Distribution of vasoactive intestinal peptide-sensitive adenylate cyclase activity along the nephron

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.

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)

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

The effect of vasoactive intestinal peptide (VIP) and related peptides [glucagon, secretin, PHI 1-27 (peptide with N-terminal histidine and C-terminal isoleucine)] on renal adenylate cyclase (AC) has been determined in several species. The largest stimulation (4.1 +/- 0.5-fold basal) of AC by 1 mumol.l-1 VIP was observed in feline cortical plasma membranes. In rabbit and guinea-pig, VIP increased AC activity 1.5 +/- 0.3- and 1.8 +/- 0.3-fold respectively but glucagon had no such action. Conversely in the rat glucagon stimulated AC some 3-fold over basal activity whereas VIP had little effect. In dog, cat and mouse both peptides were effective in increasing AC activity. For cat, half-maximal stimulation of cortical plasma membrane AC by VIP was seen at 27.0 +/- 9.0 nmol.l-1 (SE N = 9 animals). VIP also increased AC activity in both outer (red) and inner (white) medulla. In feline cortical membranes VIP and PTH (parathyroid hormone) when added in combination were fully additive. However for VIP and glucagon in combination there was no cumulative increase in AC activity, indeed the resultant activity was less than that attained by VIP alone. The VIP analogue (4Cl-D-Phe6Leu17)VIP at 10 mumol.l-1 produced a right shift in the VIP-dose response curve and increased the EC50 from 17.2 +/- 5.8 nmol.l-1 to 132.0 +/- 22.2 nmol..-1 VIP (SE N = 4). There was no reduction in the maximum response elicited by VIP consistent with a competitive type of antagonism by this analogue. PHI-stimulated AC was also reduced by (4Cl-D-Phe6Leu17)VIP resulting in a similar right shift in the dose response curve.(ABSTRACT TRUNCATED AT 250 WORDS)