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      Influence of the gonad on the degree of suppression induced by an LHRH agonist implant in the marmoset monkey.

      1 , , ,
      The Journal of endocrinology
      Bioscientifica

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          Abstract

          In a previous study pituitary-testicular function was shown to be maintained in a New World primate after the administration of an LHRH agonist implant. In the present study the mechanism of action of the same LHRH agonist (buserelin) on pituitary-gonadal function in the marmoset was investigated and a comparison made between the effects of treatment in three intact males, six adult cyclic females with regular ovulatory cycles, and six long-term ovariectomized animals. These were injected s.c. with an LHRH agonist implant (1.5 mg buserelin in a rod 0.5 cm long). In both the males and intact females, basal plasma LH concentrations were maintained within the normal range throughout the expected duration of agonist action (at least 3 months). Despite this, an absence of response to an LHRH challenge indicated that pituitary desensitization had occurred. In the intact females, ovulation was inhibited in five of six animals, plasma progesterone concentrations initially being maintained but subsequently remaining suppressed until 136 +/- 18 (S.E.M.) days after treatment. Responsiveness to administered LHRH returned prior to onset of return to ovarian cycles. In contrast, in ovariectomized marmosets, plasma LH was markedly suppressed to concentrations which were at or below the limit of detection of the assay and were therefore less than those observed in the buserelin-implanted intact animals. These results show that apparently normal pituitary-gonadal function in this species disguises an underlying pituitary desensitization to LHRH. This allows continuation of testosterone secretion in the male, but in the female ovulation is prevented, presumably as a result of failure of the desensitized pituitary to produce an LH surge.(ABSTRACT TRUNCATED AT 250 WORDS)

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          Author and article information

          Journal
          J Endocrinol
          The Journal of endocrinology
          Bioscientifica
          0022-0795
          0022-0795
          Feb 1992
          : 132
          : 2
          Affiliations
          [1 ] MRC Reproductive Biology Unit, Centre for Reproductive Biology, Edinburgh.
          Article
          10.1677/joe.0.1320217
          1541921
          a18dbe1a-e524-4ed8-8156-142d78264137
          History

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