Anti-lipolytic action of prazosin in hamster fat cells

Using isolated white fat cells of the hamster, we studied the possible inhibitory effects on lipolysis of the preferentially selective alpha-1-adrenoceptor blocking and anti-hypertensive agent prazosin. Parallel studies were undertaken with the preferentially alpha-2-adrenoceptor blocking agent yohimbine. Neither of the compounds had any significant effects on basal (non-stimulated) lipolysis. When lipolysis was stimulated by noradrenaline or isoprenaline, however, prazosin showed significant anti-lipolytic effects from a concentration of 10(-6) M. Lipolysis stimulated by methylisobutylxanthine was antagonized by prazosin only at a concentration of 10(-4) M, and dibutyrylcyclic adenosine 3'5' monophosphate-stimulated lipolysis was not inhibited at all. It is suggested that prazosin inhibits lipolysis by preventing adenyl cyclase activation by an indirect mechanism not identifiable with an alpha-2-adrenergic function but associated possibly with the formation of a local inhibitory mediator. These observations are compatible with a reduction of the outflow of free fatty acids from adipose stores in patients undergoing prazosin therapy and thus a breaking of the "vicious circle" leading to elevated plasma lipoproteins and may explain, in part at least, the reduction in plasma lipid levels observed during prazosin treatment in man.

Application of agents active at the alpha 2-adrenoceptor of fat cells to the treatment of obesity--a critical appraisal

The extent of cyclic AMP (cAMP) mediated lipolysis in adipose tissue cells of man and several other animal species is regulated by the interplay of alpha- and beta-adrenoceptors modulating adenyl cyclase activity. Although the naturally-occurring catecholamines, and isoprenaline, are thought to act at the same pro-lipolytic beta-adrenoceptor antilipolytic agents, working through the alpha 2-adrenoceptor moiety of adenyl cyclase, appear to act at separate sites for: true alpha 2-agonists such as clonidine, for adenosine and for prostaglandins. Further, such antilipolytic agents are conspicuously more potent against lipolysis stimulated by methyl-isobutylxanthine (MIX) than against that stimulated by catecholamines. The nature of the dual character of adenyl cyclase remains to be elucidated. alpha 2 Adrenoceptor antagonists which promote lipolysis, and may possibly serve a therapeutic role in the treatment of obesity, may also provoke inappropriate insulin release which is contraindicated. Thus a problem in chemotherapy exists which may be resolved by new agents with differential tissue specificities. An example of this chemotherapeutic dilemma is possibly provided by the body weight accruing actions of tricyclic antidepressant compounds whose mechanism of action involves also (central) alpha 2-adrenoceptors.

Characterization of the beta-adrenoceptor of the adipose cell of the rat

The dose-response curves of the beta-adrenergic agonists isoprenaline (mixed beta 1 and beta 2), prenalterol (beta 1-selective), noradrenaline (more beta 1 than beta 2) and salbutamol (beta 2-selective) were studied on adipose cells of the rat, in vitro. The observed lipolytic potencies were in the order: isoprenaline greater than noradrenaline greater than salbutamol greater than prenalterol. The effects of beta-adrenergic antagonists betaxolol (beta 1-selective) propranolol (non-selective) and ICI 118551 (beta 2-selective) on lipolysis stimulated by the various beta-adrenergic agonists showed that in each case propranolol was the most potent blocking agent. These observations are not compatible with the concept that regulation of lipolysis in adipose tissue is mediated exclusively either by adrenergic receptors of the classical beta 1 type, or of the classical beta 2 type. We propose therefore, that this beta-adrenergic receptor, because of its non-compliance with the current classification system, be termed a 'beta-3' or beta-hybrid' adrenoceptor. Thus cardio-selective beta-adrenergic blocking agents, like betaxolol, may offer a hitherto unrecognized clinical advantage in obese patients undergoing anti-hypertensive therapy by offering a reduced impediment to hormone-induced utilization of calorie stores in adipose tissue.

Regulation of adipose tissue metabolism via adrenergic mechanisms: actions of alpha-adrenoceptor agonists on lipolysis in hamster fat cells

The effects of two alpha-1-adrenergic agonists (phenylephrine, cirazoline) and two alpha-2-adrenergic agonists (clonidine, guanabenz) were investigated on lipolysis stimulated by noradrenaline, isoprenaline, dibutyryl cyclic AMP (dbc AMP) or methylisobutylxanthine (MIX) in hamster adipose cells, in vitro. Phenylephrine enhanced basal lipolysis and that stimulated by dbc AMP and MIX, whereas cirazoline showed no measurable effects. Clonidine produced a slight but significant decrease of basal lipolysis. Both clonidine and guanabenz (from 10(-7) M) provoked a similar and clear inhibition (50-60 per cent) of MIX-stimulated lipolysis, compatible with the view that the alpha-adrenergic receptor of the hamster white fat cell is of the alpha-2 type. Noradrenaline-stimulated lipolysis was unaffect and isoprenaline-stimulated lipolysis moderately inhibited, by clonidine and guanabenz. Since the beta-adrenergic lipolytic effects of noradrenaline are known to be associated with a simultaneous alpha-adrenergic inhibitory stimulus, and one possible explanation of the but moderate inhibition of isoprenaline-induced lipolysis could be simultaneous beta-adrenergic stimulation (resulting in lipolysis), and alpha-adrenergic stimulation (inhibition of lipolysis), as with noradrenaline, the nature of isoprenaline as a pure beta-adrenergic agonist requires clarification.

A polarographic study of pyranopyrandiones

Polarographic reductions of four methyl-substituted pyranopyrandiones (1)-(4) have been studied at various pH values. Their reducibility and the probable reduction mechanisms are discussed in relation to their structures. The half-wave potentials of their first reduction waves in neutral media show linear correlation with the HMO energies of the lowest vacant π molecular orbitals.

Anti-hypertriglyceridaemic activity of some phenylethylamine anorectic compounds

In rats allowed access to food, and in food-deprived rats, fenfluramine (20 and 100 mg kg-1) and amphetamine (10 and 20 mg kg-1) provoked a hypotriglyceridaemic effect. No changes in plasma cholesterol concentration were observed. The time course of the absorption of a lipid load differed according to the nutritional status of the animals; being bellshaped under fed, and curvilinear under fasted, conditions. However, absorption under both nutritional conditions was inhibited by amphetmine and fenfluramine. When rats which had received the test compounds were administered glycerol trioleate containing a tracer dose of glycerol [1-14C]-trioleate or [2-3H]-glycerol trioleate, there was an inhibition in the increase of plasma radioactivity only in the case when the fatty acid contained the radioactive label. The net effect of lipid absorption was a transfer of dietary lipid from the gut to adipose tissue stores. There was never more than 5 per cent of the administered load in the liver. These observations indicate that amphetamine and fenfluramine may have acute effects in reducing circulating triglycerides, separate from the effects on lipid absorption from the gut. In this latter, the palmitoyl-CoA monooleinacyltransferase enzyme probalby plays a key role and appears a major target of the overall anti-obesity of fenfluramine.

Permissive effects on adipose tissue lipolysis of a plasmatic factor which inhibits prostaglandin biosynthesis

Plasma obtained from fasted rats provoked a dose-dependent stimulation of fat cell glycerol release and was able to inhibit also generation of prostaglandins E2 and F2 alpha from arachidonate, in vitro, over a very similar range of doses. It is proposed, therefore, that a plasmatic fat-mobilizing factor may act as an endogenous inhibitor of adipose tissue prostaglandin biosynthesis, mediating in the acute (long-term not precluded) regulation of adipose tissue lipolysis. The proposed mechanism of permissive effects of the plasmatic factor in reducing the effects of endogenously-generated inhibitory prostaglandins may be implicated in the development of obesity by reduced availability of the factor and thus reduced ability to utilize fat stores.

Salivary gland hyperglycemic factor: an extrapancreatic source of glucagon-like material

Extracts of homogenates of rat, mouse, rabbit, and human submaxillary salivary glands contain a significant quantity of a material with glucagon-like immunoreactivity. Fractionation of this material on columns of Sephadex G-100 reveals a single peak immediately following a gamma globulin marker but in advance of a rat growth hormone marker, crystalline amylase, and isotopically labeled porcine insulin and glucagon. This material, which is urea stable, shows identical immunoassay dilution curves when measured with the highly specific K-30 glucagon antiserum. Study of paired glands in vitro shows that low concentrations of glucose stimulate and high concentrations of glucose suppress release of this material. Arginine promotes brisk release in vitro. Somatostatin does not influence arginine-stimulated secretion and insignificantly suppresses basal release in vitro. These findings lend support to previous speculations that the salivary glands may possess endocrine as well as exocrine functions. Salivary gland glucagon may also be the source of circulating glucagon recently reported in pancreatectomized and eviscerated rats.

Hemangiomas of the salivary glands

Five salivary gland hemangiomas in adults are reported. The feasibility of preoperative diagnosis on clinical and radiologic grounds is emphasized. Adult hemangiomas are of the cavernous type and can be differentiated from infantile capillary hemangiomas clinically as well as histologically. Cavernous hemangiomas in the adult should be treated by surgical excision.

The mercury(II)-induced aquation of trans-Chloroamminebis(dimethylglyoximato)cobalt(III) complex

The pseudo first-order rate constants for the mercury(II)-induced aquation of trans-[Co(Hdmg)2(NH3)Cl] (Hdmg = dimethylglyoximate ion) have been measured in aqueous and aqueous ethanol solutions (ethanol- water mole ratio 1 : 5.1) containing various excess amounts of mercury(II)ion at 273.2 K. Association constants of the complex formed with mercury(II) ion and rate constants for dissociation of the activated complex in both solutions have been calculated. The kinetic results are discussed in terms of formation of an activated complex Co-C1-Hg, followed by a simple rate-determining aquation in which HgCl+ acts as the leaving group.

GALVANIC STRESS POTENTIALS OF METALS

The electrode potential of silver, brass, and steel wires under tensile stress have been measured in aqueous solutions of silver nitrate, copper sulphate, and ferrous sulphate, respectively. The stress potentials were continuously measured with a stabilized d-c. microvolt amplifier which made possible the study of the transient and the steady-state period during loading and unloading. The stressed silver and steel electrodes were cathodic with respect to the reference electrode, and the e.m.f. was approximately a linear function of the stress. The slope of the e.m.f.–stress curve for silver increased with decrease in electrolyte concentration. The stressed brass electrode was anodic with respect to the reference electrode and the e.m.f. varied linearly with stress only for 1 N CuSO4.