An improved perfusion technique for fixation of sheep myocardium

A technique for in vivo vascular perfusion fixation of the sheep central nervous system

A method for perfusion fixation of the sheep central nervous system is described. The technique utilises the vascular anatomy of the spinal cord and brain to provide fixation that is comparable to transcardiac perfusion of the small animal. It can be applied with relative ease, cost effectiveness and without risking premature death of the animal due to complications of a major procedure such as thoracotomy.

Reactivity of canine isolated epicardial collateral coronary arteries. Relation to vessel structure

To study the relation between structure and vascular reactivity in mature coronary collateral arteries, we prepared 17 dogs with a casein occluder near the origin of the circumflex coronary artery. At least 24 weeks later, we examined the reactivity of surface collateral arteries (approximately 500 micron i.d.) to a range of constrictor and dilator agents and compared them with normal left anterior descending coronary arteries of similar size branching away from the collateral zone. Pairs of normal and collateral arteries 2 mm long were mounted in a double-vessel myograph for isometric force recording. Arteries were contracted by K+ (124 mM) or by cumulative addition of endothelin-1 (1-100 nM) or U46619 (1-300 nM), a thromboxane A2 mimetic drug. In each case, the collateral vessels contracted to approximately half the force generated by the normal arteries. When partially contracted by K+ (25-30 mM), the collateral vessels had a greater range of relaxation and similar sensitivity to acetylcholine, sodium nitroprusside, and cromakalim compared with normal arteries. Morphological and morphometric analyses revealed that the collateral arteries had thickened adventitia, thinner media, ruptured internal elastic laminae, and a thick neointima lined by endothelium. Theoretical calculations of luminal area were made for isotonic conditions in response to constrictor stimuli. Despite the poor contractility of the collateral arteries, the neointimal luminal encroachment further reduced the lumen to zero, an exaggerated response compared with normal arteries. Coronary collateral arteries are thus compromised flow conduits that may play a role in vasospastic angina.

Developmental morphology of vascular and lymphatic capillaries in the working myocardium and Purkinje bundle of the sheep septomarginal band

The normal development of vascular and lymphatic capillaries in the right ventricular septomarginal band of the sheep heart was studied in 9 fetuses aged 60-143 days (term = 147 days), 14 lambs aged 1 day to 16 weeks, and 3 adults. Tissue was fixed by perfusion and examined with light and transmission electron microscopy. The septomarginal band is composed of working myocardium and a well-defined peripheral bundle of Purkinje cells. Vascular capillaries of the working myocardium were closely apposed to myocardial cells. By contrast, vascular capillaries of the Purkinje bundle were situated within the connective tissue sheath and septa, at variable distances from the Purkinje cells. After birth, the capillaries of the Purkinje bundle were also found in grooves and tunnels within the Purkinje strands. The ultrastructure of fetal vascular capillaries associated with myocardial and Purkinje cells was initially similar, and characterized by an abundance of synthetic organelles in endothelial cells and pericytes. However, after 115 days in utero, capillary endothelium with diaphragmed fenestrae, 40-60 nm in width, were observed within the Purkinje bundle. The fenestrae attained an average frequency of 1 per 11 capillary cross sections just before term, and this was maintained in lambs and adults. The ultrastructure of lymphatic capillaries, which were not observed in the septomarginal band until just before term, changed little during development.