Comparative study of iodothyronine outer ring and inner ring deiodinase activities in five teleostean fishes

The presence of outer ring deiodinating (ORD) and inner ring deiodinating (IRD) activities was investigated in different tissues of Oreochromis niloticus (Nile tilapia), Clarias gariepinus (African catfish), Oncorhynchus mykiss (rainbow trout) and halmus maximus (turbot). High-K_m rT₃ ORD is present in the kidney of most of the fishes studied, except in catfish. In turbot, besides the kidney, rT₃ ORD is also present in liver, heart and ovary. Low-K_m T₄ ORD is found in the liver and low-K_m T₃ IR the brain of all the fishes studied. In addition, low levels of low-K_m T₃ IRD were demonstrated in gill and skin of Nile tilapia, liver of rainbow trout and gill and kidney of turbot. For the different teleosts, the biochemical properties of the different rT₃-deiodinating enzymes mentioned, T₄ ORD in liver and T₃ IRD in brain and tilapia gill were compared to those of the deiodinases formerly characterized in Oreochromis aureus (blue tilapia). In general, the different deiodinases demonstrate analogous sensitivities to iodothyronines and inhibitors, although minor differences occur. The various deiodinating enzymes all depend on addition of dithiothreitol and demonstrate maximal activity pH between 6.5 and 7. The optimal incubation temperature of rT₃ ORD and T₄ ORD in tilapia and catfish is 37 °C, in trout and turbot it varies, depending on the tissue, between 25 ° and 37 °C. For the different T₃ IRD activities the optimal temperature is 37 °C in warmwater as well as in coldwater species. The apparent Km values for rT₃ ORD lay in the M range, for T₄ ORD and T₃ IRD they lay in the nM range. V_max values are usually higher in tilapia as compared to the other teleosts studied. Based on the similarities in susceptibility to inhibition by different iodothyronines and inhibitors and the agreement of the apparent K_m values, we conclude that the deiodinating enzymes in teleosts are more similar to mammalian deiodinases than is generally accepted.     

Failure of adrenocorticotrophic hormone to release serum amyloid A in cattle.

The objective of this study was to determine whether adrenocorticotrophic hormone plays a direct role in the secretion of serum amyloid A (SAA) in cattle. Seven lactating Holstein-Friesian cows were given either saline or 25 iu adrenocorticotrophic hormone (ACTH) intravenously at 09.00 in a two factor crossover design. Plasma cortisol concentrations had increased significantly by one hour after the injection of ACTH, whereas the SAA level had not increased by 24 hours after injection. It is concluded that in cattle adrenocorticotrophic hormone has no direct influence on the release of SAA by the hepatocyte.     

Identification of toxigenic Pasteurella multocida in atrophic rhinitis of pigs by in vitro characterisation

Toxigenic strains of Pasteurella multocida were readily differentiated from non-toxigenic strains by an agarose overlay method using bovine turbinate cells or bovine lung cells. Cells which were young and densely confluent were best suited to this assay. The incubation period required to distinguish toxigenic strains was dependent on the confluence of the monolayers, which was affected by the seeding rate, cell passage level and growth time prior to overlay. The agarose overlay method correctly identified 11 of 11 reference strains of Pasteurella multocida, and visible cytotoxic changes were present in the monolayers after 48 to 65 h. Outbreaks of the enzootic form of atrophic rhinitis in 2 New South Wales piggeries were associated with the isolation of toxigenic type D strains of P. multocida.