Antihypertensive functions of the kidney: Arthur C. Corcoran memorial lecture

Effects of 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine (platelet activating factor) on cardiac function in perfused guinea-pig heart

The direct cardiac action of 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine (PAF) was studied in isolated perfused guinea-pig heart preparations. PAF produced a fall in left ventricular pressure, decreases in the rate of rise of the left ventricular pressure (dp/dt) and coronary flow, but had no effect on heart rate. These results indicate that PAF is a cardiodepressant with inotropic selectivity and this effect on heart is blocked by CV-3988, a specific PAF antagonist.

Hypotensive mechanism of acetyl glyceryl ether phosphorylcholine (AGEPC) in dogs. Effects on hemodynamics and humoral factors

One-O-hexadecyl-2-O-acetyl-sn-glycero-3-phosphorylcholine (AGEPC) was intravenously administered to anesthetized dogs to study the effects on hemodynamics and several endocrine factors. The effect of AGEPC on local blood flow was also studied by direct intra-arterial injection. Following intravenous injection, blood pressure and cardiac output decreased significantly (p less than 0.001). Changes in total peripheral resistance (TPR) and heart rate were biphasic. TPR increased significantly (p less than 0.01) after an initial slight reduction. Heart rate decreased significantly (p less than 0.01) with only a transient slight elevation. Femoral blood flow was increased (p less than 0.001) by intraarterial injection and decreased (p less than 0.05) by intravenous administration. Plasma norepinephrine (p less than 0.001), epinephrine (p less than 0.01), thromboxane B2 (p less than 0.001), 6-0-PGF1 alpha (p less than 0.01), aldosterone (p less than 0.001) and cortisol (p less than 0.001) were elevated, but plasma renin activity did not change. These results suggest that the hypotensive mechanism of AGEPC is due to both cardiosuppression and vasodilation. AGEPC increased plasma catecholamines, thromboxane A2, PGI2, aldosterone and cortisol which, in turn, may modify hemodynamics.

Increased renal prostanoid synthesis after unclipping the one-kidney, one-clip hypertensive rat: effect of renal denervation

Renal denervation of hypertensive one-kidney, one-clip (1K, 1C) rats resulted in a minor fall in blood pressure (216, s.e.m. = 4, to 182, s.e.m. = 4, mmHg) 24 h later, which returned to predenervation levels with 1 week. Subsequent unclipping led to a similar fall in blood pressure in denervated (202, s.e.m. = 4 to 142, s.e.m. = 3) and sham-denervated (211, s.e.m. = 5 to 147, s.e.m. = 4) rats. Unclipping also resulted in a marked rise in urinary PGE2 and 6-keto PFG1 alpha in both denervated and sham-denervated animals. It appears that 1K, 1C hypertension, 8 weeks after clipping, is only slightly dependent on renal nerves. Unclipping results in increased renal synthesis of PGE2 and PGI2 which is not dependent on intact renal innervation.

Effects of acetyl glyceryl ether of phosphorylcholine (platelet activating factor) on ventricular preload, afterload, and contractility in dogs

Acetyl glyceryl ether of phosphorylcholine (AGEPC), platelet activating factor, is a potent hypotensive agent that may mediate changes in blood pressure during anaphylaxis and may be involved in blood pressure variations of renal origin. This study was designed to characterize the hemodynamic mechanisms responsible for hypotension induced by this recently identified phospholipid. Intravenous administration of AGEPC to anesthetized open-chest dogs (n = 5) produced hemodynamic alterations which, for the purpose of analysis, were divided into three phases based on changes in the mean systemic blood pressure. During phase I (5-30 s) mean systemic blood pressure decreased to levels 5 to 10% below baseline values in association with a rise in cardiac output and a decrease in systemic vascular resistance. Phase II (30-90 s) consisted of a substantial reduction in systemic blood pressure to its nadir, 50% of baseline values, together with a decrease of similar magnitude in cardiac output and a rise in systemic vascular resistance. Phase III (90 s-60 min) exhibited a gradual recovery of mean systemic blood pressure toward normal with a several-fold rise in systemic vascular resistance and a continued low cardiac output. On the right side of the circulation, the predominant effect of AGEPC was a marked transient increase in pulmonary artery pressure in phase I, associated with an elevation of pulmonary resistance during phase II. Diethylcarbamazine blocked virtually all of these hemodynamic changes induced by AGEPC; FPL 55712 substantially blocked the rise in systemic vascular resistance in phase III. These results suggest that leukotrienes may mediate at least some of the hemodynamic effects induced by AGEPC, but further studies will be required when more specific leukotriene blocking agents become available. As assessed during phase III with the end-systolic pressure-dimension relation, myocardial performance itself was diminished. The occurrence of an AGEPC-induced negative inotropic effect was further confirmed in isolated Krebs-perfused guinea pig hearts and isolated blood-perfused rabbit hearts. The results indicate that the mechanism of AGEPC-induced hypotension is complex, affecting both vascular tone and the inotropic state of the myocardium.

Hypertension and unilateral hydronephrosis

We report 2 cases of hypertension associated with unilateral hydronephrosis. Lateralization of renal vein renins and exaggerated hyperreninemia following captopril suggested renin-mediated hypertension in 1 case, which responded well to nephrectomy.

Evidence for the lack of interaction between (+/-)-1-O-octadecyl-2-acetylglyceryl-3-phosphorylcholine and alpha-adrenoceptors in vivo and in vitro

The interactions of (+/-)-1-O-octadecyl-2-acetylglyceryl-3-phosphorylcholine (octadecyl-AGPC) with alpha-adrenoceptors were studied in rat mesenteric artery, cat nictitating membrane and on the blood pressure of the cat and spontaneously hypertensive (SH) rat. Using a direct radioligand alpha-adrenoceptor binding assay in particulate fractions of rat mesenteric arteries, octadecyl-AGPC was found to be 5 X 10(7) and 75 times less potent than prazosin and noradrenaline (NA), respectively, in displacing (2,6-dimethoxyphenoxyethyl)-aminomethyl-1,4-benzodioxane ([3H]-WB 4101--a selective probe for the identification of alpha-adrenoceptors). In the cat, intravenous infusions of octadecyl-AGPC, which produce a hypotensive response, did not attenuate nictitating membrane contractions in vivo in response to intravenous injections of NA, adrenaline (Ad) or to electrical stimulation of the postganglionic fibres of the superior cervical ganglion. In these experiments, the pressor responses to NA or Ad were not affected by octadecyl-AGPC. Phentolamine, on the other hand, attenuated nictitating membrane contractions and blood pressure responses to Ad or NA. In the SH rat, octadecyl-AGPC decreased mean arterial blood pressure (MABP). After an intravenous dose of phentolamine which lowered MABP, the depressor response to octadecyl-AGPC was reduced. When MABP in the phentolamine-treated SH rat was restored to its initial level with an infusion of angiotensin II (AII), the depressor response to octadecyl-AGPC was restored to its original magnitude. The effectiveness of alpha-adrenoceptor blockade under these experimental conditions was monitored with intravenous NA and Ad. Thus, based on radioligand binding studies and pharmacological studies, it is concluded that octadecyl-AGPC lacks the ability to interact with alpha-adrenoceptors.

Cardiovascular and renal action of platelet-activating factor in anesthetized dogs

Platelet-activating factor (PAF) has hypotensive effects similar to those of antihypertensive polar renomedullary lipid (APRL), a potent endogenous hypotensive lipid. In this study the cardiovascular and renal effects of PAF were characterized in anesthetized dogs. Intravenous infusion of PAF at 0.1 micrograms/kg/min for 1 hour caused marked reduction in arterial blood pressure and cardiac output and was accompanied by minimal changes in heart rate. Concomitantly, renal blood flow, glomerular filtration rate, urine flow, and fractional excretion of Na+ and K+ fell significantly. Plasma renin activity was greatly stimulated (11.9 +/- 1.66 vs 3.26 +/- 0.45 ng/angiotensin I/ml/hr for the placebo group). There were no significant alterations in any of these parameters following PAF at a lower dose (0.03 micrograms/kg/min for 1 hour). In a separate study, PAF at 0.1 micrograms/kg/min for 20 minutes produced a decrease in left ventricular myocardial contractile force, concomitant with bradycardia and hypotension, which indicated the presence of a negative inotropic activity. It is concluded that systemic administration of PAF has a deleterious effect on kidney function due to arterial hypotension and diminished cardiac output.

Regional hemodynamic effects of antihypertensive renomedullary lipids in conscious rats

Renomedullary tissue has been proposed to exert an antihypertensive endocrine-like action. The antihypertensive polar renomedullary lipids (APRL) and neutral renomedullary lipids (ANRL) are potential mediators of this action. We evaluated the blood pressure and regional hemodynamic responses to APRL administered peripherally (i.v.) and to the central nervous system (CNS) in normal rats and rats with sinoaortic deafferentation (SAD) to remove baroreflex buffering. Rats were chronically instrumented with Doppler flow probes for measurement of mesenteric, renal, and hind-quarter vascular resistance, with arterial pressure and intravenous catheters, and with lateral cerebroventricular cannuli for intracerebroventricular (i.c.v.) administration. Intravenous APRL (0.01 to 1.0 micrograms) produced a dose-dependent decrease in blood pressure, tachycardia, and dilation of all vascular beds studied. The dose-response relationships were shifted to the left in SAD animals. APRL administered i.c.v. had no effect on intact or SAD rats. Pressor and regional vasoconstrictor responses to norepinephrine, angiotensin, and vasopressin were markedly reduced in SAD animals during constant infusion of APRL. In a second group of conscious SAD animals instrumented for blood pressure and heart rate measurements, intravenous ANRL (500 micrograms) decreased both arterial pressure (-45 +/- 16 mm Hg) and heart rate (-50 +/- 16 bpm). When given i.c.v., however, ANRL (10-100 micrograms) had no significant effect on resting blood pressure or heart rate. These studies suggest that APRL and ANRL produce no significant cardiovascular effects that are mediated through the CNS. However, both lipids are potent depressor agents, and APRL exhibits a strong peripheral vasodilator action and nonspecifically reduces reactivity to vasoconstrictor agents.

Role of prostaglandins during reversal of one-kidney, one-clip hypertension in the rat

Unclipping the one-kidney, one-clip rat returned blood pressure to normotensive levels within 24 h and was associated with a substantial increase in urinary PGE2 and 6-keto PGF1 alpha excretion. Prior treatment with indomethacin (6.0 mg/kg) markedly reduced urinary prostaglandins after clip removal and attenuated the fall in blood pressure. Aspirin (100 mg/kg) treatment, which reduced 6-keto PGF1 alpha to a lesser degree without altering PGE2 excretion, had no significant effect on the blood pressure fall. It is suggested that in the one-kidney, one-clip rat prostaglandins are released as the result of exposing the unclipped kidney to elevated arterial pressure, and that these contribute to the subsequent fall in blood pressure.

Mechanism(s) of the hypotensive effect of synthetic 1-O-octadecyl-2-O-acetyl-glycero-3-phosphorylcholine

The mechanism of the hypotensive effect of 1-O-octadecyl-2-O-acetyl-glycero-3-phosphorylcholine (C18- AGPC ) was examined. Synthetic C18- AGPC caused dose-dependent hypotension in conscious rats. The activity was almost the same in DOCA and renal hypertensive rats. This suggests that it is not a renin inhibitor. Hypotension also appeared in pithed rats. This suggests that the effect is not due to a central mechanism. Hypotension did not result from platelet aggregation or bronchial constriction. Since C18- AGPC suppressed not only the pressor response to noradrenaline but also to angiotensin II and vasopressin, and furthermore, did not disturb the dose-response curve of noradrenaline in the isolated aorta, the possibility of the agent being an alpha-adrenergic antagonist is ruled out. In the PGF2 alpha-contracted rat aorta. C18- AGPC caused marked vasodilation, which disappeared after removal of the endothelium. Perfusion pressure decreased in the blood-perfused rat hindquarters but not in the Tyrode solution-perfused ones. C18- AGPC induced a positive inotropic effect in isolated rat atrium. The hypotensive effect of synthetic C18- AGPC seems to be mainly due to endothelium-dependent vasodilation.

Urinary 6-keto PGF1 alpha and PGE2 in two kidney-one clip hypertension in the rat

The 24 hour urinary excretion of 6-keto PGF1 alpha and PGE2 was compared in 2 kidney-1 clip rats developing hypertension within 12 weeks of renal artery clipping with rats remaining normotensive over this period. Although systolic blood pressure was markedly elevated in the hypertensive (210 +/- 5.1 mm Hg), in contrast with the normotensive (141 +/- 1.9 mm Hg) group, urinary levels of 6-keto PGF1 alpha (26.1 +/- 3.4 and 22.1 +/- 2.7 ng/24 h, respectively) and PGE2 (52.8 +/- 28 and 53.3 +/- 10.8 ng/24 h) were not significantly different. Treating the 2 kidney-1 clip normotensive group with indomethacin (3.0 mg/kg, by intraperitoneal injection) twice-weekly for 3 weeks reduced 6-keto PGF1 alpha excretion from 22.1 +/- 2.7 to 8.4 +/- 2.2 ng/24 h (P less than 0.002) and PGE2 from 53.3 +/- 10.8 to 8.7 +/- 1.8 ng/24 h (P less than 0.002) but did not change blood pressure when compared with a similar group given buffer vehicle only. These findings do not support a role for renal prostaglandins in 2 kidney-1 clip hypertension in the rat.

Antihypertensive polar and neutral renopapillary lipids. Which is a hormone?

Two antihypertensive lipids can be derived from the renal papilla, the antihypertensive polar (APRL) and the antihypertensive neutral (ANRL) renomedullary lipid. The renal venous effluent of the unclipped kidney contains both ANRL and APRL. This effluent lowers the arterial pressure (AP) of the normal rat when infused i.v. As it lowers the AP the heart rate (HR) and sympathetic nerve activity (SNA) are depressed. ANRL infused i.v. also lowers HR and SNA as it depresses the AP. Conversely, APRL elevates HR and SNA as it lowers the AP. Thus, of the two lipids in the renal venous effluent after unclipping, ANRL appears to be dominant. APRL, however, in the renal venous effluent could potentiate the action of ANRL. The net effect of these observations is to support the view that ANRL is an antihypertensive hormone liberated by the kidney after unclipping. The renomedullary interstitial cells (RIC) degranulate after unclipping. ANRL can be derived from these cells. Thus, the RIC, cells known to exert an endocrine-type antihypertensive function, may well be the source of ANRL in the renal venous effluent after unclipping. The hormonal action of ANRL appears as a major cause of the lowering of the AP after unclipping. It is not known what factors modulate the RIC endocrine system. There is a suggestion that angiotensin may be one of these factors based on the ineffectiveness of these cells toward retarding hypertension when the circulating plasma angiotensin level is high, and their effectiveness when the circulating plasma angiotensin level is low.

Chemical renal medullectomy. Effect on urinary prostaglandin E2 and plasma renin in response to variations in sodium intake and in relation to blood pressure

We have studied the possible vasodepressor role of the renal medulla by chemical medullectomy. Bromoethylamine hydrobromide (200 mg/kg) was injected to induce selective renal medullary necrosis in rats. The acute effects on sodium balance and long-term effects on blood pressure, plasma renin concentration (PRC) and urinary prostaglandin E2 (PGE2) were studied and compared with saline injected controls. There was an immediate and sustained increase in urine volume of low osmolality. Direct blood pressure in conscious free-moving animals was higher at 2 and 10 weeks after injection in medullary-damaged rats, although this was only significant at 10 weeks (136 +/- 3.3 vs 118 +/- 4.5 mm Hg, p less than 0.01). An initial negative sodium balance returned to normal by 7 days and rats with established medullary damage tolerated a wide range of sodium intakes. Although there was no evidence of sodium retention on the normal diet, with very high sodium loads some sodium retention was apparent since PRC was suppressed and body weight increased. Plasma creatinine and creatinine clearance were normal. PRC in rats with medullary damage was unchanged on normal diet and rose to similar levels as in control rats on low sodium intake. Urinary PGE2 was markedly reduced (148 +/- 54 vs 536 +/- 71 ng/day, p less than 0.01) in medullary damaged rats, consistent with the renal medulla being the major source of urinary PGE2. High salt intake increased urinary PGE2 in normal and proportionally in medullary damaged rats, whereas on a low sodium intake, urinary PGE2 was not different from that on the normal diet in either group.(ABSTRACT TRUNCATED AT 250 WORDS)

Aortic vascular and atrial responses to (+/-)-1-O-octadecyl-2-acetyl-glyceryl-3-phosphorylcholine

The effects of (+/-)-1-O-octadecyl-2-acetyl-glyceryl-3-phosphorylcholine (octadecyl-AGPC) were studied in three types of aortic vascular smooth muscle preparations, namely, strips, rubbed and unrubbed rings, and an atrial preparation in normotensive rats. In the resting tension state, octadecyl-AGPC did not elicit significant contractions in either rubbed or unrubbed ring preparations at concentrations lower than 1 X 10(-4) M. However, at a concentration of 3 X 10(-4) M, octadecyl-AGPC markedly contracted both types of ring preparations. This contractile response was partially antagonized by pretreatment with reserpine and completely blocked by phentolamine (1 X 10(-6) M). In preparations contracted with noradrenaline (NA), octadecyl-AGPC elicited biphasic responses in intact ring preparations; an initial relaxation followed by contraction. Octadecyl-AGPC induced only a slight contraction in strips and a slight relaxation in the rubbed ring preparation. Octadecyl-AGPC did not elicit any significant effect on chronotropy or inotropy at concentrations up to 3 X 10(-5) M. When the concentration was 1 X 10(-4) M, octadecyl-AGPC produced significant positive chronotropic and inotropic effects on spontaneously beating right and electrically driven left atrial preparations, respectively. Both effects were blocked by propranolol (5 X 10(-8) M); reserpine pretreatment antagonized only the chronotropic response. In [3H]-dihydroalprenolol [( 3H]-DHA) binding studies, octadecyl-AGPC had a Kd of 427.85 microM and thus was much less potent than isoprenaline (Kd = 465.10 nM) or propranolol (Kd = 4.4 nM) in displacing [3H]-DHA in rat cardiac membrane preparations. 6 In conclusion, relaxation and contraction induced by octadecyl-AGPC in aortic preparations is an indirect rather than a direct effect. An unknown factor released from endothelial cells is responsible for aortic smooth muscle relaxation by octadecyl-AGPC while released NA appears to be responsible for aortic vascular contraction and for the positive chronotropic and inotropic effects in the atrial preparations.

Structurally based changes of renal vascular reactivity in spontaneously hypertensive and two-kidney, one-clip renal hypertensive rats, as compared with kidneys from uninephrectomized and intact normotensive rats

Renal vascular beds from spontaneously hypertensive rats (SHR) at different stages of hypertension, from two-kidney, one-clip renal hypertensive rats (RHR) and from uninephrectomized rats (UNR) were in constant-flow, paired perfusions compared with kidneys from normotensive control rats (NCR) concerning vascular smooth muscle sensitivity to noradrenaline (NA) and resistance vessel reactivity, as reflected by the position, respectively the shape, of the dose-resistance response curves. None of these kidney variants differed significantly from controls concerning smooth muscle sensitivity to NA during in vitro perfusion. However, both the steepness and maximal pressor responses of the renal resistance curves increased progressively with age in SHR, to become ultimately much enhanced when related to age-matched controls. It suggests a well preserved smooth muscle contractility and a progressive elevation of the average wall/lumen ratio in the SHR renal resistance vessels. Also the untouched, "high-pressure" RHR kidneys showed increased vascular reactivity, while it was somewhat reduced in the clipped, "low-pressure" RHR kidneys and unchanged in the hypertrophied but normotensive UNR kidneys. These results, when combined with other findings concerning renal vascular design (Göthberg & Folkow 1982a), illustrate how the renal resistance vessels readily adapt structurally to hypertension, hypotension, kidney hypertrophy and also with age, and in directions which tend to chronically "autoregulate" glomerular blood supply and filtration.

Reversal of renovascular hypertension

The fall in blood pressure observed in both early and chronic phase Goldblatt 2-kidney 1-clip hypertension produced by removing or unclipping the ischaemic kidney is due to a profound fall in peripheral resistance. The two procedures have an equal effect upon peripheral resistance and the lesser efficacy of nephrectomy in lowering blood pressure is due to a greater rise in stroke volume perhaps associated with a greater degree of sodium retention. Neither changes in sodium balance, in the renin-angiotensin system nor in vascular reactivity explain the fall in blood pressure. A reduction in renal sympathetic afferent activity and a medullary based vasoactive humoral system may play a role although the nature and extent of that role remain to be defined.

Hypotensive and vasodilatory activity of (+/-) 1-o-octadecyl-2-acetyl glyceryl-3-phosphorylcholine in the normotensive rat

Synthetic (+/-) 1-O-octadecyl-2-acetyl-glyceryl-3-phosphorylcholine (octadecyl-AGPC) in microgram/kg doses given intravenously effectively and potently lowered mean arterial blood pressure in conscious and anesthetized normotensive rats. The hypotensive activity was much more pronounced in the anesthetized rat than in the conscious rat. The hypotension was associated with a significant elevation in plasma renin activity (PRA). In the rat in which the hindquarters were perfused, octadecyl-AGPC given intraarterially effectively decreased the perfusion and systemic pressures in a dose-dependent manner. Pharmacological blockade with specific cholinergic, histaminergic or beta-adrenergic receptor antagonists, did not block or attenuate the octadecyl-AGPC-induced reduction in perfusion or systemic pressure. These results suggest that the hypotensive activity of octadecyl-AGPC in the normotensive rat is the result of direct vasodilation and not the result of cholinergic, histaminergic or beta-adrenergic receptor interaction.

Antihypertensive effects of I-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine on plasma renin activity and catecholamine responses in spontaneously hypertensive rats

Fourteen 23 week old male spontaneously hypertensive rats (SHR) were randomly divided into saline control or phospholipid (I-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine) treatment groups. Four weeks of baseline systolic blood pressure (SBP) and heart rate (HR) measurements were determined via tail plethysmography. On week 25 of the baseline period a 1.5 ml blood sample was taken by tail clip for analysis of norepinephrine (NE), epinephrine (E), and plasma renin activity (PRA). On the following week, a single injection of phospholipid (11 ug/kg, s.c.) was given to the experimental animals following baseline SBP and HR determinations. A similar procedure was employed for control subjects, except they received an injection of normal saline (0.5 ml, s.c.). Systolic BP and HR responses were monitored for 24 minutes following the injection. A 1.5 ml blood sample was taken at the end of the 4th minute for NE, E, and PRA assays. A significant drop in SBP (202 +/- 5 mmHg to 124 +/- 6 mmHg) and an increase in HR (431 +/- 17 bpm to 519 +/- 21 bpm) were observed for experimental animals, but not for control subjects. Plasma NE increased significantly (446 +/- 42 pg/ml to 1099 +/- 77 pg/ml), but E remained unchanged following treatment with the phospholipid. Plasma renin activity increased for both groups, but this change was only significant for the experimental group (18.1 +/- 5.7 ng Al/ml/hr to 34.3 +/- 3.6 ng Al/ml/hr). Thus, it appears that I-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine is a potent antihypertensive vasodilating agent which stimulates baroreceptor mediated sympathetic discharge to the heart and kidneys of the SHR.

Achievements in hypertension: a 25 year overview

Only 25 years ago, the field of hypertension was challenged by retrospective clinical data and epidemiologic information suggesting that an elevated arterial pressure is a major risk factor for enhanced cardiovascular morbidity and mortality. Not only was antihypertensive therapy looked on by many as dangerous and fraught with severe and undesirable side effects, but its validity in reversing the course of disease was not yet demonstrated. This review discusses the dramatic new information amassed over the past 25 years that points to the new physiologic and clinical concepts concerning hypertension. It considers impressive new diagnostic techniques and methods designed to identify secondary forms of hypertension and target organ involvement. In summary, it outlines the feasibility of reversing overall (and cardiovascular) morbidity and mortality with an array of antihypertensive agents that provide the therapeutic ability to suppress most pathophysiologic pressor mechanisms of hypertensive disease. The lesson is clear: hypertension provides the greatest available challenge to the new era of preventive cardiology in the 21st century.

The effect of pregnancy on heart size and blood pressure in renal hypertensive rats

The main purpose of this study on rats was to examine the effect of pregnancy on experimental renal hypertension and cardiac size. Renal hypertension in the rats (RHR) was induced by standardized clamping of the left renal artery early in pregnancy (SRHR) or 4 weeks before mating (ERHR). As controls served non-pregnant RHR with the duration of hypertension matched to each above mentioned group, as well as non-pregnant and pregnant normotensive rats. Only 16% of the rats with renal artery clamping early in pregnancy (SRHR) developed hypertension in contrast to 41% of similarly operated non-pregnant rats and 56% of ERHR decreased their blood pressure to normal levels during pregnancy. Concerning left ventricular heart weight there was a slight increase in left ventricular weight during normal pregnancy in spite of a significantly reduced blood pressure. In both SRHR and ERHR an increased left ventricular heart weight was noticed during pregnancy even when arterial pressure was not increased. The present results suggest an antihypertensive effect of pregnancy and the existence of "trophic" influences and/or a volume induced adaptation of the heart causing an increased myocardial mass which is associated with pregnancy and partly independent of blood pressure influences.

Blockade of alpha-adrenergic receptors by analogues of phosphatidylcholine

The experimental evidence reviewed in this article suggests that the kidneys may have an additional function in regulating blood pressure besides their role in controlling both blood volume by urine formation and the relative state of vasoconstriction by the renin-angiotensin system. That is, the kidneys may have an additional influence upon the vasculature of a hormonal vasodilating system. The interstitial cells of the renal medulla appear to be mediating this activity and lipid compounds have been extracted from the renal medulla which display depressor activity. One such compound, the antihypertensive polar renomedullary lipid (APRL), has been demonstrated to consist of specific alkyl ether analogues of phosphatidylcholine. The vascular responses to these compounds include vasodilation of both arterioles and venules, rapid lowering of arterial blood pressure with little or no tachycardia, increased depressor activity in hypertensive animals, and blockade of vascular smooth muscle alpha 1-adrenergic receptors. Most recently, APRL and a synthetic analogue, 1-0-octadecyl-2-acetyl-sn-glycero-3-phosphorylcholine, have been used to demonstrate alpha-adrenergic receptor blockade on a smooth muscle cell line (DDT1) by radioligand assays. This action may be due to the insertion of these compounds into cell membranes causing subsequent steric interactions and blockade of the alpha-adrenergic receptor.

Human nutrition and blood pressure regulation: an integrated approach

This review highlights the complex interactions that constitute the disciplines of nutrition and cardiovascular physiology. Nutritional factors have long been considered as critical in the pathogenesis of human hypertension. Theoretical and established contributions of various nutrients to blood pressure regulation are presented. A brief historical perspective of sodium's dominance in this area is provided. "Accepted" principles of nutrient interaction are then applied to cardiovascular research. First, the interrelationships among all macronutrients and diet composition, nutrient absorption, renal elimination, and ultimate bioavailability to the vascular tissue are assessed. An analysis of dietary recall data from human studies is provided to illustrate such nutrient interaction. Second, associated factors that influence nutrition are considered in relation to both human and animal investigations of blood pressure regulation. Finally, the development and interpretation of future studies are assessed in light of these principles. Examples from both the human and animal investigations of blood pressure regulation. Finally, the development and interpretation of future studies are assessed in light of these principles. Examples from both the human and animal literature are provided to show why it is necessary to incorporate fully the established principles of nutrition into our current concepts of the pathogenesis of hypertension. Future progress in terms of nutrition, food, and health will be dependent upon such an integrated approach.

Cardiovascular and sympathetic effects of l-O-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine in conscious SHR and WKY rats

Injections of 1-)-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine (alkylacetyl-GPC, 0.2-5.0 nmol/300 g body weight) induced dose-related hypotension and tachycardia in spontaneous hypertensive (SHR) and normotensive control (WKY) rats. The hypotension that developed was more pronounced in SHR than in WKY rats and was unchanged by indomethacin pretreatment. Plasma norepinephrine (NE) and epinephrine (EPI) levels were markedly increased at the time of maximal hypotension (2 min after injection of alkylacetyl-GPC); plasma EPI (but not NE) was higher in the SHR than in WKY animals. Plasma levels of TXB2, but not 6-keto-PGF 1 alpha, increased in both groups; the increase was more pronounced in SHR than in WKY rats. In pithed SHR rats, alkylacetyl-GPC caused only short lasting hypotension without any effect on heart rate or circulating levels of NE or EPI. These data suggest that there is an increased vascular sensitivity to alkylacetyl-GPC in SHR rats and activation of thromboxane-generating elements in both SHR and WKY rats.

Baroreflex sensitivity changes during the reversal of Goldblatt two-kidney one-clip hypertension in rats

The time-course of changes in baroreceptor reflex sensitivity during the reversal of Goldblatt two-kidney one-clip hypertension was studied in male Wistar rats. Groups of animals were studied before and 1, 3, 7, 14 and 25 days after removal of a left renal artery clip of 0.18 mm internal diameter. Normotensive rats of comparable ages were included as controls. Baroreflex sensitivity increased from 0.299 +/- 0.072 ms/mmHg (n = 8) in 25 day hypertensive rats to 0.657 +/- 0.155 and 0.786 +/- 0.093 ms/mmHg (n = 8) in 1 day and 3 day declipped animals respectively. Baroreflex sensitivity in the 1 day declipped rats was inversely related to the level of blood pressure. Baroreflex sensitivity is restored early when renovascular hypertension is reversed. This is unlikely to be due solely to regression of structural vascular adaptation.

Surgical reversal of two-kidney one clip hypertension during inhibition of the renin-angiotensin system

Conscious rats with two-kidney one clip Goldblatt hypertension had the constricting clip removed during continuous infusion of either dextrose, saralasin, or captopril. Other dextrose-infused animals underwent removal of the ischemic kidney or a sham procedure. Direct arterial blood pressure (BP) was recorded throughout the 15-hour preoperative and subsequent 24-hour postoperative period. Rats were studied in the "early" phase (1-3 weeks duration) or "chronic" phase (greater than 4 months) of hypertension. Animals subjected to a sham procedure returned to preoperative BP values. The BP of animals unclipped or nephrectomized did not return to previous hypertensive levels. Instead, a biphasic response was seen where BP partially recovered from an operative fall and then slowly declined to normal at 24 hours; this effect occurred in both stages of hypertension. At 24 hours, removal of the ischemic kidney was as effective as removal of the constricting clip in the correction of both early and chronic phase hypertension. Rats infused with saralasin or captopril demonstrated an acute (within 2 hours) and sustained fall in BP, but not to normotensive levels. This fall was significant in all animals (p less than 0.01) apart from chronic phase rats infused with saralasin where no significant fall was seen. Although animals infused with saralasin or captopril commenced at a lower preoperative BP, the biphasic pattern of response to unclipping was identical to that of dextrose-infused unclipped rats. Thus, sustained inhibition of the renin-angiotensin system did not modify the correction of hypertension produced by removal of the constricting clip, and the response to surgical correction did not appear to be entirely mediated by changes in the activity of the renin-angiotensin system, particularly in the chronic stage. Equally, the rapidity of correction is not consistent with a role of vascular hypertrophy.

Alkyl ether analogs of phosphatidylcholine are orally active in hypertensive rabbits

1-0-alkyl ethers of phosphatidylcholine having an acetoyl in the second position were derived from fresh renal tissue. The main ether so derived had a 16:0 chain. The C16:0 alkyl ether was synthesized de novo. The renally derived and the synthetic ether exerted a similar and powerful antihypertensive action in hypertensive rabbits when given orally in divided doses. This action was prolonged, requiring more than 60 hours after the last input of the compound for recovery of the arterial pressure. As these ethers exerted their antihypertensive action, there was no evidence of adverse effects. Noteworthy was the failure of these depressor compounds to cause renin release. Diuresis-kaliuresis did not occur. A suggestion of sodium retention was noted.