Improved techniques for acute and chronic cannulation of renal artery in the rat

Activation of renal vascular smooth muscle TRPV4 channels by 5-hydroxytryptamine impairs kidney function in neonatal pigs

Control of microvascular reactivity by 5-hydroxytryptamine (5-HT; serotonin) is complex and may depend on vascular bed type and 5-HT receptors. 5-HT receptors consist of seven families (5-HT1-5-HT7), with 5-HT2 predominantly mediating renal vasoconstriction. Cyclooxygenase (COX) and smooth muscle intracellular Ca2+ levels ([Ca2+]i) have been implicated in 5-HT-induced vascular reactivity. Although 5-HT receptor expression and circulating 5-HT levels are known to be dependent on postnatal age, control of neonatal renal microvascular function by 5-HT is unclear. In the present study, we demonstrate that 5-HT stimulated human TRPV4 transiently expressed in Chinese hamster ovary cells. 5-HT2A is the predominant 5-HT2 receptor subtype in freshly isolated neonatal pig renal microvascular smooth muscle cells (SMCs). HC-067047 (HC), a selective TRPV4 blocker, attenuated cation currents induced by 5-HT in the SMCs. HC also inhibited the 5-HT-induced increase in renal microvascular [Ca2+]i and constriction. Intrarenal artery infusion of 5-HT had minimal effects on systemic hemodynamics but reduced renal blood flow (RBF) and increased renal vascular resistance (RVR) in the pigs. Transdermal measurement of glomerular filtration rate (GFR) indicated that kidney infusion of 5-HT reduced GFR. HC and 5-HT2 receptor antagonist ritanserin attenuated 5-HT effects on RBF, RVR, and GFR. Moreover, the serum and urinary COX-1 and COX-2 levels in 5-HT-treated piglets were unchanged compared with the control. These data suggest that activation of renal microvascular SMC TRPV4 channels by 5-HT impairs kidney function in neonatal pigs independently of COX production.

31P NMR studies of ATP concentrations and Pi-ATP exchange in the rat kidney in vivo: effects of inhibiting and stimulating renal metabolism

Previous investigators found that cyanide (CN-) is a potent inhibitor of renal Na+ transport, while the uncoupling agent 2,4-dinitrophenol (DNP) and fructose (both which lower ATP levels) are weak transport inhibitors. To examine the disparate effects of these substances measurements of ATP were performed, using 31P NMR, while simultaneously monitoring renal Na+ transport. Infusion of CN-, DNP, and fructose lowered whole kidney ATP levels by about the same extent (30%) while only CN- inhibited Na+ transport. This may be due to the fact that CN- has a potent action on the thick ascending limb of Henle, while fructose and DNP may have a more proximal action. Alternatively, ATP turnover may be a more important determinant of transport than ATP concentrations. Saturation transfer experiments were performed to measure Pi-ATP flux. Unilateral nephrectomy, high protein feeding, and methylprednisolone were used to stimulate metabolism and transport. The rate of Pi-ATP flux was 20.1 mumol/min/g. However, because oxygen consumption was stimulated, the ATP/O ratio was 0.85, considerably less than the theoretical value of 3. Finally, atrial natriuretic factor, which increased Na+ transport, had no effect on Pi-ATP flux. The results raise the possibility that the saturation transfer technique does not detect all Pi-ATP flux, especially when renal metabolism is stimulated.

Attenuated renal response to dopaminergic drugs in spontaneously hypertensive rats

Activation of renal dopamine-1 receptors decreases sodium transport. However, the spontaneously hypertensive rat retains sodium despite increased renal dopamine concentration. We tested the hypothesis that the abnormal sodium handling in spontaneously hypertensive rats (Okamoto-Aoki strain) is related to a decreased dopaminergic response by studying the effects of the intrarenal infusion of the dopamine-1 agonist SKF-38393 and the dopamine-1 antagonist SCH-23390 in hypertensive and in normotensive Wistar-Kyoto rats. Rats (9-16 weeks old) were studied with renal nerves intact under pentobarbital anesthesia (n = 5-6 in each group). Specificity of dopamine-1 effects of SKF-38393 was verified because its natriuretic effect was blocked in a dose-related manner by the dopamine-1 antagonist SCH-23390 (n = 5). Intrarenal but resulted in a dose-related natriuresis and diuresis in normotensive but not in hypertensive rats. Intrarenal arterial infusion of the dopamine-1 antagonist SCH-23390 alone induced an antinatriuresis, without affecting glomerular filtration rate, in normotensive but not in hypertensive rats. Addition of the dopamine-2 antagonist YM-09151 to the dopamine-1 antagonist infusion did not enhance the effect of the dopamine-1 antagonist. The lack of response to the dopamine-1 agonist or antagonist in hypertensive rats was not due to differences in renal dopamine-1 receptor density (1.3 +/- 0.3 pmol/mg protein for spontaneously hypertensive rats, n = 4; 1 +/- 0.2 for Wistar-Kyoto rats, n = 4) or affinity; distribution determined by autoradiography was also similar. The abnormal renal sodium handling in 9-16-week-old spontaneously hypertensive rats is in part due to decreased response distal to the dopamine-1 receptor.

Endogenous intrarenal adenosine preserves renal blood flow in one-kidney, one clip rats

Intrarenal adenosine concentration is threefold greater in the one-kidney, one clip hypertensive rat compared with normotensive animals. Since exogenously administered adenosine may increase renal blood flow by direct vasodilation, inhibition of renin release, or prejunctional interruption of adrenergic neurotransmission, these studies examined whether endogenous intrarenal adenosine maintains renal blood flow distal to renal arterial stenosis. Administration of theophylline, which blocks the direct vasodilating effect of adenosine and antagonizes the inhibitory effect of adenosine on renin release and sympathetic neurotransmission, resulted in marked renal vasoconstriction in one-kidney, one clip hypertensive animals. This theophylline-induced renal vasoconstriction was markedly attenuated by angiotensin II blockade with saralasin and was unchanged by renal denervation or beta 1-adrenergic blockade with atenolol. These findings indicate that the marked renal vasoconstriction in one-kidney, one clip hypertension during theophylline administration is mainly mediated by angiotensin II, is to a lesser degree due to inhibition of adenosine-induced vasodilation, and is independent of sympathetic influences. These data suggest that endogenous interstitial adenosine preserves renal blood flow in one-kidney, one clip hypertension mainly by inhibiting renin release.

Afferent renal nerves and hypertension

Adenosine-sensitive nerve endings have been found in the renal pelvis which when stimulated increase sympathetic activity producing hypertension. When urinary adenosine concentration is lowered by intrarenal infusion of adenosine deaminase in one-kidney one-clip rats, peripheral sympathetic nervous system activity and arterial pressure decrease if the renal nerves are intact. These data suggest that a stimulus for afferent renal nerve activity in one-kidney, one-clip hypertension is intrarenal adenosine. This intrarenal adenosine hypertensive reflex was examined further observing the responses to renal pelvic xylocaine infusion, selective renal deafferentation, adrenal demedullation and spinal cord transection (T6). The intrarenal adenosine hypertensive reflex was interrupted by renal pelvic xylocaine infusion, renal deafferentation and adrenal demedullation in normotensive and one-kidney, one-clip hypertensive animals. The intrarenal adenosine hypertensive reflex persisted after spinal cord transection (T6). These data support the concept that adenosine-sensitive intact afferent renal nerves located in the renal pelvis enhance sympathoadrenal activity resulting in the maintenance of one-kidney, one-clip hypertension and that this intrarenal adenosine-hypertensive response may occur as a spinal-level reflex in the rat.

Intrarenal adenosine produces hypertension via renal nerves in the one-kidney, one clip rat

The afferent renal nerves enhance sympathetic activity in the one-kidney, one-clip hypertensive rat. We have also found adenosine-sensitive nerve endings in the renal pelvis that, when stimulated, increase sympathetic activity producing hypertension. To determine whether adenosine, which is excreted when renal blood flow is reduced, activates the afferent renal nerves in one-kidney, one-clip hypertension, urinary adenosine concentration was lowered by infusing adenosine deaminase into the renal artery. Urinary adenosine concentration was threefold greater in one-kidney, one-clip hypertensive animals compared with normotensive controls. Intrarenal infusion of adenosine deaminase in one-kidney, one-clip rats lowered urinary adenosine to an undetectable level and attenuated the hypertension. Both plasma norepinephrine levels and the fall in mean arterial pressure after ganglionic blockade decreased during intrarenal adenosine deaminase infusion in one-kidney, one-clip animals. Renal denervation in one-kidney, one-clip animals prevented the changes in mean arterial pressure and plasma norepinephrine levels during intrarenal adenosine deaminase infusion. In contrast to findings in hypertensive animals, intrarenal infusion of adenosine deaminase produced no change in arterial pressure in normotensive controls. These data indicate that urinary adenosine concentration is enhanced in one-kidney, one-clip hypertension and suggest that when urinary adenosine concentration is lowered, sympathetic activity and hypertension became attenuated in this model if the renal nerves are intact.

Functional role of thromboxane production by acutely rejecting renal allografts in rats

We investigated the role of thromboxane in mediating the reduction in renal function and renal blood flow characteristic of acute renal allograft rejection. We transplanted kidneys from Lewis rats to Brown-Norway recipients. By the third day after transplantation, histologic changes that were consistent with cellular rejection occurred in the kidney. These changes were associated with a moderate reduction in renal function. By day 6, histologic changes of rejection were advanced and included interstitial and perivascular infiltration by mononuclear cells. The clearances of inulin and para-aminohippuric acid were also markedly reduced. As renal function deteriorated, thromboxane B2 (TXB2) production by ex vivo perfused renal allografts increased progressively from 2 to 6 d after transplantation. However, prostaglandin (PG) E2 and 6-keto PGF1 alpha production remained essentially unchanged. There was a significant inverse correlation between the in vivo clearance of inulin and the log of ex vivo TXB2 production. Infusion of the thromboxane synthetase inhibitor UK-37248-01 into the renal artery of 3-d allografts significantly decreased urinary TXB2 excretion and significantly increased renal blood flow (RBF) and glomerular filtration rate (GFR). Although renal function improved significantly after the acute administration of UK-37248-01, GFR and RBF did not exceed 33 and 58% of native control values, respectively. In other animals, daily treatment with cyclophosphamide improved the clearances of inulin and para-aminohippuric acid and reduced thromboxane production by 6-d renal allografts. These studies demonstrate that histologic evidence of rejection is associated with increased renal thromboxane production. Inhibition of thromboxane synthetase improves renal function in 3-d allografts. Cytotoxic therapy improves renal function, reduces mononuclear cell infiltration, and decreases allograft thromboxane production. Thus, the potent vasoconstrictor thromboxane A2 may play a role in the impairment of renal function and renal blood flow during acute allograft rejection.

The effect of water deprivation on the osmotic release of renin

The effect of water deprivation on the osmotic release of renin was evaluated in conscious rats previously prepared with right nephrectomy and cannulations of left renal artery and lower abdominal aorta. The osmotic signal was a 4-min intrarenal infusion of 30% crystallized bovine serum albumin. Changes in aortic plasma concentration of renin (PRC) and total protein were followed serially. In normal hydropenic rats an increase in PRC was not detected with the oncotic challenge. Following a 48-hr period of water deprivation, the same external oncotic signal increased PRC threefold above baseline within 3 min. It is concluded that some intrarenal functional or structural change induced by water deprivation sensitizes the renin-secreting mechanism to colloid osmotic stimuli. It is suggested that this change could be related to the physical conditions of the renal interstitium.