Toxoplasma gondii: a rapid method for the isolation of pure tachyzoites. Preliminary characterization of its genome.

A rapid and simple technique for the purification of Toxoplasma gondii tachyzoites was developed. Highly purified parasites were obtained from the peritoneal exudates of infected mice by means of two consecutive discontinuous sucrose gradients run at low speed (10,000xg, 30 min). Parasites obtained by this method conserved its biological activity. Hybridization studies with DNA from healthy mice and from purified tachyzoites preparations demonstrated that Toxoplasma gondii tachyzoites DNA could be obtained with better than 90% purity. Preliminary studies with DNA endonucleases showed the presence in the tachyzoites genome of highly repetitive sequences.

Further studies on the effect of cimetidine and other neurotropic drugs on rat serum prolactin.

The hyperprolactinemic effect of H2 histamine receptor antagonists has been described in the rat and in humans. The present study was undertaken to explore more fully the hyperprolactinemic action of cimetidine, and its interrelationship with other neurotropic agents. Adult ovariectomized estrogen-primed rats were injected with mepiramine, diphenhydramine, pilocarpine, atropine, dopamine, cimetidine or saline as control, at different sequences and the effect on serum prolactin was determined. The effect of cimetidine on prolactin release "in vitro" by hemipituitaries of estrogenized male rats during a short time incubation period, was also investigated. Our results indicate that cimetidine is able to release prolactin and that this effect is not prevented by atropine or the classical antihistaminergic agents mepiramine and diphenhydramine. Both pilocarpine and dopamine inhibit the prolactin release due to cimetidine. The hypoprolactinemic action of pilocarpine was completely blocked by atropine, but not by mepiramine or diphenhydramine. Finally, cimetidine was unable to modify significantly the prolactin release by incubated pituitaries. It is postulated that cimetidine acts mainly at the brain and that the hyperprolactinemic effect is not mediated by muscarinic or H1 histaminergic receptors. This action can be prevented by drugs such as dopamine that are able to act on the lactotroph, and also by pilocarpine, probably by stimulating a prolactin inhibiting pathway.

Effects of bromocriptine on [3H]estradiol binding in cytosol of anterior pituitary.

The hypothalamus may control hormone receptors in the anterior pituitary either by a direct trophic effect or indirectly by regulation of serum pituitary hormone levels. Rats whose medial basal hypothalamus had been destroyed in order to suppress neural control of the gland showed a reduction in [3H]estradiol binding in the anterior pituitary and high serum PRL levels; both changes were reversed by treatment of the lesioned rats with daily injections of bromocriptine, a dopamine agonist. In nonlesioned animals, the same treatment did not modify significantly those parameters. In another hyperprolactinemic model (rats with anterior pituitaries transplanted under the kidney capsule), [3H]estradiol binding by the in situ pituitaries of the host rats was similar to that in the nongrafted controls. These results suggest that changes due to median eminence lesion are reversible and that bromocriptine is able to act as a substitutive therapy which restores binding of estradiol in glands whose receptors have been decreased by the effect of the lesion. High PRL levels due to pituitary transplant do not account for the observed changes in the pituitary estradiol binding.

Effect of nutritional status on swine adipose tissue lipolytic activities.

Young swine (28 days of age) were fed an isocaloric and isonitrogenous diet with either a high fat or a low fat content for 3 to 4 weeks. The adipose tissue lipolytic rate was higher in the group fed the high fat diet. However, there was no effect of diet on the activities of several of the enzymes controlling the lipolytic process, i.e., adenylate cyclase, phosphodiesterase and hormone-sensitive lipase. No effect of diet on the activity of lipoprotein lipase was detected. Fasting for 72 hr, but not for 24 or 48 hr, caused an increase in the lipolytic rate. There was also a decrease in cell size after a 72-hr fast (P greater than .05) such that the increased rate was not significant when the data were expressed on a cell basis. Inexplicable transient changes in adenylate cyclase activity, as well as a decrease in the activity of the low affinity phosphodiesterase (doubtful physiological significance), were detected during starvation. Starvation depressed the adipose tissue lipoprotein lipase activity but had no effect on the hormone-sensitive lipase activity.

[Neurotransmitters, neurohormones and prolactin]. / Neurotrasmisores, neurohormonas y prolactina.

After pointing out the reasons for undertaking the study of the regulation of prolactin secretion, the neuroendocrine mechanisms implicated in such secretion are discussed. Special attention is dedicated to the participation of chemical agents. Thus, the principal effects dealt with are: the net inhibition produced by dopamine and the less generalized inhibition effects of nicotine and somatostatin; the facilitatory action of serotoninergic pathways, TRH, histamine and endorphins. The dual effect described for GABA and noradrenaline, as well as some paradoxical actions, e.g., the antiserotoninergic and antihistaminergic H2 drugs which liberate prolactin in basal conditions but abolish the prolactin releasing effect of the respective agonist, or the immediate blocking effect of muscarinic agonists and antagonists are discussed. Finally, the possibility of a new mechanism of control at anterior pituitary receptors level is postulated.

Neurotrasmisores, neurohormonas y prolactina. / [Neurotransmitters, neurohormones and prolactin]

After pointing out the reasons for undertaking the study of the regulation of prolactin secretion, the neuroendocrine mechanisms implicated in such secretion are discussed. Special attention is dedicated to the participation of chemical agents. Thus, the principal effects dealt with are: the net inhibition produced by dopamine and the less generalized inhibition effects of nicotine and somatostatin; the facilitatory action of serotoninergic pathways, TRH, histamine and endorphins. The dual effect described for GABA and noradrenaline, as well as some paradoxical actions, e.g., the antiserotoninergic and antihistaminergic H2 drugs which liberate prolactin in basal conditions but abolish the prolactin releasing effect of the respective agonist, or the immediate blocking effect of muscarinic agonists and antagonists are discussed. Finally, the possibility of a new mechanism of control at anterior pituitary receptors level is postulated.

Neurotrasmisores, neurohormonas y prolactina / [Neurotransmitters, neurohormones and prolactin]

After pointing out the reasons for undertaking the study of the regulation of prolactin secretion, the neuroendocrine mechanisms implicated in such secretion are discussed. Special attention is dedicated to the participation of chemical agents. Thus, the principal effects dealt with are: the net inhibition produced by dopamine and the less generalized inhibition effects of nicotine and somatostatin; the facilitatory action of serotoninergic pathways, TRH, histamine and endorphins. The dual effect described for GABA and noradrenaline, as well as some paradoxical actions, e.g., the antiserotoninergic and antihistaminergic H2 drugs which liberate prolactin in basal conditions but abolish the prolactin releasing effect of the respective agonist, or the immediate blocking effect of muscarinic agonists and antagonists are discussed. Finally, the possibility of a new mechanism of control at anterior pituitary receptors level is postulated.

H1 and H2 histamine receptor participation in the brain control of prolactin secretion in lactating rats.

The aim of the present research was to evaluate the histaminergic regulation of prolactin secretion in the lactating rat and the possible involvement of H1 and H2 histamine receptors in this control. Prolactin was measured by radioimmunoassay in blood samples withdrawn through an intrajugular silastic catheter from undisturbed lactating mothers 10 to 15 days after delivery. In some of those rats a stainless steel cannula was placed in the third ventricle. The tested drugs, H1 and H2 receptor agonists and antagonists, were injected either by the intrasilastic route or intraventricularly immediately before the onset of suckling and after a basal sample was taken. New samples were withdrawn 10, 20, 30 and 60 min thereafter. Suckling caused a 12- to 18-fold increase in serum prolactin by 10 min in control saline-injected mothers. In non-suckled mothers (NSM) injected with saline, prolactin levels were low at all times. Systemic or intraventricular diphenhydramine and mepyramine, H1 receptor antagonists, suppressed the increment in prolactin observed in suckled mothers (SM). Intraventricular metiamide, an H2 receptor antagonist, did not modify prolactin secretion in SM but drastically increased serum prolactin in NSM. A small but significant increase in prolactin titers was observed in NSM injected intraventricularly with histamine. 4-Methylhistamine, an H2 agonist, was ineffective when used intraventricularly in NSM, but clearly suppressed prolactin enhancement in SM. It is postulated that in lactating mothers, brain histamine has a dual control on prolactin secretion. H2 receptors mediate events related to inhibition of prolactin release, since the agonist 4-methylhistamine blocked the prolactin rise in SM, while the antagonist metiamide promoted release of the hormone in NSM. H1 receptors seem to be related to a facilitatory mechanism since classical antihistamines suppress the serum prolactin increase that follows the onset of suckling, while histamine itself is able to release prolactin in NSM.

Lipolytic activity of swine adipocytes.

Lipolysis in isolated swine adipocytes was stimulated by epinephrine, dibutyryl cyclic AMP, and weakly by adrenocorticotropin but not by glucagon or cyclic AMP. Theophylline, a phosphodiesterase inhibitor, stimulated lipolysis and greatly enhanced the activity of adrenocorticotropin. The epinephrine-stimulated lipolytic activity, expressed on a tissue or cell volume basis, was greatest at 25 days postpartum, whereas, expressed on a cell basis, the activity was maximal at day 80. Regardless of the mode of expression, the activity at day 150 was low. Cells from younger animals were more sensitive to epinephrine than cells from older animals.