A receptor subtype involved in neuropeptide-Y-induced food intake.

Neuropeptide Y (NPY) is a powerful stimulant of food intake and is proposed to activate a hypothalamic 'feeding' receptor distinct from previously cloned Y-type receptors. This receptor was first suggested to explain a feeding response to NPY and related peptides, including NPY2-36, that differed from their activities at the Y1 receptor. Here we report the expression cloning of a novel Y-type receptor from rat hypothalamus, which we name Y5. The complementary DNA encodes a 456-amino-acid protein with less than 35% overall identity to known Y-type receptors. The messenger RNA is found primarily in the central nervous system, including the paraventricular nucleus of the hypothalamus. The extent to which selected peptides can inhibit adenylate cyclase through the Y5 receptor and stimulate food intake in rats correspond well. Our data support the idea that the Y5 receptor is the postulated 'feeding' receptor, and may provide a new method for the study and treatment of obesity and eating disorders.

Non-peptide angiotensin II receptor antagonists. II. Pharmacology of S-8308.

2-Butyl-4-chloro-1-(2-nitrobenzyl)imidazole-5-acetic acid, sodium salt (S-8308), inhibited the specific binding of labeled angiotensin II (AII) to its receptor sites in rat adrenal cortical microsomes and in cultured aortic smooth muscle cells with IC50S of 15 and 4.5 microM, respectively. In the presence of S-8308 (15 microM) the dissociation constant for AII was increased 2-fold and the total number of binding sites was unaltered. In a concentration-dependent manner S-8308 blocked the 45Ca2+ influx induced by AII (3 X 10(-8) M) in rat aortic rings (IC50 7 microM) and the contractile response in rabbit aorta was competitively inhibited (pA2 = 5.74). This agent was highly specific for AII: it showed no affinity for alpha 1-adrenoceptors or Ca2+ channels and in addition, it did not alter the contractile responses to norepinephrine (10(-7) M) or KCl (55 mM). In conscious renal artery-ligated rats, S-8308 (30 mg/kg i.v.) elicited a rapid decrease of mean arterial pressure with a duration of about 30 min. The results demonstrate that S-8308 is a weak, but specific and competitive, non-peptide antagonist of AII exerting its inhibitory action at the receptor level.

Nonpeptide angiotensin II receptor antagonists. I. Pharmacological characterization of 2-n-butyl-4-chloro-1-(2-chlorobenzyl)imidazole-5-acetic acid, sodium salt (S-8307).

2-n-Butyl-4-chloro-1-(2-chlorobenzyl)imidazole-5-acetic acid, sodium salt (S-8307) displaced [3H]angiotensin II (All) from its specific binding sites in rat adrenal cortical membranes with an IC50 of 4 x 10(-5) M. In rabbit aorta, S-8307 competitively inhibited the contractile response to All with a pA2 value of 5.49 but at 10(-4) M it did not alter the response to norepinephrine or KCI. Similarly, a specific AII antagonism was shown in vivo in the spinal pithed rat model. In anesthetized rats, S-8307 did not potentiate the bradykinin vasodepressor response. In renal artery-ligated rats, a high renin model, S-8307 decreased mean blood pressure at 10 and 30 mg/kg i.v. as well as at 100 mg/kg p.o. In anesthetized rats, furosemide enhanced the hypotensive effect of S-8307. Blockade of the renin-angiotensin system by captopril, saralasin or bilateral nephrectomy inhibited significantly but did not abolish completely the hypotensive effect of S-8307 in furosemide-treated rats. Inhibition of prostaglandin synthesis by indomethacin did not significantly reduce the hypotensive effect of S-8307. Our results identify S-8307 as a selective antagonist of AII receptors. However, at higher doses, mechanisms other than AII receptor blockade may partly account for its acute hypotensive effect.

Antagonism of the analgesic effect of opioid and non-opioid agents by p-chlorophenylalanine (PCPA).

The ability of p-chlorophenylalanine (PCPA), an inhibitor of serotonin (5HT) biosynthesis to antagonize the antinociceptive effects of three classes of analgesics: opiates agonist (morphine), opiate agonist-antagonist (pentazocine) and non-steroid anti-inflammatory (aspirin and clonixin) were evaluated using the rat yeast paw test. The analgesic effect of equipotent doses of each of these drugs was abolished 48 h after PCPA (300 mg/kg i.p.) PCPA (150 mg/kg i.p.) reduced the relative potencies of morphine and aspirin to the same degree. The effect could not be attributed to a hyperalgesia or to an interaction with inflammatory mechanisms. PCPA did not alter the anti-edema activity of clonixin and it blocked morphine-induced increases in reaction times to pressure applied to the non-inflamed paw to the same extent as in the inflamed paw. The serotonin precursor 5-hydroxytryptophan (5HTP, 80 mg/kg i.p.) restored the antinociceptive activity of all four drugs. These results demonstrate serotonin can modulate sensitivity to analgesics with differing mechanisms of action.

Flunixin meglumine: a non-narcotic analgesic.

The N-methyl-d-glucamine salt of flunixin (flunixin meglumine) is a potent non-narcotic analgesic agent after parenteral administration in mice, rats and monkeys. It is significantly more potent than pentazocine, meperidine and codeine in the rat yeast paw test after subcutaneous administration in saline. Activity on intramuscular administration is comparable to that after subcutaneous administration and is enhanced when dissolved in buffered saline as compared to nonbuffered saline. In addition, flunixin meglumine also had oral activity and differs from indomethacin in having more analgesic activity per unit of anti-inflammatory activity. In mice, flunixin meglumine is equipotent to pentazocine and more potent than meperidine and codeine in the abdominal constriction test. In primates, flunixin meglumine at 10 mg/kg i.m., produced a degree of analgesic efficacy comparable to that of a clinically effective dose of morphine (0.3 mg/kg). In contrast to codeine, tolerance to the analgesic action of flunixin meglumine was not observed. Furthermore, flunixin meglumine retained its activity in rats made tolerant to codeine. Unlike narcotics, the analgesic effect of flunixin meglumine is not antagonized by naloxone after acute administration in rats. These results indicate that flunixin meglumine is a parenterally and orally effective analgesic in animals and is unlikely to have narcotic or drug dependence liability.

The effects of drugs inhibiting catecholamine uptake on tyramine and noradrenaline-induced contractions of the isolated rat vas deferens.

1. Cocaine did not antagonize the tyramine-induced contractile response of the isolated rat vas deferens at the same concentrations which markedly potentiated the contractile response to noradrenaline.2. Imipramine and amitriptyline non-competitively antagonized the contractile response to tyramine but did not potentiate noradrenaline. Desmethylimipramine produced both potentiation of noradrenaline and antagonism of tyramine.3. Dexchlorpheniramine non-competitively antagonized the contractile response to tyramine. It also produced an atypical potentiation of noradrenaline in which lower concentrations of noradrenaline were potentiated to a greater extent than higher ones.4. Imipramine inhibited the in vitro uptake of noradrenaline-(3)H in rat vas deferens as did cocaine, desmethylimipramine and dexchlorpheniramine. These results suggest that the alpha-adrenergic blocking property of imipramine masks the potentiation of noradrenaline by uptake inhibition.5. Evidence is also presented which suggests that alpha-adrenergic blockade of released noradrenaline may be the major mechanism for tyramine inhibition by imipramine-like drugs. This may explain why cocaine, which has no real alpha blocking action, is ineffective against tyramine.