In vitro macro- and microautoradiographic localization of V1 and V2 receptors in the rat kidney using OPC-21268 and OPC-31260

Structure and concentration capacity of the kidneys in brattleboro rats under conditions of long-term vasopressin treatment

The function and histochemistry of the kidney were studied in homozygous Brattleboro rats after 28-day treatment with exogenous arginine-vasopressin. The long-lasting effect of the hormone includes normalization of osmotic concentration, decrease in the number of b-glucuronidase granules in the medulla, and increasing content of hyaluronan in the interstitium. These changes promote physiological optimization of the antidiuretic reaction to vasopressin.

Mechanism of vasopressin-induced contraction of renal medullary interstitial cells

BACKGROUND/AIMS

Previous studies have identified a contractile function for renomedullary interstitial cells (RMIC). Such studies focused on the mechanism of endothelin-1-induced RMIC contraction; however, vasopressin (AVP) was also noted to contract RMIC. Since AVP-induced RMIC contraction may be relevant to the medullary effects of AVP on urinary concentration, these initial observations have been extended to examination of the mechanism of AVP-induced RMIC contraction.

METHODS

Cultured rat RMIC were exposed to AVP and other agents, and examined using video microscopy.

RESULTS

AVP caused a slowly developing and dose-dependent reduction in RMIC surface area. AVP-induced RMIC contraction was abolished by blockade of V1, but not V2, receptors. Nifedipine and nickel reduced AVP-stimulated RMIC contraction, indicating that this effect is dependent upon dihydropyridine-sensitive calcium channels. H7, a protein kinase C inhibitor, completely abrogated AVP action, while the nitric oxide synthase inhibitor, NMMA, had no effect. Indomethacin enhanced AVP-induced RMIC contraction, and addition of PGE2 together with indomethacin reduced AVP action.

CONCLUSION

These data indicate that AVP potently contracts RMIC via V1 receptor stimulation of PKC and intracellular calcium accumulation, and that AVP-stimulated prostaglandin production downregulates the contractile effect of AVP on RMIC. AVP modulation of RMIC contraction may be involved in the regulation of urinary concentration.

The effect of AVP-V receptor stimulation on local GFR in the rat kidney

AIM

Arginine vasopressin (AVP) might influence urinary concentration ability by altering the intrarenal distribution of glomerular filtration rate (GFR).

METHODS

To study this possibility we have measured the intracortical distribution of GFR following acute AVP-V1 receptor stimulation in anaesthetized female Sprague-Dawley (SPD) rats during euvolemia and water diuresis by the aprotinin method, allowing two consecutive measurements of zonal GFR in the same kidney.

RESULTS

Acute i.v. bolus injection of 50 ng V1 receptor agonist ([Phe2, Ile3, Orn8]-vasopressin) followed by a continuous infusion of 5 ng min(-1) in euvolemic rats reduced GFR by 25% in outer cortex (OC), 20% in middle cortex (MC) and 19% in inner cortex (IC) relative to vehicle infusion (all P < 0.05). In water diuretic rats V1 receptor agonist reduced GFR by 22% in OC, 10% in MC and 11% in IC relative to vehicle infusion (P < 0.05). GFR decreased slightly more in OC than in MC and IC in both euvolemic and water diuretic rats (P < 0.05) indicating a distribution of GFR towards MC and IC. Acute infusion of the selective non-peptide V1 receptor antagonist OPC-21268 in euvolemic rats reduced GFR by 14% in OC, 13% in MC and 11% in IC relative to vehicle infusion (P < 0.05), with no significant difference between the layers.

CONCLUSIONS

The change in distribution of GFR not only between OC and IC, but also between OC and MC suggests that the afferent/efferent arterioles and not the medullary vasa recta is the main site of resistance change. We conclude that acute i.v. infusion of V1 receptor agonist in high doses reduces GFR more in superficial than in deep cortex in both euvolemic and water diuretic rats and that this may be of some importance for water conservation, adding to the V2- receptor effect on water permeability of the collecting ducts.

Effects of OPC-21268, a vasopressin V1-receptor antagonist, on expression of growth factors from glomeruli in spontaneously hypertensive rats

To assess the chronic in vivo effects of OPC-21268, a vasopressin-V1 receptor antagonist, on renal injury, we investigated the mRNA expressions of platelet-derived growth factor (PDGF) B-chain, transforming growth factor (TGF)-beta1 and proliferating cell nuclear antigen (PCNA) in the glomeruli of spontaneously hypertensive rats (SHR) treated with OPC-21268 for 3 weeks. SHR aged 10 weeks were given 2% NaCl in drinking water for 3 weeks. The OPC group was fed a 0.5% OPC-21268-containing diet for 3 weeks and the control group was given a normal diet. There were no significant changes in the time course of systolic blood pressure, heart rate, urine volume, or urinary sodium, protein and N-acetyl-beta-glucosaminidase (NAG) excretion between the two groups. Serum electrolytes, protein and creatinine levels also did not differ between the groups. The mRNA expressions of PDGF B-chain, TGF-beta1 and PCNA in the glomerulus were examined using reverse transcriptase-polymerase chain reaction (RT-PCR) methods. The mRNA expressions of PDGF B-chain and PCNA among these were significantly suppressed in the OPC group. No significant differences in renal histology including the organ weights were found between the two groups; however, the glomerular size tended to be enlarged in the OPC group. These findings suggest that chronic V1-receptor blockade directly inhibits the glomerular proliferative injury of salt-loaded SHR at the established hypertension stage.