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Biomedical subjects

G Torres

Publications and source records attributed to G Torres.

At least 109 records · Page 6Linked to original sources
PubMed1991

Age and castration modulate the inhibitory action of neuropeptide Y on neurotransmission in the rat vas deferens.

The potency of neuropeptide Y (NPY) to inhibit the electrically induced contractions of the epididymal half of the vas deferens diminishes markedly with age, being at least 20 times lower in the adult than in the 26-day-old rat. Castration sensitizes the epididymal segment to NPY in a testosterone-reversible manner. [Pro34]NPY was 3 times less potent than NPY in prepubertal rats and inactive in castrated adults, while NPY-(13-36) had no effect in either group. In the prostatic half, NPY and its analogs were active in rats from all ages studied; the order of potency being NPY greater than [Pro34]NPY greater than NPY-(13-36). The sensitivity of the prostatic segment from adult rats to NPY was unchanged by castration or testosterone replacement therapy. The NPY content of the ductus increases during development being higher in the prostatic than in the epididymal half at all ages studied. Castration decreases the peptide content in the two segments and the effect is prevented by testosterone administration. The present investigation demonstrated that the effect of NPY on vas deferens neurotransmission is subject to regulation by sex steroids, which affects differently the response of the two segments of the ductus.

Aging↗
PubMed1991

Assessment of anthracycline-induced myocardial damage by quantitative indium 111 myosin-specific monoclonal antibody studies.

To assess chemotherapeutically induced myocardial damage, myosin-specific antibody scans and ejection fraction measurements were performed in 32 patients with breast cancer and in 9 patients with other tumours. All patients had received chemotherapy including anthracyclines. The ejection fraction decreased by less than or equal to 10% in 14 of 41 (34%) patients after chemotherapy. Antimyosin uptake in the myocardium was observed in 38 of 41 (92%) patients after chemotherapy. Antimyosin uptake was quantified by means of a heart-to-lung ratio, revealing a correlation between the degree of antimyosin uptake in the myocardium and the cumulative dose of anthracycline. Patients with a decreased ejection fraction showed more intense antimyosin uptake, indicating more severe myocardial damage. A higher degree of antimyosin uptake was found in 17 breast cancer patients treated with doxorubicin compared with 15 patients treated with mitoxantrone. We conclude that antimyosin studies provide a sensitive, non-invasive method to monitor myocardial damage in patients treated with anthracyclines. Antimyosin uptake in the myocardium precedes ejection fraction deterioration. This technique may be helpful in the early identification of patients at risk of congestive heart failure during chemotherapy including anthracyclines.

Adult↗
PubMed1991

Characterization of receptors mediating the effects of dopamine on gastric smooth muscle.

The effects of dopamine on circular and longitudinal smooth muscle from the body of the guinea pig stomach were examined. In circular muscle, dopamine (10(-6)-10(-3) mol/L) induced contractions that were tetrodotoxin-insensitive with a concentration of half-maximal effect (EC50) of 6.3 x 10(-6) mol/L for dopamine vs. 1.4 x 10(7) mol/L for norepinephrine. The efficacies of dopamine- and norepinephrine-induced contraction were similar. The alpha-adrenoceptor antagonist phentolamine competitively inhibited dopamine-induced circular contractions (Ki = 2.5 x 10(-8) mol/L slope 1.06), whereas the dopamine antagonist haloperidol had no effect. The alpha 1-antagonist prazosin competitively inhibited dopamine-induced contractions (Ki = 1.8 x 10(-8) mol/L, slope 1.03), whereas the alpha 2 antagonist yohimbine was slightly less potent (Ki = 2.2 x 10(-7) mol/L, slope 1.15). In longitudinal muscle, dopamine produced relaxation with an EC50 of 2.9 x 10(-5) mol/L vs. 2.4 x 10(-6) mol/L for norepinephrine. Tetrodotoxin reduced relaxation to dopamine by one third at low doses of dopamine (10(-5)-10(-4) mol/L) and had no effect above 10(-3) mol/L. Phentolamine did not inhibit dopamine-induced relaxation, whereas haloperidol demonstrated potent competitive inhibition (Ki = 5.8 x 10(-7) mol/L, slope 0.90). The selective DA1 antagonist Sch 23390 (Research Biochemicals Inc., Natick, MA) showed competitive antagonism (Ki = 6.3 x 10(-6) mol/L, slope 0.98), whereas the selective DA2 antagonist domperidone had no effect. The effect of Sch 23390 was tetrodotoxin resistant. It is concluded that in the body of the guinea pig stomach, dopamine induces contraction in circular muscle through smooth muscle alpha adrenoceptors, whereas in longitudinal muscle, dopamine induces relaxation through smooth muscle DA1 receptors.

Adrenergic alpha-Antagonists↗
PubMed1991

Bone marrow regeneration after hormonal therapy in patients with bone metastases from prostate carcinoma.

Two patients with prostate carcinoma and bone metastases were treated with hormonal therapy. Radioimmune imaging of bone marrow performed with 99mTc-labeled antigranulocyte antibody BW 250/183 before treatment demonstrated absence of granulopoietic bone marrow in extensive regions of the central and proximal peripheral skeleton, indicating diffuse bone marrow invasion. Bone marrow scans performed after treatment demonstrated presence of granulopoietic bone marrow in these regions, indicating bone marrow regeneration. This finding was consistent with favorable response to treatment.

Aged↗
PubMed1991

Choledocholithiasis in cirrhotic patients: is endoscopic sphincterotomy the safest choice?

Of the 18 endoscopic sphincterotomies performed on 18 cirrhotic patients for choledocholithiasis, a mortality rate of 16.6% was registered. However, this figure can be limited to 6.6% if we take only successful sphincterotomies (15/18, 83.3%) into account. After closely reviewing relevant literature, it would appear that operative mortality in comparable cases is much higher. We therefore recommend that endoscopic sphincterotomy, despite higher mortality rates when compared to the general population, should be the initial choice of management of choledocholithiasis in cirrhotic patients.

Aged↗
PubMed1990

Light affects neonatal rat pineal gland N-acetyltransferase activity by an extra-retinal mechanism.

To determine whether extra-retinal mechanisms mediate photoperiodic changes in neonatal rat pineal gland N-acetyltransferase activity, 4-day-old intact or bilateral orbital enucleated rats were killed during the dark phase of the lighting cycle, either in darkness or following 4 hr exposure to fluorescent light. Light suppressed the high nighttime N-acetyltransferase activity equally in intact and enucleated pups. Subsequent studies showed that at least 0.5 hr exposure and nocturnal illuminances of 109 microW/cm2 or greater were required to cause statistically significant reductions in the activity of the enzyme in 4-day-old rats. Taken together, these data indicate that relatively intense environmental light can affect neonatal rat pineal gland biochemistry via extraretinal mechanisms.

Acetyltransferases↗
PubMed1990

Light-induced changes in pineal gland N-acetyltransferase activity: developmental aspects.

In adult rats, light acting via a retino-pineal gland neural pathway influences pineal gland biochemistry in two ways: (1) it entrains endogenous circadian rhythms in melatonin biosynthesis to the environmental photoperiod and (2) exposure to even very brief periods of light during the nighttime rapidly suppresses the high levels of nocturnal melatonin production. The present studies were undertaken to determine precisely when photic stimulation first influences the enzymic activity of N-acetyltransferase (NAT), the pineal gland enzyme which rate-limits the overall biosynthesis of the hormone melatonin, and to examine some of the cellular mechanisms which might mediate light-induced effects in neonatal animals. Rats of different ages were either killed during the light phase or were exposed to darkness or light for 1 min during the dark phase of the lighting cycle, returned to their litters in darkness for 30 min and then killed. Pineal gland NAT activity in animals nocturnally exposed to 1 min of light was suppressed in animals 6 days of age or older. Nocturnal light exposure did not suppress enzyme activity in 3- to 5-day-old rats, even though these animals displayed clear light:dark differences in pineal gland NAT activity. Nocturnal light exposure also did not suppress nighttime levels of NAT activity in 7-day-old animals who had been bilaterally enucleated, suggesting that this effect is retinally mediated. Pretreatment of 7-day-old animals with the beta-noradrenoceptor agonist drug, isoproterenol, prevented the nocturnal light-induced suppression of NAT activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetyltransferases↗
PubMed1989

Xylamine enhances pineal gland N-acetyltransferase activity in vitro.

1. The action of N-2'-chloroethyl-N-ethyl-2-methyl benzylamine (xylamine) on rat pineal gland sympathetic innervation was examined. 2. This alkylating agent caused a concentration-dependent increase in pineal gland N-acetyltransferase (NAT) activity in neurologically intact pineal glands that was suppressed in glands previously subjected to bilateral superior cervical ganglionectomy. 3. Xylamine-induced elevations in NAT activity were attenuated by beta-noradrenergic antagonist drugs but not by alpha-noradrenergic antagonist drugs. 4. Since pineal gland uptake of radiolabelled norepinephrine (NE) was impaired by xylamine, the drug may increase pineal gland NAT activity by inhibiting NE reuptake into the presynaptic nerve terminal, thereby increasing the amount of the neurotransmitter available to stimulate pinealocyte beta-noradrenoceptors.

Acetyltransferases↗
PubMed1989

Catecholaminergic mechanisms mediate hypothermia-induced elevations in pineal gland N-acetyltransferase in neonatal rats.

The newly born of many mammalian species are ectothermic, and it is possible that biochemical processes important for the metabolism of endocrine hormones might vary with alterations in the environmental temperature. Temperature-induced fluctuations in pineal gland N-acetyltransferase activity were investigated in 4-, 12-, and 20-day-old rats placed for 4 hr in 23 or 34 degrees C environments. Enzyme activity increased dramatically in ectothermic 4- and 12-day-old animals exposed to the 23 degrees C environment, but not in endothermic 20-day-old rats. The elevations in daytime pineal gland NAT activity seen in cold-exposed animals were absent in rats previously subjected to chemical sympathectomy induced by 6-hydroxydopamine, or in animals treated with the beta-noradrenoceptor antagonist drug propranolol. Catecholaminergic nerves and beta-noradrenoceptors known to be important for light-induced changes in mammalian pineal gland biochemistry also appear essential for environmental temperature-dependent elevations in neonatal pineal N-acetyltransferase activity.

Acetyltransferases↗
PubMed1989

Extraretinal mechanisms mediate light-induced changes in neonatal rat pineal gland N-acetyltransferase activity.

Nocturnal light-induced changes in pineal gland N-acetyltransferase activity were investigated in intact or enucleated 4-, 6-, or 8-day-old maternally isolated rats maintained at different ambient temperatures. Nighttime enzyme activity was increased markedly in rats maintained in 23 degrees C compared to 35 degrees C environments. Four hours of nocturnal light significantly reduced N-acetyltransferase activity in intact rats at all ages studied when the animals were maintained at 35 degrees C. Shorter duration (1 min) nocturnal light reduced N-acetyltransferase activity in intact rats 6 days of age. However, the enzyme activity suppression observed after the 4 hr of nocturnal light was still present in 4-day-old rats (but not older animals) even when the younger animals had been made blind by bilateral orbital enucleation. Taken together, these data suggest that an extraretinal mechanism may mediate light-induced changes in some aspects of pineal gland indoleamine biochemistry in newborn rats.

Acetyltransferases↗