抄録
The study was undertaken in pubertal beef bulls to: (1) determine the temporal relationship of pulsatile secretion among LH, insulin-like peptide 3 (INSL3) and testosterone (T); and (2) monitor acute regulation of INSL3 secretion by LH using GnRH and hCG. Blood samples were taken at 15-min interval for 8 h from the intact Japanese Black bulls (n=6). The bulls were also treated with GnRH analogue and hCG and blood samples were taken after the treatments for 6 h and 12 days, respectively. Plasma concentrations of LH, INSL3 and T were measured by EIAs. INSL3, LH and T secretion in plasma were pulsatile and the frequency of LH, INSL3 and T pulses per 8 h was 4.7, 3.8 and 1.0, respectively. The increasing rate (peak/basal) of INSL3 pulses was lower (P<0.001) than that of T pulses. After GnRH treatment, LH concentrations increased at 1 h and remained high until 5 h (P<0.01), and a higher INSL3 concentration was observed at 1 h, 2 h and 6 h post-treatment (P<0.05). T concentrations increased at 1 h after GnRH treatment and remained high during 6 h (P<0.01). After hCG treatment, an increase of INSL3 concentration was observed at 2 h, 4 h, day 2, day 4 and day 8 of treatment (P<0.05), and T concentrations remained high till 8 day post-treatment (P<0.01). The increasing rate (maximum/pre-treatment) of INSL3 was much lower (P<0.001) than that of T after GnRH and hCG treatments. Results demonstrate that INSL3 secretion in blood is pulsatile in bulls. Endogenous and exogenous LH can stimulate INSL3 secretion soon after the treatment, suggesting the acute regulation of INSL3 by LH. Moreover, INSL3 can be used as a less-fluctuating marker than T to evaluate functions of testicular Leydig cells in bulls.
