Μg Of Gonadotrophin-releasing Hormone Research Articles

Comparison of the initial ovarian response, the synchrony of oestrus and ovulation and chronic stress response after administration of 100 or 250 μg of GnRH to randomly cycling Bos indicus cattle.

This study investigated the effects of administering saline, 100 or 250 μg of gonadotrophin releasing hormone (GnRH) on ovarian response, synchrony of oestrus and ovulation and chronic stress response in Bos indicus cattle. Randomised control. Animals were either left untreated (n=20) or on day 0 treated with an intravaginal progesterone releasing device and either saline (n=24), 100 μg (n=35), or 250 (n=35) μg of GnRH, intramuscular (IM). Blood was sampled 1.4 h after administration of treatment to monitor concentrations of luteinising hormone (LH) and P4 in serum and again 5 days later. On day 5 intravaginal P4 releasing device were removed, cloprostenol was administered IM and again 8 h later. Oestrus and ovulation were then monitored with ultrasonography for 6.5 days. Hair was clipped on day 55 for analysis of hair cortisol concentrations (HCC). No significant differences were found between Saline and GnRH treatments in the odds of inducing a new corpus luteum (CL) and the synchrony of oestrus or ovulation. HCC did not differ significantly between treatments. Mean concentrations of LH in serum on day 0 were less in the Saline compared to 100 and 250 μg GnRH treatments but did not differ between different doses of GnRH. Mean concentrations of LH and the odds of inducing a new CL were not increased after administering 250 μg compared to 100 μg of GnRH. Animal handling events in the study did not influence HCC. Further research is needed to better optimise responses to GnRH in B. indicus cattle.

Induction of luteinized unruptured follicles in the rat after injection of luteinizing hormone early in pro-oestrus

The cause of formation of luteinized unruptured follicles (LUF) is unknown. Formation of LUF was studied after injection of a varying small dose of luteinizing hormone (LH) with or without subsequent injection of gonadotrophin-releasing hormone (GnRH); in addition, the effect of suppression of prolactin on LUF formation was studied. Luteinization without ovulation occurred in virtually all graafian follicles, if 0.5-1.0 microgram of LH was injected some hours before the presumed endogenous LH surge (suppressed by Nembutal); with increasing doses of LH progressively increasing numbers of ovulations were observed. If an early pro-oestrus 1 microgram of GnRH was given 4 h after 1 microgram of LH, formation of LUF was partly prevented; if the interval between LH and GnRH was 8 h or more, the great majority of graafian follicles developed into LUF. If early in pro-oestrus 1 microgram of LH was given and 8 h later 0.1 microgram of a potent GnRH analogue, about 50% of the follicles became LUF; in similarly treated rats, suppression of prolactin by ergocryptine reduced but did not prevent LUF formation. The data support the idea that deficient LH secretion in the period before ovulation may be involved in the formation of LUF.

EFFECT OF GLUCOSE INFUSION ON METABOLIC AND REPRODUCTIVE FUNCTION IN POSTPARTUM BEEF COWS

An experiment was conducted to determine if glucose infusion could alter hypothalamic, pituitary or ovarian function in the postpartum (PP) beef cow. Twenty-six cows were assigned randomly at parturition to one of three infusion treatments. Controls (CON, n = 8) received 0.9% NaCl from days 26 to 32 PP. Glucose-infused animals (GLU, n = 8) received glucose at a constant rate of 4 mg min−1 kg−0.75 from days 26 to 32 PP, while glucose-spiked cows (SPIKE, n = 10) received glucose at rates up to 8 mg min−1 kg−0.75 for 48 h (days 26 and 27 PP), then received 0.9% NaCl as in CON. On day 32 PP 25 μg of gonadotrophin-releasing hormone (GnRH) was injected intravenously and blood samples were taken at 15- to 30-min intervals to evaluate pituitary release of luteinizing hormone (LH). During the entire infusion period, GLU had lower (P < 0.05) daily free fatty acid concentrations than either SPIKE or CON. Plasma concentrations of glucose in cows receiving the SPIKE treatment were elevated (P < 0.05) during the 48-h infusion period when compared to GLU and CON. In addition, glucose concentrations were higher (P < 0.05) in the GLU group than in the CON group during the first 48 h of infusion. For the remaining 4 d of the infusion period, plasma concentrations of glucose were similar between CON and GLU. Plasma insulin values were numerically but not significantly higher in GLU than in CON over the 6-d infusion period. During the 48-h glucose spike treatment insulin levels were elevated (P < 0.05) over preinfusion values and higher (P < 0.05) than both CON and GLU. Glucose infusion did not alter concentrations of plasma LH or the response to exogenous GnRH. The number of cows exhibiting ovarian activity by day 53 PP was similar among treatments. Key words: Beef cattle, glucose, reproduction, energy, luteinizing hormone, metabolism