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4bstract. The effect of fiber type and endurance exercise training on skeletal muscle 0-adrenoceptor properties were assessed using a direct radioligand binding technique. Six separate muscles, composed of a variety of different fiber types, were examined in treadmill trained and sedentary rats. In trained animals, sarcolemmal preparations from heart and slow twitch soleus muscle exhibited a significantly greater receptor concentration than membranes from white fast twitch glycolytic fibers of the vastus lateralis. No significant changes were observed between trained and sedentary rat muscle 0-adrenoceptor density (Omax, fmole/mg protein) or affinity (Kd, nM) within each muscle type, despite significantly increased myocardialfiody weight ratios and skeletal muscle enzyme adaptations associated with the exercise program. These results suggest that muscle 0adrenoceptor properties may be influenced in part by the motor nerve innervation to that muscle, and are further discussed with respect to a possible relationship between exercise intensity and receptor regulation.

Direct quantitation of blood flow with radioactive microspheres in conscious spontaneously obese rats indicated that the development of obesity was associated with an elevated cardiac output and stroke volume, a normotensive blood pressure, and a reduced total peripheral resistance when directly comparing obese rats with their lean counterparts. Obesity was also associated with increased blood flow and decreased regional vascular resistance in a variety of vascular beds, whereas cardiac index and total peripheral resistance per unit of body weight were similar between groups. When corrected for tissue weight, unique alterations in flow and resistance were observed in the adipose tissue. When expressed as resistance per organ, the greatest relative alterations in vascular resistance with the development of obesity also occurred in the adipose tissue. Furthermore, localized adipose tissue expansion through cellular hypertrophy was consistently associated with a different pattern of blood flow and vascular resistance than adipose tissue that expanded through both cellular hypertrophy and hyperplasia, implying an association between depot cellularity and its hemodynamic profile.

The effects of two structurally similar butyrophenones (droperidol and haloperidol) and ketamine were evaluated in an in vitro system to determine their potential for eliciting or exacerbating an episode of malignant hyperthermia. Muscle strips from patients referred for diagnostic testing for malignant hyperthermia and muscle strips from the rat diaphragm were exposed to droperidol, haloperidol, or ketamine prior to challenge with halothane, succinylcholine or caffeine. If any agent augmented the contracture response to the malignant hyperthermia triggering or diagnostic agents, then the agent was considered unsafe for use in malignant hyperthermia susceptible patients. Droperidol 10 mumol/l and ketamine 100 mumol/l did not induce contractures in human or rat skeletal muscle when added alone, nor did they augment halothane, succinylcholine or caffeine contractures. These agents appear to be safe for use in patients susceptible to malignant hyperthermia. In contrast, haloperidol 10 mumol/l augmented the response to succinylcholine about 1.5-fold and may be contraindicated in MH susceptibles.