Abstract

Male marmoset monkeys which had received gonadotrophin-releasing hormone (GnRH) antagonist treatment as neonates to block the postnatal increase in testosterone were studied, with the object of determining potential long-term effects of treatment on the reproductive system, including tests of fertilising capacity. To obtain information on the nature of the circulating testosterone during this neonatal period, sequential blood samples were collected from a further control group of ten neonates, aged between birth and 3 months, and from 11 adult, normally fertile males, to examine the relative proportions of free, sex-hormone-binding globulin (SHBG)-bound, and non-SHBG-bound testosterone. In control neonates, 11% of the circulating testosterone was free, and a further 19% non-SHBG-bound, and therefore presumed to be biologically available. The remaining 70% was SHBG-bound and considered to be biologically inert. This indicates that the neonatal increase in marmoset testosterone has a biological function. After pairing with females, time to first positive vaginal lavage and first delivery was similar for females, whether they were with control or treated male partners. Pregnancy outcome, in terms of number of young delivered and sex ratio, did not differ. This indicates that there appear to be no long-term sequelae in terms of procreative ability in male marmosets treated neonatally with a GnRH antagonist. Autopsy revealed no gross changes, except in the thymus, which was significantly heavier in the treated group. These results indicate that, although the circulating testosterone is in a biologically active form during the neonatal period, inhibition of testicular function in the neonate is without major effect on the adult male reproductive system. Treatment with a GnRH antagonist may have long-term effects on the immune system.

Journal of Endocrinology (1997) 154, 125–131

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. Since LH concentrations in buserelin-implanted ovariectomized animals were suppressed to levels less than those seen in the treated animal, the maintenance of basal LH secretion may be the result of a protective influence of gonadal factors.

Journal of Endocrinology (1992) 132, 217–224

Abstract

There is increasing molecular evidence that apoptosis is involved in the process of structural luteal regression in non-primate species. Apoptosis is dependent upon the activation of certain proto-oncogenes and c-myc protein has an important regulatory role in this process in some cell types. The aim of the present study was to determine the occurrence and localisation of c-myc protein within the primate corpus luteum, determine changes during induction of luteal regression and examine the corpora lutea for morphological evidence of apoptosis. Ovaries were studied from marmoset monkeys in the late follicular, and in the early, mid and late luteal phases. Luteal regression was induced either by treatment with prostaglandin F_2α analogue or GnRH antagonist administered during the mid luteal phase and ovaries obtained 24 and 48 h later. Immunocytochemistry was performed using a monoclonal antibody to the c-myc protein. In pre-ovulatory follicles positive staining was found in the nucleus of a few granulosal cells and in the cytoplasm of thecal cells. c-myc was present in all corpora lutea where it was localised predominantly in the cytoplasm. In early corpora lutea, scattered cells with intense staining were observed in the presence of a majority of moderately or weakly stained cells. In the mid and late luteal phases, corpora lutea were uniformly moderately stained for c-myc. Following induction of luteal regression, nuclear degeneration with condensation and fragmentation indicative of apoptosis was observed. In other luteal cells, increased cytoplasmic volume and dissolution of cellular and nuclear membranes suggested necrosis. After luteal regression the overall intensity of staining for c-myc declined, but was present at high signal concentration in the cytoplasm of those cells whose morphological integrity was best maintained following treatment. In a minority of steroidogenic luteal cells, both nuclear and cytoplasmic staining was observed. These results suggest that after ovulation there appears to be a marked increase in c-myc production in the cytoplasm of the luteal cells of the developing corpus luteum and that c-myc is present throughout the luteal phase. During induced luteal regression c-myc may undergo a transitory rise and transfer to the nucleus and both apoptosis and necrosis occur during the process of luteolysis.

Journal of Endocrinology (1995) 147, 131–137

ABSTRACT

The putative endocrine role of inhibin in the control of FSH secretion during the luteal phase in the primate was investigated by immunoneutralization. Antisera against the 1–23 amino acid sequence of the N-terminus of the human inhibin α subunit were raised in a ewe and three macaques. Antisera (10–20 ml) were administered to macaques on day 8/9 of the luteal phase and serum samples collected during the treatment cycle and post-treatment cycle for determination of FSH, oestradiol and progesterone. In addition, localization of inhibin within the macaque ovary at this stage of the luteal phase was investigated using the ovine antiserum. Intense immunostaining was localized within the granulosa-lutein cells of the corpus luteum with absence of staining in the thecalutein cells or other ovarian compartments. Administration of antisera was without significant effect on serum concentrations of FSH when compared with control animals, either during the first 24 h of detailed observation or for the following 10-day period of the late luteal phase and subsequent early follicular phase. These results provide further evidence that the corpus luteum is the major source of inhibin immunoreactivity during the primate menstrual cycle, but fail to support an endocrine role for inhibin in the suppression of FSH secretion.

Journal of Endocrinology (1992) 133, 341–347