Pierre Lacroix

Potential biological targets for anti-Alzheimer drugs

The stunning accumulation of data on the physiopathology of Alzheimers disease is a real hinderance to pharmacologists who have to make decisions as to what molecules should be assessed first in man. Considering the cumbersomeness and cost of clinical trials in that field, a review of potential targets for drugs that are supposed to be active against the disease has become necessary, for a true definition of the rational justifications of trials to be envisaged.

Cardiomyopathic Syrian Hamster as a Model of Congestive Heart Failure

Cardiomyopathic Syrian hamsters (Bio TO‐2 dilated strain) constitute an animal model of congestive heart failure, which progressively develops an alteration of cardiac function leading to decreased arterial blood pressure and musculo‐cutaneous blood flow associated with a complex process of cardiac remodeling including left ventricle dilation, wall thinning, and greater collagen density. The protocols described in this unit are designed to assess the pharmacological effects of new therapeutic strategies on cardiac and systemic hemodynamics, morphometry (body and target organs weight), cardiac remodeling (left ventricle dilation and collagen density), and survival in this model of dilated cardiomyopathy. Examples of results obtained with enalapril, an angiotensin I converting enzyme inhibitor, are provided for illustrative purposes. Curr. Protoc. Pharmacol. 42:5.50.1‐5.50.12.

Effects of dimethylformamide on in vivo fatigue and metabolism in rat skeletal muscle measured by 31P-NMR.

Dimethylformamide (DMF) is widely used as an industrial solvent in spite of well-established hepatotoxicity and adverse effects on in vitro muscle contractility. The doses used in the studies describing these effects were higher than the doses required to solubilize drugs to be injected at very low levels and the potential effects of DMF at very low levels has not yet been explored. The goal of this work was to study the effects of an acute, low dose of DMF (3 mu/100 g body weight, administered i.p.) on mechanical parameters and energy metabolism of contracting rat skeletal muscle. Metabolic changes were followed by 31P nuclear magnetic resonance spectroscopy. Tension was significantly lower during the fatigue test in DMF-treated rats than in controls. Phosphomonoesters and inorganic phosphorus level were lower, and intracellular pH was higher in DMF-treated rats than in controls, showing that energy metabolism was activated to a lesser degree, in relation with the lower mechanical performance, after DMF. Skeletal muscle is a target organ for dimethylformamide which has a major effect on muscle contractility by decreasing the tension developed. The effects of DMF suggest that it is unsuitable for use as a drug vehicle for in vivo injections, even at a very low nonhepatotoxic doses.

Gastrointestinal Models: Intestinal Transit, Gastric Emptying, and Ulcerogenic Activity in the Rat

The protocols described in this unit are designed to assess the effects of substances on intestinal transit and gastric emptying and to evaluate their ulcerogenic potential on the stomach and duodenum of the rat. Examples of results obtained with atropine or morphine (intestinal transit), loperamide (gastric emptying), or indomethacin (ulcerogenic activity) used as reference substances are provided for illustrative purposes. Atropine and morphine clearly reduce intestinal transit. Atropine, morphine, and loperamide clearly reduce gastric emptying. Indomethacin shows a marked ulcerogenic potential. Curr. Protoc. Pharmacol. 42:5.3.1‐5.3.12.

Orthostatic Hypotension Induced by Postural Change in the Rat (Tilt Test)

Postural‐change‐induced (orthostatic) hypotension is defined as an excessive drop in arterial blood pressure occurring when moving toward an upright position. This side effect, which may limit the therapeutic use of some agents, can occur with drugs, such as adrenoceptor blockers and vasodilators, that dampen sympathetic reflex activity. Described in this unit is a procedure for evaluating the effects of test substances on the changes in blood pressure and heart rate that occur in an anesthetized, normotensive rat during a tilting challenge (head‐up position). In addition to being a relatively simple technique, this assay yields reproducible orthostatic hypotensive responses and allows for the investigation, in the same preparation, of several ascending doses of a test substance. Examples of results obtained with prazosin, an α1‐adrenoceptor antagonist that is notorious for causing orthostatic hypotension, are provided for illustrative purposes. Curr. Protoc. Pharmacol. 40:5.45.1‐5.45.8.

Influence of Enalapril Therapy Schedule on the Progression of the Disease in Dilated Cardiomyopathic Syrian Hamsters (Bio TO-2 strain)

The influence of enalapril therapy schedule on the progression of the disease in terms of hemodynamics, cardiac remodeling and survival was assessed in cardiomyopathic Syrian hamsters (CMHs). CMHs (Bio TO-2 dilated strain) were treated orally with enalapril at 20 mg/kg/day from 60 to 200 (early treatment), from 120 to 200 (late treatment) or 120 to 250 (prolonged treatment) days of age. In survival studies, CMHs were treated until 90% of controls are death. Early, late and prolonged treatments significantly decreased mean arterial blood pressure (-23%, -27% and -22%, respectively), but had no effects on cardiac output and stroke volume. Late and prolonged treatments significantly decreased total peripheral resistance (-38% and -24%, respectively), but not early treatment. Only, prolonged treatment significantly decreased left ventricle (LV) end diastolic blood pressure (-60%). Early, late and prolonged treatments significantly decreased LV collagen density (-44%, -31% and -54%, respectively) and LV cavity area (-26%, -21% and -29%, respectively). Survival was significantly improved when enalapril was administered from 120 days of age, but not significantly when administered earlier. In conclusion, enalapril exerted beneficial effects (improvement of cardiac function and prolonged survival) more marked when the treatment was begun late in the evolution of congestive heart failure.

Models of Cardiovascular Disease: Measurement of Antihypertensive Activity in the Conscious Rat (SHR, DOCA‐Salt, and Goldblatt Hypertension Models)

The protocols described in this unit are used to assess the effects of new chemical entities on hypertension in conscious rats. In the spontaneously hypertensive rat (SHR) model, the results obtained with the reference compounds clonidine, prazosin, propranolol, and captopril are provided for illustration. All compounds demonstrate antihypertensive activity, with captopril and prazosin being the least and the most active, respectively. In the deoxycorticosterone acetate (DOCA)‐salt model in the rat, the test substance shown as an example (a potential endothelin ETA‐receptor antagonist) prevents the development of hypertension in the first phase. However, the effects of treatment disappear in the very last phase of the study, suggesting the development of a malignant hypertension resistant to treatment in this model. In the Goldblatt hypertension rat model (renal artery stenosis), losartan prevents the development of hypertension. It does not modify the weight of the right and left kidneys but slightly reduces the degree of cardiac hypertrophy. Curr. Protoc. Pharmacol. 44:5.53.1‐5.53.15.

Models of Cardiovascular Disease: Measurement of Arrhythmogenic/Antiarrhythmic Activity in the Guinea Pig

The protocols described in this unit are used to assess the effects of new chemical entities on arrhythmias in the guinea pig. In the anesthetized guinea pig, arrhythmias are induced by a slow intravenous infusion of digoxin, which provokes extrasystoles, ventricular tachyarrhythmias, and ultimately cardiac arrest. Imipramine precipitates the occurrence of arrhythmias, whereas propranolol shows protection against them. Curr. Protoc. Pharmacol. 44:5.1.1‐5.1.5.

In vivo31P NMR assessed effects of dantrolene on mechanics and energy metabolism in tetanic stimulated rat gastrocnemius

Dantrolene does not affect fatigue from submaximal effort and MVC while it decreases twitch tension. We hypothesize that dantrolene could modify the relation between energy metabolism and fatigue by inhibiting calcium release from the sarcoplasmic reticulum. The effects of dantrolene (10 mg) on mechanical and metabolic parameters of gastrocnemius muscle were examined by 31P NMR during an in vivo fatigue test. The fatigue test constituted of three successive 20 min periods of increased stimulation rhythms and followed by a 20 min recovery period. 31P NMR was used to determine phosphocreatine (PCr), ATP and intracellular pH changes, while tension was recorded. We showed that dantrolene increased mechanical fatigue while PCr levels were similar to those from control animals. Acidosis was most prominent in dantrolene treated rats. These results suggest that dantrolene firstly affects calcium cycling with additive effects to fatigue and, secondly, modifies the activation of oxidative metabolism and the energy cost of the generated tension.