Peripheral circulation in arterial hypertension

Pregnancy in obese women and mechanisms of increased cardiovascular risk in offspring

Pregnancy complicated by maternal obesity contributes to an increased cardiovascular risk in offspring, which is increasingly concerning as the rates of obesity and cardiovascular disease are higher than ever before and still growing. There has been much research in humans and preclinical animal models to understand the impact of maternal obesity on offspring health. This review summarizes what is known about the offspring cardiovascular phenotype, describing a mechanistic role for oxidative stress, metabolic inflexibility, and mitochondrial dysfunction in mediating these impairments. It also discusses the impact of secondary postnatal insults, which may reveal latent cardiovascular deficits that originated in utero. Finally, current interventional efforts and gaps of knowledge to limit the developmental origins of cardiovascular dysfunction in offspring of obese pregnancy are highlighted.

Hypertension and peripheral arterial disease: a plethysmographic study

Sixty patients suffering from arterial hypertension and/or obliterative arteriopathy of the lower limbs (20 hypertensive uncomplicated [H group], 20 normotensive affected by obliterative arteriopathy [A group], 20 suffering from both hypertension and peripheral arterial disease [HA group]) were studied, by strain gauge plethysmography, in comparison with 20 healthy subjects (N group). The aims were to evaluate the arterial and venous hemodynamics of the lower limbs in such conditions and also to determine whether the vascular damage is primary or represents a consequence of the hypertensive pathology in the patients affected by both hypertension and peripheral arterial disease. The resting blood flow did not show significant differences in the mean values, even if lightly decreased in hypertensive patients (with or without peripheral arteriopathy). The peak flow was reduced significantly both in the H group and in the A and HA groups. The half-time (t1/2) and total time (tT), which indicate vascular reactivity, were significantly decreased in the H group, but they were increased in the A and HA groups. Finally, the venous compliance was decreased in the H group, did not vary significantly in the A group, and showed an intermediate behavior in the HA group. These results suggest that hypertensive and arteriopathic patients develop similar arterial structural changes. However, they show a different behavior with regard to vascular reactivity and venous hemodynamics, as demonstrated by venous plethysmography.

Hypertension and peripheral arterial hemodynamics

Sixty uncomplicated hypertensive patients (30 stable and 30 borderline) were studied, by strain gauge plethysmography, in comparison with 25 normotensive subjects, in order to evaluate the arterial hemodynamics of the lower limbs in essential hypertension and to verify the different pattern in borderline and in stable hypertensives. Resting blood flow, even if slightly decreased in hypertensive groups, did not show significant differences in its mean values; peak flow, instead, was reduced proportionally to the severity of hypertension in all the hypertensive patients, but only in the stable hypertensives was it statistically significant. Minimal vascular resistance showed a similar behavior: it was significantly increased only in the stable hypertensives, whereas basal vascular resistance was raised in all hypertensive patients and also in the borderline group. Finally, the half-time and the total hyperemic response time, which indicate vascular reactivity, were significantly decreased in all the hypertensives. These results suggest that the stable hypertensive patients develop principally arterial structural changes, while the borderline hypertensive patients have only functional modifications, such as a reduced compliance and a hyperdynamic condition.

The influence of antihypertensive therapy on the structural arteriolar changes in essential hypertension: different effects of enalapril and hydrochlorothiazide

OBJECTIVES

To assess the peripheral and central haemodynamics, in particular the effect on minimal resistance in the hand, with an ACE inhibitor in comparison with a diuretic.

DESIGN

Double-blind randomized parallel group study.

SUBJECTS

Twenty-eight previously untreated men with essential hypertension (supine diastolic blood pressure > 95 mmHg repeatedly on placebo). METHODS/INTERVENTION: Causal and intra-arterial blood pressure, dye-dilution technique, water plethysmography at rest and at ischaemia, enalapril (n = 14), hydrochlorothiazide (n = 14).

RESULTS

After 6 months the mean arterial pressure was reduced from 112.7 to 96.9 mmHg (change -15.9 mmHg; 95% confidence interval (CI) -21.9, -9.8) on enalapril and from 110.1 to 101.5 mmHg (change -8.6 mmHg; CI -14.4, -2.8). Heart rate did not change on any of the therapies. Enalapril reduced blood pressure mainly through a reduction in total peripheral resistance (delta -3.0 PRU100; CI -5.6, -0.4) while hydrochlorothiazide reduced blood pressure mainly through a reduction in cardiac output (delta -0.8 l/min-1; CI -1.5, -0.07). Minimal vascular resistance (mean of right and left hand) displayed a significant time x treatment interaction indicating a different trend with enalapril than hydrochlorothiazide with a change of -0.12 PRU100 (CI -0.33, 0.05) on enalapril and a change of 0.14 (CI -0.29, 0.56) on hydrochlorothiazide. The resistance level after 6 months was significantly higher on hydrochlorothiazide than on enalapril (P = 0.0105).

CONCLUSION

Enalapril reduced blood pressure through vasodilatation and hydrochlorothiazide through decreased cardiac output. The two therapies also affected minimal vascular resistance (an indirect measure of vascular wall thickness) differently; with enalapril showing a favourable response in contrast to hydrochlorothiazide.

Regulation of sodium and body fluid homeostasis during development: implications for the pathogenesis of hypertension

The spontaneously hypertensive rat (SHR) is an important animal model of human essential hypertension. During the first month of life, increased retention of sodium is present in the SHR which appears to be mediated by the renin-angiotensin system. The present review will discuss the role that increased activity of the renin-angiotensin system plays in sodium/body fluid regulation during early development. It is hypothesized that disordered regulation of sodium/body fluid homeostasis during this stage leads to pathological cardiovascular regulation in adulthood. Through an understanding of the relationship between sodium/body fluid balance in the young and cardiovascular function in the adult insights may be gained into both the pathological state of hypertension and the critical role played by early development in shaping homeostatic mechanisms in adulthood.

Characterization of intrarenal arterial adrenergic receptors in renovascular hypertension

alpha-Adrenergic receptor subtypes were investigated using [3H]prazosin, an alpha 1 selective antagonist, and the alpha 2 selective antagonist [3H]rauwolscine in a smooth muscle plasma membrane enriched microsomal fraction prepared from rabbit intrarenal arterial vasculature. Both radioligands displayed single components on Scatchard analysis. The specific binding of [3H]prazosin was of high affinity (0.54 +/- 0.04 nM) with a maximum binding capacity (Bmax) of 212 +/- 15 fmol/mg protein. The maximum number of [3H]rauwolscine binding sites was 64 +/- 4 fmol/mg of protein with a dissociation constant (Kd) of 5.60 +2- 0.27 nM. Binding of both radioligands was rapid, saturable, and specific. alpha 1- and alpha 2-adrenergic receptors in the intrarenal arterial membrane preparation were also characterized at 2-, 4-6-, and 10-12-week intervals during the course of development and maintenance of chronic two-kidney, one clip (2K1C) Goldblatt hypertension and in age-matched sham-operated normotensive control rabbits. The alpha 1-adrenergic receptor affinity for [3H]prazosin binding in hypertensive rabbits was significantly increased in the stenotic, but not contralateral, kidney at 2 weeks; however, at 6 weeks the receptor affinity of both kidneys was significantly increased compared with those of the normotensive control group. No difference in alpha 1-adrenergic receptor affinity was seen at 12 weeks, and there were no changes in Bmax at any of the weekly intervals. Neither the Kd, nor Bmax, for [3H]rauwolscine in either kidney showed a significant difference between hypertensive rabbits and normotensive control rabbits. These studies demonstrate the existence in the rabbit intrarenal arterial vasculature of binding sites with alpha 1- and alpha 2-adrenergic receptor specificity.(ABSTRACT TRUNCATED AT 250 WORDS)

Limited maximal vasodilator capacity of forearm resistance vessels in normotensive young men with a familial predisposition to hypertension

The study was performed to determine whether there is a structural vascular abnormality in normotensive subjects with hypertensive relatives. We examined maximal vasodilator capacity of forearm resistance vessels in 23 normotensive young men (mean blood pressure 94 +/- 0.4 mm Hg, mean +/- SE) with hypertensive relatives (age 24 +/- 0.1 years) and in 17 normotensive subjects (mean blood pressure 85 +/- 0.4 mm Hg) with no family history of hypertension (age 24 +/- 0.1 years). Maximal vasodilator capacity was examined by measuring minimal vascular resistance during peak reactive hyperemia after release from 10 minutes of arterial occlusion. Minimal forearm vascular resistance after release from 10 minutes of arterial occlusion was 25% higher (P less than 0.02) in subjects with hypertensive relatives (2.0 +/- 0.02 units) than that in subjects with no family history (1.5 +/- 0.01) units. We confirmed the previous findings that increasing metabolic vasodilator stimulus by performing intermittent handgrip exercise during 10 minutes of arterial occlusion did not augment peak dilation. This suggests that 10 minutes of arterial occlusion produced maximal vasodilation. Forearm vascular responses to ice on the forehead was greater in subjects with hypertensive relatives than those in subjects with no family history. These results suggest that there may be a structural abnormality in the forearm resistance vessels in normotensive subjects with family history of hypertension.

Effect of cross-transplantation on normotensive and spontaneously hypertensive rat arterial muscle membrane

Transplantation of arteries into the anterior eye chamber of rats for 8 weeks was used to test the hypothesis that the neurohumoral environment is important in establishing the altered membrane potential (observable during electrogenic ion transport inhibition) of vascular muscle in hypertension. When caudal arteries from 12- to 16-week-old spontaneously hypertensive rats (SHR) or genetically matched Kyoto-Wistar normotensive rats (KNR) were transplanted into the opposite strain, there was no change in the transport inhibited membrane potential (Em) of the arterial muscle cells from that found in freshly excised donor arteries. However, when caudal arteries from 2-week-old animals were transplanted into the anterior eye chamber, the arteries always developed the appropriate Em for the host animal. In other words, a genetically KNR artery developed the Em of an SHR artery in an SHR host; conversely, a genetically SHR artery developed the Em of a KNR artery in the KNR host. These results provide evidence that: 1) the differences between th Em of caudal arteries from SHR and KNR are not inherent in those muscle cells; 2) the change in Em is triggered in young animals preceding development of hypertension, but not after hypertension is established; and 3) the Em alteration of the caudal artery is independent of structural changes that occur in the artery as a result of increased blood pressure (because KNR transplants were not connected in series with the host anterior eye chamber vasculature and subject to the elevated blood pressures). We conclude that the arterial muscle cells up to a certain age respond to an external factor that regulates their Em and presumably their sensitivity to vasopressor agents.

Effect of chronic hypertension and sympathetic denervation on wall/lumen ratio of cerebral vessels

The purposes of this study were to determine whether 1) cerebral vessels undergo hypertrophy during chronic hypertension and 2) sympathetic nerves contribute to cerebral vascular changes in chronic hypertension. Morphometric studies were undertaken in stroke-prone spontaneously hypertensive rats (SP-SHR) and normotensive Wistar-Kyoto (WKY) rats. Unilateral superior cervical ganglionectomy was performed in the SP-SHR at 8 weeks of age. When the rats were approximately 13 months old, they were killed and the brain was fixed with formalin at a perfusion pressure of 80% of the rat's systolic pressure. Wall/lumen ratio was measured in approximately 1200 arteries and arterioles. In parenchymal, but not pial, cerebral vessels there was pronounced vascular hypertrophy in SP-SHR: wall/lumen ratio was 0.08 in WKY and 0.14 in SP-SHR (p < 0.05). Sympathetic denervation attenuated the development of vascular hypertrophy in SP-SHR: wall/lumen ratio was 0.14 in the innervated parenchymal vessels, and 0.10 in denervated vessels (p < 0.05). We conclude that cerebral vessels undergo hypertrophy in stroke-prone SHR and speculate that vascular hypertrophy may protect cerebral vessels by reducing wall stress in chronic hypertension. Sympathetic nerves appear to exert a trophic effect on cerebral vascular muscle in chronic hypertension.

Characterization of postsynaptic alpha-adrenergic receptors by [3H]-dihydroergocryptine binding in muscular arteries from the rat mesentery

Alpha-adrenergic receptors are likely to be important determinants of the effects of catecholamines on vascular resistance. To study the alpha-adrenergic receptor in muscular arteries of the type that determine vascular resistance, we characterized and quantitated alpha-adrenergic receptors in a particulate fraction of the highly reactive, richly innervated arteries of the rat mesentery. With the ligand [3H]-dihydroergocryptine ([3H]-DHEC), specific binding (displaceable by 5 microM phentolamine) is saturable. There is a single class of binding sites with a dissociation constant (Kd) of 2.9 nM and a maximal binding capacity of 68 fmoles of [3H]-DHEC per mg of particulate fraction protein. Catecholamines compete for [3H]-DHEC binding stereospecifically and with the alpha-adrenergic potency series of (-)epinephrine greater than (-)norepinephrine greater than (-)isoproterenol. Binding is rapid (t 1/2 less than or equal to 2 mins) and rapidly reversible (t 1/2 less than or equal to 2 mins). Inhibition of [3H]-DHEC binding by the alpha-adrenergic antagonist phentolamine (Kd = 3.0 nM) is much greater than by the beta-adrenergic antagonist propranolol (Kd = 8200 nM). The alpha 1-selective antagonist prazosin (Kd = 63 nM) is 20 times more potent in competing for [3H]-DHEC binding than is the alpha 2-selective antagonist yohimbine (Kd = 1250 nM), thus suggesting that the alpha-adrenergic receptor identified is predominantly of the alpha 1 subtype that is responsible for vascular smooth muscle contraction. This extension of radioligand binding techniques to highly innervated muscular arteries of the type contributing to vascular resistance will allow the study of the role of the vascular alpha-adrenergic receptor in various physiologic states and models of hypertension.

Sympathetic and renin-angiotensin system influence on blood pressure and renal blood flow of two-kidney, one clip Goldblatt hypertensive dog

Conscious normotensive and two-kidney, one clip Goldblatt hypertensive dogs were studied to determine the influence of the sympathetic and renin-angiotensin systems on the blood pressure and renal blood flow. Renal blood flow was monitored in a single kidney of the normotensive dogs and in the contralateral kidney of the hypertensive dogs. Saralasin was infused intravenously (i.v.) at 1 microgram/kg/min for 15 minutes in untreated and guanethidine-treated animals. Guanethidine (i.v.) decreased blood pressure (BP) in the hypertensives at X = 16 days after Goldblatt clamp application, but not in the normotensives, and did not affect renal blood flow or vascular resistance in either group. Saralasin produced approximately the same BP decrease in both untreated and guanethidine-treated hypertensives at X = 12 days after Goldblatt clamp application; the combined effect of the drugs was greater than saralasin alone. Blood flow and vascular resistance of the hypertensives' contralateral kidney were not significantly affected by saralasin in these experiments. No sustained effect on BP or renal blood flow was obtained with saralasin in the normotensives. Administration of furosemide was utilized to increase plasma renin activity (PRA) in another series of experiments. In both normotensives and hypertensives, PRA was elevated at 2-3 hours after furosemide application, being greater in the hypertensives. When the renin-angiotensin system was activated in this manner, saralasin had a significant hypotensive and renal vasodilator effect in the hypertensives, but not in the normotensives.

Central hemodynamics in the developmental stage of spontaneous hypertension in the unanesthetized rat

The hemodynamic alterations associated with the developmental phase of high blood pressure were investigated in the spontaneously hypertensive rat (SHR). All hemodynamic measurements were made in unanesthetized, unrestrained SHR and Wistar-Kyoto (WKY) rats instrumented with chronic electromagnetic flow probes on the ascending aorta and arterial pressure catheters. Rats were studied at 30-41 days, 80 days, and 120 days of age. Hemodynamics of SHRs and WKYs in the 30-41 day group were monitored daily. Spontaneously hypertensive rats demonstrated a higher cardiac index than WKYs (p less than 0.05) from 32 through 41 days of age. Total peripheral resistance (TPR) was not elevated in SHRs at this time. Heart rate and stroke index were elevated in SHRs (p less than 0.05) from 34 through 41 days, however, stroke volume was not. At 80 and 120 days SHRs had higher mean arterial pressure (MAP) and TPR than WKYs (p less than 0.05), although cardiac index was not significantly different. This hemodynamic pattern of a hyperkinetic circulation prior to the development of hypertension supports the theory of total body autoregulation. A transient increase in cardiac index precedes an increase in TPR, which then normalizes cardiac index while elevating MAP.

Vasoconstrictor hyperresponsiveness: an early pathogenic mechanism in the spontaneously hypertensive rat

Factors which play a primary role in the initiation and development of hypertension in spontaneously hypertensive rats (SHR) are incompletely defined. To test the possibility that early changes in vascular function play a primary etiologic role, hindquarters of 3-week-old SHR and Wistar-Kyoto normotensive rats (WKY) were perfused at constant flow with plasma substitute. The vasculature of SHR exhibited higher resistance to flow than that of WKY. The threshold constrictor response to norepinephrine (NE) was elicited at a significantly lower concentration (6X) than required in WKY, while threshold to BaCl2 was not different. At concentrations of BaCl2 above threshold, SHR exhibited marked hyperresponsiveness compared to WKY. This resulted in a greater maximum response and thus a steeper slope. The ED50 for BaCl2 was not different. A similar dose--response relationship (greater maximum, steeper slope) was observed with NE except that the ED50 as well as threshold was significantly lower in SHR than in WKY. These data show that vasoconstrictor hyperresponsiveness and increased vascular resistance are present at the time when the hypertension is first detectable. The hyperresponsiveness includes two distinct components: (1) A specific hypersensitivity to NE and (2) non-specific hyperresponsiveness which could derive from altered excitation--contraction coupling and/or from a structural mechanism already present when pressure differences begin to appear.