Brian Roy Holloway

ICI D7114 a novel selective β‐adrenoceptor agonist selectively stimulates brown fat and increases whole‐body oxygen consumption

1 ICI D7114 is a novel, β‐adrenoceptor agonist which stimulates whole body oxygen consumption in conscious rats, cats and dogs and brown adipose tissue (BAT) activity in conscious rats. Treatment of rats with ICI D7114 stimulated oxygen consumption (ED50, 0.04 mg kg−1, p.o.) and BAT mitochondrial guanosine diphosphate (GDP)‐binding (ED50, 0.15 mg kg−1, p.o.) with no chronotropic effects on the heart at these doses. 2 Reference β‐adrenoceptor agonists, isoprenaline and clenbuterol, also stimulated oxygen consumption and BAT activity but were less selective because they also produced effects on heart rate at these doses. 3 Treatment of conscious rats with ICI D7114 did not attenuate the chronotropic effects on the heart of a subsequent isoprenaline challenge. 4 Administration of ICI D7114 or of its acid metabolite had no effect in a cat soleus muscle model of tremor or on blood potassium levels in the conscious dog, indicating lack of effects at β2‐adrenoceptors. 5 The results indicate that ICI D7114 may have activity at atypical β‐adrenoceptors in brown adipose tissue leading to increased whole body oxygen consumption.

Hypothalamic neuropeptide Y receptor characteristics and NPY-induced feeding responses in lean and obese Zucker rats

Increased hypothalamic neuropeptide Y levels have previously been demonstrated in several hypothalamic nuclei of the (fa/fa) Zucker rat. This study set out to characterise hypothalamic NPY receptors in both genotypres and to study the effect of exogenous NPY on feeding behavior in these rats. Spontaneous daytime food intake was raised in the obese rat (p less than 0.05). Total hypothalamic receptor density (Bmax) was reduced in the obese rat compared with the lean rat (by 56%, p less than 0.005), but affinity remained unaltered. The lowest dose of NPY tested (23.5 pmol) stimulated daytime feeding in lean rats after 1, 2 and 3 hours but was inaffective in the obese rat (p less than 0.05). At two higher doses (235 pmol and 2.35 nmol), NPY was equipotent in both genotypes over 1 and 2 hours but NPY-induced feeding was attenuated over 3 hours in the obese rat. These results suggest an overactive endogenous NPYergic system in the obese (fa/fa) rat which might contribute to hyperphagia and obesity in this strain.

Clobuzarit: Species differences in the morphological and biochemical response of the liver following chronic administration

Clobuzarit is structurally related to a number of hypolipidemic agents which produce characteristic changes in rodent liver morphology and biochemistry. Liver effects were determined in a number of rodents, the albino rat, C57BL/10J mouse, and Syrian hamster, and in other mammals, the beagle dog and marmoset monkey, following chronic (14-day) oral administration of clobuzarit at two dose levels. Expected (peak) serum levels of clobuzarit were achieved in all species except the marmoset in which levels were approximately half those predicted. Dose-dependent enlargement of rat and mouse liver cells (assessed qualitatively by light microscopy) was observed. This finding was accompanied by proliferation of peroxisomes and smooth endoplasmic reticulum (assessed by electron microscopy and enzymatically). In the rat and mouse, the fatty acid oxidation enzyme systems of peroxisomes and endoplasmic reticulum were markedly induced. The hamster showed no increase in liver cell size but there was a limited proliferation of peroxisomes (indicated by electron microscopy and enzymatically) and an increase in endoplasmic reticulum fatty acid oxidase. No proliferative effects were observed in the liver of the dog or marmoset. Lowering of plasma triglycerides and cholesterol was observed in the rat only. The differences in the morphological and biochemical responses to clobuzarit among the species used in this toxicity testing clearly illustrate the problems of predicting effects in man from animal data.

Selective .beta.3-adrenergic agonists of brown adipose tissue and thermogenesis. 1. [4-[2-[(2-Hydroxy-3-phenoxypropyl)amino]ethoxy]phenoxy]acetates

The ester methyl [4-[2-[(2-hydroxy-3-phenoxypropyl)amino]ethoxy]phenoxy]acetate (8) has been identified as the most interesting member of a series of selective beta 3-adrenergic agonists of brown adipose tissue and thermogenesis in the rat. In vivo it acts mainly via the related acid 10. Potency was generally markedly reduced by placing substituents on the phenyl ring of the phenoxypropanolamine unit of 8; only the 2-fluoro analogue 16 had comparable potency to 8. Other structure-activity relationships are discussed. Further testing of 8 (ICI 198157) has shown that in the rat it stimulates the beta 3-adrenergic receptor in brown adipose tissue at doses lower than those at which it affects beta 1 and beta 2 adrenergic receptors in other tissues. It increases metabolic rate, as judged by an increase in oxygen consumption, and in the genetically obese Zucker rat it causes a reduced rate of weight gain. This class of compound may be useful in the treatment of obesity in man.

ICI D7114: a novel selective adrenoceptor agonist of brown fat and thermogenesis.

Increasing energy expenditure by treatment with thermogenic drugs is not new, but available drugs have suffered from the problem of lack of selectivity. In the last decade two key findings have allowed the development of selective thermogenic drugs that have promise in the treatment of obesity. 1) The recognition that brown adipose tissue (BAT) plays a role in compensatory increases in energy expenditure has allowed an approach directed at a target organ. 2) The demonstration showing that increases in the activity of BAT may be modulated by an atypical (beta 3) adrenoceptor has led to the development of a new peripherally acting beta-adrenoceptor agonist ICI D7114, which stimulates thermogenesis at doses that have little effect on beta 1 or beta 2 adrenoceptors. Treatment with the compound activates BAT and thermogenesis even in species and situations where the intrinsic capacity is low. 3) The compound has beneficial effects in animal models of obesity and disturbed glucose and lipid homeostasis.

Zeneca ZD7114 acts as an antagonist at β3‐adrenoceptors in rat isolated ileum

1 The relaxant effects of Zeneca ZD7114, BRL37344 (putative β3‐adrenoceptor agonists) and various phenylethylamine‐based agonists were studied in isolated ileum of the rat where tone was increased with carbachol (0.5 μm). Agonist‐induced relaxation was measured under equilibrium conditions with α‐, β1‐ and β2‐adrenoceptors inhibited. 2 Relaxant responses were obtained to isoprenaline, noradrenaline, and BRL37344, although, the efficacy of this latter agent was significantly lower than that of isoprenaline. Salbutamol caused weak relaxation (<20%) at high concentrations (10 μm) and ZD7114 was without significant relaxant effect even at high concentrations (10 μm). 3 Relaxant responses to isoprenaline and BRL37344 were weakly antagonized by high concentrations of (±)‐propranolol (10 and 100 μm) yielding pKB values of 5.7 with isoprenaline as the agonist and 5.5 with BRL37344 as the agonist. 4 The non‐selective β‐adrenoceptor antagonist, (±)‐alprenolol (1–100 μm) caused competitive antagonism of the relaxant responses to isoprenaline (pA2 value = 6.5). A similar pKB value was obtained when BRL37344 was used as the agonist (6.4). 5 Relaxant effects of isoprenaline and BRL37344 were also antagonized by ZD7114 (1–100 μm) yielding pA2 and pKB values of 6.3 and 6.7 respectively. 6 The low potencies of (±)‐propranolol and (±)‐alprenolol as antagonists of the relaxant responses to isoprenaline and BRL37344 indicate that both the agonists and antagonists employed in the current study may interact with β3‐adrenoceptors in the rat isolated ileum. Contrary to the previous findings in guinea‐pig ileum, where BRL37344 and ZD7114 were full agonists, in the current study, BRL37344 was a partial agonist and ZD7114 an antagonist at the β3‐adrenoceptor in rat ileum.

Evaluation of ICI D7114, a putative stimulant of brown adipocytes, on histamine-contracted guinea-pig ileum.

1 Experiments were performed to characterize the effects of the novel brown adipocyte stimulant, ICI D7114, in the guinea‐pig isolated ileum, right atrium and tracheal chain. In the ileum, agonist‐induced inhibition of the contractile response to either histamine or prostaglandin E2 (PGE2) was assessed, along with effects on resting rate in the atrium and resting tone in the tracheal chain. In the latter two preparations, antagonism of isoprenaline‐induced responses by ICI D7114 was also assessed. 2 Inhibitory responses were obtained in the ileum to ICI D7114, isoprenaline, BRL37344, and noradrenaline. The responses to ICI D7114, isoprenaline and BRL37344 were resistant to blockade with propranolol (5 μm), naloxone (1 μm), methysergide (0.1 μm), cimetidine, indomethacin and 8‐phenyltheophylline (all 10 μm). These responses to isoprenaline, in the presence of propranolol (5 μm), were competitively antagonized by alprenolol (1–100 μm) with a pA2 value of 6.44. The responses to ICI D7114 and BRL37344 were antagonised by single concentrations of alprenolol (1 μm) with apparent pKB values of 6.53 and 6.57 respectively. These data indicate an effect of ICI D7114 at the atypical β‐adrenoceptor in the guinea‐pig ileum. 3 The order and relative potency of agonists at the atypical β‐adrenoceptor was BRL37344 (4) > isoprenaline (1) = ICI D7114 (1.1) > noradrenaline (0.5). 4 ICI D7114 (1 nm–10 μm) caused no significant change in the rate of beating or the resting tone of the guinea‐pig right atrium or tracheal chain respectively. It did, however, cause selective blockade of the responses to isoprenaline in these tissues (apparent pKB values 7.63 and 5.85 in atrium and tracheal chain respectively). Responses to histamine (atrium) and aminophylline (tracheal chain) were not significantly affected by 10 μm ICI D7114. 5 These results demonstrate that ICI D7114 possesses selective agonist activity at atypical β‐adrenoceptors in the guinea‐pig ileum and its use as a tool may help to establish a role for the atypical β‐adrenoceptor in the control of gastrointestinal motility.

The acid metabolite of ZD7114 is a partial agonist of lipolysis mediated by the rat β3-adrenoceptor

Experiments were performed to characterise the lipolytic effects of the acid metabolite, ZM215001, ((S)-4-[2-hydroxy-3-phenoxy-propylamino-ethoxy] phenoxyacetic acid) of the putative beta 3-adrenoceptor agonist, ZD7114 ((S)-4-[2-hydroxy-3-phenoxy-propylamino-ethoxy]-N-(2-methoxyethyl) phenoxyacetamide) on isolated rat white adipocytes. ZM215001 was used for these studies since it is the predominant moiety after in vivo administration of ZD7114. The agonist properties of ZM215001 were assessed in comparison to the standard nonselective beta-adrenoceptor agonist (+/-)-isoprenaline and the beta 3-adrenoceptor-selective agonist BRL 37344. Isoprenaline, BRL 37344 and ZM215001 all stimulated the rate of free fatty acid release from isolated adipocytes with the order of potency being BRL > isoprenaline > ZM215001. The maximum effect of BRL 37344 was equivalent to that of isoprenaline, but ZM215001 achieved only 30% of the maximum isoprenaline response. ZM215001 competitively antagonised the lipolytic response to BRL 37344 (pA2 = 7.26), whereas the agonist effects of BRL 37344 were not antagonised competitively by the selective antagonists ICI 118551 and CGP 20712A, at concentrations which would be expected to block beta 1- and beta 2-adrenoceptors respectively. These results indicate that ZM215001 has low intrinsic activity at the rat adipocyte beta 3-adrenoceptor, and is a partial agonist of lipolysis in rat white adipocytes.