Investigation of the effect of different regulatory peptides on adrenocortical cell proliferation in immature rats: evidence that endogenous adrenomedullin exerts a stimulating action

Pseudoachondroplasia (PSACH) is an autosomal dominant disorder characterized by disproportionate short stature and precocious osteoarthritis. Radiographic manifestations include epiphyseal, metaphyseal and vertebral abnormalities. Mutations in the cartilage oligomeric matrix protein (COMP) have been identified to cause PSACH. Most of them affect one of the eight calcium-binding domains of COMP. We describe a clinically and radiologically typical PSACH 4-year-old girl and her 31-year-old father. A novel mutation, 1345-1347CCC deletion in exon 13, of COMP was identified in both patients. The deletion would be expected to result in the loss of the conserved proline at codon 449 from the sixth calcium-binding domain. This result further supports that COMP is the only gene, discovered to date, responsible for PSACH across different populations and that the calcium-binding domains are important to the function of the normal COMP.     

Effects of leptin and leptin fragments on steroid secretion and proliferative activity of regenerating rat adrenal cortex

Leptin, an adipose tissue-secreted hormone, acts via several isoforms of specific receptors (Ob-Rs), which may variously interact with the native leptin molecule and its fragments. Evidence has been provided that leptin affects rat adrenal functions, but the results were rather conflicting depending on the experimental condition examined (e.g. regenerating vs. mature or immature adrenal gland). Hence, we investigated the effects of three subcutaneous injections of murine leptin(1-147) and several leptin fragments (3 nmol/100 g body weight; 28, 16 and 4 h before the sacrifice) on the secretory activity and growth of regenerating rat adrenal cortex. The following leptin fragments were tested: murine leptin(116-130), and human leptin fragments 150-167, 138-167, 93-105, 22-56 and [Tyr]26-39. Leptin(1-147) enhanced plasma concentration of both aldosterone and corticosterone. The blood level of aldosterone was raised by leptin(116-130), leptin(138-167) and leptin(93-105), and that of corticosterone by leptin(93-105) and Tyr-leptin(26-39). Metaphase index (stachmokinetic method with vincristine) was unaffected by leptin(1-147), and lowered by leptin(116-130), leptin(150-167) and leptin(138-167). Collectively, our findings allow us to conclude that leptin and leptin fragments enhance the secretory activity and inhibit the growth of regenerating rat adrenal cortex, the biological activity of leptin being located in the C-terminal segment of its molecule.     

Evidence that orexins A and B stimulate insulin secretion from rat pancreatic islets via both receptor subtypes

Orexins are recently identified neuropeptides that appear to play a role in the regulation of energy homeostasis and arousal. They bind to and activate two closely related G protein-coupled receptors (OXR1 and OXR2), previously described as orphans. In this study we examined involvement of orexins in regulation of insulin secretion from rat pancreatic islets utilizing an in situ perfused pancreas and isolated pancreatic islet models. By means of RT-PCR we found that both OXR1 and OXR2 are expressed in rat pancreatic islets. Furthermore, the expression levels of OXR1 were higher than OXR2. In both experimental models applied, orexins A and B (1, 10 and 100 nmol/l) concentration dependently stimulated insulin secretion at two different glucose concentrations (6.66 or 26.4 mmol/l), with orexin A being more potent than orexin B. This study demonstrates that orexins A and B modulate insulin secretion in vitro.