| pharmacology | screening | assay | |||
| digitalis | *used in ttt of CHF as it a)+ COP b)! venous pr c)! dyspnea d)! oedema *mech 1-release of ca from SR 2-+ entering of extracell ca 3-inhibit memb bound Na/K ATPase (receptor of DGS so + entracellular sod & ! Entracellular potassium this by 1-! Exchange () Na & ca >ca remain entracellular the cardiac muscle 2-displacement of ca from its binding site *DGS effect 1-+ force of contr(+ve intropic effect) 2-bradycardia (direct or vagal) 3-toxic effects (nausea & vomiting) *both therapeutic & toxic effect used in assay of DGS | 1-isolated cat papaillary muscle | *one part attached to ventricle other attached to tricusped valve *adv : sensitive , used in screening & assay *method :anaesth cat >isolate heart >squeeze >right ventricle opened >sep one pap muscle *Kreb's Henseleit soln >hang the mus at 37c & aeriated by carbogen *electrical stim *when amplitude become stable add drug >observe height of peak >if + height of contr so drug is either sympathomimetic or digitalis to diff use B blocker before addn of unknown > if no contr increase so drug is sym ,, if no effect on contr >digitalis *assay by calc % increase in contr & compare e std *it is better to use falling heart by :1-electrical stim for 1 hr ! force of contr 2-using diff p. soln contain 1/2 ca % & no NaHco3 3-addn of barbiturates ut it is not asdvisable due to chemical interaction | 1-G pig method | *depend on toxic effect *inject digitalis till AV block (atrioventricular block) >cardiac arrest *sep 2 gps of G pigs one gp take test & othe rtake std *anasth by ether *cannulation of Jugular vein *infusion of test cpd in stable rate (1ml/min) till cardiac arrest (eg from 15-20 min) detected by ECG *measure vol of test cpd till cardiac arrest occur *match cs test =cv std |
| 2-pigeon method | *2 gps of pigeon *canulatn of wing vein after anasth *infusion of test & std soln *calc vol till cardiac arrest | ||||
| G pig atria (auricles) | *either take right atr (SA node ,spontaneous contr ) or left atrium >electrical stim *best to take both as easily prep and both are beating *put in Ringer-locke soln *at 37c ,carbogen *observe normal contr *then add unknown > % + in contr *use propranolol (B blocker ) to diff () sym & digitalis | 3-cat method (toxic effect) | *EP is cardiac arreset *anasth >canulatn of Femoral vein >infusion *it take longer time than G pig (30-35m) *disadv :1- more amount of Digitalis 2-results are not reproducible *G pig method :more sensitive 2-less amount of drug 3-cheaper | ||
| 3- Langerdorff's prep | *rabbit heart from Aorta ,calc force of contr *add B blocker to diff from sym | 4-depend on toxic effect (vomiting) on pigeon | *5 gps of pigeon each (5 pigeon) *inject diff conc of std & test *calc % of vomiting *draw the graph % vomit # dose and calc dose that make 50% vomiting {quantal assay} >:all or none ,+ve or -ve | ||
| assay of minute amounts of digitalis in biological fluids (isolated embryonic chick heart method) | *very sensitive method *fertile egg of chicken *incubate for 48 hr at 38 or 39 c *formatn of tubular heart (observe atrium & ventricle beating) *isolate tubular H e the aid of microscope *then hang in warm tyrode's soln >H is spontan beaten *prep petri dishes & diff vol of std & test cpds *calc time of immertion till AV block (when contr stopped) *then the curve () vol & time *compare test & std (++ conc !! time) | ||||
| anti arrythmia | due to 1-delayed after depolarization 2-re entery mech 3-abnormal pace maker (ectopic cocci) 4-Av block (due to a)fibrosis of av node b) infarction) | induction of arrythmia : 1-cardiac glycosides in toxic dose (by infusion of G pig or rat) >tachycardia >arryth or AV block 2-Epinephrine (large dose ) esp e halogenated anasthetic agent as halothan ,CHCL3 w make myocardial more sensitive to E 3-CaCl2 >infusion 4-surgical by acute ligation of coronary artery of dog or cat (thourgh 10 min >arryth occur 5-use aconitine (very toxic) by use cotton moistened e aconitine or infusion by small amount 10 ug/kg/min on rat *then add anti arryth then aconitine again >prolong tine 6-choline esters (carbachol) > arryth accelerate repolarization of atrial fibers and shorten atrial refractory period >atrial flutter & atr fibrillation | isolated auricles | *right & left atrium >Ringer-locke soln at 30c *carbogen *2electrodes tied in atrium >elect. Stim *+ Elect stim till drop beat (frequency at drop beat is max rate for eg 260) if give anti arryth >+ refractive period > ! Max driving rate *so % reduction of max rate is plotted # log conc of anti arryth to give straight line | |