Regional mechanical and electrophysiological changes accompany most ventricular arrhythmias and, it has been suggested, by mechanoelectric feedback. We hypothesized that an intervention producing regional mechanical dispersion was associated with regional, proarrhythmic electrical dispersion and studied the regional mechanoelectric feedback in the right ventricle (RV) of anesthetized lambs. Ten lambs were deeply anesthetized, and their hearts were exposed. Three tripodal devices, each incorporating three monophasic action potential electrodes and an integrated strain-gauge system, were placed on the RV apex outflow and inflow regions. Measurements were made before, during, and after 10-s pulmonary arterial occlusion. Pulmonary arterial occlusion increased RV pressure and overall regional segment length. Length excursion became out of phase with RV pressure beats immediately after occlusion, and the strain patterns were different in the three regions at the peak of occlusion. The occlusion resulted in different alterations in regional monophasic action potential morphology, including reduction in monophasic action potential amplitude and duration by different amounts and early afterdepolarizations that were unevenly distributed in the monophasic action potential recordings. This was associated with dispersion of repolarization and recovery time. The combination of electromechanical events precipitated a variety of arrhythmias. Acute RV distension is proarrhythmic, possibly through a causal relationship among mechanically induced afterdepolarizations, dispersion (heterogeneity) of mechanical strain, and dispersion of electrical recovery. The relationship among the different wall motions, the dispersion of repolarization, and arrhythmia underscored mechanoelectric feedback as an important part of arrhythmogenesis in pulmonary embolism and commotio cordis.

Transthyretin (TTR), synthesized by the choroid plexus (CP) and secreted into cerebrospinal fluid (CSF), is involved in thyroxine (T4) transport and chelation of beta-amyloid peptide, attenuating neurotoxicity. To characterize age-related changes in TTR synthesis, CSF and CPs were collected from young adult (1-2 years) and old (>8 years) sheep anesthetized with thiopentone sodium. TTR in old sheep CSF was low compared to young (n = 4 each); however, CP messenger RNA (mRNA) for TTR did not change. CPs were perfused with Ringer containing 14C-leucine to assess de novo protein synthesis, or with 125I-T4 to assess T4 transport. Protein synthesis, including TTR, was reduced in old sheep CP and in newly secreted CSF. 125I-T4 Vmax and Kd (but not Km) were reduced in old sheep CP. These age-related changes suggest reduced capacity of CP to maintain CSF T4 homeostasis and could also reduce chelation of beta-amyloid and be an added risk for Alzheimer's disease.

Insulin-like growth factor II (IGF-II) is a major growth factor in brain and is involved in neuroprotection in later life. However, synthesis and delivery of IGF-II to brain by the choroid plexus (CP) in later life is not well understood. This study investigated these issues in old sheep (7-10 years) in comparison to young adult sheep (1-2 years). IGF-II messenger RNA expression at the CP did not change with age although cerebrospinal fluid (CSF) levels fell. 125I-IGF-II uptake in the CP was saturated from either side of the CP, whereas age-related decrease of the uptake was seen at the CSF side but not at the blood side of the CP. The insulin-like growth factor binding protein-2 (IGFBP-2) at 0.01 or 0.1 microg/mL tended to enhance IGF-II uptake at the young CP but not the old CP or other brain tissues, whereas bovine serum albumin generally inhibited the uptake. These age-related changes suggest that the normal autocrine/paracine role of IGF-II at the CP is attenuated with age.

Recent clinical results from Edmonton have demonstrated the feasibility of achieving normoglycemia in type I diabetic patients by islet transplantation. One of the key issues in obtaining this success was transplanting sufficient numbers of islets by sequential transplants. Although the development of semipurified endotoxinfree Clostridium histolyticum-derived collagenase (Liberase) has improved islet yields from the human pancreas, batch-to-batch variation and loss of activity with time still hampers progress in obtaining consistent islet preparations. In order to define key components of crude collagenase, a panel of monoclonal antibodies (McAbs) was raised against crude collagenase. Monoclonal antibodies were generated by fusions between splenocytes of BALB/c mice immunized with Boheringer P collagenase and the myeloma cell line NS-0. These monoclonal antibodies were used as probes to study molecular differences between effective and ineffective collagenase batches using Western blotting. Two monoclonal antibodies (LDS71 and LDS81) were raised and characterized as recognizing separate epitopes on a 125-kDa component. Western blotting indicated that the 125-kDa band was rapidly broken down by storage or by dialysis in the presence of dithiothreitol. However, this breakdown could be prevented by the addition of leupeptin (a protease inhibitor) to the dialysis buffer. On testing fractions at 5-min intervals from the "Ricordi" digestion circuit during porcine and human pancreas digestion, the 125-kDa component was rapidly broken down in relatively ineffective collagenase batches but in effective batches was present throughout the digestion process. The correlation between the presence of the 125-kDa band and effectiveness of pancreas digestion suggests that this may be a key component in the formulation of C. histolyticum collagenase.