Cysteinyl leukotriene D4 induced vascular smooth muscle cell proliferation: a possible role in myointimal hyperplasia.

Cysteinyl leukotrienes (i.e. LTC4, LTD4), produced by activated leukocytes or by transcellular metabolism may act at different levels on vascular smooth muscle cells (VSMC) during inflammatory process or atherosclerosis. We studied the effect of LTC4, LTD4, and LTE4 on the in vitro proliferation of rat VSMC, measured by [3H]-thymidine incorporation and cell count. LTD4 had a stronger stimulatory effect on [3H]-thymidine incorporation than LTC4, whereas LTE4 was inactive. The effect of LTD4 on [3H]-thymidine incorporation was dose-dependent, with the maximal activity at 10(-6) M. The stimulatory activity of LTD4 was inhibited in a dose-dependent manner by MK-571, a specific LTD4 receptor antagonist. In addition, MK-571 (1 mg/kg/day) given for at least 1 day after injury in a model of balloon catheter injury of rat carotid artery, provided effective inhibition of myointimal VSMC proliferation, with a 58% reduction of 5-bromo-2'-deoxyuridine (BrdU) uptake in the neointima and 69% reduction of neointimal thickening. Our data support the importance of inflammatory mechanisms in the pathogenesis of atherosclerosis and suggest a possible role for cysteinyl leukotrienes, specifically LTD4, in the control of VSMC proliferation.

Arterial lesions in hypercholesterolaemic Yoshida rats: morphological evaluation.

The aortic wall structure of genetically determined hypercholesterolaemic (Yoshida) and control (Brown-Norway) rats was investigated by transmission and scanning electron and light microscopy. Leucocyte adherence mostly at branch sites and irregular protrusive structures were observed on the endothelial surface of the thoracic aorta of Yoshida, but not of Brown-Norway rats. The subendothelial space of the aortic wall of Yoshida rats was characterized by intimal cushions consisting of smooth muscle cells of 'synthetic phenotype' associated with adhering leucocytes and lipid droplets. Lipid infiltration of the cytoplasm of medial smooth muscle cells was observed on the inner part of the aortic arch and on the lateral parts of the large branches of Yoshida rats. This model of spontaneously hyperlipidaemic Yoshida rats is an appropriate 'moderate' injury system, which may be useful for studies of multiple risk factors for atherogenesis.

Differential sites of action of 8OHDPAT, a 5HT1A agonist, on ACTH and PRL secretion in the rat.

We recently obtained evidence that activation of the 5HT1A subtype receptor enhances both plasma ACTH and prolactin (PRL) concentrations in rats. In order to explore the possible neuroanatomical structures involved in this interaction, we examined ACTH and PRL responses to intracerebral infusions of the 5HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8OHDPAT). In addition we also tested in vitro effects of 8OHDPAT added to the perifusion medium of pituitary cells or of hypothalamic slices on hormone or neurotransmitter release, respectively. The ACTH response to 8OHDPAT (0.1 mg/kg) was decreased after depletion of endogenous 5HT stores by p-chlorophenylalanine (PCPA) treatment. In contrast, the PRL response was markedly increased under that condition. Infusion of 8OHDPAT (1 microgram/microliter/15 min) into the dorsal raphe nucleus induced a slow elevation of ACTH release but was ineffective on PRL secretion while infusion of 8OHDPAT into the PVN induced a moderate elevation of both ACTH and PRL. After bilateral destruction of the PVN, PRL response to 8OHDPAT (0.1 and 0.25 mg/kg) was markedly potentiated. In contrast, PVN-lesioned animals showed a blunted ACTH response to 8OHdPAT. Basal or CRF-stimulated ACTH secretion rates from perifused dispersed adenohypophyseal cells were not affected by 8OHDPAT but the 5HT1A agonist induced a very slight and transient inhibition of PRL release. 8OHDPAT antagonized, in a dose-dependent manner, the K(+)-induced release of 3H-DA previously taken up in neurons of mediobasal hypothalamic slices. This data suggests that major sites of 5HT1A interaction in PRL and ACTH regulation are located within the CNS and not in the pituitary.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduced smooth muscle cell regeneration in Yoshida (YOS) spontaneously hypercholesterolemic rats.

Hypercholesterolemia is a predisposing factor for atherosclerosis. We studied the response to damage of vascular smooth muscle cells (SMC) from normocholesterolemic Brown Norway (BN) and from spontaneously hyper-cholesterolemic Yoshida (YOS) rats (16-24 month old). The regrowth rate of SMC from BN and YOS rats after freeze-induced damage was similar in the presence of fetal calf serum and of serum derived from normocholesterolemic rats, while it was reduced in the presence of serum from hypercholesterolemic rats. Freeze-injury of the abdominal aorta was followed by reduced neointima formation in YOS rats, as compared to BN rats, confirming the impaired response of vascular cells from hypercholesterolemic rats to injury. This defect may be due either to lipids or to unknown factors present in the hyperlypidemic serum.

Endothelialized myointimal thickening in the rat aorta as a result of extensive freeze injury.

The regeneration of rat aorta intima and medial layer was examined after extensive freeze injury that caused the death of both endothelial and smooth muscle cells. After 1 month complete re-endothelialization of the denuded area was observed. In parallel, myointimal thickening was formed by the smooth muscle cells (SMC) from the uninjured edges and its thickness increased with time. The SMC of myointimal thickening were stellate in the upper part and elongated near the internal elastic lamina. No regenerative response was seen in the medial layer, consisting only of elastic and collagen fibers, and its thickness was reduced during regeneration. These results show that the regenerative response of medial SMC to extensive freeze injury proceeds in the form of intimal thickening.

Age-related changes in hypothalamo-pituitary-adrenocortical axis activity in the rat. In vitro studies.

In the aged rat, the activity of the hypothalamo-pituitary-adrenocortical (HPA) axis was found to be increased. In fact, the plasma corticosterone concentrations in the aged (25 months) Sprague-Dawley rat were higher than in the young (3 months) Sprague-Dawley rat. To determine which component of the HPA axis principally contributes to this hyperactivity, an in vitro approach was applied. Neither the adrenal nor the pituitary revealed any age-induced modification in their basal or hormone-stimulated in vitro activity. Moreover, the ability of corticosterone to inhibit the in vitro stimulated pituitary adrenocorticotropic hormone release was preserved in aged rats. On the contrary, the in vitro hypothalamic activity was altered in aged rats. The basal and stimulated release of bioactive corticotropin-releasing factor were increased in aged rats. The results obtained in this study indicate that the hypercorticosteronemia of the aged Sprague-Dawley rat is associated with hypothalamic hyperactivity and with normal in vitro activity and reactivity of the adrenal and pituitary.

Changes in anterior pituitary hormone levels after serotonin 1A receptor stimulation.

Although the role of serotonin (5HT) in the regulation of anterior pituitary hormone secretion is well documented, the involvement of specific 5HT receptor subtypes in this action is not yet fully elucidated. In the present work we attempted to determine the neuroendocrine role of the 5HT1A receptor subtype. This was chosen mainly because highly selective pharmacological tools are available for that subtype. 8-Hydroxy-2-(di-n-propylamino)tetralin (8OHDPAT) and ipsapirone were injected iv in conscious, freely moving male rats cannulated in the jugular vein. For the sake of comparison, a 5HT receptor agonist with preference for the 5HT1B and 5HT1C receptor subtypes 1-(m-trifluoromethyl-phenyl)piperazine (TFMPP) was also administered. Plasma PRL, ACTH, and beta-endorphin levels increased in a dose-dependent manner after 8-OHDPAT (0.01-1 mg/kg) or ipsapirone (0.5-7.5 mg/kg) injection. Maximal effects were obtained between 7-15 min. Only the highest dose of 1-(m-trifluoromethyl-phenyl)piperazine (5 mg/kg) resulted in the same response. In contrast, none of the drugs used affected plasma GH, TSH, or LH levels at any dose tested. The results indicate that 5HT1A receptors are involved in the regulation of PRL as well as ACTH and beta-endorphin secretion. 8OHDPAT was almost 40 times more potent than ipsapirone. The maximal effects of the two drugs on PRL release were comparable. In contrast, ipsapirone behaved as a partial agonist only on ACTH and beta-endorphin secretion, thus suggesting that different neuronal targets are involved in the stimulation of the three hormones by 5HT.

Adenosine and pituitary-adrenocortical axis activity in the rat.

As shown by an increase in plasma corticosterone concentrations, adenosine administration stimulated pituitary-adrenocortical activity. This effect was prevented by dexamethasone (2 mg/kg i.p.). Added in vitro, adenosine reduced both adrenal basal and adrenocorticotropic hormone (ACTH)-stimulated corticosterone release, while it stimulated pituitary ACTH release. This ACTH response was blocked by dexamethasone but not by Tyr-somatostatin. Restraint stress increased adenosine content in the anterior pituitary, suggesting its possible involvement in hormonal stress response. Because the effect of adenosine on plasma corticosterone was still present in rats with a pharmacological block of the endogenous corticotropin-releasing factor release, we propose that adenosine is involved in the regulation of adrenocortical secretion at the level of the anterior pituitary and that this role is exerted through an interaction with a stimulatory adenosine receptor.

A model for later-life effects of perinatal drug exposure: maternal hormone mediation.

In the female rat chronic ethanol intake increased plasma levels of corticosterone; acute stress in the pregnant or lactating rat increased plasma levels of corticosterone in the fetuses or sucklings. In the lactating rat, corticosterone rapidly equilibrated between plasma and milk, so that variations in the mother's adrenocortical secretion could be promptly reflected in the suckling's body. The role of maternal adrenocortical hormone with regard to the development of pituitary-adrenocortical and behavioral activities was indicated by endocrine (plasma corticosterone), neurochemical (hippocampal corticosterone binding) and behavioral (avoidance performance) anomalies in the adult offspring of lactating rats with adrenocortical "hyperfunction" or "insufficiency." Further, the offspring of rats with adrenocortical "insufficiency" showed abnormalities in "in vitro" hypothalamus, pituitary and adrenocortex release of hormones. When searching for later effects in the offspring of drugs given to the mother in perinatal life one must be cognizant that, aside from their expected pharmacological action, drugs can produce variations in the mother pituitary-adrenocortical activity, sensed by the conceptus through the placenta or milk.