Adenylyl cyclase stimulation by VIP in rat seminal vesicle membranes

Prostasomes are neuroendocrine-like vesicles in human semen

BACKGROUND

Prostasomes are prostate-derived organelles that exist extracellularly in human seminal plasma.

METHODS

In this study, we have investigated and characterized human prostasomes with regard to their contents of synaptophysin, members of the chromogranin family, and some neuropeptides.

RESULTS

By radioimmunoassay measurement and electron microscopy we show the presence of the neuroendocrine markers chromogranin B, neuropeptide Y, and vasoactive intestinal polypeptide in about equimolar amount in human prostasomes and chromogranin A in about 2% of that amount. To our knowledge, such a high ratio of chromogranin B to chromogranin A has never before been observed. The membrane-bound protein synaptophysin, a well-established immunocytochemical marker for neuroendocrine cells and neurones, was also detected. Hence, we show that synaptophysin could be used as a marker for intact prostasomes.

CONCLUSIONS

The presence of synaptophysin has recently been shown in the serotonincontaining vesicles in platelets. A protein with a similar structure denoted granulophysin has been found in granulocytes and prostasomes. It is suggested that synaptophysin and granulophysin molecules are members of a family of proteins, maybe expressed in all cells that have regulated release of granule content. Our presented data indicate a neurotransmittor function of the prostasomes. The target cells are however not known but could be either the spermatozoa, the epithelial mucous cells of the uterus or tubas or perhaps the ovum.

Effect of castration on the VIPergic innervation and 125I-labelled vasoactive intestinal peptide (VIP) binding sites in the hamster seminal vesicle. A quantitative immunohistochemical and receptor autoradiographic study

In the present work we have investigated the effects of medium- (15 days) and long-term (2 months) castration on vasoactive intestinal peptide (VIP)-immunoreactive nerve fibres and 125I-labelled VIP binding sites in the adult hamster seminal vesicle. The density of VIP- and synaptophysin (general neuronal marker)-containing nerve fibres was determined in immunofluorescently stained cryostat sections using a computerised image analysis system. The morphological analysis of 125I-VIP binding sites in seminal vesicle cryostat sections was performed by quantitative receptor autoradiography. Our results show that the densities of the overall (synaptophysin immunoreactive) and VIPergic innervation increase in both medium and long-term castrated animals. In absolute terms, the quantity of VIP- and synaptophysin- containing nerves is not altered in medium-term castrates, but decreases for synaptophysin in long-term castrates. Medium-term castration does not affect the density of 125I-VIP binding sites in the gland muscular coat, but a significant decrease is observed after long-term castration. In conclusion, our results indicate that whereas VIP nerves are apparently unaffected by castration, 125I-VIP binding sites in the muscular coat of hamster seminal vesicle are sensitive to androgen levels.

Characterization of adenylyl cyclase stimulated by VIP in rat and mouse peritoneal macrophage membranes

Vasoactive intestinal peptide (VIP) stimulated adenylyl cyclase activity in rat and mouse peritoneal macrophage membranes. GTP potentiated the stimulatory effect of VIP so that it was routinely included at 10 microM GTP. Other agents like GTP, Gpp(NH)p, GTP-gamma-S, sodium fluoride, and forskolin, at a concentration of 0.1 mM, increased the basal activity of enzyme by 3.1, 5.7, 4.7, 3.6, and 7.8-fold, respectively. The stimulation of adenylyl cyclase by VIP was time, temperature, and membrane concentration dependent. Half-maximal enzyme activation (ED50) was very similar in rat and mouse peritoneal macrophage membranes (1.5 +/- 0.1 nM and 1.0 +/- 0.1 nM, respectively). However, VIP showed more efficacy in mouse macrophages membranes (about 3.1-fold basal values) than that in rat macrophage membranes (about 2.5-fold basal values). The relative potency of several peptides upon stimulation of adenylyl cyclase activity showed the following potency in both species: VIP = PACAP38 = PACAP27 > helodermin > PHI > secretin. On the other hand, a M(r)-45 kDa alpha s subunit of Gs protein was demonstrated by both ADP-ribosylation and immunoblot in mouse and rat peritoneal macrophage membranes. The present results, together other previous, strongly suggest that VIP play an important role in the regulation of macrophage function.

Vasoactive intestinal peptide in the hamster seminal vesicle: distribution, binding sites and possible functions

The presence and functional role of vasoactive intestinal peptide in the hamster seminal vesicle were studied by a combination of structural and functional approaches. The use of an immunofluorescence staining technique in both cryostat sections and whole-mount preparations revealed that vasoactive intestinal peptide-immunoreactive nerve fibres were mainly localized in the lamina propria of the mucosal layer. In double-stained preparations, vasoactive intestinal peptide immunoreactivity was found to be localized in nerves also containing acetylcholinesterase activity. At the ultrastructural level, the use of an immunogold staining method showed that vasoactive intestinal peptide immunoreactivity occurred in large granular vesicles (80-150 nm in diameter) in nerve varicosities which also contained small pleomorphic agranular vesicles. In order to evaluate the anatomical distribution of vasoactive intestinal peptide binding sites in the seminal vesicle, we have utilized an in vitro receptor autoradiographic technique. Vasoactive intestinal peptide binding sites were localized in the basal region of the secretory epithelium, in the muscle layer and in the wall of blood vessels. In vitro incorporation of [3H]L-leucine into protein by tissue slices revealed that vasoactive intestinal peptide (1 microM) significantly increases the amount of released protein. Vasoactive intestinal peptide (0.1-1 microM) did not affect the resting tension of the muscle but significantly inhibited the increase in muscle tension induced by carbachol. Atropine prevented the effect of carbachol, indicating that the latter is mediated by muscarinic receptors. Our results suggest that in the hamster seminal vesicle, vasoactive intestinal peptide is involved in the modulation of muscarinic function and in the control of secretion.

Stimulation of the adenylyl cyclase activity in human endometrial membranes by VIP and related peptides

Vasoactive intestinal peptide (VIP) has been shown to stimulate adenylyl cyclase activity in human endometrial membranes. The effect was dependent on the time and temperature of incubation as well as on the concentration of endometrial membrane proteins in the medium. In the presence of 1 microM GTP, half-maximal stimulation of adenylyl cyclase activity was observed at 25.0 +/- 7.0 nM VIP, whereas the maximal activity (at 1 microM VIP) corresponded to an increase of about 140% with respect to basal values (7.5 +/- 0.6 pmol cyclic AMP/min/mg of protein). However, the maximal stimulation of adenylyl cyclase activity was obtained with helodermin (1 microM) that increased the activity by 170% over the basal. The relative potency of VIP-related peptides upon the adenylyl cyclase activity was: helodermin (ED50 = 1.8 +/- 1.4 nM) > VIP (ED50 = 25.0 +/- 7.0 nM) > PHI (ED50 = 725.0 +/- 127.2 nM). Secretin had a faint effect upon the adenylyl cyclase activity and glucagon was completely inefficient at this level. The presence of alpha s and alpha i subunits of G proteins in human endometrium was detected by immunoblot. Preliminary results showed the presence of two classes of 125I-VIP receptors in human endometrial membranes with the following stoichoimetric parameters: high affinity receptor (Kd = 2.0 nM, binding capacity 0.1 pmol VIP/mg protein) and low affinity receptor (Kd = 0.43 microM, binding capacity 13.1 pmol VIP/mg protein). The present results together with the known presence of VIP in human uterus and the actions of this neuropeptide in the adjacent myometrial tissue support the idea that VIP and related peptides may have a role in human endometrium.

Vasoactive intestinal peptide receptor antagonists in rat seminal vesicle membranes

Vasoactive intestinal peptide (VIP) receptors coupled to activation of adenylate cyclase have been previously identified in seminal vesicle membranes of rat. In the present study we demonstrate that the synthetic peptides [4-Cl-D-Phe6,Leu17]VIP and the growth hormone releasing factor (GRF) analog [Ac-Tyr1,D-Phe2]GRF1-29-NH2 inhibit in a competitive manner the specific 125I-VIP binding to the same membrane preparation. The order of potency of the two peptides compared to VIP was: VIP (IC50 = 1.3 +/- 0.5 nM) greater than [4-Cl-D-Phe6,Leu17]VIP(IC50 = 1600 +/- 45.0 nM) greater than [Ac-Tyr1,D-Phe2]GRF1-29-NH2(IC50 = 290.0 +/- 59.4 nM). Whereas VIP showed a stimulatory activity upon adenylate cyclase with a potency (ED50 = 7.0 +/- 0.7 nM) compatible with the affinity of the VIP binding sites previously described, the other two peptides tested showed no effect at that level. The behavior as antagonists of both [4-Cl-D-Phe6,Leu17]VIP and [Ac-Tyr1,D-Phe2]GRF1-29-NH2 was confirmed by: (a) the parallel shifts of the VIP dose-response curves for stimulation of adenylate cyclase activity in the presence of the antagonists; (b) the close agreement between the binding affinity and the inhibition of adenylate cyclase activity for the two peptides; and (c) the lack of effect of the two antagonists upon the adenylate cyclase activity stimulated by the beta-adrenoceptor agonist isoproterenol which indicates the specificity of the interaction.(ABSTRACT TRUNCATED AT 250 WORDS)