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  • Author or Editor: Nani G. Ghoshal x
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Summary

Microscopic examination of the nasal mucosa of clinically normal specific-pathogen-free pigs and of toxicogenic type-D Pasteurella multocida toxin challenge-exposed_ specific-pathogen-free pigs indicated that the surface epithelium in pigs of both groups was microscopically normal; erosions or appreciable inflammatory changes were not evident. In pigs of both groups and in all 3 regions of the nasal cavity, the endothelial lining of all blood vessels appeared normal without detectable changes to the walls at postinoculation day 10. Vascular injury in the cartilage or the bone was not discernible in control or challenge-exposed pigs.

There were marked differences in the osseous structures of the conchae when the 2 groups were compared. In control pigs, active bone formation and remodeling were observed, and the septal cartilage was normal. In toxin challenge-exposed pigs, there likewise was normal bone formation and remodeling in the vestibular region, and the septal cartilage was normal. In marked contrast, conspicuous changes were observed in the osseous core of the conchae of the respiratory and, sometimes, the olfactory regions. These changes consisted of bone necrosis and resorption by large numbers of osteoclasts with variable replacement by dense mesenchymal stroma, which resulted in conchal atrophy. In the absence of any discernible damage or injury (angiopathy) to the nasal vessels, it appears that the action of the dermonecrotoxin of P multocida serotype D is on the most active osteoblasts and the associated organic matrix of the bone, with subsequent disruption of normal bone formation and remodeling of the nasal conchae.

Free access
in American Journal of Veterinary Research

Summary

Gross and histologic features of the rostral epidural rete mirabile (carotid rete) and the cavernous sinus in onehumped camels were studied. It was evident that the branches of the carotid rete share a common tunica adventitia with the veins of the cavernous sinus. Transmission electron microscopy of the rostral epidural rete mirabile and the cavernous sinus revealed gap junctions in endothelial cells lining the walls of the arterial rete branches and veins. The internal elastic lamina of rete branches were fenestrated. Some of these structural featuers could facilitate countercurrent heat exchange between the rete branches and the venous plexus of the cavernous sinus to regulate brain temperature.

Free access
in American Journal of Veterinary Research

SUMMARY

Plasma concentrations of porcine growth hormone (pgh) were similar in healthy pigs and those with atrophic rhinitis (ar), therefore, observed reduced growth rates and feed efficiency in naturally infected pigs with ar were not attributed to low concentrations of plasma pgh. Also, pituitary glands in both groups of pigs were responsive to growth hormone-releasing hormone (ghrh) challenge by increasing pgh secretion. Administration of clonidine hydrochloride to pigs naturally infected with ar failed to elicit any significant change (5.3 ± 1.4 ng/ml) in the plasma concentration of pgh within a 45-minute bleeding interval. The pretreatment concentrations of pgh were similar in specific-pathogen-free toxin-treated and specific-pathogen-free control groups, but they increased significantly in toxin-treated pigs (20.7 ± 8.2 ng/ml) within 15 minutes after ghrh injection. Porcine growth hormone release in toxin-treated pigs was variable; however, all pigs did not respond to ghrh administration: 3 responded with an increase in pgh release (35.6 ± 10.6 ng/ml), 2 did not respond (6.7 ± 0.5 ng/ml), and 1 had a decrease in pgh release (3.9 ng/ml).

Therefore, the observed reduced growth rates reported in the literature may be attributed to factors at the target level of pgh action, such as insufficient or down-regulation of pgh receptors, changes or impaired ability in the pgh receptor-binding characteristics, and inability of pgh receptor complex to transduce signal. Toxins are known to modulate signal transduction pathways. It has been speculated that serotype-D Pasteurella multocida toxin may influence growth by its effect on signal transduction from pgh receptor complex on the cell membrane to the interior of the cell. This would account for the presence of high concentrations of pgh in the plasma and a functionally competent hypophysis cerebri, which responded to ghrh injection that have retarded growth in pigs affected with ar.

Free access
in American Journal of Veterinary Research