Vasoactive intestinal peptide stimulation of renal adenylate cyclase and antagonism by (4Cl-D-Phe6Leu17)VIP

Vagal nerve stimulation during muscarinic and beta-adrenergic blockade causes significant coronary artery dilation

Vasoactive intestinal peptide (VIP) is present in post-ganglionic vagal nerve fibers in the coronary arteries and right ventricle but no significant amounts are found in the left ventricle. We determined the effects of VIP, released endogenously from cardiac vagal nerves, on the circumflex mean coronary artery pressure and on right and left ventricular (RV and LV) contractility (dP/dtmax) and relaxation (dP/dtmin). In 20 anesthetized, open chest mongrel dogs, the cervical vagus nerves and cardiac sympathetic ansa subclaviae were isolated and transected. Electrodes were applied to the cardiac segments of the right and left vagus nerves for subsequent stimulation. The muscarinic and beta-adrenergic receptors were blocked with atropine and propranolol, respectively. The heart rate was controlled by either producing atrioventricular node block in 10 dogs and pacing the ventricles (series 1) or by right atrial pacing in 10 separate dogs (series 2). Coronary artery blood flow was controlled by perfusing the circumflex coronary artery in each dog with femoral arterial blood at a controlled flow rate. Coronary artery pressure, ventricular and aortic pressures and dP/dt were continuously measured. Experiments were performed prior to and after the administration of [4Cl-D-Phe6,Leu17]VIP, a sensitive and selective VIP antagonist. Vagal nerve stimulation at 20 Hz (0.5 ms, 20 V) for 5 min significantly decreased the circumflex mean coronary artery pressure by 17% from the control value of 95+/-2 mmHg in series 1 and by 13% from the control value of 109+/-2 mmHg in series 2 (both p < 0.005). Aortic, LV and RV systolic and end-diastolic pressures, LV dP/dtmax and dP/dtmin, and the EKG did not change. In contrast, RV dP/dtmax and dP/dtmin increased by 22% (p < 0.04) and 23% (p < 0.02), respectively, in series 1 and by 26% (p < 0.02) and 33% (p < 0.01), respectively, in series 2. The VIP antagonist, [4Cl-D-Phe6,Leu17]VIP, directly injected into the left circumflex coronary artery, had no effect on coronary, aortic or ventricular pressures, ventricular dP/dt or the EKG. However, 20 Hz vagal stimulation in the presence of the VIP antagonist did not decrease circumflex mean coronary artery pressure. In addition, vagal stimulation, in the presence of the VIP antagonist, had no effect on LV pressures or dP/dt but increased RV dP/dtmax and dP/dtmin. RV dP/dtmax increased by 16% (p < 0.01) and RV dP/dtmin increased by 22% (p < 0.04), respectively, in series 1 and by 27 and 24%, respectively, in series 2 (both p < 0.01). Vagal nerve stimulation during muscarinic and beta-adrenergic blockade releases VIP or a 'VIP-like' substance that significantly decreases circumflex coronary artery vascular resistance and increases RV dP/dtmax and dP/dtmin.

Characterization of VIP receptor-effector system antagonists in rat and mouse peritoneal macrophages

In the present study we show that the synthetic peptides [4-Cl-D-Phe6,Leu17]VIP and the growth hormone releasing factor (GRF) analog [Ac-Tyr1,D-Phe2]GRF-(1-29)-NH2 inhibit in a competitive manner the specific [125I]VIP binding to both rat and mouse peritoneal macrophages. In rat peritoneal macrophages, the order of potency of the different peptides, as expressed by the IC50 values was: VIP (IC50 = 1.90 +/- 0.16 nM) > [4-Cl-D-Phe6,Leu17]VIP (IC50 = 125.8 +/- 13.2 nM) > [Ac-Tyr1,D-Phe2]GRF-(1-29)-NH2 (IC50 = 354.8 +/- 21.2 nM). In mouse peritoneal macrophages a similar pattern of potency was observed: VIP (IC50 = 1.58 +/- 0.12 nM) > [4-Cl-D-Phe6,Leu17]VIP (IC50 = 110.8 +/- 10.7 nM) > [Ac-Tyr1,D-Phe2]GRF-(1-29)-NH2 (IC50 = 251 +/- 19.2 nM). The behavior as VIP receptor antagonists of both [4-Cl-D-Phe6,Leu17]VIP and [Ac-Tyr1,D-Phe2]GRF-(1-29)-NH2 in rat and mouse peritoneal macrophages was confirmed by: (a) the shift to the right of VIP dose-stimulated cyclic AMP production curves in the presence of the two antagonists; (b) the agreement between the order of efficacy of the two peptides in competition experiments with the corresponding inhibition of cyclic AMP production; (c) the inefficiency of the two antagonists on the stimulation of cyclic AMP production by the beta-adrenoceptor agonist isoproterenol, which indicates the specificity of the interaction; (d) the synergic effect of VIP on isoproterenol-stimulated cyclic AMP production was completely abolished by [4-Cl-D-Phe6,Leu17]VIP or [Ac-Tyr1,D-Phe2]GRF-(1-29)-NH2, suggesting that both antagonists acted via specific VIP receptors. Moreover, propranolol, a beta-adrenoceptor antagonist, did not affect the VIP-stimulated cyclic AMP production and the antagonist role of [4-Cl-D-Phe6,Leu17]VIP or [Ac-Tyr1,D-Phe2]GRF-(1-29)-NH2; (e) in cross-linking experiments, the intensity of the labeling of the [125I]VIP/receptor complexes was significantly lower with the antagonists than in the control experimental situation in both mouse and rat peritoneal macrophage membranes.

Elevation of intracellular cAMP by noradrenaline and vasoactive intestinal peptide in striated ducts isolated from the rabbit mandibular salivary gland

Salivary gland intralobular ducts are responsible for the modification of the electrolyte composition of the primary fluid secreted by the acini. However, the intracellular messengers that regulate this and other intralobular duct cell processes have not been fully characterized. To investigate the possibility that cAMP-mobilizing agonists may be involved, intralobular (striated) ducts were isolated from the rabbit mandibular salivary gland by tissue dissociation and microdissection and maintained in tissue culture overnight. Individual duct fragments were stimulated with the secretory agonists noradrenaline, vasoactive intestinal peptide (VIP) and substance P and their cAMP content measured by acetylated radioimmunoassay. Both noradrenaline and VIP elevated intracellular cAMP content concentration dependently, but substance P did not. The response to noradrenaline was blocked by the beta-adrenoceptor antagonist propranolol, but not by the alpha-adrenoceptor antagonist prazosin. Application of the VIP analogue [D-p-Cl-Phe6, Leu17]-VIP decreased the VIP-induced cAMP response. These results demonstrate that striated intralobular duct cells possess beta-adrenoceptors and peptidergic receptors that are coupled to adenylate cyclase and activated by noradrenaline and VIP, respectively. By elevating ductal cAMP content, these agonists may regulate both the electrolyte content of the primary saliva and the secretion of protein(s) from the ducts.

Vasoactive intestinal polypeptide and other preprovasoactive intestinal polypeptide-derived peptides in the female and male genital tract: localization, biosynthesis, and functional and clinical significance

Vasoactive intestinal polypeptide, a neuropeptide with wide distribution in the central and peripheral nervous system, has a broad spectrum of biologic actions. The demonstration of vasoactive intestinal polypeptide containing nerve fibers within the female and male genital tract 17 years ago indicated a putative role for this peptide in the local nervous control of reproductive functions. The genes encoding the preprovasoactive intestinal polypeptide precursor molecule and the vasoactive intestinal polypeptide receptor have been identified. The gene expression has been studied by the use of specific antibodies against the functional domains of the vasoactive intestinal polypeptide precursor and the biologic action elucidated by both in vivo and in vitro methods. Evidence has been provided to support vasoactive intestinal polypeptide as a neurotransmitter in several physiologic events in the genital tracts (i.e., blood flow and nonvascular smooth muscle relaxation). In the ovary vasoactive intestinal polypeptide seems to play an important role as regulator and/or modulator of folliculogenesis and steroidogenesis. In the male genital tract vasoactive intestinal polypeptide seems to participate in the control of erection. Vasoactive intestinal polypeptide has been suggested as a causative factor in some diseases of the genital organs (e.g., it may play a pathophysiologic role in male impotence and the peptide is currently used in the treatment of this condition). Vasoactive intestinal polypeptide may be important for control of the low resistance in the fetomaternal vascular bed and is therefore a putative factor involved in the development of preeclampsia. The therapeutic potential of vasoactive intestinal polypeptide and future agonists and antagonists will be revealed by ongoing and forthcoming studies.

Vagal stimulation during muscarinic and beta-adrenergic blockade increases atrial contractility and heart rate

We determined the effects of continuous cardiac vagal nerve stimulation on atrial contractility and on heart rate in mongrel dogs in which we blocked the muscarinic and beta-adrenergic receptors. Each dog received atropine, 0.5 mg/kg and propranolol, 0.5-1 mg/kg. We stimulated the cardiac vagus nerves in each dog for three separate 5-min periods at frequencies of 0 (control), 20, and 40 Hz (5 ms, 15 V) and measured the changes in atrial contractility and heart rate. Vagal nerve stimulation increased right atrial contractility from the control value by 27% at 20 Hz and by 19% during stimulation at 40 Hz (P < 0.001). Vagal nerve stimulation also increased the heart rate from 114 +/- 5 beats/min during the control period to 146 +/- 10 beats/min (P < 0.01) during stimulation at a frequency of 20 Hz and to 140 +/- 11 beats/min (P < 0.05) during stimulation at 40 Hz. Injection of the vasoactive intestinal peptide (VIP) antagonist, [4Cl-D-Phe6,Leu17]VIP, directly into the dog right coronary artery in concentrations of 0 (control), 2, and 4 micrograms/kg did not influence spontaneous atrial contractility or the heart rate. However, 4 micrograms/kg of the VIP antagonist significantly reduced the augmentation in right atrial contractility and the increase in heart rate during vagal nerve stimulation. Our experiments suggest that cardiac vagal nerve stimulation, during muscarinic and beta-adrenergic receptor blockade, releases VIP or a 'VIP-like substance', that significantly augments atrial contractility and increases heart rate.

Structural requirements for the occupancy of pituitary adenylate-cyclase-activating-peptide (PACAP) receptors and adenylate cyclase activation in human neuroblastoma NB-OK-1 cell membranes. Discovery of PACAP(6-38) as a potent antagonist

In these structure activity studies, the 46 analogs of the 27-amino-acid form of the pituitary-adenylate-cyclase-activating peptide, PACAP(1-27), and the 38-amino-acid form, PACAP(1-38), were either monosubstituted or bisubstituted at positions 1-3, 20 and 21 or N-terminally shortened. All analogs were compared on human neuroblastoma NB-OK-1 cell membranes for their ability to occupy 125I-[AcHis1]PACAP(1-27)-labelled receptors (AcHis, N alpha-acetylhistidine) and to activate adenylate cyclase (in terms of potency and intrinsic activity). The monophasic slope of dose/effect curves on both parameters suggested interaction with one class of PACAP receptor. Residues 28-38 in the C-terminally extended peptide, PACAP(1-38), played a favorable role in recognition, in that receptors coupled to adenylate cyclase were, in general, more sensitive to PACAP(1-38) analogs than to the corresponding PACAP(1-27) analogs. At variance with PACAP(6-27), PACAP(6-38) was well recognized and acted as a potent competitive antagonist (Ki 1.5 nM). Residues 1-3 were all important in enzyme activation: modification of the beta-turn potential gave full agonists (the LAla2 and DAla2 derivatives) or partial agonists (LPhe2 and DPhe2; LArg2 and DArg2; Glu3 and Asn3). Finally, a proper alpha-helix was also important: the combined substitution of Lys21/Lys22 by Gly21/Gly22 decreased the binding affinity sharply.

Modulation of human natural killer activity by vasoactive intestinal peptide (VIP) family. VIP, glucagon and GHRF specifically inhibit NK activity

Vasoactive intestinal polypeptide (VIP) is a neuropeptide, which also modulates some immune functions. Natural killer (NK) cell activity was already found to be diminished by VIP. In the present paper we report that VIP is able to decrease NK cell activity of human large granular lymphocytes (LGL), showing maximal inhibition at doses ranging from 10(-8) to 10(-6) M. Some neuropeptides, belonging to the VIP family (secretin, glucagon, peptide histidine isoleucine, PHI and human growth hormone releasing factor, GHRF), were also tested. Among these peptides, secretin and PHI were shown to be uneffective on NK cell activity whereas glucagon and GHRF were inhibitory. The D50 of GHRF was similar to that of VIP (10(-9) M), the D50 of glucagon was 10(-8) M. A recently synthesized VIP-antagonist (4Cl-D-Phe6-Leu17) was then used to assess its ability to reverse the VIP-mediated inhibition of NK activity. The antagonist was able to completely reverse the inhibitory effect of VIP on NK activity. The VIP-antagonist was also able to reverse the inhibitory effect of glucagon and GHRF, even though to a lesser extent than for VIP. Our data provide a new physiological observation regarding the functional activity of LGL, supporting the presence of a receptor for VIP on human LGL with NK activity.

Renal sodium excretion following systemic infusion of vasoactive intestinal peptide in the rat

1. The aim of this clearance study was to examine the renal effects of systemic infusion of vasoactive intestinal peptide (VIP) in the intact rat. 2. Mean arterial blood pressure (MAP), plasma electrolytes and haematocrit, glomerular filtration rate (GFR), and urinary sodium and potassium excretion were measured in a baseline period and following VIP infusion (0.1-1.2 nmol/h per 200 g), as well as during a time control study. 3. During infusion of low doses of VIP (0.1 and 0.4 nmol/h per 200 g), a small increase in fractional and absolute excretion of sodium occurred but this did not differ from that occurring in the time control group. In the high dose VIP group (1.2 nmol/h per 200 g), significant falls occurred in MAP and GFR, and absolute sodium excretion fell (though not significantly) from its baseline level. 4. These findings suggest that systemic VIP has no net natriuretic effect in the rat, but produces haemodynamic changes associated with reduced sodium excretion at high doses. This study does not exclude the possibility of direct effects on tubular sodium transport of VIP released from renal nerves.

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)

Vasoactive intestinal peptide stimulation of human renal adenylate cyclase in vitro

1. A direct action of vasoactive intestinal peptide (VIP) upon human kidney was sought by measurement of renal adenylate cyclase in tissue homogenates and plasma membranes isolated from tissue samples excised for therapeutic reasons. 2. VIP (1 microM) produced a mean stimulation of adenylate cyclase activity of 3.5-fold compared to basal values in cortical plasma membranes; comparative stimulations of 2.8-fold and 27.3-fold were obtained with 1 microM-glucagon and 1 microM-h(1-34) parathyroid hormone respectively. 3. Half-maximal stimulation of human renal cortical plasma membrane adenylate cyclase was observed with a mean value of 35 nM-VIP. 4. The stimulation of renal adenylate cyclase by VIP appeared to be specific because stimulation by glucagon was additive to that obtained with VIP, and the VIP receptor antagonist (4 Cl-D-Phe6, Leu17)-VIP inhibited the VIP-dependent stimulation of adenylate cyclase activity.

Localisation and characterisation of functional vasoactive intestinal peptide receptors in feline kidney

Specific 125I-labelled vasoactive intestinal peptide (VIP) binding was determined in feline renal cortical and medullary plasma membranes. For the cortex, Scatchard analysis of the data resulted in a curvilinear plot with a high-affinity site K0.5 of 8.4 +/- 2.6 nmol l-1 (SE, n = 6) and a second low-affinity site K0.5 204 +/- 16 nmol l-1 with binding site concentrations (Bmax) of 385 +/- 44.5 and 2710 +/- 181.3 fmol mg protein-1 respectively. Conversely a similar analysis of the results obtained for outer medullary membranes gave a single site with a K0.5 of 1.2 +/- 0.2 nmol l-1 (SE, n = 4) and Bmax of 157.8 +/- 24.7 fmol mg-1. Inner medullary membrane binding data. Gave a single site of lower affinity (K0.5 = 62.5 +/- 21.6 nmol l-1; n = 3). Structurally related peptides, glucagon and secretin, were ineffective (up to 1 mumol l-1) in displacing VIP from specific sites in both cortex and medulla. Porcine PHI 1-27 (a peptide having N-terminal histidine and C-terminal isoleucine) and a VIP antagonist [4-Cl-D-Phe6Leu17]VIP both displaced 125I-VIP from cortical and medullary membrane binding sites with IC50 values of 43.0 nmol l-1 and 1.3 mumol l-1 (cortex) and 132.0 nmol l-1 and 1.5 mumol l-1 (medulla) respectively. The localisation of specific VIP binding sites in feline kidney was investigated further by in vitro autoradiography.(ABSTRACT TRUNCATED AT 250 WORDS)