High levels of NPY in rabbit cerebrospinal fluid and immunohistochemical analysis of possible sources

We have analyzed rabbit cerebrospinal fluid for neuropeptide Y (NPY)-like immunoreactivity, using high performance liquid chromatography (HPLC) and radioimmunoassay (RIA) and examined the anatomical relationship of NPY-containing fibers to the cerebral vasculature and the third cerebral ventricle. Cerebrospinal fluid (CSF) obtained from the cisterna magna of rabbits was injected into a C18 column and subjected to HPLC. The fractions were collected, dried and reconstituted in buffer for NPY radioimmunoassay. A single peak of NPY immunoreactivity was obtained which corresponded in retention time to synthetic porcine NPY. Analysis of CSF samples produced displacement curves parallel to the standard curve. Immunohistochemistry revealed numerous NPY-labeled fibers which penetrated the ependymal lining of the third cerebral ventricle and directly bordered the ventricular lumen. Other fibers were observed in the pia which lines the ventral aspect of the hypothalamus. The basilar artery, its branches and other cerebral vessels were surrounded by NPY-labeled fibers. The results show that: (1) approximately 1 ng/ml of NPY immunoreactivity which corresponds chromatographically to synthetic porcine NPY is present in rabbit CSF; (2) NPY-containing fibers surround the basilar artery and other cerebral vessels; (3) NPY may be released into the CSF from axons in the pia and from axons which penetrate the ependymal lining of the third ventricle. These observations form the basis for our analysis of the vasoconstrictor effects of NPY and its role in cerebrovasospasm after experimental subarachnoid hemorrhage.

Neuropeptide Y: vasoconstrictor effects and possible role in cerebral vasospasm after experimental subarachnoid hemorrhage

The possible role of neuropeptide Y (NPY) as a vasoconstrictor substance contributing to the development of cerebral vasospasm after experimental subarachnoid hemorrhage was studied. Autologous blood was injected into the cisterna magna of control rabbits and rabbits that had received bilateral superior cervical ganglionectomy 2 days before blood injection. Three days after blood injection the concentration of NPY in cerebrospinal fluid (CSF) was 5971 +/- 551 pg/ml while CSF from control animals contained 992 +/- 162 pg/ml of NPY. The effects of porcine NPY on norepinephrine-induced contraction of rabbit cerebral arteries were also studied in vitro. NPY (1.2 nM) caused a 3-fold potentiation of norepinephrine-induced contraction of cerebral arteries. CSF from control rabbits diluted by 50% with Krebs solution had no significant effect on norepinephrine-induced contraction of cerebral arteries when compared to responses in Krebs solution only; however, diluted CSF from denervated blood-injected rabbits potentiated norepinephrine-induced contraction by 2.6-fold. Antiserum containing NPY specific antibodies was used to immunoprecipitate the peptide from CSF taken from denervated blood-injected rabbits. CSF treated with this antiserum contained less than 40 pg/ml of NPY and had no effect on norepinephrine-induced contraction of cerebral arteries. These results show that the concentration of NPY in CSF of rabbits is elevated after experimental subarachnoid hemorrhage. In addition, NPY in CSF can potentiate the vasoconstrictor effect of norepinephrine which may contribute to the development of cerebral vasospasm.

Comparison of alpha 1-adrenergic receptor subtypes distinguished by chlorethylclonidine and WB 4101

We showed previously that subtypes of alpha 1-adrenergic receptors can be differentiated by selective inactivation with chlorethylclonidine (CEC) [Mol. Pharmacol. 32:505-510 (1987)] or by their affinities for the competitive antagonist WB 4101 [Nature (Lond.) 329:333-335 (1987)]. Examining eight rat tissues, the proportions of 125IBE 2254-binding sites sensitive to inactivation by CEC correlated significantly (p less than 0.05) with the proportion having a low affinity for WB 4101. However, the proportion of CEC-sensitive sites was always smaller than the proportion of low affinity WB 4101 sites. Further experiments showed that repetitive pretreatment with CEC or pretreatment under hypotonic conditions caused a larger inactivation of binding sites, suggesting that CEC did not access all sites under the isotonic conditions used previously. The proportions of binding sites inactivated by 10 microM CEC under hypotonic conditions were quantitatively similar to and correlated significantly (p less than 0.01) with the proportion having a low affinity for WB 4101. Pretreatment of hippocampus and vas deferens with CEC caused a loss of all low affinity WB 4101-binding sites, leaving only high affinity sites. In vas deferens, CEC pretreatment decreased the potency of norepinephrine in stimulating 3H-inositol phosphate accumulation but not contractile responses. In rat liver slices, CEC inactivated norepinephrine-stimulated 3H-inositol phosphate accumulation in parallel with 125IBE-binding sites. These results suggest that: 1) the CEC-sensitive and -insensitive 125IBE 2254-binding sites are equivalent to those with a low and high affinity for WB 4101, respectively, and 2) the CEC-sensitive binding sites with a low affinity for WB 4101 are the alpha 1-adrenergic receptors linked to inositol phospholipid hydrolysis.

Heterogeneity of alpha 1-adrenergic receptors revealed by chlorethylclonidine

Chlorethylclonidine (CEC) has previously been shown to inactivate only a subpopulation of the alpha 1-adrenergic receptor binding sites in rat brain. We compared alpha 1-adrenergic receptors in different tissues to determine whether such selective inactivation might reveal the presence of distinct receptor subtypes. Pretreatment of broken cell preparations with 10 microM CEC for 10 min caused a 70-80% decrease in the density of specific 125IBE 2254 binding sites in rat liver and spleen, a 25% decrease in neocortex, but no significant loss in kidney, hippocampus, heart, vas deferens, or caudal artery. The effect of CEC in liver was not reversed by extensive washing, suggesting irreversible inactivation. The selectivity between different tissues was due to differences in the efficacy of CEC inactivating the binding sites and not due to differences in binding affinity. To determine whether the effects on 125IBE 2254 binding reflected selective inactivation of functional receptors, contractile responses of rat spleen and vas deferens were examined. Pretreatment of intact tissues with 100 microM CEC for 30 min caused a large decrease in the potency and maximal contraction to norepinephrine in spleen but had no effect in vas deferens. Inhibition of specific 125IBE 2254 binding by various agonists and antagonists was determined in CEC-sensitive (liver, spleen) and insensitive (hippocampus, vas deferens) tissues. Although many drugs had similar affinities in all tissues, others were substantially less potent in the CEC-sensitive tissues. These experiments suggest that there are at least two subtypes of alpha 1-adrenergic receptors with different pharmacological properties in mammalian tissues, only one of which is inactivated by CEC.

Alpha 1-adrenoceptor subtypes linked to different mechanisms for increasing intracellular Ca2+ in smooth muscle

Receptor-mediated increases in intracellular Ca2+ levels can be caused by release from intracellular organelles and/or influx from the extracellular fluid. Noradrenaline (NA) released from sympathetic nerves acts on alpha 1-adrenoceptors to increase cytosolic Ca2+ and promote smooth muscle contraction. In many cells activation of alpha 1-adrenoceptors causes formation of inositol 1,4,5-trisphosphate which promotes Ca2+ release from intracellular stores. The mechanism by which receptor activation opens cell surface Ca2+ channels is not known, although in some cases it may be secondary to formation of inositol phosphates or release of stored intracellular Ca2+ (ref. 3). However, alpha 1-adrenoceptors have recently been shown to have different pharmacological properties in different tissues, and it has been proposed that different alpha 1-adrenoceptor subtypes may control mobilization of intracellular Ca2+ and gating of extracellular Ca2+ influx. We here report evidence for two subtypes of alpha 1-adrenoceptors which cause contractile responses through different molecular mechanisms. One subtype stimulates inositol phosphate (InsP) formation and causes contractions which are independent of extracellular Ca2+, and the other does not stimulate inositol phosphate formation and causes contractions which require the influx of extracellular Ca2+ through dihydropyridine-sensitive channels. These results suggest that neurotransmitters and hormones may control Ca2+ release from intracellular stores and influx through voltage-gated membrane channels through distinct receptor subtypes.

Neuropeptide Y potentiates contraction and inhibits relaxation of rabbit coronary arteries

The effects of neuropeptide Y (NPY) on contraction and relaxation of isolated rabbit coronary arteries were studied. NPY alone caused a weak contraction of coronary arteries with a mean EC50 value of 29 +/- 2.0 nM. Following exposure of coronary arteries to 30 nM NPY, the potencies of norepinephrine (in the presence of 3 microM timolol) and histamine in causing contraction were increased twofold, with no change in maximal contraction. After half-maximal contraction of coronary arteries with histamine and addition of 30 nM NPY, relaxation produced by norepinephrine (in the presence of 3 microM phentolamine), adenosine, and acetylcholine was inhibited. Concentration-response curves for all vasodilators were shifted to the right 10-22-fold by 30 nM NPY. Maximal relaxation caused by adenosine and norepinephrine was not changed by NPY, whereas the maximal response to acetylcholine was 37% less in the presence of NPY. Correlation of the tension produced by NPY with the shift in agonist contraction or relaxation concentration-response curves indicated that NPY-induced increases in baseline tone had no effect on the degree of shift in agonist concentration-response curves. These results show that NPY causes a modest potentiation of agonist-induced contraction and a dramatic blockade of vasodilator-induced relaxation of rabbit coronary arteries.