this invention relates to the treatment of ruminal lactic acidosis in ruminant animals . specifically , this invention relates to the use of alpha - 2 adrenoceptor antagonists in the treatment of ruminant animals suffering from ruminal lactic acidosis . examples of suitable classes of alpha - 2 adrenoceptor antagonists include imidazolines , benzodioxan - imidazolines and the benzofuroquinolizines . there are a number of examples of specific alpha - 2 adrenoceptor antagonists from each class known to persons skilled in the art . in the following examples the following alpha - 2 adrenoceptor antagonists were tested : from the class imidazolines - tolazoline ( 2 - benzyl - 2 - imidazoline ); from the class benzodioxan - imidazoline - idazoxan [ 2 -( 1 , 4 - benzodioxan - 2 - yl )- 2 - imidazoline hydrochloride ] and mvp - 1248 ( atipamezole - tm ) [ 4 -( 2 - ethyl - 2 , 3 - dihydro - 1h - inden - 2 - yl ) - 1h - imidazole hydrochloride ]; and from the class benzofuroquinolizine - l - 654 , 248 (( 2r , 12bs )- n -( 1 , 3 , 4 , 6 , 7 , 12b - hexahydro - 2h - benzo [ b ]- furo [ 2 , 3 - a ] quinolizin - 2 - yl )- n - methyl - 2 - hydroxyethanesulfonamide )), and l - 657 , 743 ( 2s , 12bs ) 1 &# 39 ;, 3 &# 39 ;- dimethylspiro -( 1 , 3 , 4 , 5 &# 39 ;, 6 , 6 &# 39 ;, 7 , 12b - octahydro - 2h - benzo [ b ] furo [ 2 , 3 - a ] quinolizine )- 2 , 4 &# 39 ; pyrimidine - 2 &# 39 ;- one ). a physiologically - acceptable carrier was chosen to facilitate a dispersion or a solution of the drug for formulation as an injectable . such a carrier could be water or saline solution . in some cases , it may be necessary to add other agents to adjust tonicity and / or acidity of the composition . the administration of the veterinary composition would be parenterally , e . g . intraperitoneally , subcutaneously , intramuscularly or intravenously . the composition could be administered after the onset of ruminal lactic acidosis as in the following examples or it could be given prior to or simultaneously with the introduction of high - energy ration or feed to prevent ruminal lactic acidosis . it would also be possible to use the alpha - 2 adrenoceptor antagonists as a feed - additive to prevent ruminal lactic acidosis . dosages should contain sufficient compound to produce an effective response when administered in a convenient manner . however , such dosages will depend on the potency of the drug being used in blocking alpha - 2 adrenoceptor sites and its selectivity for alpha - 2 adrenoceptor sites . acceptable dosages for the imidazolines ( tolazoline ), benzodioxanimidazolines ( idazoxan , mvp - 1248 ) and one of the benzofuroquinolizines ( l - 654 , 284 ), range from about 2 to about 5 mg / kg body weight . the dosage range of the benzofuroquinolizines ( l - 657 , 743 ), which is highly selective for alpha - 2 adrenoceptor sites , was about 50 to 100 μg / kg . dosage unit forms are very convenient , e . g . 25 - 50 ml of a 5 - 10 % solution in saline of tolazoline , idazoxan , mvp - 1248 or l - 654 , 284 will provide a single dose for an average steer of 500 kg . such a dose given every 6 hrs for two days will alleviate the symptoms in ruminants having this problem . dosage unit forms of the benzofuroquinolizine l - 657 , 743 may be for example from 0 . 5 - 1 ml of a 5 %- 10 % solution in physiological saline , which would provide a single dose for an average steer of 500 kg . a ) surgical preparation of animals and induction of ruminal lactic acidosis -- fifteen adult sheep ( 36 - 50 kg ) and seven calves ( 94 - 130 kg ) were anaesthetized and fitted with permanent rumen cannulas . pairs of nichrome wire recording electrodes were implanted within the walls of the reticulum and rumen to record the myoelectric discharges which preceded contractions of these forestomach regions . strain gauge transducers were also attached to the serosal surfaces of the reticulum and rumen , close to the nichrome wire recording electrodes , to record the tension generated by contractions within these areas . following recovery from surgery , the animals were individually housed and provided with hay , a salt block and water . one month after surgery , ruminal lactic acidosis was induced , following an 18 hr fast . ruminal lactic acidosis was induced by placing a slurry containing ground wheat ( 40 g / kg body weight ) or ground barley ( 50 g / kg ) body weight ) combined with a equal volume of water into the rumen , via the rumen cannula . b ) experimental protocol -- the development of ruminal lactic acidosis was assessed on the presence of marked forestomach hypomotility or ruminal stasis , ruminal acidosis , and systemic acidosis . in addition , behavioural changes associated with ruminal lactic acidosis , i . e . anorexia and depression , were also considered . following the development of ruminal lactic acidosis , afflicted animals were injected with one of the available alpha - 2 antagonists and forestomach motility , ph of rumen contents , and ph of venous blood were monitored for changes in these variables . c ) recording of forestomach motility -- to assess changes in forestomach motility , recordings of myoelectrical activity and tension changes generated by reticular and ruminal contractions began 4 hr before the intra - ruminal placement of wheat or barley and continued until the experiment ended . the level of forestomach motility was assessed by the frequency of the myoelectrical discharges and the frequency and amplitude of reticular tension recordings . d ) rumen fluid and venous blood sampling -- to monitor changes in acidity of rumen contents , samples of rumen fluid were collected 15 minutes before the intra - ruminal placement of wheat or barley and at regular intervals thereafter . the ph of these samples was immediately measured and the osmolality determined in triplicate on a model 5100c vapour pressure osmometer . to determine when systemic acidosis occurred , blood samples were anaerobically obtained , at the time of rumen fluid sampling , from a polyethylene cannula located within the right jugular vein . immediately after collection , the ph and pco 2 of these venous blood samples were measured on a corning model 178 ph / blood gas analyzer and serum hco 3 - and base excess calculated from these values . e ) sources of alpha - 2 adrenoceptor antagonists -- tolazoline ( tm ) hydrochloride was from sigma chemical company ( st . louis , mo ., usa ). mpv - 1248 hydrochloride was from the farmos group ltd . ( turku , finland ) and idazoxan ( tm ) was from reckitt and colman pharmaceutical division ( hull , england ). the alpha - 2 antagonists l - 654 , 284 and l - 657 , 743 were from merck sharp and dome research labs . ( west point , pa ., usa ). f ) effects of alpha - 2 adrenoceptor antagonists on ruminants experiencing ruminal lactic acidosis -- following administration of alpha - 2 adrenoceptor antagonists , a significant increase in the frequency of forestomach motility was evident within half an hour of treatment . an increase in contraction amplitude was , occasionally , observed , but this was not as consistent as the increases in contraction frequency . the ph values of rumen contents and venous blood were not affected by the administration of alpha - 2 adrenoceptor antagonists . all animals which received alpha - 2 adrenoceptor antagonists returned to normal within 48 hr of the induction of ruminal lactic acidosis . g ) effects of alpha - 2 adrenoceptor antagonists on forestomach motility of ruminants experiencing ruminal lactic acidosis - examples of the increases in frequency of forestomach contractions induced by alpha - 2 adrenoceptor antagonists are depicted in fig1 - 6 . increases in forestomach contractions obtained by doses of 2 . 0 , 3 . 0 and 5 . 0 mg / kg of the alpha - 2 antagonist , tolazoline , in sheep experiencing ruminal lactic acidosis are depicted in fig1 . fig2 displays the mean frequency of forestomach contractions , of six sheep suffering from ruminal lactic acidosis , before and after the administration of 5 . 0 mg / kg of tolazoline . in sheep experiencing ruminal lactic acidosis , increases in forestomach motility obtained with doses of 5 . 0 mg / kg of the alpha - 2 antagonists , idazoxan and mpv1248 and doses of 2 . 0 mg / kg of the alpha - 2 antagonist l654 , 284 , can be seen in fig3 . fig4 presents the increases in frequency of forestomach contractions , of two sheep and a calf exhibiting ruminal lactic acidosis , that were obtained with a dosage of 100 μg / kg of the highly selective alpha - 2 adrenoceptor antagonist l - 657 , 743 . increases in forestomach contractions , in calves suffering from ruminal lactic acidoses , with doses of 2 . 0 , 3 . 0 , 4 . 0 and 5 . 0 mg / kg of the alpha - 2 antagonist , tolazoline , are illustrated in fig5 . finally , fig6 demonstrates the mean frequency of forestomach contractions , of four calves suffering from ruminal lactic acidosis , before and after the administration of 4 . 0 mg / kg of tolazoline .
ruminal lactic acidosis develops in ruminant animals following the ingestion of large amounts of unaccustomed feeds that are rich in readily fermentable carbohydrates . characteristics symptoms of this disease include systemic acidosis , ruminal acidosis , forestomach stasis or forestomach hypomotility , inappetence , depression and hemoconcentration . alpha - 2 adrenoceptor antagonists have been found to be capable of re - establishing forestomach motility that has been lost or severely diminished in ruminants suffering from ruminal lactic acidosis . these antagonist compounds have also been found to be effective in the treatment of ruminants experiencing ruminal lactic acidosis .