberty since estradiol-17β, one of the key hormones affecting the onset of puberty in the rat, is antagonized by AhR agonists [11].…”

Immunological Characteristics of Hatano High-and Low-Avoidance Rats

“…Previous studies revealed that HAA rats matured earlier in terms of behavioral development [13], and puberty [21,22]. These results suggest that immunological development occurs earlier in HAA than LAA rats as well as behavioral and endocrine developments.…”

“…One of the most interesting features resulting from the genetic selection of Hatano rats has been their stress response: HAA rats are generally more reactive to stress than LAA rats [15] with the notable exception of prolactin secretion [3]. In addition, compared to LAA rats, HAA rats show earlier physical, behavioral and sexual maturation [13,21,22].…”

Endocrine Mechanisms Responsible for Different Follicular Development During the Estrous Cycle in Hatano High- and Low-avoidance Rats

“…Previous reports have shown that HAA rats ovulate more oocytes than LAA rats [2,14], and it is well known that follicular development in mammals is controlled by the two pituitary-derived glycoprotein hormones, FSH and LH [15]. During follicular development, most follicles undergo atretic degeneration, whereas a few of them, under stimulation from cyclic gonadotropins, reach the preovulatory stage [16,17].…”