Exogenous GH-releasing hormone increases GH and LH secretion in growing mithuns (Bos frontalis)

To investigate the effects of growth hormone-releasing hormone (GHRH) administration on the patterns of GH and LH secretion in growing female mithuns, 12 mithuns within the age group of 10-12 months of age were divided into two groups (treatment and control groups) of six each in such a way that average body weight between the groups did not differ significantly (P>0.05). Both the groups were administered i.v. either with synthetic bGHRH [bGHRH (1-44)-NH2] at 10 microg/100 kg body weight (treatment group) or equal volume of normal saline (control group). Blood samples collected prior to and after GHRH challenge at -60, -45, -30, -15, -10, -5 min and 5, 10, 15, 30 min, and thereafter, at an interval of 15 min up to 8 h post-injection were assayed for plasma GH and LH. Plasma progesterone was estimated in twice-a-week samples collected for six consecutive weeks preceding GHRH challenge to assess whether either group has begun ovarian cyclicity. Body weight of all animals was recorded once in a week during the period. A peak of GH was registered in all animals within 5-25 min post-GHRH administration with a mean peak of 443.5+/-25.32 ng/ml at 15 min post-administration, which was much higher than in any other bovines reported following GHRH challenge. The patterns of LH secretion were pulsatile in nature in both the groups. Interestingly, the hormone concentrations exhibited higher pulsatility with greater amplitude after GHRH challenge in GHRH-treated than in control mithuns. The GHRH-treated mithuns averaged 0.44 pulses/h (4 pulses/9 h) and the rate was 0.20/h (2 pulses/9 h) in controls. The rate of pulse frequency and amplitude differed significantly with time of sampling. The mean plasma LH levels after GHRH administration were significantly higher in treatment group than those recorded in control mithuns. The mean plasma progesterone was similar (P>0.05) in both the groups and no animal from either group had begun ovarian cycle. In conclusion, exogenous GHRH significantly increases plasma GH and also LH pulse frequency and amplitude with higher mean post-GHRH LH levels in growing mithuns suggesting thereby its possible use for enhancement of maturity process in this unique meat animal.