(Na+,K+)-ATPase and noradrenergic regulation: effects of cardiac glycoside treatment and noradrenergic manipulations

Inhibition of plasma membrane and mitochondrial transmembrane potentials by ethanol

The actions of ethanol and its primary oxidative metabolite, acetaldehyde, on plasma membrane and mitochondrial transmembrane potentials were examined in rat brain using fluorescence techniques. Subchronic treatment of adult rats with ethanol resulted in a significant depolarization of both the plasma and mitochondrial membranes when the mean blood ethanol level of the rats was 59 +/- 11 mM (mean +/- SEM, n = 6). Acute dosing of animals (4.5 g/kg, i.p.) failed to show any significant alterations. Various concentrations of ethanol, added in vitro to a crude synaptosomal preparation isolated from the rat cerebrocortex (P2) from untreated animals, depolarized both the plasma and mitochondrial transmembrane potentials in a dose-related manner. Addition of acetaldehyde in vitro did not reveal any significant effects on plasma or mitochondrial transmembrane potential.

Effects of digoxin on the anabolic response to clenbuterol

The possible involvement of increased cation exchange in the anabolic response to the beta 2-selective adrenergic agonist clenbuterol was investigated using dietary admixtures of clenbuterol and the Na,K-adenosine triphosphatase (ATPase) inhibitor digoxin. In a rat feeding trial to assess the effects on body composition, it was found that the higher of two levels (5 and 30 mg/kg diet) of digoxin had an inhibitory effect on the repartitioning effects (ie, increased body weight and fat-free mass) of clenbuterol (2 mg/kg diet). In two further experiments using 30 and 60 mg digoxin/kg diet, it was found that the anabolic effects of clenbuterol on gastrocnemius muscle protein deposition were inhibited by digoxin, but the effects of clenbuterol on soleus muscle protein were more resistant to inhibition. Given the observed dose-dependent inhibition by digoxin of gastrocnemius muscle protein deposition in the three experiments, it was concluded that at least part of clenbuterol's anabolic actions on skeletal muscle may depend on increased Na,K-ATPase activity. However, different mechanisms or a different time course of Na,K-ATPase activation may occur in different muscle fiber types.

Effects of steroidal and non-steroidal antiandrogens on the left atrium of the rat in vitro

1. The effect of steroidal-cyproterone acetate (CPA, 10(-7)-10(-5) M), clormadinone acetate (CMA, 10(-7)-10(-5) M), medroxyprogesterone acetate (MPA, 10(-7)-10(-5) M) and spironolactone (SPI, 10(-7)10(-5)M) and non-steroidal-flutamide (F, 10(-7)-6 x 10(-5) M) and cimetidine (C, 10(-7)-10(-4)M) antiandrogens on contractile force of electrically stimulated left atria of the rat have been assayed. 2. CPA, CMA, MPA and F inhibit, in a dose-dependent way, the contractile force of left atria. SPI enhanced (P less than 0.01 at 10(-6) M), and cimetidine did not modify the contractile force. 3. F, but not CPA, CMA, MPA or SPI, inhibit the contractile force induced by CaCl2 (0.9-7.2 mM) on electrically stimulated left atria. 4. The inhibitory effect of CPA (10(-7)-10(-5) M) was significantly increased by atropine (10(-6) M) and diltiazen (10(-5) M), and significantly reduced by yohimbine (10(-7) M) and in reserpinized (2.5 mg/kg, 48 and 24 hr before experiments) rats. 5. Our results suggest that the negative inotropism of steroidal antiandrogens could be related to inhibition of noradrenaline release, presumably through an alpha 2 adrenergic effect. The negative inotropism produced by F is related to inhibition of calcium dependent process on left atria contraction.

Thyroid hormone and norepinephrine: effects on alpha-2, beta, and reuptake sites in cerebral cortex and heart

Thyroid hormone produces metabolic effects similar to those of stimulation of noradrenergic receptors. It has been reported, however, that norepinephrine turnover is reduced during thyrotoxicosis and that beta-noradrenergic receptor number is increased. Metabolic effects of thyroid hormone may therefore reduce noradrenergic activity. We examined effects of thyroid hormone administration or production of hypothyroidism with methimazole on receptors associated with regulation of noradrenergic function. Treatment with thyroid hormone increased beta-receptor binding, increased alpha-2 receptor binding, and decreased desipramine binding, opposite to effects of hypothyroidism produced by methimazole. Heart was more sensitive than brain to these effects. These data are consistent with reduced noradrenergic activity during hyperthyroidism, possibly mediated by an increase in autoreceptor function.