REGIONAL DIFFERENCES IN THE MODULATORY ROLE OF THE EPITHELIUM IN SHEEP AIRWAY

Pulmonary Smooth Muscle in Vertebrates: A Comparative Review of Structure and Function

Although the airways of vertebrates are diverse in shape, complexity, and function, they all contain visceral smooth muscle. The morphology, function, and innervation of this tissue in airways is reviewed in actinopterygians, lungfish, amphibians, non-avian reptiles, birds, and mammals. Smooth muscle was likely involved in tension regulation ancestrally, and may serve to assist lung emptying in fishes and aquatic amphibians, as well as maintain internal lung structure. In certain non-avian reptiles and anurans antagonistic smooth muscle fibers may contribute to intrapulmonary gas mixing. In mammals and birds, smooth muscle regulates airway caliber, and may be important in controlling the distribution of ventilation at rest and exercise, or during thermoregulatory and vocal hyperventilation. Airway smooth muscle is controlled by the autonomic nervous system: cranial cholinergic innervation generally causes excitation, cranial non-adrenergic, non-cholinergic innervation causes inhibition, and spinal adrenergic (SA) input causes species-specific, often heterogeneous contractions and relaxations.

Effects of metformin on fertilisation of bovine oocytes and early embryo development: possible involvement of AMPK3-mediated TSC2 activation

Studies on bovine oocytes have revealed that the activation of adenosine monophosphate activated protein kinase (AMPK) by millimolar concentrations of metformin controls nuclear maturation. Tuberous sclerosis complex 2 (TSC2) has been identified as a downstream target of AMPK. The objective of this study was to investigate the effects of addition of low concentrations of metformin (1 nM to 10 μM) on the percentage of cultured cumulus-oocyte complexes (COC) giving rise to cleavage-stage embryos and AMPK-mediated TSC2 activation. Metformin was supplemented either throughout in vitro embryo production (IVP) or only during in vitro fertilization (IVF). COC were matured in vitro, inseminated, and presumptive zygotes cultured for a further 72 h post insemination before the percentage of COC that gave rise to zygotes and early embryo development was assessed. The presence of TSC2 in bovine embryos and its possible AMPK-induced activation were assessed by immunocytochemistry. Metformin had a dose-dependent effect on the numbers of cultured COC that gave rise to embryos. Drug treatment either throughout IVP or only during IVF decreased the percentage of ≥ 8-cell embryos (1 μM, P < 0.05; 10 μM, P < 0.01; and 0.1 μM, 10 μM, P < 0.01, respectively) and increased the percentage of 2-cell embryos (10 μM, P < 0.01 and P < 0.05 respectively). The percentage of cultured COC that gave rise to zygotes was not affected by metformin. TSC2 is expressed in early embryos. Metformin (10 μM) either throughout IVP or during IVF only, increased AMPK-induced PhosphoS1387-TSC2 immunoreactivity (P < 0.01) and this increase corresponded to the total TSC2 protein levels expressed in cells. Our results suggest that there is a dose-dependent negative effect of metformin on the ability of oocytes to cleave following insemination, possibly mediated through an AMPK-induced activation of TSC2.

Airway epithelium-derived relaxing factor: myth, reality, or naivety?

The presence of a healthy epithelium can moderate the contraction of the underlying airway smooth muscle. This is, in part, because epithelial cells generate inhibitory messages, whether diffusible substances, electrophysiological signals, or both. The epithelium-dependent inhibitory effect can be tonic (basal), synergistic, or evoked. Rather than a unique epithelium-derived relaxing factor (EpDRF), several known endogenous bronchoactive mediators, including nitric oxide and prostaglandin E2, contribute. The early concept that EpDRF diffuses all the way through the subepithelial layers to directly relax the airway smooth muscle appears unlikely. It is more plausible that the epithelial cells release true messenger molecules, which alter the production of endogenous substances (nitric oxide and/or metabolites of arachidonic acid) by the subepithelial layers. These substances then diffuse to the airway smooth muscle cells, conveying epithelium dependency.