Submitted to: General and Comparative Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/1998
Publication Date: N/A
Citation: N/A Interpretive Summary: Sexual maturation involves a cascade of interrelated changes in hormone secretion by the hypothalamic area of the brain, the pituitary, and the gonads. Since many genetic and environmental factors can affect sexual maturation and either promote or inhibit reproductive performance, it is important to understand the age-related developmental patterns of hormone secretion that normally occur in male and female birds. This study measured maturational changes in pituitary and plasma levels of luteinizing hormone (LH), which is essential for both semen production and ovarian function, and related these changes to production of the hypothalamic hormone (gonadotropin releasing hormone; GnRH) which regulates the production and secretion of LH. Japanese quail, which mature at an early age, were utilized for these studies. Results showed that the increases in GnRH and LH that are associated with sexual maturity occur at an earlier age in males than in females. Brain levels of this hormone began to increase at 25 days of age in both sexes, but rose more slowly at peaked at a later age in females than in males. These changes in brain levels of GnRH were clearly demonstrated to precede changes in pituitary and plasma LH that are associated with sexual maturation. These data provide support for the notion that sexual maturation is initiated by hypothalamic events which then trigger changes in the pituitary and gonads. This information will be of use to scientists in understanding developmental changes in reproductive tissues that promote normal semen and egg production.
Technical Abstract: Hypothalamic chicken gonadotropin releasing hormone I (cGnRH-I), pituitary gland luteinizing hormone (LH) and plasma LH were measured during sexual maturation in Japanese quail. Ten birds (5 males; 5 females) were sampled every 5 days between days 1 and 45 posthatch. The content of cGnRH-I in the preoptic lateral septal area (POA-SL) and median eminence area (ME) were assayed by a competitive enzyme immunoassay. Pituitary and plasma LH were assayed by radioimmunoassay. Results showed that the maturation- related increase in cGnRH-I and LH began earlier in males than females. In young chicks, POA-SL content of cGnRH-I was relatively low (1.25 to 3.89 pg/ug protein in males and 2.92 to 5.39 pg in females, respectively) until day 20. The cGnRH-I levels then rose (p<0.05) to 40.46 pg/ug protein at 35 days of age in males, but rose more slowly in females to reach 37.84 pg/ug protein at 40 days. The cGnRH-I content in the ME was relatively low, 20.46 to 59.28 pg/ug protein in males and 22.32 to 69.3 pg/ug protein in females, until day 20, then increased (p<0.01) to 391.0 pg/ug protein at 35 days of age in males, and 410.75 pg/ug protein at 40 days of age in females. Pituitary gland LH content peaked (p<0.01) at 35 days of age in both males and females. While plasma LH in males continued to increase (from 0.29 to 2.12 ng/ml) with age, plasma levels remained low in females (0.32 ng/ml) until day 30 and then significantly (p<0.05) increased to 1.36 ng/ml at 35 days of age. Based on previous data, male quail are sexually mature before females begin egg production (35 compared to 45 days of age). These data provide further evidence of sexually dimorphic ontogenetic patterns in hypothalamic and pituitary gland activity, and correlate well with the timing of maturation observed previously.