Identification, localization and functional analysis of imidazoline and alpha adrenergic receptors in canine prostate.

In nonsurgical management of benign prostatic hyperplasia, drugs which interfere with prostate contraction mediated through the alpha-1 adrenergic receptor are used. Clonidine acts at alpha adrenergic and I1-imidazoline receptors. In the present study, we found the Kd for [3H]clonidine binding to I1 sites in canine prostate to be 4 +/- 1 nM; the Bmax was 18 +/- 2 fmol/mg of protein. Inhibition of binding by imidazolines and by brain extracts containing putative endogenous ligand confirmed the identity of these sites as I1-imidazoline. Autoradiographic studies showed localization of both I1 and alpha-2 sites to the glandular epithelium. We sought to determine whether in vivo activation of the I1-imidazoline sites by clonidine mediates its contractile action in canine prostate. Dose-response curves were generated for para-aminoclonidine in the presence of vehicle alone, yohimbine (alpha-2 antagonist), idazoxan (alpha-2/I1/I2 antagonist) and prazosin (alpha-1 antagonist). Prazosin was the most effective antagonist. Yohimbine was less effective and did not effectively discriminate between para-aminoclonidine and phenylephrine, an alpha-1-selective agonist. Idazoxan antagonized para-aminoclonidine, but by not more than 50% at any dose. These results suggest that clonidine is active primarily at alpha-1 receptors on prostate smooth muscle in vivo. Thus the function of the I1 and alpha-2 receptors in the prostate remains to be determined; however, they may be involved in epithelial cell function.

Toradol, an NSAID used for renal colic, decreases renal perfusion and ureteral pressure in a canine model of unilateral ureteral obstruction.

Toradol is a new parenteral, nonsteroidal anti-inflammatory drug which is efficacious in treating renal coli. In the present experiments, Toradol was administered to both control dogs and dogs with unilateral ureteral obstruction. In control dogs, Toradol had no effect on RBF or GFR, despite inhibition of renal prostaglandin synthesis (measured as urinary prostaglandin release). In contrast, RBF fell acutely by 35% (p < 0.001) within 15 minutes of Toradol administration in the setting of ureteral obstruction; contralateral RBF was unaffected. Ipsilateral ureteral pressure also fell. Changes in RBF and ureteral pressure, together with the known effects of NSAIDs on pain pathways, may contribute to the pain relief observed clinically with Toradol. However, the abrupt changes in renal hemodynamics brought on by Toradol to the obstructed kidney may compromise renal reserve, and Toradol should be used cautiously in treating renal colic.

Medical management of benign prostatic hyperplasia: a canine model comparing the in vivo efficacy of alpha-1 adrenergic antagonists in the prostate.

Medical management of benign prostatic hyperplasia (BPH) is an alternative to surgical treatment of this disease. A major target for pharmacologic therapy is the alpha-1 adrenergic receptor, since activation of this receptor by endogenous catecholamines is thought to contribute to outlet obstruction. In the present study, we compared the potency of various alpha-1 adrenergic antagonists against epinephrine-induced contraction of the canine prostate. The drugs tested were dibenzyline, prazosin, terazosin and YM617. The rank order of potency, comparing inhibitory constants (Ki's), was found to be YM617 >> prazosin > terazosin > dibenzyline. This study is the first to compare all of these drugs directly in the prostate in vivo. The rank order of potency of the drugs is similar to the rank order of potency at other alpha-1 receptors. These results demonstrate that 1) our model is useful in confirming activity of drugs at the alpha-1 receptor and 2) the prostate alpha-1 receptor is similar to other alpha-1 receptors. Whether activity at the alpha-1 adrenergic receptor is a sufficient determinant of clinical efficacy of these drugs remains to be determined.

Involvement of platelet activating factor and thromboxane A2 in the renal response to unilateral ureteral obstruction.

Platelet activating factor (PAF) and thromboxane A2 (TxA2) are two vasoactive mediators which can decrease renal blood flow. Both are synthesized by various intrarenal cell types or by macrophages which may infiltrate the kidney during unilateral ureteral obstruction (UUO). In several experimental systems, PAF receptor activation is accompanied by TxA2 release; pharmacological modification of TxA2 synthesis or receptor activation modulates the response to PAF. The involvement of PAF in UUO has not been studied previously, and the role of TxA2 has not been clearly defined by previous investigations. The hemodynamic response to acute UUO is characterized by decreases in renal blood flow (RBF) and glomerular filtration rate and an acute increase in ureteral pressure. In the present experiments, the involvement of either PAF or TxA2 in the acute response to UUO was studied by determining if blockade of either the TxA2 or PAF receptor would affect the renal hemodynamic response to UUO. In addition, the effect of blockade of the TxA2 receptor on the renal response to PAF was determined. Our results indicate that only a small portion of the renal response to PAF is mediated by TxA2, and that neither PAF nor TxA2 can be implicated in the acute hemodynamic response to UUO. TxA2 or PAF involvement in the chronic response to UUO still remains to be determined.

The effect of acute obstruction on ureteral function.

In an effort to understand the physiologic processes which contribute to, or hinder the transport of stones through the ureter, we examined the intraluminal ureteral pressures and peristaltic activity above and below the acutely obstructed site. Because of patient differences, variability in stone size, shape and composition, an in vivo animal model was developed to study acute ureteral obstruction. Five adult mongrel dogs were anesthetized. A midline celiotomy was made and an open-ended ureteral catheter was inserted through a distal ureterotomy and advanced up the ureter. An angiographic balloon catheter was inserted through a small nephrotomy and directed down the ureter. The experiment was divided into phases: control, ureteral obstruction (balloon inflation) and release of obstruction (balloon deflation). Compared to control values, peristaltic rate above the obstruction increased significantly (p less than 0.05), as well as baseline, peak, and delta (peak minus baseline) pressures. In contrast, the peristaltic rate below the obstructed site remained approximately the same as its control, despite the significant decreases in baseline, peak, and delta (p less than 0.05) pressures. Failure of transmission of effective peristalsis across the obstructed site may hinder stone passage; however, this remains to be proven. Moreover, the failure of transmission of the increased rate of peristalsis past the balloon and persistence of peristaltic activity below the site of obstruction despite absence of urine flow suggest segmental forces influence peristaltic activity.

Dexamethasone-inhibitable stimulation of plasma prorenin by ketamine in cats.

Plasma prorenin in humans is derived from both renal and extrarenal sources, but in the cat most plasma prorenin is normally of renal origin. Sodium depletion and beta-adrenergic blockade can increase plasma prorenin in cats, but the effects of sedatives and glucocorticoids are unknown. We examined the effect of ketamine, a centrally acting nonbarbiturate anesthetic, and of the glucocorticoid dexamethasone on plasma prorenin and renin. Intramuscular injection of ketamine (20 mg/kg, three times a day) for 4 days increased plasma prorenin slowly and consistently, from 7.4 +/- 1.4 (+/- SEM) to 11.4 +/- 2.2, 17.1 +/- 2.5, 20.2 +/- 3.0, and 29.2 +/- 3.4 ng/ml.h (P less than 0.001) on days 1, 2, 3, and 4, respectively, without any effect on plasma active renin. Plasma renin substrate and cortisol were also unchanged. Bilateral nephrectomy reduced both baseline and stimulated plasma prorenin to undetectable levels. Treatment with alpha 1-blocker, beta 1-blocker, angiotensin-converting enzyme inhibitor, or Ca2+ antagonist did not affect the rise in prorenin induced by ketamine, but dexamethasone completely blocked the response. In contrast, dexamethasone alone had little effect on plasma prorenin. These results demonstrate that repetitive ketamine administration selectively increases plasma prorenin, suggesting that renal prorenin secretion may be regulated independently of active renin. Blockade of stimulated, but not baseline, plasma prorenin by dexamethasone is consistent with a negative effect of glucocorticoids on the regulatory elements of the renin gene.

An in vivo evaluation of alpha adrenergic receptors in canine prostate.

The role of alpha 2 adrenergic receptors in the prostate in vivo is unknown. A model was developed to measure canine prostatic urethral pressure in vivo, and to assess the ability of various alpha adrenergic blocking agents to affect prostatic pressure. In this model, an esophogeal pressure catheter is inserted into the prostatic urethra to record prostatic urethral pressure. We investigated the effects of alpha adrenergic agonists and antagonists on prostatic pressure using this model. Dose-response curves were generated for epinephrine, and were then repeated in the presence of either prazosin (alpha 1 antagonist), yohimbine (alpha 2 antagonist) or SK&F-86466 (alpha 2 antagonist). Prazosin was the most potent of the three drugs in competitively blocking epinephrine-induced contraction of the prostate, with an inhibition constant of 0.24 micrograms./kg. calculated from the double reciprocal plot. Clonidine, an alpha 2 adrenergic agonist, caused contraction of the prostate, which was also blocked by prazosin. Furthermore, the specific alpha 2 agonist BHT-920 was totally inactive in our system. These results demonstrate that the increase in urethral pressure caused by alpha-adrenergic agonists can be blocked by alpha adrenergic antagonists. However, the specific alpha 1 antagonist, prazosin, is more potent than alpha 2 antagonists, and is also effective against an alpha 2 agonist, clonidine. This suggests that blockade of alpha 1 receptors may be a more useful strategy for causing relaxation of the prostate than blockade of alpha 2 receptors.

Effect of thromboxane inhibition on renal blood flow in dogs with complete unilateral ureteral obstruction.

The effect of the thromboxane synthetase inhibitor OKY-046 on renal blood flow and ureteral pressure in awake dogs during 18 hours of complete unilateral ureteral obstruction was studied. OKY-046 was infused continuously throughout the period of obstruction and post-release. Renal blood flow and ureteral pressure were constantly monitored during the study. Urinary thromboxane B2 and prostaglandin E2 excretion served as markers for inhibition of renal thromboxane A2 synthesis. The triphasic relationship between ipsilateral renal blood flow and ureteral pressure previously found following unilateral ureteral obstruction was observed despite OKY-046 infusion. Inhibition of ipsilateral urinary thromboxane B2 excretion was greater than 90% compared to control while ipsilateral urinary prostaglandin E2 excretion was not consistently decreased showing specific thromboxane inhibition. These results suggest that urinary thromboxane B2 may serve as a useful marker for determining the effects of inhibition on renal thromboxane A2 production. At the level of inhibition of thromboxane synthesis achieved we did not observe any change in the late decrease in renal blood flow which is typically seen with chronic unilateral ureteral obstruction.

Relationship between renal hemodynamic and natriuretic effects of atrial natriuretic factor.

The degree by which atrial natriuretic factor (ANF)-induced renal hemodynamic changes account for its natriuretic effect was determined by early clamp experiments in six anesthetized dogs. After control periods, perfusion pressure of the left kidney (LK) was reduced to 80-90 mmHg, and synthetic ANF (auriculin A) was infused intravenously (0.3 micrograms X min-1 X kg body wt). After recovery, furosemide (F) was administered as a bolus injection (1 mg/kg body wt). In the right kidney (RK), which served as a time control, ANF increased (P less than 0.05) glomerular filtration rate (GFR) 16 +/- 4% and Na excretion (UNa V) 261 +/- 63%, whereas it decreased urine osmolality (Uosm) 36 +/- 7% without changing free water clearance. ANF also increased diuresis (V) and kaliuresis (UKV). F produced qualitatively the same results without changing GFR. In the clamped LK, ANF failed to increase GFR (22 +/- 4 vs. 26 +/- 4 ml/min), UNaV (30 +/- 9 vs. 33 +/- 11 mueq/min), V, and UKV or to decrease Uosm (841 +/- 97 vs. 840 +/- 114 mosmol/kg H2O). F had similar effects in LK as in RK. The data demonstrate that the natriuretic effect of ANF is abolished when its renal hemodynamic actions are impeded. In addition, the results demonstrate that ANF antagonizes renal vasoconstriction in the dog. The results are consistent with the view that the ANF-induced natriuresis is due in great part to an increase in the filtered load of Na into a washed-out inner medulla.

Effect of atrial natriuretic factor on renin secretion, plasma renin and aldosterone in dogs with acute unilateral renal artery constriction.

Atrial natriuretic factor (ANF) decreases renin secretion rate (RSR), plasma renin activity (PRA) and plasma aldosterone (PA) in normal dogs. To clarify further the mechanisms responsible for these effects, the left renal artery was constricted in seven anaesthetized dogs prior to ANF administration. Constriction of the left renal artery decreased (P < 0.05) ipsilateral mean renal perfusion pressure (MRPP, 29 +/- 7%), renal plasma flow (RPF, 42 +/- 11%) and glomerular filtration rate (GFR) and filtered sodium load (FLNa, 21 +/- 8.8%). Ipsilateral RSR and peripheral PRA tended to increase, although not significantly. Atrial natriuretic factor infusion did not alter GFR in the clamped kidney and failed to decrease RSR or PRA. Despite this, PA levels decreased significantly (7.8 +/- 2.4 to 5.6 +/- 1.8 ng%). These results suggest that ANF-induced inhibition of renin secretion is largely consequent on its renal haemodynamic actions and that suppression of aldosterone by ANF in vivo is due, in part, to direct effects on the adrenal cortex.

Deficiency in 15-hydroxyprostaglandin dehydrogenase activity after unilateral ureteral obstruction of the dog kidney.

In the present study, metabolism of prostaglandins (PGs) by 15-hydroxyprostaglandin dehydrogenase (15-OH PGDH) was investigated in dog kidneys with ureteral obstruction. After 24 hr of ureteral obstruction, the obstructed kidney and the contralateral kidney were removed and the cytosolic fractions (105,000 X g), enriched in 15-OH PGDH, were prepared from the cortex and medulla. 15-OH PGDH activity was estimated by radiometric assays of the metabolism of [3H]PGE2 and [3H]prostacyclin. Cortical 15-OH PGDH activity decreased by greater than 50% in the ureter-obstructed kidney as compared to the contralateral kidney. Similar results were obtained by estimating the stereo-specific release of tritium from position 15 using 15-[3H]PGF2 alpha as substrate. In contrast to the cortex, there were no differences in 15-OH PGDH activity found in the medulla of the obstructed and contralateral kidneys. Because the cortex contains higher levels of 15-OH PGDH activity, the deficiency in that site may contribute to the elevated levels of PGs in renal venous blood during ureteral obstruction.

Effects of auriculin (atrial natriuretic factor) on blood pressure, renal function, and the renin-aldosterone system in dogs.

Auriculin is a potent vasoactive and natriuretic peptide that was recently isolated and purified from rat atrial tissue. Since this peptide could be of great importance for renal, cardiovascular, and volume homeostasis, its functional properties have been characterized in dogs. The effects of synthetic auriculin on renal function, mean blood pressure, plasma renin activity, renin secretory rate, and plasma aldosterone levels were determined. Auriculin was administered intravenously as a prime (1.0 microgram/kg body weight) and constant infusion (0.1 microgram per minute/kg body weight for one hour) to five anesthetized dogs. In addition, two conscious dogs were used to verify some of the results obtained in anesthetized dogs. Auriculin decreased mean blood pressure from 134 +/- 5 to 122 +/- 4 mm Hg (p less than 0.05, paired t test) and increased glomerular filtration rate (25.5 +/- 2.7 to 32.4 +/- 4.1 ml per minute per kidney, p less than 0.05), diuresis (0.21 +/- 0.03 to 1.06 +/- 0.14 ml per minute per kidney, p less than 0.05), natriuresis (38 +/- 0.6 to 187 +/- 35 mueq per minute per kidney, p less than 0.05), and kaliuresis (14.8 +/- 1.6 to 35.7 +/- 6.3 mueq per minute per kidney, p less than 0.05). These effects were sustained throughout the infusion of auriculin and were entirely reversible. Renal plasma flow increased transiently for one to two minutes, and then returned to or below control levels. Urine osmolality decreased by 40 percent (p less than 0.05) whereas free water clearance remained unchanged (p less than 0.05). Auriculin reversibly decreased plasma renin activity (11.6 +/- 2.3 to 3.6 +/- 1.2 ng/ml per hour, p less than 0.05), renin secretory rate (895 +/- 313 to 255 +/- 28 ng per hour per minute, p less than 0.05), and plasma aldosterone levels (8.4 +/- 1.6 to 3.6 +/- 0.7 ng/dl, p less than 0.05), whereas plasma cortisol levels remained unchanged. These results demonstrate that auriculin has a unique combination of functional properties, increasing glomerular filtration rate, diuresis, and natriuresis, without a sustained increase in total renal blood flow, and lowering blood pressure, plasma renin levels, renin secretory rate, and plasma aldosterone levels. These properties suggest an important potential role for atrial natriuretic peptides in the regulation of renal function, extracellular volume, and blood pressure.

Mechanical factors and tissue stresses in chronic hydronephrosis.

From 21 dogs kidneys removed at 0, 1, 2, and 4 weeks after ureteral blockage we found the expected early increase, than subsequent decrease, in pressure and the expected continuing increase in volume and thinning of the walls. However the calculated wall stress builds up continuously with time as does the elastic modulus of the wall. By the 4th week, the wall material has become approximately 3 times as resistant to stretch as the normal ureter.

Patterns of recovery of renal function after surgical relief of chronic bilateral partial ureteral obstruction.

A canine model of bilateral chronic partial ureteral obstruction with one side severely obstructed and the other moderately obstructed was used to determine which kidney should be initially released to facilitate maximum recovery of renal function. The data show a significantly greater return of total renal function (20 per cent) if the more severely injured kidney is released first.

Patterns of recovery of renal function after surgical relief of chronic bilateral partial ureteral obstruction.

A canine model of bilateral chronic partial ureteral obstruction with one side severely obstructed and the other side moderately obstructed was used to determine which kidney should be released initially to facilitate maximum recovery of renal function. The data show a significantly greater return of total renal function (20%) if the more severely injured kidney is released first.