Substance P

The substance P receptor subtype modulating catecholamine release from adrenal chromaffin cells

Substance P (SP) has two distinct actions on catecholamine (CA) release from cultured bovine adrenal chromaffin cells: SP inhibits acetylcholine (ACh)- or nicotine-induced [3H]norepinephrine ([3H]NE) release; and SP protects against desensitization of ACh- or nicotine-induced [3H]NE release. In order to characterize the SP receptor subtypes modulating these two actions, we have tested several SP-related tachykinins and SP analogues for their ability to act as agonists of SP for these actions. The naturally occurring tachykinins, physalaemin, eledoisin and kassinin, were about equipotent and all much less potent than SP in inhibiting nicotine-induced [3H]NE release. Physalaemin and eledoisin were also approximately equipotent and much less potent than SP in protecting against desensitization of nicotine-induced [3H]NE release; kassinin slightly enhanced nicotinic desensitization. These results indicate that neither a kassinin-like nor a physalaemin-like peptide are likely to modulate adrenal CA release. The 'SP-P' receptor-selective analogue, SP-methyl ester, was an agonist, equipotent with SP, for both of SP's actions on [3H]NE release. [D-Pro2,D-Trp7,9]-SP, a potent antagonist of SP's actions in many SP-responsive tissues, was inactive as an antagonist of both of SP's actions on [3H]NE release from adrenal chromaffin cells; however, this analogue was a potent SP agonist in chromaffin cells. The rank order of potency of these and other SP-related peptides for inhibition of [3H]NE release was similar to their order of potency for protection against desensitization. Thus the chromaffin cell SP receptors mediating inhibition of nicotine-induced [3H]NE release appear to be very similar to those mediating protection against desensitization of nicotine-induced [3H]NE release. The results indicate that the SP receptors modulating adrenal CA release are different from either the 'SP-P' or 'SP-E' receptor subtypes; bovine adrenal chromaffin cells appear to possess a third subtype of SP receptor which shares similar characteristics with the SP receptors mediating histamine release from rat mast cells.

Substance P in the bovine retina: localization, identification, release, uptake and receptor analysis

Substance P-like immunoreactivity is restricted to at least three different cell types in the bovine retina. They are amacrine cells, displaced amacrine cells and interplexiform neurones. High performance liquid chromatography and radioimmunoassay have shown that the bovine retina substance P-like immunoreactive material cannot be distinguished from authentic substance P. Isolated bovine retina does not take up exogenous [3H]substance P as revealed by autoradiography. By increasing the external K+ concentration it was shown that the release of endogenous substance P from the retina was stimulated. This release is Ca2+ dependent. The binding of [3H]substance P to crude membrane preparations of bovine retina was saturable and revealed a single population of binding sites with a KD value of 0.32 nM and a Bmax of 2.45 pmol/g wet wt. The characteristics of the binding site suggest the presence of substance P receptors. It is suggested that substance P is a likely neurotransmitter in the bovine retina.

Substance P excitation of rat locus coeruleus neurones

We have made extracellular recordings from locus coeruleus neurones contained in a pontine slice preparation. The in vitro technique permits application of known concentrations of drugs in the perfusion medium. Substance P excites locus coeruleus neurones in a concentration-dependent manner. The activity of substance P was found to reside in the C terminal region of the molecule. The relative potency of substance P and related peptides suggests that the substance P receptors present within the locus coeruleus are predominately of the substance P-P type. The synthetic analogue [D-Pro2,D-Trp7.9]substance P was not found to antagonise the action of substance P on locus coeruleus neurones.

Actions of substance P, MIF, TRH and related peptides in the substantia nigra, caudate nucleus and nucleus accumbens

Neurones in the substantia nigra were found to be sensitive to iontophoretically applied substance P, substance P 1-9 methyl ester and substance P 1-9 amide. Substance P 1-2, 4-9 and 5-9 methyl esters, thyrotropin releasing hormone (TRH), Pyroglutamyl-histidyl-2 methyl prolineamide (methyl TRH), Pyroglutamyl-histidyl-2 methyl prolineamide (methyl TRH), histidyl-proline-diketopiperazine (His-Pro) and MSH releasing inhibiting factor (MIF) were without effect on neurones in this area. Thyrotropin releasing hormone (TRH), methyl TRH, His-Pro and MIF were inactive on neurones in the caudate nucleus and nucleus accumbens. Bilateral injections of substance P and substance P 1-9 methyl ester into the ventral tegmental area (VTA) of conscious rats produced locomotor activity, while similar injections of substance P 4-9 and 5-9 methyl esters did not. The locomotor activity produced by amphetamine was prolonged by TRH, while MIF was devoid of such activity. The data suggest that substance P and substance P 1-9 have similar effects in the substantia nigra, although the mechanism of action is unclear. Thyrotropin releasing hormone and MIF probably do not have acute actions in the brain areas tested.

Characterization of substance P and somatostatin receptors on adrenal chromaffin cells using structural analogues

Substance P (SP) and somatostatin (SRIF) are known to inhibit the nicotine-induced release of catecholamines (CAs) from isolated adrenal chromaffin cells in culture22,24. In order to characterize the receptors mediating this action, we have tested several SP and SRIF analogues for their effects on release of [3H]L-norepinephrine ([3H]NE) from chromaffin cell cultures. SP-free acid and a series of 11 SP analogues, in which each amino acid of SP is replaced in turn by L-alanine, all inhibited the nicotine-induced release of [3H]NE from these cultures. The rank order of potency of the analogues for this action was similar to their reported order of potency in other SP-responsive tissues. The least potent were SP-free acid, [Ala7]-SP, [Ala10]-SP, [Ala8]-SP and [Ala11]-SP, while the potencies of the Ala 1 to 6 analogues and [Ala9]-SP were closer to that of SP. [Leu7]- and [Leu7,8]-SP had potencies similar to that of SP. SP itself had no effect on basal [3H]NE release and only the highest concentrations of some of the analogues tested had an effect (enhancement) on basal [3H]NE release. The results suggest that adrenal chromaffin cells possess a specific SP receptor mediating inhibition of agonist-induced CA release and that the binding site of this receptor shares similar structural requirements with the binding site of the SP receptor on other tissues. Several SRIF analogues, which have been previously shown to be more potent than native SRIF at selective SRIF receptors2,3,31, 35, were compared to SRIF for effects on [3H]NE release from chromaffin cell cultures. These analogues were found to be active but less potent than SRIF in inhibiting nicotine-induced [3H]NE release from these cultures, suggesting that the site mediating this action differs in its structural requirements from the SRIF receptor found in some other tissues.

Demonstration of a substance P-like immunoreactivity in retinal cells of the rat

The distribution of substance P (SP)-like immunoreactivity in the rat retina was investigated by immunohistochemistry. SP-positive cells were found throughout the retina. The majority of them were located in the proximal portion of the inner nuclear layer and the processes from these cells directed to the inner plexiform layer where they ramified, suggesting that SP-positive cells located in this region probably are amacrine cells. Few SP-positive cells were seen within the ganglion cell layer. They were considered displaced amacrine cells.

Neuromorphology and neuropharmacology of the human penis: an in vitro study

The neuromorphology and neuropharmacology of the human penis are only briefly described in literature. The present study was undertaken to define the adrenergic and cholinergic neuromorphology of the human corpus cavernosum (CC) and corpus spongiosum and to evaluate the in vitro response of the CC to pharmacologic stimulation. Human penile tissue was obtained from six transsexual patients undergoing penectomy. For morphologic study, the tissue was processed for (a) hematoxylin and eosin staining; (b) smooth muscle staining; (c) acetylcholinesterase localization; (d) glyoxylic acid histofluorescence; (e) electron microscopy; and (f) electron microscopy after glutaraldehyde dichromate fixation. In addition, strips of CC were placed in in vitro muscle chambers and tension changes recorded isometrically after stimulation with norepinephrine (NE) and acetylcholine. The CC contains abundant smooth muscle, numerous glyoxylic acidfluorescent (catecholaminergic) fibers and varicosities, and a scant distribution of acetylcholinesterase-positive fibers. Fewer of all these elements were present in the corpus spongiosum. No "polsters" were observed in the CC. Although glutaraldehyde-fixed controls exhibited no typical adrenergic vesicles (small, dense core, measuring 400-600 A in diameter), some small, strongly electron-dense vesicles were found in glutaraldehyde dichromate-fixed tissue and were thought to contain NE. A variety of other vesicles were also encountered. The addition of NE to the in vitro muscle chambers caused a dose-related contraction, which was blocked by pretreatment with phentolamine in all CC strips tested. Acetylcholine in high concentration produced minimal contraction in 2 of 24 strips. Our morphologic and pharmacologic data suggest that the sympathetic nervous system may affect erection by acting not only on the penile vasculature but also by direct action on the smooth muscle of the CC itself.

Substance P stimulation of amylase release by isolated parotid cells and inhibition of substance P induction of salivation by vasoactive peptides

Substance P stimulation of salivation in rats has been studied as has its in vitro enhancement of amylase release by isolated parotid cells. The extent of the stimulation on amylase release by isolated parotid cells was dependent upon the concentration of substance P, with the minimum effective concentration being 1 nM. The substance P effect was detectable within 1 min after incubation and lasted for at least 50 min. Substance P stimulation was demonstrable at 25--37 degrees C but not at 0 degrees C. Adrenocorticotropic hormone (ACTH), thyrotropin-releasing hormone (TRH), vasopressin and neurotensin had no effect on amylase release. These results suggest that substance P may act directly on the parotid cells. Examination of the salivary-stimulating activity of fragments of substance P showed that the C-terminal octapeptide and (pyroglutamyl)hexapeptide were active, although less potent than substance P, whereas its free acid, C-terminal tetra- and tri-peptides were inactive. Vasopressin, angiotensin II and neurotensin could inhibit substance P induced salivation, whereas TRH, ACTH and somatostatin had no effect. Amylase activity per unit volume of saliva was not changed by the injection of vasopressin, angiotensin II or neurotensin. These vasoactive peptides did not affect substance P stimulation of amylase release by isolated parotid cells. The results indicate that vasopressin, angiotensin II and neurotensin inhibit the action of substance P on salivation at sites other than the parotid cells.