Antidipsogenic effects of central adenosine-5'-triphosphate

Besides other physiological functions, adenosine-5'-triphosphate (ATP) is also a neurotransmitter that acts on purinergic receptors. In spite of the presence of purinergic receptors in forebrain areas involved with fluid-electrolyte balance, the effect of ATP on water intake has not been investigated. Therefore, we studied the effects of intracerebroventricular (icv) injections of ATP (100, 200 and 300 nmol/µL) alone or combined with DPCPX or PPADS (P1 and P2 purinergic antagonists, respectively, 25 nmol/µL) on water intake induced by water deprivation. In addition, the effect of icv ATP was also tested on water intake induced by intragastric load of 12 percent NaCl (2 mL/rat), acute treatment with the diuretic/natriuretic furosemide (20 mg/kg), icv angiotensin II (50 ng/µL) or icv carbachol (a cholinergic agonist, 4 nmol/µL), on sodium depletion-induced 1.8 percent NaCl intake, and on food intake induced by food deprivation. Male Holtzman rats (280-320 g, N = 7-11) had cannulas implanted into the lateral ventricle. Icv ATP (300 nmol/µL) reduced water intake induced by water deprivation (13.1 ± 1.9 vs saline: 19.0 ± 1.4 mL/2 h; P < 0.05), an effect blocked by pre-treatment with PPADS, but not DPCPX. Icv ATP also reduced water intake induced by NaCl intragastric load (5.6 ± 0.9 vs saline: 10.3 ± 1.4 mL/2 h; P < 0.05), acute furosemide treatment (0.5 ± 0.2 vs saline: 2.3 ± 0.6 mL/15 min; P < 0.05), and icv angiotensin II (2.2 ± 0.8 vs saline: 10.4 ± 2.0 mL/2 h; P < 0.05), without changing icv carbachol-induced water intake, sodium depletion-induced 1.8 percent NaCl intake and food deprivation-induced food intake. These data suggest that central ATP, acting on purinergic P2 receptors, reduces water intake induced by intracellular and extracellular dehydration.

Red cell aspartate aminotransferase saturation with oral pyridoxine intake

CONTEXTO E OBJETIVO: A enzima aspartato aminotransferase apresenta o piridoxal fosfato como coenzima, oriunda da piridoxina existente em alimentos vegetais frescos. A anemia sideroblástica responsiva à vitamina B6, mielofibrose e síndrome de Peyronie respondem a altas doses de piridoxina. O objetivo foi investigar a máxima resposta da aspartato aminotransferase à suplementação oral com piridoxina. TIPO DE ESTUDO E LOCAL: Experimento controlado, na Seção de Hematologia, Instituto Adolfo Lutz. MÉTODOS: A atividade da aspartato aminotransferase eritrocitária foi determinada (antes e após) em voluntários que receberam suplementação por 15-18 dias (30 mg, 100 mg e 200 mg diariamente). Estudo in vitro também foi realizado, com sangue de sete indivíduos. As atividades enzimáticas antes e após a incubação foram determinadas, seguindo o mesmo protocolo do estudo in vivo. RESULTADOS: O estudo in vivo revelou um aumento gradativo da saturação da aspartato aminotransferase com doses crescentes de piridoxina. 83% de saturação foi alcançada com 30 mg diariamente, 88% com 100 mg e 93% com 200 mg. O estudo in vitro não revelou saturação de 100%.CONCLUSÕES: Tanto in vivo quanto in vitro, não se revelou saturação completa da aspartato aminotransferase por sua coenzima piridoxal-5-fosfato nos eritrócitos. Entretanto, a dose de 200 mg diariamente poderia ser empregada com segurança no tratamento da anemia sideroblástica, mielofibrose e síndrome de Peyronie. Embora a saturação máxima nos eritrócitos não seja atingida, os eritroblastos e outras células nucleadas que contenham as organelas citoplasmáticas certamente atingirão a saturação completa, possivelmente à razão dos resultados obtidos nas doenças citadas.

Reversible inhibition by pyridoxal 5'-phosphate and irreversible inactivation by urea and guanidine hydrochloride of thymidylate synthase from Lactobacillus leichmannii.

Pyridoxal 5'-phosphate reversibly inhibited thymidylate synthase from Lactobacillus leichmannii. The inhibition was competitive with dUMP (Ki = 1 microM) and non-competitive with 5,10-CH2-THF (Ki = 0.08 microM). Treatment of native or pCMB-treated enzyme with urea (5 M) or guanidine hydrochloride (4 M) resulted in inactivation and dissociation of the homodimer (74 kDa) into monomer (37 kDa).

Inactivation of a beta-glucosidase from Arthrobotrys conoides by diethyl pyrocarbonate: evidence of histidine at the active site.

Modification of A. conoides beta-glucosidase by diethylpyrocarbonate caused rapid inactivation of the enzyme. The kinetic analyses showed that the inactivation by diethylpyrocarbonate resulted from the modification of an average of one histidine residue per mole of enzyme. The modified enzyme showed an increase in absorbance at 240 nm. Sulphydryl, lysine and tyrosine residues were not modified by diethylpyrocarbonate treatment. The substrate offered significant protection against diethylpyrocarbonates modification. The results indicate that diethylpyrocarbonate was interacting with the enzyme at or near the active site.

Isonicotinic acid hydrazide inhibits cell population growth during teratogenesis of chick embryo.

In chick embryos treated with a 4 hr pulse of 7.2 X 10(-5) M isonicotinic acid hydrazide (INH) the cell population growth is inhibited with an increased population doubling time. Teratogenised blastoderm cells complete their ongoing cell cycle and arrest in G1 phase. A chase with an equimolar concentration of pyridoxal-5-phosphate restores the growth rate after a lag of 4 hr equivalent to the duration of treatment with INH. Presumptive mesoblast cells invaginated through the primitive streak and neuroectoblast cells induced prior to the application of INH differentiate, while the teratogen inhibits morphogenesis and organization of organ primordia.