Central G-alpha subunit protein-mediated control of cardiovascular function, urine output, and vasopressin secretion in conscious Sprague-Dawley rats

Abstract

The role(s) of central Galpha-proteins in the regulation of cardiovascular and renal function is unknown. We examined how inhibition/downregulation of central Galphai/Galphao, Galphaz or Galphaq proteins altered the characteristic cardiovascular (depressor), renal excretory (diuretic), and plasma AVP (inhibitory) responses to intracerebroventricular injection of nociceptin/orphanin FQ (N/OFQ) in rats. Before investigation, rats were pretreated intracerebroventricularly with saline vehicle (5 microl, 48 h, n=6), pertussis toxin (PTX; 48-h, 1 microg, n=6), or Galphaz, Galphaq, or scrambled oligodeoxynucleotide (ODN) (25 microg, 24 h, n=6 per group). On the study day, intracerebroventricular N/OFQ (5.5 nmol) or vehicle (5 microl) was injected into pretreated conscious rats. Mean arterial pressure (MAP) and heart rate (HR) were recorded, and urine was collected for 90 min. In vehicle or scrambled ODN groups, intracerebroventricular N/OFQ decreased MAP and HR and produced water diuresis (sensitive to UFP-101, N/OFQ receptor antagonist). The hypotension and bradycardia, but not diuresis, to N/OFQ were abolished in PTX-pretreated rats. In contrast, intracerebroventricular ODN pretreatment markedly blunted (Galphaz) or augmented (Galphaq) the diuresis to intracerebroventricular N/OFQ. In separate studies, the action of central N/OFQ to decrease plasma AVP levels in naïve water-restricted rats was differentially altered by intracerebroventricular Galphaz ODN (blunted) and Galphaq ODN (augmented) pretreatment. These studies demonstrate central Galphai/Galphao activity mediates intracerebroventricular N/OFQ's cardiovascular depressor function. Alternatively, central Galphaz (inhibitory) and Galphaq (stimulatory) activity differentially modulates AVP release to control the pattern of diuresis to intracerebroventricular N/OFQ. These findings highlight the novel selective central Galpha-subunit protein-mediated control of cardiovascular vs. renal excretory function.

Functional selectivity of central Gα‐subunit proteins in mediating the cardiovascular and renal excretory responses evoked by central α2‐adrenoceptor activation in vivo

“…Extending this further, in investigations performed in conscious rats, we demonstrated that the cardiovascular depressor (hypotension and bradycardia), but not diuretic, responses produced by activation of a central GPCR [the nociceptin/orphanin FQ (N/OFQ) peptide receptor] were completely abolished in rats that had been pre‐treated (48 h) centrally with Pertussis toxin (PTX). These findings highlight the novel functionally selective central Gα‐subunit protein‐mediated control of cardiovascular versus renal excretory function in vivo (Wainford et al ., 2008). However, as PTX, which was used in these studies, is an exotoxin that catalyses the ADP ribosylation of all Gα i/o subunit proteins, the specific Gα i(1–3) or Gα o subunit(s) involved in mediating central GPCR‐evoked cardiovascular depressor responses were not elucidated.…”

“…in combination with xylazine (5 mg/kg, i.m.) 5–7 days before experimentation as previously described (Wainford et al ., 2008; Wainford and Kapusta, 2009; 2010). On the day of study, rats were anaesthetized with sodium methohexital (75 mg/kg i.p.…”

“…Groups of rats were pre‐treated (24 h) by intracerebroventricular (i.c.v.) injection with an oligodeoxynucleotide (ODN) sequence targeted to Gα i1 , Gα i2 , Gα i3 , Gα o , Gα s or a scrambled (SCR) ODN sequence to acutely and selectively down‐regulate the respective target protein throughout the CNS (Wainford et al ., 2008; Wainford and Kapusta, 2010). Post‐ODN treatment (24 h), we examined the cardiovascular and renal excretory responses evoked by central α 2 ‐adrenoceptor activation in response to i.c.v.…”

Chronic high-NaCl intake prolongs the cardiorenal responses to central N/OFQ and produces regional changes in the endogenous brain NOP receptor system

“…Analogous to these findings, our present results strongly suggest that in high-salt-treated rats, the prolonged hypotension produced by central N/OFQ counters/masks the characteristic decrease in RSNA by a pathway that involves the baroreflex. Although RSNA can have significant impact on the renal excretion of water and sodium (16,17,20) our previous studies have shown the diuretic (and antinaturetic) response to central N/OFQ can occur via a renal nerve-independent pathway (19) involving the suppression of AVP release into the systemic circulation (15,34). This may explain why intracerebroventricular N/OFQ continued to produce a diuretic response in animals maintained on a chronic high-NaCl diet.…”

“…Although the cardiovascular and renal responses produced by central administration of N/OFQ are well characterized, the endogenous role(s) of the N/OFQ-NOP receptor system remain unclear. Both N/OFQ and NOP receptors are highly expressed in CNS sites that regulate cardiovascular and renal homeostasis (25,34). N/OFQ has been demonstrated to play a critical modulatory role in the adaptive behavioral fear responses to stressful stimuli (5, 12); therefore it is likely that the endogenous N/OFQ-NOP receptor system plays a physiologically important role in regulating cardiovascular and renal responses to acute/chronic stressors (18).…”