Ilza C. M. Terra

Tryptophan hydroxylase is modulated by L-type calcium channels in the rat pineal gland

Calcium is an important second messenger in the rat pineal gland, as well as cAMP. They both contribute to melatonin synthesis mediated by the three main enzymes of the melatonin synthesis pathway: tryptophan hydroxylase, arylalkylamine N-acetyltransferase and hydroxyindole-O-methyltransferase. The cytosolic calcium is elevated in pinealocytes following alpha(1)-adrenergic stimulation, through IP(3)-and membrane calcium channels activation. Nifedipine, an L-type calcium channel blocker, reduces melatonin synthesis in rat pineal glands in vitro. With the purpose of investigating the mechanisms involved in melatonin synthesis regulation by the L-type calcium channel, we studied the effects of nifedipine on noradrenergic stimulated cultured rat pineal glands. Tryptophan hydroxylase, arylalkylamine N-acetyltransferase and hydroxyindole-O-methyltransferase activities were quantified by radiometric assays and 5-hydroxytryptophan, serotonin, N-acetylserotonin and melatonin contents were quantified by HPLC with electrochemical detection. The data showed that calcium influx blockaded by nifedipine caused a decrease in tryptophan hydroxylase activity, but did not change either arylalkylamine N-acetyltransferase or hydroxyindole-O-methyltransferase activities. Moreover, there was a reduction of 5-hydroxytryptophan, serotonin, N-acetylserotonin and melatonin intracellular content, as well as a reduction of serotonin and melatonin secretion. Thus, it seems that the calcium influx through L-type high voltage-activated calcium channels is essential for the full activation of tryptophan hydroxylase leading to melatonin synthesis in the pineal gland.

Lesions of the Dorsomedial Hypothalamic Nucleus Do Not Influence the Daily Profile of Pineal Metabolism in Rats

The present study attempted to characterize the effects of electrolytic lesions of the hypothalamic dorsomedial nucleus on the daily profile of pineal metabolism as well as on the inhibition of pineal melatonin synthesis induced by acute light exposure during the night. Adult male Wistar rats (n = 107, 12:12 h light-dark cycle) were left intact (n = 47) or lesioned (n = 60). Lesioned rats and their respective controls were killed at six time points distributed throughout the light-dark cycle. At ZT (zeitgeber time) 18 the animals were killed either in the dark or after 15 min of light stimulation. Pineal glands were assayed using high-performance liquid chromatography with electrochemical detection (HPLC-ED). There was no difference in the amounts of pineal indoles between lesioned and control rats under any of the experimental situations tested. These results suggest that in rats, the hypothalamic dorsomedial nucleus does not participate in either the neural control of daily pineal metabolism or the nocturnal light-induced inhibition of the pineal metabolism.

Enhancement of sodium intestinal secretion in relation to absorption in malnourished rats: hyperosmolar challenge

Two experimental models were tried in young malnourished rats in order to study effect of an hyperosmolar challenge in the small intestine on the bi-directional fluxes of sodium. Weanling rats were fed with energy restricted diets. In model I 1 mL of NaCl 900 mOsm/kg was introduced in the small intestine of the rats and left from 5 up to 70 min, in order to determine the moment of higher net Na+ secretion, which occurred at 10 min. In model II, the bi-directional fluxes of Na+ and Cl- were studied using NaCl or mannitol 900 mOsm/kg under the effect of mecholil, atropine or 2-4 dinitrophenol, for 10 min. Mecholil decreased the Na+ absorption enhancing the net secretion. Control rats were used as reference. In the restricted diets animals occurred an increase of the net secretion stimulated by NaCl 900 mOsm/kg, and this effect was enhanced by mecholil. It is suggested that in malnutrition there is an impairment in Na- intestinal absorption.

Dietary nitrite and scavenger antioxidants trace elements

Rats initially weighing 138 +/- 14 g were fed the following diets for 150 days: control (Co), control plus nitrite-bacon-proline 24 mg/kg, 100 g/kg and 10 mg/kg, respectively (NB), NB plus 0.04 micrograms/g selenium (NBSe) and NB plus 0.020 g/kg ascorbic acid (NBC). The NB diet provoked body weight and feeding efficiency enhancement with a reduction in body density increasing serum lactic acid, uric acid and cholesterol levels. The serum selenium decreased by the presence of NB in the diet. The addition of selenium and ascorbic acid to the NB diet prevented the reduction in body density and also affected uric acid and cholesterol levels. It is suggested that the NB diet has adverse effects and that some of the alterations it causes are prevented by the reducing elements selenium and ascorbic acid.

The effect of maturation and source of dietary protein on the capacity of the small intestine to hydrolize lactose in rats

Abstract The effect of maturation and quantity and different source of dietary protein on the evolution of intestinal lactase activity (LA) was studied in rats. The diets used were casein (12 and 20% protein) and rice and beans (12% protein) completed with vitamins, minerals, oil and starch (up to 100%) with or without lactose. In the first experiment, the offspring of rats fed these diets were studied at birth, at weaning and at 51 days of age. In the second experiment, the offspring were fed the same diets with or without lactose in different sequences. The parameters studied were small intestine LA and total LA in the intestinal homogenate. The data indicate that when lactose was present in the diet, the older rats exhibited low lactase specific activity but higher total LA than at birth.

Selenium as protector of degenerative diseases

Antioxidants are scavengers of free radicals related to atherosclerosis and cancer, and probably selenium as a component of glutathione peroxidase (GSH-Px) plays an important role in this mechanism. Young rats of average initial body wt of 100 g were fed for 60 d with the following diets: I-Casein, complete, selenium free (0.0003 I~g/kg), 17% of protein (Cas) or with Se added (0.004 ~g/kg) (Cas.Se); II-As I, but with nitrite (24 mg/kg) and bacon (100 g/kg) added (Cas-NB), selenium free (0.0003 i~g/kg) or with Se added (Cas-NB-Se). The main results showed that: