The use of an automated microsampling system for the characterization of growth hormone pulsatility in newborn babies

Using Aptamers as a Novel Method for Determining GnRH/LH Pulsatility

Aptamers are a novel technology enabling the continuous measurement of analytes in blood and other body compartments, without the need for repeated sampling and the associated reagent costs of traditional antibody-based methodologies. Aptamers are short single-stranded synthetic RNA or DNA that recognise and bind to specific targets. The conformational changes that can occur upon aptamer–ligand binding are transformed into chemical, fluorescent, colour changes and other readouts. Aptamers have been developed to detect and measure a variety of targets in vitro and in vivo. Gonadotropin-releasing hormone (GnRH) is a pulsatile hypothalamic hormone that is essential for normal fertility but difficult to measure in the peripheral circulation. However, pulsatile GnRH release results in pulsatile luteinizing hormone (LH) release from the pituitary gland. As such, LH pulsatility is the clinical gold standard method to determine GnRH pulsatility in humans. Aptamers have recently been shown to successfully bind to and measure GnRH and LH, and this review will focus on this specific area. However, due to the adaptability of aptamers, and their suitability for incorporation into portable devices, aptamer-based technology is likely to be used more widely in the future.

Measuring luteinising hormone pulsatility with a robotic aptamer-enabled electrochemical reader

Normal reproductive functioning is critically dependent on pulsatile secretion of luteinising hormone (LH). Assessment of LH pulsatility is important for the clinical diagnosis of reproductive disorders, but current methods are hampered by frequent blood sampling coupled to expensive serial immunochemical analysis. Here, we report the development and application of a Robotic APTamer-enabled Electrochemical Reader (RAPTER) electrochemical analysis system to determine LH pulsatility. Through selective evolution of ligands by exponential enrichment (SELEX), we identify DNA aptamers that bind specifically to LH and not to related hormones. The aptamers are integrated into electrochemical aptamer-based (E-AB) sensors on a robotic platform. E-AB enables rapid, sensitive and repeatable determination of LH concentration profiles. Bayesian Spectrum Analysis is applied to determine LH pulsatility in three distinct patient cohorts. This technology has the potential to transform the clinical care of patients with reproductive disorders and could be developed to allow real-time in vivo hormone monitoring.

An updated view of hypothalamic-vascular-pituitary unit function and plasticity

The discoveries of novel functional adaptations of the hypothalamus and anterior pituitary gland for physiological regulation have transformed our understanding of their interaction. The activity of a small proportion of hypothalamic neurons can control complex hormonal signalling, which is disconnected from a simple stimulus and the subsequent hormone secretion relationship and is dependent on physiological status. The interrelationship of the terminals of hypothalamic neurons and pituitary cells with the vasculature has an important role in determining the pattern of neurohormone exposure. Cells in the pituitary gland form networks with distinct organizational motifs that are related to the duration and pattern of output, and modifications of these networks occur in different physiological states, can persist after cessation of demand and result in enhanced function. Consequently, the hypothalamus and pituitary can no longer be considered as having a simple stratified relationship: with the vasculature they form a tripartite system, which must function in concert for appropriate hypothalamic regulation of physiological processes, such as reproduction. An improved understanding of the mechanisms underlying these regulatory features has implications for current and future therapies that correct defects in hypothalamic-pituitary axes. In addition, recapitulating proper network organization will be an important challenge for regenerative stem cell treatment.

Novel ontogenetic patterns of sexual differentiation in arcuate nucleus GHRH neurons revealed in GHRH-enhanced green fluorescent protein transgenic mice

GH secretion and growth rates are developmentally regulated and sexually dimorphic, but the neuroregulatory mechanisms between birth and puberty are unclear. Using the GHRH-enhanced green fluorescent protein (eGFP) transgenic mouse, in which eGFP provides a strong surrogate signal for identifying GHRH neurons, we showed that numbers in the male arcuate nucleus were double those seen in females at x postnatal day (P)1 and P10, during which time numbers increased 2- to 3-fold. Thereafter (P20, P30, P60, P365) there was a significant trend for numbers to decrease in males and increase in females, such that sex differences were, surprisingly, absent in young and late adulthood. Conversely, we identified the emergence of male-dominant sex differences in the number of processes extended per GHRH perikarya across puberty. Intriguingly, prepubertal gonadectomy (P28), unlike adult gonadectomy, caused a dramatic 40% loss of GHRH cells in both sexes in adulthood and a significant (30%) increase in processes emanating from cell bodies only in females. These findings establish a novel ontogenetic profile for GHRH neurons and suggest previously undiscovered roles for peripubertal gonadal factors in establishing population size in both sexes. They also provide the first demonstration of emergent sex-specific GHRH architecture, which may signal the onset of sex-dependent regulation of activity reported for adult GHRH-eGFP neurons, and its differential regulation by gonadal factors in males and females. This information adds to our knowledge of processes that underpin the emergence of sex-specific GH secretory dynamics and hence biological activity of this pleiotropic hormone.

Placental restriction of fetal growth increases insulin action, growth, and adiposity in the young lamb

Most children who are short or light at birth due to intrauterine growth restriction (IUGR) exhibit accelerated growth in infancy, termed "catch-up" growth, which together with IUGR, predicts increased risk of type 2 diabetes and obesity later in life. Placental restriction (PR) in sheep reduces size at birth, and also causes catch-up growth and increased adiposity at 6 wk of age. The physiological mechanisms responsible for catch-up growth after IUGR and its links to these adverse sequelae are unknown. Because insulin is a major anabolic hormone of infancy and its actions are commonly perturbed in these related disorders, we hypothesized that restriction of fetal growth would alter insulin secretion and sensitivity in the juvenile sheep at 1 month, which would be related to their altered growth and adiposity. We show that PR impairs glucose-stimulated insulin production, but not fasting insulin abundance or production in the young sheep. However, PR increases insulin sensitivity of circulating free fatty acids (FFAs), and insulin disposition indices for glucose and FFAs. Catch-up growth is predicted by the insulin disposition indices for amino acids and FFAs, and adiposity by that for FFAs. This suggests that catch-up growth and early-onset visceral obesity after IUGR may have a common underlying cause, that of increased insulin action due primarily to enhanced insulin sensitivity, which could account in part for their links to adverse metabolic and related outcomes in later life.

Placental restriction of fetal growth reduces size at birth and alters postnatal growth, feeding activity, and adiposity in the young lamb

Intrauterine growth restriction (IUGR) is associated with accelerated growth after birth. Together, IUGR and accelerated growth after birth predict reduced lean tissue mass and increased obesity in later life. Although placental insufficiency is a major cause of IUGR, whether it alters growth and adiposity in early postnatal life is not known. We hypothesized that placental restriction (PR) in the sheep would reduce size at birth and increase postnatal growth rate, fat mass, and feeding activity in the young lamb. PR reduced survival rate and size at birth, with soft tissues reduced to a greater extent than skeletal tissues and relative sparing of head width (P < 0.05 for all). PR did not alter absolute growth rates (i.e., the slope of the line of best fit for age vs. parameter size from birth to 45 days of age) but increased neonatal fractional growth rates (absolute growth rate relative to size at birth) for body weight (+24%), tibia (+15%) and metatarsal (+18%) lengths, hindlimb (+23%) and abdominal (+19%) circumferences, and fractional growth rates for current weight (P < 0.05) weekly throughout the first 45 days of life. PR and small size at birth reduced individual skeletal muscle weights and increased visceral adiposity in absolute and relative terms. PR also altered feeding activity, which increased with decreasing size at birth and was predictive of increased postnatal growth and adiposity. In conclusion, PR reduced size at birth and induced catch-up growth postnatally, normalizing weight and length but increasing adiposity in early postnatal life. Increased feeding activity may contribute to these alterations in growth and body composition following prenatal restraint and, if they persist, may lead to adverse metabolic and cardiovascular outcomes in later life.