The possibility that gonadotrophin releasing hormone (GnRH) can prime the anterior pituitary to a second dose of GnRH resulting in a greatly enhanced secretion of luteinizing hormone was examined in three adult boars. Four experiments were conducted: saline injection followed one hour later by a second saline injection (control); 1 microgram of synthetic GnRH injection followed one hour later by saline injection; saline injection followed one hour later by GnRH injection; GnRH injection followed one hour later by a second GnRH injection. Immunoassayable levels of plasma luteinizing hormone resulting from GnRH plus GnRH treatment were significantly greater than the sum obtained when values from GnRH plus saline and saline plus GnRH were added. Testosterone values in plasma reached maximal concentrations about 60 minutes after peak values of luteinizing hormone were achieved. The results suggest that the first dose of GnRH, in addition to stimulating release of luteinizing hormone can also sensitize the gonadotrophs to a second dose of GnRH causing a significantly greater release of luteinizing hormone
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