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ENDOCRINOLOGICAL BACKGROUND UNDERLYING BIPOLAR DISTIBUTION OF THE ONSET OF FEMALE PUBERTY IN HIGH- AND LOW-AVOIDANCE RATS (HAAS AND LAAS).
Shirota, Mariko1, Ohta, Ryo1, Sato, Masako1, Kojima, Kohichi1, Asai, Sayaka2, Watanabe, Gen2, Taya, Kazuyoshi2, 1 2
ABSTRACT- Two inbred strains of rats, HAAs and LAAs, were selectively bred from Sprague-Dawley (SD) rats for high and low shuttlebox avoidance responses, respectively. Among various unique differences between these strains, this study focused on bipolar distribution of the onset of female puberty within the normal range of SD; i.e., mean postnatal days (PNDs) at the vaginal opening (±SE) were 32.8 (±0.2, n=58) in HAAs and 36.4 (±0.2, n=48) in LAAs. To reveal endocrinological background underlying the strain difference in the onset of female puberty, this study compared serum concentrations of gonadotropins (LH, FSH), prolactin, immunoreactive inhibin, estradiol-17
and corticosterone between HAAs and LAAs on PNDs 5, 10, 15, 21, 28 and 32 (LAAs only). Serum levels of these hormones in female SD offspring were determined on every second days from PND 5 to 15 as references. While neonatal increase in circulating LH and FSH levels in LAAs was identical to those in SD, those levels of HAAs were about 2-fold higher on PNDs 10-21 than LAAs. PRL levels were identical between HAAs and LAAs until weaning, but were higher in LAAs on PND 28. No remarkable difference was observed in the other hormonal levels, except for estradiol-17 levels on PND 5 (HAAs>LAAs) and 10 (LAAs>HAAs). The present study revealed that levels of circulating LH and FSH during the neonatal period, but not the timing of GTHs secretion, were different between two strains, of which puberty occurred at younger (HAAs) and older (LAAs) ages. These animals will provide good models to study the onset of puberty.
KEY WORDS: puberty, gonadotropins, shuttle-box avoidance response , rats