1. (+/-)-(3)H-NA and labelled metabolites of NA were estimated in rat hearts after perfusion with various concentrations of NA in the range 0.01-50.0 mug/ml. Labelled metabolites of NA accounted for only a small proportion of the total uptake of radioactivity at low perfusion concentrations, but accounted for 50% of the total uptake at 1 mug NA/ml., thereafter declining to progressively smaller proportions at higher perfusion concentrations.2. If the formation of labelled metabolites of (3)H-NA was blocked by a combination of monoamine oxidase and catechol-O-methyl transferase inhibitors, the accumulation of unchanged (3)H-NA was doubled when hearts were perfused with 1 mug NA/ml.3. In hearts perfused with 0.5 mug NA/ml., an accumulation of unchanged (3)H-NA was demonstrated in the presence of a combination of metabolic inhibitors and metaraminol. This appeared to be due to Uptake(2), since the accumulation of NA under these conditions could be prevented by a low concentration of normetanephrine.4. Phenoxybenzamine prevented extraneuronal uptake (Uptake(2)) and metabolism of (3)H-NA with an estimated ID50 of 2.5 muM. The inhibition of Uptake(2) by phenoxybenzamine (2.0 muM) was diminished at very high NA concentrations, suggesting that the drug may act competitively with NA.5. It was concluded that Uptake(2) operates at all catecholamine concentrations in the rat heart, but that in the lower range (less than 2.5 mug/ml. for NA and less than 0.75 mug/ml. for adrenaline) any catecholamine taken up by this process is rapidly metabolized. Thus the accumulation of unchanged amine is seen only at high perfusion concentrations.6. The relevance of these results to an understanding of the possible physiological and pharmacological importance of Uptake(2) is discussed.

Animals↗

PubMedDate not supplied

Comparative distribution and cardiovascular actions of substance P and substance K within the nucleus tractus solitarius of rats.

An investigation has been made into the comparative distribution and cardiovascular actions of Substance P (SP) and Substance K (SK) in the nucleus tractus solitarius (NTS) of rats. The two tachykinins were similarly distributed in the NTS region, as determined by radioimmunoassay of microdissected brain nuclei, although SP was present in an approximately 10 fold higher concentration than SK. Unilateral nodose ganglionectomy resulted in a non-significant reduction of tachykinin immunoreactivity in the ipsilateral NTS. Microinjection of synthetic SP into the NTS of urethane anaesthetised rats did not cause any significant changes in mean arterial pressure or heart rate. In contrast, SK (18 pmol) elicited a significant bradycardia which was maximal at 2 min after the injection. The bradycardic response was blocked in rats pre-treated with atropine. These results extend previous studies in which contrasting functional activities of SP and SK were demonstrated in peripheral systems, to indicate that tachykinins may exhibit different functional roles in the brain. SK, unlike SP, may be involved in central cardiovascular control via an action within the NTS.

Afferent Pathways↗

PubMedDate not supplied

Lymphocyte adhesion to cultured endothelial cells of the blood-retinal barrier.

Microvascular endothelial cells derived from the blood-retinal barrier were grown in vitro and various factors affecting the adhesion of syngeneic lymphocytes to these monolayers was evaluated. Under resting conditions 5.3 +/- 0.4% of lymphocytes derived from peripheral lymph nodes (PLN) were found to adhere to the endothelia. Adhesion of resting lymphocytes increased significantly following endothelial treatment with interferon-gamma (IFN-gamma; 11.7 +/- 1.0%), interleukin-1 (IL-1; 14.9 +/- 1.2%), astrocyte conditioned medium (ACM; 12.7 +/- 0.9%) or forskolin (13.9 +/- 1.2%). Lymphocyte activation with concanavalin A (ConA) increased adhesion to 17.0 +/- 0.9% which could be augmented by activating the endothelia with IFN-gamma (22.3 +/- 1.0%), IL-1 (24.0 +/- 1.0%) and ACM (25.7 +/- 1.6%). An antigen-specific CD4+ T cell line exhibited the greatest degree of adhesion, 40.4 +/- 2.5% on resting endothelia, 60.0 +/- 3.0% on IFN-gamma-activated cells and 54.3 +/- 1.4% on IL-1-activated cells. Although CD4+ lymphocytes predominated in the PLN population by 2:1, significantly more CD8+ cells were found to adhere.

Animals↗

PubMedDate not supplied

Presence and actions of vasopressin-like peptides in the rabbit anterior uvea.

The presence of vasopressin-like immunoreactivity (VP-IR) in the rabbit eye was demonstrated by radioimmunoassay. Trigeminal nerve denervation resulted in a significant and selective decrease in the levels of VP-IR in the iris sphincter muscle and the cornea. The isolated iris sphincter muscle contracted in response to low concentrations of [Arg8]vasopressin (AVP) and related peptides. The V1 vasopressin receptor antagonist, d(CH2)5Tyr(Me)AVP, potently inhibited the contractile responses to AVP. AVP was found to induce an increase in the accumulation of inositol phosphates in the iris sphincter muscle but not in the dilator/ciliary body preparation in vitro. The present investigation demonstrates the presence of VP-IR in the rabbit eye and that this substance may be another sensory nerve-derived mediator acting on specific target sites in the anterior uvea.

Angiotensin Receptor Antagonists↗

PubMedDate not supplied

Cardiovascular effects of neuropeptide Y in the nucleus tractus solitarius of rats: relationship with noradrenaline and vasopressin.

The central haemodynamic effects of neuropeptide Y (NPY), both alone and together with either noradrenaline (NA) or vasopressin (AVP), have been investigated by microinjecting synthetic peptide into the nucleus tractus solitarius (NTS) of anaesthetized rats. NPY alone elicited dose-dependent changes in blood pressure (BP) and heart rate (HR); 470 fmol inducing a pressor response, and 4.7 pmol a fall in BP. The hypotensive response to 20 nmol NA was significantly modified by both simultaneous and prior injection of an ineffective dose (47 fmol) of NPY. Prior injection of a similar dose of NPY also modified the NTS pressor effect of 10 ng AVP. A relationship between the action of AVP and NPY in the NTS was further indicated by the finding that prior injection of an ineffective dose of AVP (1 ng) reduced the hypotensive response to 4.7 pmol NPY, and by the demonstration of contrasting effects of 4.7 pmol NPY in AVP-deficient Brattleboro rats compared to parent strain LE rats. These results, taken together with the recent localization of NPY-like immunoreactivity in the NTS, suggest a role for NPY in central cardiovascular control. In addition, NPY has been shown to exhibit functional interactions with both an amine neurotransmitter and a neuropeptide present in the NTS of rats.

Animals↗

PubMedDate not supplied

alpha-MSH exhibits opioid antagonist-like effects in the brainstem of rats.

Unilateral microinjections of alpha-MSH (0.3, 1.2 and 12 pmol) into the nucleus tractus solitarius (NTS) of urethane-anaesthetized rats did not modify blood pressure or heart rate (HR). Using a dual microinjection technique, it has been shown that prior injection of alpha-MSH (0.3 pmol) attenuated the pressor effect of a similar injection of dynorphin 1-9 (18 pmol) but did not modify the cardiovascular effects of [Met]enkephalin (14 pmol). Since alpha-MSH has been localized in the NTS, the results indicate that this peptide may play a role in central cardiovascular control, possibly acting in an antagonistic manner to the endogenous opioid peptides.

Animals↗

PubMedDate not supplied

Osmotic regulation of substance P and neurokinin A peptide content and substance P binding sites in distinct hypothalamic nuclei of the rat.

Quantitative receptor autoradiography using Bolton-Hunter iodinated substance P (SP) was used to localize specific sites in the rat hypothalamus. The amount of SP and neurokinin A (NkA) in extracts from discrete areas of the hypothalamus was measured using specific radioimmunoassays. A high density of SP binding sites was observed in the perimeter of the magnocellular paraventricular and supraoptic nuclei, while the magnocellular nuclei themselves possessed a low receptor density. In control animals, the number of SP binding sites was also low in the arcuate nucleus and the median eminence. Substance P and NkA peptide concentrations were highest in the paraventricular nucleus (PVN), decreasing in the following order: arcuate nucleus (Arc) greater than median eminence (ME) greater than supraoptic nucleus (SON) greater than subfornical organ (SFO). In animals given 340 mmol/l NaCl instead of tap water to drink for 12 days, significant increases in the number of SP binding sites occurred in the medial parvocellular subdivision of the PVN, periamygdaloid cortex, medial preoptic nucleus, Arc, and ME, but other hypothalamic areas were unaffected. In saline-treated animals, significant increases in SP and NkA peptide concentrations were observed in the ME, while in the SFO only the concentration of NkA increased significantly. In the SON, substance P and neurokinin A levels were doubled, whereas in the PVN and Arc no changes in peptide levels were observed. Chronic osmotic stimulation is associated with lowered circulating levels of adrenocorticotropin releasing hormone (ACTH), and the present data further substantiate the hypothesis that hypothalamic tachykinin-containing neuronal terminals are centrally involved in the inhibition of anterior pituitary ACTH release observed during chronic osmotic stimulation.

Adrenocorticotropic Hormone↗

PubMedDate not supplied

Evidence for opiate receptors on pituicytes.

A hypothalamo-neurohypophyseal enkephalinergic pathway has been described and the pars nervosa of the rat pituitary contains enkephalin-like material which may coexist in vasopressin and oxytocin terminals. At the level of the pars nervosa itself, stereospecific opiate receptors with properties very similar to those of brain receptors have been described, and opiates have been shown to inhibit the release of both vasopressin and oxytocin. The location of the opiate receptors involved has been presumed to be pre-terminal on the neurosecretory fibres. Using an autoradiographic technique to visualize opiate receptors, however, we now report that destruction of the neurosecretory fibres following pituitary stalk section does not result in a significant change in the neural lobe opiate receptor population. This suggests that the opiate receptors within the neural lobe may be present on pituicytes rather than on neurosecretory fibres.

Animals↗

PubMedDate not supplied

A vasopressin-like peptide in the mammalian sympathetic nervous system.

Vasopressin was among the first mammalian hormonal peptides to be identified and to have its structure determined. Its only undisputed physiological role is as a circulating neurohypophyseal antidiuretic hormone. Other notable effects of vasopressin on peripheral tissues include contraction of vascular smooth muscle, leading to elevation of blood pressure, and activation of glycogenolysis in liver. It has long been clear that vascular smooth muscle and hepatocytes are relatively insensitive to the low concentrations of vasopressin normally present in the circulation, and the physiological significance of their responses has therefore been in doubt. We now report that a new bioactive and immunoreactive vasopressin-like peptide (VLP) is widely distributed in the sympathetic nervous system of mammals, both in the principal noradrenergic neurones of ganglia and in nerve fibres innervating peripheral tissues. In addition to other peptides described in the mammalian sympathetic nervous system, VLP must be considered as a possible mediator of the non-adrenergic responses to sympathetic activation. Moreover, many of the effects previously attributed to circulating vasopressin may be neurally evoked.

Animals↗

PubMedDate not supplied

Changes in hypothalamic preproenkephalin A mRNA following stress and opiate withdrawal.

The median eminence of the pituitary is rich in opioid receptors, and exogenous opioids have major effects on the release of adrenocorticotropic hormone (ACTH), luteinizing hormone (LH), prolactin, growth hormone (GH) and thyrotropin. Stress results in similar changes in anterior pituitary hormone secretion. Enkephalin immunoreactivity has been reported in the medial parvocellular neurons of the hypothalamic paraventricular nucleus which project to the median eminence, the site where hypothalamic releasing factors are secreted into the portal blood and thence to the anterior pituitary gland. The endocrine response to stressful stimuli might therefore, at least in part, be mediated through the activation of hypothalamic enkephalinergic neurons. We show that two stressful stimuli, opiate withdrawal and intraperitoneal injection of hypertonic saline, both result in very rapid and marked increases in enkephalin mRNA in the parvocellular paraventricular nucleus. The activation of hypothalamic enkephalin neurons may be important in the neuroendocrine response to stress.

Animals↗

PubMedDate not supplied

Interleukin-1 beta-induced effects on plasma oxytocin and arginine vasopressin: role of adrenal steroids and route of administration.

The effects of cytokines in stimulating neurohypophysial hormone release have not been well characterized. In the present study, we have investigated the effect of intraperitoneal injection of recombinant human interleukin (IL)-1 beta on oxytocin release in sham-operated controls, adrenalectomized (ADX) rats and ADX rats given either low or high doses of the synthesis glucocorticoid dexamethasone. In a second study, we determined the effect of central injection of IL-1 beta on both oxytocin and arginine vasopressin (AVP) release in sham-operated and ADX rats. We were unable to demonstrate an increase in plasma oxytocin in intact rats in response to intraperitoneal injection of IL-1 beta. In contrast, we found a substantial and sustained increase in plasma oxytocin concentrations in ADX rats. This stimulation was abolished by treatment with dexamethasone at both the low and high doses. Following central injection of IL-1 beta, we were unable to demonstrate any increase in either oxytocin or AVP, despite the ability of this dose of cytokine to stimulate the hypothalamo-pituitary-adrenal axis, as evidenced by increased circulating corticosterone. It appears that circulating glucocorticoids may exert a tonic inhibitory effect on the release of oxytocin in response to peripheral stimulation by IL-1 beta.

Adrenal Cortex Hormones↗

PubMedDate not supplied

Inhibition of the hypothalamic-pituitary-thyroid axis in response to lipopolysaccharide is independent of changes in circulating corticosteroids.

We have investigated the role of circulating glucocorticoids in the suppression of the hypothalamic-pituitary-thyroid (HPT) axis following lipopolysaccharide (LPS) injection in rats. Intraperitoneal injection of LPS (2.5 mg/kg) suppressed paraventricular nucleus thyrotropin-releasing hormone (TRH) mRNA, pituitary thyroid-stimulating hormone (TSH) mRNA and plasma triiodothyronine. In these animals LPS also increased paraventricular nucleus corticotropin-releasing hormone (CRH) mRNA, pituitary proopiomelanocortin (POMC) mRNA and plasma corticosterone levels. To investigate the role of plasma corticosterone in the suppression of the HPT axis, we clamped the plasma corticosterone level at morning baseline level by bilateral adrenalectomy and corticosterone pellet implantation. Ten days after surgery, LPS injection evoked a dramatic increase in CRH mRNA and POMC mRNA. Despite the lack of change in plasma corticosterone in the corticosterone-clamped rats, LPS was still able to suppress TRH and TSH mRNA levels in both corticosterone-clamped and sham-operated rats. These data indicate that in response to LPS, suppression of the HPT axis occurs and is independent of the LPS-induced increase in plasma corticosterone.

Adrenal Cortex Hormones↗