Noninvasive analytical estimation of endogenous GnRH drive: analysis using graded competitive GnRH-receptor antagonism and a calibrating pulse of exogenous GnRH

Gonadotrophin-releasing hormone receptor autoantibodies induce polycystic ovary syndrome-like features in a rat model

NEW FINDINGS

What is the central question of this study? Is there a causal relationship between gonadotrophin-releasing hormone (GnRH) receptor-activating autoantibodies and polycystic ovary syndrome (PCOS)? What is the main finding and its importance? Induction of GnRH receptor-activating autoantibodies in rats resulted in increased luteinizing hormone pulsatility and testosterone concentrations, disrupted oestrous cycles, increased atretic follicles, and activation of insulin signalling in the pituitary and ovary. These changes replicate those seen in humans with PCOS, suggesting that GnRH receptor-activating autoantibodies might be involved in the pathogenesis of PCOS.

ABSTRACT

Gonadotrophin-releasing hormone receptor-activating autoantibodies (GnRHR-AAb) are associated with polycystic ovary syndrome (PCOS). In the present study, we examined the impact of GnRHR-AAb on reproductive function in GnRHR-immunized female rats. All immunized rats produced high titres of GnRHR-AAb targeting a dominant epitope located in the central region of the second extracellular loop of the GnRHR. Increased pulsatile luteinizing hormone secretion and testosterone concentrations were found in immunized rats. These rats exhibited disrupted oestrous cycles, increased ovarian follicular atresia, and activation of insulin signalling in the pituitary and ovary, as indicated by increased mRNA expressions of insulin receptor substrate, phosphatidylinositol 3-kinase and glucose transporter 1. No significant changes in inflammatory cytokines were detected in the ovarian tissue. These features mimic those observed in humans with PCOS. Our findings support the concept that chronic stimulation of the GnRHR by GnRHR-AAb, with an associated increase in pituitary luteinizing hormone secretion and ovarian androgen overproduction, might represent a new aetiological mechanism for PCOS.

Pulsatility of Hypothalamo-Pituitary Hormones: A Challenge in Quantification

Neuroendocrine systems control many of the most fundamental physiological processes, e.g., reproduction, growth, adaptations to stress, and metabolism. Each such system involves the hypothalamus, the pituitary, and a specific target gland or organ. In the quantification of the interactions among these components, biostatistical modeling has played an important role. In the present article, five key challenges to an understanding of the interactions of these systems are illustrated and discussed critically.

Proinflammatory Cytokine Infusion Attenuates LH's Feedforward on Testosterone Secretion: Modulation by Age

CONTEXT

In the experimental animal, inflammatory signals quench LH's feedforward drive of testosterone (T) secretion and appear to impair GnRH-LH output. The degree to which such suppressive effects operate in the human is not known.

OBJECTIVE

To test the hypothesis that IL-2 impairs LH's feedforward drive on T and T's feedback inhibition of LH secretion in healthy men.

SETTING

Mayo Center for Translational Science Activities.

PATIENTS OR OTHER PARTICIPANTS

A total of 35 healthy men, 17 young and 18 older.

INTERVENTIONS

Randomized prospective double-blind saline-controlled study of IL-2 infusion in 2 doses with concurrent 10-minute blood sampling for 24 hours.

MAIN OUTCOME MEASURES

Deconvolution analysis of LH and T secretion.

RESULTS

After saline injection, older compared with young men exhibited reduced LH feedforward drive on T secretion (P < .001), and decreased T feedback inhibition of LH secretion (P < .01). After IL-2 injection, LH's feedforward onto T secretion declined markedly especially in young subjects (P < .001). Concomitantly, IL-2 potentiated T's proportional feedback on LH secretion especially in older volunteers.

CONCLUSION

This investigation confirms combined feedforward and feedback deficits in older relative to young men given saline and demonstrates 1) joint mechanisms by which IL-2 enforces biochemical hypogonadism, viz, combined feedforward block and feedback amplification; and 2) unequal absolute inhibition of T and LH secretion by IL-2 in young and older men. These outcomes establish that the male gonadal axis is susceptible to dual-site suppression by a prototypic inflammatory mediator. Thus, we postulate that selected ILs might also enforce male hypogonadism in chronic systemic inflammation.

Analysis of the impact of intravenous LH pulses versus continuous LH infusion on testosterone secretion during GnRH-receptor blockade

Gonadotrophin-releasing hormone (GnRH) pulsatility is required for optimal luteinizing hormone (LH) secretion, but whether LH pulsatility is required for physiological testosterone (T) secretion is not known. To test the postulate that pulses of recombinant human (rh) LH stimulate greater T secretion than continuous infusion of the same dose, a potent selective GnRH antagonist was administered overnight to 19 healthy men ages 18-49 yr. Subjects then received saline or rhLH intravenously continuously or as 6-min pulses intravenously every 1 or 2 h at the same total dose. Blood was sampled every 10 min for 10 h to quantify T responses. For the four interventions, the descending rank order of mean LH and mean T concentrations was 1-h = 2-h rhLH pulses > continuous rhLH > saline (P < 10(-3)). Plateau LH and T concentrations correlated positively (R(2) = 0.943, P = 0.029) as did LH concentrations and LH half-lives (R(2) = 0.962, P = 0.019). Percentage pulsatile T secretion assessed by deconvolution analysis (Keenan DM, Takahashi PY, Liu PY, Roebuck PD, Nehra AX, Iranmanesh A, Veldhuis JD. Endocrinology 147: 2817-2828, 2006) was the highest (P = 0.019), and half-time to attain peak T concentrations was the shortest (P < 10(-6)), for 1-h rhLH pulses. Approximate entropy (a pattern-regularity measure) revealed more orderly T secretion for 1- than 2-h rhLH pulses (P = 0.0076). Accordingly, a pulsatile LH signal, while not obligatory to maintain mean T concentrations, controls the mean plasma LH concentration and determines quantifiable patterns of T secretion. These data introduce the question whether blood T patterns in turn supervise distinctive target-tissue responses.

Modeling the Nonlinear Time Dynamics of Multidimensional Hormonal Systems

In most hormonal systems (as well as many physiological systems more generally), the chemical signals from the brain, which drive much of the dynamics, can not be observed in humans. By the time the molecules reach peripheral blood, they have been so diluted so as to not be assayable. It is not possible to invasively (surgically) measure these agents in the brain. This creates a difficult situation in terms of assessing whether or not the dynamics may have changed due to disease or aging. Moreover, most biological feedforward and feedback interactions occur after time delays, and the time delays need to be properly estimated. We address the following two questions: (1) Is it possible to devise a combination of clinical experiments by which, via exogenous inputs, the hormonal system can be perturbed to new steady-states in such a way that information about the unobserved components can be ascertained; and, (2) Can one devise methods to estimate (possibly, time-varying) time delays between components of a multidimensional nonlinear time series, which are more robust than traditional methods? We present methods for both questions, using the Stress (ACTH-cortisol) hormonal system as a prototype, but the approach is more broadly applicable.