Browsing by Author "Luft, H."

There is increasing evidence that in the rat prior to and during the preovulatory LH surge, release rates of GABA in the preoptic area (POA) are decreased while no such changes occurred in the mediobasal hypothalamus (MBH). In addition, GnRH release appears to be facilitated by an increased preoptic excitation of glutamate (GLU). To investigate whether such changes of secretory activity of intrahypothalamic GABA or GLU neurons are associated with altered gene expression of biosynthetic enzymes or transporter proteins characteristic for either neuronal system, we determined mRNA levels of the two forms of the GABA-synthesizing enzyme glutamate decarboxylase (GAD65 and GAD67), the glutamate-synthesizing enzyme glutaminase (GLS), the GABA transporter type 1 (GAT-1) and the glutamate-aspartate transporter type 1 (GLAST), Competitive RT-PCRs using mutant cRNAs as internal standards were conducted with mRNA extracted from microdissected tissue of POA and MBH from diestrous, proestrous, and estrous rats. Proestrous animals were subgrouped according to their endocrine status as follows: 'prior to', on Phe 'ascending' or on the 'descending' limb of the LH peak, and 'after the LH surge. (post)'. During the preovulatory LH surge, mRNA concentrations of GAD67 and GAT-1 in the POA were significantly increased compared to those observed on diestrous (2.8-fold for GAD67(-) and 2.5-fold for GAT-1, p < 0.01), while in the MBH the amount of both mRNAs remained constant. The expression levels of GAD65, GLS and GLAST were without any changes in the POA as well as in the MBH. These findings support the hypothesis that in rats induction of the preovulatory LH surge is controlled at the level of GnRH perikarya, and suggest that altered activities of intrapreoptic GABA neurons at both transcriptional and secretory levels are pivotal for the preovulatory activation of GnRH neurons. Copyright (C) 2000 S. Karger AG, Basel.

To address whether gonadotropin-releasing hormone (GnRH) regulates its own expression and the expression of its receptor in the hypothalamus and ovary, we treated five groups of prepubertal/peripubertal female rats from postnatal days 25-36 with either the GnRH agonist triptorelin (TRIP) or the GnRH antagonist cetrorelix (CET), each 10 or 100 mug/day, or a placebo. We compared their effects regarding pubertal development, serum gonadotropins and the expression of GnRH and GnRH-receptor in the hypothalamus, pituitary, ovary and uterus. Onset of puberty was determined by vaginal opening, and expression levels of GnRH and GnRH-receptor were determined using either quantitative real-time PCR or competitive RT-PCR. Onset of puberty was retarded by both analogs but CET (100 mug/day) inhibited while TRIP (10 and 100 mug/day) stimulated serum gonadotropins (P <0.05). The expression of GnRH in the preoptic area did not show significant differences among the treatment groups but ovarian GnRH mRNA levels were significantly stimulated by CET (100 mug/day). GnRH mRNA could not be detected in the uterus by either real-rime PCR or competetive RT-PCR. The GnRH-receptor expression ill the hypothalamus (preoptic area and medio-basal hypothalamus) did not vary among any of the groups, whereas in the pituitary GnRH-receptor mRNA levels were stimulated by TRIP (10 mug/day) but inhibited by CET (100 mug/day). In contrast, in the ovary GnRH-receptor mRNA levels were inhibited by both TRIP (100 mug/day) and CET (100 mug/day). Interestingly, the GnRH-receptor was even expressed in the uterus where it was strongly stimulated by both CET and TRIP in a dose-related manner. This shows that in addition to their different pituitary effects, the GnRH analogs cetrorelix and triptorelin exert different actions at the hypothalamic, ovarian and uterine level. This study also demonstrates an organ-specific regulation of GnRH and GnRH-receptor gene expression which is likely part of a local autoregulatory system. We conclude that the ovarian and uterine effects of GnRH analogs must be considered in addition to their known pituitary effects when deciding which GnRH analog is most suitable for treating precocious puberty.

GnRH agonists are the established treatment of precocious puberty caused by premature stimulation of gonadotropin secretion. It has been reported that after an initial stimulation ("flare-up") they reduce LH secretion by desensitization of pituitary GnRH receptors. Little has been published about the use of GnRH antagonists such as cetrorelix to control the onset of puberty and whether they are potentially advantageous compared with GnRH agonists. We conducted two multigroup experiments (12 and 10 d, respectively) treating prepubertal/peripubertal female rats with either the GnRH agonist triptorelin or buserelin and compared them with rats treated with the GnRH antagonist cetrorelix and controls to assess the effects on pubertal progress and serum hormones. In the second experiment, the effects of buserelin and cetrorelix on gene expression of the GnRH receptor, LH-beta, FSH-beta, and the alpha subunit genes in the pituitary were also investigated. Cetrorelix, triptorelin, and buserelin retarded the onset of puberty as determined by delayed vaginal opening, lower ovarian weights, and lower serum estradiol levels. However, although LH and FSH levels were stimulated by both agonists, they were inhibited by cetrorelix. In the cetrorelix versus buserelin experiment, pituitary gene expression of the GnRH receptor and LH-beta subunit were significantly lower in cetrorelix treated rats compared with controls whereas buserelin had little effect. Expression of FSH-beta and alpha subunit were stimulated by buserelin but not by cetrorelix. Even though all three of these GnRH analogues inhibited gonadal development and delayed the onset of puberty, the GnRH agonists had stimulating and inhibiting effects on the pituitary-gonadal axis whereas cetrorelix exerted only inhibiting effects. We conclude from this female rat model that cetrorelix may offer advantages for a more controlled medical treatment of precocious puberty compared with GnRH agonist treatment.