Koichi Itaya

A new micromethod for the colorimetric determination of inorganic phosphate.

Abstract A sensitive and simple technique was worked out for the colorimetric determination of inorganic phosphate, on the basis of the principle that Malachite Green at a lower pH forms a complex with phosphomolybdate with a marked shift of the absorption maximum. Inorganic phosphate as low as 0.05 μg can be determined by this method with good precision.

Adrenergic α-receptor-mediated stimulation of the glucose utilization by isolated rat diaphragm

Abstract 1. 1. The inhibition by epinephrine of glucose utilization observed upon incubation of isolated rat diaphragm in the ordinary Krebs-Ringer bicarbonate solution disappears and a significant stimulation takes place if the incubation medium is supplemented with palmitate bound to albumin. 2. 2. This stimulation of glucose utilization due to epinephrine is completely blocked by an α-blocker and potentiated by a β-blocker, whereas other metabolic alterations induced by epinephrine, e.g. glycogen breakdown, accumulation of Glu-6- P , and production of lactate, are blocked by a β-blocker but not affected by an α-blocker. 3. 3. Epinephrine stimulates an accumulation of 3- O -methylglucose in the isolated diaphragm dependent on the α-stimulation during incubation in the “aged” medium containing palmitate bound to albumin (“aged” medium refers to the medium which has been preincubated at 37° C for 10 min with large amounts of rat diaphragm and the surrounding tissues). This suggests that the α-stimulation-linked epinephrine action is directed to the membrane transport process of sugar. 4. 4. The significance of the α-stimulation in the adrenergic regulation of carbohydrate metabolism is discussed.

Differences in responsiveness to adipokinetic agents between white epididymal and brown interscapula adipose tissue from rats.

Lipolytic activity was studied in brown and white adipose tissue of rats in vitro. 5‐Hydroxytryptamine (5‐HT), phenylephrine, noradrenaline, adrenaline and isoprenaline were used as adipokinetic agents. All stimulated lipolysis in brown adipose tissue, but 5‐HT and phenylephrine did not in white adipose tissue. A β‐blocking drug, propranolol, inhibited the stimulatory effect of the agents in both adipose tissues. However, an α‐blocking drug, phentolamine, further increased the lipolysis induced by noradrenaline or adrenaline in brown adipose tissue and inhibited the effect of isoprenaline. In white adipose tissue, its action was to marginally decrease the effect of adrenaline and noradrenaline. Increase in the pH of the incubation medium stimulated FFA and glycerol release in brown adipose tissue, but not in the epididymal adipose tissue. This effect of pH on lipolysis was further enhanced by phentolamine and decreased by propranolol. Increase of lipolysis with pH was not seen with brown fat tissue from the reserpine‐treated rats. These results show that brown adipose tissue of the rat has an α‐receptor with inhibitory effects on lipolysis that is affected by α‐ or mixed‐type adrenergic agonists, noradrenaline and adrenaline.

Need for Ca ions in the lipolytic action of 5-hydroxytryptamine in rat brown adipose tissue.

y t e effect of bromocriptine on the responses to vaso&n was investigated to check the specificity of any ;tagonism of noradrenaline. The enhancement of the +ponses to vasopressin in the presence of bromocriPtine is interesting but as yet unexplained. It does not to be related to a-blockade since the effect was llOt observed with phentolamine. At low concentrations lnay bromocriptine exhibited no agonist activity on the preparation, but at high concentrations (> M) a small rise in perfusion pressure was observed. Thus it seems that in addition to a-adrenoceptor blockade bromocriptine exerts a second effect on the blood vessels which potentiates responses to vasopressin. M.S. is supported by a grant from the University Azarabadeghan, and the Ministry of Science, Iran. The authors thank Sandoz A.G. for the gift of bromocriptine. November 25, 1977

Effect of 5-hydroxytryptamine on blood glucose and cyclic AMP in the rat.

The effects of 5‐hydroxytryptamine (5‐HT) on plasma cyclic AMP (cAMP) and glucose concentrations were studied in rats in vivo. 5‐HT injected i.p. increased plasma cAMP and glucose. Injections of propranolol, hexamethonium, and cyproheptadine inhibited the 5‐HT‐induced increase in glucose but not in cAMP. Atropine did not inhibit the action of 5‐HT. These effects of 5‐HT were not seen in adrenomedullectomized rats, and 5‐HT did not elevate the concentration of plasma cAMP in anti‐glucagon antiserum‐injected rats. These results confirm the previously reported finding that 5‐HT‐induced increase in blood glucose is mediated via adrenaline released from adrenal medulla by 5‐HT and suggest that the increase in plasma cAMP, induced by 5‐HT, is due to glucagon released by an unknown factor, or factors other than adrenaline released from the adrenal medulla by 5‐HT.

Effect of ethanol on adrenaline-stimulated glucose uptake in rat white adipose tissue

The effect of ethanol on adrenaline‐stimulated glucose uptake by rat white adipose tissue has been examined in vitro. Ethanol (3%) inhibited the stimulatory effect of adrenaline on glucose uptake whereas it failed to inhibit the effect of adrenaline on free fatty acid production. Addition of calcium (12·5mM) to the incubation medium restored adrenalines effect on glucose uptake. Addition of propranolol also restored the effect of adrenaline inhibited by ethanol. Ethanol did not inhibit insulin‐stimulated glucose uptake. These results suggest that ethanol modifies the coupling of the adrenoceptor to the glucose transport system in adipose tissue that is stimulated by adrenaline.

Effect of reserpinization on insulin secretion in the rat

Reserpine‐induced supersensitivity to the insulin‐releasing action of a β‐adrenergic agonist, isoprenaline, and of glucose was studied in vivo and in vitro. The subcutaneous injection of rats with reserpine (0.05 to 10 mg kg−1) enhanced the action of isoprenaline on insulin secretion. ED50 of isoprenaline for insulin secretion was changed little after reserpinization, whereas maximum effect of the β‐agonist was enhanced by pretreating rats with reserpine. Glucose‐stimulated insulin secretion was also enhanced in the reserpinized rats. Pancreases isolated from the reserpinized rats secreted more insulin in response to phentolamine in the presence of glucose and isoprenaline. These results suggest that the supersensitivity in insulin secretion induced by reserpine may be non‐specific.

Increased absorption of iodochlorhydroxyquin by rat intestine in the presence of solubilizing agents.

The intestinal absorption of iodochlorhydroxyquin (clioquinol) by the rat was studied by determining the radioactivity in the bile, blood and several organs 90 min after direct application of 125I-labeled clioquinol into the duodenum. The addition of solubilizing agents such as carboxymethyl-cellulose and lauryl sulfate to clioquinol preparation markedly enhanced the intestinal absorption of the drug in either the presence of absence of bile secretion which, by itself, increased the drug absorption. Possible significance of the enhanced absorption of clioquinol by solubilizing agents in the etiology of subacute myelo-optic neuropathy (SMON) in Japan is discussed.

Inhibitory effect of 5-hydroxytryptamine on lipogenesis in rat adipose tissues

5‐Hydroxytryptamine (5‐HT) inhibited the incorporation of 14C from 14C‐labelIed glucose, pyruvate, citrate and acetate into fatty acids but it did not inhibit the conversion of 14C from citrate and acetate into CO2, and the citrate conversion into glyceride‐glycerol in epididymal and mesenteric adipose tissue from 24h‐fasted rats. 5‐HT stimulated the formation of lactate from glucose and pyruvate, and increased the ratio of lactate produced/pyruvate taken up. This ratio was similar to the NADH:NAD ratio. These results indicate that 5‐HT inhibits fatty acid synthesis in rat white adipose tissue by mechanisms similar to those of the catecholamines.