Ultrastructural Observations on the Platelets of the Arabian Tahr (Hemitragus jayakari)

Abstract

The ultrastructure of platelets was studied in specimens of peripheral blood from 18 healthy adult Arabian tahrs (Hemitragus jayakari). The platelets were characterized by their extreme polymorphism. The number of alpha granules, typically one to six per cell, was considerably less than that reported for most animal platelets. Similar to humans, the platelets of the Arabian tahr had nucleoids within the alpha granules. However, nucleoids were not a consistent finding. One or more electron-dense granules, most commonly contained within clear vesicles, was commonly observed. A unique feature was the lack of an open canalicular system, which is considered a hallmark feature of this cell type in most mammalian and reptilian platelets.

Ultrastructural observations on the platelets of the Arabian oryx (Oryx leucoryx)

“…Typically, most platelets of the Arabian oryx, exhibited between 1–2 electron‐dense bodies (Figure ), similar to the number found in the Arabia tahr (Johnson et al, ) but unlike those in humans and camels with 5–7 electron‐dense bodies per cell (Gader et al, ) Electron‐dense bodies have also been reported in other wild and domestic animal species including the white and black rhinoceros (Du Plessis et al, ) and buffalo (Du Plessis et al, ). They are characterized as being clear vesicles with an electron‐dense core.…”

“…Alpha granules are commonly found in the platelets of many animal species. In the Arabian oryx (Figure ), they exhibited a variety of shapes and sizes, as described for the Arabian tahr (Johnson et al, ). The α granules of humans are more homogenous in shape and size (Sharda & Flaumenhaft, ) and those from buffalo are characteristically described as large (Du Plessis et al, ).…”

“…The platelets of the Arabian oryx exhibited extreme polymorphism similar to those of the Arabian tahr (Johnson et al, ) but in contrast to platelets of most animal species, which are described as being discoid in shape (Feldman, Zinkl, & Jain, ). The size of the oryx platelets ranged from 4.25 µm in length to 2.2 µm in width for large platelets and from 1.1 µm length to 0.5 µm in width for small platelets.…”

“…Samples for electron microscopy were prepared as previously described (Johnson et al, ) with minor modifications, Briefly, within 90 min of collection, samples were centrifuged at 400 g for 20 min to obtain a buffy coat layer. After removal of the plasma, Karnovsky's fixative (2% glutaraldehyde in 2.5% paraformaldehyde in 0.2 M phosphate buffer, pH 7.38) was layered on top of the buffy coat.…”

“…They are also commonly found on camel platelets but have never been reported for horses and cows (Gader et al, ). An open canalicular system is absent in cows, horses, camels and the Arabian tahr (Johnson, Muirhead, Wood, King, & Al‐Busaidy, ; Segura et al, ). The Arabian oryx in 1986 was classified as an endangered animal on the IUCN “List of Threated Species” but subsequent to an extremely successful breeding and “Reintroduction Program” initiated in 1977 in Oman, the status of the oryx was elevated to vulnerable (Al‐Amri, ).…”