Sexually mature gilts (n = 20) were actively immunized against GnRH. Primary and booster immunizations of GnRH conjugated to bovine serum albumin induced production of antibodies in all gilts. Nineteen of the gilts became acyclic with suppressed concentrations of gonadotropins and estradiol. Intravenous challenges with 100 micrograms GnRH and 5 micrograms D-(Ala6, des-Gly-NH2(10)) ethylamide GnRH (a GnRH agonist that did not cross-react with antibodies produced by the gilts) caused release of LH and FSH, indicating maintenance of secretory capacity of pituitary gonadotropes in the immunized animals. Gilts were given 100 ng GnRH agonist at 2-h intervals for 72 h (n = 4) or 144 h (n = 10) or did not receive agonist (n = 5). Blood samples were taken every 6 h, and detectable concentrations of LH were observed in 42% and 52% of samples taken from gilts treated with or without agonist. In contrast, serum concentrations of FSH and estradiol were undetectable. Reproductive tracts and anterior pituitaries were taken from gilts at the conclusion of pulsatile administration of GnRH agonist or at 144 h for controls. Pituitary concentration of LH and FSH, uterine wet and dry weight, and size of the uterus were similar among groups. Paired ovarian weights for treated gilts pulsed with GnRH agonist for 72 h were heavier (P less than .05); however, ovaries from all immunized gilts were atrophied without follicular structures.(ABSTRACT TRUNCATED AT 250 WORDS)
Passive immunization of chronically ovariectomized gilts against gonadotropin releasing hormone (GnRH) resulted in an abrupt cessation of pulsatile secretion of luteinizing hormone (LH) accompanied by clearance from serum with a mean half-life of 30.9 +/- 2.3 (mean +/- SE) and 918 +/- 200 min for the first and second compartment, respectively. Serum follicle stimulating hormone (FSH) was unaffected immediately by passive immunization against GnRH and declined slowly with a half-life of 4.9 +/- .7 d. After LH and FSH had declined to basal levels in passively immunized gilts, injection of a bolus of LH and FSH resulted in peak values within 5 min and depletion curves with half-lives for the first compartment of 28.0 +/- 1.3 and 36.4 +/- 2.6 min and for the second compartment of 679 +/- 98 and 1,230 +/- 54 min, for LH and FSH respectively. These results show that the half-life of LH is similar following immunoneutralization of GnRH or administration of a bolus of LH in immunized gilts and a difference in clearance rates of LH and FSH after initial passive immunization. These results suggest that secretion of FSH in the ovariectomized gilt is controlled by factors in addition to hypothalamic GnRH.
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