Gonadotrophin Concentrations in Sheep Plasma after Injections of GnRH with or without a Mixture of Serine and Threonine


Abstract: This study was designed to test the effect of Serine and Threonine mixture with or without a GnRH dose on plasma LH and FSH concentrations in naturally cycling ewes. Two experiments were conducted. In the first experiment, the ewes were intravenously injected by jugular vein twice at 11.00 am and 2.00 pm as Saline/Saline (S/S, control), Saline/GnRH (S/GnRH), Saline/Amino acids and GnRH (S/AA+GnRH); Amino acids/GnRH (AA/GnRH), Amino acids/Amino acids with GnRH (AA/AA+GnRH). Blood samples were collected at 15, 30 and 60 min intervals from 60 min before, until 360 min following the first injection. In the second experiment, control and treatment groups received five saline or aminoacids mixture at two hours intervals beginning at 10.00 am. Injection of GnRH significantly increased plasma LH concentrations in all groups between 180 and 300 min following the first injections (P < 0.05). When amino acid mixture were injected three hours before the GnRH injection or three hours before and then together with GnRH there were further significant increases in plasma LH concentrations in AA/GnRH and in AA/AA+GnRH groups between 180 and 300 min following the first injections. In the second experiment, injection of amino acid mixture at two hour intervals did not cause any significant changes in plasma LH concentration (P > 0.05), while plasma FSH concentrations were suppressed (P < 0.05). The suppression of FSH concentration might be the result of an increased negative feedback of ovarian derived factors (most likely inhibin) on FSH secretion.

Keywords: Serine, threonine, ewe, GnRH, LH and FSH

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