Effect of Novel Melanocortin Type 2 Receptor Antagonists on the Corticosterone Response to ACTH in the Neonatal Rat Adrenal Gland In Vivo and In Vitro

Stress-induced increases in neonatal corticosterone demonstrate a unique shift from ACTH independence to ACTH dependence between postnatal day 2 (PD2) and day 8 (PD8) in newborn rats. This shift could be due to the binding of a bioactive, non-immunoreactive plasma ligand to the adrenocortical melanocortin 2 receptor (MC2R) (ACTH receptor). A potent MC2R antagonist would be useful to evaluate this phenomenon in the neonate. Therefore, we investigated the acute corticosterone response to ACTH(1–39) injection in rat pups pretreated with newly developed MC2R antagonists (GPS1573 and GPS1574), which have not been tested in vivo. The doses used in vivo were based on their in vitro potency, with GP1573 being more potent than GPS1574. GPS1573 (PD2 and PD8), GPS1574 (PD2 only), or vehicle were injected intraperitoneally (ip) 10 min before baseline sampling. Then, 0.001 mg/kg of ACTH(1–39) was injected ip, and subsequent blood samples obtained for the measurement of plasma corticosterone. Pretreatment of PD2 pups with GPS1573 demonstrated augmentation, rather than inhibition, of the corticosterone response to ACTH. In PD8 pups, pretreatment with 0.1 mg/kg GPS1573, but not 4 mg/kg, augmented the corticosterone response to ACTH. Pretreatment with GPS1574 attenuated the plasma corticosterone response to ACTH at 30 min in PD2 pups. The activity of these two compounds in vivo do not match their potency in vitro, with GPS1573 leading to a small augmentation of the corticosterone response to ACTH in vivo while GPS1574 resulted in inhibition

Adrenocortical sensitivity to ACTH in neonatal rats: correlation of corticosterone responses and adrenal cAMP content

A coordinated hypothalamic-pituitary-adrenal axis response is important for the survival of newborns during stress. We have previously shown that prior to post-natal day (PD) 5, neonatal rats exposed to hypoxia (one of the most common stressors effecting premature neonates) exhibit a large corticosterone response without a drastic increase in immunoassayable plasma ACTH and without a detectable increase in adrenal cAMP content (the critical second messenger). To explore this phenomenon and to further our knowledge of the mechanism of steroidogenesis in the neonate, we investigated the adrenal response to exogenous ACTH in the normoxic neonatal rat. Rat pups at PD2 and PD8 were injected (IP) with porcine ACTH at a low, moderate, or high doses (1, 4, or 20 µg/kg body weight). Trunk blood and whole adrenal glands were collected at baseline (before injection) and 15, 30, or 60 minutes after the injection. ACTH stimulated corticosterone release in PD2 and PD8 pups. In PD2 pups, plasma corticosterone at baseline and during the response to ACTH injection was greater than values measured in PD8 pups, despite lower adrenal cAMP content in PD2 pups. Specifically, the low and moderate physiological ACTH doses produced a large corticosterone response in PD2 pups without a change in adrenal cAMP content. At extremely high, pharmacological levels of plasma ACTH in PD2 pups (exceeding 3000 pg/mL), an increase in adrenal cAMP was measured. We conclude that physiological increases in plasma ACTH may stimulate adrenal steroidogenesis in PD2 pups through a non-cAMP mediated pathway

Epidemiology of pathogenic enterobacteria in humans, livestock, and peridomestic rodents in rural Madagascar.

BACKGROUND: Among the families of enteric bacteria are globally important diarrheal agents. Despite their potential for zoonotic and environmental transmission, few studies have examined the epidemiology of these pathogens in rural systems characterized by extensive overlap among humans, domesticated and peridomestic animals. We investigated patterns of infection with Enterotoxigenic Escherichia coli, Shigella spp., Salmonella enterica, Vibrio cholerae, and Yersinia spp. (enterocolitica, and pseudotuberculosis) in Southeastern Madagascar where the potential for the aforementioned interactions is high. In this pilot project we conducted surveys to examine behaviors potentially associated with risk of infection and if infection with specific enterobacteria species was associated with diarrheal disease. METHODOLOGY/PRINCIPAL FINDINGS: PCR was conducted on DNA from human, livestock, and rodent fecal samples from three villages. Overall, human prevalence was highest (77%), followed by rodents (51%) and livestock (18%). Rodents were ∼2.8 times more likely than livestock to carry one of the bacteria. The incidence of individual species varied between villages, with the observation that, E. coli and Shigella spp. were consistently associated with co-infections. As an aggregate, there was a significant risk of infection linked to a water source in one village. Individually, different pathogens were associated with certain behaviors, including: those who had used medication, experienced diarrhea in the past four weeks, or do not use toilets. CONCLUSIONS/SIGNIFICANCE: Different bacteria were associated with an elevated risk of infection for various human activities or characteristics. Certain bacteria may also predispose people to co-infections. These data suggest that a high potential for transmission among these groups, either directly or via contaminated water sources. As these bacteria were most prevalent in humans, it is possible that they are maintained in humans and that transmission to other species is infrequent. Further studies are needed to understand bacterial persistence, transmission dynamics, and associated consequences in this and similar systems

Incidence of each Enterobacteriaceae species in humans, livestock, and rodents by village.

<p>*Cattle and pigs.</p

Risk factors for infection with Enterobacteriaceae in people living in villages in Southeast Madagascar.

<p>*Total n varies due to incomplete notation on some surveys or respondents do not participate in the given activity (e.g. tend livestock).</p><p><b>Bold</b>  =  statistically significant associations.</p

Risk factors for infection with individual Enterobacteriaceae species in people living in villages in Southeast Madagascar.

<p>*Total n varies due to incomplete notation on some surveys or respondents do not participate in the given activity.</p

Summary of significant findings for infection with Enterobacteriaceae in human, livestock, and rodent populations.

<p>Summary of significant findings for infection with Enterobacteriaceae in human, livestock, and rodent populations.</p

Prevalence of Enterobacteriaceae infection by subject and location.

<p>Prevalence of Enterobacteriaceae infection by subject and location.</p

Bacterial strains (positive controls), target genes, and primers^* used in this study.

<p>*All primer sequences and sensitivities obtained from Wang et al. (1997) except <i>Yersinia</i> obtained from Thoerner et al. (2003).</p>a<p>Product size with <i>Y. enterocolitica</i> serogroup 03 or 09 strains.</p>b<p>Product size with <i>Y. enterocolitica</i> serogroup 08 strains.</p

Adrenocortical sensitivity to ACTH in neonatal rats: correlation of corticosterone responses and adrenal cAMP content

A coordinated hypothalamic-pituitary-adrenal axis response is important for the survival of newborns during stress. We have previously shown that prior to post-natal day (PD) 5, neonatal rats exposed to hypoxia (one of the most common stressors effecting premature neonates) exhibit a large corticosterone response without a drastic increase in immunoassayable plasma ACTH and without a detectable increase in adrenal cAMP content (the critical second messenger). To explore this phenomenon and to further our knowledge of the mechanism of steroidogenesis in the neonate, we investigated the adrenal response to exogenous ACTH in the normoxic neonatal rat. Rat pups at PD2 and PD8 were injected (IP) with porcine ACTH at a low, moderate, or high doses (1, 4, or 20 µg/kg body weight). Trunk blood and whole adrenal glands were collected at baseline (before injection) and 15, 30, or 60 minutes after the injection. ACTH stimulated corticosterone release in PD2 and PD8 pups. In PD2 pups, plasma corticosterone at baseline and during the response to ACTH injection was greater than values measured in PD8 pups, despite lower adrenal cAMP content in PD2 pups. Specifically, the low and moderate physiological ACTH doses produced a large corticosterone response in PD2 pups without a change in adrenal cAMP content. At extremely high, pharmacological levels of plasma ACTH in PD2 pups (exceeding 3000 pg/mL), an increase in adrenal cAMP was measured. We conclude that physiological increases in plasma ACTH may stimulate adrenal steroidogenesis in PD2 pups through a non-cAMP mediated pathway